Late Palaeozoic cold-climate aeolianites, southern Cooper Basin, South Australia

Abstract

Summary Core facies analysis of the Permo-Carboniferous Gidgealpa Group of the southern Cooper Basin, South Australia has revealed sandstones of aeolian origin within the glacigenic Merrimelia Formation. The aeolianites comprise exclusively porous, poorly cemented, medium- and fine-grained sandstones dominated by parallel lamination. Sharp, planar truncation surfaces divide the suite into units composed mainly of translatent windripple lamination and minor amounts of sandflow bedding with primary depositional dip (post-compaction) varying between 0° and 25°. Distinctive compressional, tensional and dissipation structures are preserved in deformed lee-slope deposits and the inclusion of low-angle cross-strata and wedge-bedded units locally indicate deposition on the basal aprons of dunes or in contiguous sand sheets. Wet interdune sediments with adhesion ripples are also exhibited in the cores. The aeolianites, up to 232 m thick, have been traced subsurface by integrating core facies, wireline logs and seismic reflection analysis. A low-interval transit time on sonic logs is characteristic of the porous aeolianite sand and has facilitated mapping of the dune field using seismic data. The sandstone body trends SE-NW, is 6 to 8 km wide and passes laterally into outwash fan and fluvioglacial, braidplain deposits. Potential hydrocarbon traps may occur at the top of the aeolianites, or within them beneath intraformational seals formed by possible muddy interdune facies. The overall high-latitude, cold-climate nature of the Merrimelia Formation, deposited during the extensive Gondwanaland glaciation, is well known but this discovery not only records the first Gondwanan aeolianite suite but may also detail the first pre-Quaternary example of paraglacial aeolianites.