LATE PLEISTOCENE, CALCAREOUS AND SILICEOUS AEOLIAN AND ALLUVIAL FAN DEPOSITS, CAPE LIPTRAP, SOUTHEASTERN VICTORIA, AUSTRALIA

Cape Liptrap, projecting into the Southern Ocean, lies at the boundary between predominantly siliceous (east) and calcareous (west) dune fields. This location, the well-exposed nature of the dunes along coastal cliffs, and optically stimulated luminescence (OSL) and radiocarbon ages allow for reconstruction of late Pleistocene paleoclimates and depositional environments.

Nine overlapping calcareous aeolian deposits, totaling 40m thick and separated by paleosols, are exposed in sea cliffs at Arch Rock. The sand fraction ranges from 31 to 56% Tertiary marine shell fragments. Thick (5-15m) tabular cross-bed sets indicate winds from the west. OSL ages range from <130ka to >68ka. Immediately to the south (along Morgan's Beach), alluvial fan deposits (20m thick) exposed in sea cliffs consist of generally horizontally bedded, calcarenite sands derived from the aeolian calcarenites. These sands coarsen upward into lenses of angular, local bedrock-derived pebbles and cobbles or a laterally extensive, finely laminated clay. Minor, thin (<1m thick) tabular cross-beds indicate a southerly transport. The alluvial fan unit, with four OSL ages ranging from 23-25ka, is underlain by a peat and capped by a well-developed paleosol. Along the eastern side of Cape Liptrap, a siliceous dune field caps a flight of marine terraces that extends up to ~160m amsl. Longitudinal and parabolic dunes indicate an easterly wind direction with a local sediment source from Waratah Bay and the Wilson Promontory granite to the east. Five OSL ages range from 19-21ka.

We propose that calcareous aeolian deposition began during sea level fall after the last interglacial marine highstand (IOS 5e). Temperate Westerlies transported sand from the increasingly exposed continental shelf. Deposition at Arch Rock continued into early OIS 4. The southeastern coast experienced an increasingly cold climate and flashy surface runoff conditions into IOS 2 that resulted in reworking of the calcarenites into alluvial fans. At the LGM (~20ka), atmospheric circulation had compressed northward sufficiently to allow the Antarctic Front to reach Cape Liptrap resulting in aeolian sand transport from exposed Warath Bay by the Polar Easterlies. Previously, the LGM in southeastern Victoria was interpreted as a time of aridity and predominantly westerly winds.