Middle Weichselian Pleniglacial sedimentation in the Krasówka river palaeovalley, central Poland

Abstract

This study from the Szczerców field of the Bełchatów open-cast mining complex, central Poland, reveals the local geomorphic and stratigraphic history of the Krasówka river palaeovalley – a major western tributary of the river Widawka. The data are from the western flank of the N-trending palaeovalley and the study combines detailed lithofacies analysis of outcrop sections, sediment petrology, AMS measurements and palynological evidence. Radiocarbon dates are of crucial importance for the reconstruction of the palaeovalley history. The study contributes to a better understanding of the response of the Central European river systems to the Vistulian Pleniglacial conditions.

The Vistulian Pleniglacial sedimentation in the study area commenced with the accumulation of the latest Eemian to earliest Weichselian (≥45 ka) deposits by sheetwash processes in a local karstic topographic depression. The Krasówka river then formed to the east and shifted farther eastwards, but later approached twice the study area with a net aggradation prior to 43 ka BP – flooding it with overbank deposits. The river subsequently incised by nearly 20 m around 40 ka BP and began to fill in its valley by aggradation around 35 ka BP, while migrating eastwards and markedly decreasing its flooding capacity from 33 to 24 ka BP. The fluvial system was rejuvenated around 21 ka BP, with some initial erosion, and kept filling its valley by aggradation while flooding the valley flank. The river after filling its valley continued to aggrade, but gradually ran out of vertical accommodation and migrated westwards. The fluvial activity at this stage was increasingly accompanied by aeolian sedimentation. Once the Mid-Weichselian Pleniglacial came to an end around 14.5 ka BP, the Krasówka river had re-incised by nearly 5 m and assumed its present-day altitude in response to the post-glacial regional isostatic rebound of crustal basement.