MELLO, M. R.
Carbon and hydrogen isotopic data and biomarkers from oils, allowed the assessment, identification and differentiation of lacustrine and marine source rock depositional environments. The samples studied were recovered from Latin American syn-rift, sag and drift stages of Cretaceous and Tertiary ages. Two environments were identified in the syn-rift stage: (i) Lower Neocomian deep, fresh to brackish water lacustrine (Reconcavo basin, Brazil), (ii) Upper Neocomian shallow hypersaline lake (Sergipe basin, Brazil). Two environments were identified in sag basins: (iii) Tithonian semi-restricted shallow marine carbonate (Chiapas basin, Mexico), (iv) Aptian marine evaporitic. Four environments were identified in a drift stage: (v) Cenomanian-Turonian deep marine carbonate (Maracaibo basin, Venezuela), (vi) Miocene marine deltaic siliciclastic system (Lower Magdalena basin, Colombia), (vii) Miocene marine deltaic system with carbonatic influence (Foz de Amazonas basin, Brazil), and (vii) Oligocene marine deltaic proximal (Plato basin, Colombia).
Within the tectono-sedimentary settings, successive sea level changes or expansions and contractions of the lacustrine water bodies, created variations in water column salinity and temperature and, hence, the development of water stratification and bottom water anoxia. These differences can be identified using only oil samples, without the need of actual source rock data. Even when oils or depositional environments are mixed, individual components and their relative contributions can be assessed.