Abstract

High-latitude carbonate rocks that formed in subpolar Paleozoic oceans contain critical information about past climate, but they are neither well documented nor fully understood. Lower and middle Permian limestones that were deposited in such paleoenvironments at 45°S to 55°S along the southeastern margin of Gondwana are now exposed in eastern Australia. Such carbonates constitute a small but important and well-preserved part of the siliciclastic glacigene succession in the Bowen Basin from southern and central Queensland. Cleanest limestones accumulated on topographic highs in the eastern (seaward) parts of the basin that were isolated from siliciclastic sediment input from the western craton. Shallow-water deposits are composed of large eurydesmid bivalves, spiriferid and productid brachiopods, bryozoans, infaunal and epifaunal benthic foraminifers, calcareous sponge spicules, and abundant crinoids in the form of locally cross-bedded rudstones and grainstones. Deeper-water, muddy carbonates are dominated by bryozoans, crinoids, and productids (shells and spines). Deepest-water sediments are argillaceous floatstones or shales containing fenestrate bryozoans, thin-walled productids, and siliceous sponge spicules. When integrated with recent studies of coeval sedimentary rocks along the 2000-km-long paleocontinental margin, a clear pattern of sedimentation emerges wherein deposition took place in similar settings during three discrete periods of deglaciation: late Sakmarian, late Artinskian, and Wordian. All of the carbonates are distinguished by a low-diversity, high-abundance heterozoan biota with no phototrophs and express a recurring deepening-upward stratigraphic motif that is interpreted to reflect rising sea level accompanying glacial meltdown. They also record a strong poleward gradient of increasing ice-rafted debris, increasing skeleton size, decreasing invertebrate diversity, decreasing epifaunal calcareous benthic foraminifers, and reduction in crinoids; glendonites are confined to siliciclastic sediments deposited during glacial periods. Comparison with coeval northern hemisphere carbonates indicates a strong parallelism of facies and depositional systems. This study helps to establish these deposits as a template for a global Paleozoic high-latitude carbonate facies model.

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