Inception of a Continental-Scale River From Segmented Paratethys Basins: Possible Timing and Size of the Danube River Flowing Into the Black Sea

Abstract

The modern Danube River is the largest fresh water and sediment volume contributor to the semi-enclosed Black Sea Basin, and likely was the same in the past. Along its course of 2,800 km from central Europe to the Black Sea, the Danube River passes through a string of Para-Tethyan (Vienna, Pannonian, and Dacian) basins. During the late Miocene these basins were active sinks, most of them with bathyal water depths and deep lake turbidites. The basins along the Danube fairway fragmented the sediment routing and partitioned the sediment budget to the extent that makes the possibility of an active “proto-Danube” at that time highly unlikely. However, the Black Sea, the ultimate sediment sink in the region, and hydrocarbon exploration showed that received significant sediment volumes from the north-west area throughout the Miocene. Such observations raise questions about (1) the timing of the Danube River inception, and (2) upstream paleogeography that made delivery of large sediment volumes to the north-west Black Sea possible. The regional paleogeography and timing of fill of the adjacent Pannonian and Dacian basins are analyzed. Despite previous suggestions on the location and Messinian crisis timing (5.5-5.8Ma) of inception of the initial paleo-Danube in the Dacian Basin such hypotheses are problematic. At the time of the Mediteranean Messinian Crisis the Pannonian and Dacian basins were underfilled. Even during lowstand conditions they would still be local sinks and unable to connect and sustain a continental-scale proto-Danube river. Our arguments for a later integrated river drainage and proto-Danube formation are based on the presence of thick, Romanian age (3.2-4.8 Ma) fluvial channel belts in the Dacian Basin with pointbars over 10 m high and more than 300 m wide, with associated with thick coal deposits. The size of such channel belts requires a drainage basin that was larger than the area east of the Carpathian Mts., and therefore suggests that the Pannonian and the Dacian basins were connected. A proto-Danube river of Romanian age most probably discharged into the western Black Sea in the area of the present Danube Delta.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016