Organic geochemical characterisation of depositional palaeoenvironments of source rocks and oils in Brazilian marginal basins

• Published in: Organic geochemistry Vol. 13; no. 1; pp. 31 - 45
• Main Authors: Mello, M.R, Telnaes, N, Gaglianone, P.C, Chicarelli, M.I, Brassell, S.C, Maxwell, J.R
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1988
• Subjects: biological markers; Brazilian basins; carbon isotope ratios; evaporitic sediments; multivariate analysis; oils; palaeoenvironment of deposition; petroleum source rocks; porphyrins; palaeoenvironment of deposition; petroleum source rocks; Brazilian basins; oils; evaporitic sediments; biological markers; carbon isotope ratios; multivariate analysis; porphyrins
• DOI: 10.1016/0146-6380(88)90023-X
• ISSN: 0146-6380

An investigation of bulk, isotopic and molecular features of a wide selection of source rocks and oils from Brazilian marginal basins, ranging from Lower Cretaceous to Tertiary in age, provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo-environments. The methods employed include evaluation of organic carbon contents, Rock-Eval pyrolysis, vitrinite reflectance measurements, determination of carbon isotope ratios, elemental and visual kerogen analysis, assessment of oils and solvent extracts by liquid and gas chromatography, and quantitative biological marker investigations using GC-MS for aliphatic hydrocarbons and UV/Vis spectrophotometry for metalloporphyrins. Selected data were evaluated using principal component analysis. The results enable the recognition and differentiation of seven depositional regimes: lacustrine freshwater; lacustrine saline water; marine evaporitic; marine carbonate; marine deltaic; marine highly anoxic with a predominance of calcareous mudstone lithology, and marine anoxic with predominance of siliciclastic lithology. Diagnostic features in the biological markers from these depositional environments include: the carbon number distributions of n-alkanes, pristane/phytane ratios; absolute concentrations of β-carotane, higher acyclic isoprenoids, C 30 αβ hopane and steranes, and the abundance of the latter relative to 4-methylsteranes; the occurrence and abundance of particular biological markers such as gammacerane, tricyclic and tetracyclic terpanes, 18α (H)-oleanane, 28,30-bisnorhopane and 25,28,30-trisnorhopane, and the relative abundances of nickel and vanadyl porphyrins.