Showing papers by "Arjen P. Stroeven published in 1999"

Age of Sirius Group on Mount Feather, McMurdo Dry Valleys, Antarctica, based on glaciological inferences from the overridden mountain range of Scandinavia

Abstract: A striking difference in the geomorphology of the ice-sheet overridden lowlands and ranges in Scandinavia and the Wilkes Basin–Transantarctic Mountains region in Antarctica is the occurrence of basal till sequences (of the Sirius Group) on summits and interfluves in the Transantarctic Mountains and the lack of basal tills on corresponding surfaces in Scandinavia. From the pattern of glacially eroded surfaces and preserved preglacial surfaces in northern Sweden, we infer altitudinal and lateral patterns of glacial erosion and deposition governed by topography-dependent basal thermal regimes. Furthermore, summits and interfluves in northern Sweden are often remnants of preglacial surfaces. Consequently, these preglacial surface remnants were preserved underneath patches of cold-based ice. We conclude that the subglacial thermal zonation of ice sheets overriding peripheral mountain ranges is self-sustained by topography; i.e., cold-based ice relates to topographic highs and warm-based ice to topographic lows. We use these inferences to explore the glaciological implications for the Sirius Group sequence on Mount Feather, McMurdo Dry Valleys. A glaciologically plausible explanation for this deposit and similar Sirius Group sequences on dissected summit and interfluve surfaces in the Transantarctic Mountains is that deposition occurred before the bulk of the relief formed. The present relief in the Mount Feather vicinity is at least 11 Ma old. Consequently, the Sirius Group at Mount Feather is at least of middle Miocene age.

Stereological analysis of ice flow-induced preferred orientation of small clasts in tertiary tillite matrix of Mt Feather

Abstract: The Sirius Group tillite at Mt Feather, McMurdo Dry Valleys, Antarctica, is a deposit of considerable importance to tl1e early glacial history of the Antarctic Ice Sheet. We investigate the power of stereological analysis for a11 objective (determination of the preferred direction of small clasts (< 5 mm) in two cores and, hence, in two core samples drawn at different depths below the tillite surface. Orthogonal sets of vertical thin sections were prepared on this core material. Images measuring 34x22 mm were prepared of 14 subareas, jointly representing most of the area, of at vertical thin section. From each of these sub-areas, a field of constant 340x340 pp-size was analysed. This involved at systematic line scanning operation, in which the number of intersections between particle traces and the line system was determined. To reduce structural scatter, the resulting 14 roses of the number-of-intersections were averaged per vertical section. These roses reveal the signal coming from the preferred orientation of the clasts to be weak, but above the sensitivity level of the approach. However, this signal is camouflaged by the effect of digitization on the intersection counts, preventing under the present conditions to assess a reliable estimate for the tilt angle of the clasts.