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Inception of the Continental Scale Danube River: On the Time of Its Arrival Into the Black Sea Basin as It Formed From Segmented Paratethyan Basins

Abstract

The modern Danube River is the largest fresh water and sediment volume contributor to the semi-enclosed Black Sea Basin. Over its actual 2,800 km length from central Europe to the Black Sea, the Danube River pass through a string of Paratethys (Vienna, Pannonian, Dacian) basins. During Late Miocene these basins were active sinks, some of them with bathyal depths and deep water deposits. The basins along the Danube River fragmented the sediment routing within a paleogeography difficult to form a “proto-Danube”. However, the Black Sea, ultimate sediment sink in the region, received significant sediment volumes to the north-west area throughout the Miocene. High sediment volumes raise the question about (1) the timing of the Danube River inception and (2) the paleogeography conducive to large sediment volumes in addition to (3) basin fill of the adjacent Pannonian and Dacian basins which will be analyzed. The Late Miocene deposits in the Black Sea show a significant deposition style change from sandy deposits to more mixed sandy-muddy deposits. The depositional change point to the integration of the Danube River through Pannonian and Dacian basins and deliver sediments to the Black Sea. The Pannonian basin was filled (become alluvial) at around 4.5 Ma and then allowed the sediments drained from Pannonian bypass to the east into the Dacian Basin. The study documents the deposits of a large Pliocene “proto-Danube” river in the Dacian Basin in Romania, and despite previous suggestion on the time of Danube inception in the Dacian Basin around the Messinian crisis (5.5-5.8 Ma) such hypothesis is problematic. The underfilled Pannonian and Dacian basins at the time of Mediteranean Messinian Crisis, even under lowstand conditions, were still local sinks and not able to connect and sustain a continental scale river. Our additional arguments for a latter than Messinian integrated river drainage and proto-Danube formation are based on the large, Romanian age (3.2-4.8 Ma), pointbars and thick fluvial channel deposits in Dacian Basin. The pointbar is over 10 m high, over 300 m wide and is associated with thick coal deposits. The size of large fluvial channel requires a drainage basin larger than the area east of Carpathians Mts. A drainage area larger than the Carpathians indicate that the Pannonian and the Dacian basins were connected during Romanian (3.2-4.8 Ma) to form proto-Danube that discharged into the western Black Sea in the area of the present Danube Delta.