Cretaceous oceanic anoxic events and their relations to carbonate platform drowning episodes

Cretaceous greenhouse conditions were characterized by the expansion of Tethyan carbonate platforms on the continental shelf and by widespread deposition of organic-rich sediments representing "oceanic anoxic events (OAEs)". Many Cretaceous carbonate platforms were temporarily drowned several times, indicating that environmental factors frequently stressed carbonate factories on these platforms. Nine global Cretaceous episodes of carbonate platform drowning are recognized. Recent bio- and chemostratigraphic studies revealed that three episodes were probably coincident with OAEs and with events of global carbon accumulation: the mid-Valanginian carbon isotope event, the mid-Aptian event (OAE1a), and the Cenomanian-Turonian boundary event (OAE2). These three breaks in carbonate platform development were associated with mass extinctions of carbonate platform biota, such as rudists, benthic foraminifers and calcareous algae. The major changeovers of Cretaceous hermatypic fossil assemblages came during the periods following these biotic crises. These lines of evidence suggest some causal relationships among some OAEs, carbonate platform drowning episodes and extinctions of carbonate platform biota.