THE CONNECTIONS BETWEEN THE BLACK SEA AND MEDITERRANEAN DURING THE LAST 30 KY

The evidences of water exchanges between the Black and Mediterranean Seas extends to 30 ky BP in the Istanbul Strait and the Marmara Sea, and are mostly in agreement with each other. However the history of the reconnection of the two basins during Holocene are still contradictory. The lowermost sedimentary unit above the Paleozoic basement reflects a freshwater shallow environment at about 26 ky BP, with yellow-brown, well sorted medium to fine sands containing neo-euxinian fresh water mollusc species. It indicates a connection between the Black Sea and the neo-euxinian-lake part of the Strait. The sediments from the Marmara Sea also indicates a prevailing freshwater lake conditions until 12 ky BP, before the Mediterranean waters inundate it with globally rising sea level. Between the last glacial maximum and the main period of deglaciation, the Marmara Sea and small depressions of the Strait became site of isolated neo-euxinian lake sedimentation, with the lowering of sea level in the Black Sea. Deposition of sapropelic layers in the Marmara Sea between 10.6 and 6.4 ky BP is shown to be associated with the strong outflow from the Black Sea, while Mediterranean waters were prevented from entering the Istanbul Strait. Available seismic profiles from the southern shelf of the Black Sea indicate a major erosional surface. This eroded surface, varying in a water depths of between –95 and 125 m, is almost exposed to the sea floor and covered only by a thin veneer, indicating the lowstand of sea level before the latest rise in the Black Sea. The absence of onlap in the thin veneer suggests that the latest rise/transgression must have occurred relatively fast or steady. The beginning of this latest transgression, regardless of Black Sea or Mediterranean originated waters, was found to be at about 11.8 ky BP in the southwestern shelf, whereas 8.5 ky in the southeastern shelf from the coarse-grained shelly (mixed neo-euxinian and Mediterranean fauna) sedimentary unit lying at or close to erosional surface.