The Middle–Late Pleistocene Bridgewater Formation on Cape Bridgewater, south-western Victoria: chronostratigraphy and palaeoclimatic significance

Abstract

The Pleistocene Bridgewater Formation is well exposed at Cape Bridgewater and surrounding areas in south-western Victoria, where field studies, mineralogical and isotopic analyses and OSL dating have shown that it can be divided into three members, here named (in stratigraphic order) the Descartes Bay, Bats Ridge and Duquesne members. Each member consists of aeolian calcarenite deposited as a coastal dune, that was karstified (with solution pipe development) and then overlain by a red or purple palaeosol. The aeolianites were deposited in three distinct phases corresponding to interglacials MIS 11, MIS 9 and MIS 7, respectively, when the shoreline was near present sea level. Karstification occurred as a result of the high effective precipitation characteristic of the transition between interglacial and glacial periods, followed by aeolian dust accession and palaeosol formation during the drier, windier glacial climates. Comparison with the coeval Tamala Limestone in south-western Western Australia shows simultaneous changes in palaeoclimate: high effective precipitation during the transition from MIS 11 to MIS 10, and a relatively dry transition from MIS 9 to MIS 8. Abundant rainfall during MIS 5 caused extensive limestone dissolution (solution pipes in Victoria, pinnacles in Western Australia) and the resulting quartz sand residue was redeposited during MIS 2-4.