Paleoecologic and paleoceanographic evolution of the Tethyan Realm during the Paleocene-Eocene transition

Analyses of planktic foraminifera and stable isotopes from sections in Kaza kstan (Kaurtakapy), Spain (Alamedilla, Zumaya) and the Bay of Biscay (DSDP Site 401) suggest similar overall paleoecologic, paleoceanographic and pale oclimatic patterns during the Paleocene-Eocene (P-E) transition, although r egional differences are apparent. The major difference in delta(13)C values measured in benthic Cibicidoides spp, is seen in the gradual decrease of s imilar to 1 parts per thousand in Subzones P5a and P5b in the Tethys and it s absence elsewhere. In planktic foraminifera, regional differences are mar ked by changes in the relative abundances of warm water taxa and cool water subbotinids. Overall, the P-E transition is marked by the following sequen ce of faunal and isotopic events. Near the P-E boundary (Zone P5b) and coin cident with the benthic foraminiferal extinction event and the delta(13)C e xcursion, 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 hy poxic conditions at thermocline depths that may have been due to changes in watermass stratification and upwelling, This cooling is followed by a seco nd more gradual warming, where acarininids slowly replace morozovellids as the dominant surface dwellers. The biozonation of Berggren and others (1995) has been modified by subdivid ing Zone P5 into Subzones P5a and P5b based on the first appearance of Acar inina sibaiyaensis and/or Acarinina africana. This modification of Zone P5 provides greater age control for the P-E event with the P5a/P5b boundary co incident with the BFEE and the delta(13)C excursion.