EVOLUTION OF A SUPRASALT MINIBASIN: NEOPROTEROZOIC (EDIACARAN) PATAWARTA SALT SHEET, FLINDERS RANGES, SOUTH AUSTRALIA

Neoproterozoic strata deposited above the allochthonous Patawarta salt sheet display thickness trends and stratal pinchouts that define the timing and location of suprasalt minibasin subsidence, salt inflation and cessation of diapir-related accommodation change. Patawarta suprasalt minibasin thickness and facies trends of the Wonoka Fm., Patsy Hill Mbr., and Bonney Sandstone are compared to regional thicknesses stated in the literature. The Wonoka outer shelf, turbiditic limestone facies on the distal margin (not directly overlying salt) of the suprasalt minibasin is 693m thick, which is consistent with the regional 600m thickness of the Wonoka. The Wonoka thickens from the distal margin into a suprasalt depositional syncline to 1638m. The Wonoka thins to 1m and displays a series of onlap stratal terminations onto the diapir proximal margin of the suprasalt minibasin. The overlying Patsy Hill peritidal dolomite and shoreface arkosic sandstone facies follows the same trend with a distal margin thickness of 152m, which is consistent with the regional Pasty Hill thickness of 100m. The Patsy Hill thickens to 217m into the suprasalt depositional syncline and thins by stratal onlap to 20m onto the diapir proximal margin. The overlying Bonney Sandstone, shoreface arkosic sandstone facies retain a uniform 460m thickness across the syncline, consistent with the regional Bonney thickness of 400m.

Thickness and onlap trends of the Patawarta suprasalt minibasin suggest subsidence initiated and was greatest during deposition of the Wonoka turbidite facies. Syncline axis strata are nearly 2.4 times the regional thickness and onlap the proximal salt-inflated syncline limb. Subsidence rate decreased during deposition of the Patsy Hill, where syncline axis strata are only 1.4 times the regional thickness and onlap stratal terminations are rare. Bonney Sandstone displays isopachous thickness indicative of the halting of the mini-basin subsidence and corresponding salt diapir rise. We conclude from these relationships that differential loading and high sedimentation rates of the Wonoka turbidite facies initiated subsidence on top of the Patawarta salt sheet.