The geology and glacial history of the Walls of Jerusalem, Central Tasmania – a preliminary study

Abstract

The Walls of Jerusalem, in Tasmania’s Central Plateau, is marked by several dolerite escarpments, or “walls”, enclosing sheltered grassy valleys with Pencil Pine forests. Geologically, the area is a structurally raised block between two faults, with the peaks and plateaus being 100 m or so higher than the surrounding plateau. The valleys and escarpments may be mainly due to intense faulting and shattering of the dolerite by cross-faults, and removal of this material by glaciers. The higher peaks and plateaus have all been abraded by ice, except for an extraordinary patch at Solomons Throne, which retains irregular scree piles coloured red with lichen. Virtually all the valley floors are covered by glacial till, which probably relates to the younger glacial episodes. It consists mostly of dolerite boulders and clay, and shows subdued morainal forms in most places, with a few matrix-free boulder deposits probably representing lag after meltwater washing. Bedded clay deposits formed in lakes and meltwater streams as the ice retreated are extensive within the drift deposits, reflecting the confined nature of the two glacier lobes which entered the valleys from north and south. Dolerite screes along the scarps appear to post-date most of the morainal deposits, but some older screes may also be present. The Temple eminence within the centre of the Walls consists of fragmented dolerite overlying Triassic sandstone, almost completely covered by periglacial and glacial deposits, including superb examples of solifluction flows. There are many unanswered questions concerning the glacial deposits, but the lack of any dates means it is not yet possible to establish a comprehensive glacial chronology.