Sediments recovered during Leg 207 from the Demerara Rise consist of different mixtures between biogenous carbonate and detrital material. Lithologic Units II–IV show high carbonate contents, whereas Unit I and V are dominated by terrigenous detritus. Major element analysis indicates a common origin of the terrigenous detritus similar to AS, whereas the clay-dominated Unit I reveals a more weathered terrigenous component. Heavy mineral phases and quartz-bearing sands display a high-energy synrift deposit in Unit V.
The Cretaceous black shales of Unit IV are clearly enriched in redox-sensitive and stable sulfide–forming elements. This indicates high paleo-productivity and severe oxygen depletion in the water column. The complete sulfidation of the black shales and significant excess sulfur report a sulfidic environment, leading to sulfur incorporation into organic matter.
Ba enrichments in sediments above the black shale sequences show former diagenetic mobilization of barite in underlying sediment layers. Pore water data evidence that sulfate reduction due to anaerobic methane oxidation is still driving barite diagenesis.