IGCP Project No. 381

South Atlantic Mesozoic Correlations

SAMC NEWS No. 8 - October 1997

ISSN 1413-6813

Dear Colleague,

This issue of SAMC News includes contributions presented to the Local Meeting of IGCP Project 381 held in São Pedro, Brazil, 1-9 August 1997, in association with the 15th Brazilian Paleontological Congress; and to the Regional Meeting of IGCP Project 381 "South Atlantic Mesozoic Correlations", held in conjunction with the Second European Meeting on the Palaeontology and Stratigraphy of South America and the 18th Regional IAS Meeting, Heidelberg, Germany, 2-4 September 1997.
Also included are the technical programmes and information about forthcoming meetings related to SAMC, as follows:
- Joint IGCP 381/362 Cretaceous Correlation Symposium, Margarita Island, Venezuela, 16-19 Nov. 1997;
- AAPG/ABGP Joint Research Symposium on Petroleum Systems of the South Atlantic Margins, Rio de Janeiro, 16-19 November 1997;
- Joint IGCP 381/362 Field trip to study Mesozoic sequences of western and central Cuba, March 1998;
- 1998 AAPG International Conference & Exhibition (RIO98), Rio de Janeiro, 8-11 November 1998;
- Third Annual Conference (SAMC III) and related field trips, Universidad Nacional de La Patagonia, Comodoro Rivadavia, Argentina, 17-19 November 1998.

An updated list of project participants may be found on page 36.

Project Leaders:
Eduardo A. M. KOUTSOUKOS - PETROBRAS-CENPES/Divex, Cidade Universitária, Quadra 7, 21949-900 Rio de Janeiro, RJ, BRAZIL. Tel.: +55-21-5986417 or 5986440, Fax: 5986795, Tel./Fax (home): 3254982 E-mail: koutsoukos@cenpes.petrobras.com.br

Peter BENGTSON - Geologisch-Paläontologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, GERMANY. Tel.: +49-6221-548293, Fax: 548640 or 545503, E-mail: Peter.Bengtson@urz.uni-heidelberg.de

"IGCP is interdisciplinary, covering all specialities of geology, geophysics and geochemistry. IGCP maintains active interfaces with disciplines related to the geological sciences such as marine sciences, atmospheric sciences and biological sciences."

Editor of SAMC News: E. A. M. Koutsoukos (Rio de Janeiro)

SAMC-Net: Mailing list "SAMC-Net" through listserv@vm.urz.uni-heidelberg.de

- SAMC-Net
- Contacts and further information
- SAMC Secretariat
- Regional coordinators and national representatives for IGCP Project 381 (September 1997)
- IGCP Project 381 Working Groups and Chairmen
- South Atlantic index microfossil species: systematics, biostratigraphy and paleoecology
- Related IGCP Projects
- SAMC - Thematic volumes
- Third Annual Conference of IGCP Project 381 (SAMC III), Argentina, 17-20 November 1998
- Outline of next annual project meetings
- Record of the Local Meeting of IGCP Project 381, held in conjunction with the 15th Brazilian Palaeontological Congress, São Pedro, São Paulo, 1-9 August 1997
- Contributions
- Record of the Regional Meeting of IGCP Project 381, Heidelberg, Germany, 2-4 September 1997
- Contributions
- Forthcoming meetings related to IGCP Project 381 :
- AAPG/ABGP Joint Research Symposium on Petroleum Systems of the South Atlantic Margins, Rio de Janeiro, 16-19 November 1997 Technical Program
- Joint IGCP 381/362 Cretaceous Correlation Symposium, in conjunction with the VII Venezuelan Geological Congress and 1st Latin-American Congress of Sedimentology, 16-19 November 1997, Margarita Island, Venezuela
- Joint IGCP 381/362 field-trip to study Mesozoic sequences of western and central Cuba, 28 March-1 April 1988
- 1998 AAPG International Conference and Exhibition (RIO98), 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 Meetings of Interest :
- International Symposium on Palaeodiversification, land and sea compared, 6-8 July 1998, Lyon, France
- Announcements :
- The Llewellyn Ivor Price Paleontological Research Center, Uberaba, Minas Gerais, Brazil
- List of Participants
- Acknowledgements

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.com.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.com.br

ANGOLA: Mário Gil Pereira BRANDÃO - SONANGOL, P.O. Box 3506, 1000 Luanda, Angola. Tel.: +244 2 36-1681 (home), Fax: +244 2 33-5426.

ARGENTINA: Eduardo A. 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.com.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 12000, 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

GHANA: Lawrence APAALSE - Ghana National Petroleum Corporation (GNPC), PMB, Tema, GHANA. Tel.: +233 21 712930, Fax: +233 21 712916, E-mail: gnpcexplo@ncs.com.gh

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

U.S.A. : Thomas W. DIGNES - Chevron Overseas Petroleum, Inc., 6001 Bollinger Canyon Rd., P. O. Box 5046, San Ramon, CA 94583, USA. Tel.: 510 8423367, Fax: 8423030, E-mail: twdi@usho01.chevron.com
William V. SLITER - U.S. Geological Survey, Western Regional Geology Group, 345 Middlefield Road, MS 915, Menlo Park, California 94025, USA. Tel.: +1-415-3294988, Fax: +1-415-3294975, E-mail: wsliter@octopus.wr.usgs.gov

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.

The following thematic Working Groups reflect the diversity of geological understanding and needs within the Project area:

- Aptian/Albian and Albian/Cenomanian Stage Boundaries: E. Koutsoukos
- Cenomanian/Turonian and Turonian/Coniacian Stage Boundaries: P. Bengtson
- Coniacian/Santonian, Santonian/Campanian and Campanian/ Maastrichtian Stage Boundaries: Eduardo Olivero (CADIC, Ushuaia, Argentina)
- Atlas of Cretaceous Carbonate Microfacies: D. Dias-Brito (IGCE-UNESP, Brazil)
- Chemostratigraphic Correlations: René Rodriques (PETROBRAS- CENPES)
- Cretaceous Continental Ecosystems: Ismar Carvalho (UFRJ, Rio de Janeiro, Brazil)
- Dating of the First Marine Transgression: E. Koutsoukos
- K/T Boundary: E. Koutsoukos
- Biochronostratigraphy and Biogeography of Non-Marine Microfossil Assemblages: E. Musacchio (Universidad Nacional de la Patagonia, Comodoro Rivadavia, Argentina)
- Paleogeographical and Paleoclimatical Maps: Antonio J. Vasconcellos Garcia (UNISINOS) and Biostratigraphic Group of PETROBRAS-CENPES
- South Atlantic Evaporites: Peter Szatmari (PETROBRAS-CENPES)
- Regional Tectonics: P. Szatmari
- Biochronostratigraphic Framework for the Mesozoic Successions: biostratigraphic groups of EXXON and PETROBRAS-CENPES.

For additional information please contact the WGs' chairmen.

IGCP Project 381 decided to initiate a research project comprising several working-groups on the various types of index fossils on both sides of the South Atlantic. Each WG should have a co-leader on each side of the ocean, who would, in addition to contributing, coordinate the collecting and publishing of data. The final aim would be, among others, the publishing of iconographic atlases of index fossils for the various basins. This would made possible the establishment of an integrated stratigraphic scale. The following WG's have been set, though most of the WG coordinators have not been chosen yet:

Mesozoic ostracodes
Coordinator for West Africa: Jean-Paul Colin - ESSO Rep., 213 Cours V. Hugo, 33323 Bègles cedex, FRANCE. Fax: +(33) 56 49 85 43; Ray Bate - (lacrustine Basin Research, London)
Coordinators for South America: Eduardo Musacchio (Universidad Nacional de La Patagonia); Marta Cláudia Viviers (PETROBRAS-CENPES)

Mesozoic [benthic] foraminifers.
Coordinators for South America: E.A.M. Koutsoukos and M. C. Viviers (PETROBRAS-CENPES)
Coordinator for West Africa: Ivan de Klasz (Nice, France)

Mesozoic [planktonic] foraminifers. W.V. Sliter (U.S. Geological Survey, Menlo Park)

Ammonites. Coordinators: Peter Bengtson (Heidelberg University)
Eduardo Olivero (CADIC, Ushuaia, Argentina)

Inoceramids. Coordinators: not chosen yet.

Calcareous nanofosils. Coordinators: not chosen yet.

Palynomorphs. Coordinators for West Africa: Chris Denison (CHEVRON), Mohamed Ibrahim (Alexandria University)
Coordinators for South America: Rodolfo Dino and Mitsuru Arai (PETROBRAS)

SAMC participants wishing to work in close collaboration with any of these WG's are invited to contact directly the coordinators or the SAMC Secretariat. Suggestions are welcome.

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.

As a contribution to the aims of SAMC two thematic volumes have been proposed to be edited with collections of papers addressing specific issues within the framework of IGCP Project 381:

Information: Please contact E. Koutsoukos (e-mail: koutsoukos@ cenpes.petrobras.com.br) or the Editor-in-Chief of Cretaceous Research, Prof. David J. Batten, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, Wales, UK (e-mail: dgb@aber.ac.uk).

(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.

The deadline for manuscripts has been postponed to 15th May 1998.

For further information please contact L. A. Trindade (e-mail: luizt@ cenpes.petrobras.com.br) or the SAMC Secretariat.

Argentina is the venue for the 1998 3rd Annual Conference (SAMC III).. The meeting will be held at the Universidad Nacional de La Patagonia in Comodoro Rivadavia, Argentina, and supported by the Asociacion Paleontologica del Golfo San Jorge. It will commence shortly after the International AAPG meeting in Rio de Janeiro.

Field Trip No. 1 (pre-Conference): Neuquen Basin (4 days)
Neuquen Basin (Andean Domain); five overnigth stays in Chos-Malal and Zapala cities.
Jurassic System at Cordillera del Viento (marine sequences).
Andico System, lower part, at Puerta Curaco profile (well-dated marine Neocomian units).
Andico System, upper part, at Villa del Agrio and Agrio del Medio profiles. Mainly non-marine regressive, brackish and red beds facies of mid-Cretaceous age. Upper Cretaceous non-marine units.
Jurassic and Cretaceous facies, in part non-marine, at the proximal southern part of the basin; South of Zapala City.

Field Trip No. 2 (post-Conference): San Jorge Basin (3-4 days).
Days 1-2: Chubut River, Medium Valley: North San Jorge Gulf Basin (three overnight stays in Los Altares village).
Lower and Middle Jurassic volcanic Complex (Rift I).
Upper Jurassic non-marine units (Post-rift II).
Neocomian continental sequence (Rift II).
Pyroclastic and terrigenous units of middle Cretaceous age (Post-rift II).
Upper Cretaceous sediments (marine and non-marine) of Sag style.
Day 3: San Jorge Gulf Basin (one day in Sarmiento; overnight in Comodoro Rivadavia).
Aptian lacustrine facies (Post-Rift II).
Middle to Upper Cretaceous non marine facies of sag style.

Field Trip No. 3 (post-Conference): Austral-Marginal Basin of Tierra del Fuego (4 days)
For this last part CADIC at Ushuaia could offer the following facilities and organization:
- Accomodations at very low cost (U$S 10 per day per person in triple rooms) total capacity 21 persons, and/or in local hotels at the cost of U$S 40-60 in single rooms.
- The CADIC auditorium, capacity for 60 peoples, with slide and transparency projectors, and IBM-based computer projection.
- Field trip guide and assistance covering the following:

Day 1: Geology of the National Park area, visiting the polyphased-deformed basement and/or Jurasic volcanics in Lapataia-Ensenada area; the copper-lead old mine; basaltic espilites; and the Yahgan Formation. The area includes important structural features of stratigraphic invertion by thrusting and a magnificent scenery of C. Darwin and Cpt .Fitzroy first entrance into the Beagle Channel. Round trip from Ushuaia about 50 km. 1 day, departing from Ushuaia early in the morning; lunch at Casita del Bosque in the National Park area, returning late-evening.

Day 2 (in combination with Day 3): Geological transect across de the Andes Fueguinos visiting the main outcrops of the Upper Jurassic silicic volcanics of the Tobifera/Lemaire Formation; the deep-marine Early Cretaceous Yahgan Formation; and the main strike-slip fault of the Tierra Mayor Valley. Geological subjects include: stratigraphy, sedimentology, trace fossils, and structures of the Jurassic-Early Cretaceous marginal basin of Tierra del Fuego. Departing early in the morning from Ushuaia, lunch at Hosteria Petrel (Lago Escondido), about 70 Km from Ushuaia, continued with the following:

Day 3: Geology of the folded-thrusted belt of the Upper Cretaceous-Cenozoic Austral foreland basin, visiting the Paleocene Rio Claro Formation and the spectacular syntectonic clastic dykes of the Rio Penia-Sierra Leona Complex (Uppermost Eocene-Oligocene). Night dinner and breakfast at Hosteria San Pablo, 240 km from Ushuaia (about U$S 40 for dinner and room per person).

Day 4: Continues the field trip with the magnificent, 1.5 Km thick exposures of the foreland Eocene La Despedida Group along the Atlantic shore of Tierra del Fuego, including the recognition of shelf mudstones and spectacular channeled and cross-stratified estuarine sandstones. About 20 km from Hosteria San Pablo. Best viewing of the geology is at low tide (tide amplitude in the order of 8/9 meters); depending on the date and time of low tide during the visit we should prevent the possibility of having lunch at the field site. Returning to Ushuaia at late evening.
Transportation costs and expenses could be lowered depending on the number of participants, which should be made known with at least 2 month in advance.

Information. Please contact (Organizing Committee):
Eduardo A. 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

For information about Field-Trip No. 3:
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; E-mail: eolivero@satlink.com

The locations for the next annual project meetings are as follows (provisionally):

- The 1999 meeting (SAMC IV) is planned to be held in Africa, in Marrakech, Morocco, April 1999.

