TIMING OF ALLOCHTHONOUS SALT EMPLACEMENT OF THE NEOPROTEROZOIC (EDIACARAN) PATAWARTA SALT SHEET, FLINDERS RANGES, SOUTH AUSTRALIA: EVIDENCE FROM THE SUBSALT MINIBASIN

Neoproterozoic strata currently in a subsalt minibasin position below the allochthonous Patawarta salt sheet display thickness trends and stratal pinchouts that constrain the timing and location of the Patawarta salt sheet breakout. Patawarta subsalt minibasin thickness and facies trends of the Wonoka Fm., Patsy Hill Mbr., and Bonney Sandstone are compared to regional stratigraphic thicknesses stated in the literature. The Wonoka outer shelf, turbiditic limestone facies on the distal margin (away from the salt sheet) is 975m thick and thins to 117m through a series of onlap stratal terminations onto the Patawarta diapiric high. The overlying Patsy Hill peritidal dolomite and shoreface arkosic sandstone facies follows the same trend with a distal margin thickness of 135m, consistent with the regional Patsy Hill thickness of 100m and thinning to 42m onto the diapiric high. The overlying Bonney Sandstone succession is approximately 400m thick regionally with a facies succession of coarsening-upward shoreface to fluvial sequences. However, the subsalt Bonney Sandstone thins from 212m to 163m toward the diapir. It contains thinned lower shoreface facies and is missing the upper most shoreline facies where it is overlain by the Patawarta salt sheet. We conclude from these relationships that the Patawarta salt sheet was actively uplifting and inflating during the deposition of the Wonoka Fm., Patsy Hill Mbr and lowermost Bonney Sandstone. Salt break out and allochthonous flow of the Patawarta salt sheet took place during the deposition of the lower shoreface facies of the Bonney Sandstone when sedimentation rates were relatively low compared to salt rise rates.