PRELIMINARY RESULTS FROM THE PLIOCENE PART OF ODP DRILL SITE 188-1165, EAST ANTARCTIC CONTINENTAL MARGIN

Site 188-1165 was drilled on the Wild Drift on the Continental Rise off Prydz Bay, East Antarctica (64° 22.77'S, 67° 13.14'E, 3537 m) to a total depth of 999.1 mbsf. It recovered terrigenous and hemipelagic sediments of early Miocene to Pleistocene age.

We are currently carrying out detailed analyses of sand-sized material at that site. Our efforts are concentrated on the interval between 15 and 50 mbsf, which contains the Gauss Normal Chron (2.581 to 3.580 Ma) including the Kaena (3.040 to 3.110 Ma) and Mammoth (3.220 to 3.330 Ma) subchrons which are well identified at this site (timescale of Berggren et al., 1995).This interval is important because it contains the PRISM2 (Middle Pliocene Paleoenvironmental Reconstruction) time slab (3.15 to 2.85 Ma) described by Dowsett et al. (1999). The global ice volume, and consequently, sea-level stand during this period of past global warmth is important because it may provide an indication of how Earth may respond to future global warming (Dowsett et al., 1999). Although our investigations are still in progress, preliminary results are described below:

· All samples, regardless of textural classification, have a sand-sized component (0.0625 to 2 mm), but many samples are without a gravel component. The 0.15 to 2 mm fractions of the sand-sized components consist primarily of lithogenous (terrigenous) material-biogenous components (mainly radiolarians) are rare. Lithogenous components are quartz, feldspar, mafic minerals, lithic fragments of all three rock families, coal, etc. Quartz consists of several populations, including clear and clouded quartz, quartz with rutile and other inclusions, and quartz as component of lithic fragments. · Although some quartz grains are well rounded, a few having the characteristics of wind-blown grains, the vast majority of quartz grains exhibit the mechanical breakage features typical of glacial environments such as conchoidal fractures, step-like fractures etc.

This fact indicates that during the time period studied here, Antarctic glaciers reached the coast and had marine termini. Any reconstruction of Antarctic ice volume during the Pliocene must consider this constraint.