A local meeting of IGCP Project 381 held as a thematic symposium in conjunction with the 15th Brazilian Palaeontological Congress, at the Hotel Fazenda Colina Verde, city of São Pedro, state of São Paulo, 1-9 August 1997

Twenty-four (24) participants attended the meeting where seven oral contributions were presented. The meeting was introduced by the President of the IGCP Brazilian Comission, Diógenes A. Campos, who presented a brief comment about the scope and aims of IGCP. The first oral presentation (Research cooperation in geosciences: the I.G.C.P. Project 381 (1995-2000) - an overview; by E. K.) showed an overview of the objectives, current research activities of individuals and working-groups and of forthcoming meetings of IGCP Project 381. Thematic sessions were held jointly with the 15th Brazilian Palaeontological Congress with the presentation of several SAMC-related oral and posters contributions by project participants.

Calcareous nannofossils biostratigraphy of the Brazilian Cretaceous: state of the art

Rogério Loureiro Antunes1 & Francisco Henrique de Oliveira Lima2
1Petrobras-Cenpes/Divex/Sebipe, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil. (E-mail: antunes@cenpes.petrobras.com.br)
2Petrobras/E&P-ES/Gexp/Gelab. BR-101, Km67,5, Nova Esperança, São Mateus, Espírito Santo, 29.930-000Brasil. (E-mail: henrique@EP-ES.petrobras.com.br)

The first biostratigraphic zonation of the Brazilian continental margin based on calcareous nannofossils was proposed by Troelsen & Quadros (1971). According to their zonal scheme the Cretaceous section (Aptian-Maastrichtian) included five biozones (Fig.1). Subsequent studies (see Antunes, 1997, and in press for futher references) have introduced many modifications to Troelsen & Quadros´ (op. cit.) scheme, some of which related to changes of chronostratigraphic assignment of the biozones. These changes were based on new information from either literature or ongoing Petrobras studies. On the other hand, additional modifications resulted from the introduction of new biostratigraphic units. By the end of the 80´s the Albian-Maastrichtian section was being subdivided into nine biozones (Fig.1)
During the 90´s the equatorial margin (including the Sergipe/Alagoas Basin) was demonstrated to present a biostratigraphi succession distinct from that of the southern margin. The differences are most noticeable in the Albian-Turonian section, which contains the earliest marine record of the South Atlantic Ocean. It was also verified that certain biological events are useful for a more detailed subdivision of the Cenomanian-Campanian section (Antunes, in press; Oliveira, 1997). Similar conclusion was reached for the Maastrichtian, where Oliveira & Costa (1996) recognized two subzones in the Arkhangelskiella cymbiformis Zone. Such evidence allowed another rearrangement of the calcareous nannofossil biozonation. At the same time, additional biological events have bee traced through several basins, which may prove useful in further subdividing the Maastrichtian section.
Up to the present it has not been possible to test in all brazilian marginal basins the biostratigraphic innovations introduced during the 90´s. However, most of them have shown good consistency in the Santos, Campos, Espírito Santo, Sergipe/Alagoas and Potiguar basins.
In conclusion, the calcareous nannofossil biozonation of the Cretaceous in Brazilian marginal basins evolved from five biozones in the early 70´s to a total of 17 biozones at present time, considering that all proposed bioevents prove to be useful biostratigraphic markers.

Referencces :
Antunes, R.L., 1997. Introdução ao estudo dos nanofósseis calcários. Instituto de Geociências, Universidade Federal do Rio de Janeiro, 115 pp., Rio de Janeiro.
Antunes, R.L., in press. Biozonas de nanofósseis do Cretáceo da margem continental brasileira: problemas e possíveis soluç›es. Boletim de Geociências da Petrobras, Rio de Janeiro.
Oliveira, L.C.V., 1997. Arcabouço estratigráfico do Albo-Maastrichtiano da bacia de Campos: um estudo com base em nanofósseis calcários e suas relaç›es com marcos elétricos-estratigráficos e a estratigrafia química. Dissertação de Mestrado, Universidade Federal do Rio Grande do Sul, Curso de Pós-Graduação em Geociências, 212 pp., Porto Alegre.
Oliveira, L.C.V. & Costa, S.O., 1997. Proposal of new boistratigraphic units on calcareous nannofossils for the Maastrichtian of the Santos Basin. Anais da Academia Brasileira de Ciências, Vol. 69 (1), pp. 37-58, Rio de Janeiro.
Tröelsen, J.C. & Quadros, L.P. de, 1971. Distribuição bioestratigráfica dos nanofósseis em sedimentos marinhos (Aptiano-Mioceno) do Brasil. Anais da Academia Brasileira de Ciências, Vol. 43 (Suplemento), pp. 577-609, Rio de Janeiro.

Mitsuru Arai & Eduardo A.M. Koutsoukos
Petrobras-Cenpes/Divex/Sebipe, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil. (E-mail: arai@cenpes.petrobras.com.br/ koutsoukos@cenpes.petrobras.com.br)

Foraminiferal organic linings (palynoforaminifera) that appear in palynological preparations have been largely ignored or underused by most paleontologists, although some authors have emphasized their potential applicability in biostratigraphy and paleoecology. Palynological analyses of the upper part of the Macaé Formation (Campos Basin) reveal the importance of palynoforaminifera as a biostratigraphical and paleoecological tool.
Palynoforaminifer usefulness was demonstrated by the following aspects:
1) their occurrence is usually more regular and easily detected than that of calcareous foraminifera;
2) they are recoverable even from very indurated/cemented sedimentary rocks;
3) they constitute an additional group to be considered in the overall improvement of palynological characterization;
4) they present a peculiar environmental behavior in the marine realm;
5) they may be present even under incipient marine conditions;
6) in some marine sequences, they may outnumber dinoflagellates and terrestrial palynomorphs (pollen grains and spores).
In the Vraconian of the Campos Basin, the frequency ratio between palynoforaminifera and dinoflagellates has been a very useful tool in characterizing the different units of petroleum reservoir and associated rocks, providing biostratigraphical data to the improvement of high-resolution stratigraphy.
In addition, because some palynoforaminifer morphologies so closely resemble those of calcareous foraminifera, it is possible to establish the relation between some palynoforaminifera and foraminiferal genera. For example, in the studied section, a biserial type is probably related to Heterohelix moremani, and a trochospiral type is probably related to Ticinella cf. primula. This represents an indisputable record of planktonic foraminifera in the form of organic linings, whose existence has been long in debate. Furthermore, these occurrences are consistent with the Vraconian age determined by dinoflagellates, calcareous nannofossils and calcareous foraminifera. Improvements in the knowledge of relationships between morphological types of linings and formal foraminiferal taxa may result in greater accuracity of the biostratigraphical and paleoecological applications of palynoforaminifera.

Paleolimnological significance of ostracode assemblages: example from the Aratœ local stage (Lower retaceous) of the Recôncavo Basin, NE Brazil

Jarbas Vicente Poley GUZZO - Petrobras-Cenpes/Divex/Sebipe, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil. (E-mail: guzzo@cenpes.petrobras.com.br)

Paleoecological analyses of lacustrine strata using ostracodes are deficient in actualistic models for the occurrence and distribution of these microfossils in large lakes. For most of studies, where examples from the Quaternary are largely predominant, a set of environmental parameters is usually related to an especific faunal modification. Variations in bathymetry, temperature, pH, oxygen levels, nutrients and chemical characteristics of the waters are generally pointed out as the controlling factors. Many of those parameters are interdependent variables, frequently grouped and associated to paleoclimatic changes.
An itegrated aproach of sedimentological, geochemical (oxygen and carbon isotopes, TOC and Rock-Eval pyrolysis) and paleontological (ostracodes and palynology) data from a cored interval (28 meters long) of the Pojuca Formation (Recôncavo Basin) allowed to recognize the paleolimnological significance of facies successions and to evaluate the climate control on lacustrine sedimentation and on ostracode assemblages. Climatic changes appears to modify simultaneously lake level, sediment supply and bottom oxygen levels.
It is suggested that the occurrence, preservation and structure of the ostracode assemblages are mainly influenced by bottom-water oxygen levels. Oxygenated bottom lake waters supported abundant, diverse, well-preserved and ornamented ostracode faunas. Intervals with indication of low bottom-water oxygen levels yielded a distinctive impoverished fauna of smooth and thin-shelled ostracodes. Thaphonomic features, notably cement-filling of the ostracode carapaces, also distinguished both assemblages: calcite filled carapaces of the oxigenated lake bottom assemblages, while assemblages adaptated to low oxygem levels shown extensive pyritization. Stratigraphicaly intermediate mixed assemblages, with both cements (calcite and pyrite), were interpreted as time-averaging assemblages adaptated to different bottom conditions and revealing the cumulative nature of the fossiliferous record.
The set of stratigraphic data indicates the water column circulation/stratification events, related to climatic changes, of the Reconcavo paleolake, as the main controlling factor of the observed ostracode successions. Paleobathymetry seems to play a secondary role.

Campanian macrofaunas and depositional environments of the Calumbi Formmation, Sergipe-Alagoas Basin, Brazil

Wagner Souza LIMA

Curso de Pós-graduação em Paleontologia e Estratigrafia-UFRJ / PETROBRAS-E&P SEAL-GEXP-GEINT. Rua Acre, 2504, Aracaju, Sergipe, Brazil. (E-mail: wagnersl@ep-seal.petrobras.com.br)

The Sergipe-Alagoas Basin, located in the northeastern Brazil, represents one of a series of basins created by the South Atlantic opening during Mesozoic. It has one of the most complete stratigraphic records among the Brazilian marginal basins. This fact has attracted foreign travellers and researchers since late eighteenth century. Petroleum prospection in the last three decades has provided a considerable increment on the geological knowledge of this region.
The effective open marine sequences exposed on surface ranges in age from Upper Aptian to probably Lower Maastrichtian. They are represented by the Riachuelo, Cotinguiba and Calumbi formations. Biostratigraphic studies were done mainly with the Riachuelo and Cotinguiba formations. The Cenomanian-Coniacian section has been particularly well studied, with a refined zoning based on ammonites. This is in part consequence of the good exposure and abundance of outcrops of these units.
The Calumbi Formation strata ranges on surface from Campanian to lower Maastrichtian. They were deposited unconformably over the carbonatic Cotinguiba ramp. The Calumbi Formation outcrops are rare and poorly preserved, usually covered by pliocenic sediments from the Barreiras Formation or recent deposits. Studies exclusively dedicated to the Calumbi section were done as earlier as 1940, when inoceramids found in the type-locality allowed the first trustful dating, considered as maastrichtian. However during the last five decades, except for the subsurface studies related to petroleum prospecting, little has been done.
Considering the absence of a significant exposed section and the unfavourable preservation of the outcrops, it is almost impossible to establish a biostratigraphic zoning for the Calumbi Formation. The recent collection of an interesting ammonite fauna associated with other abundant macrofossils encourage the creation of a project aiming at the detailed macrofauna survey. This could help to better characterise the depositional environments and the stratigraphic and paleoecologic relationships of this campanian-maastrichtian section. This project is part of a M.Sc. dissertation, presently being developed at the Universidade Federal do Rio de Janeiro.

Calcareous nannoplankton as an indicator of sea - level changes in the upper Campanian - lower Maastrichtian in the Campos basin (SE Brazil)

Luiz Carlos Veiga de OLIVEIRA - Petrobras-Cenpes/Divex/Sebipe, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil. (E-mail:lcveiga@cenpes.petrobras.com.br)

Multivariate analysis was used on the nannofossils from one 18 m upper Campanian-lower Maastrichtian core to understand better the relationship between the different species. Multiple regression helped to the determine the best counting method. Watznaueria barnesae and Micula decussata dominate the fossil assemblage and have inverse abundances to each other. Both were opportunistic species in competition for nutrients.

Q mode factorial analysis (57 samples, 19 variables) was applied to the same upper Campanian - lower Maastrichtian core and shows that two factors explain 99,2% of the total variance of the microfossil assemblage. The first factor represents 83,6% of the total variance and the second factor only 15,6%. The first is associated with Watznaueria barnesae, Cribrosphaerella ehrenbergii and Stradneria crenulata, which represent the original population of nannoplankton, while the second factor is associated with Micula decussata, which is believed to represent the effect of solution at the sediment-water interface. Both factors were used to developed a dissolution-sea level curve for nannofossils. This curve, when combined with oxygen and carbon isotopes, clearly shows that higher dissolution occurred when d18O, d13C and TOC all had lower values during late Campanian-early Maastrichtian times. These correlations indicate a strong link between high sea levels, high temperatures and lesser amount of continental organic debris.

Maria Helena ZUCON - Universidade Federal de Sergipe/Depatamento de Biologia/Laboratório de Paleontologia - Aracaju-SE, Brazil.

A regional project meeting organized by the Project Leaders was held at the Geologisch-Paläontologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany, on 2 September 1997. The meeting was a forum for scientific exchange between project participants from Europe and its immediate surroundings (e.g., northern Africa and Middle East).
The joint meeting was attended by thity four (34) SAMC participants from 11 countries (Argentina, Belgium, Brazil, Egypt, France, Germany, Italy, Russia, UK, USA, Venezuela). Thirteen oral communications and ten posters were presented. In addition, several contributions to the subsequently held Second European Meeting on the Palaeontology and Stratigraphy of South America on 3 September (co-organized by P. Bengtson) were of direct or indirect interest to Project 381.
A project working-group was established for dealing with the contruction of palaeogeographical and palaeoclimatical maps for the continental Mesozoic sequences, to be coordinated by Dr. Antonio J. V. Garcia of UNISINOS (e-mail: GARCIA@dgeo.unisinos.tche.br).

Manuscripts of project-related papers presented at both meetings will be collected in a special thematic issue of the proceedings.

Lower Cenomanian ammonites from the Sergipe Basin, Brazil

Suzana BENGTSON - Geologisch-Paläontologisches Institut, Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany.

