Late Quaternary fan gravels and slope deposits at Rocky Cape, northwestern Tasmania: their palaeoenvironmental significance

Abstract

The paper describes a sequence of stratified quartzite slope deposits and alluvial fan gravels from a small catchment at Rocky Cape. A lower series of indurated slope deposits overlain by a podzol soil profile suggests that cold climatic conditions, which favoured frost fracturing of exposed 13 rock surfaces and gelifluction of detritus, occurred prior to the Last Glacial Stage. An upper series of unconsolidated slope deposits contains wedge structures. These deposits appear to have resulted from frost fracturing and to have been moved downslope by gelifluction processes. The wedge structures may have been produced by seasonal freezing of the ground surface during the period of maximum cold in the Last Glacial Stage (after 22,000 and before 10,000 BP). Radiocarbon dating of charcoal and wood from organic horizons and a buried soil in the lower part of a thick sequence of alluvial fan gravels shows that they began to accumulate mainly between about 33,000 and 22,000 BP, when strong but episodic erosion of the open Eucalyptus forested catchment occurred. The upper part of the alluvial fan gravels does not contain organic horizons but probably accumulated after 22,000 and before 10,000 BP. The gravels were largely derived from the upper series of slope deposits which were formed in a non-forested environment.