Organic carbon and total sulfur content and concentrations of selected molecular fossils for C/T black shales (Table 1)

Here, we provide the first direct evidence for an open ocean OMZ in the Cenomanian/Turonian (C/T) southern North Atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in C/T black shales.

This, together with evidence for bottom water anoxia and accumulation of redox-sensitive trace metals and hydrogen-rich organic matter, indicates a continuously euxinic water column. Concurrent with the high Corg accumulation rates, which are 15-150 times greater in the southern than in the northern North Atlantic, and the low biological productivity, this suggests that preservation controlled the accumulation of Corg in C/T black shales.