A diverse fauna of lower Cenomanian ammonites is described from the Sergipe Basin in north-eastern Brazil (Bengtson 1983). The material derives from the base of the Cenomanian-Coniacian Cotinguiba Formation exposed at Itaporanga (Fig. 1). This locality is of particular importance, as it represents the only known outcrop of ammonite-bearing lower Cenomanian rocks on the western margin of the South Atlantic. The fauna has a dominantly Tethyan character and shows close palaeobiogeographic relationships with the Texas-Mexico region, notably through the common occurrence of Graysonites lozoi Young, 1958, and through a specimen of Forbesiceras brundrettei (Young, 1958). There are also significant ties with southern and western Africa and Algeria-Tunisia, e.g. through Sharpeiceras vohipalense Collignon, 1964, Sharpeiceras laticlavium nigeriense Zaborski, 1985, and abundant Stoliczkaia (Shumarinaia) africana Pervinquière, 1907. A conspicuous, common element is the elsewhere poorly represented Hypoturrilites betaitraensis Klinger & Kennedy, 1978, which through paedomorphosis provides an evolutionary link between Mariella and Hypoturrilites. Other taxa include Puzosia (Anapuzosia) dibleyi (Spath, 1922), Tetragonites jurinianus (Pictet, 1847) and Anagaudryceras madraspatanum (Stoliczka, 1865). In addition, Phylloceras (Hypophylloceras) seresitense Pervinquière, 1907, S. (Lamnayella) cf. tetragona Neumayr, 1875, S. (L.) cf. crotaloides Stoliczka, 1864, Paracalycoceras wiestii Sharpe, 1857, and Sharpeiceras florencae Spath, 1925, occur but are rare. The fauna is referred to the Mantelliceras mantelli "Standard Zone", although the diagnostic genus Mantelliceras appears to be missing in Brazil.

References :
Bengtson, P., 1983. The Cenomanian-Coniacian of the Sergipe Basin, Brazil. Fossils and Strata, 12, 1-78, 1 map.
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, 125, 241-262.

E. BRACCINI¹, C. N. DENISON², J. R. SCHEEVEL³, P. JERONIMO⁴, P. ORSOLINI⁵ and V. BARLETTA⁶
1 Elf Aquitaine Production, Pau, France; e-mail: Braccini-Eric-pau@elf-p.fr
2 Chevron Overseas Petroleum, San Ramon, USA
3 Chevron Petroleum Technology Co., La Habra, USA
4 Sonangol, Luanda, Angola
5 Elf Exploration Angola, Luanda, Angola
6 Agip Angola, Luanda, Angola

The Pre-Salt sedimentary section of Cabinda, Angola, is located in the lower Congo Basin. The stratigraphic section consists of lacustrine siliciclastics and carbonates that predate the extensive mid-Aptian Loeme Salt. Over 500 MMBO of recoverable reserves have been proven in Pre-Salt objectives of offshore Cabinda, Area A, between 1967 and 1983. Production is from lacustrine siliciclastic and carbonate reservoirs.
A year-long comprehensive re-evaluation of Cabinda Pre-Salt stratigraphy, undertaken by the Cabinda Association (Sonangol, Chevron, Elf, Agip), was completed in June 1996. This re-evaluation used well log data from all 190 onshore and offshore wells with Pre-Salt penetrations. New regional interpretations were made from high quality 3D seismic data. Existing core descriptions were reviewed and revised, and more than 2500 ft of core was described and interpreted anew.
Biostratigraphic data, involving palynomorphs and ostracodes, was generated for 34 wells, providing a level of biozonation resolution that was essential for the stratigraphic revisions discussed here. A combination of biostratigraphic and lithostratigraphic data with seismic and well logs has been used to define a new tectono-stratigraphic framework.
The Pre-Salt tectono-stratigraphic framework can be briefly described as follows (Fig. 1):
The lower laterally continuous sandy unit of the Lucula Formation (Lucula sensu stricto) was deposited during the early Neocomian (NE1 to NE2) in a slowly subsiding setting (incipient rift phase). The upper limit is a regional unconformity interpreted as the onset of the active rift phase during the middle Neocomian (NE2).
The Lower Bucomazi and Erva Formations are time equivalent. Their upper limit is a regional unconformity interpreted as marking the end of high amplitude vertical movements in this part of the basin (BA1 relaxation phase). The Lower Bucomazi sands are laterally discontinuous and are in part reworked from the previous Neocomian sandstones. They can overlie the Lucula sensu stricto.
The Middle (organic) Bucomazi Formation post-dates the active rift phase. It was deposited during a regional lake transgression on a flattened rift topography during the later part of BA1.
The Upper Bucomazi Formation does not show any major change in depositional or tectonic style from the Middle Bucomazi.
Toca carbonates are laterally equivalent to the Middle and Upper Bucomazi formations. They were deposited throughout middle and late Barremian time.
The upper Barremian Dentale Formation was deposited on the western edge of Area A. Increased terrigenous input recorded by this deposit probably marks the beginning of the next phase of active rifting on the Cabinda margin.
A new phase of rift extension occurred during the latest Barremian and middle Aptian (BA4 to AP3) with selective reactivation of previous fault blocks and development of a major regional unconformity.
The middle Aptian (AP3) Chela Formation is a post-tectonic transgressive sequence. Its upper part is transitional to the upper Aptian (AP4) Loeme Formation evaporites.

J.A. CRAME -British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB30ET, UK. E-mail: jacr@pcmail.nerc-bas.ac.uk

Recent stratigraphical correlations have established that a total thickness of more than 1400 m of Maastrichtian strata may be present within the James Ross Basin, Antarctica. This comprises a monotonous sequence of essentially fine-grained, richly fossiliferous clastic sediments that are themselves part of a major Late Cretaceous shallow-marine succession (the Marambio Group). Macro- and microfossil correlations have permitted regional correlations of the Antarctic Maastrichtian, and a programme of strontium isotope dating is underway to attempt global correlation with the standard Northern Hemisphere sections. This extensive sequence of latest Cretaceous strata is also providing an invaluable opportunity to investigate palaeoenvironmental and palaeobiological phenomena leading up to the mass extinction event at the K-T boundary. Already, there are indications of a significant phase of Maastrichtian cooling and the early extinction of a number of key marine invertebrate taxa.

Dimas Dias-Brito - UNESP - Universidade Estadual Paulista at Rio Claro, Departamento de Geologia Sedimentar, IGCE, C.P. 178 - CEP 13506-900 - Rio Claro - SP, Brazil. E-mail: dimasdb@caviar.igce.unesp.br

This study deals with the Cretaceous pelagic calcispheres Pithonella sphaerica, P. ovalis, P. Trejoi, P. perlonga and Boneto-cardiella conoidea of the Subfamily Pithonelloideae sensu Keupp 1987 (calcareous dinoflagellate cysts). This stratigraphy, palaeobiogeography and palaeoecology are presented, including a significative amount of new data from the western South Atlantic Ocean. The widely dispersed literature on this subfamily, whose components are traditionally called calcisphaerulidis, is reviewed. Pithonelloids are of limited use as biostratigrapical markers for the purposes of a fine subdivision of the Cretaceous sequences. However, when combined with other biostratigraphical data, pithonelloid information can be useful for refining the stratigraphy of carbonates sequences. Ther vertical quantitative variation has a good potential for application in event stratigraphy. Pithonelloids were opportunistic thermophilic organisms that inhabited warm, saline and CaCO3-rich surface waters of epicontinental and marginal seas. Pithonelloid-rich accumulations are associated with fine-grained carbonates deposited in deep shelf to shallow bathyal environments. They appear to have flourished in changing environments under the influence of upwelling. Therefore, they are useful palaeoceanographical tools for identifying Cretaceous Tethyan open-sea carbonate ecosystems. They reached their acme simultaneously all over the world in late Albian to Conician time, during the most important thalassocratic episode of the Mesozoic-Cenozoic interval. In post-Coniacian times, the subfamily declined progressively accompanying global changes in the Cretaceous oceanic world (decrease in salinity and temperature of marine surface waters and/or significant reduction of shelf areas).
The global distribution of Pithonelloideae defines a Tethyan realm occupying both hemispheres, approximately between latitudes 40¡ N and 40¡ S, in the Albian-Turonian interval. During the late Aptian-Albian, this Megatethys Ocean included the northern part of the South Atlantic, north of the São Paulo-Walvis Ridge. This South Atlantic Tethyan carbonate gulf had its open sea waters inhabited by other typical thermophilic organisms, including stomiosphaerids, cadosinids, calpionellids (colomiellids), favusellids, nannoconids, microcalamoidids, and stemless (planktonic ?) crinoids (roveacrinids). On the other hand, shallow sea-floor areas were occupied by cyanobacteria, which produced oncoidal packstones and grainstones commoly associtated with colitic carbonate deposits. In these shallow waters, high temperatures and hypersalinity excluded coral and rudistid reefs as well as large foraminifera such as orbitolinids, discyclinids and alveolinids. This Tethyan South Atlantic lost most of its distinctive character in the latest Albian, a time in which the entire South Atlantic experienced radical oceanographical changes, probably involving the complete submersion of the São Paulo-Walvis Ridge.

Dimas DIAS-BRITO1 & Bruno FERRÉ2

1 UNESP - Universidade Estadual Paulista at Rio Claro - Geologia Sedimentar CP178, CEP 13506-900, Rio Claro-SP, Brazil; e-mail: dimasdb@caviar.igce.unesp.br
2 Laboratoire de Geologie, Université d'Angers, 2 Boulevard Lavoisier, F-49045 Angers Cedex, France; e-mail: ferre@univ-angers.fr

The Santos Basin is an Atlantic-type passive marginal basin on the continental shelf off southeastern Brazil. The basin is totally submersed and, as its counterpart on the other side of the South Atlantic, it is directly related to the rupture of the African-South American plate. From the base to the top its sedimentary record comprises three main tectonic-sedimentary phases: Barremian to early? Aptian fluvial-lacustrine deposits (rift phase), Aptian evaporites (transitional proto-marine phase), and late Aptian-early Albian to Recent marine sediments (drift phase). From the late? Aptian to late Albian, the basin was characterized by extensive tropical carbonate sedimentation. In the shallow platform areas, oolitic-oncolitic-peloidal carbonates were formed, whereas in the open sea there was extensive accumulation of calcimudstones and wackestones. The carbonate sedimentation was interrupted by the end of the Albian. From the Cenomanian to the Maastrichtian, the Santos Basin was subjected to heavy siliciclastic deposition.
Microfacies analysis of Albian open-marine fine-grained carbonates from borehole 1-SP-6 in the Santos Basin has demonstrated an unusual fossil assemblage for the Brazilian continental margin (Dias-Brito, 1994). Within an early Albian wackestone sequence (core 7, 5486.7-5495 m) there occur fragments of stemless crinoids, calpionellids (Colomiella recta, C. mexicana), radiolarians, favusellids, hedbergellids, calcisphaerulids and buliminids. This micritic rock is dotted with authigenic pyrite and contains a high quantity of detrital quartz as silt to very fine sand. This unusual deposit is interpreted as a result of an allochtonous accumulation in a deep-neritic environment (Dias-Brito, 1995). The age assignment is based on the co-occurrence of C. recta and C. mexicana, as also observed in the Gulf of Mexico and in the West Carpathians, where this assemblage identifies the lower portion of the Colomiella Zone and indicates an early Albian age, very close to the Aptian-Albian boundary (Borza, 1984; McNulty, 1985).
Besides common undetermined roveacrinidal remains (so-called "saccocomid-like cross-sections") the only determinable cross-sections are thecal plates of Poecilocrinus dispandus elongatus Peck, 1943. This species is only known from its original material from the Weno Formation in Texas (Peck, 1943) and additional material from coeval rocks of Texas (Rasmussen, 1961). The Brazilian material thus extends its record to at least the early Albian and also geographically farther south. It is not only the earliest representative of the family Roveacrinidae in Brazil (for areview, see Ferré et al. , this volume) but also for the whole South Atlantic, as the Angolan assemblages are of late Albian age (Ferré and Granier, this volume). If one considers the original site of dispersal from the location of the earliest representative, i. e. from the Hauterivian deposits of Busot (Alicante, Spain; Ferré & Granier, in preparation) and their Albian palaeogeographical distribution (Ferré et al. , in prep.), the Roveacrinidae inhabited the whole western Tethys, as did their two sister families Somphocrinidae (Kristan-Tollmann, 1970) and Saccocomidae.
The fact that these stemless crinoids are Tethyan in origin is another evidence of warm-water influence during Aptian-Albian times into the northern part of the South Atlantic, from the Walvis-São Paulo Ridge northwards. This mid-Cretaceous long and narrow gulf, with the Santos Basin in its southernmost portion, has been termed "the Tethyan South Atlantic", as its open marine water mass was inhabited by typical Tethyan planktonic organisms like calpionellids, nannoconids, favusellids, calcisphaerulids and roveacrinid broods (Dias-Brito, 1994, 1995).
References :
Borza, K., 1984. The Upper Jurassic-Lower Cretaceous parabiostratigraphic scale on the basis of Tintinninae, Cadosinae, Stomiosphaerudiae, Calcisphaerulidae, and other microfossils from the West Carpathians. Geologia Carpathica, 35 :5, 539-550.
Dias-Brito, D., 1994. Comparação dos carbonatos pelgicos do Cretáceo mdio da Margem Atl‰ntica Brasileira com os do Golfo do México: novas evidências do Tétis Sul-Atlantiano. Boletim do 3¼ Simpósio sobre o Cretáceo do Brasil, UNESP, Rio Claro-SP , 11-18.
Dias-Brito, D., 1995. Calcisferas e microfcies em rochas carbonticas pelgicas mesocretceas. Doctorate Thesis, UFRGS, Porto Alegre, Brazil, 688 pp.
Kristan-Tollman, E., 1970. Die Osteokrinusfazies, ein Leithorizont von Schwebcrinoiden im Oberladin-Unterkarn der Tethys. Erd. Kohl. , 23 , 781-789.
McNulty, D., 1985. Micropaleontological stratigraphic framework for the Cretaceous black lime wackestone-mudstone facies of the Gulf of Mexico. Annual Research Conference of the Gulf Coast, 4. Tulsa, Proceedings, SEPM, 1176-1191.
Peck, R. E., 1943. Lower Cretaceous crinoids from Texas. J. Palaeont., 22 , 451-475.
Rasmussen, H. W., 1961. A monograph on the Cretaceous Crinoidea. Biol. Skr., Kongel. Danske Vidensk. Selsk, 12 , 428 pp.
The research was supported by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo).

