Paleoecologic and paleoceanographic evolution of the tethyan realm during the paleocene-eocene transition

Analyses of planktic foraminifera and stable isotopes from sections in Kazakstan (Kaurtakapy), Spain (Alamedilla, Zumaya) and the Bay of Biscay (DSDP Site 401) suggest similar overall paleoecologic, paleoceanographic and paleoclimatic patterns during the Paleocene-Eocene (P-E) transition, although regional differences are apparent. The major difference in δ¹³C values measured in benthic Cibicidoides spp. is seen in the gradual decrease of ∼1% in Subzones P5a and P5b in the Tethys and its absence elsewhere. In planktic foraminifera, regional differences are marked by changes in the relative abundances of warm water taxa and cool water subbotinids. Overall, the P-E transition is marked by the following sequence of faunal and isotopic events. Near the P-E boundary (Zone P5b) and coincident with the benthic foraminiferal extinction event and the δ¹³C excursion, warm water planktic foraminiferal assemblages (e.g., acarininids, igorinids and morozovellids) rapidly diversified, suggesting surface water warming. Thereafter (Zone P5b/P6a), increased abundance in cool-temperate planktic foraminifera (e.g., subbotinids) and a concomitant increase in the abundance of low oxygen tolerant chiloguembelinids, suggest cooling and hypoxic conditions at thermocline depths that may have been due to changes in watermass stratification and upwelling. This cooling is followed by a second more gradual warming, where acarininids slowly replace morozovellids as the dominant surface dwellers. The biozonation of Berggren and others (1995) has been modified by subdividing Zone P5 into Subzones P5a and P5b based on the first appearance of Acarinina sibaiyaensis and/or Acarinina africana. This modification of Zone P5 provides greater age control for the P-E event with the P5a/P5b boundary coincident with the BFEE and the δ¹³C excursion.