Middle–Late Miocene Paleogeography of the Eastern Paratethys. Part IV. Karaganian Basin: Stratigraphy, Facies, Paleogeography and Biota

The Karaganian basin was characterized by strongly impoverished, highly endemic fauna inherited from the previous Late Chokrakian basin and not reflecting the influence of open sea waters. A positive water balance following the isolation of the basin resulted in the expansion of its area. The area covered by the Karaganian sea significantly exceeded that of the previous Miocene basins and the Karaganian sediments in the marginal parts unconformably overlie older beds, often with a basal conglomerate layer. Intensive filling of deep-sea and shelf depressions with coarse terrigenous sediments, which began in the Middle Chokrakian, continued in the Karaganian. Algal-microbial buildups were common in the nearshore areas, along with sandy-clayey and calcareous-shelly sediments. Stress conditions of unstable hydrological regime, hot dry climate and sharp changes in water geochemistry resulted in stromatolite formation. The occurrence of coarse terrigenous sediments, terrestrial and freshwater mollusks in the foothills of the Mountainous Crimea and on the northern and southern slopes of the Greater Caucasus indicates uplifts in orogenic zones that became areas of denudation and erosion. At the same time, there is no significant difference in the distribution of sediments in the Karaganian time compared to the Chokrakian. Only the increased size of the basin in the north and east affected the location and configuration of lithofacies and terrigenous-mineralogical provinces. The climate was similar to the modern Mediterranean, it was seasonal with hot dry summers and precipitation mainly in autumn and winter. Despite the widespread accumulation of salts and gypsiferous facies in the basin’s margins, especially in the Turan part, the degree of desalination of the Karaganian basin was significant as evidenced by the frequent occurrence of freshwater mollusks, ostracods and diatoms in the sections.