Ice-crevasse sedimentation in the eastern part of the Głubczyce Plateau (S Poland) during the final stage of the Drenthian Glaciation

Tomasz Salamon

doi:10.1515/geo-2020-0182

Abstract

AbstractGlacial sediments in the eastern part of the Głubczyce Plateau, at the Krowiarki site, were studied. Two units were distinguished within the sedimentary succession. The lower unit is composed of mainly sandy sediments with diamicton interbeds, the upper unit of very fine silt and clay sediments that exhibit rhythmic lamination in parts. Based on the textural and structural features of deposits, local deformations and palaeoflow directions, it was found that the sediments had been deposited within an ice crevasse, which was initially open and functioned as an ablation flow artery. The sediments were deposited in the form of a small fan dominated by sheetflows. Glacial tills were also redeposited on its surface. In a later phase, the crevasse was blocked. As a result, it was filled with water, leading to the development of a crevasse lake in which low-energy deposition dominated. The crevasse style of deposition indicates that, in the final stage of glaciation, the marginal part of the ice sheet was in a stagnant phase. This conclusion applies to the part located on the southern side of the watershed of the eastern Głubczyce Plateau. The probable reason for the stagnation of the ice sheet was the distinct loss of ice supply above the local topography barrier due to the decreasing thickness of the ice sheet in the studied area.

Highlights

Research on glacial landforms deposited in various types of depressions within stagnant ice, lake crevasses, kettle holes
In understanding this sedimentary environment, characterised by great variability in the conditions and course of deposition [4,5,6,7], an important role is played as well by research on contemporary glacial systems [e.g. 8–10]. Glacial landforms of this type are very well preserved and documented in many areas of Poland, especially those glaciated during the Weichselian and Warthanian Glaciations [e.g. 11–21]. They are known from areas located further south, such as the forelands of the Sudetes Mountains [e.g. 22,23] and Polish Uplands [e.g. 24,25], which were glaciated during older glaciations; the degree of recognition of glacial landforms is generally much lower there
The sediment succession at the Krowiarki site is a record of deposition within a continually expanding ice crevasse

Summary

Introduction

Research on glacial landforms deposited in various types of depressions within stagnant ice, lake crevasses, kettle holes, Glacial landforms of this type are very well preserved and documented in many areas of Poland, especially those glaciated during the Weichselian and Warthanian Glaciations [e.g. 11–21]. They are known from areas located further south, such as the forelands of the Sudetes Mountains [e.g. 22,23] and Polish Uplands [e.g. 24,25], which were glaciated during older glaciations; the degree of recognition of glacial landforms is generally much lower there. Its relatively best-known aspect is the stage of maximum glaciation and the first phase of the ice-sheet recession

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