ICE SCOURS AND STORMS IN THE MARINOAN (NEOPROTEROZOIC) ELATINA FORMATION OF SOUTH AUSTRALIA

The Elatina Formation of South Australia (c. 580 Ma; ~100 m thick) is the type section for low-latitude Neoproterozoic Marinoan glaciation. Despite its global paleoclimatic significance there remain fundamental uncertainties about the precise depositional environments recorded by diamictites regarded by previous work as ‘ice push tillite', associated sandstone and mudstone facies, and the wider basinal setting. Here we illustrate and interpret sedimentary facies from two principal sections exposed at Trezona Bore and Bulls Gap in the central Flinders Ranges. Diamictites typically consist of thin (< 1 m) horizons of unorganized, non-oriented clasts suspended in sandstone that are laterally discontinuous along section. They are thickest (5 m) where they fill scours cut into deformed sandstones showing folds and extensive dewatering structures. Imbricated thrust rafts of underlying sandstone occur in the scours and reworked sand accounts for much of the diamictite matrix. A key contextual observation is that associated sandstones display hummocky and swaley cross-stratification typical of a storm-influenced shoreface setting. Diamictites and sandstones are typical of an ice-stressed nearshore environment where floating ice rafts coarse debris, and ice keels scour into the substrate. This is the first report of ice scours in the Neoproterozoic and has bearing on recent paleoclimate models that stress the role of dynamic sea ice.