Published 1995 as part of Studies in Geology 40
Copyright © 1995 The American Association of Petroleum Geologists.   All Rights Reserved.
 

A geochemical survey of Brazilian marginal basins using a wide selection of source rocks and oils, ranging from Early Cretaceous to Tertiary in age, has been undertaken. The aims were to review, assess, and characterize the paleoenvironment of deposition of source rocks and to correlate reservoired oils with their putative source rocks using an approach based mainly on the distribution and absolute concentrations of biological markers. The survey included evaluation of organic carbon contents, Rock-Eval pyrolysis data, vitrinite reflectance measurements, carbon isotope ratios, elemental and visual kerogen analyses and molecular studies involving liquid and gas chromatography, qualitative and quantitative biological marker investigations using gas chromatography-mass spectrometry (GC-MS) and metastable ion monitoring GC-MS of saturated hydrocarbons. The metastable ion GC-MS data were evaluated using principal component analysis.

Integration of the results with geological and paleontological data facilitates the recognition and differentiation of seven depositional regimes: lacustrine fresh/brackish water, lacustrine saline water, marine evaporitic, marine carbonate, marine deltaic with carbonate influence, open marine anoxic with a predominance of calcareous mudstone lithology, and open marine anoxic with a predominance of siliciclastic lithology.

The analyses of the oils reveal significant differences among groups which enable a correlation with putative source rocks deposited in six of the afore-mentioned depositional regimes. Although siliciclastic rocks derived from an open marine environment show high lipid-rich organic carbon contents,