U series dating of secondary U phosphates ? potential for improving chronologies of Late Pleistocene pluvials

Abstract

Some of the minerals formed during weathering are amenable to radiometric dating and may be used to establish chronologies of weathering, which in turn relate to climate and the history of water in the landscape. Here we explore the potential of secondary U phosphates from the weathering zone of the Lake Boga Granite, northern Victoria, for U-Th dating and construction of a robust weathering history over the last »500 ky. The ages obtained are in the interval 115-560 ky, with some samples having 230Th-234U systematics beyond the range of the method. In principle, U-phosphate deposition is expected to occur under humid conditions, raising the possibility that U-phosphate ages may provide independent time-scales for the pluvial periods represented by Australia?s Quaternary megalakes. The data available now provide some support for a link with pluvials but a number of issues, largely related to the exact significance of the measured U-Th ages, need to be sorted out first before we can be confident about secondary U-phosphate chronologies.