IGCP Project No. 381

Dear Colleague,
In SAMC News 5 you can find the agenda of papers to be presented at the First Annual Conference of IGCP Project 381 (SAMC I) and thematic symposia, held jointly with the XXXIX Brazilian Geological Congress, 2-5 September 1996 in Salvador, Bahia, and all contributions to the SAMC I core meeting and the Thematic Symposium on Tectonics and Sedimentation in South American Basins. The Second Annual Conference (SAMC II) will be held in Yaoundé, Cameroon, during 8-13 March 1997, in conjunction with the 13th Colloquium of African Micropalaeontology and the 3rd Colloquium on the Stratigraphy and Palaeogeography of the South Atlantic (details on page 84).

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INDEX

SAMC-Net
Contacts and further information
SAMC Secretariat
Regional coordinators and national representatives for IGCP Project 381 (August 1996)
Call for papers
Related IGCP Projects
PROGRAMME
First Annual Conference of IGCP Project 381 (SAMC I), Salvador, 2-4 September 1996
Thematic Symposia:
Symposium on Petroleum Systems, 4 September 1996
Symposium on Tectonic, Depositional and Evolutionary Aspects of Rift Type Basins, 5 September 1996
Symposium on Tectonics and Sedimentation in South American Basins, 4 September 1996
Contributions for SAMC I
Contributions for the Symposium on Tectonics and Sedimentation in South American Basins
Second Annual Conference of IGCP Project 381 (SAMC II), Cameroon, 8-13 March 1997
Registration Form for SAMC II
Outline of next annual project meetings
Reports :
Research Project: Origin and History of the South-Atlantic Cretaceous Echinoid Faunas
Working Group Proposals :
Cuban Working Group for IGCP Project 381
Announcements :
Forthcoming meetings related to IGCP Project 381 :
4th Symposium on the Brazilian Cretaceous, Rio Claro, São Paulo, 18-23 August 1996
The Oil and Gas Habitats of the South Atlantic, London, 25-26 February 1997 .
Regional Meeting of IGCP Project 381 and Second Europpean Meeting on the Palaeontology and Stratigraphy of South America, Heidelberg, 2-4 September 1997
AAPG Hedberg Conference on Petroleum Systems of the South Atlantic Margins, Rio de Janeiro, September 1997
1998 AAPG International Conference and Exhibition, Rio de Janeiro, 8-11 November 1998
5th Symposium on the Brazilian Cretaceous and First Symposium on the Cretaceous of South America, São Paulo, August 1999
Other IGCP Meetings of Interest : Annual Assembly of IGCP Project 362 , Freiberg, 16-24 September 1996
Paleogene of South America, Buenos Aires
New Participants
Changes of address and amendments
Acknowledgements

Contacts and further information:
Anyone interested in participating in SAMC should send a registration form or write (letter or e-mail) to E. Koutsoukos, P. Bengtson or the SAMC Secretariat (addresses below) giving the following information: name and full address; telephone, fax, e-mail address; main research interests and, if you wish, a short account of current research related to SAMC.

SAMC Secretariat:
For English-speaking participants:
Márcio R. MELO - PETROBRAS-CENPES, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, BRAZIL. Tel: +55-21-5986460, Fax: 5986799, E-mail: marcio@cenpes.petrobras.gov.br
Nick R. CAMERON (Correspondent Secretary) - Dept. of Geology, Royal School of Mines, Imperial College, Prince Consort Road, London SW7 2BP, UK. Tel.:/Fax: +44-149-4774559, E-mail: nick.cameron@ic.ac.uk or nick@topaz.primex.co.uk
For French-speaking participants:
Mitsuru ARAI - PETROBRAS-CENPES, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, BRAZIL. Tel.: +55-21-5986452, Fax: 5986795, E-mail: arai@cenpes.petrobras.gov.br

Regional Coordinators and National Representatives for IGCP Project 381 (August 1996)

Responsible for liaison among participants, for disseminating information about the progress of the project and forthcoming meetings, for stimulating and coordinating research in their fields of expertise, and for reporting national research activities related to SAMC.
ARGENTINA: Eduardo MUSACCHIO - Universidad Nacional de La Patagonia, Ciudad Universitaria km 4, 9000 Comodoro Rivadavia, Chubut, ARGENTINA. Tel./Fax: +54-97-550339, E-mail: aldo@unpbib.edu.ar
Eduardo B. OLIVERO - Centro Austral de Investigaciones Científicas (CADIC), Av. Malvinas Argentinas s/n , C.C. 92, 9410 Ushuaia, Tierra del Fuego, ARGENTINA. Tel.: +54-901-22 310/312/314, Fax: 30644
BRAZIL: Eduardo A. M. KOUTSOUKOS - PETROBRAS-CENPES, Cidade Universitária, 21949-900 Rio de Janeiro, RJ, BRAZIL. Tel. +55-21-5986440, Fax 5986795, E-mail: koutsoukos@cenpes.petrobras.gov.br
Peter SZATMARI - PETROBRAS-CENPES/Divex, Cidade Universitária, 21949-900 Rio de Janeiro, RJ, BRAZIL. Tel.: +55-21-5986435, Fax: 5986792
COLOMBIA: Luis VERGARA - Ingeominas, Universidad Nacional de Colombia, A.A. 5997, Bogotá, COLOMBIA. Fax: +57-1-3681326/2220797, E-mail: lvergara@ciencias.campus.unal.edu.co
CUBA: Jorge R. SANCHEZ-ARANGO - Centro de Investigaciones del Petróleo (CEINPET), Washington No. 169, Esquina a Churruca - Cerro, La Habana 1200, CUBA. Tel.: +53-7- 408900, 411132, Fax: +53-7- 333072, 338027
EGYPT: Mohamed I.A. IBRAHIM - Faculty of Science, Dept. of Environmental Sciences, Alexandria University, Moharram Bay 21511, Alexandria, EGYPT. Tel.: +2-3-4 835578, Fax: +2-3-4836618, E-mail: mibrahim@alex.eun.eg
FRANCE: Edwige MASURE (Correspondante Française pour le PICG 381) - Laboratoire de Micropaleontologie, Département de Géologie Sédimentaire, URA 1761, Université P. & M. CURIE, 4 PLACE Jussieu, 75252 Paris Cedex 05, FRANCE. Tél. : +33- 44 27 49 87, Fax. +33- 44 27 38 31, E-mail: edmasure@ccr.jussieu.fr
Ivan de KLASZ - La Verdiane, 74 Av. du Mont Alban, F-06300 Nice, FRANCE. Tel.: +33-93-268843, Fax: 894820
Jean MASCLE - Laboratoire de Géodynamique Sous-Marine, BP No. 48, 06230 Villefranche-sur-Mer, FRANCE. E-mail: mascle@ccrv.obs-vlfr.fr
GERMANY: Peter BENGTSON - Geologisch-Paläontologisches Institut der Universität Heidelberg,, D-69120 Heidelberg, GERMANY. Tel.: +49-6221-548293, Fax: 548640 or 545503, E-mail: Peter.Bengtson@urz.uni-heidelberg.de
IVORY COAST: Victor N'DA LOUKOU (Coordinateur national au niveau de la Côte d'Ivoire) - Société Nationale d'Opérations Pétrolières (PETROCI), B.P.V. 194, Abidjan, IVORY COAST. Tel.: 221-466820 or 466816, Fax: 221-216824
NIGERIA: Sunday W. PETTERS - Department of Geology, MOBIL/NNPC Chair of Petroleum Geology, University of Calabar, P.O. Box 3654, Calabar, NIGERIA. Tel.: +234-84-224747 or 224748, ext. 350, Telex: 65103 UNICAL
NIGER: Madame Kadi ALZOUMA (Représentante de la section nigérienne du Project PICG No. 381) Département de Géologie, Université Abdou Moumouni de Niamey, BP 10662 Niamey, NIGER. Tel.: 227 733072, Fax: 733072.
SWEDEN: Joen WIDMARK - Dept. of Marine Geology, Earth Sciences Centre, University of Goeteborg, 413 81 Goeteborg, SWEDEN. Tel.+46-31-773 44 70, Fax +46-31-773 49 03, E-mail: joen@gvc.gu.se / joen@marine-geology.gu.se
UNITED KINGDOM: Nick R. CAMERON (UK National Representantive at the Royal Society to IGCP Project 381) - Dept. of Geology, Imperial College, Prince Consort Road, London SW7 2BP, UK. Tel.:/Fax: +44-149-4774559, E-mail: nick@topaz.primex.co.uk
Alistair CRAME - British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK. Tel.: +44-223-251443, Fax: 62616, E-mail: jacr@pcmail.nerc-bas.ac.uk
VENEZUELA: Francia A. GALEA-ALVAREZ - CORPOVEN S.A., filial of P.D.V.S.A., Laboratorio Geológico, Apartado Postal 4326, Puerto La Cruz 692, VENEZUELA. Tel.: +58-81-606429, Fax: +58-81-606445.

CALL FOR PAPERS

*** Thematic Volume No. 1 ***

*********************************

List of Contributors

*** Thematic Volume No. 2 ***

Editors: M. R. Mello, E. A. M. Koutsoukos, et alii
(Potential publisher: American Association of Petroleum Geologists)
Main Topics: stratigraphic framework, depositional models, palaeogeographic reconstructions, source rock characterization, oil vs. source rock correlations and petroleum systems.

If you are interested in submitting a paper to either one of the above thematic volumes, you are invited to send an abstract to the SAMC Secretariat for review, as soon as possible. The complete manuscripts will be collected at a later date. Send your abstract in English, no longer than four letter-sized (A4) pages, including illustrations.
We look forward to receiving the proposals for more thematic volumes to be edited with collections of papers addressing specific issuess relevant to the project.

RELATED IGCP PROJECTS

IGCP Project 362: Tethyan and Boreal Cretaceous (TBC)
Co-leaders: Jozef Michalik (Bratislava, Slovakia) and Han Leereveld (Utrecht, The Netherlands)
Interaction between IGCP Projects 362 and 381 is of foremost importance to unveil the geological connections, palaeoceanographic links and biogeographic affinities between the Cretaceous northern South Atlantic and low-latitude, western Tethyan regions, which are common goals to both projects. Contacts and further information: TBC-Secretariat: M. TIEMESSEN - Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3584 CD Utrecht, THE NETHERLANDS. Tel.: +31-30-2532629, Fax: +31-30-2535096, E-mail: M.Tiemessen@boev.biol.ruu.nl

IGCP Project 301: Paleogene of South America
Contacts and further information:
Norberto MALUMIAN (Chairman)
Dirección Nacional del Servicio Geológico (CONICET), Tte. Fgta. Benito Correa 1194, 1107 Buenos Aires, Argentina. Tel.: +54-1-3617320, Fax: 3493160, E-mail: postmaster@mpgeo1.gov.ar.

PROGRAMME

Chairmen: Eduardo A. M. KOUTSOUKOS & Peter BENGTSON

9:30 Welcoming Remarks.

Session on "Gondwana palaeogeography and stratigraphic correlations"

9:40 Ronaldo L. MINCATO, A. SCHRANK & J. ENZWEILER (UNICAMP, Campinas, SP, Brazil) "The Paraná Continental Igneous Province and models of South Atlantic opening: a review"
10:00 Ana M. P. MIZUSAKI (UFRGS, Brazil), A. THOMAZ Filho & P. de CÉSERO (UFRJ, Brazil) "The magmatism related to the opening of the South Atlantic Ocean"

10:20 Nick R. CAMERON (Department of Geology, Imperial College, London, UK) "The salt: a deepening enigma?"
10:40-11:00: Coffee-break.
11:00 Cláudio Pires FLORENCIO (Universidade Federal do Ceará, Fortaleza, CE, Brazil) "Lés évaporites Paripueira du Bassin Sergipe-Alagoas"
11:20 M. LIMA Filho, M. S. S. VIANA & J. M. MABESOONE (LAGESE/DGEO/UFPE, Recife, PE, Brazil) "Tectonic and stratigraphic relationships between the Afrobrazilian and Araripe-Potiguar depressions (NE Brazil)"
11:40 Narendra K. SRISVASTAVA (Departamento de Geologia, UFRN, Natal, RN, Brazil) "Cretaceous continental stromatolites from the Araripe Basin, northeast Brazil"
12:00 J. M. MABESOONE (LAGESE/DGEO/UFPE, Recife, Pernambuco, Brazil) "Significance of Pernambuco-Paraíba-Rio Grande do Norte basin (NE BRazil) for Atlantic Cretaceous"
12:20-14:00: Lunch. Session on "Lower Cretaceous stratigraphic correlations"
14:00 Patricia VALLATI (Lab. de Bioestratigrafía, Universidad Nacional de La Patagonia, Argentina) "Palynology of Pozo D-129 Formation in the San Jorge Gulf Basin, Lower Cretaceous, Patagonia, Argentina"
14:20 Eduardo A. MUSACCHIO (Universidad Nacional de La Patagonia, Argentina) "Fossil Charophytes from South America"
14:40 Augusto Carlos da SILVA-TELLES Jr. (PETROBRAS-CENPES, Rio de Janeiro, Brazil) "Events of marine ingression of Jiquiá age (early Aptian?) in the Afro-Brazilian rift and tectono-eustasy relationships"
15:00-15:20: Coffee-break.
15:20 Ismar de Souza CARVALHO (Departamento de Geologia, UFRJ, Rio de Janeiro, Brazil) "Paleogeographic distribution of esthereliideans conchostraceans on the Cretaceous rift interior basins of northeastern Brazil"
15:40 Eduardo A. MUSACCHIO & M. SIMEONI (Universidad Nacional de La Patagonia, Argentina) "Biogeographic relationships of Lower Cretaceous calcareous microfossils from Patagonia: an approach to causal factors" Session on "Upper Cretaceous stratigraphic correlations"
16:00 Dimas DIAS-BRITO (UNESP, Rio Claro, São Paulo, Brazil) "Correlation of mid-Cretaceous events in the South Atlantic based on calcispheres and calpionelids: were they connected to the Tethyan events?"

16:20 Christian MEISTER (Muséum d'Histoire Naturelle de Genève, Switzerland), M. M'BINA & J. LANG (Centre des Sciences de la Terre, Université de Bourgogne, Dijon, France) "Les ammonites Cenomano-Turoniennes du Gabon: interet pour la Liaison Tethys-Atlantique Sud et correlations"
16:20 A. Scarparo CUNHA & S. SHIMABUKURO (PETROBRAS-CENPES, Rio de Janeiro, Brazil) "Evidence of Braarudosphere bloom at the Cenomanian-Turonian boundary of the Santos Basin, Brazil"
16:20 Luiz C. V. OLIVEIRA & Simone O. COSTA (PETROBRAS-CENPES, Rio de Janeiro, Brazil) "New calcareous nannofossil biostratigraphic units for the Maastrichtian of the Santos basin, SE Brazil"
16:20 Oscar STROHSCHOEN Jr. & E.A.M. KOUTSOUKOS (PETROBRAS, Rio de Janeiro, Brazil) "Upper Cretaceous palaeoecology of the south area of Campos Basin, southern Brazil"

Session on "Upper Cretaceous stratigraphic correlations" (continuation)

9:40 T. L. DUTRA, B. H. LEIPNITZ, U.F. FACCINI & Z. LINDENMAYER (UNISINOS, RS, Brazil) "A non-marine Upper Cretaceous interval in West Antarctica (King George Island, northern Antarctic Peninsula)"
10:00 Mitsuru ARAI & José BOTELHO NETO (PETROBRAS-CENPES, Rio de Janeiro, Brazil) "Biostratigraphy of the marine Cretaceous of the Southern and Southeast Brazilian marginal basins, based on dinoflagellates"
10:20 Zéli B. DIGBEHI, Konan R. YAO & Juliette TEA-YASSI (Université Nationale de Côte d'Ivoire) "Analyse palynologique du Senonien Supérieur de Côte d'Ivoire. Implications paléoenvironnementales" (Remarks: not-attending, presentation was cancelled.)
10:40-11:00: Coffee-break.
11:00 T. PLETSCH, T. WAGNER, W. KUHNT & Leg 159 Scientific Party (Universität Kiel, Germany) "Paleoenvironment of Upper Cretaceous black claystones from Leg 159 (Côte d'Ivoire-Ghana Tranform Margin)"
11:20 Peter BENGTSON, W.S. LIMA, K.-A. TRÖGER, E. A. M. KOUTSOUKOS & M.H. ZUCON (Geologisch-Paläontologisches Institut der Universität Heidelberg, Germany) "Campanian ammonites and inoceramids from the Sergipe Basin, Brazil" Session on "Upper Cretaceous palaeogeography and palaeoceanography"
11:40 Eduardo A. M. KOUTSOUKOS (PETROBRAS-CENPES, Rio de Janeiro, Brazil) "Late Cretaceous foraminiferal community dynamics and palaeoceanographic events in NE Brazil"
12:00 W.S. LIMA, P.R.S. SANTOS, P.C. GALM & J.D. ORTIZ (PETROBRAS-E&P, Sergipe, Brazil) "Preliminary biostratigraphic and paleontological survey in the Pernambuco-Paraíba Basin, northeastern Brazil"
12:20-14:00: Lunch.
14:00 Gerson FAUTH (Geologisch-Paläontologisches Institut der Universität Heidelberg, Germany) "History of research on Upper Cretaceous-Lower Tertiary ostracodes of the South Atlantic Ocean"
14:00 L. VERGARA & G. I. RODRIGUEZ (Universidad Nacional de Colombia, Bogotá, Colombia) "Upper Cretaceous stratigraphy and biostratigraphy of the Eastern Bogotá Plateau and Llanos foothills, Colombia: nomenclature and sequence stratigraphy implications" (Remarks: not-attending, presentation was cancelled.)
14:40 Abdoulaye DIOP (Université Cheikh Anta Diop, Dakar-Fann, Senegal) "A turbidite system with laminar gypsum facies (Upper Cretaceous, Western Senegal, West Africa)"
15:00-15:20: Coffee-break.
15:20 Victor N'DA & Pierre SAINT-MARC (PETROCI, Abidjan, Côte d'Ivoire) "Donnes stratigraphiques nouvelles sur le Cretace du Golfe de Guinee" (Remarks: not-attending, presentation was cancelled.)
15:40 Mohamed I.A. IBRAHIM & M. Rashad ABDEL-KIREEM (Alexandria University, Egypt) "Late Cretaceous palynofloras and foraminifera from Ain El-Wadi area, Farafra Oasis, Egypt"
16:00 Hussein Orabi ORABI (Faculty of Science, Menoufia University, Shiben El Kom, Egypt) "Biostratigraphy and paleoecology of the Campanian-Paleocene agglutinated foraminifera from Gabal Um El Ghanayim, Kharga Oasis, Egypt" (Remarks: not-attending, presentation was cancelled.)

16:20 Jorge O. CALVO & Leonardo SALGADO (Universidad Nacional del Comahue, Argentina) "A land bridge connection between South America and Africa during Albian-Cenomanian times based on sauropod dinosaur evidences"
16:20 Dilce F. ROSSETTI (Museu Paraense Emílio Goeldi- (DEL/MPEG/CNPq), Belém, PA, Brazil) "Depositional evolution of two estuarine successions: the upper Itapecurú Formation, São Luis basin, northeastern Brazil"
16:20 E. PEDRÃO, I. M. R. BARRILARI & H. P. LIMA (PETROBRAS, Brazil) "Palynological studies of the Cretaceous section of Parnaíba Basin"
16:20 El Hassane CHELLAÏ (Université Cadi Ayyad, Marrakech, Maroc) "The K/T boundary in the High Atlas of Marrakesh, Morocco" (Remarks: attendance not confirmed.)

Session on Gondwana palaeogeography and stratigraphic correlations (supplement)

9:40 Luis SPALLETTI (Centro de Investigaciones Geológicas, La Plata, Argentina) "Geological evolution of southern South American and South Atlantic basins"
10:00 Renato Rodolfo ANDREIS (Instituto de Geociências, UFRJ, Rio de Janeiro, Brazil) "The Cretaceous-Tertiary boundary around the Somuncurá Massif, northern Patagonia, Argentina, at Cerro Quadrado (Los Alamitos Formation) and Bajo de Santa Rosa (Allen Formation)"
10:20 Paulo P. MARTINS Jr. (Escola de Minas/DEGEO, Ouro Preto, MG, Brazil) & Gilberto A. ALBERTÃO (PETROBRAS-E&P/BC, Macaé, RJ, Brazil) "Geochemical aspects of the Cretaceous basins of the South Atlantic western margin in Brazil"
10:40-11:00: Coffee-break.
11:00 Malcolm B. HART & Archana TEWARI (University of Plymouth, Plymouth, Devon, UK) "A comparison of Brazilian marginal basins with those of the same age in Southern India"
11:20 Jorge R. SANCHEZ-ARANGO & R. TENREYRO (CEINPET, La Habana, Cuba) "Stratigraphy and geologic evolution of the continental margins of Cuba"
11:40 Evellio LINARES-CALA (CEINPET, La Habana, Cuba) "Geochronological studies of rocks from Cuba"
12:00 Sunday W. PETTERS (Department of Geology, University of Calabar, Calabar, NIGERIA) "Cretaceous sedimentary cycles of Nigeria" (Remarks: attendance not confirmed.)
12:20-14:00: Lunch.
14:00-16:20 Plenary Session of IGCP Project 381
Discussion of general issues, presentations of working-groups' Chairmen, proposal of further working-groups and of new research projects, and conclusion of the meeting proceedings.

Contributions from non-attending participants (see expanded abstracts):

Ahmed S. Kassab (Geology Department, Faculty of Science, Assiut University, Assiut 71516, Egypt): "Bioevents around the Turonian sub-stage boundaries in the Egyptian Eastern Desert and their inter-regional correlation"
Edwige MASURE & Raymond RAUSCHER (Laboratoire de Micropaleontologie, Département de Géologie Sédimentaire, Université P. & M. CURIE, Paris, France): "Les kystes de dinoflagellés du Santonien au Paléocène du Bassin ivoirien, au large du la Côte d'Ivoire, forage 959, croisière ODP 159"

Chairman: Márcio R. MELLO

9:40 Adroaldo M. CAMÕES & Nivaldo DESTRO "Fraturas naturais no campo de Candeias: uma nova abordagem visando a prospecção e a explotação de reservatórios de baixa permeabilidade."
10:00 Felix T. F. GONÇALVES & H. L. BENTEADO & R. P. BEDREGAL "Modelagem quantitativas da geração e migração do petróleo aplicada à exploração de hidrocarbonetos".
10:20 Marcio R. MELLO & Leslei B. MAGOON "Aplicação do conceito de sistema petrolífero como método preditivo na redução do risco exploratório".
10:40-11:00: Coffee-break.
11:00 Gordon D. WOOD "Integration of palynological and geochemical techniques for refining basin modeling parameters: Examples from Pakistan, Myanmar, Argentina and Paraguay".
11:20 José R. CERQUEIRA & Luiz A. F. TRINDADE "Geoquímica de reservatórios: Métodos e aplicações".
11:40 Frederico A. F. GOMES & L. G. da SILVA & Romero P. NEVES "Utilização da sísmica 3D na estimativa de propriedades de reservatório na Bacia Potiguar".
12:00 Sidnei Pires ROOTIROLLA & Paulo César SOARES & Rodoílton STEVANATO "Alguns aspectos da análise sistêmica aplicada à exploração: Sistema petrolífero versus sistema formador de minério".
12:20-14:00: Lunch.
14:00 Marcelo BASSETO & Webster U. MOHRIAK & Ines Santos VIEIRA "Modelagens gravimétrica e magnética utilizadas como ferramentas de apoio à análise regional de bacias sedimentares".
14:20 João de Deus Souto FILHO "Utilização de simulador numérico no estudo da migração secundária de petróleo, análise do fenômeno em escala de laboratório".
14:40 Carbeny Ramiro Capote MARRERO "Falhas verticais de longa vida como um novo critério no prognóstico petrolífero em Cuba"
15:00-15:20: Coffee-break.
15:20 Claudio Vinicius TAGLIARE "A sedimentação mista (siliciclásticos x carbonatos) e o exemplo da plataforma de Regência - Bacia do Espírito Santo".
15:40 Josemar S. Pereira FILHO & Claudio V. TAGLIARI & Antonio C. GUIRRO "Modelo deposicional da formação São Mateus no Campo de Fazenda Santa Luzia".
16:00 Armando Luiz de PAULA "Poços horizontais para produção de petróleo no Campo de Estreito, Bacia Potiguar (RN), Brasil".

16:20 Eduardo B. RODRIGUES & Carlos M. de A. SILVA & René RODRIGUES "Geoquímica de cimentos carbonáticos aplicada à modelagem diagenética".
16:20 Soraya G. CARELLI & Cacilda N. de CARVALHO. "Distribuição espacial de características geoquímicas - Uma ferramenta útil na prospecção de óleo e gás no município de Pilar - AL".
16:20 José D. ALECRIM, A. G. NEVES, G. B. BEZERRA, N. M. ANDRADE, T. S. FERREIRA, R. R. BORGES & F. A. de OLIVEIRA "Hidrogeoquímica ambiental aplicada à província petrolífera do Urucu, AM - Resultados preliminares".

Symposium on Tectonic, Depositional and Evolutionary Aspects of Rift Type Basins

Chairman: Hércules Tadeu F. da SILVA

9:40 Hercules Tadeu Ferreira da SILVA "Caracterização do início da fase sin-rifte na Bacia do Recôncavo, Estado da Bahia - Discussão sobre a Formação Água Grande e o reconhecimento da erosão do início do rifteamento".
10:00 Luciano P. MAGNAVITA "A implantação da fase sin-rifte em riftes continentais".
10:20 Luciano Seixas CHAGAS "Tectono-sedimentação em bacias rifte".
10:40-11:00: Coffee-break.
11:00 Cilmar Vital BUFNO "Análise de bacia em riftes não-marinhos com enfoque na exploração de petróleo: Tucano-Jatobá, uma experiência".
11:20 Egberto PEREIRA, Maria A. RODRIGUES, Sergio BERGAMACCHI & Sandra de F. OLIVEIRA. "Reconhecimento e caracterização de um rifte pós-Devoniano no flanco setentrional da Bacia do Paraná, no domínio da Serra Azul, nas regiões de Barra do Garças e Nova Xavantina, MT".
11:40 Luiz Felipe C. COUTINHO & Flávio G. GONZAGA "Evolução tectono-sedimentar e termomecânica da Bacia do Amazonas".
12:00 Hamilton D. RANGEL, Mario CARMINATTI & Carlos E. S. PONTES. "Evolução tectono-estratigráfica da fase rift na Bacia de Campos".
12:20-14:00: Lunch.
14:00 Paulo Cesar Romeiro SILVA "A fase rifte da Bacia de Campos".
14:20 Jane Leão de AMORIN, Marimônica R. Jaeger de CARVALHO & Luiz F. C. COUTINHO. "A sedimentação Alagoas nas bacias de Camamu e Almada. Uma interpretação preliminar".
14:40 Norberto RODOALHO, Luiz Ferradans MATO, Aurino J. F. ARAGÃO & Flávio E. TSCHIEDEL "Caracterização estrutural da porção noroeste da zona de falha de Mata-Catu, Bacia do Recôncavo".
15:00-15:20: Coffee-break.
15:20 José Milton Cronemberger MENDES "Seção neo-aptiana/eocenomaniana da Bacia de Sergipe-Alagoas (Fm. Riachuelo): Caracterização de rifteamento marinho na marges leste brasileira".
15:40 Mario F. Lima FILHO "Correlação da Bacia Cabo com as Bacias do Oeste Africano".
16:00 Adalberto da SILVA "Bacia de São Paulo: Contorno Estrutural integrando dados de poços e de superfície".

16:20 Renato M. Darros de MATOS & Ricardo N. WAICK & Vicente de P. Caldas PIMENTEL "Bacia do Ceará (Mundaú): Uma fase rifte não convencional ?"
16:20 Virginio H. NEUMANN, Luis CABRERA, Francesco CALVET & Maria Somália S. VIANA "Faciologia dos calcários da segunda fase lacustre na borda da chapada do Araripe-NE do Brasil".
16:20 Gordon D. WOOD "Sequence stratigraphy, palynofaceis, petrography and thermal maturation in a graben system: A case history from the reelfoot rift (mid-continent, USA)".
16:20 Ana Maria GÓES & Armando M. COIMBRA "Bacia das Alpercatas: Um sistema de rifts interiores".
16:20 Patricia Pamela ALVAREZ, Daniel J. PEREZ & Victoria A. RAMOS "Secuências de synrifte de la formacion rancho de Lata Alta Cordillera de San Juan (320LS-700LO), Argentina".

Symposium on Tectonics and Sedimentation in South American Basins

Chairman: Peter SZATMARI 09:45 Evandro de Mello XAVIER, Cristina WIEDMANN & Peter SZATMARI "Reativação meso-cenozóica do limite estrutural norte da Serra do Mar no Brasil e na África".
10:00 Claudio RICCOMINI "Tectônica da Bacia Bauru no Estado de São Paulo".
10:20 Daniel J. PÉREZ & Ernesto O. CRISTALLINI. "La cuencia de antepais de manatiales y su relacion con la estructura de la alta Cordillera de Los Andes a los 320S, Argentina".
10:40-11:00: Coffee-break.
11:00 Rogério Luis PEREIRA "SDR (Seaward Dipping Reflectors) e a transição na Bacia de Pelotas".
11:20 Webster U. MOHRIAK, Marcelo BASSETO & Ines S. VIEIRA "Estrutura crustal, tectônica e sedimentação na Bacia de Sergipe-Alagoas".
11:40 Peter SZATMARI & João B. L. FRANÇOLIN "Controle tectônico da evolução da margem equatorial".
12:00 Jorge A. L. POLONIA, C. M. VALERIANO, Marta C. M. GUERRA & Mônica A. PEQUENO "Modelagem física da deformação geradora do rifte do Cabo Litoral Sul do Estado de Pernambuco".
12:20-14:00: Lunch.
14:00 Marta C. de Mello GUERRA, Peter SZATMARI & Mônica A. PEQUENO "Modelagem subaquática um importante avanço na tectônica experimental".
14:20 Flávio L. FERNANDES, S. Rostirolla, N. C. de AZAMBUJA Filho & Luis A. M. de AGUIAR "A técnica de balanceamento de seções geológicas - aplicação na evolução dos domos de sal na área do Campo de Namorado. Bacia de Campos".
14:40 Pedro Edson L. BEZERRA & João Batista S. COSTA "Evolução tectônica da região de Carolina (MA, TO), Bacia do Parnaíba".
15:00-15:20: Coffee-break.
15:20 Paulo C. SOARES, S. P. ROSTIROLLA, Francisco J. F. FERREIRA & Rodoilton STEVANATO "O alto estrutural Pitanga - Quaticuá - Jacutinga na Bacia do Paraná: Uma estrutura litosférica"
15:40 Mario Luis ASSINE "Correlação entre as seqüências pré-carboníferas da Bacia do Paraná e as orogêneses pré-andinas"
16:00 Marcelo A. Martins NETO "Aspectos tectono-deposicionais da tectono-seqüência Galho do Miguel, Bacia do Espinhaço, MG"

16:20 Jorge Fiori Fernandes SOBREIRA "Complexo vulcânico de Abrolhos - Proposta de modelo tectono-magmático"
16:20 João Claudio J. CONCEIÇÃO, Ana M. P. MIZUSAKI, Daisy B. ALVES & Peter SZATMARI "Controle tectônico do magmatismo do complexo vulcânico de Abrolhos, Bacia do Espírito Santo"
16:20 Rosilene FRANÇA & Gilberto Machado RAGAGNIN "A influência do vulcanismo de Abrolhos na sedimentação terciária da Bacia de Mucuri"
16:20 C. L. FAMBRINI, M. A. B. MARTIN, A. R. S. FRAGOSO, Cesar J. MORFATH, A. CHIARINI, W. F. da SILVA Filho, R. S. SATEG, R.MACHADO & T. I. Ribeiro de ALMEIDA "Registro preliminar sobre o vulcanismo Bom Jardim na borda sudoeste da Bacia do Camaquã, RS: Evidências de atividade piroclástica subaquática sob a ação de ondas e correntes de turridez"
16:20 João B. L. FRANÇOLIN, Osmar A. ZANOTTO & Peter SZATMARI "Análise estrutural de eventos pós-jurássicos na Bacia do Paraná"
16:20 Wellington Ferreira da SILVA Filho, A. R. S. Fragoso CESAR, R. MACHADO, H. S. SAVEG, G. L. TAMBRINI & T. I. Ribeiro de ALMEIDA "O magmatismo Rodeio Velho e a Formação Guaritas no eopaleozóico do Rio Grande do Sul: uma reavaliação de suas relações de contato"
16:20 Mauro Rodrigues REIS & Iran Carlos Stallivieri CORREA "Paleovale do sistema fluvial tubarão sobre a plataforma continental de Santa Catarina: Evidências e importância estrutural".
16:20 Márcia C. L. QUINTAS & Marta S. M. MANTOVANI "Modelagem do processo erosivo no estudo da evolução mecânica da Bacia do Paraná (resultados preliminares)".

FIRST ANNUAL CONFERENCE OF IGCP PROJECT 381 (SOUTH ATLANTIC MESOZOIC CORRELATIONS) Salvador, Bahia, Brazil, 2-5 September 1996

CONTRIBUTIONS

Campanian ammonites and inoceramids from the Sergipe Basin, Brazil

Peter BENGTSON(1), W.S. LIMA(2), K.-A. TRÖGER(3), E. A. M. KOUTSOUKOS(4) & M.H. ZUCON(5)
(1) Geologisch-Paläontologisches Institut, Universität Heidelberg, In Neuenheimer Feld 234, D-69120 Heidelberg, Germany.
(2) Petrobras S.A.-E&P-SE/AL-GEXP, Rua Acre, 2504, Siqueira Campos, 49080-010 Aracaju, Brazil.
(3) Institut für Geologie, TU Bergakademie Freiberg, Bernhard-von-Cotta-STR. 2, D-09596 Freiberg, Germany.
(4) Petrobras-Cenpes, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, Brazil.
(5) Departamento de Biologia/CCBS, Universidade Federal de Sergipe, Cidade Universitária, Av. Marechal Rodon, s/n - Jardim Rosa Elze, 49.100-000 São Cristovão, SE, Brazil.

