23. Sedimentary History of the Red Sea

Numerous studies have been made of Recent Red Sea sediments concerning their paleontology, mineralogy, or geochemistry. In addition, over 50 reports have been published on the sedimentary environment of the hot brine area (21°N) in the central axial valley (see Degens and Ross, 1969, and contained references; Backer and Schoell, 1972). These studies generally indicate considerable climatic fluctuations within the Holocene and Late Pleistocene that are reflected by changes in fauna and sediment characteristics. In general, aragonite-cemented lithic layers formed during periods of glacially or tectonically lowered stands of sea level when salinity increased in the Red Sea (Milliman et al., 1969). Lowered sea level would restrict inflow of Indian Ocean water from the Straits of Bab el Mandeb. This, combined with the high evaporation rate prevailing over the Red Sea, would result in increased salinity during these periods. Benthonic foraminifera also reflect higher salinities in that there is an increased presence of forms tolerant of high salinity during the times of lowered sea level. Geochemical investigations (Deuser and Degens, 1969) likewise show increased δ 0 1 8 / δ 0 1 6 during these periods, indicating evaporitic loss of lighter O 1 6 .