Development and controls of the final Cretaceous black-shale event, Coniacian to lower Campanian (OAE 3):A reference section from the tropical Atlantic at Milankovitch time-scales

Abstract

The study focuses on high-resolution investigation of marine sediments accumulated during the Coniacian-Campanian oceanic anoxic event 3 (OAE 3) to obtain a model of black shale formation in the equatorial Atlantic Ocean at ODP Site 959 off Ivory Coast. Selected geochemical parameters display cyclic fluctuations that are attributed to orbital forcing of Milankovitch frequency. Marine and continental geochemical proxy-data indicate two depositional modes defining boundary conditions for black shale accumulation and OC-lean sedimentation in relation to African climate across the OAE 3. Variable amplitudes in continental proxy records suggest climate contrasts alternating between arid and humid conditions. Continental runoff was identified as main trigger for productivity cycles, with extreme variations in redox-conditions across the water column. Simulations using a global climate model validated the assumption of freshwater discharge resulting in circulation reversal, the development of ocean anoxia and finally black shale deposition. Results from this study support a highly dynamic climate-ocean system during the Upper Cretaceous.