Comparatively little is known about the uppermost Cretaceous macropalaeontology of the Sergipe Basin. The lithology of this part of the marine succession is dominated by shales with intercalations of locally calcareous siltstones and fine-grained sandstones; these make up the Calumbi Formation (formerly Piaçabuçu Formation). There are few fossiliferous outcrops, in sharp contrast to the extensively exposed fossil-rich underlying clastic and carbonate sequence (Riachuelo and Cotinguiba formations, Aptian to Coniacian). Biostratigraphy of the uppermost Cretaceous of Sergipe has until now relied almost entirely upon microfossil work on subsurface material (e.g., Koutsoukos & Bengtson, 1993). The recent finds of ammonites and inoceramid bivalves from an outcrop of the Calumbi Formation are therefore of considerable importance. Here we present a systematic and biostratigraphical study of these macrofossils, together with supporting biostratigraphical data on the accompanying foraminifera.
For a summary account of the Cretaceous development of the Sergipe Basin, the reader is referred to Koutsoukos et al. (1993) and Koutsoukos & Bengtson (1993) and references therein. The carbonate platform and subsequent ramp regime of the Riachuelo and Cotinguiba formations lasted until the mid-Coniacian. As a result of the final structural detachment of South America from Africa the basin tilted seawards, which caused uplif of the marginal areas, widespread regression and a breakdown of the previous carbonate-dominated depositional cycle. The subsequent transgression reached the present onshore parts of the basin in the late Santonian or early Campanian, with deposition of the chiefly terrigenous clastic Calumbi Formation. A number of macrofossils, mainly molluscs, have been described from these beds (Oliveira, 1940, Löfgren & Oliveira, 1943, Santos & Castro, 1970, Muniz et al., 1981, Muniz, 1984, Santos et al., 1994); however, very few of these are of any biostratigraphical significance. No ammonites have been reported and the only description of an inoceramid dates back to 1940 (Oliveira, 1940). The material described here comes from the "type locality" of the formation, an isolated small outcrop northeast of the state capital Aracaju, near the village of Calumbi, which once lent its name to the formation (Duarte, 1936, Bender, 1959). Previous workers suggested a Campanian/Maastrichtian or Maastrichtian age to the siltstones exposed at this locality. The association of ammonites and inoceramids together with foraminifera now indicate a more precise, late Campanian age; nevertheless, further work is needed in order to achieve a reliable correlation with the surrounding south and central Atlantic basins.
Although macrofossils are common at the Calumbi outcrop, ammonites and inoceramids are rare; so far only seven specimens of each have been found. The limited number of specimens, in combination with their poor preservation, makes taxonomic work difficult, as the full ontogenetic development and the range of intraspecific variation cannot be assessed. This concerns particularly the ammonites, of which as many as six of the seven specimens found belong to different species. The ammonite fauna of the Calumbi section includes Eulophoceras sp., Vertebrites cf. kayei (Forbes, 1846), Diplomoceras? sp., and an apparently new kossmaticeratid genus, all previously unknown from Brazil. The inoceramids belong to the group of Inoceramus (Endocostea) balticus Böhm, 1907, which have been reported from the Pernambuco-Paraíba Basin further north (Muniz, 1993). The association of benthic foraminifera extracted from the macrofossil specimens is referred to the early to late Campanian Lacosteina gouskovi-Orthokarstenia clavata Zone of Koutsoukos & Bengtson (1993), which is typical of an outer shelf to upper bathyal environment, near the shelf edge, below the euphotic zone. Planktonic foraminifera are less abundant and less diagnostic (Contusotruncana fornicata, Globigerinelloides multispina, G. prairiehillensis, Rugoglobigerina ex gr. rugosa), although consistent with a Campanian age. Other, non-diagnostic fossils from the Calumbi outcrop include abundant small bivalves and gastropods and fish remains.
References
BENDER, F., 1959. Zur Geologie des Küsten-Beckens von Sergipe, Brasilien. Geologisches Jahrbuch, Vol. 77, pp. 1-33.
DUARTE, A. G., 1936. Petróleo e condições para sua ocorrência no Estado de Sergipe. Mineração e Metalurgia, Vol. 1, No. 3, pp. 116-117
KOUTSOUKOS, E. A. M. & BENGTSON, P., 1993. Towards an integrated biostratigraphy of the upper Aptian-Maastrichtian of the Sergipe Basin, Brazil. Documents du Laboratoire de Géologie de Lyon, Vol. 125, pp. 241-262.
KOUTSOUKOS, E. A. M., DESTRO, N., AZAMBUJA FILHO, N. C. de & SPADINI, A. R., 1993. Upper Aptian-lower Coniacian carbonate sequences in the Sergipe Basin, northeastern Brazil. In: SIMO, T., SCOTT, B., MASSE, J. P. (Eds), Cretaceous Carbonate Platforms. American Association of Petroleum Geologists Memoir, No. 56, pp. 127-144.
LÖFGREN, A. & OLIVEIRA, P. E. de, 1943. Fósseis cretáceos de Aracaju, Sergipe. Divisão de Geologia e Mineralogia, Boletim, No. 106, pp. 1-54.
MUNIZ, G. C. B., 1984. Um novo macrofóssil da Formação Piaçabuçu (Bacia Sergipe/Alagoas) e respectivas especulações paleoecológicas. In: XXXIII Congresso Brasileiro de Geologia, Anais, pp. 517-521, Rio de Janeiro.
MUNIZ, G. C. B., 1993. Novos moluscos da Formação Gramame, Cretáceo Superior dos estados da Paraíba e de Pernambuco, Nordeste do Brasil. Departamento de Geologia da Universidade Federal de Pernambuco, Publicação Especial, No. 1, pp. 1-202, Pls. 1-16.
MUNIZ, G. C. B., NEVES, B. B. B. & ZUCON, M. H., 1981. Icnofósseis da Formação Piaçabuçu (Nordeste do Brasil) e respectivo significado paleoecológico. In: II Congresso Latino Americano de Paleontologia, Anais, Vol. 1, pp. 359-371, Porto Alegre.
OLIVEIRA, P. E. de, 1940. Idade do calcário de Calumbi (Sergipe). Divisão de Geologia e Mineralogia, Notas Premilinares e Estudos, Vol. 19, pp. 1-12.
SANTOS, M. E. C. M., CASTRO, J. S., 1970. O gênero Roudairia Munier-Chalmas no Brasil. Anais da Academia Brasileira de Ciências, Vol. 42, No. 4, pp. 731-738.
SANTOS, E. A., ZUCON, M. H. & HESSEL, M. H. R., 1994. Observações paleoecológicas sobre Lopha aracajuensis (Bivalvia, Ostreidae) do Neocretáceo de Sergipe, Brasil. Acta Geologica Leopoldensia, Vol. 16, No. 39/2, pp. 723-731.

A land bridge connection between South America and Africa during Albian-Cenomanian times based on sauropod dinosaur evidences

Jorge O. CALVO & Leonardo SALGADO - Museo de Geología y Paleontología. Universidad Nacional del Comahue. Buenos Aires 1400. (8300) Neuquén, Patagonia, Argentina.

The discovery of sauropods from Lower Cretaceuous beds in Africa and South America shows that they had a cosmopolitan distribution across this part of Gondwana before the onsed of continetal fragmentation. Some of the sauropod specimens recorded allow us to infer when Africa and South America siplit apart.
The primitive titanosaurs Andesaurus delgadoi (Calvo & Bonaparte, 1991), from the Albian-Cenomanian of Argentina, and Malawisaurus dixeyi (Jacobs et al., 1993) from the Lower Cretaceous of Malawi, share undivided dorsal vertebrae, ischium transversely expanded, anterior procelos caudal vertebrae, ischium transversely, expanded anterior procuelous caudal vertebrae amphiplatyan middle and posterior caudals, and open haemal arches. A combination of characters presents only in these two species.
On the other hand, the primitive Diplodocimorpha (Calvo & Salgado, in press) Rebbachisaurus garasbae (Lavocad, 1954), from the Aptian-Albian of Morocco, and Rebbachisaurus tessonei (Calvo & Salgado, 1991, in press) from the Abian-Cenomanian of Argentina, share: a broad, paddle-like scapular blade, and a very high and undivided neural spine on dorsal vertebrae with a deep pleurocoel on the centrum. These characters are seen only in these two species. Recently, Bonaparte (1995) described a new sauropod Rayososaurus agrioensis from the Aptian of Neuquén, Argentina, based on an scapula and very few other poor fragments; the broad distral scapular blade and the direction of the acromion process (a regarded autopomorphy of Rebbachisaurus) resemble to much to that of Rebbachisaurus tessonei. The characters used by Bonaparte to erect Reyososaurus are, instead, Rebbachisaurus apomorphies; so that we propose to include these materials within Rebbachisaurus sp. until more material be discovered. Therefore, we assign Rebbachisaurus agrioensis as nomen dubia. The strong similarities on the saropod fauna in Africa and South America are consistent with the presumed proximity of both continents by that time. Probably, both continents were connected by a land bridge at least up to Albian-Cenomanian times.
This evidence our knowledge on the vertebrate fauna common to both continents during the Albian-Cenomaniam times. Up to know the vertebrate fauna present in both continents is composed by: the Mesosuchian crocodiles Araripesuchus from the Aptian of Northeastern Brazil and Niger (Buffetaut & Taquet, 1979);. the giant crocodilian Sarcosuchus from the Aptian of Brazil and Niger (Buffetaut & Taquet, 1977); the turtles Araripemydae from the Aptian of Niger an Brazil (de Broin , 1980) and the coelacanths Mawsonia from the Aptian-Albian of Brasil and Africa (Wenz, 1980).
Funding: This research was funded by The Dinosaur Society Foundation and the National University of Comahue , Neuquén, Argentina.
References
Bonaparte, J. F., 1995. Dinosaurios de América del Sur. Mus. Arg. Cs. Nat., 175 pp. Buffetaut, E. &Taquet, P., 1977. The giant crocodilan Sarcosuchus in the Early Cretaceous of Brazil and Niger. Paleontology, Vol. 20, pp. 203 208.
Calvo, J. O. & Bonaparte, J. F., 1991. Andesaurus delgadoi gen. et. sp. nov. (Saurischia-Sauropoda), dinosaurio Titanosauridae de la Formacion Rio Limay (Albian-Cenomanian), Neuquén, Argentina. Ameghiniana, Vol. 28, No. 3-4, pp. 303-310.
Calvo, J. O. & Salgado, L., 1991. Posible registro de Rebbachisaurus Lavocat (Sauropoda) en el Cretácico medio de Patagonia. Ameghiniana, Vol. 28, p. 404. La Rioja.
Calvo, J. O. & Salgado, L., in press. Rebbachisaurus tessonei, a new Sauropoda from the Albian-Cenomanian of Argentina; new evidence on the origin of the Diplodocidae. GAIA.
De Broin, F., 1980. Les tortues de Gadoufaoua (Aptian du Niger) apercu sue le paleobiogeographie des Pelomedusida (Pleurodira). Memoirs de la Societé Geologique de France. N. S.
Jacobs, L. L., Winkler, D. A., Downs, W. R. & Gomani, E. M., 1993. New material of an Early Cretaceous Titanosaurid Sauropod dinosaur from Malawi. Paleontology, Vol. 36, No. 3, pp. 523-534.
Lavocat, R., 1954. Sur les Dinosauriens du continental intercalaire des Kem Kem de la Daoura. C.R. 19th Internat. Geol. Congr. (1952), Vol. 3, pp. 65-68.
Wenz, S., 1980. A propos du genre Mawsonia, Coelacanthe geant du Cretace Inferieur d'Afrique et du Brasil. Memoirs de la Societé Geologique de France, N.S. Vol. 139, pp. 187-190.

The Salt: a deepening enigma?

Nick R. CAMERON - Imperial College, London: Department of Geology, Royal School of Mines, Consort Road, London SW7 2BP, U.K. E-mail: nick.cameron@ic.ac.uk (or) nick@topaz.primex.co.uk

Until the late-1980s it was sufficient for most purposes to treat the Salt as a single unit defining the boundary between drift and rift successions of the South Atlantic. The oceanwards limits of the Salt marked, after allowing for the subsequent translational tectonism, the pre-drift boundary between western Africa and Brazil. The Salt basin was separated from the ocean to the south by the volcanic ridges created by the Tristan Hot Spot. Sulphates were important in Angola and potassium salts together with unusual calcium and magnesium chlorides were known from the Congo northwards.
It is now apparent, both from well results and more especially from basin modelling, that the Salt can no longer be usefully considered as a simple blanket unit. For example, two Aptian aged salts separated by transitional/paralic beds are present in the Sergipe-Alagoas basin. In addition, Barremian salts are known from both the Congo and Angola. Modelling suggests that even for single horizon salts synchronous deposition was most unlikely. This is because sufficient remnant topography existed across the rift generated hinge lines to prevent at any one time more than the strip deposition of salts. The trace of the West African Atlantic Hinge is considered to have been defined in end-Aptian times by a scarp exhibiting several hundred metres of relief.
Two salt models for the South Atlantic permit strip deposition. McGinnis and others, aware of the palaeo-relief difficulties and the recent discoveries of older salts, suggested that the in-place salt west of the Atlantic Hinge was pre-late Aptian in age and, therefore, unrelated to the break-up succession. They suggested that marine environments existed to the west of the Atlantic Hinge during the deposition of the Aptian salts. Provided there were multiple flood events during the deposition of the Aptian salt, Burke's inundation theory provides a totally different explanation. This ingenious model, prepared some twenty years before the work of McGinnis and others, postulates that all the salts are the product of a Messinian-type flood into a dry ocean scale basin. Maximum floods would permit salt deposition east of the Atlantic Hinge and the accumulation of marine beds to the west. Lesser floods would permit salt deposition in the deep basins. In the Sergipe-Alagoas Basin, which may contain the most complete accessible Aptian succession, the flood event can be associated with the transgressive base of the Carmópolis Formation. Burke and Sengör calculated that the late Aptian flood would generate a 10 metre draw down in the world's ocea»
Interestingly, on the Haq Chart the base of the Carmópolis Formation as defined by Bruhn et al. (1988) ties to the 112 Ma lowstand. On the Harland timescale this lowstand plots at about 122 Ma and the deposition of the oldest salt begins at about 121 Ma. With the increasing interest of the oil companies in deepwater exploration, IGCP 381 presents the ideal vehicle for the examination of the detailed stratigraphy of the Salt and its associated sediments. Until the issues briefly introduced in this abstract are resolved it will not be possible to prepare meaningful palaeogeographic maps for this critical period in the history of the South Atlantic. The immediate task is to determine the age limits of the Salt and to describe the geology of the associated deposits.
References
Bruhn, C. H. L., Cainelli, C., de Matos, R. M. D., 1988. Hábitos do petróleo e fronteiras exploratórias nos rifts brasileiros. Bol. da Geociencias da Petrobras, Vol. 2, No. 2-4, pp. 217-253.
Burke, K., 1975. Atlantic evaporites formed by evaporation of water spilled from the Pacific, Tethyan and Southern oceans. Geology, Vol. 3, pp. 613-616.
Burke, K. & Celal Sengör, A. M., 1988. Ten metre global sea-level change associated with South Atlantic Aptian salt deposition. Marine Geology, Vol. 63, pp. 309-312.
McGinniS, J. P., Driscoll, N.W., Karner, G.D., Brumbaugh, W.D. & Cameron, N., 1993. Tectonic significance of synrift sediment packages across the Congo continental margin. Bulletin American Association Petroleum Geologists, Vol. 77, No. 9 (September), pp. 1646.

Paleogeographic distribution of esthereliidean conchostraceans on the Cretaceous rift interior basins of northeastern Brazil

Ismar S. CARVALHO - UFRJ / Departamento de Geologia, Rio de Janeiro, RJ, Brazil.

Among the various groups of Cretaceous conchostraceans from northeastern Brazil, the esthereliideans were restricted to the initial development stages of interior rift basins such as Souza, Jatobá and Tucano (Figure 1). The two known species - Estheriella brasiliensis and Esthereliella lualabensis - are only found in Lower Cretaceous rocks (Rio da Serra and Aratu local stages).
Estheriella brasiliensis occurs in Souza, Jatobá and Tucano basins. In the African basins of Congo, Mayo Oulo Léré and Mayo Tafal, the species Estheriella camerouni and Estheriella moutai show a morphological pattern similar to the Brazilian species (Carvalho, 1993). According to Oliveira (1953), Estheriella brasiliensis is a good index-fossil for the biostratigraphy of Lower Cretaceous continental rocks (Rio da Serra and Aratu stages). The original description of Estheriella lualabensis comes from Upper Jurassic-Lower Cretaceous of the Lualaba Series (Congo Basin). In the northeastern Brazilian basins, it is found in the Souza Basin, exclusively in Lower Cretaceous rocks (Rio da Serra and Aratu stages). The small area of paleogeographic distribution of these two species may reflect local taphonomic conditions. The fossilization through mouldage, could lead to the loose of fine morphological details (such as the radial ribs), which allow them to be classified. Despite this, the great number of conchostraceans on the Cretaceous basins of the northeastern Brazil required specific environmental conditions. In this way we can infer the palaeocological aspects of the small lakes from these interior rift basins. The living conchostracofauna are typical of alkaline shallow freswaters (pH between 7 and 9), in well-oxygenated environments with argillaceous substrates. The water temperature was probably between 200 - 300C, the ideal to the conchostraceans (Massal, 1954). The ponds where this low-diversity conchostracofauna thrived were shallow and ephemeral. Such stressing ecological parameters are highly restrictive to the settlement of and abundant and diversified biota.
References
CARVALHO, I. S., 1993 Os conchostráceos fósseis das bacias interiores do Nordeste do Brasil. Tese de Doutorado, Vol. 1, 319 pp., Universidade Federal do Rio de Janeiro, Departamento de Geologia, Rio de Janeiro.
MASSAL, L., 1954. Deuxième note sur le milieu e la croissance des esthérias. Bulletin de la Societé des Sciences Naturelles de Tunisie, Vol. 7, pp. 163-181.
OLIVEIRA, P. E., 1953. Sobre um novo conchostráceo fóssil do Estado da Bahia. Divisão de Geologia e Mineralogia, DNPM. Notas preliminares e estudos, Boletim No. 63, 13 pp., Rio de Janeiro.

The K/T boundary in the High Atlas of Marrakesh, Morocco

El Hassane CHELLAÏ - Université Cadi Ayyad, Faculté des Sciences Semlalia, Marrakech, Maroc.

Résumé Les dépôts maastrichtiens et paléogènes du versant nord du Haut-Atlas of Marrakech ont été découpés en deux systèmes sédimentaires, séparés par une discontinuité régionale. Le système inférieur est d'âge Maastrichtien. Ses séquences de dépôt de 3e ordre, de plus en plus développées vers l'Est, dans le sens proximal à distal de la rampe carbonatée de l'époque, sont interprétées comme la fin d'une séquence de comblement après le Sénonien inférieur en période régressive de 2e ordre. Le système supérieur (Paléocène supérieur à Lutétien) est composé de plusieurs séquences de 3e ordre, plus lacunaires à l'Ouest, traduisant des ingressions successives de la mer suivies de retraits. II correspond à la séquence rétrogradante ou agradante de la période transgressive d'un cycle régressif/transgressif de 2e ordre (au sens de Jacquin et al., 1992). A partir de l'Eocene supérieur/Oligocène, le secteur fonctionne en avant-pays de la chaîne de l'Atlas en cours de plissement.

Abstract
The Maastrichitian and Palaeogene deposits of the northern side of the High Atlas of Marrakesh have been subdivided into two sedimentary systems, separated by a regional disconformity. The former is of Maastrichitian age. Their third order deposition sequences are more developed going from West (proximal deposits) to East (distal deposits) and constitute a carbonate ramp system of this epoch. They are interpreted as the end of a filling sequence in a second order regressive period after the early Senonian. The latter (late Palaeocene to Lutetian) is composed of several sequences of third order which constitute a sedimentary hiatus to the West. These sequences represent successive ingressions followed by the withdrawal of the sea. This last system corresponds to the aggradation or retrogressive sequence of the transgressive period of the second order of a transgressive/regressive cycle (according to Jacquin et al., 1992). From the late Eocene to Oligocene, the sector functions as a Atlasic chain foreland basin.

Correlating mid-Cretaceous South Atlantic events based on calcispheres and calpionellids: are they connected to the Tethyan ones?

Dimas DIAS BRITO - Universidade Estadual Paulista - UNESP - IGCE/DGS, C. P. 178, 13506-900, Rio Claro, SP, Brazil. E-mail: dimas@geo001.uesp.ansp.br

Mid-Cretaceous pelagic carbonates from South Atlantic are rich in planktonic content. Sensible to the water masses variations, they can be used to correlate events occurred at local, regional or global scales. This note intends: a) to present and discuss the occurrences of calcispheres (Pithonelloideae Keupp 1987 - calcareous dinoflagellates) and colomiellids (Calpionelleae Bonet 1956 - incertae sedis planktonic organisms) in South Atlantic areas; b) to analyse and compare stratigraphic successions of bio-events (i.e. first and last occurrences of species) envolving calcispheres and colomiellids in the Brazilian Atlantic Margin (BAM); c) to establish comparisons with coeval successions from the African Atlantic Margin (AAM); d) to verify if these successions of bio-events are connected to those from the classic Tethyan realm.
More than 2,000 thin sections have been investigated using optical microscope. Analyses carried out with the S.E.M. allowed the observation of more than 5,000 calcispheres. Essentially, the studied material is originated from pelagic carbonate cores of 18 wells drilled by PETROBRAS along the equatorial and eastern Brazilian coastal basins, including, from the north to the south: Barreirinhas, Potiguar, Sergipe-Alagoas, Jequitinhonha, Espírito Santo, Campos and Santos. The taxa were chronostratigraphically arranged using the framework established for different groups of planktonic organisms, i.e., organic-walled dinoflagellates, foraminifers and calcareous nannofossils (Dias-Brito, 1995a). Thus it was possible to evaluate the successions of bio-events and, synthetically, group them into a figure used for comparisons with those from AAM, the Gulf of Mexico and the West Carpathian in Central Europe.br> The Pithonelloideae of BAM: Pithonella sphaerica, P. ovalis, P. cf. P. perlonga, P. trejoi and Bonetocardiella conoidea [recognized as typical Tethyan taxa, with long stratigraphic range (except B. conoidea, upper Albian-Turonian)]. Amongst other microfossils, P. trejoi is also an index to the upper Albian-Turonian. Based on their first occurrence levels, the latter two species may indicate upper Albian deposits. Quantitatively, the group occurs in an irregular and discrete way in the lower- middle Albian (in this interval it does not occur in Barreirinhas Basin), but it presents a strong and remarkable bloom in upper Albian strata. This fact, in connection with a sensible increase in biodiversity, it is recorded in the Campos, Espírito Santo, Santos and Barreirinhas basins. At these levels, they are often associated with radiolarians, suggesting coastal upwellings.
In the southeastern basins, the pelagic carbonate sedimentation cycle came to an end during latest Albian times (Vraconian), due to strong subsidence of the region, with the definitive oceanization of the system. A such ecologic impact resulted in mass mortality of the pithonelloids, which were opportunistic organisms highly dependable upon warm, salt and CaCO3-rich neritic water masses. This phenomenon determined an abrupt and irreversible disappearance of the pithonelloids in the region. However, in the northeastern basins these calcareous dinoflagellates remained to flourish, though less abundantly, in post-Albian neritic waters. In the Sergipe-Alagoas Basin, with a longer-lasting carbonate sedimentation, the pithonelloids occurred until the Santonian. Rare specimens were detected in upper Campanian levels of Sergipe-Alagoas and Potiguar basins. Therefore, the figures of quantitative distribution for these temporal long-ranging bioelements reflect fluctuations in the oceanographic conditions - driven chiefly by minor or major tectonic-climatic alterations - on local, regional, multiregional or global scales. They can be excellent paleoceanographic tools on a global scale. Pelagic carbonate deposits rich in Pithonelloideae reveal Tethyan water masses, best noticed from the late Albian to the Coniacian, the climax phase of the Subfamily Pithonelloideae all over the world in association with the highest sea-level phase of Meso-Cenozoic times. In addition, it is possible to estimate its high aplicability when combined to graphoeletric profiles and isotopic data on a basin scale.
Colomiellids recorded at BAM: Colomiella recta, Colomiella mexicana. Typical index-fossils of the Tethyan realm, these organisms have been only detected in the Santos Basin in association with pelagic carbonates accumulated in deep neritic area. Stratigraphically, these species are highly significant: their co-occurrence indicate the base of the lower Albian.
Pithonelloids and colomiellids of AAM: pithonelloids have been recorded in wells of DSDP (Leg 40), the site 363, offshore Namibia, being the richest section (Bolli, 1978). Colomiellids (sensu lato) occur in Aptian Angolan limestones and Colomiella recta was detected in lower Albian calcimudstones of Gabon (Chevalier & Fisher, 1982).
Comparing the mid-Cretaceous sections from Campos Basin to the section of the site 363, one can see the remarkable biostratigraphical correspondence between them (Dias-Brito, 1985). Thus it is possible to identify that the Vraconian oceanographic event that has caused the end of the carbonate sedimentation in the southeastern Brazilian Coast has also impacted the African equivalent (on a multiregional scale).
The above mentioned information and the synthetized figure elaborated for the BAM, added to the Namibian one, compared to the figures from the Gulf of Mexico and the West Carpathians (Fig. 1), show that there is an evident relation between oceanographic events occurred in these areas during the mid-Cretaceous. This is noticeable in two aspects: a) in the different regions it was registered in the same order of vertical succession of taxa appearances, what happened according to chronological correspondence (the equivalence between the BAM and the Gulf of Mexico is particulary marked, as more widely discussed in Dias-Brito, 1994); b) it was registered during the late Albian from the herein considered areas (as reported in all places with Tethyan pelagic carbonate deposits) a corresponding and surprising increase in the species diversity and specimens abundance. Such evidence is one that has led the author to propose that the Northern South Atlantic (to the north of the São Paulo-Walvis Ridge barrier) was originated as an extension of the Tethys (Dias-Brito, 1995 a, b).
References
BOLLI, H. M., 1978. Cretaceous and Paleogene Calcisphaerulidae from DSDP Leg 40, southeastern Atlantic. In: BOLLI, H. M. & RYAN, W. B. F. (Eds.). Init. Repts. DSDP, Vol. 40, pp. 819-837.
BORZA, K., 1984. The Upper Jurassic - Lower Cretaceous parabiostratigraphic sacale on the basis of Tintinninae, Cadosinae, Stomiosphaeridae, Calcisphaerulidae, and others micraofossils from the West Carpathians. Geologica Carpathica, Vol. 35, No. 5, pp. 539-550.
CHEVALIER, J. & FISCHER, M., 1982. Présence de Colomiella BONET (Calpionellidae) dans le Crétacè inferieur (Madiéla) du Gabon. Cahiers de Micropaléontologie, Vol. 2, pp. 29-34.
DIAS-BRITO, D., 1994. Comparação dos carbonatos pelágicos do Cretáceo médio da margem Atlântica Brasileira com os do Golfo do México: novas evidências do Tétis Sul-Atlantiano. In: Simpósio sobre o Cretáceo do Brasil, Boletim, Vol. 3, pp. 11-18, Rio Claro.
DIAS-BRITO, D., 1995,a. Calcisferas e microfácies em rochas carbonáticas pelágicas mesocretáceas. Tese de Doutoramento, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil, 688 pp.
DIAS-BRITO, D., 1995c. The South Atlantic Albian carbonates: their organogenic content and paleoceanographic significance. First Workshop of Paleoceanography with emphasis on Micropaleontology and Stratigraphy (Gramado, Rio Grande do Sul, 12-15 November 1995), Extended Abstracts, pp. 47-48.
McNULTY, D., 1985. Micropaleontological stratigraphic framework for the Cretaceous black lime wackestones-mudstone facies of the Gulf of Mexico: In: Annual Research Conference on the Gulf Coast, Proceedings, Vol. 4, pp. 1176-1191, SEPM, Tulsa.

A turbidite system with laminar gypsum facies (Upper Cretaceous), Western Senegal, West Africa

Abdoulaye DIOP - Départment de Géologie, Faculté des Sciences et Techniques Université Cheikh Anta Diop, Dakar, Senegal.

The study area is located in the most western the Senegal Basin. The Senegal Basin with 340,000 km2 is the largest West African marginal sag basin. It extends from Mauritania to Guinea Bissau.
The northern boundary of the Senegal-Mauritania basin is formed by a piece of the Precambrian West African craton : the Reguibat high. Along the eastern and southern boundary it is bordered by a Paleozoic fold belt that stretches more than 1,800 km from southern Morocco to Sierre Leone : the Mauritanides.
Like other East Atlantic basins, the Mauritaia-Senegal Basin is a marginal sag basin resulting from the opening of the Atlantic Ocean. It dips gently westwards and continue under the Atlantic Ocean.
According to gravimetric data, this basin apparently stable, is a rift. During the openning of the Atlantic Ocean, faulting created horsts and grabens. Pre-rift, syn-rift and post-rifts sediments were deposited.
The basin was filled in during the post-rift phase. The thickness of the post-rift Mesozoic and Cenozoic section waries between a wedge on land to approximately 10,000 meters in the offshore. The openning of the ocean was followed by numerous marine transgressions and regressions over the newly formed continental shelf. The post-rift stratigraphic section began in the Upper Jurassic with a regional transgression of the Tethian sea from the north moving progressively southward. A thick carbonate shelf began to built up during this tectonically quiet period. The Upper Jurassic deposits are known in the Western part of the basin. The border of the continent facing the new ocean began progressively to sink below sea level due to sediment load and eustatic changes in sae level.
During Neocomian uplift effecting the continent ended the proceding quiet period and a supply of detrital sediments began to be deposited on the Upper Jurassic carbonate shelf. During the Cretaceous period the sea prograded eastward across a surface that already refected the future structures. A thick series of siliciclastic sediments was deposited in the western part of the basin and offshore. Shales, sands and sandstones alternated.
The Maastrichitian consists of two facies. The first, onshore, is medium to coarse grained sands with rare intervals of black shales containing lignite in some areas. This unit is called "the acquifer sands of Senegal". The second facies, in the western and offshore is represented by light to dull fissile shales with thin intercalations of silt and fine grained sands. The interfingering of the two facies takes place at 170 west where sedimentation begins with blanck shales and rare intercalations of fine sands with sands increasing upwards. These sand lenses are oil and gas reservoir. The thickness in the Dakar region increases up to 2,000 meters because of subsidence related to syn-sedimentary faulting. At the end of Maastrichtian there was a general regression. The Laramian phase developped horsts and grabens at the and of Maastrichtian.
Tertiary sedimentation, on the contrary of Cretaceous, is represented by carbonates, marls and shales. It thickness is between 300 to 1,000 meters. Subsidence of the basin and erosion on the bordering continent ceased. A continental regime was installed at the end of Middle Eocene. Upper Eocene, Oligocene and Miocene deposits were laid down in gulfs along the coastline. As in the Alps there was a Oligocene folding in area. The study area is tectonically active compared to the rest of the basin. It was subject to syn-sedimentary faulting that produced horsts and grabens. It constituted a transition from a stable wide eastern zone to a subsiding western one. Facies changes occured there : sands, argilaceous sands and sandstones to sandy shales and shales; carbonates to marls and shales.
Upper Cretaceous (Maastrichtian) sedimentation took place in a slope environment. In the western slope turbidite sheet sands were deposited. Further east on the slope turbidite channel sands were laid down along with shales.
The Upper Cretaceous turbidite sands in Western Senegal is a fine grained sandstone (125 to 63 microns) associated with shales including laminar gypsum. It outcrops along the shoreline as cliffs, about 18 km long. In the hinterlands it suboutcrops and is covered by Quaternary laterite and sands.
The turbidite system consists of an interbedded graded sands tone and shales. Proximal, distal and basin facies have been distinguished Westward. Proximal, turbidite is sandstone dominated, alternation of sandstone and shales characterises the distal turbidite. Channel fills are also present. The basin facies is a thick shale with lenses of sands. Erosional surface, pebbles, channel scour and fill, lamination and cross lamination can be noticed. The occurence of laminar gypsum within shales suggests deep water deposits. The sedimentary environment was an unstable slope. The siliclastic sediments contain bones and teeth fish, pelecypods, gastropods associated with ammonites and benthonic foraminifera. Thus they derived from the outer edge of a wide platform at East of the outcrop by turbidity flow.

A non-marine Upper Cretaceous interval in West Antarctica (King George Insland, Northern Antarctic Peninsula)

Tânia Lindner DUTRA, B. H. LEIPNITZ, U. F. FACCINI & Z. LINDENMAYER Centro de Ciências Tecnológicas - Universidade do Vale do Rio dos Sinos (UNISINOS), Av. Unisinos, 950 - 93022-000, São Leopoldo, RS, Brazil.

Many sites in southwestern King George Island and at least one in eastern Nelson Island (both in South Shetland Islands) exhibit non-marine rocks with volcanoclastic levels that contain plant assemblages of the Upper Cretaceous (Fig. 1). Two of these sites are in coal-bearing lacustrine and fluvial settings formed in erosional phases of syneruption conditions (sensu Smith, 1991).
The first, Half Three Point, was considered Campanian-Maastrichtian in age by Shen (1994) based on its palynological content and K-Ar ages of 71 Ma in the upper lavas. The other was found during the expeditions of the Brazilian Antarctic Program at the northeastern part of Fildes Peninsula and named as Price Point.
The aim of the present work is to discuss the taphofloras (leaves and palynomorphs) and their response to geological events ocurring in that place and time so critical for plant evolution.
The units herein discussed are included in the Fildes Peninsula Group form Harkes (1961) in its basal unit, Half Three Point Formation (Shen, 1994). At Half Three Point, palynomorphs were preserved in laminated grey tuffs and fine tuffaceous rocks interbedded with coal, deposited in a lacustrine setting between two magmatic flows and during a humid and warmer climatic period (Cao, 1992). The recovery of few Acritarcha from these rocks confirms the near sea setting of deposition. The pollen assemblage is overwhelmed by spores of Bryophyta, fungi and ferns (81%), Araucariaceous and Podocarpaceous conifers (5%) and broad leaf angiosperms. The presence of Cranwellia, Gothanipollis and Tricolporopollenites, among other early angiosperms, and Nothofagidites senectus, a primitive form of Nothofagus, confirms the Late Cretaceous assignment and the existence of Nothofagidites palynofloral Province (Traverse, 1988) at that time.
The micro- and macrofossil assemblages at Price Point were preserved in a similar geological context. These assemblages are included in a 3 meters sucession composed by three coarsening upward beds of laminated dark grey tuffaceous beds with contorted lamination and fine to very coarse lapilistones in elongated lenses. The coal (mainly vitrinite) appears as fine intercalations without lateral continuity, or, in the top, as a continous layer of 5cm thick. With an erosional contact, the upper conglomerate shows chaotically arranged clasts (10 to 50 cm in diameter), and includes pieces of wood and coal (Fig. 2). The layers exhibit a high level of alteration and disaggregation, wich makes difficult to obtain complete samples of the rare macrofossils. Many of them are covered by a white film (chlorite ?) as a consequence of the breakdown of clay minerals, volcanic glass and plagioclase and only permit supposed Nothofagus, ferns, probable Ginkgoaceae and laurophyllous leaves.
The bulk pollen composition shows 50% of angiosperms, 10% of gimnosperms and 30% of the components distributed between Lycophyta and Pteridophyta. The great amount of fungi and organic matter confirms the non-marine character of deposition and the wet climate. The presence of Botryococcus in bed III confirms their subaquous nature. Marine elements were not found.
Eight palynological samples were taken along the succession. Through this procedure it was possible to observe that angiosperms change their proportion in the assemblage with time, passing from 50% at the base to 70% in the upper layers. So the balance in the dominance of understorey and pioneers ferns against riparian and upland/canopy elements changed along the section. These fact and sedimentological characteristics of the deposits show that the site were located in a position wich is more proximal to the volcano (probably the low-relief alluvial-plain ring plain of Smith, 1991) than that of Half Three Point, in a braided river depositional context with interdistributary lakes, in non-confined regime.
Nothofagus (N. senectus, N. ex gr. fusca and N. ex gr. brassii) became more common in the upper layers also, passing from 2% to 20%. The angiosperms primitive character (Magnoliidae, Dillenidae and Rosidae subclasses), the Mesozoic types of gimnosperms (leaves) and the absence of Menziesii group of Nothofagus pollen probably indicate a Campanian age for the deposits, through correlation with other sites of southern hemispheres (Dettman et al., 1990).
References
CAO, L., 1992. Late Cretaceous and Eocene palynofloras from Fildes Peninsula, King George Island (South Shetland Islands), Antarctica. In: YOSHIDA et al. (Eds), Recent Progress in Antarctic Earth Science, pp. 363-369, Terrapub, Tokyo.
DETTMANN, M. POCKNALL, D. T. ROMERO, E. & ZAMALOA, M. C., 1990. Nothofagidites Erdtmann ex Potonié, 1960; a catalogue of species with notes on the paleogeographic distribution of Nothofagus Bl. (Southern Beech). New Zealand Geological Survey Paleontological Bulletin, Vol. 60, pp. 2-52.
HAWKES, D.D., 1961. The geology of the South Shetland Islands. I. The petrology of King George Island. Scientific reports of the Falkland Islands Dependency Survey, Vol. 26, pp. 1-28.
SHEN, Y.B., 1994 (Ed.). Stratigraphy and palaeontology of Fildes Pensinsula, King George Island, Antarctica. Monograph, Vol. 3, pp. 37-49, Beijing Science Press, China.
SMITH, G., 1991. Facies sequences and geometries in continental volcaniclastic sequences. SEPM Special Publication, Vol. 45, pp. 109-122.
TRAVERSE, A., 1988. Paleopalynology. Unwin Hyman, Boston, 265 pp.

History of research on Upper Cretaceous-Lower Tertiary ostracodes of the Atlantic Ocean

Gerson FAUTH - Universität Heidelberg, In Neuenheimer Feld 234, D-69120 Heidelberg, Germany.

