Revista de Geomorfologie (Dec 2021)
A history of the circum-pontic river channels marked by climate and sea level changes during the Late Quaternary (25-8 ka BP)
Abstract
The present paper synthesizes the evolution of fluvial systems tributary to the Black Sea (within 25 – 8 ka BP time frame) by reviewing the existing paleoclimate, hydro-geomorphology, sedimentology and Late Quaternary chronology. These studies are unevenly distributed throughout the Black Sea (BS) drainage basin and were used to decipher the river response to climatic, eustatic, tectonically induced or vegetation cover changes. The river response was sensitive overall and is visible particularly in terms of the channel planform. The alternation of cold and warm climate phases has controlled to a significant degree the water and sediment inputs along the drainage networks, such that river channels planforms shifted from the braided type to the anastomosed type (with various transitional phases, either wandering or anastomosed), and from macro-meanders to small scale meanders. The climatic model of fluvial evolution was altered by the other controlling factors specific to the large BS drainage basin, including tectonics (in the Pannonian Plain, Western Plain of Romania, Lower Siret Plain), the proximity to coarse-grained sediment sources (typical for medium-sized Carpathian tributaries), the obstruction exerted by glacial sediments generated by the ice cap retreat (as illustrated on the Upper Dnieper), eustatic oscillations (detected on the Danube or Sakarya River). The sea level drop by more than 100 m during the Last Glacial Maximum resulted in the conversion of ca. 30% of the present sea surface to dry land (mostly on the NW continental shelf); several sinuous-anastomosed paleo-channels pertaining to major rivers (Danube, Dniester, Dnieper) with depths ranging between 30 and 90 m were reconstructed on the surface of this emerged land. Black Sea became connected to the Planetary Ocean during the Early Holocene (ca. 9.4 ka BP). The sea waters flooded extensive areas at the NW and advanced upstream along tributary river valleys. The effects of base level rise were reflected in the anastomosed style of river channels and the accumulation of deltaic formations.
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