Gerson FAUTH1, Eduardo A. M. KOUTSOUKOS2 & Peter BENGTSON 1

1 Geologisch-Palontologisches Institut, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany; e-mail: gfauth@ix.urz.uni-heidelberg.de
2 Petrobras-Cenpes-Divex-Sebipe, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil; e-mail: koutsoukos@cenpes.petrobras.com.br

The Cretaceous-Tertiary (K-T) boundary beds are well exposed in the Poty Quarry, Pernambuco-Paraba Basin, northeastern Brazil. This section is arguably the most complete marine K-T boundary section at low latitudes of the Atlantic Ocean and has recently been the target of intense discussions, with conflicting arguments presented about the precise dating and positioning of the boundary and depositional nature of its related beds. The Gramame Formation and lowermost Maria Farinha Formation, of latest Maastrichtian age, contain a rich ostracode microfauna. A comprehensive taxonomic study of the ostracodes has been carried out on samples collected from closely spaced intervals of an uppermost Maastrichtian cored sequence at Poty. Abundant specimens of the genus Cytherella are recorded together with subordinate representatives of the genera Cytheropteron, Bairdia, Cythereis and Brachycythere. A preliminary palaeoenvironmental interpretation is presented.

Bruno FERRÉ1 & Peter BENGTSON2

1 Laboratoire de Géologie, Université d'Angers, 2 Boulevard Lavoisier, F-49045 Angers Cedex, France; e-mail: ferre@univ-angers.fr
2 Geologisch-Paläontologisches Institut, Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany; e-mail: Peter.Bengtson@urz.uni-heidelberg.de

During work on a biostratigraphic framework for the middle Cretaceous of the Sergipe Basin in north-eastern Brazil (Bengtson, 1983), microfacies analysis revealed the existence of common saccocomid-like cross-sections (Bengtson & Berthou, 1983; Berthou and Bengtson, 1988). These were subsequently identified as parts of roveacrinids, a poorly known group of pelagic microcrinoids (Ferré and Berthou, 1994). However, until now, no complete, articulated specimens have been known, which could render support to the assignment of these cross-sections to the family Roveacrinidae.
Roveacrinids are stemless pelagic microcrinoids, devoid of any anchoring device. Besides the roveacrinids, the saccocomid Applinocrinus cretaceus (Bather) is the only other Cretaceous representative of the order Roveacrinida (Peck, 1973). Whereas the morphology of saccocomids is well known from Jurassic specimens, the anatomy of roveacrinids could until now only be inferred from isolated plates (Rasmussen, 1961) and articulated brachials (Scott et al., 1977). Recently, Ferré & Berthou (1994) compiled additional data into a morphological reconstruction. To this can now be added the information derived from a complete articulated specimen of Roveacrinus spinosus Peck, 1943, from the upper Turonian of Sergipe, Brazil.
As previously evidenced by loose plates, the theca (or calyx) consists of two sets of five plates, of which the basals form the dorsal cavity and the radials the ventral cavity. The ornamentation of the radials expands downwards onto the basals and rivets the ventral bowl. The fulcral articular facet of each radial bears a dichotomous arm which branches at the second secundibrach. The overall shape is comatulid-like, as suggested by Ferre and Berthou (1994), but with more incurvate arms. The arms raise a basket-like feeding net reinforced by pinnular outgrowths. This adaptation illustrates their poor taxonomic value, if one accepts that spinose brachials do not occur only in R. spinosus. Unfortunately, the ventral resting position of the specimen studied hampers observation of the cryptodicyclic nature of the theca reported by Schneider (1987) from related species.
Besides the taphonomic setting of the specimen, the morphology of the arms and their thecal connection exclude a planktic mode of life, as suggested by Milsom (1989). Adult roveacrinids must have been able to swim actively, albeit for a short period of time, in search for food or to escape from predators. As in Recent echinoderms, surface currents carried the broods as zooplankton, which enhanced their geographic dispersal. The thecal architecture reflects this transition in mode of life, as the basals appear vestigial and in later ontogenetic phases become covered by the radials. Ontogenetic analysis of the thecal architecture may provide a key to the reconstruction of the mode of sinking, with the ratio between the ventral and dorsal cavities as a possible bathymetric indicator.
Roveacrinus spinosus was originally recorded from the Albian-Cenomanian Grayson Formation of Texas (Peck, 1943). The Brazilian specimen extends its stratigraphical record to the upper Turonian, as well as its geographical distribution significantly farther to the south. The information provided by this single, articulated specimen adds support for the use of Roveacrinidae in the Cretaceous biostratigraphy of the Brazilian and adjacent South Atlantic basins, as suggested by Berthou & Bengtson (1988) and Ferré et al. (1996). Besides the obvious regional applications, the Brazilian occurrences also contribute to a more reliable application of roveacrinidal microfacies on a global scale.

References :
Bengtson, P., 1983. The Cenomanian-Coniacian of the Sergipe Basin, Brazil. Fossils and Strata, 12, 1-78.
Bengtson, P. & Berthou, P.-Y., 1983. Microfossiles et Echinodermes incertae sedis des dépôts albiens à coniaciens du bassin de Sergipe-Alagoas, Brésil. Cahiers de Micropalontologie, 1982:3 [for 1982], 13-22.
Berthou, P.-Y. & Bengtson, P., 1988. Stratigraphic correlation by microfacies of the Cenomanian-Coniacian of the Sergipe Basin, Brazil. Fossils and Strata, 21, 1-88.
Ferré, B. & Berthou, P.-Y., 1994. Roveacrinidal remains from the Cotinguiba Formation (Cenomanian-Turonian) of the Sergipe Basin (NE-Brazil). Acta Geologica Leopoldensia, 17:1, 299-313.
Ferré, B., Berthou, P.-Y. & Bengtson, P., 1996. Apport des Crinoides rovacrinids " la stratigraphie du Crétacé moyen du bassin de Sergipe (Nordeste, Brésil). Strata, Série 1, 8, 101-103.
Milsom, C., 1989. In search of truly pelagic crinoids. Palaeontological Association, Annual Conference, Abstracts, p. 13.
Peck, R. E., 1943. Lower Cretaceous crinoids from Texas. Journal of Paleontology, 22, 451-475.
Peck, R. E., 1973. Applinocrinus, a new genus of Cretaceous microcrinoids and its distribution in North America. Journal of Paleontology, 47, 94-100.
Rasmussen, H. W., 1961. A monograph on the Cretaceous Crinoidea. Biologiske Skrifter, Kongelige Danske Videnskabernes Selskab, 12:1, 1-428, Pls. 1-60.
Schneider, L. H., 1987. Zur Kelchmorphologie und Systematik der Roveacrininae Peck, 1943 (Crinoidea, Oberkreide). Neues Jahrbuch fr Geologie und Palontologie, Abhandlungen, 175, 181-206.
Scott, R. W., Root, S. A., Tenery, J. H. & Nestell, M., 1977. Morphology of the Cretaceous microcrinoid Poecilocrinus (Roveacrinidae). Journal of Paleontology, 51, 343-349.

Bruno FERRÉ1 & Bruno GRANIER2

1 Laboratoire de Géologie, Université d'Angers, 2 Boulevard Lavoisier, F-49045 Angers Cedex, France; e-mail: ferre@univ-angers.fr
2 TOTAL Exploration Production, Scientific and Technical Centre, Domaine de Beauplan, Route de Versailles, F-78470 Saint-Rémy-lès-Chevreuse, France. Present address: PPP-Geology N4, ADMA-OPCO, P.O. Box 303, Abu Dhabi, United Arab Emirates.

The Congo Basin is partitioned in three subbasins by the Mayumba and the Ambrizete spurs, isolating the Angolan subbasin from the Gabon and Kwanza basins. With respect to oil-field exploitation, the Angolan basin is subdivided in several blocks. South to the River Zaire, offshore Block 2 displays Cretaceous to Tertiary sedimentary deposits. There Well BAGRE-1 cored the Albian-Cenomanian transgressive Pinda Formation, which is composed mainly of mudstones-wackestones, dolosparites and dolomicrosparites (former oolitic and bioclastic grainstones). The Pinda Formation was subjected to late dolomitization that obliterated the original sedimentary structures. Microfacies study evidenced prominent dolomitized echinodermal wackestones-packstones, the abundance of which was emphasized by the absence and-or scarcity of stratigraphical markers. Isolated crinoidal fragments appeared most promisin, with two facies events found widespread across the basin. These facies are similar to the roveacrinidal facies described from the Sergipe Basin (NE Brazil: Bengtson & Berthou, 1983; Berthou & Bengtson, 1988; Ferré & Berthou, 1994). Roveacrinids are stemless pelagic microcrinoids, devoid of any anchoring device. Their specific determination is based on the morphology of isolated theca, with the brachial plates only indicative of the family level. Cross-sections are easily confused with those of saccocomids or even ophiuroids. Specific determination of brachials is nearly impossible, but their abundance can nevertheless be used in quantitative stratigraphy and in microfacies study. Our current work focused primarily on thin section orientation. By means of geometrical reconstructions, we were able to recognize within the microfacies assemblages the following species: Roveacrinus communis Douglas, 1908, R. cf. communis Douglas, 1908, R. aff. geinitzi Schneider, 1989, R. pyramidalis Peck, 1943, R. sp. and undetermined plates exclusive to the family Roveacrinidae. Despite the scarcity of biostratigraphical studies, the occurrence of R. pyramidalis and R. communis (gracile morph) suggests a late Albian age (Peck, 1943; Rasmussen, 1961; Destombes, 1984). This dating agrees with the occurrence of the planktic foraminiferid Favusella washitensis (Carsey). Compared to former datings, these results are more precise and shed new light on the stratigraphical importance of the roveacrinids. Besides taxonomy, their quantitative study defined a Cretaceous roveacrinidal microfacies, which is very similar to the Triassic facies described by Kristan-Tollmann (1970). This facies is characteristic of transgressive outer-shelf to upper-slope deposits. In addition to their stratigraphical importance, the Angolan assemblages are the southernmost and also among the oldest ones recorded. Their extreme geographical position, far from the Tethyan realm, poses questions about their mode of dispersal. Their presence in Angola during the late Albian is in accordance with the existence of a seaway through the Gulf of Guinea (e.g., Berthou et al., 1991; Granier et al., 1991; Bengtson & Koutsoukos, 1992). Finally their thorough stratigraphical study appears particularly interesting not only for trans-Atlantic correlations but also on a worldwide scale. They would provide an additional first-order biostratigraphical tool for large-scale high-resolution correlations.

References :
Bengtson, P. & Koutsoukos, E. A. M., 1992. Ammonite and foraminiferal dating of the first marine connection between the central and South Atlantic. In: Géologie Africaine (Ed. by R. Curnelle), p. 403. Bull. Cent. Rech. Explor.-Prod. Elf Aquitaine, Mém., 13.
Bengtson, P. & Berthou, P.-Y., 1982. Microfossiles et échinodermes incertae sedis des dépôts albiens à coniaciens du bassin de Sergipe-Alagoas, Brésil. Cah. Micropalontologie, 1982: 3 [for 1982], 13-22.
Berthou, P.-Y., Amedro, F. & Brito, I. M., 1991. Révision bibliographique préliminaire ˆ une étude des ammonites de l'Albien (Fm. Riachuelo) du Bassin de Sergipe (Nord Est du Brésil). Geociências, 10, 183-190.
Berthou, P.-Y. & Bengtson, P., 1988. Stratigraphic correlation by microfacies of the Cenomanian-Coniacian of the Sergipe Basin, Brazil. Fossils and Strata, 21, 1-88.
Destombes, J.-P., 1984. Roveacrinidae nouveaux de l'Albien du Bassin de Paris. Bull. trim. Soc. Géol. Normandie, 71, 9-16.
Ferré, B. & Berthou, P.-Y., 1994. Roveacrinidal remains from the Cotinguiba Formation (Cenomanian-Turonian) of the Sergipe Basin (NE-Brazil). Acta Geologica Leopoldensia, 17: 1, 299-313.
Granier B., Berthou, P.-Y. & Fourcade, E., 1991. The Dasycladacean algae from the Cretaceous of the New World. In: Transactions of the 2nd Geological Conference of the GSTT (ed. by K.A. Gillezeau), pp. 178-183. Geol. Soc. Trinidad & Tobago.
Kristan-Tollman, E., 1970. Die Osteokrinusfazies, ein Leithorizont von Schwebcrinoiden im Oberladin-Unterkarn der Tethys. Erd. Kohl., 23, 781-789.
Peck, R. E., 1943. Lower Cretaceous crinoids from Texas. J. Paleont., 22, 451-475.
Rasmussen, H. W., 1961. A monograph on the Cretaceous Crinoidea. Biol. Skr., K. Danske Vidensk. Selskab, 12: 1, 1-428.

