QUATERNARY CASPIAN SEA: DYNAMICS OF LEVEL FLUCTUATIONS AND RESPONSE GEOCHEMICAL CHANGES

Quaternary history of the Caspian Sea –lake represents an uninterrupted changes of the trangressive and the regressive phases. For the example on the background of the general tendency of the Caspian Sea level fall since the beginning of XXth century repeated temporary rises (measured by from some tens of centimeters to 1-2 m) have taken place. Analyzing climatic conditions through the Quaternary time one can say that the Caspian Sea level has been rising in a humid (pluvial) setting in the Caspian basin, which is characterized by the increase of atmospheric precipitation and the decrease of temperature and evaporation. Such conditions existed at the borders of interglacial and glacial periods that is proved by direct correlation of the Caspian Sea transgressions with climatic events of Europe on the base of absolute age data. The regressive phases in Caspian Sea Pleistocene history took place both in the maximum of glaciation epochs and interglacial periods, which have been followed by reducing of atmospheric precipitation led to sea level drop. Thus, Caspian Sea level short-periodical fluctuations have been initiated by general Eurasian climate change reflecting the eustatic processes of the North Atlantic Ocean. Such dramatic environmental changes led to considerable shifts in geochemical setting. Through the Late Pliocene-Quaternary section one can observe significant variations in bionomic conditions of the basin expressed in differentiating of Fe/Mn, Sr/Ba values. Late Pliocene Caspian Sea was characterized by the largest salinity and depth- (Fe/ Mn - 5; Sr/ Ba - 0.41), which then significantly reduced in the Early Pleistocene (Fe/ Mn - 7.1; Sr /Ba - 0.134). Middle-Upper Pleistocene basins’ depth and salinity underwent numerous variations, reaching the lowest values at the end of Pleistocene time- 6-7 promiles. Being based on ferrous/ferric oxide ratio one can observe unstability of geochemical regime in studied basins. The strong reduction conditions in Late Pliocene have been changed by weak reduction geochemical facies at the beginning of Early Pleistocene transforming then into moderate reduction setting at the end of Lower Pleistocene. Analogous geochemical environment preserved during Middle- Upper Pleistocene.