MELLO, M. R., Petrobras, Rio de Janeiro, Brazil

ABSTRACT: The Habitat of Petroleum in the Brazilian Marginal Basins: A Paleoenvironmental and Biological Marker Approach

A geochemical survey of Brazilian marginal basins using a wide selection of oils and source rocks. ranging from Lower Cretaceous to Tertiary in age, has been undertaken. The aims were to review and assess the hydrocarbon source potential, characterize the depositional paleoenvironment of the source rocks and to correlate reservoired oils with their putative source rocks. This approach was based mainly on the distribution and absolute concentrations of biological markers.

Integration of the results with geological and paleontological data Provides recognition and differentiation of six source rock systems deposited in the following environments: lacustrine freshwater, lacustrine brackish to saline water. marine hypersaline, marine carbonate, open marine anoxic and marine deltaic with carbonate influence.

The analyses of the oil samples reveal significant differences among groups which enable a correlation with putative source rocks laid down in all the six of the above depositional environments.

Presently, the Brazilian marginal basins have a potential reserve of about 40 billion barrels of oil-in-place, with 95% of them being sourced by rift-phase lacustrine environments.

This study also provides a framework of bulk. elemental, and especially environmental and biological marker characteristics which can be compared with samples from other basins of the world.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.