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Unexpectedly old luminescence ages as an indicator of the origin of the upper Volga River valley sediments
Affiliation:1. 119311 Vernadskogo Prospect, 9, Moscow, 388, Russia;2. 121359 Orshanskaya Str., 9, Moscow, 258, Russia;3. 117437 Profsoyuznaya Str., 104, Moscow, 517, Russia;4. Nordic Laboratory for Luminescence Dating, Department of Geoscience, Aarhus University, DTU Risø Campus, Roskilde, DK-4000, Denmark
Abstract:Although the Upper Volga has been the focus of extensive research for several decades, its origin and evolution remain uncertain. According to the most popular model, the Upper Volga drainage network formed at the end of the last deglaciation (MIS 2); before that, the river basin was occupied by a large MIS2 proglacial lake. In this study we test this hypothesis by luminescence dating several fluvial terraces in the Upper Volga valley. Despite the expected late-MIS 2 age, our results show that quartz is in saturation, and the feldspar pIRIR290 signal gives much older dates than expected (∼300–∼500 ka). We argue that, in most sections, feldspar was very likely to be well bleached prior to deposition. Thus, if the ages of sedimentary structures are overestimated, this could only result from sediment transport in darkness. It is widely accepted that the MIS 6 glaciation was the last to cover the Upper Volga basin, and so such conditions would be most easily attributed to a subglacial environment. But this explanation is confounded by the absence of till on top of most sections. The alternative explanation, that the ages accurately reflect last deposition, calls into question the well-established MIS 6 border on the Russian plain, and we conclude that further studies are required to resolve this inconsistency.
Keywords:OSL dating  Feldspar luminescence dating  Sediment bleaching  Volga river  Russia
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