The role of roveacrinids in study of the mid-Cretaceous of the Sergipe Basin, north-eastern Brazil

Bruno FERRÉ1, Simone WALTER2 & Peter BENGTSON2

1 Laboratoire de Géologie, Université d'Angers, 2 Boulevard Lavoisier, F-49045 Angers Cedex, France; e-mail: ferre@univ-angers.fr
2 Geologisch-Paläontologisches Institut, Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany; e-mail: be2@ix.urz.uni-heidelberg.de

As part of a comprehensive investigation of the Cenomanian-Coniacian succession of the Sergipe Basin in north-eastern Brazil, microfacies analysis was originally carried out in order to complement the chronostratigraphic framework primarily based on ammonites (Bengtson, 1983). The microfacies work revealed the existence of common and widespread saccocomid-like cross-sections (Bengtson & Berthou, 1983; Berthou & Bengtson, 1988). Study of thin sections of similar microfacies types from coeval beds in the Anglo-Paris Basin (Ferré, 1995) confirmed the roveacrinidal affinity of these constituents in both these basins, representing the Boreal and the South Temperate realms, respectively. Ferré & Berthou (1994) suggested that roveacrinidal remains might provide a new biostratigraphic tool for microfacies correlation. Where the carbonates of the Sergipe Basin are dolomitized, extraction and determination of calcitic microfossils are hampered. However, the magnesian-calcitic roveacrinidal remains are more resistant against dolomitization and commonly constitute the only remaining biological structures, thus offering possibilities for chronostratigraphic correlation where other fossils are scarce or lacking. In addition, since both macrofossils and microfossils occur throughout the Sergipe sequence, there are also potentials for calibrating these occurrences with those of the roveacrinids to arrive at an integrated biostratigraphy for the basin. Microfacies analysis is nowadays a routine procedure in the study of sedimentary rocks and sequences, although microbiofacies work is hampered by the difficulty of identifying fossil fragments. To support these identifications a sound biostratigraphic framework or at least a thoroughly sampled succession is needed. The preliminary results from Sergipe provided significant complementary data for the chronostratigraphic framework as well as stratigraphic and palaeoenvironmental data for the reconstruction of the mid-Cretaceous development of the basin. Thus, roveacrinidal microfacies was shown to be useful for complementary dating on an intrabasinal scale, down to stage or even substage. In addition, these microfacies may also characterize local stage boundaries, such as the Cenomanian-Turonian boundary, where Jefferies (1962) reported several abundance horizons within the Plenus Marls of the Anglo-Paris Basin and Ferré (1995) demonstrated the coincidence of abundance peaks between assemblages of roveacrinids, ostracodes and foraminifers. This ecological coincidence also occurs in the Sergipe Basin and is apparently related to sea-level changes. With respect to palaeoenvironmental conditions, the Cenomanian-Coniacian succession of Sergipe is partly hypoxic. It seems that roveacrinids thrived in such environments, where they frequently developed abundant opportunistic populations. A thorough stratigraphic and palaeoenvironmental survey of the Sergipe sequence is in progress, focusing initially theCenomanian-Turonian transition. Because of discontinuous outcrops and patchy occurrences of diagnostic microfossils, roveacrinidal microbiofacies provides an additional means of chronocorrelation. Although the stratigraphic study of roveacrinids is in its early stage, a distribution chart has been established (Ferré et al., 1996). This scheme is being refined for the Cenomanian-Turonian transition (S. Walter, in preparation) with the aim of extending it to regional or possibly even global applications. Besides providing palaeoenvironmental and palaeogeographic data for the Sergipe Basin, this study is of considerable importance for its immediate bearing on the history of development of the South Atlantic. Furthermore, the worldwide occurrence of roveacrinidal microfacies makes the Brazilian framework a suitable object for the establishment of a reliable chronostratigraphy. The present study will provide a basis for comparisons and correlations with surrounding areas, i.e. the marginal Brazilian basins, the West African basins and South Atlantic ODP-DSDP drill cores. With their relative resistance against dolomitization, their widespread occurrence and their opportunistic behaviour, roveacrinids can be utilized in biostratigraphy either qualitatively (presence"absence patterns) or quantitatively (ecoevent patterns). We emphasize here their application as a natural component of any integrated microfacies study.

References :
Bengtson, P., 1983. The Cenomanian-Coniacian of the Sergipe Basin, Brazil. Fossils and Strata, 12, 1-78.
Bengtson, P. & Berthou, P.-Y., 1983. Microfossiles et échinodermes incertae sedis des dépôts albiens à coniaciens du bassin de Sergipe-Alagoas, Brésil. Cahiers de Micropalontologie, 1982: 3 [for 1982], 13-22.
Berthou, P.-Y. & Bengtson, P., 1988. Stratigraphic correlation by microfacies of the Cenomanian"-Coniacian of the Sergipe Basin, Brazil. Fossils and Strata, 21, 1-88.
Ferré, B., 1995. Incidences des évènements anoxiques sur les microfaunes cénomano-turoniennes du Bassin de Paris. Universit Pierre & Marie Curie, Memoire des Sciences de la Terre , 95-10 , 1-391.
Ferré, B. & Berthou, P.-Y., 1994. Roveacrinidal remains from the Cotinguiba Formation (Cenomanian-Turonian) of the Sergipe Basin (NE-Brazil). Acta Geologica Leopoldensia, 17: 1, 299-313.
Ferré, B., Berthou, P.-Y. & Bengtson, P., 1996. Apport des Crinoides rovacrinids ˆ la stratigraphie du Crétacé moyen du bassin de Sergipe (Nordeste, Brésil). Strata, Série 1, 8 , 101-103.
Jefferies R. P. S., 1962. The palaeoecoogy of the Actinocamax plenus Subzone (lowest Turonian) in the Anglo-Paris Basin. Palaeontology, 4 , 609-647.

Antonio Jorge Vasconcellos GARCIA, çtila Augusto Stock DA ROSA & Karin GOLDBERG

Sedimentary Geology Program, UNISINOS University, Av. UNISINOS, 950, 93022-000 São Leopoldo, RS, Brazil. (E-mail: garcia@dgeo.unisinos.tche.br)

Preservation and abundance of fossils in sedimentary rocks are related to pre- and post-burial taphonomic processes, including: (1) preferential habitat of each species; (2) death environment and time of surface exposure, especially in continental environments; (3) reworking potential (responsible for disarticulation of vertebrate skeletons) and (4) distribution and intensity of diagenetic processes related to decay and replacement of dead organisms. These aspects impose different opportunities and constraints on the preservational features and on paleocommunity reconstruction and evolution analysis. Early Cretaceous pre-rift continental sequences in northeastern Brazil (Rio do Peixe, Araripe, Recôncavo-Tucano and Sergipe-Alagoas basins) and the Late Cretaceous continental deposits of the Bauru Group in the Paraná Basin (Brazil) offer a good opportunity to analyse the different controlling agents. These sequences were deposited in braided fluvial, eolian and lacustrine environments, under semi-arid to arid conditions. Paleoclimatic imprints suggest important differences with respect to potential fossil preservation in the fluvial deposits. In some places, the pre-rift deposits near the northern margin of the paleobasin (Afro-Brazilian Depression, Garcia 1991) contain rare records of a dinosaur fauna that lived near an exuberant forest, the silicified woods of which are found in proximal and middle coarse fluvial deposits of the Misso Velha, Sergi and Serraria formations. At the southern margin of the basin abundant dinosaurs (bones, eggs and teeth) are found with other vertebrates, in middle to distal fluvial deposits of the Bauru Group, in the Paraná Basin.
The continental Cretaceous sequences in Brazil have been studied with a multidisciplinary approach, including paleogeographic, paleoclimatic and paleoecologic reconstructions (Garcia & Wilbert, 1995; Garcia et al., 1996; Goldberg & Garcia, 1996; Goldberg et al., 1996). The petrologic analyses of the host rocks and fossils are intended to reveal the diagenetic and taphonomic conditions during and shortly after deposition. Integration with field evidences has led to a more complete interpretation of the fossil preservational potential.
The main objective of this contribution is to show the significance of an integrated approach to a better understanding of the fossil record of the Cretaceous continental sequences in Brazil.

References :
Garcia, A. J. V., 1991. Paleogeografia do nordeste brasileiro no Jurássico Superior-Cretáceo Inferior. Brazilian Cretaceous Basins Meeting. Rio Claro (SP, Brazil), Geociências-UNESP, 10, 37-56.

Garcia, A. J. V. & Wilbert, A., 1995. Paleogeographic evolution of pre-rift sequence of coastal and interior basins of northeastern Brazil. In: Pangea - Global Environments and Resources (Ed. by A. F. Embry, B. Beauchamp & D. J. Glass), Can. Soc. of Petrol. Geol., Memoir, 17, 123-130.

Garcia, A. J. V., Morad, S., De Ros, L. F. & Al-Aasm, I. S., 1996. Paleogeographic, paleoclimatic and burial-history controls on the diagenetic evolution of Lower Cretaceous Serraria Sandstones in Sergipe-Alagoas Basin, NE Brazil. In: Carbonate diagenesis in sandstones (Ed. by S. Morad), IAS Spec. Public., Oxford, UK.

Goldberg, K. & Garcia, A. J. V., 1996. Stratigraphic correlation and paleoclimatic inferences from diagenetic and taphonomic analysis of Neo-Cretaceous dinosaur bones in Baur Group (Paraná Basin), Brazil. II Reunin sobre Tafonomeda y Fosilizacin - Taphos 96 (Zaragoza, Spain 1996), Proceedings, 135-139.

Goldberg, K., Da Rosa, A. A. S. & Garcia, A. J. V., 1996. Paleobiogeographic considerations on the Juro-Cretaceous of Paraná and northeastern basins, Brazil. In: Géologie de l'Afrique et de l'Atlantique Sud, Compte-rendu des Colloques de Géologie d´Angers, 16-20 juillet 1994 (Ed. by S. Jardiné, I. de Klasz and J.-P. Debenay), Bulletin des Centres de Recherches Exploration-Production Elf-Aquitaine, Mémoire, 16, 373-381.

PDVSA and affiliated Biostratigraphical Committee, Planktonic Foraminifers Working Group: F. A. GALEA-ALVAREZ1 (Coordinator), R. ARNSTEIN1, M. CANACHE2, M. CARRILLO2, H. CARVAJAL2, S. Crespo de CABRERA1, M. FURRER3, G. GIFFUNI3, M. ODEHNAL3, R. PITTELLI3, I. TRUSKOWSKI4, L. de ROMERO5, R. FALCîN6 & W. V. SLITER7

1 Corpoven, S.A., Laboratorio Geológico, Apartado Postal 4326, Puerto La Cruz 6023A, Venezuela; e-mail: gesp33@cpvop3.pdv.com
2 Intevep, S.A., Gerencia de Ciencias de la Tierra, Apartado Postal 76343, Caracas 1070A, Venezuela
3 Lagoven, S.A., Gerencia de Geologa, Apartado Postal 889, Caracas 1010-1, Venezuela
4 Maraven, S.A., Gerencia de Exploracin, Apartado Postal 829, Caracas 1010A, Venezuela
5 Escuela de Ingeniera Geológica, Universidad de Los Andes, Mrida, Venezuela
6 Escuela de Geologa, Minas y Geofsica, Facultad de Ingeniera, Universidad Central de Venezuela, Los Chaguaramos, Caracas, Venezuela
7 U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA

This is the first attempt by the Biostratigraphical Committee to create an integrated biostratigraphy for the Venezuelan Cretaceous. Our work concerns primarily foraminifers, as well as palynomorphs and calcareous nannoplankton.
Surface and subsurface samples were studied from the western and eastern Venezuelan basins. The dominant sediments are indurated marls, hard laminated calcareous black shales, and limestones, from where recovery of individual foraminifers is rare. Consequently, almost all identifications are based on thin section examination. At some stratigraphic levels we matched these identifications with well preserved specimens. The zonation for planktonic foraminifers proposed by Sliter (1989) has proved to be the best for the biostratigraphic zonation of the Venezuelan sedimentary basins.
The main marine pelagic sediments are Late Cretaceous in age and mostly represented by organic-rich facies of the La Luna and Querecual formations. These formations represent the focus of our studies as both are the principal source rocks for hydrocarbons in Venezuela. The Lower Cretaceous is represented by sandstones, shallow-marine carbonates and mixtures of siliciclastics and carbonates ranging in age from ?Hauterivian to Albian, with short pelagic intervals in the Aptian and late Albian Leupoldina cabri (KS 7) and Rotalipora appenninica (KS 16) biozones, respectively.
A regional hiatus was detected in the lower Cenomanian, where the Rotalipora brotzeni (KS17) and Rotalipora reicheli (KS 18) zones are missing. In the eastern basin no other hiatuses have as yet been observed; however, an upper Campanian hiatus is noted in the La Luna Formation of the Mrida Andes Cordillera of western Venezuela. This hiatus is not found in the northern section near the Venezuelan-Colombian border. Differences between the basins are also observed at the K-T boundary. To the west there is a rapid shallowing-upward section, whereas to the east, an outer marine to upper bathyal setting continues up section into the lower Eocene.

References :
Sliter, W. V., 1989. Biostratigraphic zonation for Cretaceous planktonic foraminifers examined in thin section. J . Foram. Research , 19 , 1-19.

M. GAYET1, F. J. MEUNIER2 & C. WERNER3

1 UMR 5565 CNRS, UFR Sciences de la Terre, Université Lyon I, 27 bd du 11 novembre 1918, F-69622 Villeurbanne cedex, France; e-mail: gayet@univ-lyon1.fr
2 URA 1137 CNRS, Laboratoire d'Anatomie Compare, Université D. Diderot, 2 place Jussieu, et Laboratoire d'Ichtyologie, Muséum National d'Histoire Naturelle, F-75232 Paris cedex 05, France
3 Technische Universität Berlin, FSP Geosys, Ackerstrasse 71-76, D-13355 Berlin, Germany

The fourteen species and subspecies of the living Polypteriformes (Polypterus and Erpetoichthys) belong to only one family, the Polypteridae, today limited to Africa. These taxa can be identified, among other diagnostic features, by the presence of several dorsal fins (so-called finlets) including a peculiar spine (pinnula), and vertebrae with neural arches showing special articulation (cupula) for supraneural process. A major diagnostic feature of Polypteriformes is the possession of special 'palaeoniscid' ganoid scales which consist of the three superimposed layers (basal bony plate, dentine and ganoine), but are characterised by a typical plywood-like structure (between dentine and basal plate), unique in this group.
Both fossil and recent Polypteriformes were originally considered to be endemic to Africa, their oldest records being from the Cenomanian of Egypt, Sudan, and Morocco. Some younger remains are also described from the Coniacian-Santonian of Niger, the Miocene of Kenya and Tunisia, the Pliocene of Egypt and Kenya, and the Holocene of Mali. A total of seven fossil genera including sixteen species have been recognized in Africa. In Bolivia, several Maastrichtian (Pajcha Pata, Vila Vila) and early late Paleocene (Tiupampa, Criadero de Loro) localities have yielded polypteriform remains, which have been attributed to two genera, namely Dagetella and Pollia . Taking into account the histology of the scales and the pinnulae, Dagetella belongs to Polypteridae as do the African polypteriforms. Pollia , however , cannot be integrated into this family, due to the characteristic histology of its scales (with the specific plywood-like structure) and the lack of true pinnulae. Therefore, the determination of its family level (incertae sedis) remains open until more specimens are available. Furthermore, it is noteworthy that both South American genera have a peculiar vertebral structure - that is, a close cupula for the articulation of the supraneural process. However, there is no evidence of complete polypteriform vertebra from the Maastrichtian or Paleocene of Africa known at the moment.
Preliminary comparative studies of the fossil South American Polypteriformes indicate that Pollia - in spite of its Maastrichtian-Paleocene record - is more primitive than all other known fossil Polypteriformes. In South America, a Maastrichtian or Paleocene locality in Brazil (Acre), probably belonging to the Bolivian Basin, yielded time-equivalent polypteriform remains. However, there are as yet no older records of this group, for example from the Aptian-Albian sequences of the African Congo-Equatorial Guinea Basin or the Brazilian Ceará Basin.

