Organic and isotope geochemistry of the Early Cretaceous rift sequence in the Camamu Basin, Brazil: paleolimnological inferences and source rock models

摘要: Abstract The Camamu Basin, located at the eastern Brazilian continental margin, is characterized by a thick Early Cretaceous organic-rich rift sequence. integration of bulk geochemical, isotopic and biomarker data with paleontological geological information provided basis for better assessment lake evolution (hydrological regime, redox potential, salinity, etc.) its impact on source rock development. Pyrolysis visual kerogen analyses reveal dominance lipid-rich algal (bacterial?) type I through entire Paleolimnological reconstruction suggests that lower sequence (Morro do Barro Formation, Neocomian) was deposited in fault-bounded deep fresh to brackish water, stable water column stratification bottom anoxia. High hydrogen indices (700–900 mg HC/gTOC) 13C-depleted carbon composition organic matter (δ13C values around −30‰) might reflect enhanced preservation, recycling light CH4 generated methanogenesis, incorporation isotopically bacterial biomass. On other hand, upper (Rio de Contas Barremian) probably within broader/shallower higher frequency water-column overturn deeper thermocline. contents strong 13C enrichment excursions up −23‰) are interpreted have resulted from primary productivity triggered an increased input/recycling nutrients favored morphology humid climate.