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Calcareous nannofossil assemblages were investigated across the Oceanic Anoxic Event (OAE) at the Cenomanian/Turonian Boundary (CTB) in a section from the Western Interior Basin and a borehole from the New Jersey coastal plain. The objective was to determine the surface-water response to environmental perturbations during the OAE. A decrease in surface water fertility at the two localities is suggested by an increase in relative abundances of taxa with oligotrophic affinities and a concomitant decrease in taxa with mesotrophic or eutrophic affinities. Oligotrophy and anoxia at both localities are likely responses to increased water-column stratification associated with the incursion of warmer waters from lower latitudes. [ABSTRACT FROM AUTHOR]

Abstract: Carbon isotope measurements have been made on bulk carbonate and organic matter in three sections across the Cenomanian–Turonian boundary. The stratigraphy records the positive carbon isotopic excursion that is associated with the major oceanic anoxic event (OAE2). Comparison of TOC and isotopic data in sections from a range of different environments suggests that the positive excursion is a response to increased burial of organic matter in the deep ocean. The lack of coupled negative shifts in δ13Corg and δ13Ccarb records at the onset of OAE2 does not support a causal role for volcanism or methane hydrate dissociation. [Copyright &y& Elsevier]

The Paleocene-Eocene Thermal Maximum (PETM, approximately 55 million years ago) was an interval of global warming and ocean acidification attributed to rapid release and oxidation of buried carbon. We show that the onset of the PETM coincided with a prominent increase in the origination and extinction of calcareous phytoplankton. Yet major perturbation of the surface-water saturation state across the PETM was not detrimental to the survival of most calcareous nannoplankton taxa and did not impart a calcification or ecological bias to the pattern of evolutionary turnover. Instead, the rate of environmental change appears to have driven turnover, preferentially affecting rare taxa living close to their viable limits.