Neogen diatom biostratigraphy of ODP Leg 138 sites

These sediments represent the most complete stratigraphic sequence recovered since the start of scientific ocean drilling by the Deep Sea Drilling Project (DSDP) and ODP. The diatoms observed generally are common to abundant and well-preserved throughout the samples examined.

The assemblages are characterized by species typical of low-latitudes and regions of high surface-water productivity and are dominated by Thalassiothrix longissima, Thalassionema nitzschioides, Azpeitia nodulifer, and numerous species of Thalassiosira and Nitzschia. Fifty-six biostratigraphic events were identified at Sites 844 through 852, allowing us, in part, to use the diatom zonation of Barron (1985a). This zonation was modified by replacing the Rhizosolenia preabergonii Zone and the upper portion of the Nitzschia jouseae Zone, as used by Barron (1985a), with the Nitzschia marina and Nitzschia jouseae zones, as used by Baldauf (1984, 1987).