Tremolada, F., and Bralower, T. J., 2004 - Penn State University

114F. Tremolada, T.J. Bralower / Marine Micropaleontology 52 (2004) 107–116Fig. 7. Palaeoceanographic model for causes and effects of the PETM in greenhouse conditions.combination of somewhat higher oxygenation andlower productivity (Fig. 6).The PETM triggered the rapid radiation of theplanktonic foraminifera (e.g., Kelly et al., 1996) andland mammals (e.g., Clyde and Gingerich, 1998).The rate of extinction in the benthic foraminiferalcommunities varies from tropical to high latitude sites(e.g., Kaiho et al., 1996; Speijer et al., 1996). Theextinction of the northern temperate-latitude and highlatitudenannofossil species, Octolithus multiplus, waslikely caused by increasing temperature, and theelimination of Fasciculithus possibly resulted fromcompetition with Zygrhablithus bijugatus. Furthermore,palynofloras show no extinctions and onlymoderate changes in composition and diversity duringthe Paleocene–Eocene transition (e.g., Wing andHarrington, 2001).6. ConclusionsNannofloral changes associated with the PETMtransition at DSDP Sites 213 and 401 correlate withthose documented from several other locations, suchas ODP Site 690 (Bralower, 2002) and Alamedilla,southern Spain (Monechi et al., 2000). The PETM canbe subdivided into a lower part and a upper part on thebasis of nannofossil assemblages. The lower part ischaracterized by high abundances of Discoaster spp.,Ericsonia spp., and Fasciculithus spp., interpreted asindicators of warm surface waters and probably oligotrophicconditions (Wei and Wise, 1990; Aubry,1992; Kelly et al., 1996; Bralower, 2002). The upperpart shows an increase in abundance of Toweius spp.and Zygrhablithus bijugatus, which likely reflectsmore eutrophic and cooler conditions.The major nannofloral changes at DSDP Site 213seem to be strongly affected by diagenesis. Theincrease in abundance of genera most resistant todissolution, such as Discoaster, Ericsonia, and Fasciculithus,inversely correlates with the nannofossilspecies richness at Site 213.The appearance of asymmetrical Discoaster andRhomboaster species might indicate the developmentand availability of new ecological niches, resultingfrom major palaeoceanographic changes during thePETM (Bralower, 2002). The last occurrence ofOctolithus multiplus might be a reliable bioevent atnorthern intermediate and high latitudes.AcknowledgementsWe gratefully acknowledge K. von Salis, J. Young,J. Lees, and an anonymous reviewer for criticalcomments that helped us improve the manuscript.Many thanks to I. Premoli Silva, E. Erba, I. Raffi, J.Backman, and G. Dickens for thoughtful discussions.Samples were provided by the Ocean DrillingProgram, and we thank the curatorial staff for their