Sedimentary processes at the entrance Gulf of Aden / Red Sea

Abstract

Coastal and shallow water biogenic carbonate and detrital silicate near Bab el Mandeb are transported northward by surface currents until they are trapped by the central channel and carried southward into the northwestern Gulf of Aden. Here, the highest sedimentation rate with more than 50 cm carbonate and 50 cm silicate per 1000 years is found. On the narrow shelves widespread shell beds, calcareous crusts, and "mummies" with sessile fauna demonstrate intermittent deposition. The floor of the channel is devoid of sediments or covered with gravel and sand. A living in situ sessile and burrowing fauna as well as displaced shallow water organisms and Pleistocene (?) relict sediments have also been observed here down to watet depths greater than 500 m. Increasing grain size with depth on the channel slope indicates a current velodty profile at extreme conditions different from that measured by oceanographers. With some exceptions corals and bryozoans are the most important (by weight) carbonate producing organisms of beach, shelf, and channel sands. Heavy minerals from the hinterland of the African and Arabian coasts are mixed and frequently reworked in the channels in the same mannet as the biogenic constituents. Crevasses paralleling a channel in the western Gulf of Aden as well as the range of the South Arabian heavy mineral province indicate young tectonic movements. A simplified model may help to interpret andent sediments of similar environment (Text-figs. 18 b and c)