B. HATHWAY1, A.M. DUANE1, S.P. KELLEY2 & D.J. CANTRILL1

1 British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK; e-mail: b.hathway@bas.ac.uk
2 Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, UK

The upper part of the Upper Jurassic to Lower Cretaceous Byers Group, exposed on Byers Peninsula, at the western end of Livingston Island in the South Shetland Islands, consists of non-marine volcaniclastic strata assigned to the Cerro Negro Formation (CNF; Hathway, 1997). This 1.4-km-thick succession unconformably overlies a similar thickness of marine clastic rocks, and records the expansion of continental arc facies into a major marine basin on the Pacific margin of the Antarctic Peninsula magmatic arc. In addition to its regional stratigraphic and tectonic significance, the CNF is of considerable palaeobotanical interest owing to the presence of a rich, locally well-preserved macroflora. Hernández and Azcrate (1971) and Askin (1983) tentatively assigned this assemblage, and associated palynomorphs, to the Barremian based on similarities to the Baqueró Formation flora of southern Argentina. However, the potential importance of the CNF as a reference section for southern hemisphere terrestrial floras has been limited by the lack of independent age control.
Silicic pyroclastic units close to the base of the CNF have yielded new laser-fusion 40Ar/39Ar ages of 120.3 + 2.2 Ma on plagioclase from one horizon; and 119.4 + 0.6 and 119.1 + 0.8 Ma on biotite and plagioclase from a second horizon. Plagioclase from a welded ignimbrite unit 140 m below the topmost exposed part of the formation has given a 40Ar/39Ar age of 119 + 3 Ma. These dates indicate that the CNF was deposited during a relatively short period in early Aptian times. The implied rate of accumulation, of the order of 1 km-my, is similar to those seen in modern fault-bounded intra-arc basins in Japan and New Zealand.
Antarctic Peninsula palynofloras are known to show a similar chronology of appearances to that observed in Australia (e.g. papers in Duane et al. 1992). The identification of key palynomorph index species has enabled us to correlate what is now probably the best radiometrically dated Mesozoic palynoflora in Antarctica with the palynological zonation proposed for Australia by Helby et al. (1987). Based on this scheme, the consistent presence of Foraminisporis asymmetricus and other accessory palynomorphs in the CNF supports assignment to the Cyclosporites hughesi Zone of early to late Aptian age. However, rare occurrences of Crybelosporites striatus and ?Clavifera triplex indicate that it may be possible to correlate the CNF with the younger, C. striatus or Coptospora paradoxa zones, with Australian age ranges of latest Aptian to early Albian, and early to late Albian, respectively. This would indicate marked intra-Gondwanan heterochroneity of terrestrial palynomorphs: a factor known to affect some index taxa within Australia, and likely to be of even greater importance over larger distances (e.g. Dettmann, 1986).

References :
Askin, R. A., 1983. Tithonian (uppermost Jurassic)-Barremian (Lower Cretaceous) spores, pollen and microplankton from the South Shetland Islands, Antarctica. In: Antarctic Earth Science (Ed. by R. L. Oliver, P. R. James & J. B. Jago), Australian Academy of Science, Canberra and Cambridge University Press, Cambridge, 295-297.

Dettmann, M. E., 1986. Significance of the Cretaceous-Tertiary spore genus Cyatheacidites in tracing the origin and migration of Lophosoria (Filicopsida). Spec. Papers in Palaeontology, 35, 63-94.

Duane, A. M., Pirrie, D. & Riding, J. B. (Eds), 1992. Palynology of the James Ross Island area, Antarctic Peninsula. Antarctic Science, 4, 259-362.

Hathway, B., 1997. Non-marine sedimentation in an Early Cretaceous extensional continental-margin arc, Byers Peninsula, Livingston Island, South Shetland Islands. J. Sedim. Res., 67, 686-697.

Helby, R., Morgan, R. & Partridge, A. D., 1987. A palynological zonation of the Australian Mesozoic. Aust. Assoc. Palaeontol. Mem., 4, 1-94.

Hernández, P. J. & Azcrate, V., 1971. Estudio paleobotanico preliminar sobre restos de una tafoflora de la Peninsula Byers (Cerro Negro), Isla Livingston, Islas Shetlands del Sur, Antartica. Serie Cientfica Instituto Antartico Chileno, 2, 15-50.

Mohamed I. A. IBRAHIM1, Nabil M. ABOUL ELA2 & Suzan E. KHOLEIF 3

1 Department of Geology, Faculty of Science, University of Qatar, P.O. Box 2713, Doha, State of Qatar, Arabian Gulf Region; e-mail: m.ibrahim@qu.edu.qa
2 Geology Department, Faculty of Science, Cairo University, Giza, Egypt
3 Institute of Oceanography and Fisheries, Kayed Bey, Anfooshy, Alexandria, Egypt

The Jurassic to Lower Cretaceous sequence in wells Abu Hammad-1, Q-71-IX and Kabrit-1, north Eastern Desert of Egypt, have yielded palynofacies assemblages of varying composition. Organic petrography allows the identification of seven environmentally-controlled palynofacies within the sequence; source rock potential is also suggested.
Eight formations are studied paleoecologically using spores, pollen grains, dinoflagellate cysts and other particulate organic matter. The lower part of the Rajabiah Formation (Toarcian-Aalenian) was formed in shallow marginal marine or sabkha environment, whereas the upper part of the Rajabiah and the Shusha formations were deposited in shallow marine environment (inner shelf) under warm subtropical climatic conditions. Deposition of the Bir Maghara Formation is believed to have taken place in shallow marine waters of inner to middle shelf depth. The mixed clastic and carbonate sequence of the Khatatba Formation (Bathonian-Callovian) was formed in middle to outer shelf conditions (30-100 m). The Masajid Formation (latest Callovian-Kimmeridgian) is a massive carbonate shale, which was deposited in normal marine conditions of the outer shelf to upper slope (100-600 m). The siliciclastic deposits of the Alam El Bueib Formation (Barremian-Aptian) accumulated in near-shore to inner shelf (<30 m) environment, under arid to semiarid conditions. The Alamein Formation (Aptian) was probably deposited in shallow marine environment of the middle shelf, whereas the clastics of the Kharita Formation (lower Albian) probably formed in inner shelf environment.
Spore-pollen colour is used to discriminate the organic maturation levels and thermal alteration for the studied sequences. Immature thermal facies is determined for the following depths: 1308-1950 m in the Abu Hammad-1 well,
1615-2515 m in the Kabrit-1 well and 655-775 m in the Q-71-IX well. Mature thermal facies is determined for depths: 1950-4248 m in the Abu Hammad-1 well, 2515-2926 m in the Kabrit-1 well and 775-1253 m in the Q-71-IX well.
Shales of the lower Masajid, the Khatatba and the middle Rajabiah formations are presumed to possess a high source potential for crude oil, whereas moderate source-rock potential can be attributed to the upper Masajid Formation in the Abu Hammad-1 well, the Rajabiah Formation in the Kabrit-1 well, and the middle part of the Khatatba and Shusha formations in the Q-71-IX well.
Gas-prone, mature source- rocks are detected for the upper Rajabiah Formation in the Abu Hammad-1 well, Bir Maghara in Kabrit-1, upper part of the Khatatba, Bir Maghara and Rajabiah formations in Q-71-IX well.

Eduardo A. M. KOUTSOUKOS1 & Peter BENGTSON2

1 Petrobras-Cenpes/Divex/Sebipe, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ, Brazil; e-mail: koutsoukos@cenpes.petrobras.com.br
2 Geologisch-Paläontologisches Institut, Heidelberg Universität, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany; e-mail: Peter.Bengtson@urz.uni-heidelberg.de

The main goals of integrated biostratigraphic work are (1) to refine the chronostratigraphic frameworks for sedimentary sequences, thereby enhancing stratigraphic correlation, (2) to provide a set of regional data that allow reconstruction of the palaeogeographic development of the area, and (3) to identify regional biostratigraphic events and assess their global significance. The upper Aptian-Albian succession in north-eastern Brazil represents the record of the initial marine sedimentation in the northern South Atlantic (Bengtson & Koutsoukos, 1992). The nature of the deposits was largely controlled by the tectonic setting and overall palaeoceanographic conditions in the respective marginal basins. Along the Brazilian continental margin the late Aptian-Albian sedimentation was generally dominated by oolitic-oncolitic-bioclastic packstones and grainstones with subordinate carbonate mudstones and sandstones in shallow neritic environments. In the well-exposed Sergipe Basin, the system of horsts and grabens, which developed during the Early Cretaceous rift phase, created marine environments varying from paralic (lagoons and tidal flats) to upper slope, with mixed carbonate-siliciclastic deposition (Riachuelo Formation). Fine-grained carbonates, marls and clay accumulated in structurally controlled lows, ranging from deep neritic to upper bathyal settings toward the depocentre. During the mid-Cretaceous intermittent dysoxic-anoxic events in the shelf and slope basins prevailed in the northern South Atlantic.
In this dominantly shallow-neritic environment favusellids and nannoconids were the most common calcareous planktonic protists; these forms allow only broad biostratigraphic assignments of the sequences. In the structural lows of the Sergipe Basin, and in localized portions of the northern and equatorial Brazilian margin, deep-water biotopes yield a diverse, diagnostic assemblage of hedbergellids, ticinellids and globigerinelloids. Few specimens of Ticinella from the upper Aptian-Albian of Sergipe display the characteristic intraumbilical supplementary apertures, a morphological feature which has been regarded as an ecophenotypic character (Price, 1976). Rotaliporids, typical deep-water dwelling planktonic foraminifers (and biozonal markers for the Tethyan upper Albian-Cenomanian) are extremely rare or completely absent in most sections of the northern South Atlantic. The main constraint for these lineages seems to be a combination of widespread shallow neritic settings, overall mesotrophic-eutrophic epipelagic conditions and the presence of an oxygen-minimum layer, which expanded periodically across outer shelf areas during the mid-Cretaceous.
On the basis of composite outcrop and subsurface sections in the Sergipe Basin, the microbiostratigraphy has been calibrated with ammonite occurrences (Koutsoukos & Bengtson, 1993). However, correlation of the basal marine beds with the international scale, which is based mainly on ammonites, is problematic. In many parts of the world, the Aptian-Albian transition is characterized by the Procheloniceras-Cheloniceras-Diadochoceras-Eodouvilleiceras-Douvilleiceras ammonite lineage. In Europe, the base of the Albian is usually taken at the appearance of Leymeriella spp.; however, this genus is unknown outside the Boreal realm. Douvilleiceras is cosmopolitan but appears higher in the sequence. There is marked provincialism both in the Aptian and Albian, with few species in common between the Boreal and the Tethyan realms. There may even have occurred a widespread hiatus near the Aptian-Albian boundary in the southern hemisphere (Owen, 1984). The taxonomy of the Cheloniceras-Douvilleiceras lineage is in a state of flux, and many species wander up and down across the stage boundary, depending on the author. Douvilleiceratids are extremely variable ammonites, which causes problems of separating species and even genera. Large populations of well preserved specimens are required for reliable taxonomic conclusions. Unfortunately, the Sergipe ammonites are relatively scarce, mostly incomplete or crushed, and lacking inner whorls. The reliability of the dating of the initial transgression in the northern South Atlantic must be viewed against this background. Nevertheless, the presence of the genera Epicheloniceras, Diadochoceras, and Eodouvilleiceras in Sergipe is a strong indication of a late Aptian age.
In conclusion, the variable palaeoenvironmental settings of the initial marine depositional phase in the northern South Atlantic controlled the composition of the biotopes, constraining the occurrence of biostratigraphically significant fossils, of which many were deep-water dwellers.

References :
Bengtson, P. & Koutsoukos, E. A. M., 1992. Ammonite and foraminiferal dating of the first marine connection between the central and South Atlantic. In: R. Curnelle (ed.): Géologie Africaine, Recueil des Communications, p. 403. Elf Aquitaine Mémoire, 13.

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, 125, 241-262.

Owen, H. G., 1984. Albian stage and substage boundaries. Bulletin of the Geological Society of Denmark, 33:1-2, 183-189.

Price, R. J., 1976. Palaeoenvironmental interpretations in the Albian of western and southern Europe, as shown by the distribution of selected foraminifera. In: C. T. Schafer & B.R. Pelletier (eds.): First International Symposium on Benthonic Foraminifera of Continental Margins (Halifax, 1975), 625-648. Maritime Sediments, Special Publication 1 B, Biostratigraphy and Palaeoecology.

Robaszynski, F. & Caron, M., 1995. Foramminifères planctoniques du Crétacé: commentaire de la zonation Europe-Méditerranée. Bull. Soc. géol. France, 166 (6): 681-692.

