Variations of the northwest Australian summer monsoon over the last 300,000 years: the paleohydrological record of the Gregory (Mulan) Lakes System

Monsoon rains in the Kimberley region feed an interconnected chain of lake basins, the Gregory Lakes system in northwestern Australia, a terminal syst em surrounded by dunefields of the Great Sandy Desert. This semi-arid region records a sequence of Quaternary climatic changes, at times much wetter, at times much drier than today. A morphostratigraphic sequence defines episodic formation of dunes and rela ted sediments reflecting past hydrologic and climatic changes which caused them. Thermoluminescence dating provides a broad temporal framework identifying m ajor hydrologic changes of the past 300 ka. Ancient foreshore dunes define shorelines of mega-lake phases, the largest of which covered some 6500 km(2) with ages near 300 ka. Later lacustral exp ansions near 200 and 100 ka, reflect wet phases broadly comparable to marin e isotope stages 7 and 5 with a trend towards increasing aridity through ti me. Longitudinal quartz dune formed within the mega-lake confines between succe ssive wet phases with at least two dune building episodes near (or just bef ore) 230 and 70 ka. Monsoon activity today produces short-lived flood events such as recorded i n 1993. Climates of the mega-lake phases need not be drastically different from today's although a substantial increase in the frequency of high magni tude events was certainly involved. (C) 2001 Elsevier Science Ltd and INQUA . All rights reserved.