Mineralogy and Lithofacies of Black Sea Sediments, Leg 42B Deep Sea Drilling Project

Abstract

In general, three types of sediments were encountered in the three sites drilled during Leg 42B in the Black Sea: terrigenous, chemical (calcite, high-magnesian calcite, aragonite, dolomite, siderite), and biogenic (mainly diatomaceous). Terrigenous muds predominate in the Pleistocene whereas chemical sediments are abundant in the lower Pleistocene and Pliocene sediments. Biogenic constituents play a minor role only. Five different lithofacies could be recognized which are related to the changing environmental conditions in the Black Sea. The facies are: terrigenous muds, Seekreide, sapropelic diatomaceous clay, siltstone with dolostone intercalations, and siltstone. In many intervals a cyclic sedimentation of carbonate-free sapropelic sediments and carbonate layers were noted which is explained by an oscillating density boundary with anoxic conditions and the dissolution of carbonates below the interface. Stratification is often caused by the influx of marine waters into a fresh water Black Sea. The changes in the Mg/Ca ratio of the Black Sea water determine the carbonate mineralogy. Dolomitized crusts, oolites, algae mats, intraclasts, and pellets found in the Pliocene sediments suggest deposition in a shallow marine to supratidal environment with subsequent diagenetic alteration under meteoric conditions. The Pleistocene sediments are basically influenced by the climatic fluctuations related to glacial and interglacial periods. A distinct shift in the importance of the different source areas is noted. The late Miocene-Pliocene to lower Pleistocene sediments characterized by abundant smectite are mainly derived from the south (Turkey) whereas the increased amount of illite and detrital dolomite which occur in the Pleistocene sediment sequence indicate sediment transport mainly from the north (Danube).