Abstract
Abstract North Norfolk is a classic area for the study of glacial sediments with a complex glaciotectonic deformational history, but the processes leading to the formation of some structures can be ambiguous. Anisotropy of magnetic susceptibility (AMS) analyses, providing quantitative fabric data, have been combined with the analysis of visible structures and applied to the Bacton Green Till Member, exposed at Bacton, Norfolk. Thermomagnetic curves, low temperature susceptibility and acquisition of isothermal remanent magnetism (IRM) reveal that the magnetic mineralogy is dominated by paramagnetic phases. The magnetic foliation is parallel to fold axial planes and weakly inclined to bedding, whilst the magnetic lineation is orientated parallel to stretching, indicated by the presence of stretching lineations and the trend of sheath folds. Variations in the orientation of the magnetic lineation suggest that the Bacton section has been subject to polyphase deformation. After subaqueous deposition, the sequence was overridden by ice and glaciotectonically deformed which involved stretching initially north–south, then east–west. These results show that AMS can be used to detect strain in three dimensions through a glaciotectonite where paramagnetic mineralogy is dominant. This approach therefore provides further support to the use of AMS as a fast, objective and accurate method of examining strain within deformed glacial sediments.
Highlights
In this paper we demonstrate the power of an under-utilised geophysical technique for determining the fabric of dynamically deposited glacial deposits and the directions of the flows that created them
The primary evidence used to infer dynamic processes has been through the properties of the glacigenic sediments and landforms left behind by the large ice sheets that covered much of North America and Europe during the Pleistocene Epoch (Licciardi et al, 1998; Piotrowski et al, 2001)
These results indicate that paramagnetic minerals are controlling the susceptibility and the anisotropy of the sediments
Summary
In this paper we demonstrate the power of an under-utilised geophysical technique for determining the fabric of dynamically deposited glacial deposits and the directions of the flows that created them. A wider definition is used to encompass a body of unlithified or weakly lithified sediment deformed by glacial stresses (Benn and Evans, 2010; van der Wateren, 2002). Within such sediments, distinct structures form such as folds, faults, boudins and fabrics (Hart and Rose, 2001).
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