SUPRASALT TO SUBSALT MINIBASIN HISTORY: DEPOSITIONAL AND HALOKINETIC SEQUENCE STRATIGRAPHY AT PATAWARTA DIAPIR, FLINDERS RANGES, SOUTH AUSTRALIA

Outcrop analysis is vital to the development and testing of salt tectonic models because of the low resolution of seismic images near salt diapirs. Our goal is to explore whether suprasalt minibasin facies distribution, stratal geometry, and structural style can be utilized to effectively predict these characteristics in coeval, subsalt minibasins. We employ outcrop studies of the Neoproterozoic Patawarta Diapir in the Flinders Ranges of South Australia. Patawarta Diapir is a leaning diapir/ramping allochthonous salt sheet exposed in an oblique plane of section, whereby both subsalt and suprasalt minibasin strata can be observed. Previous studies of the subsalt minibasin focused on mixed carbonate/siliciclastic strata of the Neoproterozoic Wonoka Formation and Patsy Hill Member of the Bonney Sandstone that record regional regression from outer wave-dominated shelf (Wonoka) to tidally-dominated barrier bar complex (Patsy Hill). A halokinetic drape fold expressed in subsalt strata displays upturn and thinning (1100 to 110 m) toward the diapir over a distance of 560 m. Subsalt Wonoka and Patsy Hill strata combine to form a single tapered composite halokinetic sequence.

Data collected from the suprasalt minibasin indicate significant differences in facies distribution, thickness, stratal geometry, and structural style. Suprasalt Wonoka strata show good correlation laterally across the coeval minibasins in facies distribution and depositional setting. In contrast, Patsy Hill facies show significant lateral variation both within the suprasalt minibasin and in comparison to the subsalt, suggesting deposition of shallower water facies was strongly controlled by the topographic high of the diapir. In particular, quartzite pebble conglomerates record the unroofing of the diapir as it was exposed and eroded, ultimately leading to salt breakout. In the suprasalt minibasin, Wonoka and Patsy Hill strata display significant but gradual thinning (1,638 to 19 m) over a distance of 4-5 km and form a broad, open fold with local upturn. Suprasalt Wonoka and Patsy Hill strata represent a very broad tapered CHS geometry with minibasin-scale folding and thinning. Further evaluation will define progressive stages of minibasin depositional and halokinetic development, as well as mechanisms and controls of salt movement.