Paleocene and Early Eocene Microfacies, Benthonic Foraminifera, and Paleobathymetry of Deep Sea Drilling Project, Sites 236 and 237, Western Indian Ocean

Abstract

A significant and abrupt change in the sedimentary regime at Site 237 provides evidence for an early Tertiary subsidence of the Mascarene Plateau area in the western Indian Ocean. Between approximately 62 and 57 m.y.B.P. pelagic sediments were deposited at Site 237 in upper bathyal (200-600 m) depths with admixtures of slumped material from nearby shoals at a rate of about 68 m/m.y. The sea floor began to sink in the late Paleocene (57-58 m.y.B.P.). Introduction of shallow-water material ceased and normal pelagic sedimentation proceeded, at a rate about six times slower, at lower bathyal (600-2500 m) depths. Deepening at Site 237 at this time permitted development of deep-water benthonic foraminiferal faunas similar to those at Site 236 to the north. A further decrease in the rate of sedimentation occurred near the end of the Paleocene and in early Eocene, from approximately 54 to 50 m.y.B.P. During that period of time an interval of nondeposition spanned the Paleocene/Eocene boundary at Site 236. The area at Site 237 has subsided approximately 2000 meters over the past 52 m.y. This sequence of events on the Mascarene Plateau is similar to, and synchronous with, the subsidence history of the Chagos-Laccadive Ridge to the east.