Since the 1960s studies of the distribution and biostratigraphy of the Cretaceous and Tertiary ostracodes of the South Atlantic Ocean are being carried out, based on African and South American sequences. The first studies were carried out by Reyment (1960, 1963) and Apostolescu (1961, 1963). Reyment studied the taxonomy and biometry of 87 Nigerian species, whereas Apostolescu described 106 species from the sedimentary basins of Senegal, Ivory Coast, Togo and Sudan. Bertels (1969, 1975a,b) studied the Maastrichtian and Danian ostracodes of Argentina and observed a high similarity with the faunas of West Africa. Neufville (1979) analysed the ostracodes of the Cretaceous-Tertiary boundary in the Sergipe-Alagoas Basin (Brazil) and confirmed Bertelsê observation about the relationship between the South American and West African assemblages. Neufville also found an affinity between the Danian ostracodes of Sergipe with those of the Caribbean and the Gulf Coast. Dingle (1969, 1982), based on work on Cretaceous ostracodes of the sedimentary basins of South Africa and Tanzania, demonstrated the lack of correlation between the Upper Cretaceous assemblages of Argentina and South Africa, in spite of the notable resemblance between those of the Lower Cretaceous in the same areas. He characterized two geographically distinct associations in the Upper Cretaceous. The first comprises the genera Anticythereis, Togoina and Nigeria, which occur in Brazil, Argentina and West Africa, whereas the second comprises Cythereis, Gibberleberis, Dutoitella and Akrogmocythere, genera found in South Africa and Tanzania. An important paleogeographical study of 783 species of Cretaceous South Atlantic ostracodes were carried out by Tambareau (1982), who interpreted the establishment of a Santonian system of currents as the reason for the migration of species from Northwest Africa to Argentina. On the other hand, she explained the arrival of ostracodes in South Africa, as coming from West Central Africa through late Campanian-Maastrichtian transgression.
Ostracodes from Cretaceous-Tertiary boundary of the Poty Quarry:
The Poty Quarry is located in the Pernambuco-Paraíba Basin, aproximately 20 Km north of the city of Recife, Pernambuco, north-eastern Brazil. It displays an exceptional palaeontological record with good exposures of the Cretaceous-Tertiary boundary. The quarry has been the subject of micropalaeontological studies and is today the subject of intensive discussions about the extinction at the Cretacoeus-Tertiary boundary as well as about its chronostratigraphic position. Until today no detailed work has been done on the ostracodes of the basin. The first records of ostracodes from the Poty Quarry were by Tinoco (1967) in his micropalaeontological study of the coastal belt between the cities of Recife and João Pessoa. According to him the genera Cyntherella, Cytheropteron and Cythereis occur in the calcareous facies of the Maastrichtian Gramame Formation. Overlying the Gramame Formation are the more pure Danian carbonates of the Maria Farinha Formation, which contain a microfauna different from that of the Gramame Formation. Characteristic and abundant genera of this formation are Cytherella, Costa, Cytheretta, Protocythere, Paracypris and Cytheropteron. Stinnesbeck & Reyment (1988) reported an ostracode assemblage of the Gramame Formation consisting of species of Bythocypris, Cytherella and Bairdia, whereas the Maria Farinha Formation contains rare occurrences of Soudanella, Brachycythere and Dahomeia. The species Soudanella laciniosa Apostolescu, which is typical for West Africa, is also present in the Danian of Sergipe-Alagoas and Pernambuco-Paraíba, thus providing evidence for correlation between Brazil and West Africa. The genus Soudanella also occurs in Argentina, Nigeria, Mali and Libya. Nevertheless, these authors pointed out the need for more detailed information on the ostracode associations of the eastern part of South America in order to better correlate the faunas of West Africa and South America.
A research project on the Poty Quarry was initiated in April 1996, in order to study the palaeoenvironment, palaeogeography and biostratigraphy distribution of the marine ostracodes of the Cretaceous-Tertiary boundary in the Pernambuco-Paraíba Basin. The research is being done as a Ph.D. project at the Institute of Geology and Palaeontology of the University of Heidelberg, under the supervision of Peter Bengtson and Eduardo A. M. Koutsoukos.
References
Apostolescu, V., 1961. Contribution à paleontologie (ostracodes) et stratigraphique des bassins crétacés et tertiaires de lêAfrique Occidentale. Revue de lêInstitut Français de Pétrole et Annales des Combustibles Liquides, Vol. 16, No. 7/8, pp. 779-867.
Apostolescu, V., 1963. Essai de zonation par les ostracodes dans le Crétacé du Bassin du Senégal. Revue de lêInstitut Français de Pétrole et Annales des Combustibles Liquides, Vol. 18, No. 12, pp. 1675-1694.
Bertels, A., 1969. Micropaleontologia y estratigrafia del limite Cretácico-Terciario en Huantrai-Co (Provincia de Neuquen). Ostracoda. Parte I. Ameghiniana, Vol. 5, No. 8, pp. 279-295.
Bertels, A., 1975a. Upper Cretaceous (middle Maastrichtian?) ostracodes of Argentina. Micropaleontology, Vol. 21, No. 1, pp. 97-130.
Bertels, A., 1975b. Ostracode ecology during the Upper Cretaceous and Cenozoic in Argentina. Bulletins of American Paleontology, Vol. 65, No. 282, pp. 317-351.
Dingle, R. V., 1969. Upper Senonian ostracods from the Coast of Pondoland, South Africa. Transations of the Royal Society of South Africa, Vol. 38, No. 4, pp. 347-385.
Dingle, R. V., 1982. Some aspects of Cretaceous ostracod biostratigraphy of South Africa and relationships with other Gondwand localities. Cretaceous Research, Vol. 3, pp. 367-389.
Neufville, E. M. H., 1979. Upper Cretaceous-Paleogene marine ostracods from the Sergipe-Alagoas Basin, northeastern Brazil. Bulletin of the Geological Institutions of the University of Uppsala, Vol. 8, pp. 135-172.
Reyment, R.A. 1960. Studies on Nigerian Upper Cretaceous and Lower Tertiary Ostracoda. Part 1: Senonian and Maastrichtian Ostracoda. Stockholm Contributions in Geology, Vol. VIII, 238 pp.
Reyment, R.A. 1963. Studies on Nigerian Upper Cretaceous and Lower Tertiary Ostracoda. Part 2: Danian, Paleocene and Eocene Ostracoda. Stockholm Contributions in Geology, Vol. X, 286 pp.
Stinnesbeck, W. & Reyment, R. A., 1988. Note on further ocurrence of Soudanella lanciniosa Apostolescu in northeastern Brazil. Journal of African Earth Sciences, Vol. 7, No. 5/6, pp. 779-781.
Tambareau, Y., 1982. Les ostracodes et lêhistore géologique de lêAtlantique Sud au Crétacé. Bulletin des Centres de Recherche et Exploration-Production Elf-Aquitaine, Vol. 6, No. 1, pp. 1-37.
Tinoco, I. M., 1967. Micropaleontologia da faixa sedimentar costeira Recife-João Pessoa. Boletim da Sociedade Brasileira de Geologia, Vol. 16, No. 1, pp. 81-85.

Lés évaporites Paripueira du Bassin Sergipe-Alagoas

Cláudio P. FLORENCIO - USP / Instituto de Geociências, Programa de Recursos Minerais - Depto. de Geologia Econômica, Caixa Postal 11.348 - CEP 05422-970 - São Paulo - SP, Brazil.

Introduction
Dans la portion dêAlagoas du Bassin Sergipe-Alagoas, NE du Brésil, on constate la déposition dêévaporites de la phase Paripueira en régions distinctes, apparemment isolées des autres, qui appartiennent stratigraphiquement au Membre Maceió, Formation Muribeca (Schaller, 1969). Elles forment trois sous-bassins dénommés, informellement Paripueira, Maceió et Coruripe (Florencio, 1996). Ces évaporites sont dêâge Alagoas - ou Aptien Supérieur, selon les donnés palynologiques obtenues sur les argilites laminées intercallés dans les sels (Caldas & Florencio, 1992). Lêintervalle évaporitique Paripueira a été étudié à partir de profils de sondage, lignes sismiques et, principalement, de données de carottage continu dans le domaine du sous-bassin de Maceió. Des analyses pétrographiques ont été effectuées sur ces derniéres, ainsi quêune détermination du brome, chlore et sodium des halites et une géochimie organique des argilities laminées intercallés.

Caractérisation des Intervalles Évaporitiques
Les évaporites Paripueira sont caractérisés par dêépais dépôts de halite, avec des roches carbonnatées et siliciclastiques intercallées, sand que puisse être caractérisée la présence de sels plus solubles, comme la silvinite ou la carnalite. Les résultats analytiques pour les teneurs de brome en échantillons de halite montrent des valeurs situées entre 38 et 104 ppm, avec un relation sodium/chlore de 0,647 en moyenne. Les analyses géochimiques organiques, en argilities laminées noirs intercallés dans les sels, présentent des teneurs de carbonne organique total (TOC) qui varient entre 5,87% et 17,94%. La pyrolyse Rock-Eval a montré que ces argilites laminées possèdent un bon potentiel, malgré lêétat thermique immature pour la formation dêhydrocarbures. Les résultats de la chromatographie ont révélé une prédominance de résines e asphalténes par rapport aux fractions saturées, avec un rapport pristane/fitane inférieur à 1. Les extraits totaux des échantillons de argilites riches en matière organique présentent des valeurs situées entre -23ä et -27ä (PDB) pour les rapports isotopiques d13C.

Apréciation des Résultats
La déposition des évaporaties a été marquée par de grands apports de terrigènes, avec dêinnombrables intercallaisons, principalement de argilites laminées. On admet lêhypothése dêun mileu caractérisé par des eaux peu profondes, avec une énergie faible à modérée, sur la base des analyses des carottes de sondage qui mettent en évidence de fréquentes expositions sub-aériennes de ces sédiments. La fin des conditions de restriction est représentée par dêépais paquets de argilites laminées au sommet des sels dans lesquels on enregistre la présence de fossiles de conchostracés (Cyzicus ?) et de poissons (Dastilbe ?).
Lêirrégularité de la distribution des couches salifères et les différences dêéppaisseur dans des puits relativement proches sont des évidences quêil y a eu des avançées et reculs sucessifs de la saumure, aliés à lêaction de lêactivité tectonique, contemporaine, dans la région, de la déposition du sel, avec, comme résultat, de fortes variations latérales de facies entre clastiques et évaporites.
Les résultats analytiques pour les teneurs de brome aliés à la géochimie organique montrent un origine marine pour les saumures responsables de la formation des évaporites Paripueira. Les teneurs de brome rencontrées sont compatibles pour des halites primaires dêorigine marine et présentent, en moyenne, une concentration de 69 ppm. La relation sodium/chlore obtenue dans les halites est de 0,647, ce qui est cohérent avec les valeurs théoriques.
Remerciements
Lêauteur remercie le géologue Renato Senna de Carvalho pour ses enseignements et la direction de la PETROBRAS et de SALGEMA MINERAÇÃO pour avoir fourni des données de sondages. Références
CALDAS. E. B. & FLORENCIO, C. P., 1992. A idade dos evaporitos Paripuera na região de Maceió, Bacia Sedimentar de Sergipe/Alagoas. In: II Simpósio sobre Bacias Cretáceas Brasileiras (Rio Claro), Resumo Expandido, UNESP, pp. 22-24.
FLORENCIO, C. P., 1996. Geologia dos evaporitos Paripueira na porção alagoana da Bacia de Sergipe/Alagoas. Dissertação de Mestrado, 94 pp., Universidade de São Paulo, Instituto de Geociências.
SCHALLER, H., 1969. Revisão estratigráfuca da Bacia Sergipe/Alagoas. Boletim Técnico PETROBRAS, Vol. 12, No. 1, pp. 21-86, Rio de Janeiro.

A comparison of Brazilian marginal basins with those of the same age in Southern India

Malcom B. HART & Archana TEWARI - Departament of Geological Sciences, University of Plymouth, Drake Circus, Plymouth PL 4 8AA, Devon, U. K. Tel.: + 44(0) 1752-232156, Fax: + 44 (0) 1752-232155, E-mail: MHART@PLYMOUTH.AC.UK

The marginal basins of peninsular India contain a geolical record of the rifting of India and Antarctica, a process which - like that in the South Atlantic Ocean - began in the Early Cretaceous. The Cauvery Basin, which located on the east coast of India south of Madras, has been the subject of research since the 1860's when British geologists first mapped the area. In recent years the Oil and Natural Gas Corporation of India have investigated the basin, both on-shore and off-shore. The exposed areas of the basin, around Ariyalur, preserve a succession much like that known from the marginal basins of Brazil.
Our work,which began in 1993, has completely revised the lithostratigraphy of the exposed part of the basin. The subdivisions currently used by Indian geologist are a modified version of the stratigraphy developed by Blanford in the 1860's. The terminology adopted is based on many errors of correlation and number of assumptions as to the environments represented in the basin. Using internationaly agreed criteria and the identification of clearly documented stratotypes we have created 7 units of formational status arranged within three 'groups'. The ages of the various units have been established using foraminifera and/or available macrofossil data.
The succession begins with massive conglomeratic units, overlain by sandstones and fresh-water clays (with abundant plant remains). The first marine strata are Early-Middle Albian in age and comprise fossiliferous carbonate sediments on, and adjacent to, basement massifs but with deep water marine clays (with planktonic foraminifera) in more basinal areas. In these marine clays (the Karai Clay Formation) there are abundant rotaliporids, marginotruncanids, dicarinellids and other associated planktonic taxa. All are beautifully preserved, strongly ornamented and characteristic of the ages they represent. In the Early Turonian the individual species are much more ornamented than their European equivalents and, along with parts of N.W. Australia, form a quite distinctive biogeographic province. The developing Eastern Indian Ocean was probably open northwards into Tethys but closed, apart from surface currents, to the south. The faunas of the South Atlantic Ocean, Southern Ocean and the Indian Ocean are, therefore, quite different in terms of appearance although the taxa belong to the same groups. Work on this biogeographic province continues.
In the Late Turonian there is a major regression and the hinterland was clearly forested as the overlying transgressive sands of the Garudamangalam Sandstone Formation contain abundant wood material, including trees up to 18 m in length. It is assumed that the trees represent tropical or sub-tropical vegetation as no seasonal growth rings have been found. Much of the wood is intensely bored by Teredolites. Associated with this woody material are monospecific shell banks and conglomeratic units.
The Upper Campanian and Lower Maastrichtian is represented by a carbonate ramp system in which planktonic foraminifera are quite rare. The succession is, however, dominated by the presence of Siderolites calcitrapoides and Lepidorbitoides socialis. These larger foraminifera are extremely abundant and parts of the succession can be described as an orbitoid sand. Towards the close of the Maastrichtian sedimentation became terrestrial in nature and is represented by cross-stratified sands with dinosaur remains.
Throughout much of the succession there appears to have been continued subsidence although a period of intra-Cretaceous faulting occurred in the mid-Albian. The earliest sediments are demonstrably terrestrial or lacustrine and there is no evidence (on-shore) of evaporites - as there are in Brazil and Angola.
Using the modelling methodology of Koutsoukos & Hart (1990) it is possible to reconstruct the history of the Cauvery Basin in considerable detail and compare this to that known from Brazil. As both the Cauvery Basin and the Sergipe-Alagoas Basin were deposited at similar palaeolatitudes the study contributes much to our knowledge of Cretaceous successions in the southern hemisphere.
References
KOUTSOUKOS, E. A. M. & HART, M. B., 1990. Cretaceous foraminiferal morphogroup distribution patterns, palaeocommunities and trophic structures: a case study from the Sergipe Basin, Brazil. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 81, pp. 221-246.

Late Cretaceous palynofloras and foraminifera from Ain El-Wadi area, Farafra Oasis, Egypt

Mohamed I. A. Ibrahim* & M. Rashad Abdel-Kireem** *Department of Environmental Sciences, Faculty of Science, Alexandria University, Egypt. E-mail: MIBRAHIM@alex.eun.eg **Department of Geology, Faculty of Science, Alexandria University, Egypt.

The Farafra Oasis occupies the heart of the Egyptian Western Desert, located between latitudes 26o 30' and 27o 30' and longitudes 27o 30' and 29o 00'. It exhibits excellent exposures of Upper Cretaceous and Lower Tertiary. Surface and subsurface Cretaceous sediments from the Ain El-Wadi area, NNE Farafra Oasis have yielded diverse assemblages of microfloras and foraminifera. The sequence is composed of siliciclastic sediments of the El-Hefhuf Formation unconformably overlained by the carbonate platform of the Khoman Formation.
The palynomorph species recovered from the El-Hefhuf Formation are of potential biostratigraphic utility according to published information on the palynology of Egypt, West and North Africa and northern South America. The El-Hefhuf Formation is dated late Turonian-Santonian on the basis of the presence of Droseridites senonicus, Foveotricolpites cf. tienabaensis, F. giganteus, F. cf. gigantoreticulatus, Arecipites spp., Liliacidites spp., Scabratriporites simpliformis, in addition to other triporate and tricolporate pollen. One new pollen species Liliacidites farafraensis Ibrahim & Abdel-Kireem sp. nov. is described.
The overall composition of the palynomorph indicates that deposition of the El-Hefhuf Formation probably took place in freshwater swamp or marsh fringed by marine shrubs and the palmae. This freshwater swamp was inundated by marine or brackish water for short duration, as deduced from the low occurrence of dinocysts and the abundance of freshwater chlorococcales. It was probable that the prevailing low salinity and the stagnant conditions after the marine incursion was intolerable to either benthic or planktonic foraminifers which is totaly barren in the El-Hefhuf Formation.
The present sporomorph content suggests affinities of the Egyptian assemblages with the African and northern South American tropical-subtropical Palmae Province of Herngreen & Chlonova (1981) as documented by: 1) the decrease in number of polyplicate pollen, 2) an increase in number and diversity of monocolpate palmae-types, 3) abundance of triporate pollen, 4) abundance of Droseridites senonicus, 5) abundance of large-sized Foveotricolpites pollen, and 6) conspicuous spores are Gabonisporis and Zilivisporis. The very low percentage (1%) of the bisaccate pollen in the present material may reflects a weak input from the European Normapolles Province to the Egyptian microfloras.
The snow dazzling chalk of the Khoman Formation exposed in the Ain El-Khadra section and is resting unconformably over the El-Hefhuf Formation in the studied area is dated middle to latest middle Maastrichtian of the Gansserina gansseri and the Contusotruncana contusa Zones.
Analysis of the recorded planktonic assemblage reveals that the keeled forms of globotruncanid exceed both the heterohelicids and the non-keeled forms (Rugoglobigerina, Hedbergella, Archaeoglobigerina, Globotruncanella and Globigerinelloides). Moreover, the double-keeled globotruncanids are dominated over the single keeled ones. Also, in the studied sections the P/B ratio is generally >1 (i.e. 1-4) which supports that the deposition of the Khoman Formation was under deep marine environment, probably of the outer shelf (palaeodepth 100-200 m). An exception is the lower part of the G. gansseri Zone in Ain El-Khadra section which is characterized by low P/B ratio ( <1). This can be attributed to a local shallower conditions.
The whole planktonic foraminiferal population is almost exclusively dextrally coiled throughout the studied sequence. Only few numbers of Rugoglobigerina rugosa and R. hexacamerata were found sinistrally coiled tests (~ 0.5-2%). Therefore, the percentage of sinistral tests never exceeds 2% at any sample of the studied sections which may indicates the effect of cool Tethyan water mass to the warm Tethyan water prevailed during the deposition of the Khoman Formation in Late Cretaceous.
The sharp changes in depositional environment from swampy (late Turonian-Santonian) to open marine (Maastrichtian) environment through the studied sequences can be related to the global changes associated with tectonic activity and sea floor spreading, whereas the Tethys invaded southward to cover most of the Egyptian territory as a result of the fourth and major transgressive climax occurred in Late Cretaceous. This resulted in the deposition of the Upper Cretaceous carbonates, i.e. Khoman Formation.
The structural picture of the Farafra Oasis can be considered as a perfect domal area of the stable shelf of Egypt. Palaeontologic break at the K/T boundary may prove that the Farafra dome seems to have been uplifted at the end of Maastrichtian time (Syrian arc system) where erosion removed part of the uppermost Maastrichtian, i.e. mayaroensis Zone and did not permit the deposition of the basal Paleocene, i.e. eugubina Zone and the lower part of pseudobulloides Zone.

Bioevents around the Turonian sub-stage boundaries in the Egyptian Eastern Desert and their inter-regional correlation

Ahmed S. Kassab -Geology Department, Faculty of Science, Assiut University, Assiut 71516, Egypt.

In the Eastern Desert of Egypt, Turonian stratigraphic sequences are well exposed at many localities forming conspicuous outcrops. They encompasses upper part of the Galala Formation and lower part of the Umm Omeiyed Formation. The Galala Formation is composed mainly of marine carbonate succession. The Umm Omeiyed Formation consists of mixed marine siliciclastic and carbonate beds intercalated with continental sediments. The marine strata are rich in macro- as well as micro-faunas. Published works on the detailed stratigraphy and events of the Turonian stage in Egypt are scarce, as is the case for literature dealing with its sub-stage boundaries. The present study aims at utilizing more than one fossil group of indisputable occurrence to trace the sequence of events around the Turonian sub-stage boundaries in the Egyptian Eastern Desert. Consequently, a precise definition for these boundaries will be established. The present study is based on the integration of three fossil groups : ammonites, echinoids, and foraminifera.
Evolutionary trends, morphological changes and faunal diversity have been followed throughout the Turonian Sequence of the study area.
The basal Turonian is marked by the first appearance of Vascoceras proporium and/or Pseudaspidoceras flexuousum. Interval of this ammonite zone corresponds to the occurrence of the echinoid Micraster leskei and the foraminifer Whiteinella archaeocretacea. The lower/middle Turonian boundary is well established by the appearance of the ammonites of Choffaticeras segne group coinciding with the appearance of the echinoid Echinobrissus balli and the foraminifer Helvetoglobotruncana praehelvetica.
The middle/upper Turonian boundary is clearly drawn according to the appearance of the ammonites of Coilopoceras requienianum group coinciding with the appearance of the echinoid Micraster corbovis and Echinobrissus ammonis as well as the foraminifer Helvetoglobotruncana helvetica.
The Upper Turonian boundary is marked by the disappearance of Coilopoceras, Micraster corbovis and Helvetoglobotruncana helvetica as well as by the first appearance of the ammonite Metatissotia fourneli, the echinoid Echinobrissus brathoxi and the foraminifer Dicarinella primitiva.
Contacts between the Turonian sub-stages coincide either with a clear contrast in lithofacies or with erosive surfaces. The transgressive-regressive cycles, the eustatic sea-level changes, the palaeobiogeographic relations and inter-regional correlation of the studied sequence are also discussed.

Late Cretaceous foraminiferal community dynamics and palaeoceanographic events in NE Brazil

Eduardo A. M. KOUTSOUKOS - PETROBRAS-CENPES/DIVEX/SEBIPE, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, Brazil. E-mail: koutsoukos@cenpes.petrobras.gov.br

The late Coniacian to Maastrichtian of NE Brazil (Sergipe and Pernambuco-Paraíba basins) represents a time-interval of relatively stable environmental conditions (e.g., well mixed and overall well-oxygenated water masses). By late Coniacian-early Santonian times there occurred a major oceanographic event in the northern South Atlantic, brought about by the final structural detachment of the South American and African plates. It resulted in the establishment of a deep-oceanic circulation regime, which resulted in a remarkable change in the nature of the sedimentary sequence, from carbonate-dominated (Cenomanian-"middle" Coniacian) to siliciclastic. An accentuated submarine topography developed (Koutsoukos & Hart, 1990, Fig. 13) with the abrupt seaward tilting of the continental margins on both sides of the Atlantic.
Simultaneously there was a rapid change from a dominantly dry to a more humid and warm climate, probably caused by the development of a high-pressure atmospheric cell at low-latitudes over the widening Atlantic watermasses (e.g., Chang et al., 1988. Episodes, Vol. 11, No. 3, pp. 194-202). This climatic turnover caused increased basinward siliciclastic influx, which was supplied by increased continental runoff from nearby uplifted areas.
Foraminifera diversity patterns are a direct response to palaeoceanographic conditions and can reflect long-term cumulative changes induced by seasonal cycles in sea-level and changes in sediment type, redox conditions and rates of food supply. A significant increase in diversity is more likely to result from a corresponding increase in the variety of habitat types. More niches would be created (higher biogeographic differentiation) leading to higher taxonomic diversity and exploitation of new habitats. Cumulative percentage diagrams, total diversity histograms and palaeobathymetric countour curves are presented for the upper Coniacian-Maastrichtian succession of the Sergipe basin, in NE Brazil (Koutsoukos, 1992, Fig. 2A-D). The total diversity histogram for the benthic foraminifera shows a certain regular, stepwise pattern of diversification.
During Cenomanian-"mid" Coniacian times the species diversity was low, as well as in number of specimens (Koutsoukos, 1992, Fig. 2C-D). Upper Coniacian-Maastrichtian shelf and bathyal, siliciclastic-dominated deposits yield abundant and highly diversified K-selected, "equilibrium" foraminiferal communities, with a complex trophic structure (Koutsoukos & Hart, 1990). The evidence suggests a well developed photic zone and widespread oligotrophic conditions in epipelagic layers of outer neritic and oceanic settings (Koutsoukos & Hart, 1990). Oligotrophic conditions may result not only in a high spectrum of food supply heterogeneity in the water column and on the sea-floor, but also in an increased variety of utilisable habitat types (Koutsoukos & Hart, op. cit.).
There is a sharp increase in diversity during late Coniacian-Santonian to Campanian times, with a maximum in the early Campanian (Koutsoukos, 1992, Fig. 2B), corresponding most likely to the palaeobathymetric maximum of the northern South Atlantic.


The total diversity of the benthic foraminifera progressively declines after the early Campanian maximum, in a stepwise pattern. This is concomitant with the general trend of palaeobathymetric decrease (of 3rd order of magnitude) induced by progradation of the continental margin, initiated at about the same time as the palaeobathymetric maximum. The number of last appearance datums (LAD's) by far exceeds that of first appearances (FAD's) (Fig. 1), suggesting that habitat loss was the most likely cause for the local "extinction" events.
Long-term (2nd order) high-stands of sea-level during the Late Cretaceous, coupled with widespread aerobic and oligotrophic pelagic conditions, contributed to create niches and promote evolutionary diversification, with the development of polytaxic planktonic and benthic foraminiferal palaeocommunities with complex trophic structures (mixed groups) in the Late Cretaceous. On the other hand, the establishment of new oceanic circulation patterns in the northern South Atlantic, dramatically increased the chances for species migrations from low-latitude, central North Atlantic-western Tethyan biogeographic provinces. This is evidenced by the very close biogeographic affinities observed in the benthic and planktonic foraminiferal assemblages (cf. Koutsoukos, 1992). So, it appears that most of the "local" first appearance datums (FAD's; Fig. 1) may represent not truly evolutionary first appearances, but instead, colonization of the newly available niches by immigrating benthic species. These "new" species quickly replaced by vacancy occupation the older low-diversity, r-selected, "opportunistic" benthic foraminiferal communities of the carbonate-dominated cycle (Cenomanian-"middle" Coniacian), which probably either became extinct or shifted to other areas. A similar pattern could also account for the local "extinction" events recorded for the prograding cycle.
References
Butt, A., 1982. Micropaleontological bathymetry of the Cretaceous of western Morocco. Palaegogeography, Palaeoclimatology, Palaeoecology, Vol. 37, No. 2-4, pp. 235-275.
Koutsoukos, E.A.M., 1992. Late Aptian to Maastrichtian foraminiferal biogeography and palaeoceanography of the Sergipe Basin, Brazil. In: Malmgren, B.A. & Bengtson, P. (Eds), Biogeographic Patterns in the Cretaceous Ocean. Palaeogeog., Palaeoclim., Palaeoec., Spec. Issue, Vol. 92, No. 3/4, pp. 295-324.
Koutsoukos, E.A.M. & Hart, M.B., 1990. Cretaceous foraminiferal morphogroup distribution patterns, palaeocommunities and trophic structures: a case study from the Sergipe Basin, Brazil. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 81, pp. 221-246.
Macellari, C.E. & de Vries, T.J., 1987. Late Cretaceous upwelling and anoxic sedimentation in northwestern South America. Palaeogeog., Palaeoclim., Palaeoec., Vol 59, No. 4, pp. 279-292.
Petters, V., 1955. Development of Upper Cretaceous foraminiferal faunas in Colombia. Journal of Paleontology, Vol. 29, No. 2, pp. 212- 225.
Tinoco, I.M., 1971. Contribuição ao conhecimento da gênese do fosfato de Olinda. Arq. Museu Nacional, Rio de Janeiro, Vol. 54, pp. 117-182.
Viviers, M. C., 1990. Associações micropaleontológicas relacionadas aos fosfatos do Cretáceo Superior da bacia Potiguar, margem continental brasileira. XXXVI Cong. Bras. Geol., Anais, Vol. 1, pp. 436-454.

Preliminary biostratigraphic and palaeontological survey in the Pernambuco-Paraíba basin, northeastern Brazil

Wagner S. Lima (*), Paulo Roberto Silva Santos (**), Paulo C. Galm (**) & Jorge Darlan Ortiz (*) (*) PETROBRÁS-E&P SE/AL-GEXP-GEINT, Aracaju, SE, Brazil.
(**) PETROBRÁS-E&P SE/AL-GEXP-GELAB, Aracaju, SE, Brazil.

Introduction
Due to the recent exploration interest of Petrobras in the Pernambuco-Paraíba and Cabo basins, northeastern Brazil, and because of the paucity of information that could propitiate further investments, a geological research program has been elaborated. It includes surface geochemistry, regional seismic survey, sedimentologic and stratigraphic analysis and geological mapping.
This work presents the preliminary results achieved after a bistratigraphic-paleontologic-sedimentologic expedition sponsored by Petrobras and by the National Museum, Rio de Janeiro, on December 1994.
Field data sampling
The following table synthetizes the outcrops described, though palaeontological material has not been collected from all of them. At some points referred to in the literature only a geographical recognition was done. The geographical coordinates were acquired by "GPS" (Global Positioning System).
Detailed material collection for microfossil analysis has been carried out, mainly at the quarries. On smaller outcrops, material has been collected at levels whose characteristics were more propitious to microfossil recovery.
Data description and preliminary interpretation
At the studied area the Beberibe, Gramame, Maria Farinha and Barreiras formations occur. These units range from Upper Cretaceous to Tertiary.
The Beberibe Formation is characterised by poorly sorted quartz-sandstones, yellowish to greyish, partially argillaceous, with some feldspar grains, extremely unconsolidated, sometimes iron and carbonate-cemented. Upward, a calciferous-high fossiliferous sandstone occurs, that progressively grades into the basal calcarenites and calcirudites of the Gramame Formation. To the south, this horizon is represented by an unconsolidated, calciferous, phosphate-enriched sandstone, typically of shoreface facies.
A preliminary outcrop evaluation shows that these calciferous sandstone from the Beberibe Formation laterally interdigitate with the siliciclastic calcirudites / bioclastic calcerinites of the Gramame Formation, characterising high fossiliferous levels (CD-06, AL-01). The invertebrate association suggests a shallow marine environment, locally with fluvial-deltaic influence.
These high fossiliferous beds change upward to a sucession of calcilutites (shaly biomicrites) and marls distributed in well marked cycles (JP-01, JP-02, CD-03, AL-04, CA-03, GO-01, PT-01), sometimes with interbedded gray shales. The marls are highly bioturbated, with ichnofossils from the Thalassinoides group. Both ichnofossils and invertebrates (mainly Spatangoid echinoids) show strain evidences, being roughly oriented, defining tectonic-like augen. Some bioturbation is also found in the calcilutite beds but is usually pyrite-enriched.
This benthic-planktonic faunal association characterises the beginning of the transgressive process over the Beberibe Formation, with a shallow and warm marine environment, locally with siliciclastic influx, that progressively changes to a neritic, distal and deeper sea system, where the eventual siliciclastic influx allowed the marl generation. The macrofossils association in very similar to that encountered in the Cotinguiba Formation and, partially, to that found in the Calumbi Formation, both in the Sergipe-Alagoas basin.
On some outcrops, notably on those at the CIPASA quarry (CA-03), toward the basal portion of the Gramame Formation, the calcilutite-marls cycles show internally a fining-upward pattern. They define extensive sub-horizontal beds which gently dip to east. These beds are intersected by east/west channels ca. 3 meters width. This reflects a turbiditic deposition over a low-angle platform, in a deep-sea environment. Upward, the sequence shows otherwise a gradative shallowing-up so that the marl beds become progressively thinner, at a point they represent only delicate film-like beds between the thicker calcilutites beds. The environment is well characterised by faunal associations which reflect deep-water deposition.
At an unique outcrop (JP-02) an invertebrate assemblage suggesting a somewhat more shallow water level (up to 40m) was found. This is evidenced by abundant specimens of Atrina reginamaris (Maury) apparently short-distance transported, associated with shallow-water echinoids (cidaroids). At the upper levels, decapods fragments (Callianassa ?) are often found. These features suggest that during the deposition of the upper portion of the Gramame Formation regressive conditions had already been established. The maximum transgressive surface shall be indentified within the Gramame Formation, not in the Maria Farinha Formation. The abundant ammonites that occur in the Gramame Formation undoubtely will provide a local definition for the Late Cretaceous zonation (Campanian/Maastrichtian), associated with palynologic/nannofossil data.
The basal deposits of the Maria Farinha Formation are represented by detritic fossiliferous limestones, locally with phosphate nodules, interbedded upward with marls and greyish argillaceous beds. These rocks represent a somewhat rapid regressive event from the upper Maastrichtian to Tertiary. The rocks suffered some dolomitization toward the top of the sequence and increase in the siliciclastic influx, grading to a succession of shaly calcilutites, marls and shales. Tinoco (1967) and Beurlen (1967b) characterised this environment as a warm, limpid, shallow-water sea (up to 50 m) that episodically evolved to estuarine-like conditions, attested by the widespread Plagiolophus and Retrocypoda carapaces (decapods) found in argillaceous levels at the top of the sequence. At the Paraíba State coast, highly fossiliferous, bioclastic calcarenites and calcirudites (CD-04) presumably Eocene/Oligocene (?) crop out. Stratigraphically, they are positioned at the uppermost portion of the Maria Farinha Formation, though further investigation is required.
The Barreiras Formation covers unconformably both the Gramame and Maria Farinha formations. On the field it is evident that great extensions of the so-called Barreiras Formation is actually the Beberibe Formation. These units are sometimes very similar lithologically. The former occurs as coastal hills and the latter forms extensive inland plateaus ("tabuleiros"), particularly in the Paraíba State (Beurlen, 1967a).
New data will be available on the continuity of the studies and will be properly published.
References
AMARAL, A. J. R. do, MENOR, E. A. & SANTOS, S. A., 1977. Evolução paleogeográfica da sequência clástica basal da bacia sedimentar costeira Pernambuco-Paraíba. In: VIII Simpósio de Geologia do Nordeste (Campina Grande), Atas, Boletim No. 6, pp. 37-63, Sociedade Brasileira de Geologia.
BEURLEN, K., 1962. O gênero Callianassa nas formações cretáceas de Pernambuco. Universidade do Recife, Arquivos de Geologia, Vol. 2, pp. 1-10.
BEURLEN, K. 1967a. Estratigrafia da faixa sedimentar costeira Recife-João Pessoa. Bol. Soc. Bras. Geol., Vol. 16, No. 1, pp. 43-53, São Paulo.
BEURLEN, K., 1967b. Paleontologia da faixa sedimentar costeira Recife-João Pessoa. Bol. Soc. Bras. Geol., Vol. 16, No. 1, pp. 73-79, São Paulo.
MABESOONE, J. M., 1967. Sedimentologia da faixa sedimentar costeira João-Pessoa. Bol. Soc. Bras. Geol., Vol. 16, No. 1, pp. 57-72, São Paulo.
MAURY, C. J., 1930. O Cretáceo da Paraíba do Norte. Monographia Serv. Geol. Mineral., Rio de Janeiro, Vol. 8, 305 pp.
MENOR, E. A. & AMARAL, A. J. R. do., 1978. O Cretáceo-Paleoceno da faixa costeira Pernambuco-Paraíba e depósitos fosfáticos associados. In: XXX Congresso Brasileiro de Geologia (Recife), Resumo das comunicações, Boletim No. 2, pp. 65-86, Sociedade Brasileira de Geologia.
MUNIZ, G. da C. B., 1993. Novos moluscos fósseis Gramame, Cretáceo superior dos Estados da Paraíba e de Pernambuco, Nordeste do Brasil, com dados gerais sobre a formação e revisão de diversas espécies anteriormente descritas. Universidade Federal de Pernambuco. Departamento de Geologia, Publicação Especial No. 1, 203 pp.
TINOCO, I. M., 1967. Micropaleontologia da faixa sedimentar costeira Recife-João Pessoa. Bol. Soc. Bras. Geol., Vol. 16, No. 1, pp. 79-83, São Paulo.

