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Victoria University Antarctic Research Expedition Science and Logistics Reports 1996-97: VUWAE 41

3.1 A Preliminary Report on Sirius Group Deposits, Table Mountain James Goff and Ian Jennings

3.1 A Preliminary Report on Sirius Group Deposits, Table Mountain James Goff and Ian Jennings

Sirius Group deposits on Table Mountain appear to result from both advancing and retreating glaciers. The topography, however, is the result of glacial retreat and includes patterned ground, water-lain deposits, and mass movement features. Cores taken through the Sirius Group should help explain the role played by water in ice advance and retreat at the site, and in dating the event.

Fabric data from deposits at the southern end of Table Mountain indicate that this area was a confluence zone for ice emanating from the directions of the contemporary Tedrow and Ferrar Glaciers. However, the imprint of "Ferrar" ice dominates Sirius Group sediments at Table Mt. Other minor contributions of sediments were made from small mountain glaciers emanating from the saddle area between Table Mt and Navajo Butte. We believe that ice from these sources may have been sufficient to occupy the anomalous hollow (Figure 1) at Table Mountain which is devoid of glacial deposits.

Deposits that contain a small percentage of granitic clasts are found several hundred metres upslope from the prominent dolerite sill at Table Mt (Figure 1). The abundance of granitic clasts appears to increase down slope suggesting it was sheared up by glacial flow immediately downglacier of a confluence zone. Fabric measurements, taken from south to north along the length of Table Mt, indicate a reorientation of ice flow from west to southwest. Reorientation was caused by Table Mt obstructing ice flow which has resulted in the deposition of thrust-faulted lodgment tills and associated deposits. Lodgment and thrust-faulting may represent a period of glacial advance.

Ice retreat and down wasting has left an extensive ridge and hollow topography. Ridges generally consist of glacial diamictite, covered by a boulder lag, while the hollows consist of either conglomerate or sand. The deglacial environment appears to be dominated by water-lain deposits of which the conglomerate and sand suggest that both high and low energy regimes were involved.

Three distinct mass movement features cut across the ridge and hollow topography. Patterned ground, which is pervasive throughout the Table Mt area, is most prominent on these mass movement features but less prominent on the ridge and hollow topography. It is not clear if the degree of prominence expressed by the patterned ground, represents different degrees of activity, different ground materials, or different periods of generation.