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Chapter 11
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The Hydrocarbon
Source Potential in the Brazilian Marginal Basins: A Geochemical and  Paleoenvironmental
Assessment
M. R. Mello
Petrobrás/Cenpes/Divex
Rio de Janeiro, Brazil
N. Telnaes
Norsk Hydro Research Center
Bergen, Norway
J. R. Maxwell
University of Bristol
Bristol, U.K.
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ABSTRACT
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,
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