Palaeomagnetism of ferricrete from Vale of Belvoir, Western Tasmania: Implications for Tasmanian cenozoic glacial history

Abstract

The preliminary results of paleomagnetic studies of ferricretes associated with glacigenic sediments from the Vale of Beivoir, western Tasmania, have important implications for Tasmanian Cenozoic glacial history. The geology of the Vale of Beivoir (Fig. 1) is dominated by glacigenic drift and Tertiary basalt which overlie karstified Ordovician Gordon Group limestones. Ferricrete, up to 2 m in thickness, is developed within and adjacent to the weathered glacigenic sediments and is exposed in road cuttings, as well as in scattered blocky outcrops across the area (Fig. 1). Widely spaced joints in the ferricrete outcrops sometimes give the appearance of crude bedding. The ferricrete blocks appear to have developed in situ, rather than being deposited as erratics. The ferricrete is mainly developed adjacent to basalt in the valley. This suggests derivation of the iron from chemical weathering of the basalt, and its lateral migration and accumulation to produce massive and concretionary horizons controlled by local water-tables.