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Ribbed moraine formed by subglacial folding, thrust stacking and lee-side cavity infill.
- Source :
-
Boreas . Feb2008, Vol. 37 Issue 1, p102-131. 30p. 6 Color Photographs, 7 Diagrams, 2 Charts, 1 Graph, 2 Maps. - Publication Year :
- 2008
-
Abstract
- Transverse-to-iceflow ribbed moraine occurs in abundance in the coastal zone of northern Sweden, particularly in areas below the highest shoreline (200–230 m a.s.l.), but occasionally also slightly above. Based on detailed sedimentological and structural investigations of machine-dug sections across five ribbed moraine ridges, it is concluded that these vertically and distally prograding moraine ridges were formed as a result of subglacial folding/thrust stacking and lee-side cavity deposition. The proximal part of the moraines (Proximal Element) was formed by subglacial folding and thrust stacking of sequences of pre-existing sediments, whereas the distal part (Distal Element) was formed by glaciofluvial and gravity-flow deposition in lee-side cavities. The initial thrusting and folding is suggested to be a result of differences in bed rheology at the ice-marginal zone during the early or late melt season, and that generated a compressive zone transverse to ice flow as a result of a more mobile bed up-glacier compared to a less mobile bed down-glacier. It is considered that the lee-side cavities were formed as a result of ice-bed separation on the distal slope of the thrust/fold-created obstruction. The lee-side cavities formed an integral part of a subglacial linked-cavity drainage network regulated in their degree of interconnection, size and shape by fluctuations in basal meltwater pressure/discharge and basal iceflow velocity. The proximal and distal elements of the ribbed moraine ridges are erosively cut and/or draped with a consistently more homogeneous deforming bed till (Draping Element) marking the final phase of ribbed moraine formation considered to be contemporaneous with De Geer moraine formation further down-flow at the receding ice-sheet margin. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 03009483
- Volume :
- 37
- Issue :
- 1
- Database :
- Academic Search Index
- Journal :
- Boreas
- Publication Type :
- Academic Journal
- Accession number :
- 34185239
- Full Text :
- https://doi.org/10.1111/j.1502-3885.2007.00002.x