Abstract

The Neoproterozoic sedimentary rocks on the eastern margin of the Adelaide "Geosyncline" include two major glacigenic successions. The lower of these, the Yancowinna Sub-Group (as much as 5,000 m thick), can be divided into four stratigraphic units deposited in a northwest-trending graben. Dramatic thickness variations are attributed to contemporaneous normal fault movements. The thin basal granite-boulder diamictite/conglomerate of Unit 1 is considered to represent ice-proximal deposition in a temperate glacial setting. Unit 2 is a heterogeneous mudstone-dominated succession formed from fine material provided by meltwater streams during glacial recession when the basin was starved of coarse debris. Coarser grained facies were deposited by sediment gravity-flow mechanisms. The thick diamictites of Unit 3 are interpreted as rain-out deposits formed during a second glacial advance. Unit 4 records the terminal glacial recession. Paleo-current measurements suggest that the sediment source was the Curnamona Cratonic Complex to the northwest. These rocks are the most easterly preserved Neoproterozoic glacigenic deposits of the Adelaide "Geosyncline" and are therefore relevant to comparisons with regions such as western North America, which were possibly adjacent, prior to the breakup of a Neoproterozoic supercontinent.

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