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

F. Tremolada, T.J. Bralower / Marine Micropaleontology 52 (2004) 107–116 109not represented due to an unconformity (Müller,1979).DSDP Site 213 was drilled on the eastern side ofthe Ninetyeast Ridge in the Indian Ocean at a palaeolatitudeof 28jS (Fig. 1). A sedimentary successionspanning the Upper Paleocene to Holocene was recovered(von der Borch et al., 1974). The PETMinterval lies in Core 16 and consists of brown, clayeysediments and nannofossil oozes of latest Paleocene–earliest Eocene age, directly overlying basement. Thebrown clay contains the upper part of the CIE indicatingthat the onset of the event is missing (Ravizzaet al., 2001).The PETM at both sites was sampled every centimetre.Quantitative analyses were carried out on 120samples from Sites 213 and 78 samples from Site 401.The PETM interval was investigated in 49 samplesfrom Site 213 and 51 samples from Site 401. Smearslides were prepared from well-mixed and unsettledsediment suspensions, and no ultrasonic cleaning orcentrifuge concentration was applied in order to retainthe original nannofossil composition. Nannofossilswere observed in the light microscope at 1250 magnification and identified following the taxonomicschemes of Aubry (1984, 1988, 1989, 1990), Perch-Nielsen (1985), and Varol (1998). Three hundredspecimens were counted in each smear slide. The firstseries of analyses on samples from Site 401 revealedthat the genus Toweius dominated the nannofossilassemblages. Supplementary counts of 250 specimens,excluding the genus Toweius, were thus undertakenin order to raise the percentages of other taxa tostatistically significant levels (Bralower, 2002). Interpretationsat Site 401 are based on the non-Toweiusfraction. If possible, specimens were identified at thespecies level during counts, and grouped at thegeneric level for analysis (Figs. 2–5).3. ResultsThe calcareous nannofossil assemblages throughthe PETM at Sites 401 and 213 show similar trends,but the magnitudes of the fluctuations are different.Nannofossils at Site 401 are very well preserved anddisplay a high species richness throughout the intervalFig. 2. Calcareous nannofossil (placoliths and Octolithus multiplus) assemblage fluctuations across the PETM at Site 401. NP biozonation afterMartini (1971); CP biozonation after Okada and Bukry (1980). Grey band indicates thermal maximum. Dashed line marks the boundarybetween the lower and upper parts of PETM.