Frederik M Van der Wateren

8.1 INTRODUCTION

During the Middle and Late Pleistocene, the Scandinavian Ice Sheets repeatedly covered the northern half of The Netherlands and Germany, most of Poland, Estonia, Latvia, Lithuania and Belarus, a small part in the north of the Czech Republic and the northern parts of Ukraine and Russia (Fig. 8.1). This chapter focuses on the southern part of the area glaciated by the Scandinavian Ice Sheets, between 49°N and 60°N, 3°E and 30°E.

The landscapes left behind by the Southern Scandinavian Ice Sheets show the typical characteristics of glaciated sedimentary basins, including interaction of the ice sheet with weakly lithified and unlithified sediments. Expanding from their core region, the Scandinavian shield — including Norway, Sweden and Finland — the ice sheets invaded the northern and northeastern European plains, underlain by major sedimentary basins filled with sequences of Mesozoic and Cenozoic sediments of up to 8 km in thickness (Ziegler, 1990). The distribution, morphology, structural geology and sedimentology of glacigenic deposits and landforms are strongly influenced by the geological structure of these basins. Existing crustal scale structures, such as the central European Variscan and Alpine orogens, rifts, major faults and salt structures, affected the geometry of aquifers over which the ice sheets advanced and the distribution of sediments of varying mechanical properties. This, in turn, controlled the hydrology, and thus the dynamics of the ice sheets, determining the location of ice sheet limits, ice streams, tills, thrust moraines and other moraines.

There has been considerable debate about the physical properties of the geological substrate over which the Fennoscandian Ice Sheets advanced and their consequences for ice sheet volumes, advance and retreat rates, sea level change and atmospheric circulation (e.g. Boulton, 1996b and references therein). Arguments for widespread deformable bed conditions beneath temperate ice sheets include features that are regarded as typical of subglacial deformation of saturated sediments. These range in scale from megaflutes and drumlins to smaller scale boudins, augen, 'pods', and tectonic laminations developed within tills (Boulton, 1987; Hart, 1994; Hart and Roberts, 1994). Arguments against a deformable bed model originate from the interpretation of laminated diamicts as glacimarine deposits and subaquatic, melt-out or lodgement tills (Eyles and McCabe, 1991; Piotrowski and Kraus, 1997; Piotrowski et al., 2001; Piotrowski and Tulaczyk, 1999).

Boulton (1996b) argued that it would be highly unlikely for a temperate ice sheet not to deform the underlying sediments. Large volumes of meltwater are produced at the base of temperate ice sheets, which are drained through the bed. Over large areas subglacial drainage is likely to produce high pore water pressures in the subglacial sediments, reducing the effective stresses to levels low enough for these sediments to deform, or even fluidize. Identification of features resulting from subglacial deformation may therefore help to reconstruct the dynamics of former ice sheets.

A recent debate on the distribution and relative importance of subglacial deformation (Hart et al, 1996, 1997; Piotrowski et al, 1997, 2001; Piotrowski and Kraus, 1997; Piotrowski and Tulaczyk, 1999) made it clear that widely accepted criteria to distinguish sediments that have been deformed by subglacial simple shear from sediments, that are undeformed — or deformed by other mechanisms — are largely lacking. Part of the disagreement stems from the lack of understanding of the various deformation histories and the resulting till fabrics. It is also the consequence of not consistently applying a structural approach to the analysis of subglacial tills, as is clear from the statement by Piotrowski et al. (2001): "It is easier to show that some tills were not pervasively deformed, than to demonstrate that others were". Most likely the reverse is true.

In a recent paper, Van der Wateren et al. (2000) use a structural approach to analyse unlithified to weakly lithified sediments, which have been subglacially deformed. The primary objective is to establish a set of criteria to distinguish undeformed sediments from those that have been subglacially sheared or otherwise deformed, and produce reliable tools for the reconstruction of past ice movement directions. The former is of critical importance for studies of piston or drill cores where the structural and sedimentological context is much less clear than it is in a good outcrop. Structural analysis is not a stand-alone tool; a multi-scale approach including sedimentological, morphological and geophysical data is strongly preferred (Kluiving et al.,

This chapter reviews the glacial landsystems of the Southern Scandinavian Ice Sheets. The following section presents a brief history of Middle and Late Pleistocene glaciations in Northern Europe. Glacial landsystem analysis seeks to reconstruct the dynamics of past ice sheets. As the Fennoscandian Ice Sheets expanded across regions of greatly varying structure and lithology it is important to consider first how glacial landsystems are affected by subsurface geological conditions. The regional geology of the Northern European Plains is then introduced with a discussion of the distribution of glacial landforms and glacitectonic styles produced subglacially as well as at the ice margin, and how these styles can be used to reconstruct glacial landsystems. This is followed by a focus on one particular glacitectonic style, structures developed in response to subglacial deformation, as these have been a continuous source of misunderstanding. Aspects of glacifluvial outwash, ice-marginal valleys and lakes in relation to end moraines are then discussed and the chapter concludes with examples of glacial landsystems of the Northern European Plains with a focus on Central and Northern Germany, and The Netherlands.

Glacial Deposition SystemsEasy Way Draw Image Moraines
Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

Get My Free Ebook


Post a comment