ORIGIN OF LATE GLACIAL-HOLOCENE HEMIPELAGIC SEDIMENTS IN THE AEGEAN SEA - CLAY MINERALOGY AND CARBONATE CEMENTATION

Four hemipelagic lithological units are identified in the late glacial to Holocene sediments in the Aegean Sea. These lithologies are silty-clay and clay in texture and include a varying mixture of loose terrigenous sediments supplied from the adjacent landmass, gravel- to sand-sized cemented carbonate clasts and nodules, sand- to silt-sized air-born volcanic debris and biogenic remains. Sediment dispersal during the past 14,000 years was controlled mainly by the fluvial discharge rate, by sea-level variations which determined the proximity of basins to river mouths and by oceanographic conditions in the Aegean Sea. Cemented carbonate clasts and nodules occur in all sediments except Unit C (sapropel Si). They are well- to friably-cemented, mottled to peloidal micrite or microcrystalline inter-granular cement between terrigenous and bioclastic debris, and the carbonate is 10-11 mole % magnesium calcite. During the deposition of sapropel S1 (Unit C) the Aegean Sea was strongly stratified, with colder, more saline water masses occupying the deep basins, which prevented the development of cemented carbonate nodules and clasts. Aragonite, as pteropods and microcrystalline aragonite is present throughout the cores, and together with the cemented carbonate clasts and nodules, show that shallow pore waters in the Aegean Sea have been saturated to supersaturated with respect to both aragonite and magnesium calcite for at least the past 14,000 years. Results of XRD studies show that Unit C (sapropel S1) is characterized by lower smectite and kaolinite and higher illite and chlorite than the other units. Lower smectite/illite and kaolinite/chlorite ratios in Unit C may reflect increased supply of illite and chlorite from European lowland rivers flowing into the Black Sea, from rivers discharging directly into the northern and eastern Aegean Sea, and decreased supply of kaolinite which is mainly of North African origin.