Black shale deposition, atmospheric CO2 drawdown, and cooling during the Cenomanian-Turonian Oceanic Anoxic Event

Oceanic Anoxic Event 2 (OAE2), spanning the Cenomanian-Turonian boundary (CTB), represents one of the largest perturbations in the global carbon cycle in the last 100 Myr. The δ 13C carb, δ 13C org, and δ 18O chemostratigraphy of a black shale-bearing CTB succession in the Vocontian Basin of France is described and correlated at high resolution to the European CTB reference section at Eastbourne, England, and to successions in Germany, the equatorial and midlatitude proto-North Atlantic, and the U.S. Western Interior Seaway (WIS). 13C (offset between δ 13C carb and δ 13C org) is shown to be a good pCO 2 proxy that is consistent with pCO 2 records obtained using biomarker δ 13C data from Atlantic black shales and leaf stomata data from WIS sections. Boreal chalk δ 18O records show sea surface temperature (SST) changes that closely follow the 13C pCO 2 proxy and confirm TEX 86 results from deep ocean sites. Rising pCO 2 and SST during the Late Cenomanian is attributed to volcanic degassing; pCO 2 and SST maxima occurred at the onset of black shale deposition, followed by falling pCO 2 and cooling due to carbon sequestration by marine organic productivity and preservation, and increased silicate weathering. A marked pCO 2 minimum (∼25% fall) occurred with a SST minimum (Plenus Cold Event) showing >4C of cooling in ∼40 kyr. Renewed increases in pCO 2, SST, and δ 13C during latest Cenomanian black shale deposition suggest that a continuing volcanogenic CO 2 flux overrode further drawdown effects. Maximum pCO 2 and SST followed the end of OAE2, associated with a falling nutrient supply during the Early Turonian eustatic highstand. Copyright 2011 by the American Geophysical Union.