Development and infill of Vistulian glacial Lake Gniew (N Poland): a sedimentological analysis

Mirosław Błaszkiewicz, Beata Gruszka

Abstract


A substantial glaciolacustrine unit in northern Poland, between the valleys of the Vistula and Wierzyca rivers, was deposited in glacial Lake Gniew during the climatic amelioration of the Late Vistulian. It covers an area of 35 km2 and has an average thickness of 7 m, but locally reaches over 20 m. Four sedimentary facies are distinguished. The silty/clayey rhythmites of facies A are interpreted as varves from the central lake bottom. They represent the initial stage of lake development. Facies B is formed by a single sand layer that is interpreted as a turbidite originating during lake shallowing due to self-drainage. Facies C consists of massive clay with dropstones and dump structures. Two hypothesis regarding its genesis are put forward: the first assumes sedimentation in a shallow basin with a high input of homogenous fine-grained suspended sediment, whereas the second explains the facies as a result of a muddy jökulhlaup, pouring into Lake Gniew and being sourced from another glacial lake; further research is required to interpret this facies reliably. Facies D consists of thick silty/clayey rhythmites that are interpreted as prodeltaic deposits.

Keywords


Vistulian; glacial lake; sedimentology; glaciolacustrine deposits; massive clay; jökulhlaup

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