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Abstract

AAPG Bulletin, V. 87, No. 5 (April 2003),

P. 873-894.

Copyright 2003. The American Association of Petroleum Geologists. All rights reserved.

The Sao Tom deep-sea turbidite system (southern Brazil Basin): Cenozoic seismic stratigraphy and sedimentary processes

A. Viana,1 A. Figueiredo,2 J.-C. Faugres,3 A. Lima,4 E. Gonthier,5 I. Brehme,6 S. Zaragosi7

1Petrobras, EP, UN-EXP, 500, General Canabarro St., Rio de Janeiro, 20271-200, Brazil; email: [email protected]
2Laboratorio de Geologia Marinha, Instituto de Geociencias, Universidade Federal Fluminense, Avenida Litoranea, 24210-340, Niteroi, RJ, Brazil
3Departement de Gologie et Ocanographie, UMR 5805 "EPOC," Universit Bordeaux I, Talence 33405, France; email: [email protected]
4Instituto Oceanografico, USP, Praa do Oceanografico, 191, 05508-900 Sao Paulo, SP, Brazil
5Departement de Gologie et Ocanographie, UMR 5805 "EPOC," Universit Bordeaux I, Talence 33405, France
6Laboratorio de Geologia Marinha, Instituto de Geociencias, Universidade Federal Fluminense, Avenida Litoranea, 24210-340, Niteroi, RJ, Brazil
7Departement de Gologie et Ocanographie, UMR 5805 "EPOC," Universit Bordeaux I, Talence 33405, France

AUTHORS

Adriano Viana is an advisor for sedimentology at Petrobras EP, which he joined in 1986. He received his bachelor's degree in geology from the Universidade Federal do Rio Grande do Sul in Brazil in 1982, and his Ph.D. in marine geology from the Universit Bordeaux 1 in France in 1998. From 1988 to 2001, he studied deep-water sedimentation in the Brazilian Atlantic margin, including the characterization of modern deep-water depositional systems, turbidite and contour-current-controlled depositional systems, and geohazards assessment. In 2001, he joined the Petrobras Santos Basin Exploration Group. He also coordinates several industry-academy joint projects.

Alberto G. Figueiredo, Jr. was born in Mococa, Brazil, in 1947. He is a full professor at Fluminense Federal University, Niteroi, Brazil; he is also researcher of the Brazilian National Research Council. Alberto obtained a Ph.D. at the University of Miami in 1984 and undertook postdoctoral work at the State University of New York at Stony Brook in 1991. His major research interests focus on marine sedimentation, processes and products, and shelf and deep-sea environments.

Jean-Claude Faugres graduated from Paris University (France) where he received a third-cycle degree in sedimentology. After a seven-year stay as lecturer at Rabat University (Maroco), where he subsequently undertook sedimentological research on the South Rifan series, he moved back to France at Bordeaux University where he obtained a Doctorat d'Etat Es Sciences in 1978. Since that time, his research involved the modern deep-sea sedimentation in passive and active continental margins with a major interest on the contour-current-controlled deposits. He was professor of geology since 1991 and is now just retired.

Andra Frana Lima is a Ph.D. student in the Institute of Oceanography of the University of Sao Paulo, Brazil. She graduated in geology and has an M.S. degree on shallow seismic in coastal region. Presently, she works on the recognition of contourite and turbidite-current processes in the Brazilian continental margin.

Eliane Gonthier is researcher in a Centre National de Recherche Scientifique laboratory of Bordeaux I University (France). Eliane obtained a Ph.D. in 1972. Since that time, she has worked on modern deep-sea sediments with a major interest on sedimentary facies characteristics and deposit origin and distribution in turbidite and contourite systems.

Isa Brehme is a geology professor at Fluminense Federal University, Niteroi, Brazil. She received her Ph.D. at the University of Bremen in 1991. Since that time, her major research interest focus on glaciomarine and marine deep-sea sedimentation, especially in the Antarctic and the south Brazilian margins.

Sbastien Zaragosi received a Ph.D. in 2001 from Bordeaux I University (France). He investigates the physiography and Quaternary sediment distribution and processes of deposition of the deep-sea fans in the Bay of Biscay in response to sea level and global climatic variations. He is now a lecturer in Bordeaux and focuses his interest on deep-sea sand accumulation and paleoenvironments.

ACKNOWLEDGMENTS

The research presented in this paper was conducted under a program of cooperation between the Universit Bordeaux I (France) and the Universidade Federal Fluminense (Laboratorio de Geologia Marinha), Nitero, Brasil. Lowrie and Kumar are gratefully acknowledged for their reviews that helped to significantly improve the paper. The job done by the editor to improve the final copy and the English writing is highly appreciated. This is an UMR/EPOC CNRS 5805 contribution no. 1475.

ABSTRACT

The Sao Tom deep-sea turbidite system, elongated parallel to the rise of the south Brazilian continental margin, was first interpreted as a channel-levee system resulting from contour-current activity. Study of new seismic data permits the proposal of a stratigraphy for the system and a new interpretation of depositional processes. Three major depositional units have been recognized that are separated by major erosive discontinuities. The basal unit seems to be Paleocene to lower or middle Eocene, and the second one, subdivided into two subunits, is probably upper Oligocene to middle Miocene. Both units show superimposed north-to-southchannelized turbidite systems, with supply provided directly from a channel network that crosses the upper margin in the north. The third unit is upper Miocene(?) to Pliocene or Quaternary and is still under predominantly gravity processes: turbidite processes in the lower and upper subunits, and major mass-flow processes in the median subunit. The sediment sources are located either in the north or in the south, with sediment provided by major deep-sea channels. The base of the upper subunit is well marked by an erosive discontinuity (late Pliocene or PlioceneQuaternary boundary). Impact of the contour currents is mainly recorded as widespread erosive surfaces (seismic discontinuities) correlated to global hydrological events and transparent or wavy deposits. Because this system contains a significant amount of upper Quaternary sands, it suggests the occurrence of petroleum reservoirs along the rise and the Sao Paulo Plateau in the lower continental slope.

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