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

The Konkian basin, during its widest extent in the Early Konkian (Kartvel) time, covered approximately the same areas as the preceding Karaganian basin. Subsequently, the area of the basin was reduced in the Sartagan time and again slightly expanded in the Veselyanka time. In the deepest parts of the sea (in the Black Sea and South Caspian depressions, in the West Kuban and Terek-Caspian troughs) carbonate silts continued to accumulate as background sediment, often bearing thin beds of marls or dolomites. Sand devoid of fauna or containing shells of pteropods (Limacina), planktonic foraminifera (usually of the genus Globigerina), and in places radiolarians, repeatedly entered the depressions located closer to the source areas. In the Late Konkian (Veselyanka) time, the reduced connections of the Konkian Sea with the global ocean resulted in the alteration of polyhaline fauna and phytoplankton to impoverished euryhaline assemblages. Water haline stratification along with increased river runoff caused a sharp growth of monospecific calcareous nannofossils Reticulofenestra pseudoumbilicus association at the hydrological front and accumulation of a marker horizon of nannofossil marl traced along the entire northern flank of the Greater Caucasus. The northern and eastern shores of the Konkian Sea were flat with a wide gentle shelf and deep gulfs, among which the most significant were Borysthenes, North-Ustyurt and Fore-Kopetdagh ones dominated by muddy-sandy and shelly substrates. The Caucasian and Crimean islands represented large but low structures, as evidenced by a small proportion of terrigenous input. In Ciscaucasia, the input was associated primarily with the Russian Plate and, to a lesser extent, with Caucasus Island. The Lesser Caucasus and Dziruli uplifts provided more significant proportions of coarse terrigenous material. In the west the Konkian basin was connected to the Late Badenian Sea via the Birlad and Fore-Dobrogea corridors, and in Transcaucasia, via the Middle-Araks Strait. The climate was humid, subtropical in the Transcaucasian areas, and closer to temperate along the northern coast, with signs of aridity in Transcaspia inherited from the Karaganian-Chokrakian time.