A biophysical model for the formation of late Pleistocene valley-fills in the Flinders Ranges of South Australia

Abstract

There are scattered remnants of Mesozoic and Cainozoic deposits flanking the arid Flinders Ranges of South Australia but within the massif proper the most widespread Cainozoic deposits are the dominantly silty clay Late Pleistocene valley-fills, the most recent of which accumulated from -35 000 until -15 000 years ago (35-15 ka). Such valley-fills are not accumulating today. The valley-fills have been variously interpreted as fluviatile, lacustrine or wetland deposits. Among the questions raised by these deposits are the respective former roles of winter and summer rainfall, the influence of lower glacial temperatures and evaporation, the contributions from loess, the effect of past variations in atmospheric carbon dioxide on plant cover, the abrupt nature of post-depositional incision, evidence for episodic flooding during the Last Glacial Maximum between -24 ka and -18 ka, the entrapment and reworking of loess slope mantles, and the influence of higher regional ground-water levels. This paper puts forward a simple, speculative and integrated biophysical model that takes into account each of these factors and is able to account for the formation of fine-grained Late Pleistocene valley-fills in this presently arid region.