First recorded evidence of subaqueously-deposited late Pleistocene interstadial (MIS 5c) coastal strata above present sea level in Australia

摘要

Significant differences in the elevation of late Pleistocene interstadial coastal strata have been noted at the global scale resulting from the combined effects of tectonism, proximity of field sites to Pleistocene ice sheets, and the variable effects of glacio-hydro-isostatic adjustment processes. Here we report the first recorded example of subaqueously deposited late Pleistocene interstadial coastal sediments above present sea level in Australia, in a far-field location to Pleistocene ice sheets and characterised by minimal to modest rates of vertical crustal movements. Located at Port MacDonnell, in Southern Australia, the sedimentary succession is represented by a flint conglomerate beach facies with interstratified shells. An optically stimulated luminescence (OSL) age of 53 ± 4 ka for an aeolianite unit that unconformably overlies the shelly deposit indicates that the beach facies is older than early MIS 3. OSL analysis also confirms that the MacDonnell Range, located 7 km inland from the present coastline, is of last interglacial age (124 ± 10 ka; MIS 5e). Radiocarbon dating on the operculum of Turbo undulatus from the shelly conglomerate yielded a minimum age of 47,905 ± 2106 yr BP [Wk-34733]. The extent of amino acid racemization (AAR) for Turbo sp. from the shelly unit beneath the aeolianite suggests an interstadial age (102 ± 16 ka). Uplift-corrected palaeo-sea level at the time of deposition of the shelly flint conglomerate was at least -14 m during MIS 5c. These results are consistent with palaeo-sea level estimates from other far-field settings as well as oxygen isotope-inferred sea levels for this interval and further highlight the regional tectonic stability of Australian coastal landscapes in a global context.