Tectonic and stratigraphic relationships between the Afrobrazilian and Araripe-Potiguar depressions (NE Brazil)

Mário LIMA Filho, Maria Somália S. Viana & J. M. Mabesoone LAGESE/DGEO/UFPE, Recife, PE, Brazil.

The pre-Cretaceous basement of NE Brazil (Borborema Province) and its adjoining region in Africa (Cameroun Shield) are composed of a patchwork of crystalline and sedimentary rocks, cut into small tectonic units by faults and shear zones. Irregular epeirogenetic uplift of this area in Late Jurassic and Early Cretaceous formed two SW-NE trending elongate depressions, separated by basement highs. The depressions are called Afrobrazilian (in the SE) and Araripe-Potiguar (in the NW) in which various individual sedimentary basins were developed (Fig. 1).
Rifting started in the South Atlantic between Neocomian and early Barremian, affecting the Afrobrazilian depression where the Sergipe-Alagoas and Cabo basins were established, both separated into highs and lows. In those basins, a lower continental sequence was accumulated reflecting rifting processes. Depositional environment include alluvial-fans which pass into fluvial and lacustrine systems, with and endemic freshwater fauna and flora.
The rift event also exercised its influence upon the Araripe-Potiguar depression, although latter in this one, developing a number of individual small basins due to basement heterogenesis. Intense taphrogenesis caused the deposition of coarse to conglomeratic sandstone, alternating with finer clastics during quiescent periods. As above, depositional environments were again alluvial-fan, river and lake systems. In late Barremian rifting shifted toward the Equatorial Atlantic branch, reactivating faulting in the Araripe-Potiguar depression. At the same time in the Afrobrazilian depression, rifting continued reaching its northernmost point in the Aptian. Sedimentation remained in terrestrial realms, reflecting tectonic activity and quiescence.
In late Aptian-Albian times regional subsidence took place, allowing the sea to invade the area, perhaps during the worldwide Albian transgression. Marine transgression reached the Sergipe-Alagoas Basin. In the Equatorial Atlantic, in the easternmost Potiguar Basin, the sea invaded the Pendência graben which forms part of the Araripe-Potiguar depression. Subsidence and consequent marine transgression reached even more inland situated basins along this latter depression, and also the westward Parnaíba Basin.
In the South Atlantic basins clastic depositional systems occur along the borders, and shales and biomicritic limestones in shelf to slope environments. In the intracontinental basin, lacustrine dark-coloured calcareous shales, gypsum, and intercalated alternations of shales, marls and limestones are commonly found. Even in the more westward Parnaiba Basin correlated sequences have been identified. The endemic fossil content of the basins in both depressions is suprisingly similar, with ostracods, conchostracans, gastropods, bivalves, fishes, reptiles, pollen, spores and silicified trunks. Besides those in the Albo-Aptian fossil assemblages became richer, also including insects, arthropods, amphibians and birds. In the marine limestones gastropods, mollusks and echinoids are present. The ichthyofauna in the Sergipe-Alagoas, Araripe and Parnaiba Basins can be correlated based on biostratigraphic data. Also in the remaining between the, Sergipe-Alagoas and Araripe Basins (Serra Negra, in Jatobá Basin; Serra do Tonã, in North-Tucano Basin), similar limestones and fossil assemblages occur. The occurrences of some marine mollusks in the Malhada Vermelha Basin, located between Araripe and Potiguar basins, point also to a marine connection in that trend. Based on the arguments above the marine ingressions here proposed as follow (Fig. 2): (1) from W, through the Parnaiba Basin, (2) from NE, through the Pendência graben of the Potiguar Basin and (3) from SE, through the Sergipe-Alagoas Basin. No unanimity exists about it, but sediment and fossil record, as well as age determinations and tectonic situation, suggest that the sea could have invaded the basins from all three sides, leaving the crystalline highs as islands in between.
The end of the Albian is marked by a return of the continental realm in which fluvial systems became established over the whole area, loosing thus the Afrobrazilian and Araripe-Potiguar depressions their proper identities.
Acknowledgements. This paper was partially financed by FACEPE.

Geochronological studies of rocks from Cuba

E. LINARES-CALA - Centro de Investigaciones del Petróleo. Calle Washington No. 169, Cerro, La Habana 12000, Cuba. Fax: +5-37-666021.

Over thirty year the author had compiled the imformation published with respect to absolute age of Cuban rocks. Over 300 age determinations are know from year 1963 to year 1996. Several methods and minerals were used. With respect to rocks older than Cretaceous, we observe a marked Alpine orogenic influence concerning unstable minerals; although some researchers during recent years obtained good results with more stable atomic mineral structures (P. R. Renne et al., 1989). K-Argon methods have been widely employed to date metamorphic and magmatic rocks; and though world standards indicate monomineral fractions, several samples were analyzed as a whole.
In year 1985 M. L. Somin et al. tested the method known as thermoisocronic in rocks from the Escambray Mountains range, South-Central Cuba, and compared them with the results obtained in similar metamorphic ones from the Alpine regions. This method is a variant of the advantage that only few grains of the minerals are needed. They studied samples coming from the Granitic Manicaragua Belt, North of the Escambray, and very low figures of radiogenic Pb were obtained, so this diminished the accuracy of determinations. During this same period, Igor Tijomirov used the U-Pb method in Soviet institutions with metamorphic rocks from Isle of Youth, south of Cuba, using zircons, and obtained a Proterozoic age, but it is not clear if the samples were"redeposited".
At the University of Santa Barbara in California, USA, good results were obtained dating samples from the areas of the Manicaragua granites, eclogites and several metamorphic rocks from the Escambray Region. Also samples were analyzed from the Cretaceous Volcanic Are known as TSU Zaza.
This author and Mr. Renne studied the Sierra Morena marbles and the Argon 40-Argon 39 method was used. In year 1992 M. Iturralde et al. presented a preliminary interpretation of isotopic dating using K-Ar, and concluded that always is obtained basic facts of Cuban geology. Continental magmatism, and generation of oceanic crust in betweem 130-160 Ma, Cretaceous Volcanic Island Arc 125-73 Ma, Palcogenic Volcanic Arc 60-45 Ma. Also other opisodes are observed as main oceanic rifting 160-130 Ma, and several deformations and metamorphism 190±25 Ma, 120 Ma, 95 Ma, 85 Ma, 72 Ma and 45 Ma.
Our presentation shows datings of the most older Cuban rocks of Precambrian age based on Argon 40-Argon 39 using flogopite. The values obtained are 903.5±7.1 Ma in several samples. By the thermoisocronic method testing rocks from the Mabujina Formation ages were obtained from Precambriam to Carboniferous. Also in the catalog are show Mesozoic datings of different places and laboratories.
Important age determinations were obtained from the Paleogene Volcanic Arc rocks of Eastern Cuba. Using Graphs, charts and the catalog, it is possible to obtain information to understand better the geotectonic models of Central and South America as well as the Caribbean region.
References
Adamovich, A. & Chejovich, V., 1964, Principales características de la Geología y de los minerales útiles de la región nordeste de la provincia de Oriente. Revista Tecnológica, Vol. II, No. 1, pp. 14-20.
Hallen, C. W., Sornin, M., MillÁn, G., Renne, P., Kistler, R. W. & Mattinson, J. M., 1988. Tectonostratigraphic unit of Central Cuba. In: Barker, I. (Ed.), Trans. 11th Carib. Geol. Conf., Vol. 35, pp. 1-35.
IturraldE-Vinent, M., Wolf, D. & Thieke, H. V., 1989. Edades radiométricas del territorio Camagücyano. Resumen del Primer Congresso Cubano de Geología, La Habana, p. 117.
IturraldE-Vinent, M., MILLÁN, L., KORPÁS, Y., NAGY, E. & PAJÓN, J., in press. Geological interpretation of Cuban K-Ar database (Chapter 1).
IturraldE-Vinent, M., KORPÁS, Y., NAGY, E., PAJÓN, J. & OROPESA, P., 1992. Resumenes 13ra. Conferencia Geológica del Caribe, pp.79-80.
Linares-Cala, E. & Judoley, C., 1985. Catálogo de edades por métodos radiométricos de la Republica de Cuba. (Inédito).

Significance of the Pernambuco-Paraíba-Rio Grande do Norte Basin (NE Brazil) for the Atlantic Cretaceous

J. M. MABESONE - LAGESE/DGEO/UFPE, Recife, PE, Brazil.

Introduction. The final opening of the Atlantic Ocean, establishing the definitive connection between its equatorial and southern parts took place between NE Brazil and Nigeria-Cameroun. The Brazilian part of this last link is a represented by the Pernambuco-Paraiba-Rio Grande do Norte coastal sedimentary basin in which the clue for this opening has to be sought.
Caracteristics of Basin. The Pernambuco-Paraiba-Rio Grande do Norte Basin is limited in the south by the Pernambuco Lineament, extending northward to the Carnaubais fault system in the Potiguar Basin, including its so-called Touros Platform. Tectonically it may be considered as a relay ramp with transfer zones, reflected by its subdivision in sub-basins (Fig. 1). The various sub-basins suffered a differential subsidence due to the different competences of the Precambrian crystalline basement rocks. The most important faults separting the sub-basins are those of Goiana and Mamanguape, with significant depth differences of the basement at both sides. S of Mamanguape the sub-basins dip towards S; N of this fault they dip towards N and in the Touros Platform towards NE. The important Mamanguape fault divides the basin in two somewhat different parts. The southern part showns a South Atlantic affinity in lithic fill and fossil assemblages, and the northern part an Equatorial affinity. Just north of this fault the basement is high and no lithic connection between the Late Cretaceous-Early Tertiary basin fill has been found. It seems that here existed the very place of the last intercontinental connection, idea reinforced by the offshore Paraíba seamounts, basement highs too.
The lithic fill of the whole basin is rather uniform, consisting of a lower sandstone sequence of late Turorian-Campanian ages, and an upper limestone sequence of late Campanian-Eocene ages, as one transgression-regression cycle. The depositional environment of the sandstones was fluvial to coastral, of the limestone lagoonal to outer shelf. When compared with the other Atlantic-margin basins of Brazil, the Pernambuco-Paraíba-Rio Grande do Norte Basin originated certainly much later, meaning that the area was undoubtedly the last link before the final separation of the continents.
Implication for the Atlantic Connection. Thus, no doubt exists about the fact that the very last link between Brazil and Africa existed in the eastern part of NE Brazil, represented by the here considered basin. However, still no unanimity exists about how and when this link broke up.
The South Atlantic opened wedgewise by S-N rifting, finishing at the Pernambuco Lineament where the processes diverted eastward. The Equatorial Atlantic opened by strike-slip movement and a gradual deviation of Africa from South America, from W to E. This opening seemed to have finished against the Araripe-Potiguar depression in Brazil and its continuing Benue trough in Africa. The region in between both is the here considered sedimentary basin which stayed for a longer time connected to Africa. The basin being a relay ramp with no faults at the continental side, must have originated by stretching and thinning of the continental crust, with the development of a flexure. When this relay ramp started to form, before the break-up, continental sandstone could deposit on the subsiding flanks of the continent. Only in the latest Cretaceous the sea could invade the area. Apparently until that time the Atlantic connection consisted of two individual ocean parts, equatorial and southern, separated by the remainders of continental crust as thresholds in the form of submerged sills during world-wide transgressional phases and maybe as a landbridge during regressional periods. In such a way one may explain the planktonic marine fauna exchange between the ocean parts in the Albian, during its high sealevel stand. During sealevel lowstands as, for instance, in Cenomanian and early Campanian, benthic marine fauna and flora exchange could take place between Brazil and Africa. Furthermore, the occurence of phosphatic sediments in the Olinda and Alhandra sub-basins could only occur by upwelling against a sill in a still narrow ocean. Only from the Maastrichtian on, the seaway connection between Equatorial and South Atlantic established definitively, after the break-up of the last link. From then on the continents could freely drift away from each other, although until a least the Eocene they remained still so close that occasionally a land connection could exist, permitting the South American terrestrial fauna to migrate into Africa. Thus, the beginning of the Tertiary belongs still to the Cretaceous history of the opening Atlantic Ocean.

Geochemical aspects of the South Atlantic western margin in Brazil

Paulo Pereira MARTINS Jr.* & Gilberto Athayde ALBERTÃO**
* Escola de Minas / DEGEO, Ouro Preto, MG, Brazil. ** PETROBRAS-E&P/BC, Macaé, RJ, Brazil.

Introduction: Geochemical profiling is an useful tool for stratigraphic correlation and environmental analysis of the stratigraphical record. With this purpose some of the brazilian coastal basins were submitted to geochemical analysis for the differences of depositional environments between the Upper Cretaceous and Lower Tertiary (K-T) phases as far as the quality of the sampling would permit it.
Three coastal basins were selected: Campos (RJ), Espírito Santo (ES), and Sergipe-Alagoas (SE) basins. (Albertão, 1993, Albertão & Martins, 1995). Geochemical analysis comprised 46 elements but 15 of them were considered of good quality for the analytical description The criteria for selecting them were the chemical afinities and relative abundances. The following elements are considered in this paper: K, Mg, Na, AL,Cl, Ca, Fe, Ti, Ba Ce, Th and Cr.
Micropaleontological dating was determined with foraminifer varietes such as Eoglobigerina fringa, Parvularugoglobigerina egubina, Parasubbotina pseudobulloides, P. trinidadensis, for the lower Paleocene deposits. The Upper Cretaceous varieties are Rugoglobigerina ex gr. rugosa, Pseudoguebelina palpebra, Globotruncana aegyptiaca, Pseudoguembelina excolata, Heterohelix planata and others (Albertão, 1993).
The depositional environments of the these coastal basins are generaly recognized as complex systems with terrestrial, sub-acquatic and turbiditic deposits with high content of terrestrial clastics submitted to a highly intensive diagenesis. Geochemical of major and traces elements will thus represent all these factors together. They can be taken at their face value for a bulk comparison between different strata and wells. For a more detailed environmental perspective it would demand specific studies in other wells with continuous sampling for the Cretaceous-Tertiary transition.
Geochemical profile evaluation:
Elements concentrations were studied accordingly to depth. Statistical parameters are: Pearsonês correlation coeficient R for elementsê concentration versus depth, avarage M of elements concentrations and standard deviations S. Na, Mg and K present net increment with depth. K and Na present a likely tendence in ES-1 but the increment is smaller in general. Na in RJ-2 presents an opposite tendence with depth. S values in the southern region points to a general tendence of concentration increments in a north-south direction. It is noteworthy for Mg in RJ-1 well and K for RJ-1 and RJ-2 permits the discrimination of differing tendencies below and above the K-T limit. K values have a more monotonous tendency for all wells though R values do not clearly indicate this increment with the RJ-2 exception. High values of R for Al and Fe were determined in RJ-1, RJ-2 and ES-1. Ca is the most representative element with low values at the boundary but in T it increases significantly after having attained a minumum. The avarages M indicate a progressive increment in Al and Fe from south to north though the higher values are in ES-1; these elements present smaller values for S (exception ES-2) which means smaller variations around the avarage with increasing concentrations from south to north. Ca is the element with the most representative aspect. The limit K-T presents low Ca contents with an exception in RJ-2. It is noteworthy the opposite tendencies of the K and Ca contents in RJ-2.
Ti and Ba have high values for R in RJ-1. High avarages for Ba in RJ-2 are coherent with with Ca values. Higher contents for Cl are in agreement with Na content in RJ-2. High correlation values for Na and Cl in ES-1, 0.73 and 0.88 in ES-1 and ES-2 respectively, seem to indicate an evaporite environment. In general the K-T limit is very well discriminated by Ba content for all wells, and specially Cl in RJ-1 and ES-1. Ti is discriminative in RJ-1.
Cr, Ce and Th have high values for R with the exception of SE-1. An increase with depth is common to RJ-1 and ES-1 and an opposite tendence in RJ-2 and ES-2. Cr and Th present a general tendence from south to north up to ES-2 with variations in ES-1. Th is the element with sharper discriminant aspect in the K-T limits. All three elements present a high correlation coeficient greater than 0.95 with the exception of ES-1. There is not a pattern of concentration tendencies for all wells but some similarities between RJ-1 / ES-1 and RJ-2 / ES-2 are present. Nevertheless ciclicity is a remarkable aspect in each well. In RJ-1 ciclicity is less defined. It may be a consequence of strong variations of the concentrations with depth though some ciclicity might be determined with an harmonic analysis.
Conclusions:
The discriminant geochemical aspects of the K-T boundary (1) is not easely perceptible with a simple profiling analysis, (2) further evaluations with canonical analysis permitted to discriminate the K-T boundaries very sharply (Albertão, 1993; Albertão et al., 1995), (3) ciclicity is a notheworthy aspect for all the elements in each well without exception and it can be best demonstrated with a logarithmic function. Local factors are very important and can explain the intensive local variations, (4) nevertheless ciclicity is indicative of inter-regional common factors in depositional processes.
References
ALBERTÃO, G. A., 1993. Abordagem interdisciplinar e epistemológica sobre as evidências do limite Cretáceo-Terciário com base em leituras no registro sedimentar das bacias da costa leste brasileira. M. Sc. Dissertation, 2 vols, Universidade de Ouro Preto, 251 pp.
ALBERTÃO, G. A. & MARTINS Jr., P. P., 1995. Abordagem estatística para discriminação geoquímico-estratigráfica de depósitos da transição meso-cenozóica em bacias costeiras do Brasil. Rio Claro: VI Simp. Quantificação em Geociências, Bol. Res. Exp., UNESP, pp. 3-5.

Les kystes dedinoflagellés du Santonien au Paléocène de la marge transformante de Côte d'Ivoire-Ghana, forage 959D, croisière ODP 159

E. MASURE* & R. RAUSCHER**
* Laboratoire de Micropaléontologie, URA 1761, Université P. & M. CURIE, 4 place Jussieu, 75252, Paris, Cedex 05, France. ** Institut de Géologie, 1 rue Blessig, 67084 Strasbourg, France.

Le puits 959D a été foré lors de la campagne à la mer, ODP 159. Il est situé sur le flanc nord de la marge transformante de Côte-d'Ivoire-Ghana (3°ree;37. 656'N, 2°ree;44.149'W). Les objectifs de la campagne étaient d'étudier l'évolution structurale de cette marge et d'en dater les évènements majeurs. Quatre sites (959 à 962) ont été choisis,13 puits ont été forés, seul le forage 959D, a livré de riches associations de dinoflagellés. Dans les autres puits, des spores et grains de pollens ont été observés. Seul, les résultats concernant les dinokystes sont présentés içi.
C'est la première fois qu'une coupe continue du Santonien au Paléocène permet d'analyser la répartition stratigraphique des dinokystes dans cette région. Les données bibliographiques publiques sont rares, citons pour mémoire les travaux de : Jain & Millepied, 1973, 1975; Boltenhagen, 1977; Jan Du Chene & Aderiran, 1985. Les datations proposées içi sont fondées en priorité sur les données de ces travaux et par défaut sur ceux des régions téthysiennes (Corradini, 1972; Schrank, E., 1987; Kirsch, 1991) ou d'autres régions du monde (Williams & Bujal, 1985).
Le forage 959D a atteint la profondeur de 1158.9 m (carotte 78R) sous le fond de la mer, situé à plus de 2 100m. Les échantillons analysés s'intercallent, entre les carottes 76R (1 130 mbsf) et 44R (820 mbsf), dans l'unité lithologique III, formée par les argiles noires du Crétacé supérieur-Paléocène Lors de la campagne, les foraminifères, les nannofossiles calcaires, les silicoflagellés et les spores et grains de pollen ont été étudiés. Leurs résultats sont consignés dans le volume des rapports initiaux ( Mascle, J., Lohmann, G. P., Clift, P. D. et al., 1996, Shipboard Scientific Party, pp. 87-93) Il ressort de ces études que la carotte 68R est d'âge Albien terminal et que la 65 R et d'âge Santonien terminal. Entre les carottes 65R à 44R les échantillons sont dépourvus de foraminifères planctoniques et nannofossiles. Les grains de pollen prècisent que l' intervalle compris entre la carotte 54R et la carotte 49R ne peut pas être plus récent que le Maastrichtien et que celui compris entre les carottes 46R à 44 R est vraisemblablement d'âge Paléocène inférieur.
Plus de quatre-vingt kystes de dinoflagellès ont été identifiés dans les 56 échantillons étudiés. Ils permettent de fournir des datations dans l'intervalle compris entre les carottes 65R à 45R.
Les échantillons situés à la base du forage (carottes 76R - 72R) s'avèrent aphytiques. Les premières associations de dinokystes apparaissent dans la carotte 67R (1 050 m). Dans l'échantillon de la carotte 67R, l'association de dinokystes est pauvre. Elle se diversifie à partir de la carotte 66R où la présence de Xenascus gochtii permet de suggérer un âge Santonien Cette espèce est répertoriée dans le Santonien et le Campanien de Haute Bavière par Kirsch (1991).
Un âge Campanien est proposé à partir de la section 60R-04 (980 mbsf) où se produit la première apparition des espèces index suivantes : Andalusiella mauthei et Phelodinium magnificum. En Afrique équatoriale les Andalusiella sont connues du Campanien au Maastrichtien (Malloy, 1972, Jain & Millepied, 1973, Boltenhagen, 1977) et P. magnificum apparaît à la base ou au cours du Campanien dans le Monde (Williams & Bujak, 1985) et dans les régions téthysiennes (Kirsch, 1991).
Le Maastrichtien est suggéré à partir de la section 57R-04 ( 953 mbsf) sur la base de la première présence de Ceratiopsis diebelii et Andalusiella ivoirensis. C. diebelii est un marqueur classique du Maastrichtien de l'hémisphère nord. A. ivoirensis est connu dans les sédiments maastrichtiens du Bassin Ivoirien (Masure, Tea & Yao, 1996). Les espèces associées significatives sont, entre autre: Andalusiella rhomboides, Cerodinium granulostriatum et Palaeocystodinium australinum. Les espèces du genre Areoligera sont diversifées. Le Danien est caractérisé à partir de la section 53R-06 (915 mbsf) avec l'apparition de Danea californica, les autres espèces importantes sont Spiniferites hyalospinosus, Kenleya pachycerata, Fibrocysta radiata, F. axialis et Impagidinum celineae. Le dernier échantillon analysé, 44R-06, 60-62 cm est soupconné d'être Eocène sur la base de la présence de Adnatosphaeridium multifurcatum. La répartion stratigraphique des kystes de dinoflagellés à permis de préciser les limites des étages dans l'intervalle Santonien, Paléocène, Eocène basal ?, alors que celles-ci étaient inconnues jusqu'à présent
References
BOLTENHAGEN, E., 1977. Microplancton du Crétacé Supérieur du Gabon. Cahiers de Paléontologie,
C.N.R.S., 1972. Non-calcareous microplankton from the Upper Cretaceous of the Northern Apennines. Bollet. Paleont. Italiana, Vol. 11, No. 2, pp. 119-197.
JAIN, K. P. & MILLEPIED, P., 1973. Cretaceous microplankton from Senegal Basin, N.W. Africa. 1. Some new genera species and combinations of dinoflagellates. Palaeobotanists, Vol. 20, pp. 22-32.
JAIN, K. P. & MILLEPIED, P., 1975. Cretaceous microplankton from Senegal Basin, N.W. Africa. 2. Systematics and biostratigraphy. Geophytology, Vol. 5, pp. 126-171.
JAN DU CHENE, R. & ADEDIRAN, S. A., 1985. Late Paleocene to Early Eocene dinoflagellates from Nigeria. Cahiers de Micropaléontologie, Vol. 3, pp. 5-38. KIRSCH, K.-H., 1991. Dinoflagellaten-Zysten aus der Oberkreide des Helvetikums und Nordultrahelvetikums von Oberbayern. Münchner Geowissenschaftliche Abh. Reihe A, Vol. 22, pp. 1-306.
MASCLE, J., LOHMANN, G. P., CLIFT, P. D. et al., 1996 (Eds). Proc. ODP, Init. Repts., Vol. 159, College Station, TX (Ocean Drilling Program), pp. 65-150.
MALLOY, R. E., 1972. An upper cretaceous dinoflagellate cyst lineage from Gabon. West Africa Geosciences and Man, Vol. 4, pp. 57-65.
MASURE, E., TEA, J. & YAO, R., 1996. The dinoflagellate Andalusiella; emendation of the genus, revision of species, A. ivoirensis MASURE, TEA and YAO, sp. nov. Rev. Paleob. Palynol., Vol. 91, pp. 171-186.
SCHRANK, E., 1987. Palaeozoic and Mesozoic palynomorphs from northeast Africa (Egypt and Soudan) with special reference to Late Cretaceous pollen and dinoflagellates. Berliner Geowissenschaften, Abh. (A), Vol. 75, pp. 249-310.
WILLIAMS, G.L .& BUJAK, J.P., 1985. Mesozoic and Cenozoic Dinoflagellates. In: BOLLI, H. M., SAUNDERS J. B. & PERCH-NIELSEN, K. (Eds), Plankton Stratigraphy, Cambridge Univ. Press, pp. 847-964.
Liste des espèces citées :
Adnatosphaeridium multispinosum WILLIAMS & DOWNIE, 1966
Andalusiella mauthei RIEGEL, 1974, emend. MASURE et al., 1996
Andalusiella rhomboides BOLTENHAGEN, 1977 emend. MASURE et al., 1996
Andalusiella ivoirensis MASURE, TEA & YAO, 1996
Cerodinium diebelii (ALBERTI, 1959b) LENTIN & WILLIAMS, 1987
Cerodinium granulostriatum (JAIN & MILLEPIED, 1973) LENTIN & WILLIAMS, 1987
Danea californica (DRUGG, 1967) STOVER & EVITT, 1978
Fibrocysta axialis (EISNACK, 1965) STOVER & EVITT, 1978
Fibrocysta bipolaris (COOKSON & EISENACK, 1965) STOVER & EVITT, 1978
Impagidinium celineae JAN DU CHENE, 1988
Kenleya pachycerata COOKSON & EISENACK, 1965
Palaeocystodinium australinum (COOKSON, 1965b) LENTIN & WILLIAMS, 1976
Phelodinium magnificum (STANLEY, 1965) STOVER & EVITT, 1978
Spiniferites hyalospinosus (HANSEN, 1977) STOVER & WILLIAMS, 1987
Xenascus gochtii (CORRADINI, 1973) STOVER & EVITT, 1978

Les ammonites Cenomano-Turoniennes du Gabon: interet pour la liaison Tethys-Atlantique Sud et correlations

Christian MEISTER*, M. M'BINA** & Jacques LANG**
*Muséum d'Histoire Naturelle, Département de Géologie et de Paléontologie, 1 route de Malagnou, c.p. 434, CH - 1211 Genève 6, Suisse.
** Centre des Sciences de la Terre, Université de Bourgogne, 6 Bd Gabriel, F - 21000 Dijon, France.

Au Cénomanien-Turonien, le Gabon et le Brésil (Bassin de Sergipe), tant par la composition des faunes d'ammonites que par leur position paléogéographique, occupent une position clef pour la compréhension des relations avec la Téthys via la mer saharienne et pour l'ouverture de l'Atlantique sud. Une partie de ce travail est consacrée à une coupe lithologique de la région de Libreville (Gabon) où ont été trouvé, dans un contexte stratigraphique précis: Pseudaspidoceras sp., Choffaticeras sp. et Thomasites nigeriensis (WOODS) et à une rediscussion des ammonites décrites précédemment dans ce pays. Le second volet a trait aux corrélations entre la Téthys occidentale (Tunisie) et l'Atlantique sud (Gabon - Brésil) via le fossé de la Bénoué (Niger - Nigéria). Le bilan des successions des ammonites cénomano-turoniennes présenté pour ces différentes régions, permet de mettre en évidence 10 événements fauniques corrélables à grande échelle (Fig. 1):
Evénement à Eucalycoceras pentagonum - En Tunisie l'espèce index est associée, entre autre, à Calycoceras s.l. et Metengonoceras sp. On ne retrouve cet événement qu'au Brésil, avec Acanthoceras jukesbrownei (SPATH). Il n'est pas connu dans la mer saharienne. La liaison nord-sud via la Bénoué n'était encore réalisée.
Evénement à Thomelites - L'épisode à Neolobites vibrayeanus (d'ORB.) ne peut être observé que jusque dans le Damergou (Niger); plus au sud il n'y a pas de faunes aisément corrélable avec cet épisode. La faune associée est composée de Thomelites, Calycoceras s.l. et Eucalycoceras en Tunisie et de "Mammites" aff. conciliatum (STOL.) (Niger). Il est suivi par un épisode à Thomelites qui correspond aux horizons à Metengonoceras dumbli (CR.) et à Thomelites tenereensis ME. et al. du Niger; en Tunisie à l'association Thomelites sp., Calycoceras s.l., Eucalycoceras et au Brésil à la présence des T. aff. sornayi (TH.) et de Pseudocalycoceras harpax (STOL.)
Evénement à Euomphaloceras septemseriatum - Représenté au Brésil et en Tunisie, cet ensemble est peut-être corrélable avec les niveaux à Nigericeras du Niger-Nigéria où l'on trouve aussi Metoicoceras geslinianum (d'ORB.). Thomelites, par contre, n'est plus représenté.
Evénement à Pseudaspidoceras pseudonodosoides - Reconnu partout, il semble correspondre à la première apparition des Pseudaspidoceras; au Niger-Nigéria, Nigericeras est encore présent. Lui succède un épisode à Fagesia thomi (RE.)-evolutum (SCH.) (Nigéria) - Vascoceras gamai CH. (Brésil) encore avec P. pseudonodosoides (CH.). Ce dernier épisode pourrait correspondre à l'association P. pseudonodosoides (CH.), Vascoceras et Fagesia de Tunisie.
Evénement à V.(Paravascoceras) cauvini - La seule succession détaillée se trouve au Nigéria et cet ensemble ne peut être corrélé qu'avec la Tunisie où il existe quelques V. (Paravascoceras).
Evénement à Vascoceratidae globuleux [V. (P.) proprium sensu Meister et al.] - Il reste encore difficile à situer. Les V. (P.) durandi (T. & P.), classiquement mis dans le Turonien basal, semblent être déjà présents dans le Cénomanien terminal (Egypte et Tunisie). Les V. (P.) proprium REY. (Nigéria) et les V. (P.) hartii (HYATT) (Brésil) présentent également la même ambiguïté. La présence de P. footeanum (STOL.) ou P. paganum REY. ne permet pas de résoudre ce problème.
Evénement à Pseudaspidoceras flexuosum - P. flexuosum PO. et Watinoceras indiquent sans ambiguité le Turonien inférieur auquel peut être rattaché la presque totalité de la zone à V. hartii - P. footeanum du Brésil. Au Nigéria et en Tunisie des Vascoceras globuleux sont aussi présents: V. costatum (REY.) et V. (P.) durandi (T. & P.).
Evénement à Thomasites - Il correspond à trois épisodes; le premier avec T. gongilensis (WOODS) (Nigéria) est un équivalent probable de la partie inférieure de l'épisode à T. rollandi PERV. de Tunisie. Le second à T. nigeriensis (WOODS) et le troisième à T. wallsi REY. sont représentés aussi bien dans les zones sahariennes qu'au Brésil et au Gabon, ce sont d'excellents indicateurs de l'existence d'une liaison entre la Téthys et l'Atlantique sud via la Bénoué. En Tunisie, Choffaticeras apparaît dès la base de cet événement; au Niger, Nigéria et Gabon, sa présence est plus ponctuelle. Les épisodes à T. nigeriensis (WOODS) et T. wallsi REY. sont les équivalents en Tunisie d'une partie de l'épisode à T. rollandi PERV. ou, déjà de l'épisode à H. ingens (von K.)- Ch. luciae PERV.
Evénement à Hoplitoides ingens - En Tunisie, comme au Nigéria, les Thomasites sont encore présents mais associés à des H. gr. ingens (von K.). Au Brésil on trouve un assemblage à K. seitzi (RIE.) et W. amudariense (ARK.), un équivalent probable de cet évènement.
Evénement à Mammites nodosoides - Reconnu dans toutes les régions c'est un bon marqueur de la fin du Turonien inférieur. Kameruniceras turoniense (d'ORB.) apparaît un peu plus tardivement aussi bien en Tunisie qu'au Brésil; il semble être présent au Gabon. Fagesia, S. (Jeanrogiceras), Morrowites, Watinoceras, Choffaticeras, Neoptychites et Thomasites sont également connus dans cet évènement à M. nodosoides.

The Paraná continental igneous Province and models of South Atlantic opening: a review

Ronaldo Luiz MINCATO*,**, Alfonso SCHRANK** & Jacinta ENZWEILER**
* Instituto de Ciências Biológicas - PUCCAMP, ** Instituto de Geociências - UNICAMP, Campinas, SP, Brazil.

