Late Neoproterozoic periglacial aeolian sand sheet, Stuart Shelf, South Australia

Abstract

The late Neoproterozoic (ca 600 Ma) Whyalla Sandstone covers 25 000 km2 in outcrop and subcrop on the Stuart Shelf, South Australia, and is coeval with the Marinoan glaciogenic succession in the adjacent Adelaide Fold Belt. The flat‐lying formation is up to 165m thick and comprises mainly reddish brown, medium‐ to very coarse‐grained, well‐rounded, commonly bimodal quartzose sandstone that shows regional south‐southeastward fining. Low‐angle (≤15°) strata form the principal stratification type. Large‐scale cross‐bedded sets up to 7 m thick occur mainly in the central area; cross‐strata usually have dips of ≤20–23° and rarely up to 30°, and display grainfall and grainflow deposits, inversely graded subcritically climbing translatent strata, and pin stripe lamination’. Periglacial cryogenic structures in the basal 5 m of the formation include two generations of primary sand wedges, drop involutions, periglacial injections, frost‐heaved blocks, water‐escape structures, and thermokarst microtopography. Small‐scale tensional faults suggest collapse caused by snow melt. The sedimentary features of the Whyalla Sandstone together indicate an aeolian origin and the periglacial structures imply a cold, arid and strongly seasonal climate. The preponderance of low‐angle strata accords with a periglacial sand‐sheet environment, with dune forms confined mostly near the centre of the sand sheet. Cross‐bedding attitudes and the direction of regional fining, together with palaeolati‐tudes inferred from palaeomagnetic data for Marinoan glaciogenic strata in the Adelaide Fold Belt, imply the movement of cold, dry palaeowinds obliquely toward or across the palaeoequator during the Marinoan glaciation. © 1998 Taylor & Francis Group, LLC.