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- Reinardy, Benedict T. I., et al.
(författare)
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Streaming flow of an Antarctic Peninsula palaeo-ice stream, both by basal sliding and deformation of substrate
- 2011
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 57:204, s. 596-608
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Tidskriftsartikel (refereegranskat)abstract
- Acoustic sub-bottom profiler surveys on the northeast Antarctic Peninsula shelf indicate that parts of the seabed are underlain by an acoustically transparent layer that is thin on the inner shelf and becomes thicker and more extensive towards the outer shelf. Sedimentological and geophysical data are combined to construct a bed model where streaming ice flow, by both deformation and basal sliding, took place within cross-shelf troughs. The model suggests only limited deformation contributed to fast flow on the inner shelf, i.e. in the onset zone of ice streaming, where the bed was predominantly underlain by a stiff till. Thus, fast ice flow in this area might have been by basal sliding, with deformation confined to discontinuous patches of soft till <40cm thick. Towards the middle and outer shelf, extensive, thick sequences of soft till suggest a change in the dominant subglacial process towards widespread deformation. This downstream change from basal sliding to subglacial deformation is manifest in the transition from stiff-till dominance to soft-till dominance, while a downstream increase in ice flow velocity is evident from the complex geomorphic imprint on the inner shelf evolving to the more restricted set of bedforms on the outer shelf.
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| 2. |
- Reinardy, Benedict T. I., et al.
(författare)
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Till genesis at the bed of an Antarctic Peninsula palaeo-ice stream as indicated by micromorphological analysis
- 2011
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 40:3, s. 498-517
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Tidskriftsartikel (refereegranskat)abstract
- Sediment cores from cross-shelf troughs on the NE Antarctic Peninsula shelf recovered tills with variable shear strengths that represent different subglacial depositional regimes. In addition to detailed qualitative micromorphological descriptions, a quantitative method was applied, which revealed a higher abundance of boudins and intraclasts and a lower abundance of crushed and fractured grains in samples from the soft till compared with samples from the underlying stiff till. This is the first evidence of significant (micro-scale) differences between the two types of till and thus strengthens previous interpretations that were based primarily on shear strength. The differences between the soft and stiff till relate to a deforming continuum whereby the initial deposition of till as ice advanced across the shelf produced ductile structures before dewatering and compaction led to the formation of brittle structures such as crushed and fractured grains in the now stiff till. A change in ice-flow dynamics led to streaming flow and the deformation of the upper parts of the stiff till that was being reworked into a soft till. The soft till facilitated ice streaming, and progressive shearing led to the homogenization of the ice stream substrate, which was partially advected downstream. The resulting till thus contains poly-deformational structures, with deformation structures inherited from the stiff till being generally poorly preserved. Our micromorphological analysis of the soft till provides the first widespread sedimentological evidence of deformation across the palaeo-ice stream bed on the NE Antarctic Peninsula shelf.
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