Continental flood basalt (CFB) provinces represent extensive outpourings of lava associated with the intrusion of mafic material into continental crust. They have volumes in the range of 105-107 km3 and are distributed throughout geological time from Early Precambrian to Recent. Currently they are considered as a particular type of the Large Igneous Provinces - LIP. The CFB provinces are characterized by thick accumulations of sheet-like sub-horizontal lava flows and their magmatic compositions are dominated by tholeiitic basalts.
The origin of the CFB provinces has not yet been well established because the absence of modern active analogues. Nevertheless, Peate (1990) highlighted that all CFB have in common a –tensional tectonic setting” and pointed out some examples of large flood basalt provinces which are connected in some way to the break-up of the continents. The Paraná Continental Igneous Province - PCIP - of southeastern South America is one of the largest examples of a CFB province, with a present area in excess of 1.2 x 106 km2 (Peate, 1990). The eruption of this vast Early Cretaceous (circa 115-135 Ma) lava field largely covered the pre-existing Paleozoic Paraná sedimentary basin, whose boundary is limited by up-arching structures. The PCIP lava sequences are dominated by tholeiitic basalts (>90% by volume) with large quantities of acid rocks and subordinate intermediate lavas.
The broad geologic similarities between Paraná and Karoo basins, respectively in southern part of South America and the southern Africa, was already mentioned by Du Toit (1937). However, it was only after the 1960ês, with the plate tectonics theory that many of these similarities were accepted as previously continous. The paleomagnetic studies carried out on Paraná and Etendeka lavas showed a concidence of paleomagnetic poles a further evidence of a previous single magmatic province. The South Atlantic opening was a continuous drift process just after the end of continental activity. The later stages before the South Atlantic Opening are characterized by basalt flows and dolerite dykes with transitional geochemical signature from CFB to MORB (Fodor & Vetter, 1984, Peate, 1990). The development of the Paraná - Etendeka magmatic province and its linkage with the transition from a lithospheric rifting to a oceanic opening are unsolved questions. Few geodynamic models have been proposed in order to constrain the PCIP and South Atlantic relationship. Some of these models are briefly discussed here.
Piccirillo et al. (1988) postulated an eastward migration of the Paraná volcanism, possibly related to the clockwise rotation of the South American plate. Their model is based on a) the asymmetric distribution of magmatism (hugest in Brazil); b) the acid rock-types occurrence just over the continental margin; and c) the paleomagnetic poles coincidence between the volcanics of the Etendeka and that of the southern Paraná basin. The authors stressed too that a major rifting and sea-floor spreading phase has begun after the eruption of acid volcanics, which are believed to be related to crustal anatexis during a process of lithospheric (crustal) thinning at the base of the crust.
Later, Peate (1990) presented and discussed some models to explain the asymmetrical continental extension and distribution of lavas between the Paraná and Etendeka provinces. Considering the great thickness of flows and sills at the basin axis, he adopted the Braun & Beaumont (1989) theoretical model, according to which the magma had been intruded from beneath the Paraná basin, between 400 and 500 km westward from the original South Atlantic Rift - SAR. During the initial stages of rifting, extension was transferred to a lateral offset of pre-existing crustal weakness zone (Paraná basin). The basaltic magmas used the resultant shear zone as a conduit to the surface. When the lithospheric thinning became more intense, the shear was abandoned and the crustal extension was concentrated on the main rift zone (SAR), above the deeper lithospheric mantle extension. This extension was accompanied by crustal anatexis and resulted in concentration silicic volcanic rocks in the main rift zone.
Recent Ar-Ar studies on Paraná - Etendeka CFB (Turner et al., 1994) indicated that the lavas erupted between 137 and 127 Ma. Their data also indicate that the magmatism migrated from NW to SE, prior and during the opening of the South Atlantic, providing a possible explanation for the asymmetry of the Paraná - Etendeka province.
Mincato (1994), evaluating the literature data, suggested that the early stages of magmatism ocurred in close association with the SAR.
Based on geophysical data Quintas (1995) presented evidences of paleo-rift structures on the western portion of the PCIP. These structures may have been the feeders during the early stages of the magmatism, which agrees with Turner et al. (1994)'s model.
The mentioned models, proposed to explain the already accepted PCIP and SAR relation, show that more data are needed in order to clarify some discrepancies among them.
References
BRAUM, A.J. & BEEAUMONT, C. 1989. Earth Planet. Sci. Lett., Vol. 93, pp. 405-423.
DU TOIT, A. L., 1937. Edinburgh, Oliver & Boyd. 366 pp.
FODOR, R. V. & VETTER, S. K. 1984. Contrib. Mineral Petrol., Vol. 88, pp. 307-321.
MINCATO, R. L., 1994. Dissertação de Mestrado, IG-UNICAMP. Campinas, 113 pp.
QUINTAS, M. C. L., 1994. Tese de Doutoramento, IAG-USP. São Paulo, 213 pp.
PEATE, D.W. 1990. Ph.D. Thesis, Open University. Milton Keynes, England, 359 pp.
PICCIRILLO E. M., MELFI, A. J., COMIN-CHIARAMONTI, P., BELLIENI, G., ERNESTO, M., MARQUES, L. S., GIARETTA, A., NARDY, A. J. R., PACCA, I. G., ROISENBERG, A., STOLFA, D., 1988. In: MACDOUGALL, J. D. (Ed.). Dordrecht, Kluwer. pp. 195-238.
TURNER, S., REGELOUS, M., KELLEY, S., HAWKESWORTH, C., MANTOVANI, M., 1994. Earth Planet. Sci. Lett., Vol. 121, pp. 333-348.

Magmatism related to the opening of South Atlantic Ocean

Ana M. P. MIZUSAKI*, Antônio THOMAZ FILHO**) & Pedro de CÉSERO**
* Instituto de Geociências - UFRGS, Porto Alegre, RS, Brazil.
** Faculdade de Geologia - UERJ, Rio de Janeiro, RJ, Brazil.

This paper is based on 368 radiometric K/Ar data of igneous rocks in the range of basic to alkaline composition and discuss the study of magmatic process that occur in Brazilian sedimentary basins (both inland and marginal). These rocks were associated with tectonic events related to the opening of the South Atlantic Ocean, especially developed along Mesozoic and Cenozoic. Almost 70% of these ages resulted from analytical procedures accomplished at São Paulo University through agreement with the Petrobras Research and Development Center. Additional K/Ar data already published in the literature were added to these data.
The spatial and temporal position of magmatic rocks were interpreted according to the relation with the geologic evolution that marks the expressive rifting process responsible for the opening of the South Atlantic Ocean. This subject is discussed utilizing the classical subdivision of the Brazilian continental margin into three portions: equatorial, east and southeast margins.
Volcanic episodes initially registered at equatorial margin were dated as Jurassic-Triassic and were associated with the South Equatorial Atlantic Ocean. This volcanism is observed in marginal basins, from northwest to southwest to southeast, up to the Amazon mouth. On the other hand, the evolution of this volcanism to the southeast of the Amazon mouth probably found a strong resistance from the basement transverse structures represented by the São Luiz/West African craton. This event is linked to a great energy liberation resulting in a magmatic event. The expressions ot this event are the occurrences of basic igneous extrusions and intrusions especially in sedimentary basins like Tacutu, Acre, Solimões, Amazonas, Parnaíba and Cassiporé region (Amapá coast).
The same is proposed to the southeast margin, Upper Jurassic-Lower Cretaceous, but, in this case, with the rifting process opening the continental crust northwards, up to the Espirito Santo basin. In this case, the resistance offered by the São Francisco/Salvador/Congo craton promoted manifestation of an expressive volcanism to the interior of the separated continents, reaching, mainly, the Paraná Basin. This pouring should have promoted attenuation of the energy process during the rifting evolution. By this way, the equatorial margin, east of the Amazon mouth, was submitted to transcurrence (Szatmari et al., 1987). Due to the clockwise rotation of the South American plate, transtension was produced to the east of Fortaleza city (creating the Potiguar Basin) and transpression on the west of this city (where developed the Ferrer-Urbano Santos Arch, the basement uplift on the Pará and Maranhão platform and the non sedimentation of Neocomian layers in this area).
The apparent absence of basic magmatic rocks in the Brazilian east margin is significative. By recording the known distribution of the K/Ar ages of these rocks in the Espirito Santo and Potiguar basins, each considered to be the southern and northern limits of the east margin, respectively, it is possible to note a peculiar characteristic in the east margin evolution. Ages between the interval 100-120 Ma are absent in these basis. This fact allow us to suggest that the structural separation between the South American and African continents, in the east margin, probably was more recent than 100 Ma. Until this event, the lithosphere of the east margin was submitted only to crustal stretching and faulting processes. This fact associated with results of sedimentological, micropaleontological and geochemical studies (Dias-Brito, 1987; Schlanger et al., 1981; Chang & Kowsmann, 1987; Koutsoukos, 1992; Koutsoukos et al., 1991a,b; Koutsoukos & Bengtson, 1993; Pereira, 1992, 1994) allow us to visualize marine sedimentation on the east margin since Aptian times, although the effective separation between the South and South Equatorial Atlantic Ocean only happened in Cenomanian/Turonian times (circa 90 Ma).
Therefore, the prediction of Pereira (1992, 1994), about the occurrence of magmatic process forming oceanic crust in the eastern margin, with ages around 90 Ma, is viable.
The data presented in this work led to conclude to the probable presence of tholeiitic volcanism in deeper portions of the actual coast, with radiometric ages around 90 Ma, but not reached by drillings up to the present moment.
References
CHANG, H. K. & KOWSMANN, R. O., 1987. Interpretação genética das sequências estratigráficas das bacias da margem continental brasileira. Rev. Bras. Geoc., Vol. 17. pp. 74-80.
DIAS-BRITO, D., 1987. A Bacia de Campos no Mesocretáceo: uma contribuição à paleoceanografia do Atlântico Sul primitivo. Rev. Bras. Geoc., Vol. 17, pp. 162-167.
KOUTSOUKOS, E. A. M., MELLO, M. R. & AZAMBUJA-FILHO, N. C., 1991a. Micropaleontological and geochemical evidence of Mid Cretaceous dysoxic-anoxic palaeoenvironments in the Sergipe Basin, northeastern Brazil. In: Tyson, R. V. & Pearson, T. H. (Eds), Modern and Ancient Continental Shelf Anoxia, Geol. Soc. Special Publ., No. 58, pp. 427-447.
KOUTSOUKOS, E. A. M., MELLO, M. R., AZAMBUJA-FILHO, N. C.; HART, M. B. & MAXWELL, J. R., 1991b. The upper Aptian-Albian succession of the Sergipe Basin, Brazil: an integrated paleoenvironment assessment. Bull. Am. Assoc. Petr. Geol., Vol. 75, No. 3, pp. 479-498.
KOUTSOUKOS, E. A. M., 1992. Late Aptian to Maastrichtian foraminiferal biogeography and palaeoceanography of the Sergipe Basin, Brazil. Palaeogeogr., Palaeocl., Palaeoc., Vol. 92, pp. 295-324.
KOUTSOUKOS, E. A. M. & BENGTSON, P., 1993. Towards an integrated biostratigraphy of the upper Aptian-Maastrichtian of the Sergipe Basin, Brazil. Docum. Lab. Géol. Lyon, No. 125, pp. 241-262.
PEREIRA, M. J., 1992. Considerações sobre a estratigrafia do Cenomaniano-Santoniano em algumas bacias marginais brasileiras e sua implicação na histórica tectônica e sedimentar da margem continental. Bol. Geoc. Petrobras, Vol. 6, No. 3/4, pp. 171-176, Rio de Janeiro.
PEREIRA, M. J., 1994. Seqüências deposicionais de 2a. e 3a. ordens (50 a 2,0 Ma) e tectono-estratigrafia no Cretáceo de cinco bacias marginais do Brasil; comparação com outras áreas do globo e implicações geodinâmicas. Bol. III Simp. sobre o Cretáceo do Brasil, Rio Claro, São Paulo, pp. 1-2.
SCHLANGER, S. O., JENKYNS, H. C. & PREMOLI-SILVA, I., 1981. Volcanism and vertical tectonics in the Pacific Basin related to global Cretaceous transgressions. Earth Planet. Sci. Lett., Vol. 52, No. 2, pp. 435-449.
SZATMARI, P., FRANÇOLIN, J. B. L., ZANOTTO, O. & WOLF, S., 1987. Evolução tectônica da margem equatorial brasileira. Rev. Bras. Geoc., Vol. 17, No. 2, pp. 180-188, São Paulo.

Fossil charophytes from South America

Eduardo A. MUSACCHIO
Laboratorio de Bioestratigrafía, UNPSJB. (9005) Comodoro Rivadavia, Argentina.

The fossil record of South American charophytes remains still poorly known. However, when they were methodically searched and studied for stratigraphic and biogeographic purposes, charophytes have often provided valuable information. The present report accounts the information available for the author, focusing in the biogeographic relationships and the stratigraphic significance of the different assemblages. In one of the pioneer contributions dealing with South American charophytes, Leonardosia was proposed for Permian gyrogonites of the Paraná Basin (Sommer, 1954, Herbst, 1981). This Genus is also well represented in China (Lu, H.n. & Zhang S.z., 1990).
In Patagonian Jurassic deposits, Porochara was found in thin lenses interlayered among basalts of the Sierra de Olte Complex. This is the most conspicuous unit of the lower rift-facies in the Northern San Jorge Gulf Basin. The Sierra de Olte Complex includes more than 2,000 meters thick of Lias to early Dogger volcanic and sedimentary rocks. The mentioned charophytes constitute part of a Darwinula magna / Darwinula sarytirmanensis ostracod-assemblage (Musacchio, 1993). The later assemblage characterizes sediments of the Chinese Dogger (Li, Z.w., 1985, Qi, H., 1985).
The organ-species of the minute gyrogonites of Mesochara are diversified as well as abundant, in several charophyte-microfloras of Neocomian age from the Argentine Patagonia. The genus Mesochara is well represented in different Neocomian lacustrine facies (Musacchio, Beros & Pujana 1990), belonging to the second regional rift-facies episode of the San Jorge Gulf Basin (Fitzgerald, Mitchum, Uliana & Biddle, 1990). Some assemblages from this basin share species with others in the Neuquén Basin at West Central Argentina. Such is the case of Mesochara maruchoensis, which was found in levels interlayered with marine beds bearing early Hauterivian ammonoids. Besides, in the same Neuquén Basin, levels with the widely-distributed gyrogonite Mesochara stipitata, were found together with the clavatoracean Triclypella patagonica and Atopochara triquetra, of the Zone of Triquetra. The last assemblage, overlies marine Hauterivian deposits with ammonoids of the H. neuquensis Zone(Musacchio, 1989, 1990).
In Aptian times, assemblages from different geological regions of the Continent are characterized by utricules of Flabellochara harrisi. Aptian sediments from several geologic provinces, rests discorformable upon confined or more restricted Neocomian units. This fact suggests the presence of a regional unconformity at the beginning of the mid Cretaceous. In West Central Argentine, the levels with F. harrisi rest on paraconformity with Barremian beds bearing ammonoids (Musacchio & Palamarczuck 1975). In the Alagoas Stage, of the Potiguar and Santos basins (Musacchio & Viviers, 1993), F. harrisi was recently found. In the Santos Basin, the same species appears together with Atopochara trivolvis. In the Chubut Basin, at the Central Argentine Patagonia, the charophytes F. harrisi and Porochara mundula are associated with non-marine ostracods. A number of species of this association seems identical to taxa previously recognized in the Rocky Mountain Domain for the same age (Musacchio & Chebli, 1975). Charophytes of mid Cretaceous ages in sediments of the Baurú Group, Paraná Basin (Petri, 1955), and others of Albian age in the Maranhão Basin (both from Brasil), include large gyrogonites of Mesochara of ample distribution.
Late Cretaceous microfloras display the highest diversity, in the number of taxa, known at the present. However, clavatoraceans were not reported yet. Some species belonging to Gobichara, Lamprothamnium, Mesochara, as well as allied ostracods belonging to the genera Neuquenocypris, Timiriasevia and Talicyprideinae spp., resemble taxa well represented in Asya (Wang Z., 1978, Musacchio & Simeoni, 1990, Musacchio, 1990, 1993). At the end of the Cretaceous, two biogeographic areas can be distinguished: Patagonia and the West-Central South America.
In Patagonia (Neuquén and the Western Colorado Basin), the non-marine stratigraphic units near the K/T boundary can be gauged by two interbedded marine episodes of reliable Maastrichtian and Danian ages. These episodes allow to span three non-marine Zones of charophytes and ostracods (Musacchio, 1989). At the eastern passive margin, Campanian gyrogonites and ostracods from the Campos Basin (Brasil) compare well with presumably coeval species of the Western Colorado Basin. The K/T boundary can be well recognize by marine microfossils in the Neuquén/Western Colorado basins (south of Mendoza Province of Argentina). However, a sharp change of flora charophytes was not observed but a reduction of taxonomic diversity. In West-Central South America (Peruvian Andes and the –Oriente”, Acre Basin, Puna and Northern Argentina), the Maastrichtian assemblages are characterized by the pair: Porochara gildemeisteri/Amblyochara spp. (Fritzche, 1924, Peck & Reker, 1947, Horn & Rantzien, 1954, Koch & Blisenbach, 1960, Rivera, 1961, Grambast, Martínez, Mattauer & Thaler, 1967, Musacchio, 1972, Gutiérrez Chávez, 1975, Grambast in Megard, 1978, Feist in Mourier et al., 1988, Musacchio in Rodrigo & Branisa, 1990).
Early Paleogene deposits in Patagonia include Peckichara cf. varians meridionalis Musacchio & Morroni (1982). Sediments of similar age in the West-Central South America can be recognized when Nitellopsis supraplana appears (Peck & Reker, 1947, Koch & Blisenbach, 1960, Rivera, 1961, Gutiérrez Chávez, 1975, Grambast in Megard, 1978, Musacchio & Morroni, 1983, Feist in Mourier et al., 1988). Species of Chara and Grovesichara characterize Neogene sediments in Perú (Ucayali-Contamana Region), Brazil (Acre Basin) and Northern Argentina (Rivera, 1961, Gutiérrez Chávez, 1975, Grambast in Megard, 1978, García & Herbst, 1994).
Summarized References
MOURIER, T., BENGTON, P., BONHOME, M., BUGE, E., CAPPETA, H., CROCHET, J., FEIST ,M., HIRSCH ,K., LAUBACHER, G., LEFRANC, J., MOULLADE, M., NOBLET, C., REY, J., SIGÉ, B., TAMBAREAU, Y., TAQUET, P. H., 1988. The Upper Cretaceous-Lower Tertiary marine to continental transition in the Baguá basin, Northern Perú. Newsl. Strat., Vol. 19, No. 3, pp. 143-177, Stuttgart.
MUSACCHIO, E., 1981. South American Jurassic and Cretaceous Foraminifera Ostracoda and Charophyta of Andean and Sub-Andean regions. In: Volkheimer, W. & Musacchio, E. (Eds), Cuencas sedimentarias del Jurásico y el Cretácico de América del Sur, Vol. 2, pp. 461-498, Buenos Aires.
MUSACCHIO, E., 1993. Use of the global time scale in correlating nonmarine Cretaceous rocks in Southern South America. Cret. Res., Vol. 14, pp. 113-126.

Biogeographic relationships of Lower Cretaceous calcareous microfossils from Patagonia: an approach to causal factors

Eduardo A. Musacchio & M. Simeoni
Laboratorio de Bioestratigrafía, UNPSJB. Ciudad Universitaria. (9005) Comodoro Rivadavia, Argentina.

Introduction. The paleobiogeographic relationships of different marine and non marine Cretaceous assemblages of ostracods, foraminifers and charophytes from Southern South America, known by the authors, suggest a changing framework of the paleogeographic design of the region. Similarities or disjunctions between distanced but coeval analogous assemblages, might be explained by biogeographic factors. In this frame, it is well known how a connection between continents installs, on turn, a barrier for the adjacent marine biota and vice versa. The free interchange among the continental species entails the disjunction for the marine ones. Besides, the temperature rules the latitudinal as well as altitudinal differentiation of the biota. Both factors, barriers and climate, are relevant when explanations for the biogeographic design are demanded.
Non-marine assemblages. Neocomian and Aptian a»

The provincial differentiation between Patagonian faunas and those well known by PETROBRAS from the basins on the continental margin of Brazil, seems ruled both by geographic and climatic factors. First, the design of isolated grabens, where the lacustrine sedimentation is settled. Second, the role of the intermittent barrier played by the East-Western Colorado Through (see below). Third, the latitudinal stretching that separates both climatic and physiographic regions.
Differing of the previous case, the Aptian non-marine microfossils assemblages share conspicuous elements of wide geographic distribution, such as Mantelliana angulata angulata (Kömmelbein & Weber) nov. comb. (Mantelliana angulata angulata nov. comb. Musacchio & Simeoni 1996, pro Hourqia angulata angulata Krömmelbein & Weber 1971) and Mantelliana ulianai Musacchio & Palamarczuck 1975. The charophytes markers Atopochara trivolvis Peck 1938 and Flabellochara harrisi (Peck 1941), are conspicuous utricules of charophytes found in several Aptian sediments of the World. The mentioned Aptian sequences in South America overlie unconformably upon more restricted Neocomian sediments. This feature of the main Aptian sequence, including widely-distributed Aptian microfossils, suggests the existence of a free interchange of continental biota between North and South America. The results of a widespread orogeny, involving the West side of the main continent, can be invoked to explain the presence of an South-North continental connection.
Marine assemblages. For Valanginian-Hauterivian times, some genera as Aracajuia Krömmelbein 1967 (= Sondagella Dingle 1969), Rostrocytheridea Dingle and Cytherelloidea Jones, deserve interest when the evolution of the early South Atlantic involves the dispersion and distribution of austral faunas. Thus, several species of the Sundays River Formation, of Upper Valanginian-Lower Hauterivian age, from the Algoa basin (South Africa), were also found in similar sediments of the Neuquén Basin at West Central Argentina (Musacchio & Simeoni, 1995). These finds confirm previous data, based on fossil molluscan, accounted by Reyment & Tait (1972).
The explanations given by the later mentioned authors, suggesting the role of the Colorado basin operating as corridor for marine biota can not be rejected yet. The fauna of foraminifers and ostracods of the Sundays River Formation compare better to the Neuquean faunas than the similar ones from the Austral Basin (southernmost Patagonia). On turn, it might be taked into account that the Colorado Basin operated as corridor during the Maastrichtian, Danian and, in many occasions, in the Cenozoic. Finally, it must be mentioned the significance of ostracods in levels of the Late Cretaceous Pehuenche Group (= estratos con dinosaurios = Neuquén Group) resembling taxa recovered from marine Atlantic sites. The corresponding outcrops of these Late Cretaceous sediments are lying near the Andean domain in the most Western part of the Colorado Basin at Zampal, South of Mendoza Province, 69o 40êW (for additional literature see: Musacchio & Simeoni, 1995).
Dealing with North-South faunal interchange, some cases such as the Cenomanian marine Tethyan faunas in the Central Bolivia, and the early Cretaceous –cold faunas” from North-Eastern Brazil, demonstrates the dynamic of the palaeoceanographic design (Musacchio & Simeoni, 1995).
To the last cases (–cold faunas”), the distribution of the Aracajuia genus is particularly interesting (Musacchio & Simeoni, 1995; Figure 2). This genus is known in the Jurassic (Musacchio & Volkheimer, 1994), and it appears taxonomically well diversified during the Lower Cretaceous in the Gondwanian domain. The type species of the genus was described by Krömmelbein from late Aptian to Albian sediments belonging to the Sergipe Basin. During the last mentioned ages, however, related species as –Amphicytherura” asqelonensis Rosenfeld & Raab (1984) in Israel, suggest the colonization of this Gondwanian taxa beyond the South Atlantic. The dispersion North to South of Tethyan faunas as well, is documented in the young South Atlantic (Dias-Brito, 1994, 1995). The presence of cold water faunas (see also Sheibnerová, 1978, and Koutsoukos, 1995) north of the Walvis Ridge can be explained by the effect produced by deep cold countercurrents existing in the Cretaceous paleoceanography.
Summarized References
KRöMMELBEIN, K., 1967. Ostracoden aus der marinen –Küsten Kreide” Brasiliens. 2: Sergipella transatlantica n.g., n. sp. und Arcajuia benderi n. g., n. sp. Senck. Leth., Vol. 48, No. 6, pp. 525-533, Frankfurt am Main.
MUSACCHIO, E. A. & SIMEONI, M., 1995. Ostrácodos de Argentina y el diseño de las áreas oceánicas durante el Cretácico. First Workshop of Paleoceanography with emphasis on Micropaleontology and Stratigraphy (Gramado, Rio Grande do Sul, 12-15 November 1995), Extended Abstracts, pp. 63-71, IG/CPGEO/UFRGS, Porto Alegre.
REYMENT, R. A. & TAIT, E. A., 1972. Biostratigraphical dating of the early history of the South Atlantic Ocean. Phil. Tran. Roy. Soc. London, Vol. B 164, pp. 55-95.

Données stratigraphiques nouvelles sur le Crétacé du Golfe de Guinée

Victor N'DA* & Pierre SAINT-MARC**
*Lab. d'Analyses Géologiques PETROCI, B.P. V 194, Abidjan, République de Côte d'Ivoire.
**Geo-Sciences Azur, CNRS Sophia Antipolis, rue Albert Einstein, 06560 Valbonne, France.

Le forage D1-1X, localisé au sud-ouest d'Abidjan dans la partie off-shore du bassin sédimentaire de Côte d'Ivoire, fournit des données géologiques sur le Crétacé qui présente deux grands ensembles sédimentaires.
La séquence basale, très puissante (plus de 2000 m de sédiments ont été traversés sans atteindre le socle), est clastique et constituée de grès grossiers. Les strates sommitales présentent quelques intercalations argileuses à ticinelles (Ticinella raynaudi, T. primula) et hedbergelles (Hedbergella gorbachikae, H. planispira, H. delrioensis), d'âge Albien supérieur.
La séquence supérieure (? Vraconien-Maastrichtien), gréso-argileuse à la base, argileuse au sommet, présente de nombreuses discontinuités dont certaines correspondent parfois à d'importantes lacunes de dépôt décelées par l'analyse micropaléontologique. Malgré la rareté et la conservation médiocre des foraminifères, l'étude des associations permet de distinguer 4 unités:
- le ? Vraconien-Cénomanien moyen, d'une puissance de 400 m, est essentiellement caractérisé par une association de foraminifères planctoniques (Favusella washitensis, Hedbergella delrioensis, H. libyca, H. planispira, Praeglobotruncana delrioensis, Rotalipora ssp.). De rares foraminifères benthiques (Cassidella tegulata, Lingulogavelinella modesta) confirment l'attribution de ces niveaux gréso-argileux au Cénomanien.
- le Turonien-Coniacien, d'une puissance de 80 m, est également caractérisé par des foraminifères planctoniques (Whiteinella archaeocretacea, W. paradubia, W. baltica, Heterohelicidae, Herbergella ssp.) et une association très pauvre de foraminifères benthiques (Siphogenerinoides parva, Gabonita laevis).
- l'unité sus-jacente, d'une puisance de 400 m, a été attribuée au Campanien (?). La microfaune est uniquement constituée de foraminifères benthiques, avec une prédominance de lituolidés (Pseudogaudryinella capitosa, Gerochammina lenis, Spiroplectammina dentata, Reophax duplex, Recurvoides, Bathysiphon) et de buliminidés (Praebulimina bantu, Buliminella carseyae).
- l'unité sommitale, d'une puissance de 140 m, est caractérisée par une association de foraminifères planctoniques du Maestrichtien (Globotruncana aegyptiaca, Globotruncanita stuartiformis, Hedbergella holmdelensis, H. monmouthensis, Rugoglobigerina rugosa, R. macrocephala, Pseudoguembelina ssp., Pseudotextularia elegans) et une association de foraminifères benthiques qui est dominée par les Orthokarstenia (O. clavata, O. cretacea) et les Eponides pseudoelevatus. Ces strates argileuses, après une lacune du Maestrichtien supérieur (zone à mayaroensis) et de l'extrême base du Paléocène (zone à eugubina), sont surmontées sans discontinuité apparente par les argiles du Paléocène inférieur (zone à pseudobulloides).
Ces données stratigraphiques mettent en évidence dans cette partie septentrionale de l'Atlantique Sud l'évolution complexe de la sédimentation durant le Crétacé, conséquence d'un contrôle structural actif lié à la proximité de la marge continentale transformante de Côte d'Ivoire-Ghana.

Biostratigraphy and paleoecology of the Campanian-Paleocene agglutinated foraminifera from Gabal Um El Ghanayim, Kharga Oasis, Egypt

Hussein Orabi ORABI - Gelogy Departament, Faculty of Science, Menoufia University, EGYPT.

A detailed study of the Campaniam-Paleocene agglutinated foraminifera from Gebel Um El Ghanayim, Kharga Oasis in the Western Desert of Egypt yielded 55 species beloging to 22 genera.
The paleoecological implications of the investigated species are discussed and the biostratigraphical classification of the agglutinated foraminiferal assemblages is attempted. Four biozones of agglutinated foraminifera are distinguished in the Upper Cretaceous and three in the Paleocene.
The Cretaceous-Tertiary boundary (K/T) is marked by a disconformity surface covered by a conglomerate rich in rewoked Maastrichtian macrofossils. This conglomerate bed at the K/T boundary is overlies claystone beds contain the foraminiferal genus Ammoastuta. This genus is regarded as a facies index fossil for brackish littoral environments.
The Paleocene sequence is characterized by a higher percentage of calcareous agglutinated foraminifera than in the Upper Cretaceous. It is believed that the higher content of CaCO3 in the Paleocene sequence (particularly the Upper Kharga Shale Member and Tarawan Formation) is responsible for the predominance of calcareous agglutinated foraminifera in these rock units.

Palaeoenvironment of Upper Cretaceous black claystones from ODP Leg 159 (Côte dêIvoire-Ghana transform margin)

Thomas Pletsch*, Thomas Wagner**, Wolfgang Kuhnt* & Leg 159 Scientific Party
* Geologisch/Paläontol. Institut, Univ. Kiel, Olshausenstr. 40, 24148 Kiel, Germany.
** Fachbereich 5, Geowissenschaften, Univ. Bremen, Klagenfurter Str. 5, 28359 Bremen, Germany.

To investigate the changing depositional environments along the Côte dêIvoire-Ghana Transform Margin was one of the main objectives for drilling of Leg 159 in the eastern Equatorial Atlantic. One of the drill sites (959) was located near the southern border of the Deep Ivorian Basin. The Deep Ivorian Basin is separated from the Guinea Abyssal Plain towards the southeast by a prominent ridge which forms the eastward prolongation of the Romanche Fracture Zone on continental crust (Fig.1). This –Marginal Ridge” probably acted as a morphologic barrier between the Deep Ivorian Basin and the open ocean since the opening of the Equatorial Atlantic Gateway in the late Early Cretaceous.
We studied Turonian to Eocene sediments of Hole 959D of ODP Leg 159 which comprise a prominent black claystone facies using sedimentologic, clay mineralogic, organic geochemical and micropalaeontologic techniques. Fourty metres of Turonian to Coniacian coarse-grained detrital limestones, sometimes intermixed with significant amounts of siliclastic grains, unconformably overlay diagenetically altered Lower Crtaceous sediments. Close to the Coniacian/ Santonian boundary, sedimentation became dominantly clayey. Several hardgrounds and accumulations of phosphatic debris occur at the transition to the basal claystones. The overlying black, carbonaceous claystone facies (Lithological Unit III of the Shipboard Scientific Party [1996]) extends into the Palaeocene. More than 200 metres (812.3 to 1043.3 metres below seafloor) of this facies were penetrated in Hole 959D. Carbonate carbon contents in these claystones are close to zero, whereas organic carbon reaches very high levels. The shipboard age assignments were based on calcareous nannofossils and planktic foraminifers in the carbonate-bearing sediments above and below the claystones. Because the claystones themselves are barren of calcareous planktic microfossils, a further subdivision of this interval has been based on benthic foraminifers. Studies of the clay minerals, organic and carbonate carbon content, and benthic foraminiferal assemblages reveal remarkable variation during the deposition of this apparently monotonous sequence. Some of the variations correlate with super-regional sea-level and climatic events, whereas others appear to be related to the peculiar tectonic situation along the transform margin. Our preliminary data will be compared to results from West African basins in Nigeria and Senegal.
References
Shipboard Scientific Party (1996) Site 959. In: MASCLE, J., LOHMANN, G. P. & CLIFT, P. D. (Eds), Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 159, pp. 65†150, College Station, TX, USA.

Données stratigraphiques nouvelles sur le Crétacé du Golfe de Guinée

Victor N'DA* & Pierre SAINT-MARC**
*Lab. d'Analyses Géologiques PETROCI, B.P. V 194, Abidjan, République de Côte d'Ivoire.
**Geo-Sciences Azur, CNRS Sophia Antipolis, rue Albert Einstein, 06560 Valbonne, France.

Le forage D1-1X, localisé au sud-ouest d'Abidjan dans la partie off-shore du bassin sédimentaire de Côte d'Ivoire, fournit des données géologiques sur le Crétacé qui présente deux grands ensembles sédimentaires.
La séquence basale, très puissante (plus de 2000 m de sédiments ont été traversés sans atteindre le socle), est clastique et constituée de grès grossiers. Les strates sommitales présentent quelques intercalations argileuses à ticinelles (Ticinella raynaudi, T. primula) et hedbergelles (Hedbergella gorbachikae, H. planispira, H. delrioensis), d'âge Albien supérieur.
La séquence supérieure (? Vraconien-Maastrichtien), gréso-argileuse à la base, argileuse au sommet, présente de nombreuses discontinuités dont certaines correspondent parfois à d'importantes lacunes de dépôt décelées par l'analyse micropaléontologique. Malgré la rareté et la conservation médiocre des foraminifères, l'étude des associations permet de distinguer 4 unités :
- le ? Vraconien-Cénomanien moyen, d'une puissance de 400 m, est essentiellement caractérisé par une association de foraminifères planctoniques (Favusella washitensis, Hedbergella delrioensis, H. libyca, H. planispira, Praeglobotruncana delrioensis, Rotalipora ssp.). De rares foraminifères benthiques (Cassidella tegulata, Lingulogavelinella modesta) confirment l'attribution de ces niveaux gréso-argileux au Cénomanien.
- le Turonien-Coniacien, d'une puissance de 80 m, est également caractérisé par des foraminifères planctoniques (Whiteinella archaeocretacea, W. paradubia, W. baltica, Heterohelicidae, Herbergella ssp.) et une association très pauvre de foraminifères benthiques (Siphogenerinoides parva, Gabonita laevis).
- l'unité sus-jacente, d'une puisance de 400 m, a été attribuée au Campanien (?). La microfaune est uniquement constituée de foraminifères benthiques, avec une prédominance de lituolidés (Pseudogaudryinella capitosa, Gerochammina lenis, Spiroplectammina dentata, Reophax duplex, Recurvoides, Bathysiphon) et de buliminidés (Praebulimina bantu, Buliminella carseyae).
- l'unité sommitale, d'une puissance de 140 m, est caractérisée par une association de foraminifères planctoniques du Maestrichtien (Globotruncana aegyptiaca, Globotruncanita stuartiformis, Hedbergella holmdelensis, H. monmouthensis, Rugoglobigerina rugosa, R. macrocephala, Pseudoguembelina ssp., Pseudotextularia elegans) et une association de foraminifères benthiques qui est dominée par les Orthokarstenia (O. clavata, O. cretacea) et les Eponides pseudoelevatus. Ces strates argileuses, après une lacune du Maestrichtien supérieur (zone à mayaroensis) et de l'extrême base du Paléocène (zone à eugubina), sont surmontées sans discontinuité apparente par les argiles du Paléocène inférieur (zone à pseudobulloides).
Ces données stratigraphiques mettent en évidence dans cette partie septentrionale de l'Atlantique Sud l'évolution complexe de la sédimentation durant le Crétacé, conséquence d'un contrôle structural actif lié à la proximité de la marge continentale transformante de Côte d'Ivoire-Ghana.

Biostratigraphy and paleoecology of the Campanian-Paleocene agglutinated foraminifera from Gabal Um El Ghanayim, Kharga Oasis, Egypt

Hussein Orabi ORABI - Gelogy Departament, Faculty of Science, Menoufia University, EGYPT.

A detailed study of the Campaniam-Paleocene agglutinated foraminifera from Gebel Um El Ghanayim, Kharga Oasis in the Western Desert of Egypt yielded 55 species beloging to 22 genera.
The paleoecological implications of the investigated species are discussed and the biostratigraphical classification of the agglutinated foraminiferal assemblages is attempted. Four biozones of agglutinated foraminifera are distinguished in the Upper Cretaceous and three in the Paleocene.
The Cretaceous-Tertiary boundary (K/T) is marked by a disconformity surface covered by a conglomerate rich in rewoked Maastrichtian macrofossils. This conglomerate bed at the K/T boundary is overlies claystone beds contain the foraminiferal genus Ammoastuta. This genus is regarded as a facies index fossil for brackish littoral environments.
The Paleocene sequence is characterized by a higher percentage of calcareous agglutinated foraminifera than in the Upper Cretaceous. It is believed that the higher content of CaCO3 in the Paleocene sequence (particularly the Upper Kharga Shale Member and Tarawan Formation) is responsible for the predominance of calcareous agglutinated foraminifera in these rock units.

Palaeoenvironment of Upper Cretaceous black claystones from ODP Leg 159 (Côte dêIvoire-Ghana transform margin)

Thomas Pletsch*, Thomas Wagner**, Wolfgang Kuhnt* & Leg 159 Scientific Party
* Geologisch/Paläontol. Institut, Univ. Kiel, Olshausenstr. 40, 24148 Kiel, Germany.
** Fachbereich 5, Geowissenschaften, Univ. Bremen, Klagenfurter Str. 5, 28359 Bremen, Germany.

