O kopalnej pradolinie w Wielkopolsce

Stanisław Dąbrowski, Marek Szynalski



In the course of groundwater prospecting in the Wielkopolska region Quaternary sandy-gravel and silt deposits were found beneath tills of the Last Glaciation in some areas. The analysis of spatial distribution of these deposits (Fig. 1) and their sedimentary profile made it possible to assume their fluvial origin related to an ancient stream channel. The deposits were divided into proglacial-stream-valley, interglacial-stream-valley, stagnant-lake and fluvioglacial. Their thickness is estimated at 10 to 30 m. Proglacial stream valley deposits form sedimentary cyclotheme comprising gravels, medium-grained sands and fine-grained or silty sands. Deposits of interglacial valley occur in the belt 1-1,5 km wide, erosionally cutting proglacial-stream-valley deposits and forming sedimentary cyclotheme about 10 m thick. Stagnant-Iake and fluvioglacial deposits related to sedimentation in the time of subsequent Glaciation, occur in the top of both proglacial-stream and interglacial-stream-valley deposits. All these deposits occur in a marked erosional incision 25-50 m deep and 8-20 km wide. In the base of the proglacial-stream-valley deposits there occur clay and brown-coal Miocene and Pliocene deposits and tills of older Glaciations in erosional fragments. The margins of the proglacial stream valley are eroded in Tertiary "Poznań clays" and older tills. The proglacial and interglacial stream valley deposits as well as stagnant-lake and fluvioglacial deposits are covered by a series of tills and fluvioglacial deposits of Baltic Glalciation, 30-65 m thick. The setting of this form in the structure of Quaternary, and paleomorphology and paleogeography of this area suggest that its origin may be dated at the Mława stage of the Mid-Polish Glaciation. This valley represents a pre-Warta stream from the Eemian Interglacial.

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