Daniel R. MARTINIONI - Centro Austral de Investigaciones Cientficas (CADIC - CONICET), Av. Malvinas Argentinas s-n, (9410) Ushuaia, Tierra del Fuego, Argentina; e-mail: danymart@satlink.com

Early attempts to depict the surface geology of the northern front of the Argentinean Andes of Tierra del Fuego were only made by extrapolating data from nearby localities across the island, but in place supporting evidence was lacking. Although the geological picture is still far from being complete, recent research by the author introduces significant new evidence for the stratigraphy and tectonic evolution of the previously unexplored mountainous area north of Lago Fagnano. The lithology is essentially dominated by mudstone facies; sandier sections and interbedded sandstone are less frequent, and conglomerate packages are restricted to a few stratigraphic intervals. The general trend suggests that the outcrops become progressively younger to the north; nevertheless, there are north verging reverse faults that locally repeat and invert the stratigraphic column.
The oldest rocks in the area belong to the Upper Jurassic Lemaire (or Tobfera) Formation, cropping out in the Rio Azopardo - western Lago Fagnano surroundings. Black slates prevail along the northern shore of Lago Fagnano - southern Sierra de Beauvoir. These rocks yield only scarce inoceramid fragments and radiolarians. A ?Late Jurassic-Early Cretaceous age (s.l.) is ascribed to them considering the field relationships with the Upper Jurassic Lemaire Formation, and their strong slaty cleavage, typical of the former and almost trivial in the younger units.
Similar black mudstones, without a metamorphic imprint, form the thick pile of sedimentary rocks in the centre of Sierra de Beauvoir. A poorly preserved ?Barremian-Albian fossil assemblage suggests a late Early Cretaceous (s.l.) age. Basaltic dykes, yet to be isotopically dated, cut through this unit after the main deformation phase. At Monte Taarsh - Hito XIX a thrust sheet involving roughly age-equivalent rocks in the northern edge of the focused zone, the Hito XIX (or Vicu-a) Formation with diagnostic late Early Cretaceous fossil invertebrates, can be partly correlated with this interval, although there is some lithologic dissimilarity.
A slightly different succession is recorded in parts of northern Sierra de Beauvoir and along the east-west trending Rio Mio and Rio Claro valleys. This unit can roughly be divided into a lower mudstone-dominated part and an upper succession of mudstone with intercalated sandstone. The lower portion is composed by massive to faintly laminated mudstone and siltstone resembling the rocks of Sierra de Beauvoir, but containing distinct, possibly younger fossil invertebrates tentatively attributable to the Late Cretaceous (s.l.). The upper section shows a definite change in the homogeneous Cretaceous lithostratigraphy of Sierra de Beauvoir. It has alternating packages of moderately burrowed mudstone and massive mudstone with typical calcareous concretions and randomly intercalated parallel-laminated, cross-stratified, or partially ripple cross-laminated fine to very coarse sandstone beds. Their lower contacts are sharp and mainly erosive, bed geometry ranges from lenticular to tabular, and the average maximum thickness is ca. 50 cm. Paleocurrents point to the north-northwest. The uppermost strata of this younger unit show up in Sierra de Apen, just north of Sierra de Beauvoir, along a section ca. 700 m thick, that yielded Maastrichtian dinocysts, as well as ammonite fragments. The top of this unit is cut by an erosive surface that might have a regional extent.
A sandier unit rests above the erosive unconformity in Sierra de Apen. The thickness involves about 100 m of a thin basal conglomerate layer succeeded by alternating sandstone with lesser siltstone and mudstone beds. The conglomerate consists of well rounded clasts of black mudstone and calcareous concretions, eroded from the underlying uppermost Cretaceous unit, and quartz, indurated mudstone and acidic volcanics, probably derived from the Lemaire and Yahgan formations. The dinocyst assemblage in this unit has an Early Paleocene age.
Coarser clastics with a thick basal polymictic orthoconglomerate rest in Sierra de Apen on an apparently major erosive unconformity that laterally eliminates all the Lower Paleocene and part of the Upper Cretaceous. There, this unit, over 200 m thick, is made up of lenticular conglomerates that form a fining and thinning upward succession. These lenses are encased in thin-bedded mudstone and very fine sandstone rhythmites. The conglomerate clasts are composed of bluish grey sandstone and coquina, possibly derived from the lowermost Tertiary, plus similar components to those in the Lower Paleocene unit and sparse granite. Paleoflows were directed towards the northeast. Dinocysts in this unit suggest an Early to Late Paleocene age. Lithologically equivalent coeval successions appear nearby Lago Yehuin in the southeastern portion of the study area.
A detached comparable conglomerate unit shows up just north of Hito XIX. These rocks were assigned to the Eocene Ballena Formation (surface and subsurface of Chilean Tierra del Fuego) on the basis of lithological affinities and the presence of a dinocysts assemblage also recorded in the Eocene Leticia Formation (eastern Tierra del Fuego).
The subsurface stratigraphy of the Austral (or Magallanes) and western Malvinas basins is roughly consistent with the observed surface geology. The stratigraphy of Sierra de Beauvoir reflects a long period of basin fill during the Early Cretaceous and the onset of the transition to a foreland basin foredeep starting in the Late Cretaceous with regionally significant major breaks during the latest Cretaceous-Palaeogene.

Eduardo B. OLIVERO - Centro Austral de Investigaciones Cientficas (CADIC-CONICET), Avda. Malvinas Argentinas s-n, 9410 Ushuaia, Tierra del Fuego, Argentina; e-mail: eolivero@satlink.com

Jurassic-Paleogene sedimentary rocks exposed along the eastern tip of the Andes of the Isla Grande de Tierra del Fuego, Argentina, reflect the complex evolution of tectonic regimes that guided development of sedimentary basins and final separation of South America and Antarctica. Three sedimentary basins are recognized in the area: The Malvinas Basin to the NE; the Austral Basin to the NW; and the Rocas Verdes Marginal Basin to the S. The origin of all these basins is related to Jurassic crustal stretching and rifting but their subsequent Cretaceous-Tertiary evolution differs markedly. The Rocas Verdes evolved as a backarc basin filled with Cretaceous volcaniclastic, deep marine rocks derived from a Pacific-facing andesitic volcanic arc. Late Cretaceous tectonic inversion and closure of the basin resulted in strong deformation and metamorphism; initial uplift of the Andes Fueguinos; development of an elongated foredeep flanking the northern continental front of the rising cordillera; and initiation of the foreland Malvinas and Austral basins in the latest Cretaceous-Paleogene. Neogene drifting of continental blocks, associated with the opening of the Scotia Sea, brought together the northern and southern boundaries of these basin along the present Magallanes-Fagnano fault system. This scenario is mainly derived from geologic and geophysical data obtained in the subsurface and the sea, with only limited surface data on the Chilean, western part of the Island. Recent geological mapping along the Beagle Channel, Peninsula Mitre, and the SE Atlantic shore of Tierra del Fuego resulted in important new stratigraphic data allowing for a better understanding of the evolution of the area and for a more precise timing of geological events.

The basal unit of the Rocas Verdes Marginal Basin - the Upper Jurassic Lemaire or Tobfera Formation - is a complex association of submarine acidic volcanic and volcaniclastic rocks, including rhyolitic flows and shallow intrusives, breccia, resedimented conglomerate, turbidite, massive sandstone, and black, probably radiolarian mudstone. Basaltic spilites, arealso present. Dominant composition of volcaniclastic rocks is quartz, alkaline feldspar, and rhyolitic fragments, suggesting derivation from simultaneous acidic vulcanism. To the N and NE, in the platform of the Austral and Malvinas basins, coeval or slightly older similar volcanic rocks are mostly continental, deposited in NW trending grabens or hemigrabens. The following, Early Cretaceous Yahgan Formation, consists of deep marine, black mudstone, tuff, turbidite, and massive sandstone. Dominant composition is of andesitic fragments, suggesting derivation from the Pacific volcanic arc. Except for a few bioturbated horizons, trace fossils are generally absent, suggesting anoxic bottom conditions. Late Albian inoceramids near the top of the Yahgan Formation allow correlation with the thick Tekenika conglomerates developed to the S, near the volcanic arc, and with the Hito XIX Formation and other black marls with Aucellina, recently found in distal platform or slope environments to the N. These new data, together with previous thickness estimates, suggest a clastic-wedge geometry for the filling of the marginal basin, with thicker and coarser facies of the Yahgan Formation restricted to the S, near the volcanic arc. These coarse facies thin markedly to the N, grading to chiefly fine-grained basin plain rocks, and finally to slope and-or distal platform lime-rich black mudstone and marls of the Austral Basin. This clastic-wedge geometry suggests a strong tectonic control and a sedimentary system dominated by aggradation near the volcanic arc. Both the Lemaire and Yahgan formations show strong, ductile deformation and low-grade metamorphism, characterized by north-vergent folds associated with a penetrative, axial plane cleavage. The time of deformation and closure of the marginal basin is bracketed by the late Albian inoceramids and by previous Late Cretaceous isotopic ages of cross-cutting plutons. In the mapped area, superimposed Tertiary tectonics masks the transition to the subsequent foreland stage. Between the southern margin of Pennsula Mitre and the main strike-slip Magallanes-Fagnano fault zone the following belts, from S to N, are recognized: strongly deformed Lemaire rocks; cleaved, late Early Cretaceous fossiliferous, black, lime-rich mudstone; thoroughly bioturbated, thrusted and folded, siltstone and mudstone with Santonian-Campanian inoceramids; and faulted and folded Paleocene (Early Eocene?) micrites, coquina, and sandstone, referred to the Río Bueno-Ro Claro formations. The Río Bueno Formation is comparable to similar Paleocene limestone recorded in the subsurface of the Malvinas Basin and the sandstones are comparable to the Río Claro Formation of the Austral Basin. These two units overlie in angular unconformity the Upper Cretaceous, and are strongly sheared and brecciated over a distance of about 4-5 km across the Magallanes-Fagnano fault system. To the north of this fault system, a thick Eocene succession of mudstone and sandstone, exceeding 1,600 m in thickness, represents the first undoubtedly foreland strata. Clastic derivation is clearly from southern, previously uplifted Jurassic-Cretaceous rocks and coeval andesitic, pyroclastic fragments. These rocks are correlated with La Despedida Formation and the subsurface Margosa inferior, Glaucontico B, and Margosa media of the Austral Basin and similar rocks in the subsurface of the Malvinas Basin. The Eocene rocks are thrusted and faulted and covered in angular unconformity by subhorizontal but also faulted Oligocene? beds. The age and structural relationships of the Paleogene strata indicate that main thrusting and folding in the foreland basin occurred during the Eocene, probably mid-late Eocene. The initiation of the E-W strike-slip faulting system, as indicated by field evidence, has a post-late Eocene lower age limit, and is probably younger, as is suggested by strongly brecciated Paleocene rocks and left-lateral offsetting, in the order of 20-30 km, of Cretaceous-Eocene rocks.

Thomas PLETSCH1, Thomas WAGNER2, Ann HOLBOURN1, Wolfgang KUHNT1, Jochen ERBACHER3 & Michel MOULLADE4

1 Geol.-Paläntol. Institut, Univ. Kiel, Olshausenstr. 40, D-24148 Kiel, Germany; e-mail: tp@zaphod.gpi.uni-kiel.de 2 Fachbereich 5, Geowissenschaften, Univ. Bremen, Klagenfurter Str. 5, D-28359 Bremen, Germany
3 Geol.-Paläntol. Institut, Univ. Tübingen, Sigwartstr. 10, D-72076 TŸbingen, Germany
4 Lab. de Micropaléontologie & Géologie Marine, Univ. Nice, Parc Valrose, F-06108 Nice, France

Cretaceous sediments from Ocean Drilling Program Leg 159 on the Côte d´Ivoire-Ghana Transform Margin (CIGTM, eastern Equatorial Atlantic) are characterized by distinct stratigraphic changes in sedimentary facies associated with changes in the composition of the clayey and organic fractions, and of the radiolarian and benthic foraminiferal assemblages. Seven depositional phases are defined:

Phase 1 (undated, probably pre-Aptian): Siliciclastic, possibly lacustrine or deltaic sediments are characterised by diagenetic alteration suggesting either an anomalously high heating or significant burial followed by uplift and erosion.
Phase 2 (late Albian): The earliest dated sediments are siliciclastic sandstones, siltstones and claystones, indicating that marine conditions existed by the late Aptian-early Albian. The occurrence of redeposited late Aptian to middle Albian benthic foraminifers above late Albian assemblages and the presence of ordered mixed-layer minerals and thermally overmature organic matter point to the erosion of older marine deposits, possibly from an uplifting area adjacent to the drill site.
Phase 3 (latest Albian to early Turonian): Siliciclastics are overlain by very coarse-grained detrital limestones with siliciclastic rock fragments, shed from different sources, one of which was a productive carbonate platform probably on top of the Marginal Ridge.
Phase 4 (Turonian): Coarse-grained detrital carbonates are intercalated with organic-rich shales (type II kerogen, close to 4% TOC). Clay mineral assemblages comprised of both smectite and chlorite testify to a mixed detrital source from a rapidly eroding hinterland. Organic immaturity and the presence of thermally unstable smectite indicate little or no diagenetic alteration. Coeval sediments from the adjacent abyssal plain are carbonate-free, thus pointing to sub-CCD conditions.
Phase 5 (early to mid-Coniacian): A few metres of dolomitic sandy marls with low TOC are capped by organic-rich limestones with phosphatic-glauconitic hardgrounds. Clay minerals still point to a mixed detrital origin, although typical diagenetic minerals such as chlorite and mixed-layers, disappear towards the end of Phase 5. Coeval sedimentation on the crest of the Marginal Ridge consists of 130 metres of very coarse-grained carbonates, similar to those of Phase 3 on the crest of the Marginal Ridge.
Phase 6 (mid-Coniacian to early Campanian): Middle Coniacian marls with generally high TOC above an erosional surface that cuts into the limestone of Phase 5 consist of laminated intervals containing up to 16% TOC of type II kerogen intercalated with homogenous or pebbly claystones (c. 4% TOC). The siliciclastic input was reduced and clay minerals indicate dominant chemical weathering and reworking of soils. Intermittent restriction of the Deep Ivorian Basin due to higher order sea-level fluctuations may have enhanced oxygen-deficient conditions at the sea floor.
Phase 7 (mid-Campanian to late Palaeocene): 200 metres of monotonous black, carbonaceous claystones (av. of 1% TOC) devoid of calcareous microfossils contain abundant clay-sized quartz as well as smectite and a little kaolinite. Desert dust from distant arid zones is a possible source for the quartz. Kaolinite, which strongly increases below the Cretaceous-Tertiary boundary and drops to zero shortly above, probably reflects a deteriorating climate during a regressive period. A decrease in TOC and in clay mineral diversity during the Palaeocene is interpreted as the installation of more pelagic conditions during a period of continous subsidence and ongoing, slow peneplenation of the hinterland.
The existence of marine depositional environments as early as the late Aptian to early Albian close to the Leg 159 drill sites puts constraints on the timing of the opening of the equatorial Atlantic gateway. The absence of lower to middle Cretaceous sediments from drill sites on the crest of the Marginal Ridge probably results from the elevated position of this ridge and its concurrent erosion, during the mid-Cretaceous. Marine sedimentation both towards the north and the south of the ridge suggests that the West African and South American cratons were largely detatched at this segment of the margin by the middle Albian. However, it may have taken until after the Turonian that a deep-water connection between the Central Atlantic and the South Atlantic became established.
Lithofacies, clay mineral assemblages, types of kerogen, and microfossil assemblages indicate that the CIGTM developped from (1) an Early Cretaceous stage with mainly siliciclastic sedimentation and strong local and temporal variations in subsidence and uplift over a (2) mid-Cretaceous stage when the attained topographic differences between the sites remained, but when temporal inversions in subsidence diminished, giving way to sea-level and climatic controls on sedimentary facies, to a (3) Late Cretaceous stage, when all sites subsided to water depths where palaeoceanography controlled sedimentation.

