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Six sites (759-764) were drilled on the Exmouth Plateau during Ocean Drilling Program Leg 122. Nannofossilrich Cenozoic sediments were recovered at all six sites, reflecting the open-ocean conditions that prevailed over the Exmouth Plateau during the Cenozoic. Calcareous nannofossils are abundant, diverse (250 different species identified), and generally well preserved throughout the composite lower Paleocene to Quaternary section. The diversity and preservation of nannofossils permits a high degree of stratigraphic resolution at each site. Site 762 on the central part of the Exmouth Plateau contains an almost unbroken Cenozoic record (only Miocene Zones NN3, NN8, and NN10 are missing). This site may prove to be a useful Cenozoic biostratigraphic and biomagnetochronologic reference section for the eastern Indian Ocean. INTRODUCTION The Exmouth Plateau is a rifted and subsided fragment of continental crust lying off the coast of northwestern Australia (Fig. 1). The relatively thin cover of post-rift sediments over this plateau makes it an ideal location for study of the evolution of the plateau by drilling through the overburden to pre-rift rocks. The Exmouth Plateau has, moreover, consistently remained elevated above the calcite compensation depth during its post-rift history, a circumstance favorable for preservation of the carbonate record. Six sites (759-764) were drilled on the Exmouth Plateau during Leg 122 of the Ocean Drilling Program (ODP). Two of the sites (762 and 763) are located on the central Exmouth Plateau; the remaining four are on a northern marginal horst named the Wombat Plateau (Fig. 1). Sedimentology, lithostratigraphy, and other details of these sites are described in detail in the Leg 122 Initial Reports (Haq, von Rad, O'Connell, et al., 1990). Results of the Exmouth Plateau drilling have provided a much clearer understanding of the evolutionary development of this part of the Indian Ocean from the time of initial rifting (Triassic), through breakup and separation (Late JurassicNeocomian) and the development of a juvenile ocean (AptianConiacian), to the establishment of mature ocean conditions (post-Coniacian). Integrated geologic studies on the plateau rely on a refined stratigraphic framework for placing events in an accurate chronostratigraphic context. The purpose of this paper is to document the biostratigraphy of the major portion of the mature ocean phase, the Cenozoic, using calcareous nannofossils. BIOSTRATIGRAPHY Smear slides of core samples were examined using a light microscope. The appendix lists the calcareous nannofossil 1 von Rad, U., Haq, B. U., et al., 1992. Proc. ODP, Sci. Results, 122: College Station, TX (Ocean Drilling Program). 2 Department of Geology, Vanderbilt University, Nashville, TN 37235, U.S.A. 3 Department of Geology, Florida International University, Miami, FL 33199, U.S.A. (Current address: Department of Geology, University of North Carolina, Chapel Hill, NC 27599, U.S.A.) species found in the Cenozoic sediments on the Exmouth and Wombat plateaus. Nannofossils are abundant in almost all Cenozoic samples examined and preservation ranges from moderately well preserved to very well preserved. Where range charts are given in the following sections, the relative abundances of individual species are indicated as follows: A = abundant, more than 10 specimens of a single species per field of view at a magnification of 1000×; C = common, 1 to 10 specimens per field of view; F = few, one specimen per 2-10 fields; R = rare, one specimen per 11-100 fields; and V = very rare, one specimen per 101-1000 fields (Tables 1-5). Selected species (mostly those used in the biomagnetochronologic assessment) are illustrated in Plates 1-5. Smear slides and photographic negatives of these species are stored in the Micropaleontology Collection, Department of Geology, Vanderbilt University. TAXONOMIC NOTES The following notes on taxa are arranged in the general order the taxa are encountered in the cores, from oldest to youngest. Prinsius spp. A number of small (2-6 μm) species of Prinsius occur in Zones NP1 and NP2. Perch-Nielsen (1985) has recognized P. petalosus, P. dimorphosus, P. tenuiculum, P. africanus, and P. martinii. These small forms could not be resolved with consistency using the light microscope, so all have been included in the range-chart tables under the category "small Prinsius spp." P. bisulcus is a larger (>6 μm), distinctive form, which is listed separately in the tables. Zygodiscus bramletteilZ. herlynii. The distinction between these two species is based on the relative thickness of the coccolith wall and the relative size of the central openings. We found it difficult to make confident assignments to one species or the other, and have elected to combine the two forms into a single category in the range charts. Ericsonia cava and Coccolithus pelagicus. Where both species occur together in the Paleocene, we have used E. cava for elliptical forms with a distinctive open central area that is usually about one-third the total width of the specimen. C. pelagicus looks somewhat similar at the start of its range, but has a smaller central opening, or contains a structural element in the central opening. Dictyococcites callidus and Dictyococcites daviesii. We could not differentiate these two species using the light

Cenozoic Calcareous Nannofossil Biostratigraphy on the Exmouth Plateau, Eastern Indian Ocean