Micromorphological evidence for polyphase deformation of glaciolacustrine sediments from Strathspey, Scotland
Published:January 01, 2000
E. R. Phillips, C. A. Auton, 2000. "Micromorphological evidence for polyphase deformation of glaciolacustrine sediments from Strathspey, Scotland", Deformation of Glacial Materials, Alex J. Maltman, Bryn Hubbard, Michael J. Hambrey
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A combination of field investigation and micromorphological analysis has been applied to polydeformed Late Devensian rhythmites and glacigenic diamicton, exposed in Strathspey, Scotland. This provided information on the geometry, kinematics and relative ages of ductile and brittle structures, and records a complex subglacial deformation history. The deformation is interpreted as resulting from a single progressive event, associated with over-riding of proglacial lake sediments by wet-based ice. The earliest deformation (‘D1’) resulted from compaction/loading (pure shear) and imposed a bedding-parallel (S1) fabric throughout the rhythmites. S1 was subsequently deformed by kink bands and minor ductile shearing during ‘D2’. A later ‘D3’ event, characterized by soft-sediment deformation and fluidization of matrix-poor sands, was accompanied by an increase in pore water pressure. This lead to hydrofracturing of the rhythmites. The most intense deformation (‘D4’), which resulted from simple shear, was partitioned into the upper part of the sequence. It produced folding, thrusting and brittle microfaulting in response to NNW-directed ice-push. These findings indicate that, in general, subglacial deformation is not homogeneous and can extend to depths of >3 m below the presumed ice-sediment interface.
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Deformation of Glacial Materials
The flow of glacier ice can produce structures that are striking and beautiful. Associated sediments, too, can develop spectacular deformation structures, and examples are remarkbly well preserved in Quaternary deposits. Although such features have long been recognized, they are now the subject of new attention from glaciologists and glacial geologists.
This collection of papers addresses how the methods for unravelling deformation structures evolved in recent years by structural geologists can be used for glacial materials, and the opportunities offered to structural geologists by glacial materials for studying deformation in rocks.