Geographia Polonica (1976) vol. 33 1

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On glacial origin of Grudziądz Basin, Lower Vistula River Valley

Eugeniusz Drozdowski

Geographia Polonica (1976) vol. 33 1, pp. 23-40

Abstract

The characteristic features of the lower Vistula River valley are numerous widenings known from the literature as basins. Their geologic structure and relief differ considerably from the adjacent valley reaches as a result of differential action of both glacial and fluvial processes. This is particularly true for the largest widening of the lower Vistula River valley — the Grudziądz Basin.

The origin of this basin have been discussed for a long time. So far, two hypotheses have prevailed: the first, put forward by A. Jentzsch (1911), relates the formation of the Grudziądz Basin to a large proglacial lake at the mouth of the Mątawa River outwash, the second, advanced by R. Galon (1934), regards lateral erosion of the meandering Vistula River as the main process responsible for its origin.

The present paper is a new attempt at solving the problem based on geo-logic and geomorphologic research (E. Drozdowski 1974, 1975), including re-sults of pollen analysis and radiocarbon dating. It emphasizes the hitherto unrecognized glacial landforms and deposits associated with the melting of dead-ice blocks which — as it turned out during the field examination — occur in that area together with distinctive fluvial features. This fact justifies the conclusion that the fluvial processes operating in the valley in the Late Glacial period were intimately associated with glacial processes. Consequently, the former existence of the Scandinavian ice sheet and its geomorphologic activity are regarded here as a substantial factor which affected the formation of the discussed widening of the Vistula River valley.

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Eugeniusz Drozdowski, Institute of Geography and Spatial Organization, Polish Academy of Sciences, Toruri, Poland