Carbon–sulfur–iron relationships and δ13C of organic matter for late Albian sedimentary rocks from the North Atlantic Ocean: paleoceanographic implications

Cores from six Deep Sea Drilling Project Sites (367, 369, 137, 386, 387 and 603) of the late Albian North Atlantic Ocean were investigated for organic carbon content, δ13C values of the kerogens, maceral composition of the organic matter, C/S ratios, Fe–TOC–S relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter-rich black shale deposits. The results show a clear separation of the Albian North Atlantic into an anoxic eastern part and a mostly oxic western part. The eastern North Atlantic is dominated by organic matter-rich deposits. Sulfate reduction occurred in an oxygen-free water column and resulted in characteristic C/S ratios, Fe–TOC–S relationships and framboidal pyrite size distribution patterns. Elevated productivity, anoxia and high sedimentation rates supported the formation of black shale deposits. For most of the western and central parts, organic matter sedimentation took place through an oxygenated water column. The accumulated organic matter is dominantly of terrigenous origin. The deposition of marine derived organic matter was most likely controlled by productivity, paleobathymetry and low sedimentation rates.