PERMIAN POLAR LIMESTONES, TASMANIA

Tasmania was located adjacent to Antarctica and mainland Australia, at approximately 80°S, throughout the Late Paleozoic. Continental and fjord glaciers covered much of the area during the Late Carboniferous, but had largely disappeared by the beginning of the Permian. The Lower Parmeener Supergroup records marine and terrestrial sedimentation across a cold-water ramp during this time and can be divided into two large-scale sequences, with a similar distribution of facies in all but the most proximal environments. The lower sequence begins with glaciomarine diamictites; the upper sequence begins with fluvial and coastal sandstones and coals. Inner ramp sediments consist of bioturbated siltstones with glendonites that pass outboard into sparsely fossiliferous siltstones containing small brachiopods, diminutive bryozoans, and ostracodes. Such deposits are interpreted to record sedimentation in a stressed environment, possibly beneath sea ice. Mid-ramp deposits are characterized by fossiliferous siltstones and clean to silt-rich limestones with abundant bivalves (Eurydesma), brachiopods, bryozoans, and crinoids. Numerous dropstones were deposited in this environment that was periodically invaded by icebergs. Phosphates occurring within the fossiliferous silts and limestones as nodules, resedimented grains, and replaced bryozoans, signal episodic upwelling. Outer ramp sediments are mainly fossiliferous siltstones, and local turbiditic sandstones. Facies were controlled by variations in the position of relative sea level, temperature, salinity and upwelling across the cold-water ramp. The two sequences had a similar range of depositional environments, but differences are interpreted to reflect changing oceanographic conditions during the Early Permian.