To investigate the changing depositional environments along the Côte dêIvoire-Ghana Transform Margin was one of the main objectives for drilling of Leg 159 in the eastern Equatorial Atlantic. One of the drill sites (959) was located near the southern border of the Deep Ivorian Basin. The Deep Ivorian Basin is separated from the Guinea Abyssal Plain towards the southeast by a prominent ridge which forms the eastward prolongation of the Romanche Fracture Zone on continental crust (Fig.1). This –Marginal Ridge” probably acted as a morphologic barrier between the Deep Ivorian Basin and the open ocean since the opening of the Equatorial Atlantic Gateway in the late Early Cretaceous.
We studied Turonian to Eocene sediments of Hole 959D of ODP Leg 159 which comprise a prominent black claystone facies using sedimentologic, clay mineralogic, organic geochemical and micropalaeontologic techniques. Fourty metres of Turonian to Coniacian coarse-grained detrital limestones, sometimes intermixed with significant amounts of siliclastic grains, unconformably overlay diagenetically altered Lower Crtaceous sediments. Close to the Coniacian/ Santonian boundary, sedimentation became dominantly clayey. Several hardgrounds and accumulations of phosphatic debris occur at the transition to the basal claystones. The overlying black, carbonaceous claystone facies (Lithological Unit III of the Shipboard Scientific Party [1996]) extends into the Palaeocene. More than 200 metres (812.3 to 1043.3 metres below seafloor) of this facies were penetrated in Hole 959D. Carbonate carbon contents in these claystones are close to zero, whereas organic carbon reaches very high levels. The shipboard age assignments were based on calcareous nannofossils and planktic foraminifers in the carbonate-bearing sediments above and below the claystones. Because the claystones themselves are barren of calcareous planktic microfossils, a further subdivision of this interval has been based on benthic foraminifers. Studies of the clay minerals, organic and carbonate carbon content, and benthic foraminiferal assemblages reveal remarkable variation during the deposition of this apparently monotonous sequence. Some of the variations correlate with super-regional sea-level and climatic events, whereas others appear to be related to the peculiar tectonic situation along the transform margin. Our preliminary data will be compared to results from West African basins in Nigeria and Senegal.
References
Shipboard Scientific Party (1996) Site 959. In: MASCLE, J., LOHMANN, G. P. & CLIFT, P. D. (Eds), Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 159, pp. 65†150, College Station, TX, USA.

Depositional evolution of two estuarine successions: the upper Itapecurú Formation, São Luís Basin, northern Brazil

Dilce de Fátima Rossetti - Museu Paraense Emílio Goeldi (DEL/MPEG/CNPq), Av. Magalhães Barata, 376, 66040-170 Belém, Pará, Brazil. Fax: +55-(0)91-249-0466, E-mail:rossetti@museu. goeldi.br

This study focuses on the Itapecurú Formation, which contains the main record of Cretaceous rocks from basins of the Brazilian North Equatorial Margin. Despite the growing scientific interest in investigating Cretaceous deposits from sedimentary basins of the South Atlantic, the Itapecurú Formation has not been intensively studied, in large part because of its presumed lack of mineral resources. As a result, the available sedimentological data are still insufficient to successfully interpret its depositional systems and understand the evolution of these deposits through the geological time.
Detailed facies analysis of the early Cenomanian to early Tertiary (?) upper Itapecurú Formation exposed in the eastern margin of the São Luís Basin, northern Brazil, led to the recognition of seven depositional settings, including: mid- to upper-shoreface, foreshore, tidal channel, lagoon/washover, subtidal bay fill, tidal shoal/sand flat, and tidal delta. Stratigraphic correlation of these deposits within the study area indicates two depositional intervals, informally assigned as lower and upper successions. The lower succession is up to 35 m thick and consists of a regressive interval represented by the upward transition from more seaward (i.e., mid- to upper-shoreface and foreshore) to more landward (i.e., tidal channel and lagoon/washover) settings.
Sedimentological and paleontological evidences suggest that the succession is the subaqueous record of barrier and barrier-related environments located in the outermost (seaward) portion of a wave-dominated (lagoonal) estuary (e.g., Galloway & Hobday, 1983; Reinson, 1992; Dalrymple et al., 1994; Zaitlin et al., 1994 a,b).
The upper succession is up to 25 m thick and consists entirely of tidal-dominated deposits attributed to channel, sand shoal/sand flat, delta, and bay fill depositional settings, which are also parts of an estuarine system. Despite the apparent lithologic uniformity, the upper succession shows several, laterally continuous bounding surfaces overlain by lags of one or all of the following components: quartz, granite, mudstone, wood fragments, and ferruginous nodules. Mapping of surfaces with lags allowed the upper succession to be subdivided into five stratigraphic units, termed US1 to US5. The subsurface to outcrop tie shows that the lower and upper successions are part of incised valley fills from two distinct incised valley depositional sequences. The paleovalleys are recognized by a combination of criteria, mostly including: a) the dominant estuarine nature of the fills, which are typical of incised valleys; b) the erosive nature of the basal bounding surfaces, as suggested by the correlation of gamma-ray e-log patterns; c) the overall blocky- to bell-shaped configuration of the deposits overlying the regional basal surfaces (unconformities), which is a pattern typically found in many incised valley fills; and d) the elongate-shaped geographic distribution in the surface, which suggest deposition within a depression. Application of sequence stratigraphic concepts led to infer that the lower succession formed at a time of slow rise in relative sea level during the highstand systems tract of the oldest incised valley. The upper successsion records deposition at the transition from the transgressive to the highstand systems tract of the youngest incised valley. The units bounded by surfaces with lags in the upper succession are attributed to high frequency changes in relative sea level. The surfaces with lags would have formed during periods of high frequency floodings, and the deposition of US1-US5 units would have taken place during successive periods of stillstands that followed each flooding.
References
Dalrymple, R. W., Boyd, R. & Zaitlin, B.A., 1994. Incise-Valley Systems: Origin, and Sedimentary Sequences. S.E.P.M., Special Publication, Vol. 51, 399 pp., Tulsa Galloway, W. E. & Hobday, D. K., 1983. Terrigenous Clastic Depositional Systems- Applications to Petroleum, Coal, and Uranium Exploration. Springer-Verlag, New York, 423 pp.
Reinson, G. E., 1992. Transgressive barrier island and estuarine systems. In: Walker, R. G. & James, N. P. (Eds), Facies Models- Response to Sea Level Change, Geological Association of Canada, Ontario, Canada, pp. 179-194.
Zaitlin, B. A., Dalrymple, R. W., Boyd, R. & Leckie, D., 1994 a. The stratigraphic organization of incised valley systems: implication to hydrocarbon exploration and production- with examples from the Western Canada Sedimentary Basin. C.S.P.G., Calgary, Alberta.
Zaitlin, B. A., Dalrymple, R. W. & Boyd, R., 1994 b. The stratigraphic organization of incised valley systems associated with relative sea-level change. In: Dalrymple, R. W., R. Boyd, R. & Zaitlin, B. A. (Eds), Incised-Valley Systems: Origin and Sedimentary Sequences, S.E.P.M. Special Publ., Vol. 51, pp. 45-60, Tulsa.

Stratigraphy and geologic evolution of the continental margins of Cuba

J. R. SANCHEZ-ARANGO & R. TENREYRO - Centro de Investigaciones del Petróleo. Calle Washington No. 169, Cerro, La Habana 12000, Cuba. Fax: +5-37-666021.

The continental crust of Pangaea was rifted and the Proto-Caribbean oceanic basin developed between North and South American continents.
The northern part of Cuba includes the overthrust belt whose rocks correspond to the syn-rift and drift stages of a stable continental margins, which belongs to the known Yucatan and Bahamas margins.
Deposition of syn-rift terrigenous sediments ocurred from the Early Jurassic to Early Oxfordian and are about 3,000 m thick. Pre-marine evaporite strata were deposited in the Middle Jurassic with no less than 1,500 m thick.
The rocks of the passive margin conform the Pinar del Rio and the Las Villas paleogeographic domains divided into several tectono-stratigraphic units (TSU) or belts: Organos, La Esperanza, Rosário, Placetas, Camajuani, Coco Sur, Remedios and Coco Norte.
Carbonate sedimentation dominated in these belts since the Late Oxfordian and persisted into the Turonian.These sedimentary rocks were deposited on an extensional continental margin and were subsequently overthrusted northwards over this margin during Late Cretaceous-Early Tertiary north-south compression. Thickness in starved basin sediments ranges from 1,200-1,500 m and 4,000 m for the carbonate banks.
In north central Cuba, one or several paleo-seaways existed from the Early Albian to the Maastrichtian south of the Bahamas platform as a result of the backstepping of the Remedios plataform.
Basin-plataform transitional facies were recognized in the Colorados belt. In this unit the dolomites, muddy dolomites and limestones of Upper Jurassic to Lower Cretaceous are considered as an intermediate facies between the dense to pseudoolitic limestones of the Camajuani belt with Calpionellids and Nannoconus spp., and those with miliolids and algae of the Remedios belt. Likewise, the calcareous breccias of the Cenomanian and the calcarenites of the Upper Cretaceous, are typical deposits of a carbonate ramp (carbonate slope and turbidite deposits). The total thickness is about 3,000 m.
By the Campanian, the volcanic are and associated oceanic basement were obducted onto the continental margin. Consequently, the sedimentary cover was folded to form a thick thrust suture.
References
CUPET/CEINPET (CUBA) & ROBERTSON (UK) (Eds), 1995. Geology of the petroliferous systems of Cuba. I-II, La Habana.
ECHEVARRIA, G., HERNANDEZ, G., LOPEZ, J. O., LOPEZ, J. G., RODRIGUEZ, R., SANCHEZ, J. R., SOCORRO, R., TENREYRO, , YPARRAGUIRRE, J., 1991. Oil and gas exploration in Cuba. Jour. Petrol. Geol., Vol. 14, No. 3, pp. 259-274. ITURRALDE, M., 1994. Cuban Geology: a new plate-tectonic synthesis. Jour. Petrol. Geol., Vol. 17, No. 1, pp. 39-70.
SPT LIMITED/CUPET (Eds), 1993. The Geology and Hydrocarbon Potencial of the Republic of Cuba. SPT. Text and Enclosures, Llandudno, UK.

Marine ingression events of Jiquiá (early Aptian?) age in the Afro-American rift system from the viewpoint of tectono-eustasy

Augusto Carlos da Silva-Telles Jr. - PETROBRAS-CENPES/DIVEX/SEBIPE, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, Brazil.

A correlation of marine events recorded within the Limnocypridea? subquadrata (OS-1100) Biozone (early Aptian ?) with the sea-level curves of Haq et al. (1987) is herein proposed.
The suggested model for comparison of the records of episodic marine ingressions to the global curves of Haq et al. (1987) is based on the hypothesis of cause-and-effect between the entry of large volumes of oceanic waters into the Afro-American rift system and a rapid, intense global eustatic fall.
From early Valanginian to early Aptian there occurred an eustatic rise related to a transgression of the coastal onlap, which can be correlated with the process of lithosferic stretching which originated the Afro-American rift. This gave rise to a relative increase in continental area at the expense of the global oceanic area, thus leading to a reduction in the volume of oceanic basins and consequently to a global eustatic rise (Worsley et al., 1984, Heller & Angevine, 1985). This was immediately succeeded by a sudden, intense eustatic fall recorded as a strong global regression which exactly coincides with the boundary of second-order cycles LZB-3 and LZB-4. The proposed cause of this global regressive event is the ingression of large volumes of oceanic waters into the Afro-American rift system, resulting in the extinction of the abundant, diversified nonmarine ostracode fauna of the Hourcqia africana africana (OS-1020) Biozone (Figs 1 and 2).
The upper limit of the chronozone of the Hourcqia africana africana (C-1020) Biozone (Silva-Telles, 1996) is characterized by the graphoelectric marker LF-60 (Baumgarten, 1983). In order to best illustrate the biochronostratigraphic intervals defined by the correlation between zonal upper boundaries and graphoelectric markers, the chronozones of the biozones Salvadoriella? pusilla (C-930), Reconcavona? retrosculpturata (C-1010), Hourcqia africana africana (C-1020) and Limnocypridea? subquadrata (C-1100) are indicated (Fig. 1).
In consequence of the evolving rifting process, the whole area submitted to extension tends to subside (Pitman & Golovchenko, 1983), as a result of crustal stretching and thinning. Hence, episodic ingressions of large volumes of oceanic waters would be expected to occur during the late rifting phases, for the above explained reasons, so flooding all lacustrine basins and tectonic troughs associated with the rift system.
The marine ingressions would have occurred at the end of the rifting process which preceded the opening of the South Atlantic Ocean, when oceanic waters overflowed the Florianópolis High-São Paulo-Walvis Ridge. This was a positive structural feature south of the Santos Basin, and interposed between the ocean and the system of nonmarine rift basins (Gamboa, 1981). Such overflow would account for the drastic transference of huge water masses from oceanic basins into the Gondwana Supercontinent while the latter was still undergoing its latest rifting phases. The massive removal of oceanic waters would have caused a very rapid, intense eustatic fall which gave rise to the type 1 sequence boundary between second order supercycles LZB-3 and LZB-4.
Based on this hypothesis, a correlation is herein proposed between the top of the Hourcqia africana africana (OS-1020) Biozone, also related to the graphoelectric marker LF-60, and the upper boundary of the second-order supercycle LZB-3, dated 112 Ma according to Haq et al. (1987).
Hsü (1976) envisaged a relationship between deposition of a dark gray marl layer immediately overlying the highest evaporites in the Mediterranean Sea and the restablishment of marine conditions. According to this author, this must have occurred as a catastrophic event, when large volumes of oceanic waters started cascading over the Gibraltar Strait with an estimated flow of about 30,000 Km3/year. The Mediterranean Basin floor was as down as 3,000 m below sea-level, and it took over 100 years to become completely full.
After Hsü (1976), the total desiccation of the Mediterranean Sea would have caused a global eustatic rise of about 10 m. It can therefore be assumed that the subsequent flood of the Mediterranean Basin by oceanic waters would have originated an eustatic fall of similar extent.
This model may be applicable to the record of marine ingression events of Jiquiá age in the Campos Basin, particularly to those coeval with deposition of the Limnocypridea? subquadrata (OS-1100) Biozone. The Afro-American rift system was characterized by fluvio-lacustrine sedimentation, at a time when intense crustal stretching lowered the basin floor well below sea-level, whilst global sea-level was rising in response to the continued rifting process. As oceanic waters overflowed the structural high that no longer could hold them, they quickly flooded the rift basins and caused a major environmental impact, recorded in the Campos Basin by the extinction of the abundant, diversified nonmarine ostracode fauna of the Hourcqia africana africana (OS-1020) Biozone. This event would have represented the sudden replacement of an alkaline lacustrine athalassic paleoenvironment by a chlorinic thalassic paleoenvironment.
References
BAUMGARTEN, C. S., 1983. Evolução estrutural da Formação Lagoa Feia em Pampo-Badejo-Linguado. PETROBRAS/Depex/Dirsul, Internal Report, 10 pp.
GAMBOA, L. A. P., 1981. Marine geology of the Brazilian continental margin and adjacent oceanic basin between the latitudes of 23o and 37o S. Columbia University, Ph.D. Thesis, 200 pp.
HAQ, B. U., HARDENBOL, J. & VAIL, P. R., 1987. Chronology of fluctuating sea level since the Triassic. Science, Vol. 235, pp. 1156-1167.
HELLER, P. L. & ANGEVINE, C. L., 1985. Sea level cycles during the growth of Atlantic type oceans. Earth and Planetary Science Letters, Vol. 75, pp. 417-426.
HSÜ, K. J., 1976. ¿Se seco el Mediterraneo? In: Deriva continental y tectónica de placas, Selecciones de Scientific American, 2nd edición, pp. 219-230.
PITMAN III, W. C. & GOLOVCHENKO, X., 1983. The effect of sealevel change on shelfedge and slope of passive margins. In: STANLEY, D. J. & MOORE, G. T. (Eds), The shelf break: critical interface on continental margins. Society of Economic Paleontologists and Mineralogists, Special Publication, No. 33, pp. 41-58.
SILVA-TELLES, Jr., A. C., 1996. Estratigrafia de seqüências de alta resolução do Membro Coqueiros da Formação Lagoa Feia (Barremiano ?/Aptiano da Bacia de Campos - Brasil). Universidade Federal do Rio Grande do Sul, Dissertação de Mestrado, 2 Volumes, 268 pp., 65 figuras, 24 estampas, Porto Alegre.
SILVA-TELLES, Jr., A. C., HENZ, G. I. & ARAI, M., 1994. Evidências das primeiras ingressões marinhas na fase rift da margem leste brasileira. Boletim de Geociências da PETROBRAS, Vol. 8, No. 2/4, pp. 409-410.
VAIL, P. R., MITCHUM Jr., R. M. & THOMPSON, III, S., 1977. Seismic stratigraphy and global changes of sea level, part 4:global cycles of relative changes of sea level. In: PAYTON, C. E. (Ed.), Seismic stratigraphy - applications to hydrocarbon exploration. American Association of Petroleum Geologists, Memoir, No. 26, pp. 83-97, Tulsa. WORSLEY, T. R., NANCE, D., MOODY, J. B., 1984. Global tectonics and eustasy for the past 2 billion years. Marine Geology, Vol. 58, pp. 373-400.

Evolution of southern South American basins during the Mesozoic

Luis A. SPALLETTI & Juan R. FRANZESE
Centro de Investigaciones Geologicas, Universidad Nacional de La Plata, CONICET. Calle 1 no. 644, 1900 La Plata, República Argentina.

This study, designed to develop ten palaeogeographic maps between the Late Triassic and the Late Cretaceous in 15 to 30 Ma steps, shows the main facies associations and the paleoenvironmental evolution of the Patagonian basins (southern South America). More than 300 references relevant to the interval 210-75 Ma were selected to compile a palaeogeographic database including stratigraphic, structural, sedimentologic, geotectonic and palaeoenvironmental information.
In the Late Triassic, Patagonia was an almost positive land. Narrow and isolated continental rifts, filled with volcaniclastic sediments developed in NW Patagonia and in the Deseado Massif (south-central Patagonia). Calc-alkaline intrusions (Central Patagonian Batholith) and the Comallo volcanics are emplaced at the NW end of the Gastre Fault System.
During the Early Jurassic, shallow to deep marine deposits related to a palaeopacific transgression are recognized in the Neuquen and the Pampa de Agnia basins. Near the boundary between the early and middle Jurassic times, a dominantly acidic volcanism (Marifil Complex) covered large areas of northern Patagonia. The older evidence of an Andean magmatic arc occurs at the southern margin of the Pampa de Agnia depocenter. For the Bathonian-Callovian transition (165 Ma), most of the Patagonian region to the south of the Gastre Fault System was characterized by the (Chon Aike and Tobifera) bimodal volcanism. In central and southern Patagonia, several NW-SE and NNW-SSE trending grabens formed as a result of widespread extensional tectonism. Transcurrent displacement along the Gastre Fault System controlled the Caoadun Asfalto depocenter (north-central Patagonia), characterized by fluvial and lacustrine facies associations. In the Late Jurassic (150 Ma), significant palaeogeographic changes occurred. The Andean magmatic arc reached the 50o S.L, and the silicic Tobifera volcanism is restricted to SW Patagonia, where submarine rhyolite-flows intercalate with deep marine siliciclastics. The Rio Mayo-San Jorge and the Magallanes basins are enterely developed. The early rift continental deposits of the San Jorge Basin laterally grade into continued shallow marine sediments of the intra-backarc Rio Mayo basin. Shallow marine facies in most of the Magallanes basin indicate the onset of widespread extension, and to the west, deep marine deposits suggest an effective connection between the Magallanes basin and the Pacific Ocean.
No major palaeogeographic changes are recorded for the Valanginian-Hauterivian times (135 Ma). However, the Andean magmatic arc extends along the whole western Patagonian margin. Though the Pacific connection of the Magallanes basin still persists, the marginal Rocas Verdes basin, floored by oceanic crust, develops in a backarc position.
The Aptian (120 Ma) was a time of transition. Continental red beds are widespread in the Neuquén and San Jorge basins. The topographic barrier of the magmatic arc produced the closure of the Rio Mayo basin. To the south, several paths through the volcanic chain connect the Magallanes basin with the Pacific Ocean.
The Albian panorama (105 Ma) is characterized by a continuous positive volcanic chain (Andean Magmatic Arc), that separated Patagonia from the Pacific Ocean. Fluvial redbeds are widespread in the Neuquén Basin, and in the San Jorge basin extended fluvial systems terminate in deltaic-lacustrine depocenters. The Magallanes Basin passes by an early foreland stage, the marginal basin is closed and from the northwest corner a very active deltaic system prograded towards the south where prodeltaic and deep marine shales are associated to axial (N-S oriented) turbidite systems.
During the Cenomanian-Turonian (90 Ma), the Neuquén and the San Jorge basins are integrated in a single continental depocenter dominated by continental red beds. In northeastern Patagonia, the newly opened Colorado rift is also filled up of continental deposits. Along the western margin of southern South America, the topographic barrier of the Andean magmatic arc separates Patagonia from the Pacific Ocean. In the Magallanes basin, the foreland stage causes strong detrital contributions from the west and progressive migration of the depocenter to the east.
The Campanian-Maastrichtian palaeogeography (75 Ma) shows a widespread transgressive episode embracing the Colorado basin and the North Patagonian shallow platform. The San Jorge basin becomes again a large and isolated continental depocenter. A general regression is recorded in the Magallanes basin, caused by both renewed uplift along the Andean margin and a marked NNW to SSE fluvio-deltaic progradation.

Cretaceous continental stromatolites from the Araripe Basin, northeast Brazil

Narenda K. Srivastava - Department of Geology (UFRN), Natal, RN, Brazil.

Introduction. The Araripe Basin, with an area of about 9000 km2, and situated in the states of Ceará, Pernambuco and Piauí, appears to be an infinite source of evidence of a great variety of Cretaceous fauna and flora. The recent discoveries of dinosaur-tracks in the presumed Lower Paleozoic Cariri Formation of the basin attest to yet undiscovered Cretaceous life (Carvalho et al., 1994). During the past few years we are carrying out a detailed geological mapping and sedimental investigations of the so-called –Bacias Interiores do Nordeste Brasileiro” (Northeastern Cretaceous-Rift-Basins), which number about twenty-two in all. All these basins, of various sizes and lithologic nature, are intimately associated with the opening of the South Atlantic Ocean, hence their importante for the South Atlantic Mesozoic Correlations. To date, we were able to –rediscover” two very small (up to 100 km2) intracratonic basins in the northeastern State of Rio Grande do Norte (Rio Nazare and Pau dos Ferros basins), which proved tobe of great stratigraphical importance because of their geographical location, situated between the Araripe Basin and the oil-rich Cretaceous Potiguar Basin (states of Rio Grande do Norte and Ceará).
No stromatolities have so far been reported from other Cretaceous rift-basins of the Northeast, excepting the Araripe Basin, where Cavalcanti & Viana (1990) and Martill (1994) first mentioned their presence, however without offering detailed taxonomical or paleoenvironmental data.
Results. During field excursions, since 1990, we have been able to recognize and carry out detailed investigations on various types of stromatolites from all three lithostratigraphic units of the Santana Formation, viz. Crato, Ipubi and Romualdo Members, whereas the best outcrops were recognized in various gypsum and limestone quarries in the states of Ceará and Pernambuco: IBACIP Quarry (Barbalha/CE), Pedra Branca Quarry (Nova Olinda/CE), Conceição Preta Quarry (Santana do Cariri/CE), Limestone Quarry (Nova Olinda/CE), Gypsum Quarry (Ipubi/CE) and Gypsum Quarry (Araripina/PE).
At the localities of Calderão (12 km shoutheast of Simões-Piauí) and Sitio Lagoa Seca (about 5 km south of Simões), excellent stromatolite-bioherms outcrop in immediate contact with the Precambrian basement complex, and are, in their turn, highly fractured and faulted, indicating a post depositional Tertiary (?) reactivation of NE-SW Precambrian faults.
The stromatolites in the Araripe Basin form small tabular bioherms and domal bistromes, rarely attaining a height of more than a few meters, and are normally associated with marls, gypsum, shale and limestones. The more frequent morphological types of stromatolites are: stratified (microbial-mat), domal and branched columnar, this last type appears to be of great importance for paleoenvironmental and biostratigraphical zonations. The stromatolite mineralogy is represented by calcite, opal, gypsum and clay-minerals.
The nomenclature and the classification of Araripe Basin stromatolites are problematic, for the classical binominal nomenclature of stromatolites was established for Proterozoic ones, utilizing the concepts of morphological features and microstructures. Hence, it becomes rather difficult to assign taxonomic affinities to these well-built and conspicuous Cretaceous stromatolites, although such nomenclature could still be utilized for practical purposes employing external morphological features, nature of laminations and other statistical parameters.
Thus, in the Santana Formation of the Araripe Basin the following tentative distribution of stromatolites has been established:
Crato Member : The characteristic finely laminated lacustrine limestones contain various horizons of stratiform stromatolites, tentatively assigned to Irregularia Korolyuk and pseudo-domal stromatolites (LLH-s and -c), of typically shallow, calm and protected environments. These microbial-mats do not offer any biostratigraphical significance, for they have an ample distribution, both horizontally as well as veritically, whithout demonstrating any significant textural or statistical variation. The best outcrops are located in the Limestone Quarry in the outskirts of Nova Olinda (Ceará).
Ipubi Member : The gypsum-rich sediments of this stratgraphic unit contain essentially stratiform, domal and columnar stromatolites in micritic-limestones and marl intercaleted with gypsum and anhydrites in the limestones quarry of IBACIP (Barbalha-CE) and Gypsum-Quarry of Conceição Preta (Santana Cariri-CE), as first reported by Cavalcanti & Viana (1990). Some of the stratiform stromatolites show an external morphology similar to well-known Proterozoic Stratifera Komar. Unfortunately, it was not possible to investigate these occurrences in detail, for the extracting activities for gypsum and limestones have obliterated considerably the mentioned quarries.
Romualdo Member : This unit, composed of diverse limestones, marls and siliciclastic sediments, is famous for its proliferous and well preserved fauna and flora throughout the world. However, at the extreme western tip of the Araripe Basin, in the municipality of Simões (state of Piauí), the limestones just below the marine transgressive gasteropod rich strata contain rich and diverse forms of stromatolites, viz. stratiform, domal and columnar with active and passive ramifications. These columnar stromatolites attain a hight of up to 10 cm and a diameter of up to 3.5 cm. The Convexity-Index of internal laminae could reach up to 0.086, and the thickness of organic-rich, dark laminae varies between 0.016 and 0.02 mm, and that of clear, organic-poor-up to 0.026 mm. The crestal length varies between 2.9 and 3.5 cm. These synoptic relief of the columnar branched stromatolites is normally very low. Some of these stromatolites, in their external morphology and internal texture ressemble the Proterozoic forms Irregularia Korolyuk, Stratifera Korolyuk and Kussiella Krylov.
These similitarities, as mentioned earlier, do not necessarilly imply the taxonomical affinity, for the Proterozoic stromatolites had their formation and growth controlled by entirely different factors contrary to those existed in the Mesozoic, as is the case with the stromatolites from the Araripe Basin.
Conclusions. The diverse forms of stromatolites, so far encountered in the Santana Formation of the Araripe Basin, are interpreted to have been formed in continental (lacustrine) and mixohaline environments, as evidenced by the mineralogy and textural fabrics of the cements. It is inferred that the depositional environment was characterised by a shallow depth of the carbonate-flats in the –Araripe Lake” with low hidraulic energy. The variation in the Santana Formation was controlled by secular varioation in the microbial association and hydrodynamic conditions. Anyhow, more detailed investigations are necessary to understand the importance of these stromatolites for local and regional stratigraphic correlations.
References
CARVALHO, I. S., VIANA, M. S. S. & LIMA FILHO, M. F., 1994. Dinossauros do Siluriano: um anacronismo crono-geológico nas bacias interiores do Nordeste? - Bol. XXXVIII Congr. Brasil. Geol. (Camboriú, SC), Vol. 3, pp. 213-214.
CAVALCANTI, V. M. M. & VIANA, M. S. S., 1990. Faciologia dos sedimentos não lacustres da Formação Santana (Cretáceo Inferior) da Bacia do Araripe, Nordeste do Brasil. In: I Simpósio sobre a Bacia do Araripe e Bacias Interiores do Nordeste (Crato), Atas, pp. 193-207, DNPM.
MARTILL, D. M., 1994 The Stratigraphy, Sedimentology and Paleoenvironment of the Crato Formation (Lower Cretaceous) of the Araripe Basin, North-East Brazil. XIV Intern. Sedimentological Congr. (Recife, PE), p. G-48

Upper Cretaceous foraminiferal palaeoecology of the South area of Campos Basin, southeastrrn Brazil

Oscar STROHSCHOEN Jr.* & Eduardo A. M. KOUTSOUKOS**
* PETROBRAS-E&P-BC, Av. Elias Agostinho 665, 27913-350 Macaé, Rio de Janeiro, RJ, Brazil.
** PETROBRAS-CENPES, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, Brazil.

The present study aims to reconstruct the palaeoecology of Late Cretaceous foraminiferal assemblages recovered from 300 ditch- and core samples of 17 well sections drilled in the southern-central area of the Campos Basin, southeastern Brazil. In addition to the taxonomic assessment, the distribution of benthic foraminiferal morphogroups (Koutsoukos & Hart, 1990), relative abundance ratios of planktonic foraminifera, calcareous and agglutinated benthic specimens, and the degree of dissolution of calcareous tests, were complementary criteria taken into account for the palaeoecological study. Cluster analyses of the data allowed the characterisation of 5 main benthic foraminiferal biofacies for the Upper Cretaceous. Palaeobathymetric interpretations were based on comparison with models proposed by Sliter (1968), Nyong & Olsson (1984) and Koutsoukos & Hart (1990).
The biofacies distribution indicates the predominance of bathyal environmental conditions in the whole studied area, and a general trend of bathymetric increase from Coniacian to Maastrichtian, with a maximum in the Campanian. Slope benthic foraminiferal assemblages have in general wide ranges of bathymetric distribution, and show similar species composition within a chronostratigraphic interval. The composition and distribution of the biofacies was mainly controlled by the water-depth at the time of deposition and its relation to the lysocline and CCD, and by the concentration of dissolved oxygen in the sediment and sediment-water interface. The main biofacies characteristics are summarized on Table 1.
Biofacies 1 (Gavelinella/ Bathysiphon): dominated by the genera Gavelinella, Gyroidinoides, Dentalina, Lagena, and Lenticulina. Single-chambered, tubular, agglutinated specimens (Bathysiphon), epifaunal suspension feeders, are common. Planktonic foraminifera are composed of abundant heterohelicids, with frequent globose (Archaeoblobigerina, Globigerinelloides, Globotruncanella) and keeled (Globotruncana, Contusotruncana, Globotruncanita) morphoypes. There is a sharp increase in abundance and dominance of keeled, high trochospiral morphotypes in distal offshore sites. This evidence is of further support to a model of stratified distribution in distinctive pelagic niches for the planktonic foraminifera morphotypes (e.g., Leckie, 1987; Koutsoukos & Hart, 1990). Biofacies 2 (Bathysiphon/ Gyroidinoides): there is an abundance of suspension-feeding agglutinated specimens (Bathysiphon, Rhizammina, Hyperammina, Dendrophyra), with subordinate numbers of most infaunal deposit feeders (Gyroidinoides, Dentalina, Haplophragmoides, Ammodiscus, Glomospira, Gavelinella, Rzehakina). Test dissolution causes many changes in the abundance and occurrence of the planktonic foraminifera. Biofacies 2 grades into the Textulariina biofacies by the progressive increase of dissolution of the calcareous tests.
Biofacies 3 (Textulariina): characterised by the predominance of agglutinated specimens (Haplophragmoides, Trochammina, Glomospira, Ammoglobigerina, Ammodiscus, Rzehakina). The rare calcareous tests are partially dissolved. This biofacies is restricted to the uppermost Campanian and, probably, lowermost Maastrichtian. There occurs a progressive decrease in dissolution of the calcareous tests towards the lowermost Maastrichtian, when biofacies 3 grades into biofacies 2 (Bathysiphon/ Gyroidinoides).
Biofacies 4 (Gyroidinoides/ Gavelinella/ Dentalina): dominated by the calcareous genera Gyroidinoides, Gavelinella, Dentalina, Lagena, Quadrimorphina, Osangularia, Nodosaria, Nutallinella and Globorotalites, with subordinate numbers of agglutinated specimens (Glomospira, Recurvoides, Haplophragmoides, Bathysiphon, Rhizammina and Dendrophyra). Associated planktonic foraminifera are represented by abundant globose morphotypes (Hedbergella, Archaeoglobigerina, Whiteinella, Globigerinelloides, heterohelicids) and few keeled forms (Marginotruncana and Dicarinella).
Biofacies 5 (Praebulimina/ Gavelinella): characterised by the dominance of calcareous-hyaline, tapered rounded to flattened elongate morphotypes, infaunal deposit feeders (Praebulimina, Orthokarstenia, Neobulimina, Bandyella, Fursenkoina, Bolivina), and compressed, nearly biconvex-lenticular morphotypes, epifaunal/shallow infaunal deposit feeders (Gavelinella, Osangularia, Planulina). There also occur in subordinate numbers the genera Gyroidinoides, Gavelinella, Allomorphina, Oolina, Glomospira, Pullenia, Quadrimorphina, Lagena, Lenticulina and Dentalina. The planktonic foraminifera are dominated by globose morphotypes (Hedbergella, Globigerinelloides, Whiteinella, heterohelicids), with only rare keeled forms. The foraminiferal assemblage, with predominance of calcareous-hyaline deposit-feeding species, suggests oxygen-depleted bottom water conditions and/or large amounts of particulate, detrital organic matter in the sediments (e.g., Koutsoukos & Hart, 1990). In addition, the paucity of keeled planktonic morphotypes may be related to the conspicuous presence of an oxygen minimum layer, which would constrain the development of deep-water dwellers and favor shallower dwelling morphotypes in the well-oxygenated epipelagic layer.
References
DENNE, R. A. & SEN GUPTA, B. K., 1991. Association of bathyal foraminifera with water masses in the northwestern Gulf of Mexico. Mar. Micropaleontol., Amsterdan, Vol. 17, pp. 173-193.
KOUTSOUKOS, E. A. M. & HART, M. B., 1990. Cretaceous foraminiferal morphogroup distribution patterns, palaeocommunities and trophic structures: a case study from the Sergipe Basin, Brazil. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 81, pp. 221-246.
LECKIE, R. M., 1987. Palaeoecology of mid- Cretaceous planktonic foraminifera: a comparision of open ocean and epicontinental sea assemblages. Micropaleontol., Amsterdan, Vol. 33, pp. 164-176.
NYONG, E. E. & OLSSON, R. K., 1984. A paleoslope model of Campanian to lower Maestrichtian foraminifera in the North American Basin and adjacent continental margin. Marine Micropaleontol., Amsterdan, Vol. 8, pp. 437-477.
SLITER, W. V., 1968. Upper Cretaceous foraminifera from Southern California and Norhwestern Baja California, Mexico. The Univ. Kansas Paleontol. Contrib., Series No. 49, Protozoa, Article 7, pp. 1-141, figs.1-9, pl. 1-24, tab. 1-15.

Palynology of Pozo D-129 Formation in the San Jorge Gulf Basin, Lower Cretaceous, Patagonia, Argentina

Patricia VALLATI - Laboratório de Bioestratigrafia, Universidade Nacional de La Patagonia, Comodoro Rivadávia, Argentina.

