Modification of sedimentary rock clasts in high Arctic polythermal valley glacier environment: case study from the Bertilbreen, central Svalbard
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| Year of publication | 2012 |
| Type | Conference abstract |
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| Description | Bertilbreen is polythermal valley glacier located on the Spitsbergen Island. The valley are made of paleozoic snadstones and limestones. All these rocks are present as clasts in different glacial deposits. Clast shape characteristics in moraines and glaciofluvial stream were studied. Approx. 40–50% of the clasts is striated in the frontal and ice-cored (ablation) moraines and the till plains of the Bertilbreen. We can assume that at least half of clasts creating these landforms initially underwent an active transport at the glacier base. The striation could thus be used to determine the minimum amount of actively transported clasts at the glacier base in sediments with abundant sedimentary rocks clasts. This phenomenon could not be use when crystalline rocks are dominant, because striation is created much less on the surface of the crystalline rocks. In the braided outwash fan the limestone and sandstone clasts shapes differ. This is probably caused by the primary rock conditions influencing strongly the clast modification during the glaciofluvial transport. This might be seen in a trend of changing the limestone clasts towards the more isometric ones and to the predominance of subrounded projections. Sandstones create clast with lower sphericity and that are clearly more angular than limestone clasts (sandstones clasts are predominantly subangular in the distal part of the fan). Breakages of sandstone clasts towards more angular platy clasts before and during the transport were probably affected by the primary bedding and jointing of these rocks. Limestones were, however, rounded and did not break apart. A clear trend of gradual diminishing of clast striation with an increasing glaciofluvial transport distance was not found here. |
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