Composition and accumulation rates of eolian sediments in ODP Site 128-798

Preliminary bulk and clay mineralogy data as determined by XRD as well as accumulation rates of quartz and feldspar at Oki Ridge Site 798 give important information about the paleoclimate in Asia and transport mechanisms of the siliciclastic sediment fraction. The (?uppermost Miocene/) lowermost Pliocene sediments at ODP Site 798 are characterized by high amounts of feldspars, smectites, and additionally abundant sand-sized terrigenous components. This is taken as an indication for turbiditycurrent-influenced deposition and a source area of the material different from that of the upper Pliocene/Pleistocene sediments. A distinct increase in accumulation rates for quartz and feldspar occurs near the Gauss/Matuyama boundary. We attribute this prominent shift to higher eolian sediment supply, caused by the increased aridification of Asia, which was probably triggered by the development of major Northern Hemisphere glaciation near 2.5 Ma. The late Pliocene/Pleistocene interval is characterized by short-term "Milankovitch-type" cyclic changes in terrigenous sediment composition most probably reflecting glacial/interglacial arid/humid climate cycles.