This conference will be held with three supplemental field trips November 20-22.

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 country´s 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.

Participation: In addition to the approximately 40 oral and 20+ poster presentations there will be at least an additional 150 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 region´s 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 region´s diverse basins.

Co-Sponsors: This research symposium is 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:
Márcio Rocha Mello (Secretary of IGCP Project No. 1) - 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: 598-6799, E-mail: marcio@cenpes.petrobras.com.br
Barry J. Katz - E&P Tech. Dept., TEXACO, 3901 Briarpark, Houston, TX 77042, USA. Tel.: +1-713-954-6093, Fax: 954-6113, E-mail: 103021.3227@compuserve.com

Oral presentations are scheduled for 45 minutes including questions and discussion. Poster presentations will be on display for theentire conference, with Monday evening set aside for the authors to be present for discussion.

The petroleum system and exploration. L. Magoon (USGS)
Petroleum geochemistry applied in the petroleum system approach. M. R. Mello (Petrobras), J. M. Moldowan and J. Dahl (Stanford Univ.)
An overview of reservoir systems of the South Atlantic petroleum systems. Wm. C. Dawson et al. (Texaco) Seals compartmentalization and reservoir simulation of faulted seals. F. Wehr (Exxon)
Structural evolution of the South Atlantic. G. Karner (Lamont) and N. Driscoll (Woods Hole)
Integrated 2D and 3D basin modelling helps to decipher petroleum systems. J. L. Rudkiewicz, J. Wendebourg, J. M. Gaulier, F. Schneider (IFP), S. Duppenbecker, A. Wear (BP), F. Brigaud (ELF), F.T.T. Gonçalves and H. L. B. Penteado (Petrobras)
Tectonic habitat of petroleum in the South Atlantic margin. Petrobras

Petroleum Systems in the Offshore Falkland Island Basins. P. Richards (British Geological Survey)
The postrift development of the Walvis Basin, Namibia; results from the exploration campaign in Quadrant 1911. E. Holtar and A. Forseberg (Norsk Hydro Exploration and Production)
The petroleum systems of the west coast of South Africa. E. Jungslager (Soekor)

Petroleum systems of the Camamu-Almada basin; a 2D compositional modelling approach. F. T. T. Gonçalves, B. P. Bedregal, L. F. Carvalho and M. R. Mello (Petrobras)
Petroleum systems of Cabinda. N. Schoellkopf and B. Peterson (Chevron)
Petroleum systems of the Campos basin. L.R. Guardado, A.R. Spadini, M.R. Mello and J.S.L. Brand (Petrobras)
Petroleum systems of the offshore Cuanza and Benguela coastal basins, Angola. Texaco
Petroleum systems of the Sergipe-Alagoas basin. W.U. Mohriak, M. R., M. Basseto, I. S. Vieira and E. A. M. Koutsoukos (Petrobras)
The pre-salt hydrocarbon system in the Phenix marine permit area of southern Gabon: a 3-D seismic based perspective. G. Walters (Amoco) and S. Osborne (Forcenergy)
Petroleum system modelling in Congo - the Moho-Nkossa case. F. Brigaud and D. Levache (Elf)

Niger Delta petroleum system. R. Haack, S. Sundararaman (Chevron) and J. Dahl (Stanford)
Integration of geological and geophysical tools toward understanding of reservoir distribution in the deepwater Niger Delta, Nigeria. L. Nordby, M. Sola and P. Ventris (Statoil)
A petroleum system of the Potiguar basin; a numerical secondary migration approach. J.D. Souto Filho, A. F. Correa, E. V. Santos Neto and L. A. F. Trindade (Petrobras)
The Petroleum Potential of Equatorial Guinea. A. R. Stephens, G. D. Monson, T. A. Williams and B. FamaKinwa (Mobil).

A final overview of the petroleum systems of the South Atlantic - rift to drift. B. Katz (Texaco)

This symposium will be held under the auspices of the Venezuelan Geological Society (SVG), during the joint VIII Venezuelan Geological Congress and First Latin American Sedimentological Congress, at the Margarita Hilton Hotel, November 16-19, 1997. Cretaceous Correlation Symposium is being organized by Maria Lorente, Eduardo Koutsoukos and Han Leereveld.

1. Integrated view of Misoa Formation, Maracaibo Basin (3 days). Post-Congress.
2. Margarita Flysh (1 day). Pre and Post-Congress.
3. Continental Margin Evolution during Mesozoic and Paleogene Times in Northwestern Venezuela (3 days).
4. Stratigraphy and Sedimentation of Cretaceous and Tertiary Carbonate Rocks in the Venezuelan Eastern Basin (3 days).
5. Recent Carbonate Environments (3 days).
6. Margarita Island Ophiolites (1 day) Pre and Post-Congress.

The meeting will be held under the auspices of the Cuban Geological Society and the Cuban National Committee for IGCP, during the Third Cuban Geological Congress, at Palacio de las Convenciones, La Habana, March 24-27, 1998. A field trip jointly by IGCP Projects No. 381 and 362 is offered to project participants to study Mesozoic sequences of western and central Cuba, March 28-April 1, 1998.

Objectives: The meeting will focus on interdisciplinary presentations of key topics of research and progress reports of geological correlations for the South Atlantic Mesozoic.

Main topics of interest:
- Caribbean and Central America Mesozoic correlations.
- Cretaceous links between central North Atlantic-western Tethyan provinces and the incipient South Atlantic.
- Remnants of the Caribbean-Tethys oceanic basin between north and south America.

Programme:
24 March: Arrival and registration at Palacio de las Convenciones in Havana.
25-26 March: SAMC Scientific meeting. Two days will be used for the oral and posters presentations.
25-27 March: Scientific meetings of the Cuban Geological Congress.
28 March-1 April: Excursion. IGCP Projects 381 and 362
2 April: Departure

Field Trip:
This post-meeting field trip will be leaving Havana on 28th March and ending in Escambray, central Cuba on 1st April. The Cordillera de Guaniguanico embraces the mountains of western Cuba north of Pinar fault. The cordillera contains the most extensive outcrops of the passive mesozoic continental margin in Cuba which exhibit great similarities to the mesozoic sequences of south east Mexico. The syn-rift sediments of Lower and Middle Jurassic age known as San Cayetano Formation will also visited. In central Cuba mesozoic sequences of the continental margin closed to Bahamas exhibit good outcrops of thrusted pelagic facies and carbonate platform. The ophiolites near Santa Clara city and metasedimentary outcrops in the Escambray area are included in the excursion.

Fees: Registration fee is estimated no more than US $650, which will cover the excursion fee (500 USD) (including meals, accomodation and transportation during the five excursion days) as well as the meeting fees (150 USD), which make possible to take part in all scientific activities of both SAMC and Congress on Geology of Cuba meetings. Fees will be paid on site, at arrival in Havana.

Abstracts-Posters: Each participant who will have and oral or poster presentation is invited to submited a manuscript of the abstract to the Abstract Book. The abstract should not exceed 400 words. The extended abstract should not exceed three A4 sheet including illustrations. The format will be according to the instructions given in the circulars of the Congress which will be issued in September. All project-related papers (extended abstracts and articles) will be considered as contributions to IGCP Project 381 and submitted to the project leaders for publication in SAMC News.

Language: The official language of the Congress will be Spanish. However, to optimize the diffusion of knowledge at the international level, we strongly recommend the use of English for the oral presentations at the SAMC Meeting.

Deadlines:
Abstracts: 31 December 1997
Extended abstracts and articles: submitted to the organizers during the meeting.

Name: ____________________________________
Company: ________________________________
Address: __________________________________
__________________________________
Phone: __________________________________
E-mail: __________________________________

Are you presenting a paper? YES __ NO __

For: SAMC Meeting: __________________________________

III Cuban Geological Congress: __________________________________

The provisional title of my presentation is: __________________________________

__________________________________

__________________________________

Are you intereted in participating in the field trip? YES __ NO __

Please, send this information and abstracts to any of these coordinators:

Jorge R. Sánchez-Arango
Centro de Investigaciones del Petróleo
Washington 169 esq. a Churruca, Cerro
La Habana 12000, Cuba
Fax: (53-7) 66 60 21
E-mail: ceinpet@ceniai.inf.cu
Phone: (53-7) 402611; 411132

Jorge L. Cobiella-Reguera
Departamento de geología
Universidad de Pinar del Río
Pinar del Río 20100, Cuba
Fax: (53-7) 82 5813
E-mail: univpr@reduniv.edu.cu

Note: More information will be given in the circulars of the Third Cuban Geological Congress. You can contact with the mentioned coordinators or directly to:

Evelio Linares-Cala
President, Cuban Geological Society
Gaveta Postal 370
La Habana 10100 Cuba
Fax: (53-7) 66 6021
E-mail: ceinpet@ceniai.inf.cu

The Conference will be conducted jointly by the American Association of Petroleum Geologists (AAPG) and the Brazilian Association of Petroleum Geologists (ABGP).

Poster Session #P26 will be held dedicated to IGCP Project 381, coordinated by E.A.M. Koutsoukos and P. Bengtson.

Important Note: Deadline for abstracts is 15 December 1997.

For more information please contact:
AAPG Convention Department
P.O. Box 979, Tulsa, OK 74101-0979, USA. Offices at 1444 S. Boulder Av., Tulsa, OK 74119.Tel.: +1-918-560 2679, Fax: +1-918-560 2684, E-mail: convene@aapg.org

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-(0)195-340327; E-mail: dimasdb@caviar.igce.unesp.br

About the project:
- how should we interpret different levels of taxonomic diversification (macro- and/or microevolution)?
- was the rate of diversification constant over geological times or were there bursts of such artivity during certain periodes (post-extinction recoveries, palaeogeographic reorganisation, climatic events, etc.)?
- what where the relations between palaeodiversification and the structure of ecosystems?
- what intrinsic forces were at work during diversification processes?

Organisers and contacts:
The conference is held under the auspices of the UMR 5565 of the CNRS and is organized by:

Mireille GAYET - UFR des Sciences de la Terre, Université Claude Bernard, Lyon I, 27-43 bd du 11 novembre 1918, 69622 Villeurbanne cedex - France. Tel.: +33-(0)4-72448398; Fax: +33-(0)4-72448436; e-mails: gayet@univ-lyon1.fr (or) lysiane.thevenod@univ-lyon1.fr

Since the mid-forties Uberaba´s region located in the state of Minas Gerais, has been targeted as a place of intense paleontological investigations, that resulted in a considerable recovery of vertebrate fossil material.

The L.I.P. Paleontological Research Center was opened in 1992 by the city government in order to support the research works and is located in Peirópolis, 20 km from Uberaba.

Aiming to protect the fossil deposits, carry out and support researches and disseminate knowledge in Geology and Paleontology, the Center has become an important supporting basis to researchers in the area.

Geologically the region is located in the Paraná Basin, where there are deposits associated to the Baurœ Group, represented locally by the Uberaba (Adamantina) and Marília formations (Upper Cretaceous). These lithological units consist mostly of sandstones, associated to a river-lake depositional environment where the fossils are concentrated. The fossil preservation of the vertebrate fossil collection is outstanding, with original colors and peculiar characteristics, like tooth enamel.

The fauna is diverse, being represented by Teropods dinosaurs (teeth) and sauropods -Titanossauridae family (egg, teeth and bones), fish debris (bone, teeth and scales), mollusks (moulds and shells), crocodile-like (skin plaques and teeth), turtles (varied pieces) and also small samples associated to frogs.

The Center count with a staff for fossil collection and preparation, that has supplied the collection with approximately 1,000 specimens for the last 5 years.

To help the development of the studies, the Research Center offers its fossil collection to researchers, along with lodging and some support, and it is currently open to research exchange. Next to the center, there is the Dinosaur Museum, where part of the collection is exhibited, along with boards, photos and explanatory texts, in a didatic way to the public.

Untill now the Museum has been visited by 80,000 tourists from 600 counties (states) and 25 countries, improving the local tourism. The Research Center is a real example of union between government and the scientific comunity.

For further information please contact:
Luiz Carlos Borges Ribeiro
Llewellyn Ivor Price Paleontological Research Center - Director
Rua Senador Pena, 575/ Ap. 901, 38010-400 Uberaba, MG, Brazil
Fax: +55-(0)21-3333767/ 3339293, E-mail: fcu@ldc.com.br

We would like to express our gratitude to PETROBRAS-CENPES, Rio de Janeiro, for support involved in editing, photocopying and mailing all the copies of SAMC News 8.