GEOCHEMICAL AND BIOLOGICAL MARKER ASSESSMENT OF DEPOSITIONAL-ENVIRONMENTS USING BRAZILIAN OFFSHORE OILS

A combined geochemical and molecular characterization of a wide selection of oils from the major Brazilian offshore basins has been undertaken. The elemental (sulfur, nickel and vanadium) and bulk ( degree API and delta **1**3C) properties of each sample have been considered, together with its molecular composition determined using liquid and gas chromatography, and quantitative biological marker investigations using gas chromatography-mass spectrometry for alkanes. The results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups. The distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils. Each group is correlated tentatively with source rocks laid down in a specific depositional regime, namely lacustrine freshwater, lacustrine saline water, marine evaporitic, marine carbonate or marine deltaic. Additional aspects of the subject are discussed.