Ocean Drilling Program (ODP) Leg 183 Hole 1140A was rotary cored on the northernmost Kerguelen Plateau (KP), ~270 km north of the Kerguelen Islands (Fig. F1) in a water depth of 2406 m. The KP is a large igneous province (LIP) in the southern Indian Ocean and is believed to have formed via magmatism of the Kerguelen hotspot over the last 120 m.y. (Shipboard Scientific Party, 2000a). This feature is ~2500 km long, between 200 and 600 km wide, and rises ~2-4 km above the surrounding abyssal plain. The present location of Hole 1140A is 46°15.6´S, 68°29.5´E (Fig. F1). The main science objective of drilling Hole 1140A was to core igneous basement, to characterize the petrography of the igneous rock, to provide minimum age constraints on the emplacement of igneous basement, and to test the hypothesis that the northern Kerguelen Plateau (NKP) formed at ~40 Ma. Hole 1140A reached a total depth of 321.9 meters below seafloor (mbsf), and 234.52 m of sediment was recovered that ranged in age from late Eocene to middle Miocene based on shipboard paleontological data (Shipboard Scientific Party, 2000b). Previous Eocene to Miocene diatom sections were recovered on the NKP during ODP Legs 119 and 120 (Baldauf and Barron, 1991; Harwood and Maruyama, 1992).
The main purpose of this study is to describe the abundance, preservation, and biostratigraphic distribution of Oligocene to Miocene diatoms in Hole 1140A. This site has been above the calcite compensation depth (CCD) since the late Eocene, allowing nannofossils and foraminifers to be preserved along with diatoms. Thus, there is the potential for an improved multi-microfossil biostratigraphic scheme for the Kerguelen Plateau region. This study will provide a lower Oligocene-middle Miocene diatom biostratigraphy for the NKP and will contribute to the overall diatom biostratigraphic scheme being developed for the Southern Ocean (Fenner, 1984, 1991a, 1991b; Gersonde and Burkle, 1990; Baldauf and Barron, 1991; Harwood, 1991; Harwood and Maryuma, 1992; Harwood et al., 1998; Scherer et al., 2000; Harwood and Bohaty, 2001).