Organic carbon isotopic composition in Cretaceous sediments, Angola Basin, southeastern Atlantic Deep Sea Drilling Project Site 530.

Abstract

Cretaceous sediments from DSDP Site 530 have been analyzed for organic carbon isotopic composition. The delta 13C values in the sediments decrease from -22.7 per mille to -27.5 per mille in the following order: light-olive green mudstone/claystone, dark brown-red mudstone/siltstone/claystone, and black shale. This large range is primarily the result of variation in the relative amounts of terrestrial organic carbon superimposed on that derived from marine organisms. The black shales have an average delta 13C value of -25.9 per mille (range is from -23.7 per mille to -27.5 per mille). These values indicate that they originated primarily in terrigenous organic materials. The average delta 13C value present throughout the Cretaceous suggests that a large amount of terrestrial organic matter was supplied into this paleoenvironment, except during the Campanian, when an average delta 13C of -23.9 per mille is found near the marine end of the range.-Authors