The geology of Permian sediments and erratics, Troubridge Basin, South Australia

Abstract

The Troubridge Basin lacks obvious tectonic control. It probably was a broad topographic depression, which had an irregular topography of 700-100m relief. Sub-glacial till occurs only in isolated patches. Sedimentation was initiated by glacial retreat, possibly influenced by isostatic or eustatic movements. Massive sands, claystones and shales of lacustrine, fluviatile and brackish facies predominate. Glacial outwash and aeolian deposits may also occur. Most diamictites are density flows or ice-rafting deposits. Original tills were probably reworked by meltwater and post-glacial erosion. A sediment thickness of at least 700m accumulated. There are two erratic assemblages, a local and an exotic one. The local assemblage occurs in till and slumped till and is not common. It is not known whether exotics occur in the local assemblage. The exotic assemblage is ubiquitous and occurs in outwash and in ice-rafted facies. The source area had a metamorphic basement, cut by younger intrusives, which were in turn overlain by a thick volcanic sequence. It has been impossible to unambiguously relate the erratics to areas of known outcrop.