The Pozo D-129 Formation (Lesta 1968) in the San Jorge Gulf Basin includes source-rich facies. A lacustrine environment of deposition has been proposed for these beds. Recently, probable marine fossils (dinoflagellates and foraminifera) were reported from these levels, suggesting a marine connection (Fitzgerald et al., 1990). This unit was previously known only for the basin subsurface, where it can reach a considerable thickness. In spite of intensive search, the recovery of fossils from these beds has proved to be difficult.
The uppermost part of this unit was later on recognized outcropping a few kilometres north of Sarmiento Town, in the center of Chubut Province. In these levels, at Cerro Chenque locality, an important microfossil assemblage (Zone of Flabellochara barrisi) was reported by Musacchio (Hechem et al., 1987, Musacchio 1989). Precisely, these strata have yielded the well-preserved microflora that is now reported. Among others, the following taxa are present in this assemblage: Taurocusporites segmentatus, Foraminisporis microgranulatus, Antulsporites baculatus ?, Concavisporites sinuatus, Interulobites sp., Leptolepidites sp., Cyclusphaera psilata, Cyclusphaera sp. A Volkheimer et al. (1976), Balmeiopsis limbatus, Classopollis classoides and the –monosulcate” reticulate pollen grains of primitive angiosperms. Some of the last mentioned grains show an ill-defined sulcus. They can be well compared with grains included in the Clavatipollenites-Asteropollis group (Schrank, 1983). Besides, Clavatipollenites hughesii and Retimonocolpites sp. were also recognized.
Age of the microflora and paleoecological considerations:
The primitives angiosperm pollen income allows to consider this assemblage undoubtelly younger than the late Neocomian microfloras in the Chubut Province. These microfloras, recovered from outcrops of the Albornoz Formation and Los Adobes Formation (Vallati, 1993, Musacchio et al., 1995), were included in the Cyclusphaera psilata-Classopollis assemblage (Volkheimer et al., 1976).
Dealing with Patagonian microfloras outside the Chubut Province, the association from the Baqueró Formation, in Santa Cruz Province, is well compared with the Pozo D-129 microflora. The presence of Clavatipollenites hughesii and Antulsporites baculatus suggests a late Barremian?-Aptian age for this last assemblage (Archangelsky et al., 1984).
The Neuquén Basin, which is also productive, includes marine facies with ammonites interbedded with continental beds. This fact allows a reliable calibration of the palynological assemblages. The Ranquiles Formation, in the Huitrin/Rayoso Group, includes an Aptian microflora with primitive angiosperm pollen (Vallati, 1995). Among these, the following genera are present: Clavatipollenites, Asteropollis, Retimonocolpites, Liliacidites and Afropollis. This assemblage shares many species with the Pozo D-129 microflora. Among the angiosperm pollen grains, the genera Clavatipollenites and Retimonocolpites are common in both associations. Besides, some grains probably represent specimens of Asteropollis asteroides, with the exine collapsed on one pole (Fig. 7). More samples and further studies, including SEM, would be necessary to get some conclusions in this sense.
Taking into account the Patagonian references mentioned above and the generally accepted worldwide income of agiosperm pollen grains in the Barremian, a late Barremian?-Aptian age is suggested for the Pozo D-129 palynological association. The present microflora is better compared with a similar one from the Ranquiles Formation. The Aptian age of this Neuquean microflora was previously settled by the calcareous microfossil assemblage (Musacchio & Palamarczuk, 1975) as well as by the palynological association (Vallati, 1995).
The only phytoplanktonic elements present in the Pozo D-129 microflora are Botryococcaceous colonies (Fig. 9). Dinoflagellates and acritarchs were not found in the studied samples.
Classopollis grains are clearly dominant in this association. This situation is repeatedly observed in Early Cretaceous microfloras of Southern South America and West Africa. This fact is accepted as suggestive of semi-arid conditions.
References
ARCHANGELSKY, S., BALDONI, A., GAMERRO, J. C. & SEILER, J., 1984. Palinología estratigráfica del Cretácico de Argentina austral. Distribución de especies y conclusiones. Ameghiniana, Vol. 21, No. 1, pp. 15-33.
FITZGERALD, M. G., MITCHUM, J. R., ULIANA, M. A. & BIDDLE, K. T., 1990. Evolution of the San Jorge Gulf Basin. The American Association of Petroleum Geologists, Bulletin, Vol. 74, No. 6, pp. 879-920.
HECHEM, J. J., FIGARI, E. G. & MUSACCHIO, E. A., 1987. Cuenca del Golfo de San Jorge. Hallazgo de la Formación D-129. Información estratigráfica y paleontológica. Petrotecnia, Vol. 11, pp. 13-15.
MUSACCHIO, E. A., 1989. Biostratigraphy of the non-marine Cretaceous of Argentina based on calcareous microfossils. In: WIEDMANN, J. (Ed), Cretaceous of the Western Tethys. 3rd International Cretaceous Symposium, Proceedings, pp. 811-850.
MUSACCHIO, E. A., VALLATI, P. S. & SIMEONI, M., 1995. Micropaleontologia del Neocomiano lacustre en el Centro de Chubut (Argentina). XIV Congresso Brasileiro de Paleontologia, Atas, pp. 100-101.
SCHRANK, E., 1983. Scanning electron and light microscopic investigations of Angiosperm pollem from the Lower Cretaceous of Egypt. Pollen et Spores, Vol. XXV, No. 2, pp. 213-242.
VALLATI, P. S., 1993. Palynology of the Albornoz Formation (Lower Cretaceous) in the San Jorge Gulf Basin (Patagonia, Argentine). N. Jb. Geol. Palaont. Abh, Vol. 187, No. 3, pp. 345-377
VALLATI, P. S., 1995. Una Microflora com Afropollis (Polen de Angiosperma) en el Cretácico Inferior de la Cuenca Neuquina. VI Congresso Argentino de Paleontologia y Bioestratigrafia, Actas, pp. 277-290
VOLKHEIMER, W., CACCAVARI DE FILICE, M. A. & SUPULVEDA, E., 1976. Datos palinológicos de la Formación Ortiz (Grupo La Amarga), Cretácico Inferior de la Cuenca Neuquina (República Argentina). Ameghiniana, Vol. XIV, No. 1/4, pp. 59-74.

Upper Cretaceous stratigraphy and biostratigraphy of the Eastern Bogotá plateau and Llanos foothills, colombia: nomenclature and sequence stratigraphy implications

Luis Vergara* & G. I. Rodriguez**
*Departamento de Geociencias, Universidad Nacional de Colombia, Bogotá, A.A. 5997, Colombia.
** José Maria Jaramillo M. y Cia. Ltda, A.A. 246159, Bogotá, Colombia.

The Upper Cretaceous stratigraphic record of the eastern Bogotá plateau and Llanos foothills of Colombia was studied in several outcrop sections. The standing stratigraphical nomenclature has been revised and reference sections have been proposed for a few units scanty described in the literature. The Chipaque Formation (Cenomanian-Campanian) represents shelf deposition in the Bogotá plateau that interfinger with shoreface sediments in the foothills. The Los Pinos Formation (Maastrichtian) is extended to the eastern Bogotá plateau between the Arenisca de Labor and Arenisca Tierna Formation (Maastrichtian) of the Guadalupe Group. In the Llanos foothills the equivalent unit to the Guadalupe Formation together with the El Morro Sandstone (Paleocene) have been mapped under the name of Palmichal Group (Campanian-Maastrichtian). In this work, the El Morro Sandstone has been excluded from the Palmichal Group because of its unconformable relation to the underlying rocks in some localities. Depositional environments have been identified and the array of paleoenvironmental shifts, commonly between shoreface and open shelf deposits, shows six depositional sequences of third order, most of them bounded by transgressive surfaces. Major transgressive episodes are represented by the Chipaque, Plaeners and Los Pinos Formations. Only the youngest sequence described here, of Paleocene age, represents a forced regression that caused incision of the shelf and diverse degree of loss of stratigraphic record according to the basin position. Both conventional lithostratigraphy as well as sequence stratigraphy are useful tools in correlation and in the reconstruction of the geologic history of the basin. Palynology is the only chronological tool available so far for the foothills area, but its resolution still needs to be improved to warrant correlation of oil wells and outcrops.

THEMATIC Symposium

Tectonics and Sedimentation in South American Basins

Seaward dipping reflectors and crustal transition in the Pelotas Basin

Rogério Luiz Fontana - PETROBRAS/E&P/GEREX/GEIEST

Concomitantly with the phase of crustal extension, responsible for the formation of the continental margin of SE Brazil, basalt flows extruding over the continental crust formed part of the basement on which the Pelotas basin developed. In this basin, most reflection seismic perpendicular to the coast, show a wedge of superimposed, planar or upward convex reflectors with high accoustic impedence which dip oceanwards without an apparent basal limit. These are named seaward dipping reflectors (SDR). Their lithologies, which are responsible for the appearance of a strong magnetic anomaly (G) on the southern Brazilian continental margin, were sampled by the near-shore well RSS-3, which drilled 800 m of basaltic rocks beneath 2700 m of sediments (mainly sandstones and conglomerates, with subordinate shales and limestones). The basalts show abundant vesicles filled with zeolites and calcite, and strong red coloring indicative of oxidation, suggesting that they were extruded over the continental crust subaereally or under very shallow water. This is in agreement with crustal thicknesses estimated from deep refraction profiles near the Uruguay coast, and also with stretching (b) and crustal thickness data below the basalt suite, obtained by backstripping (Ewing et al., 1963, Fontana, 1996).
The envelope of the tips of basalt wedges, mapped on most seismic profiles perpendicular to the coast, arch activities, related to SAMC and to your fields of expertise, carried out at your country as well as within the project working-groups, together with a list of recently published papers concerning with SAMC. We will have to revise these documents within the next two months in order to include them in the October Annual Report to UNESCO. Part of these reports will be published in SAMC News 6. Send your report to E. Koutsoukos, by e-mail, fax or on a diskette containing the text-file in Microsoft Word or is almost perfectly superposed on the trace of magnetic Anomaly G. A new set of seismic data was obtained recently along the margin of southern Brazil, in water depths varying from 2500 to 6000 m, by the Leplac IV (Continental Shelf Survey IV) project, a cooperative program between the Brazilian Navy and Petrobras whose purpose is to define Brazil's teritorial waters. The majority of these lines are perpendicular to the trace of the coastline and cross the limit between continental and oceanic crust in front of the Pelotas Basin.
The systematic analysis of these lines, from the shallow shelf to the beginning of the abyssal plain, together with earlier deep refraction profiles and gravimetric modelling (report on LEPLAC IV by Gomes et al., 1993, in print), helped to attempt locating the crustal contact along the SE Brazilian margin.
There is strong seismic, gravimetric and magnetometric evidence against a previous suggestion (Rabinowitz & La Brecque, 1993) according to which Anomaly G marks the crustal limit in the Pelotas Basin. A better candidate for the crustal limit is Anomaly M0 and, in the extreme south, Anomaly M3. This "jump" in magnetic anomaly might reflect the difference in age between the different crustal segments, from south to north; the youngest ages should occur in the extreme northeast of the Brazilian continental margin.
Fig. 1 shows the major tectonic features of the continental margin in front of the Pelotas Basin, as well as the location of the seismic line shown on Fig. 2. Reflection seismic lines recording two-way travel times of 18 sec were obtained in the Pelotas basin. Apart from helping in geologic interpretation for exploration, the aim of these lines was to help to understand basin tectonics. One of these lines (Fig. 2, with only 12 seconds shown) shows some of the tectonic features of the continental margin in the northern portion of the Pelotas Basin. The most conspicuous feature is a wedge of superposed reflectors, whose tip is close to the hingeline, and which, crossing the entire continental crust, thickens greatly near the Moho where it probably originated. These wedges (SDR) show recurrence in space and probably also in time, suggesting a succession of magmatic events, with the youngest wedges lying over true oceanic crust.
The presence of these basaltic rocks over the continental crust might be explained by the extrusion through feeding dikes (geofractures) of lava derived from a subcrustal, mantle source. This mechanism would have favored the piling up of successive lava flows in zones where crustal stretching was smaller; in areas of greater crustal stretching (Fig. 3) the process would be accelerated.
The basalt wedge is faulted in places, indicating that the rift continued tectonically active after the tectonic phase that produced it. In this the Pelotas Basin is different from other similar occurrences where the basaltic rocks do not appear to be associated with normal faults. Thus, unlike other extensional models, the Pelotas Basin shows the characteristics of both a volcanic margin and a typical marginal rift. A brief summary of the different models proposed for the formation of SDR in some continental mrgins can be found in Morton & Taylor (1987).
References
Ewing, M., Ludwig, W. J. & Ewing, J. I., 1963. Geophysical investigation in the submerged Argentine coastal plain. Part 1: Buenos Aires to Peninsula Valdez. Bull. Geol. Soc. America, Vol. 74, pp. 275-292.
Fontana, R. L., 1996. Geotectônica e sismoestratigrafia da Bacia de Pelotas e Plataforma de Florianópolis. Doctorate Thesis, UFRGS, Porto Alegre, 214 pp.
Gomes, P. O., Severino, M. C. G. & Gomes, B. S., 1993. Projeto LEPLAC: Interpretação integrada dos dados geofísicos do prospecto LEPLAC-IV Margem continental Sul-Brasileira. 3rd Internat. Cong. Bras. Geophys. Soc., Rio de Janeiro, RJ, Exp. Abstr. Vol. 2, pp. 1275-1280.
Morton, A. C. & Taylor, P. N., 1987. Lead isotope evidence for the structure of the Rockall dipping-reflector passive margin. Nature, Vol. 326, pp. 281-283.
Rabinowitz, P. D. & La Brecque, J., 1979. The Mesozoic South Atlantic Ocean and evolution of its continental margins. J. Geophys. Res., Vol. 84, No. B11, pp. 5973-6002.

Structural analysis of post-Jurassic events in the Paraná Basin

João B. L. Françolin*; Osmar Zanotto**; Peter Szatmari*
*Petrobras/Cenpes/Divex - Rio de Janeiro, RJ, **Petrobras/Nexpar - Curitiba, PR, Brazil.

The Paraná Basin formed during the Ordovician (about 450 Ma). Since that time there have been 5 pulses of subsidence, each of which generated a distinct depositional sequence: 1. Siluro-Ordovician sequence; 2. Devonian sequence; 3. Permo-Carboniferous sequence; 4. Triassic sequence; and 5. Juro-Cretaceous sequence.
The purpose of this work is to discuss the geologic significance of the structural features in the basalt lava flows which reflect syn- and post-basalt events taking place after late Jurassic times. The area studied is about 150 km by 145 km in size and is near the town of Guarapuava in the state of Paraná. The data presented here have been collected in the field or interpreted on Landsat TM images. During field work 178 outcrops were described. The Landsat TM images were acquired in digital form and processed by computer.
The geologic map was prepared in 4 stages which are briefly summarized below. 1. Interpretation of color composition (RGB) on bands 5, 4, and 2 of Landsat TM satellite images, where vegetation appears in different shades of green, drainage in shades of blue, and bare soil or scant vegetation in shades of red. They show the major elements of regional geology, including lithologic variations and linear features (faults, fractures and dikes). This image served as a basis for all subsequent interpretation.
2. Interpretation of regional morphologic features through the analysis of a color composite (IHS) in which intensity (I) was obtained from the RGB image and the other two channels (H and S) were calculated from a digital elevation model (DEM). The colors represent varying altitudes which are closely related to the geology because the region is covered by lavas and sediments forming subhorizontal tabular layers which differ in their resistance to erosion.
3. Interpretation of the stereoscopic image of the area which integrates spectral and toppographic informations. This is a colored image (RGB) obtained by the combination of two images in shades of grey: one is a Landsat TM image and the other is the same image deformed by parallaxis in function of the altimetric data of the DEM. These two images were combined to be viewed through two-color glasses, with different, complementary colors in front of each eye, so that stereoscopic vision is obtained by each eye perceiving only one of the two superposed images. On this combined image both geologic and topographic features can be observed, greatly facilitating the mapping of different lithologies and structural features.
4. Preparation of a regional geologic map obtained by the interpretation of the stereoscopic image and field data. This map synthetizes all geologic and geographic information for the region.
The geologic map thus prepared distinctly shows the major, regional features. Outcrops of the terrigenous sediments of the Teresina and Rio do Rasto Fms. are in the eastern part of the mapped area. The Teresina Fm. is restricted to the low regions and has a dendritic texture on the images owing to the erosion of clayey terraines. The Rio do Rasto Fm. outcrops in regions of somewhat sharper and topographically higher relief, showing a not very dense dendritic texture. The Botucatu Fm. outcrops on the slopes of basalt scarps and erosion-resistant hills. A major part of the mapped area is dominated by the Serra Geral Fm., which consists of basalts and sustains the highest topography in the area (1300 m). The sandstones of the Caiuá Fm. lie over the Serra Geral basalts, dominating the NW portion of the map. The NE portion of the map is dominated by the diabase dikes of the Ponta Grossa Arch, which generally trend 315-135. The most conspicuous structural features are fault zones tens of kilometers long which trend 290/110. Some of these faults, like the Rio Piquiri lineament, had been mapped before, others, like the Santa Maria, Pitanga, Manoel Ribas and Ivaporã faults, were described in our work for the first time. Other NW/SE faults are only a few kilometers long and trend 330/150. There are also long faults trending close to E/W, as the Trevo, Roncador and Rosário do Ivaí faults. All other faults, although great in number, are short and trend NE/SW.
Field observations permitted verification and kinematic analysis of the above features. Folds varying in amplitude and faults varying in throw were seen in outcropping sedimentary rocks. Major deformation zones were seen in the outcropping basalt, represented by individual faults.
Of all the faults analyzed, 398 planes were selected whose shear criteria based on striation were determined in the field. Of these, 17 faults are predominantly normal, 149 dextral, 162 sinistral, and 70 reverse faults. These data were processed by the ESTRIA program and divided into two groups, compatible with two different stress regimes. The first group is made up of 1623 faults, the second group of 236 faults.
Dynamic analysis by Right Dihedra of the ESTRIAS program showed that the data of the first group are compatible with horizontal compression along an axis of 320/140 and subhorizontal extension along an axis of 050/230. The same analysis applied to the data of the second group showed horizontal compression along 58/238 and similarly horizontal extension along 28/148. The dynamic analysis of striated faults measured in outcrops shows that two stress regimes, nearly perpendicular to each other, were active in the basin. Field observations show that the great majority of the data of the "first group" were collected either in outcropping sediments, in which they represent the most conspicuous faults, or in fresh basalts. The data of the "second group" were measured primarily on minor faults in sediments and weathered basalts. This suggests two conclusions: 1. that stress intensities in the "first group" were higher than in "second group" (which deformed only weaker rocks); 2. that stresses in the "first group" preceded those of the second group because affected the fresh basalts but not the weathered basalts.
The data of the "first group" indicate compression parallel and extension perpendicular to the axis of the Ponta Grossa Arch. Such stress regime is compatible with the emplacement of the dikes and therefore this event can be dated as Early Cretaceous, concomitant with the formation of the dikes. The stress regime defined by the "second group" is nearly orthogonal to the first and weaker, being probably related to a tectonic event in late Cretaceous, Tertiary or more recent times.

Subaquatic modelling - an advance in experimental tectonics

Marta C. M. Guerra*, Peter Szatmari*, Mônica A. Pequeno**
*PETROBRAS/CENPPES/DIVEX/SEMBA, **Fundação Gorceix, Rio de Janeiro, RJ, Brazil.

Introduction. Experiments in physical modelling in the Geotectonic Laboratory of the Petrobras Research Center (CENPES), as in most such laboratories, are performed subaereally. In early experiments, at the beginning of this century, salt tectonics was modelled by using two immiscible fluids of different density to simulate both the salt and the sedimentary cover. The denser fluid was placed on top, creating gravitational instability that causied the less dense lower fluid to rise forming diapirs (Odé, 1968, Ramberg, 1981). More recently, physically more correct representation of the sedimentary sequence of evaporite basins was achieved by using a ductile layer, such as silicone, to model the salt, and a brittle layer, made of a granular material such as dry sand, to model the overlying brittle sediments. Unlike the liquids, the use of the brittle layer permitted faults to form, but it also imposed restrictions on the rise of diapirs from the ductile layer, favoring the formation of pillows and walls. An alternative to these models would be physical modelling under water, as suggested by Peter R. Cobbold on his visit to the laboratory as consultant in June 1993. The water covering the sand layer replaces the air in its pores, thereby increasing the density contrast beween the sand layer and the underlying silicone. At the same time, cohesion between the sand grains and hence the strength of the sand layer also decreases. The greater buoyancy of the silicone, coupled with the diminished strength of the overlying sediment layer, create good conditions for the rise of diapirs. The encouraging results of the first experiments in 1993 have led to further research along these lines, aiming at an improved modelling of salt tectonics on Brazil's eastern margin.
Experimental procedures and results. Modelling is done in acrylic boxes, with silicone representing the salt layer and sand the clastic sedimentary cover. In contrast to the usual experimental procedure, however, here the two layers are covered by water. Sand is thicker in the proximal and thinner in the distal portion of the box, simulating continental shelf, slope and deep water. Silicone flows horizontally under the differential load, causing extension in the proximal and compression in the distal region. As modelling continues, silicone rises behind listric faults and reaches the surface in a great number of compressional structures, forming the equivalent of salt canopies on the surface. Such salt canopies are formed in nature by the coalescence of the top bulbs of individual diapirs or salt lenses (Jackson et al., 1987; Jackson & Talbot, 1989). As a result of canopy formation, a second, almost continuous salt layer develops and can be observed both on the surface and in vertical sections of the model. These sections show the formation of diapirs in the most varied forms and sizes (triangular structures, some with a drop on their peak, mushrooms, detached lenses, and lenses still connected to the feeding channel). Rollovers and growth in thickness are common near the diapiric structures. The layers become arched, forming turtleback structures; folds are created by silicone flow. Locally, isolated sand pockets can be observed below silicone canopies and between their feeding stems.
Discussion. Salt structures observed in the vertical sections of the subaquatic models are more similar to those seen on seismic lines than are structures obtained by subaereal experiments. The highly varied shapes of silicone lenses and diapirs resemble salt structures on seismic lines, e.g., in the Espirito Santo Basin (Guerra et al., 1992, Guerra & Szatmari, 1994). In these experiments, the silicone shows strong tendency to diapirization and extrusion, forming a secondary layer detached from the mother bed. The sand pockets isolated by the feeding ducts of this secondary layer suggest that some of the structures interpreted in seismic profiles as continuous salt walls may in fact be salt canopies which overprinted the seismic signature of sedimentary sequences with petroleum potential.
Conclusions. The Tectonics Laboratory at CENPES is developing an innovating model of subaquatic modelling whose first results are promising. For the first time, it was possible to obtain diapiric structures similar to those observed in seismic profiles. It is still necessary to study the physical behaviour of analog materials when used under water. Nevertheless, the fact that preliminary results are closer to reality than those obtained by conventional, subaereal modelling is a strong indication that physical modelling in subaquatic environment might lead to a major advance in experimental tectonics.
References
Guerra, M. C. M., Szatmari, P. & Conceição, J. C. J., 1992. Fluxo de sal na Bacia do Espirito Santo e seu relacionamento ao vulcanismo dos Abrolhos. Petrobras Internal Report, 26 pp.
Guerra, M. C. M. & Szatmari, P., 1994. O Banco dos Abrolhos como agente modificador do fluxo de sal na Bacia do Espirito Santo (ext. abstr.). XXXVIII Congr. Bras. Geol., Camburiu, Proceedings, Vol. 1, pp. 559-560.
Jackson, M. P. A., Cornelius, R. R., Craig, C. H., Talbot, C. J., 1987. The Great Kevir salt canopy: a major new class of salt structue. Geol. Soc. America, Abstracts with Programsn, Vol. 19, pp. 714.
Jackson, M. P. A. & Talbot, C. J., 1989. Salt canopies. GCS-SEPM Foundation10th Ann. Res. Conf., Program and Abstacts, 1989, pp. 72-78.
Odé, H., 1968. Review of mechanical properties of salt relating to salt dome genesis. AAPG Mem. 8, Diapirism and diapirs, pp. 53-78.
Ramberg, H., 1981. Gravity, deformation and the earth's crust. Academic Press, London, 452 pp.

Crustal structure, tectonics and sedimentation in the Sergipe-Alagoas Basin

Webster Ueipass MOHRIAK, Marcelo BASSETTO & Ines Santos VIEIRA
PETROBRAS-E&P/GEREX/GEINOF, Rio de Janeiro, RJ, Brazil

The increasing use of new technologies, especially deep resolution seismics, integrated with other geophysical and geophysical methods, optimizes the interpretation of the tectonic framework and aids in the evaluation of the exploratory potential of deep-water regions in continental margin basins (e.g., Pinet & Bois, 1990). This method of multi-disciplinary integration deepens the understanding of crustal architecture and leads to better definition of rift phase depocenters on a mega-regional scale, beyond clarifying some of the processes active in the tectonic-sedimentary evolution during and after the formation of early oceanic crust (Mohriak et al., 1995b).
Seismic reflection, gravimetric and magnetometric data were also integrated with results obtained from some wells drilled on the continental shelf and in the deep-water region of the Sergipe-Alagoas and Jacuípe basins. This work describes some of the results of the consequent reavaliation of the tectonic-sedimentary evolution of the Sergipe-Alagoas Basin.
Among the major results of the re-interpretation was the preparation of integrated maps of the tectonic framework of the Sergipe-Alagoas and Jacuípe basins, from the coastline to the transition to oceanic crust. Our data show that major extension occcurred along crustal faults that penetrate to reflectors close to the upper mantle (Mohriak et al., 1995a), controlling and rotating the major blocks of sediments deposited during the rifting phase of Gondwana. This contrasts with previous interpretations according to which the rift sequence thickens towards the deep-water region (Pontes et al., 1991).

Figure 1 shows the major anomalies of the total magnetic field, integrated with the simplified map of the tectonic framework, and the location of a deep seismic line that crosses the Mosqueiro Low and extends towards the deep-water region. Figure 2 is the schematic interpretation of this line, showing the following features which are crucial to the analysis of the basin:
1. the presence of major blocks of pre-rift and rift sediments tilted by basement-involved synthetic faults which, in the deep-water region, offset a reflector near the Moho;
2. the erosion of rift blocks during post-Aptian uplift;
3. the characterization of salt tectonics in deep waters (Mohriak, 1995);
4. significant thickening of the sequence of thermal subsidence on the continental shelf and in deep waters, contrasting with the reduced thickness of the thermal phase in the rift-phase depocenters in Alagoas;
5. association of a major arc-shaped magnetic anomaly with the beginning of transition from continental to oceanic crust;
6. identification of stratigraphic and structural features that permit interpretation of thick wedges of seaward-dipping reflectors as volcanic rocks (Hinz, 1981, Mutter et al., 1982); and
7. the presence of igneous rocks forming volcanoes along oceanic fracture zones.
References
HINZ, K., 1981. A hypothesis on terrestrial catastrophies: wedges of very thick oceanward dipping layers beneath passive continental margins. Geol. Jb. E-22, pp. 3-28.
Mohriak, W.U., 1995. Elusive salt tectonics in the deep-water region of the Sergipe-Alagoas basin: evidence from deep seismic reflection profiles. 4th Internat. Congr. Bras. Geophys. Soc., Rio de Janeiro, RJ, Ext. Abstr., Vol. 1, p. 51-54.
Mohriak, W. U., Rabelo, J. H. L., Matos, R. D. & Barros, M. C., 1995a. Deep seismic reflection profiling of sedimentary basins offshore Brazil: geological objectives and preliminary results in the Sergipe Basin. J. Geodyn., Vol. 20, pp. 515-539.
Mohriak, W. U., Bassetto, M. & Vieira, I. S., 1995b. Deep seismic constraints on the crustal architecture of sedimentary basins in the Brazilian margin: tectonic and exploratory interpretations. 5th Simpósio Nac. Est. Tectônicos (SNET 95), Gramado, Brazil, Boletim de Resumos Expandidos, pp. 246-248.
Mutter, J. C., Talwani, M. & Stoffa, P. L., 1982. Origin of seaward-dipping reflectors in oceanic crust off the Norwegian margin by "subaerial seafloor spreading". Geology, Vol. 10, pp. 353-357.
Pinet, B. & Bois, C., 1990. The potential of deep seismic profiling for hydrocarbon exploration. IFP, E&P Research Conf., Editions Technip.
Pontes, C. E. S., Castro, F. C. C., Rodrigues, J. J. G., Alves, R. R. P., Castellani, R. T., Santos, S. F. & Monis, M. B., 1991. Reconhecimento tectônico e estratigráfico da Bacia de Sergipe-Alagoas em águas profundas. In: II Cong. Bras. Geofísica, Salvador, Bahia (Soc. Bras. Geofísica), Bol. Resumos Expandidos, Vol. II, pp. 638-643.

Tectonics of the Bauru Basin in the State of São Paulo

Caudio RICCOMINI - Institute of Geosciences, USP / Research scholar of the Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq, Brazil.

Introduction. The Bauru Basin, as defined by Coimbra & Fernandes (1994), is a tectonic entity distinct from the Paraná Basin. It formed between Santonian and Maastrichtian times in the center-south portion of the South American Platform. With an extension of about 370,000 sq. km, of which about 100,000 sq. km are in the State of São Paulo, and with a preserved thickness of about 300 m, this basin contains the sedimentary sequence overlying the Cretaceous ignous suite of the Serra Geral Fm. The Bauru Basin comprises a single sedimentary sequence (with subordinated volcanic rocks), made up mostly of sandy continental deposits divided into two chrono-correlated groups, the Caiuá and the Bauru Groups. Through the analysis of structural, stratigraphic and geophysical data a preliminary model has been established for the tectonic regimes that formed and deformed the Bauru Basin in the State of São Paulo.
Basin forming tectonics of the Bauru Basin. The depocenter of the Bauru Basin was in the area of Pontal do Paranapanema (SP) and NW Paraná State, where the maximum thickness of the volcanic pile of the Serra Geral Fm. (Zalán et al., 1991), maximum crustal thinning related to that volcanic event (Quintas, 1995), and minimum preserved thicknesses of the sediments (Fernandes, 1992) show a good correlation between the highest values of these three paramenters and a clear NE-trending elongation of the sedimentary basin. The large area of the basin, its endorheic character, the continuity of sedimentation (forming a single sequence) and its relationship to the distribution of basalt lava flows indicate that the basin formed by slow and gradual subsidence in response to the cooling of its substrate (Coimbra & Fernandes, 1994).
Synsedimentary tectonic pulses are attested by the presence of seismites in the eolic deposits of the Caiuá Group, in the area of Pontal do Paranapanema, SP (Coimbra et al., 1992). Additional evidence is provided by occurrences of sandstones silicified by hydrothermal processes penecontemporaneous with sedimentation, aligned along a NE trend both in this region and in the NW portion of the State of Paraná (Fernandes et al., 1993). Both the seismites and the silicified sandstone occurrences appear to be clearly related to reactivations along preexisting structural discontinuities.
Deforming tectonics of the Bauru Basin. The first signs of the closure (inversion) of the Bauru Basin would be provided by the increased arrival of course sediments (Marília Fm.) and extrusive alkaline volcanic activity in Maastrichtian times, both related to the tectonic activity along the present eastern border of the basin. The style of deforming tectonics is brittle, forming faults and joints of diverse orientation. Magalhães et al. (1992) analysed the joints and faults present in the sandstones of the Rio Paraná Fm. (Caiuá Gp) in the rocky foundations of the Porto Primavera dam, and related them to a single post-Late Cretaceous tectonic event with a stress regime where s1 trends nearly E-W, horizontally, s2 is nearly vertical and s3 trends nearly N-S, horizontally.
In the area limited by the towns of São Manuel, Cafelãndia and Echaporã, strike slip faults and families of orthogonal, hybrid and extensional conjugate joints, which cut through the deposits of the Marília and Adamantina Fms. of the the Bauru Group, show superposition in time. The initial stress regime was characterized by the axis of maximum principal stress, s1, trending E-W, horizontally, the axis of minimum principal stress, s3, trending N-S, horizontally, and the intermediate stress axis, s2, being vertical. The younger stress regime is characterized by s1 trending N-S, horizontally, s3 trending E-W, horizontally, and s2 being vertical. Field observations and the analysis of structures show that faults formed by localized reactivation of preexistent joints. On the other hand, the orientation of stress axes obtained for the younger fault population is compatible with the strike slip and normal faults that cut through the Quaternary deposits of fluvial terraces, stone-lines and colluvia formed over the sedimentary rocks of the Bauru Broup, indicating that they are related to the neotetonic activity in the region (Riccomini, 1995).
The pattern of the basin's eastern border, the distribution of the Itaqueri Fm. (Paleogene), and reentrances in the present area of occurrence of the Serra Geral igneous rocks suggest fault movements with dextral and sinistral components, respectively along WNW and NNW trending alignments. These may be related to synthetic (R) and antithetic (R') Riedel structures in a strike slip model with a right lateral binary oriented approximatedly E-W. Although there are direct evidences for these dislocations, there are also equally direct indications of movements in the opposite direction, suggesting reactivation processes. The occurrences of alkaline igneous rocks of Early Cretaceous (Ipanema) and Late Cretaceous (Taiúva, Jaboticabal) age are additional elements in favor of the existence of recurrent tectonic activity along these alignments.
Such megastructure formation, younger than the Serra Geral igneous event, can also be observed on a mesoscopic scale (faults and joints studied in outcrops) both in geometric (spatial pattern) and in kinematic terms.
Acknowledgments. The Fundação de Amparao à Pesquisa do Estado de São Paulo (FAPESP) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) provided financial support for the research that resulted in this work.
References
Coimbra, A. M. & Fernandes, L. A., 1994. A paleogeografia da Bacia Bauru (Cretáceo Superior, Brasil). In: Congresso Argentino de Paleontologia y Bioestratigrafia, Vol. 6, Trelew, 1994. Actas., Museo Paleontológico Egidio Feruglio. (in print).
Coimbra, A. M., Fernandes, L. A., Hachiro, J., 1992. Sismitos do Grupo Caiuá (Bacia Bauru, Ks) no Pontal do Paranapanema (SP) (ext. abstr.). In: XXXVII Cong. Bras. Geol., São Paulo, Boletim de Resumos Expandidos, SBG, Vol. 2, pp. 503-504.
Fernandes, L. A., 1992. A cobertura cretácica suprabasáltica no Paraná e Pontal do Paranapanema (SP): os grupos Bauru e Caiuá. São Paulo, 129 pp., M.S. Dissertation in the Institute of Geosciences, University of São Paulo.
Fernandes, L.A. & Coimbra, A.M., Brandt Neto, M., 1993. Siclicificação hidrotermal neocretácea na porção meridional da Bacia Bauru. Rev. IG, Vol. 14, pp. 19-26.
Magalhães, FF.S., Marques, J.D., Serra Jr, E., 1992. Análise estrutural do maciço rochoso de fundação da Barragem de Porto Primavera, Rio Paraná (SP/MS). In: Hasui, Y. & Mioto, J. A. (Coords), Geologia Estrutural Aplicada, São Paulo, ABGE/VOTORANTIM, pp. 297-311.
Quintas, M. C. L., 1995. O embasamento da Bacia do Paraná: reconstrução geofísica de seu arcabouço. São Paulo, 100 pp., Doctorate Thesis, Instituto Astronômico e Geofísico da USP.
Riccomini, C., 1995. Tectonismo gerador e deformador dos depósitos sedimentares pós-gondvânicos da porção centro-oriental do Estado de São Paulo e áreas vizinhas. São Paulo, 100 pp., Tese de Livre-Docência, Instituto de Geociências da USP.
Zalán, P. V., Wolf, S., Conceição, J. C., Astolfi, A. M., Vieira, I. S., Appi, V. T., Zanotto, O. A., Marques, A., 1991. Tectonics and sedimentation of the Paraná Basin. In: Ulbrich, H. H. G. J. & Rocha-Campos, A. C. (Ed.), Gondwana Seven. São Paulo, Instituto de Geociências da Universidade de São Paulo, pp. 83-117.

The Pitanga-Quatingua-Jacutinga structural high in the Paraná Basin: a lithospheric structure

Paulo César Soares, Sidnei Pires Rostirolla, Francisco José Fonseca Ferreira & Rodoilton Stevanato - Dept of Geology, UFPR, P. O. Box 19011, Curitiba, PR, Brazil.

