Date of this Version
Well-preserved nannofossil and stable isotope records from the mid-Cretaceous of Ocean Drilling Project Leg 171B (western North Atlantic) indicate cyclical, productivity-based variations in surface water characteristics, suggesting orbitally paced changes in upwelling intensity and the strength of deep mixing associated with oceanic anoxic event (OAE)1d. Paleontologic and isotopic evidence suggest that collapse of upper water column stratification associated with OAE1d was preceded by approximately 1 m.y. of progressively decreasing water column stability and increasing surface water fertility. Thirteen species went extinct during a short (ca. 200 k.y.) interval associated with OAE1d. Nine of these have morphological characters suggesting adaptation to specific depths in the photic zone. Simultaneous extinction of these depth-zoned species suggests that stratification collapse disrupted the habitat space for these specialized forms, resulting in extinction. A cyclostratigraphic model provides age estimates of several important nannofossil datums including the first appearances of Eiffellithus turriseiffelii (100.95 Ma) and Corollithion kennedyi (99.55 Ma).