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The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Facts and Principles of World Petroleum Occurrence — Memoir 6, 1980
Pages 857-886
Worldwide Petroleum Provinces

Petroleum Habitats in the Mesozoic-Cenozoic of the Continental Margin of Brazil

F. Celso Ponte, J. Dos Reis Fonseca, A. V. Carozzi


The Mesozoic-Cenozoic basins of the Brazilian continental margin were formed through four main stages of tectonic evolution. These stages, typical of the Atlantic-type continental margins are: pre-rift arch stage, intracratonic rift-valley stage, proto-oceanic gulf stage and continental margin stage. Each of these stages is documented by a typical tectonic style imposed upon distinctive sedimentary sequences. These tectono-sedimentary environments correspond to well-defined petroleum habitats, namely: lacustrine rift-valley habitat; transitional and restricted marine habitat; and marine transgressive habitat.

In the lacustrine rift-valley habitat petroleum migrated from pro-delta lacustrine shales, and was trapped on the crests of faulted block structures. The Miranga, Aracas, Dom Joao and Agua Grande Fields in the Reconcavo Basin are good examples of this type of oil accumulation. Although no oil is known to have been generated in pre-Cretaceous fluvial sequences deposited during the intracratonic pre-rift stage, the Upper Jurassic blanket-sandstones are good reservoir rocks and may have accumulated oil whenever they were in fault contact with Neocomian source rocks, as in the Agua Grande, Dom Joao and some other fields of the Reconcavo and Sergipe-Alagoas basins. Minor stratigraphic fields associated with lacustrine turbidite sandstone lenses and with fractured shales, such as the Candeias Field in the Reconcavo Basin are also present.

In the restricted marine and transitional habitat petroleum was generated in the Aptian euxinic shales and has accumulated in conglomerates and sandstones associated with the evaporite sequence deposited during the final phase of the rifting stage. The oil traps are broad and gentle paleogeomorphic highs, associated with a pre-Aptian regional unconformity. The Carmopolis and Riachuelo Fields in the Sergipe-Alagoas Basin are among the best examples of this type of accumulation.

In the marine transgressive habitat the hydrocarbons seem to be genetically related to the lower part of the marine transgressive subsequence of Late Cretaceous age. The oil pools are formed by block faulting, stratigraphic or paleogeomorphic traps associated with porous limestones and/or turbidite sandstone lenses as reservoirs. The Garoupa and Namorado Fields in the Campos Basin as well as the Guaricema Field in the Sergipe-Alagoas Basin and the Fazenda Cedro Field in the Espirito Santo Basin are typical examples.

As of now, five petroleum provinces have been discovered by PETROBRAS on the Brazilian continental margin: Reconcavo-Tucano, Sergipe-Alagoas, Potiguar-Ceara, Espirito Santo and Campos. The known petroleum reserves of Brazil are distributed among those provinces as follows: Reconcavo-Tucano, 53%; Campos, 32%; Sergipe-Alagoas, 11%; Espirito Santo, 2% and Potiguar-Ceara, 2%.

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