Introduction. Major structural lineaments have been known for some time in the Paraná Basin (Soares, 1991). They are fault zones defined on satellite images, by morphological features, by surface and subsurface geology, or by aeromagnetic methods. They occur in zones of high intensity of fracturing, in the following directions, Pitanga N55+ 5E; Paraná N30+ 10E; Ivaí N45+ 5W; Middle Piquiri N60+ 10W; Goioxim N15+ 5W; Tapirapui NS+ 5 and Paranápanema EW+ 10. The Ivaí and Middle Piquiri trends are recognized by topographic features and magnetic anomalies, due to the presence of diabase dike swarms 130 Myr old. The Pitanga and Paraná trends are represented by features assotiated with fracture zones and small discontinuous faults rarely containing dikes. They are also expressed by a change in the behavior of the magnetic field. The ENE trends marked as PT-1, PT-2, PT-3 and PT-4, show a long history of tectonic activity; the depth of the Curie surface shows the rise of the isotherms under these structures.
PT-3 - Pitanga-Quatiguá-Jacutinga Structural High. The PT-3 trend is the best defined among all the NE trending structures (Fig. 01). It is formed by a belt of fractures about 15 km wide which extends from the region of Missiones, in Argentina, to the cristaline basement in Minas Gerais continuing as the Ouro Fino-Jacutinga Fault Zone. The PT-3 trend is consistently assotiated with petroleum shows and ocurrences (Chapéu do Sol, Cândido de Abreu, Quatiguá, Anhembi, Pitanga), including sub-commercial gas production in Cândido de Abreu and oil production in Sao Pedro. The majority of these wells were located over structures mapped on the surface, or by morphostructural analysis showing an alignement of domic structures.
The structural contour map of the top of the Irati Formation between the Cândido de Abreu and Fartura dike swarms over the PT-3 trend shows the present geometry of the structure, an narrow elongated and asymmetric high trending N55E, cut by NW trending structures. The Cândido de Abreu structure is a good example of a feature assotiated with this discontinuity, the major directions being N45W and N50E. The NW trending faults are concentrated between the faults and dikes of Cândido de Abreu and the Serra da Mesa, with the structural high forming a horst. The NE trend is dominated by the Pitanga trend with post-volcanic activity and assotiated highs and lows.
The Quatiguár High is also a local structure formed by the modification of the PT-3 high by NW trending structures. N50E trending faults with kinematics indicators of horizontal and oblique fault movement are present, locally assotiated with diabase dikes as in the Joaquim Tavora fault. In this fault kinematic indicators show pre-dike clockwise compression and sin-dike as well as post-dike anticlockwise extension. In the Quatiguár High early Cretaceous igneous activity, forming sills, laccoliths and dikes, produced faults with complex kinematics, with vertical fault movements overprinting wrenching.
Although at the present time the PT-3 forms a structural high, reconstituion of events shows that the southeastern block formed a low at the end of the Silurian and of the Devonian, a high at the beginning of sedimentation in the late Carboniferous and again a low in the Permian. During Triassic time the structure seams to have controlled eolic and alluvial deposition to the NW of the axis of the structure. During the early Cretaceous igneous activity, the axis of the structure was the site of major intrusions forming sills. In the Cretaceous sedimentary cicle the structure controlled sedimentation of the Bauru Group only in the northwestern block. The uplift of the southeastern block continues during the Cenozoic times, reaching relative high rates. This long history of the PT-3 reflects its character as a lithospheric discontinuity which forms a preferential zone of deformation in which attenuation processes transform horizontal in-plane stresses within the lithospheric plate into thermal energy during the ductile deformation within the crust and the upper mantle, raising locally the isotherms and promoting the propagation of cristal defects and increased percolation by diffusion of ions and fluids as well as hydraulic fracturing which result in deformation of convection cells at shallower levels. The convection accelerates the rise of the isotherms reducing the fracture strength and resistance to the mechanical block movements so that these discontinuities become permanentely fragile.
In the area between the Sao Jerônimo-Curiuva and Guapiara lineaments, the estimated depth of the Curie surface (Ferreira et al., 1996) clearly shows three linear structures trending N55E. Along these structures the depth of the 580 C isotherm, corresponding to the demagnetization of magnetite, is reduced by about 40 %. These hot linear zones must have been produced by the convertion of the mechanical energy and by deformation of channels for heat propagation (Fig. 02).
Implications: The high geothermal gradient in the crystalline basement of these structures may result in the transport of energy to the sedimentary cover, and create sites for the convection of hot fluids, with the formation of metallic mineral deposits. This might explain the high concentrations of Zn, Pb, Mo, V, and occasionally U in the soils and even mineralizations of these elements in the rock along the PT-3 axis between Ortigueira and Sarutaiá. The preferential sites of coal deposition would also be favored both by differential subsidence in a region tectonically active during sedimentation, and by the accelerated thermal evolution of organic matter which diminishes loss by decomposition.
The preferential occurrence of petroleum along the PPT-3 belt may also be associated with the termal structure, aiding localized maturation and organic matter preservation as well as concentrated flow of water which favors petroleum migration and accumulation.
Acknowledgments. The authors thank professors M.L.B. Blum and A.C.B. Pires of IG/UNB for pprocessing the Curie surface. Reseach supported by FINEP/PADCT (CT 65910303).
References
Soares, P. C., 1991. Tectônica sin-sedimentar cíclica na Bacia do Paraná. Tese de Titular, UFPR/Curitiba/PR. 148 pp.
Ferreira, F. J. F., Blum, M. L. B., Forlin, M., Soares, P. C. & Rostirolla, S. P., 1996. Superfície Curie da região de Fartura (at this Congress).

Tectonic control of the evolution of Brazil's equatorial margin

P. SZATMARI & J. B. L. FRANÇOLIN - Petrobras/Cenpes, Rio de Janeiro, RJ, Brazil.

The eastern, South Atlantic margin of Brazil trends N30E, nearly orthogonal to the present drift of the continent. The northern, Equatorial margin of Brazil, on the other hand, trends N70W, forming only a narrow angle with the present westerly drift of the continent. As a result, the larger component of the drift is parallel to the margin. The question is whether the continent has moved westward relative to Africa already from the start of rifting, so that the rift along the Equatorial margin formed as a set of rhomb grabens bordered by E-W trending strike slip faults, or the westward motion started only after rifting had been completed.
Part of the information to this question is provided by the stratigraphic record. Along the eastern, South Atlantic margin, in the Santos and Campos basins, continuous syntectonic sedimentation following closely upon an early syn-rift volcanic event witnesses to the continuity of extension. In the Camamu, Recôncavo, Tucano and Sergipe-Alagoas basins, where early syn-rift volcanics are absent on land, nearly continuous syntectonic sedimentation also indicates continuous extension. Farther to the north, however, as we approach the Equatorial margin, the situation changes. Pre-Albian sediments are unknown in the northernmost segment of the South Atlantic margin, between Natal and João Pessoa. This indicates that there was a relative clockwise rotation between South America and Africa since the start of rifting, with the rift propagating to the north (Szatmari et al., 1987).
Recent paleomagnetic studies on the Ponta Grossa dike system by Raposo & Ernesto (1995) are in agreement with clockwise rotation of South America relative to Africa during rifting. They found that in the 10 Myr time interval that separates the age of the surface flood basalts in the Paraná Basin from the age of the dikes, the continent rotated clockwise by 6.9 degrees. The clockwise rotation of South America pulled away the southern end of Brazil's South Atlantic margin from Africa but pressed the northern end of the same margin against Africa. Thus the northeastern tip of Brazil moved southward, away from Africa in the north, but pressed against Africa in the east. This created a special stress regime in NE Brazil, characterized by nearly N-S extension and nearly E-W compression. An alternative interpretation has been offered by Matos (1992).
The small Neocomian basins in NE Brazil, surrounded by outcropping Precambrian, provide excellent opportunities to verify this stress regime. Françolin & Szatmari (1987), Françolin (1992), and Françolin et al. (1994) chose the inland Rio do Peixe basin for such study. A systematic analysis of 138 striated faults in this basin revealed strong stress anisotropy. The horizontal axes of compression, ENE-WSW, and extension, NNW-SSE, were in good agreement with the interpretation by Françolin & Szatmari (1987) according to which crustal blocks were thrust against Africa to the east while being pulled away southwards from Africa's Equatorial margin.
Continental rotation and rift propagation, marked along the South Atlantic margin by decrease in the rate and delay in the start of rifting from Campos to João Pessoa, necessarily produced a similar decrease in the rate and delay in the start of rifting along the Equatorial margin.
Along the Equatorial margin, compression against the African continent increased to the west, causing or intensifying the temporary breakup of the African continent into two sub-plates separated by the Benue and Chad rifts. On the Brazilian side of the Equatorial margin, this compression resulted in the formation (or reactivation) of the Ferrer - Urbano Santos Arch, that now separates the Paleozoic Paranaiba basin from the young rift basins of the Equatorial margin. These basins were created during Aptian time, as break-up between Brazil and Africa progressed and the rift propagated westward through this region.
Thus two phases of rifting can be distinguished:
1. During Neocomian times, there was strong compresion between Brazil and Africa in the extreme north of the South Atlantic margin (between Natal and João Pessoa) and in the western portion of the Equatorial margin. In these regions the future plate limits were yet ill-defined and stresses in the interior of the South American continent were high. This resulted in the reactivation of Precambrian shear zones with predominantly strike-slip movement, but also with abundant normal and reverse faults, depending on the large-scale stress regime and local fault orientation. The interior rift basins of NE Brazil, such as the Pendência and Rio do Peixe basins, formed during this period.
2. During Aptian time, a new system of faults propagated to the west along the Equatorial margin through the previously compressed region of the Ferrer - Urbano Santos Arch. This fault system finally detached the South American continent from Africa, connected the South Atlantic to the Central Atlantic ocean and caused stresses to be dislocated to this newly creaated plate margin. As a result, stresses acting on Precambrian shear zones in the continental interior decreased and fault movement along them eventually ceased. Thus the Rio da Serra and Aratu stages were characterized by intense faulting and high rates of subsidence in the intracontinental Pendência rift as well as in lesser rifts. During the subsequent Buracica and Jiquiá stages these interior rifts became progressively inactive, as tectonic activity was transferred to the newly formed plate margin. During Aptian times, activity along this new fault system became progressively intensified, starting at biozone 230 and reacting its maximum during biozone 270. The intense subsidence at this time accompanied the stress concentration at the plate limit that introduced the formation of oceanic crust.
References
Françolin, J. B. L., 1992. Analyse structurale du bassin du Rio do Peixe (Brésil). Mém. et Docum. Centre Armoricain d'Étude Struct. Socles, Rennes, 46: 1-240.
Françolin, J., Cobbold, P.R. & Szatmari, P., 1994. Faulting in the early Cretaceous Rio do Peixe basin (NE Brazil) and its significance for the opening of the Atlantic. J. Structural Geology, Vol. 16, pp. 647-661.
Françolin, J. B. L. & Szatmari, P., 1987. Mecanismo do rifteamento da porção oriental da margem norte brasileira. Rev. Bras. de Geociências, Vol. 17, pp. 196-207.
Matos, R. M., 1992. The northeast Brazilian rift system. Tectonics, Vol. 11, pp. 766-791. Raposo, M. I. & Ernesto, M., 1995. An Early Cretaceous paleomagnetic pole from Ponta Grossa dikes (Brazil): Implications for the South American Mesozoic apparent polar wander path. J. Geophys. Res., Vol. 100B, pp. 20,095-20,109.
Szatmari, P., Françolin, J. B. L., Zanotto, O. & Wolff, S., 1987. Evolução tectônica da Margem Equatorial brasileira. Rev. Bras. de Geociências, Vol. 17, pp. 180-188.

SECOND ANNUAL CONFERENCE OF IGCP PROJECT 381

The Second Annual Conference of IGCP Project 381 (SAMC II) will be held between 8-13 March 1997 in conjunction with the 13th Colloquium of African Micropalaeontology and the 3rd Colloquium on the Stratigraphy and Palaeogeography of the South Atlantic, organized by the Société Nationale des Hydrocarbures (SNH) in Yaoundé, Cameroon.

Registration fees: (up to 1 August 1996) (after this date) Participant member 600 FF 750 FF Student member (attach proof) 300 FF 400 FF Accompanying Member 500 FF 600 FF

All advanced payments must be made by bank checks or money orders in French Francs payable to:
Colloques 97 - 31.904351.3716/L - SCB-CL Yaoundé Cameroun Télex: 8213KN-CRELYCAM
On site payments will be effected in French Francs or CFA Francs. Registration fees refunds can be made only until 1st January 1997 upon a request duely made.

HOTELS - (Rates are in FF as for 1996) - The rates may increase by the date of the holding of the meetings.

Single Double Suite Breakfast Lunch HILTON (5*) 1100 1200 2000 85 120 MONT FEBE (5*) 800 - - 50 100 DEBUTES (3*) 135 - - 25 50 PRESTIGE (2*) 140 170 - 30 60 MANSEL (3*) 120 160 - 28 60 MEUMI (3*) 120 180 - 20 60

To be sure you will benefit from the reduced rates, it is advised to chanel your reservation through the Organizing Committee., using the form hereby attached. You can also make your reservation directly to the hotel of your choice.

Field Trip No. 2: 13-17 March 1997
Cretaceous deposits and geological phenomena such as Dinosaur tracks in the Garoua, Mayo Oulo-Léré and Barbouri-Figuil basins, North Cameroon. This field trip will include the visit of indigenous populations of Toro and National Parc of Waza.

Field Trip No. 3: 13-15 March 1997
The third field trip is primarily touristic-cultural and will feature the cultures and traditions of the peoples of West Cameroon.

ABSTRACTS. Deadline is 30 October 1996. Abstracts should be typewritten single-spaced, on high-quality white paper and be camera ready,. Abstracts shouldnot exceed 2 pages (14 x 20 cm) including the drawings and tables, and be mailed flat to Yaoundé (address below). All selected abstracts will be published in a volume which will be distributed to all the participants. The Organizing Committee reserves itself the rigth to refuse any abstract on the advise of the Advisory Committee. Papers can be presented in English or French. Each oral presentation will be 15 minutes in length followed by 5 minutes of discusions. Translation in both languages will be provided. Posters must also be in English or French.

Travel informations. The Company CAMEROON AIRLINES (CAMAIR) offers the following reductions in all its international itineraries: Economy Class: 70%, "J" Class: 30%, First Class: 20%
For regional (African) and local flights, a rebate of 50% is granted for the Economy Class.
Please contact the following CAMAIR offices: Paris: Tel.: 33(1)43123010/3020/3030, Fax: 49249398
Marseille: Tel.: 33(91)142215, Fax: 561593. London: Tel.: 44(171)7347676, Fax: 4393349.
Rome: Tel.: 39(6)4828275/4872207, Fax: 4828543
All the participants will be welcomed upon their arrival at the Yaoundé-Nsimalen Airport and their local transportation during the meetings will be ensured by the Organizing Committee.

Further information. Please contact (Colloquia Yaoundé 1997 - Organizing Committee):
Mr Adolphe MOUDIKI - Executive General Manager, Société Nationale des Hydrocarbures (SNH), B.P. 955 - Yaoundé - Camerron. Fax: (237) 204651/ 209869.
or call: François Roger NGUENE - Directeur/ Manager Exploration Division, Société Nationale des Hydrocarbures (SNH), B.P. 955 - Yaoundé - Cameroon. Tel.. (23)203253, Fax: (237) 204651/ 209869.

Outline of Next Annual Project Meetings

The locations for the next annual project meetings are as follows: Argentina is the venue for the 1998 meeting. This meeting is likely to be split between two centres, Ushuaia in Tierra del Fuego and Comodoro Rivadavia in Patagonia, to allow the maximum opportunities for field geology.
The 1999 meeting will be held in Africa, either in Nigeria (Calabar) or the Ivory Coast. The final annual meeting, in 2000, will be in South Africa.

RESEARCH REPORTS

Origin and History of the South-Atlantic Cretaceous Echinoid Faunas

Didier NÉRAUDEAU* & Bernard MATHEY**
* Muséum National dêHistoire Naturelle de Paris, Laboratorie de Paléontologie 8 rue Buffon, 75005, Paris, France.
** Centre des Sciences de la Terre and UMR-CNRS no. 5561, Université de Bourgogne, 6 Bld Gabriel, 21000, Dijon, France.

Current Reseach Account: The purpose of our current research is the synthetic analysis of the Cretaceous colonization of the South Atlantic shelf-seas by echinoids. The faunal inventory was based on bibliographical data and unpublished material, and concerns the West African margin (Senegal, Ivory Coast, Nigeria, Gabon, Cameroon, Congo, Zaire, Angola), the eastern South America (Venezuela, Brazil, Argentina) and Antarctica (Seymour Island, James Ross Island). All told, 27 genera and 67 species were identified, if we eliminate synonyms. The echinoid faunas were compared with those of Mediterranean Tethys (Morocco, Algeria, Tunisia, Niger), Southeast Africa (Zululand, Madagascar), western South America (Colombia, Ecuador, Peru, Chile), and Caribbean and Central America (Cuba, Honduras, Mexico, Texas). Cladistic vicariance analyses were carried out, with a special attention to Albian and Cenomanian echinoids, particulary well diversified and well documented in the fossil record.
Paleobiogeographic maps of echinoid distribution were established for Barremian, late Aptian, late Albian, late Cenomanian, late Turonian, late Coniacian and early Maastrichtian times, with plotting of the paleocurrent patterns responsible for the species dispersal and the Cretaceous colonization of the South Atlantic.
As conclusions, five main steps can be distinguished in the colonization of the Cretaceous South Atlantic shelf-seas by echinoids. In addition, at the specific level, the number of taxa common to South America and West Africa decreases more and more as the South Atlantic Ocean enlarges.

Working Group Proposals for IGCP Project 381

Cuban Working Group for IGCP Project 381
Coordinator: Jorge R. SÁNCHEZ-ARANGO - Centro de Investigaciones del Petróleo (CEINPET), Washington No. 169, Esquina a Churruca - Cerro, La Habana 1200, CUBA.
Tel.: +53-7- 408900, 411132, Fax: +53-7- 333072, 338027
Teams
1. Aptian/Albian and Albian/Cenomanian Stage Boundaries. Chairman: Silvia Blanco (CEINPET, CUBA)
2. Campanian/Maastrichtian Stage Boundary. Chairman: Lourdes Pérez (CEINPET, CUBA)
3. Atlas of Carbonate Microfacies and Sedimentology. Chairman: Rafael Segura (CEINPET, CUBA)
4. Dating of the First Marine Transgression. Chairman: Rolando García (CEINPET, CUBA)
5. K / T Boundary Chairman: Maria Lizette Díaz (CEINPET, CUBA)
6. Biochronostratigraphy and Biogeography of Mesozoic marine microfossils. Chairman: Carlos Perera (CEINPET, CUBA) Consuelo Díaz (IGP, CUBA)
7. Biostratigraphical Zonation Schemes. Chairman: José Fernández (CEINPET, CUBA)
8. Cuban Index Microfossil Species Chairman: Ana M. Escobar (CEINPET, CUBA)
9. Stratigraphy, Regional Correlation Charts, Tectonostratigraphy Chairman: Jorge R. Sánchez (CEINPET, CUBA)
10. Paleogeography Chairman: Rafael Tenreyro (CEINPET, CUBA)
11. Tectonic Modelling Chairman: Rafael Tenreyro (CEINPET, CUBA)
12. Organic Geochemistry Chairman: José Orlando López (CEINPET, CUBA)
13. Petroleum Systems Chairman: Juan Guillermo López (CEINPET, CUBA)

It will be discussed if these teams will work as part of the currently international working groups following the subject basis as the best option.
However if the status of the Cuban Working Group is accepted, the teams will organize the Cuban investigations.
Regional works could be planned in coordination with other Working Groups for Central America and the Caribbean.
Anyway the Cuban specialists will work in the manner that the Project Leaders consider effective to fully reach the project goals.

ANNOUNCEMENTS

Forthcoming Meetings related to IGCP Project 381

4th Symposium on the Brazilian Cretaceous
to be held at Águas de São Pedro, São Paulo, Brazil, 18-23rd August 1996, organized by the Departamento de Geologia Sedimentar, University of Rio Claro (UNESP).
The following papers will be presented as contributions to IGCP Project 381:
Mitsuru ARAI, Seirin SHIMABUKURO & Marta C. VIVIERS (PETROBRAS-CENPES, Rio de Janeiro)
"Characterization of the Vraconian (uppermost Albian, Lower Cretaceous) in Brazil: a paleomicroplanktonic contribution."
Peter BENGTSON (Universität Heidelberg) & E. A. M KOUTSOUKOS (PETROBRAS-CENPES)
"Understanding the Mesozoic history of the South Atlantic: the work of IGCP Project 381 (SAMC)"
Ismar de Souza CARVALHO (UFRJ, Rio de Janeiro)
"Dinosaur footprints in Uiraúna-Brejo das Freiras Basin (Lower Cretaceous, Paraíba State)."
Dimas DIAS-BRITO (UNESP, Rio Claro)
"Brazilian carbonate basins during the Albian-Cenomanian: its paleobathymetric evolution based on microfacies analysis."
Dimas DIAS-BRITO (UNESP, Rio Claro)
"Evolution of the marine mid-Cretaceous geosystem in southeastern-eastern margin of Brazil, as suggested by microfacies analysis."
Lars E. HOLMER (Uppsala Universitet) & Peter BENGTSON (Universität Heidelberg)
"Implications of the rare occurrences of brachiopods in the Upper Cretaceous of Sergipe, Brazil"
E. A. M KOUTSOUKOS (PETROBRAS-CENPES)
"Upper Aptian-Maastrichtian benthic foraminiferal morphogroups and paleoenviroments from Northeastern Brazil: a review"
E. A. MUSACCHIO, P. VALLATI & M. SIMEONI (Universidad Nacional de La Patagonia, Argentina)
"Cretaceous non-marine microfossils fromm Patagonia: their relationships with similar assemblages from Brazil"

The Oil and Gas Habitats of the South Atlantic

to be held at The Geological Society, Burlington House, Piccadilly, London WIV 0JU, UK, 25-26th February 1997.

Call for Papers/Posters
This conference on the oil and gas habitats of the South Atlantic continues the Petroleum Group's successful series of meetings on major oil and gas provinces of the world. Though the South Atlantic is a centre of E&P expenditure, little of the knowledge that now exists on the region has been released. The objective is to provide the petroleum industry, support companies, researchers and government bodies with an authoritative review of the future petroleum potential of the region. There will be a strong focus on economic issues and new markets. Papers and posters are, therefore, invited that focus on the modern understanding of the South Atlantic, the current round of discoveries, and future opportunities. The theme for the meeting is "using science and technology to ensure continued success". Session topics are:
Evolution of the margins
Giant field habitats
Shallow to deep water E&P
Gas - next century's resource
It ë
For the purposes of this meeting, we have restricted the South Atlantic to the African margin from South Africa to Senegal, and the South American margin from Argentina to Venezuela.
Additional information on the meeting and its objectives is available from the Convenors:
Nick CAMERON - Dept. of Geology, Royal School of Mines, Imperial College, Prince Consort Road, London SW7 2BP, UK. E-mail: nick.cameron@ic.ac.uk (or) nick@topaz.primex.co.uk
Dave BAMFORD - BP Exploration Operating Company Limited, Uxbridge One, 1 Harefield Road, Uxbridge, Middlesex UB8 1PD, UK. Tel: +44-(0)1895-877241, Fax: +44-(0)1895-877704.
Joe PAPE - BP Exploration Operating Company Limited, Uxbridge One, 1 Harefield Road, Uxbridge, Middlesex UB8 1PD, UK. Tel: +44-(0)1895-877702, Fax: +44-(0)1895-877118.

Abstracts: these should be sent to Nick Cameron at Imperial College to arrive no later than September 27th 1996. The maximum length is two pages. A short bibliography and illustrations in the form of monochrome text figures may be included. E-mail or PC format diskette submissions are preferred. Microsoft Word will be used to prepare the abstract book. Graphics should be compatible with CorelDraw 3 or higher. The programme for the meeting will be announced during the week beginning October 21st. Every effort will be made to accommodate all submissions.

Regional Meeting of IGCP Project 381 "South Atlantic Mesozoic Correlations" and Second Europpean Meeting on the Palaeontology and Stratigraphy of South America

to be jointly held at the Geologisch-Paläontologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany, 2-4 September 1997.
The Heidelberg regional meeting of IGCP Project 381 is intended as a forum for scientific exchange between project participants from Europe and its immediate surroundings (e.g., northern Africa and Middle East). The first circular of the 1997 European regional meeting of SAMC, to be held in conjunction with the "2nd European Meeting on the Palaeontology and Stratigraphy of South America", is available through the Internet at:

http://ix.urz.uni-heidelberg.de/~dc8/geo/1st-381.html
and at
http://ix.urz.uni-heidelberg.de/~dc8/geo/1st-sam.html

The joint meeting will take place in Heidelberg, Germany, 2-4 September 1997. The circular is also available by post from the organizers at the following address: Prof. Dr. Peter Bengtson - Geologisch-Paläontologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg Germany. Tel.: +49 6221 548293, Fax.: 548640, E-mail: Peter.Bengtson@urz.uni-heidelberg.de

AAPG Hedberg Conference on Petroleum Systems of the South Atlantic Margins to be held in Rio de Janeiro, Brazil, September 1997

Subject: The petroleum geology of the South Atlantic marginal basins has grown in importance over the past several years and will continue to do so for the foreseeable future. This interest is a result of the growing impetus on deep water exploration along the West African Margin and the prospects of changes in governmental restrictions in Brazil which will open the countryês sedimentary basins to international exploration. These basins offer many challenges to petroleum geologists including: (1) the nature and distribution of Lower Cretaceous lacustrine source rocks; (2) the chrono- and biostratigraphy of lacustrine rift sequences (including problems associated with interbasinal correlations); (3) the nature, origin and distribution of the Aptian salt basin and salt tectonnics; (4) hydrocarbon migrational patterns (including assessment of the relative importance of vertical vs. lateral migration and the role of –windows” in the salt); (5) reservoir developmental patterns (including carbonate reservoirs and the role of changes in river drainage patterns on sandstone deposition); and (6) the tectonic and sedimentary evolution of the margin (including the role of sea level, and the development of oceanic circulation patterns). The aim of this conference will be to bring together a number of experts from several technical disciplines to examine the various processes which have controlled the known hydrocarbon occurrences from within the region in order to better predict where future exploration opportunities may exist. It is envisaged close collaboration with IGCP Project 381 –South Atlantic Mesosoic Correlations”. Participation: In addition to the approximately 40 oral and 20+ poster presentations we anticipate that there may be at least an additional 50 to 100 participants. The actual number of anticipated formal presentations has been limited in order to permit the authors to more fully develop their topics.
As the conference title suggests, the technical program will examine all aspects which combine to form the regionês multiple petroleum systems, participation will therefore be mutidisciplinary. It is anticipated that participants will include geochemists, reservoir geologists, stratigraphers and regional geologists who are familiar with the geologic evolution of the regionês diverse basins. Co-Sponsors: This research symposium will be co-sponsored by the American Association of Petroleum Geologists (AAPG) and the Brazilian Association of Petroleum Geologists (ABGP), in cooperation with PETROBRAS and the Brazilian Petroleum Institute (IBP).

Convenors:
Marcio Rocha MELLO - PETROBRAS-CENPES/Divex/Cegeq, Cidade Universitária, Quadra 7, Ilha do Fundão, BR-21949-900 - Rio de Janeiro - RJ, Brazil.
Tel.: +55-21-598-6460, Fax: +55-21-598-6799, E-mail: marcio@cenpes.petrobras.gov.br
Barry J. KATZ - E&P Technology Department, TEXACO Inc., 3901 Briarpark, Houston, TX 77042, USA. Tel.: +1-713-954-6093, Fax: 713-954-6113, E-mail: 103021.3227@compuserve.com

1998 AAPG International Conference and Exhibition

to be held in Rio de Janeiro, Brazil, November 8-11, 1998.
The Conference will be conducted jointly by the American Association of Petroleum Geologists (AAPG) and the Brazilian Association of Petroleum Geologists (ABGP).
For further information please contact: Caroline M. Woods (International Events Coordinator)
AAPG - P.O. Box 979, Tulsa, OK 74101-0979, USA. Offices at 1444 S. Boulder Av., Tulsa, OK 74119. Fax: +1-918-560 2684, E-mail: cwoods@aapg.org
It is planned to be held simultaneously a South American regional meeting of IGCP Project 381.

5th Symposium on the Brazilian Cretaceous and First Symposium on the Cfetaceous of South America

to be held at São Paulo, Brazil, August 1999.
For more information write to: Dimas DIAS BRITO - Departamento de Geologia Sedimentar, UNESP, Av. 24-A No. 1515, 13506-900 Rio Claro, SP, BRAZIL (Fax: +55-195-340327, E-mail: dimas@geo001.uesp.ansp.br).

Other IGCP Meetings of Interest

Annual Assembly of IGCP Project 362 "Tethyan and Boreal Cretaceous"

to be held on the campus of Freiberg University of Mining and Technology, Germany, in conjunction with the 5th International Cretaceous Symposium, 16-24 September 1996. For additional information please contact:
Silke Voigt - Institute of Geology, Freiberg University of Mining and Technology Bernhard- von- Cotta- Str. 2, D-09596 Freiberg, Germany.
Fax: +49-3731-393599; E-mail: voigt@coffee.geophysik.tu-freiberg.de

Symposium of IGCP Project 301 "Paleogene of South America"

to be held at the Dirección Nacional del Servicio Geológico, on 11 October, and on 15 October 1996 during the XIII Argentine Geological Congress and the III Hydrocarbon Exploration Congress, Buenos Aires, Argentina.
For additional information please contact:
SIMPOSIO PALEOGENO DE AMERICA DEL SUR
Dirección Nacional del Servicio Geológico,Tte. de Fragata Benito Correa 1194, 1107 Buenos Aires, Argentina. Tel.: +54-1-3617320, Fax: 3493160, E-mail: postmaster@mpgeo1.gov.ar.

NEW PARTICIPANTS

(In addition to the lists of participants appended to SAMC News 4).

ABDEL-KIREEM, Mohamed Rashad - Geology Department, Faculty of Science, Alexandria University, Alexandria, Egypt. Tel.+02-03-5701049, Fax:+02-03-4911794, E-mail:M.R.Abdel-Kireem@Alex.eun.eg
Research interests: Cretaceous-Tertiary micropaleontology (Foraminifera), paleoecology and sequence stratigraphy.

TISI, Antonio Luis - Pecten do Brasil, Praia de Botafogo, 370 - 9º andar, 22250-040 Rio de Janeiro-RJ, Brazil. Tel.: +55-(0)21) 552-8947 or 240-7182, Fax: (021)-552-0893.
Research interests: Basin analysis and oil exploration.

BAECKER-FAUTH, Simone - Curso de pós-graduação em Geociências, Instituto de Geociências, UFRGS, Av. Bento Goncalves, 9500 Bl.1, Prédio 43113, sala 207, 90501-970 Porto Alegre-RS, Brazil. Tel.: +55-(0)51-3166391, Fax: +55-(0)51-3365011, E-mail: baeckers@if.ufrgs.br
Research interests: radiolarians, Upper Cretaceous, Biostratigraphy, Paleoecology, Paleogeography.

EL FIKY, Anwar A. - Geology, Department, Faculty of Science, Alexandria University, Egypt. Tel.+02-03-5718469, Fax: +02-03-4911794, E-mail:Mibrahim@Alex.eun.eg
Research interesst: Hydrogeology and groundwater modelling.

Fogarasi, Attila - Dept. of Geology, Eotvos University, Muzeum krt. 4/A, H-1088 BUDAPEST, HUNGARY. Tel.: +36-1-266-3956, Fax: +36-1- 266-4947, E-mail:fogarasi@ludens.elte.hu
Research Interests: Cretaceous calcareous nannofossils, biostratigraphy, cyclostratigraphy, Hungary, Benin.

FONTANELLI, Paola de Rossi - PETROBRAS/E&P-ES, GEXP/GELAB, Rodovia BR-101, Km 67,5. 29930-000 São Mateus-ES, Brazil. Tel.: +55-(0)27-763-1222 Extn. 4449, Fax: +55-(0)27-763-4410.
Research interests: sedimentology, stratigraphy.

GUIRRO, Antonio Celso - PETROBRAS/E&P-ES, GEXP/GELAB, Rodovia BR-101, Km 67,5. 29930-000 São Mateus-ES, Brazil. Tel.: +55-(0)27-763-1222 Extn. 4441, Fax: +55-(0)27-763-4410. Research interests: sedimentology, stratigraphy.

KHOLEIF, Suzan E.A. - National Institute of Oceanography and Fisheries, Kayed-Bey, Alexandria, Egypt. Tel.+02-03-849833, E-mail: Mibrahim@Alex.eun.eg Research interests: Jurassic and Cretaceous palynology and paleoecology.

KLINGER, Herbert C. - S.A. Museum, P. O. Box 61, Cape Town 8000, South Africa. Tel.: +55-(0)21-243330, Fax: +55-(0)21-246716, E-mail: hklinger@nv1.samuseum.ac.za.
Research interests: Cretaceous biostratigraphy, systematics ammonites Southern Africa.

LIMA, Francisco Henrique de Oliveira - PETROBRAS/E&P-ES, GEXP/GELAB, Rodovia BR-101, Km 67,5. 29930-000 São Mateus-ES, Brazil. Tel.: +55-27-763-1222 Extn. 4449, Fax: +55-27-763-1222 Extn. 4410.
Research interests: stratigraphy, biostratigraphy, micropaleontology.

McLAUGHLIN, Peter P. - Exxon Exploration Co., P. O. Box 4778, Houston, TX 77210-4778, USA. Tel.: +1-713-7795424, Fax: +1-713-4235896, E-mail: pete.mclaughlin@exxon.sprint.com
Research interests: planktonic foraminiferal biostratigraphy, foraminiferal paleoecology, sequence stratigraphy.

de SOUZA, Vladimir - Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, UFRGS, Av. Bento Goncalves, 9500 Bl.1, Prédio 43127, sala 213, 90501-970 Porto Alegre-RS, Brazil. Tel.: +-55-(0)51-3166391, Fax: +55-(0)51-3365011.
Research interests: radiolarians, mid-Cretaceous, cherts, South Atlantic, marginal Brazilian basins, São Francisco basin.

TOKUTAKE, Lúcio Riogi - PETROBRAS/E&P-ES, GEXP/GELAB, Rodovia BR-101, Km 67,5. 29930-000 São Mateus-ES, Brazil. Tel.: +55-27-763-1222 Extn. 4449, Fax: +55-27-763-1507.
Research interests: stratigraphy, Cretaceous and Tertiary Palynology, fossil dinoflagellates.

TRUSKOWSKI, Irene - MARAVEN SA, Apdo 829, Caracas 1010A, VENEZUELA. E-mail: pxg16@bioserv.maraven.pdv.com
Reseach interests: Cretaceous foraminifera, La Luna Formation, biostratigraphy.

UMENWEKE, Meshach O. - Dept. of Geological Sciences, Nnamdi Azikiwe University, PMB 5025, Awka, NIGERIA.
Research interests: sedimentology, stratigraphy, Cretaceous biostratigraphy (ammonites and dinoflagellates), environmental hazards

Changes of address and amendments

ANDREIS, Renato Rodolfo - Departamento de Geologia, Instituto de Geociências, UFRJ, Cidade Universitária, Ilha do Fundão, 21910-240 Rio de Janeiro, RJ, BRAZIL. Tel.: +55-(0)21-5983292, Fax: 5983280., E-mail: andreis@igeo.ufrj.br
Research interests: sedimentology, petrofacies - palaeosoils.
Research Comments: "Presently studying continental and mixed successions of northern Patagonia (Argentina) together with Sergio Archangelsky and José Bonaparte (Museo de Ciencias Naturales "Bernardino Rivadavia", Buenos Aires, ARGENTINA)."

DêAVILA, Roberto Salvador Francisco - PETROBRAS/E&P-ES, GEXP/GELAB, Rodovia BR-101, Km 67,5. 29930-000 São Mateus, ES, BRAZIL. Tel.: +55-(0)27-7631222 Extn. 4450, Fax: +55-(0)27-7631507.
Research interests: sedimentology, stratigraphy.

GALEA-ALVAREZ, Francia Antonia (newly appointed Venezuelan representative for IGCP Project 381) - CORPOVEN S.A., filial of P.D.V.S.A., Laboratorio Geológico, Apartado Postal 4326, Puerto La Cruz 692, VENEZUELA. Tel.: +58-81-606429, Fax: +58-81-606445.
Research Comments: "Studying the La Luna Formation in the Maracaibo Basin in collaboration with Irene Truskowski and Bill Sliter (core samples) and two surface studies, both in the La Luna Formation in the Venezuelan Andes, with Gregg Blake (Unocal) and T. Bralower (University of Carolina)."

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This page was last modified on 19 January 1996.