A TIME-SLICE APPROACH TO THE HISTORY OF CENOZOIC SEDIMENTATION IN THEINDIAN-OCEAN

Results from drilling at over 100 sites have been combined with a new plate tectonic model to produce a series of palinspastic maps which re present ''snap-shots'' of the changing patterns of sediment accumulati on in the Indian Ocean through the Cenozoic. The maps clearly delineat e the main sedimentary depocenters and show how the sedimentary record has responded on an oceanwide scale to major changes in paleogeograph y (tectonics), paleocirculation and/or climate. Paleogene sediment acc umulation rates were generally low, with significant accumulation in o nly limited areas, suggesting weak ocean circulation and stable, well- stratified conditions. By contrast, the vigorous thermohaline circulat ion of the Neogene resulted in substantial widespread sedimentation. A ccumulation rates were generally high and displayed a wide range of va lues. Following rapid growth of the East Antarctic ice sheet in the Mi d-Miocene. carbonate sedimentation has been progressively restricted t o the shallow ridges and plateaus of the western Indian Ocean, but acc umulates there with locally high rates. The link between tectonics and terrigenous sedimentation is exemplified by the major deep-sea fans o ff East Africa (Zambezi fan) and India (Indus and Bengal fans) which d eveloped in response to uplift and erosion beginning in Late Oligocene time in the East African Rift System and the Himalayas, respectively. Although maps from only five widely spaced times are shown, the metho dology is such that a continuous series of maps, at intervals as close as 1 m.y. can readily be generated. Ultimately the combination of suc h time-slice maps with the results of detailed time series studies wil l provide a powerful tool for understanding past oceanic environments.