Millennial- to centennial-scale record of African climate variability and organic carbon accumulation in the Coniacian–Santonian eastern tropical Atlantic (Ocean Drilling Program Site 959, off Ivory Coast and Ghana)

Abstract

Millennial- to centennial-scale geochemical records of Coniacian to Santonian deposits from the Deep Ivorian Basin are used to develop a model for the accumulation of black shales in equatorial regions during the final of the Cretaceous oceanic anoxic events (OAE). Proxy records from Ocean Drilling Program Site 959 document a strong precessional signal in the occurrence of black shales, the abundance of quartz, and clay mineralogy during OAE 3. We hypothesize that this signal reflects changes in atmospheric circulation patterns, which in turn caused latitudinal shifts of continental climate belts across western Africa. Furthermore we propose that the periodic deposition of black shales occurred in response to adjustments of oceanic circulation in the Deep Ivorian Basin resulting from climate-controlled fluctuations in continental runoff. A new high-resolution cyclostratigraphic framework allowed us to estimate a rapid change—within <1000 yr—from dysoxic (background) to anoxic or euxinic (black shale) environmental conditions, followed by black shale deposition for ∼10 k.y. and a gradual return to the initial dysoxic conditions. Our findings imply a highly dynamic Late Cretaceous atmosphere-ocean system.