The Lower Cretaceous in sedimentary basins of the Brazil south-eastern border: isotopic analysis and their paleoecological implications

Carbon isotope data of bitumen, and carbon and oxygen isotope data of limestone provided additional knowledge to the sedimentation environment of the Lower Cretaceous sedimentary sequences of Campos and Espirito Santo basins. In the Buracica stage the carbon isotope data of bitumen suggest a deposition in fresh water lake. The isotope data of bitumen and limestone from lower and middle section of Jiquia stage could indicate a sedimentation in fresh water lake but gradually more saline on the top. More positive δ 13C values of limestone in the upper portion of the Jiquia stage and in the Alagoas stage suggest a restrict marine environment or deposition in hippersaline lakes. During the Albian, the carbonate sedimentation could have occurred still in a marine environment and above normal salinity. According to δ 18O data, the surface waters were warm, with a tendency to become gradually cooler towards the top of Albian. (author)