The development of criteria to distinguish glaciotectonic and glaciomarine sedimentary environments

Roberts, David Howard (1995) The development of criteria to distinguish glaciotectonic and glaciomarine sedimentary environments. University of Southampton, Doctoral Thesis.

Abstract

The palaeoenvironmental interpretation of many of Britain's glaciogenic sedimentary formations has been highly contentious over the last decade. The main reason for this has been a renewed interest in glaciomarine environments, which has led to a number of contrasting glacial sedimentary reconstructions within the glaciological literature. In particular, there has been vigorous debate between those advocating glaciotectonic models and others who have favoured glaciomarine models, with many of Britain's more complex glacial formations being subjected to glaciomarine re-interpretations.

These differences in interpretation have arisen as a basic consequence of glacioterrestrial and glaciosubaquatic processes producing sediments that in many instances are visually very similar. This is particularly the case where glacial diamicts are deposited, as distinguishing sedimentary features of any kind are often lacking. The correct identification of such deposits is essential not only for the accurate assessment of contemporary and ancient glaciogenic sedimentary processes, but also for the wider implications that relate to ice sheet behaviour, sea-level and climate interaction. If the sedimentary processes that control glacier dynamics cannot be understood, the correct prediction of the future relationships between glaciers and their broader environment will not be possible.

This research has attempted to identify criteria to distinguish glaciotectonic and glaciomarine sediments using macroscale and microscale analytical techniques. On the macroscale these include analysis of: lithofacies associations, sedimentological and structural style, and macrofabric data. The utilisation of macroscale analysis alone however, cannot identify the features which make one glacial deposit distinct from another and sedimentary micromorphological techniques have been extensively applied in order to accurately reconstruct sediment history. The methodology that has been adopted necessitates the investigation of a number of contemporary glacioterrestrial and glaciomarine environments from which a range of glaciogenic sedimentary criteria have been established. Having established these criteria, they have been used to test the depositional origins of a number of Quaternary glaciogenic formations that have recently been the subject of contradictory glacioterrestrial and glaciomarine models.

This research shows that subglacial glaciotectonic sediments are deposited and deformed by a range of ductile and brittle shear mechanisms which determine the structural morphology of the sediment matrix. Ductile intergranular pervasive shear mechanisms tend to produce massive, isotropic sediment matrices in contrast to brittle shear mechanisms which impart a higher degree of anisotropic character to a sediment matrix. The interrelationship between these two shear mechanisms, and the rheological controls that determine their distribution may play a dominant role in the stratified form of many subglacial diamicts. (DX191283)

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