Comparison of the Depositional and Halokinetic History of Suprasalt and Subsalt Minibasins at Patawarta Diapir, Flinders Ranges, South Australia

摘要

Outcrops of mixed carbonate/siliciclastic strata comprise the Neoproterozoic Wonoka Formation and Patsy Hill Member of the Bonney Sandstone at Patawarta diapir in the Flinders Ranges, South Australia, which is a ramping allochthonous salt sheet flanked by suprasalt and subsalt minibasin strata. Lithofacies distribution, thicknesses, and stratal geometries are analyzed to correlate suprasalt and subsalt Wonoka and Patsy Hill strata within a depositional and halokinetic sequence stratigraphic framework. Wonoka and Patsy Hill strata represent regional deposition in a storm-dominated carbonate shelf environment. The subsalt minibasin at Patawarta diapir contains upward-shallowing outer wave-dominated shelf to coastal plain facies in the Wonoka Formation and tidally dominated barrier bar facies in the Patsy Hill Member. The Patsy Hill Member records a major shift in depositional systems from the underlying carbonatedominated Wonoka Formation to the overlying siliciclastic-dominated Bonney Sandstone. Wonoka strata correlate laterally between the suprasalt and subsalt minibasins in terms of facies distribution and depositional setting. In contrast, Patsy Hill facies show significant lateral variation between suprasalt and subsalt positions, suggesting strong control on deposition by a diapiric high. This is especially evident from the lateral distribution of quartzite pebble conglomerates, which record different periods of exposure and erosion of the allochthonous salt sheet during deposition. Subsalt Wonoka and Patsy Hill strata compose a tapered composite halokinetic sequence that displays upturn over a distance of 560 m and stratal thinning (1100 to 110 m) toward the diapir. Suprasalt Wonoka and Patsy Hill strata display significant but gradual thinning (1,882 to 19 m) over a distance of 3-5 km forming a broad, open fold with local upturn at the saltsediment interface. The suprasalt and subsalt minibasins at Patawarta diapir have been evaluated to generate a depositional model that accounts for lateral and vertical salt migration and salt-modified bathymetry in a shallow marine environment characterized by allochthonous salt.