Sequencing the Sturtian icehouse: dynamic ice behaviour in South Australia

Abstract

The Cryogenian record of South Australia includes the type region of the Sturtian glaciation, the oldest of three pan-global icehouse intervals during the Neoproterozoic. Data are presented from previously little described sections at Holowilena Creek, Oladdie Creek and Hillpara Creek in the central and southern Flinders Ranges, where five facies associations are recognized. These are (1) diamictite and conglomerate, (2) interbedded heterolithic deposits, (3) hummocky cross-stratified sandstone, (4) lonestone-bearing siltstone, and (5) ferruginous siltstone and sandstone. The succession reveals significant lateral and vertical facies variation, which is linked to a complex inherited palaeotopography and distance from the sediment source. Repeated stratigraphic occurrences of striated clasts and abundant ice-rafted debris strongly support recurrent glacial influence on sedimentation. The intercalation of gravitationally reworked diamictites, dropstone-bearing siltstone and dropstone-free siltstone testifies to dynamic sedimentation within a periodically glacially influenced subaqueous environment. Sequence stratigraphic analysis identifies four glacial advance systems tracts, separated by three glacial retreat systems tracts, wherein hummocky cross-stratified sandstones attest to open water conditions. These findings support dynamic ice sheet behaviour in South Australia, and provide clear evidence for repeated intra-Sturtian ice sheet recession.