ABSTRACT

Studies of eight sediment cores from deep-water environments in the Red Sea show four lithologic facies: light lutites, hard layers, dark lutites and reef-derived debris. Carbonate minerals are dominant in all four facies. Terrigenous material is present in all but the reef-derived debris.

The light lutites are the common facies of the Red Sea. Mineralogically, they are composed predominantly of high-and low-magnesian calcite. Aragonite, where contributed by Pteropods, is progressively removed at depth by dissolution. In the hard layers, which are interbedded with light and dark lutites, aragonite was precipitated, binding the grains together and providing drusy fibrous infilling and syntaxial fibrous growth on grains. High salinity and temperature are necessary to the precipitation of aragonite; the lutite/hard layer couplets reflect fluctuating temperature and salinity at sea bottom. However, aragonite is subject to dissolution in the hard layers after temperature and salinity return to normal. High-magnesian calcite forms part of the matrix in some of the shallower h rd layers, and appears to serve as a cement under more normal marine conditions. The dark lutites represent reducing conditions prevalent in the southern part of the Red Sea basin. The reef-derived debris, found in the shallowest of the cores studied, is brought in from nearby reefs occupying shelves of the basin.