GLENDONITES AS PALEOCLIMATE INDICATORS WITHIN THE MIDDLE PERMIAN WANDRAWANDIAN SILTSTONE, SOUTHERN SYDNEY BASIN, AUSTRALIA

Glendonite, a mineral psuedomorph after ikaite (CaCO₃·6H₂0), appears in numerous horizons within the middle Permian Wandrawandian Siltstone of the Southern Sydney Basin. Ikaite, stable at near-freezing temperatures, precipitates authigenically at or below the sediment-water interface in deep marine settings, and the presence of its psuedomorphs has been used as a proxy for paleotemperature. Approximately 25 horizons within the Wandrawandian Siltstone preserve some record of glendonites, either as molds or as crystals. These horizons typically correspond to intervals of abundant outsized clasts, which have been interpreted as ice-rafted debris. In the lower part of the formation, glendonites are found proximal to and contained within a slumped interval. Glendonite horizons in the upper part of the formation occur in the silty sandstones that are interbedded with tuffaceous claystones. The position of the glendonites relative to hiatus and their association with outsized clasts points towards a climatic trigger of these features. Three glendonite morphologies are present: bladed, stellate, and rosette forms. The bladed forms are typically found in fine-grained sandstone, whereas rosettes are found in slightly finer grained facies ranging from admixed sand and silt to fine-grained sandstone. Stellate forms are commonly found together with either bladed or rosette forms in fine-grained silty sandstone. Where glendonites are present, Zoophycus and Helminthopsis dominate the trace fossil assemblage and brachiopods, fenestrate bryozoans, stony bryozoans, rugose coral, and crinoids are among the fossils present. Bioturbation intensities and fossil concentrations range from sparse to abundant. Within the glendonites numerous calcite phases demonstrate multiple generations of cementation. Cathodoluminescence and geochemical analysis are used to evaluate diagenesis and identify the least-altered calcite within the glendonites. A detailed delineation of the paragenetic relationships of the calcite phases and the paleoclimatic significance of the isotopic data will be addressed.