Late Pleistocene Glaciation of the Kosciuszko Massif, Snowy Mountains, Australia

Monsoon events in northwestern Australia during the last c. 300 000 years - a summary of the paleohydrological findings

Karl-Heinz Wyrwoll¹, Jim Bowler², Lu Yanchou³ and Lindsay Collins⁴

^{1Department of Geography, The University of Western Australia, Nedlands, WA 6907
^{2School of Earth Sciences, University of Melbourne, Melbourne,Victoria 3010
^{3Institute of Geology, China Seismological Bureau, P.O. Box 100029, Beijing, P.R. China
^{4School of Applied Geology, Curtin University of Technology, Bentley, WA 6102}}}
Only a limited understanding of the Quaternary history of the Australian monsoon is presently available. And even fewer studies make any attempt at understanding the dynamics which may have controlled Quaternary paleomonsoon variations. Here we present our findings from the Lake Gregory region of northwestern Australia, which demonstrate that the region experienced a wide range of hydrological conditions during the last c. 300 000 years, indicative of variations in monsoon activity over this time. We link this work to related field findings from the Fitzroy Trough, to provide a more comprehensive outline of Quaternary monsoon events in northwestern Australia.

Luminescence dating of lake marginal dunes at Lake Gregory indicate that large extensions of the lake were middle Pleistocene events. During the Late Pleistocene the areal extent of the lake was still significantly greater than today. During Marine Isotope Stage 5, the lake was more extensive than during the Holocene. The morphostratigraphic evidence indicates a progressively contracting lake during marine Isotope Stages 5-4. No evidence of early/middle Holocene lake events have been found. The early Holocene is also not represented in the flood stratigraphies of the Fitzroy basin. The apparent absence of early Holocene events may be taken to indicate more subdued monsoon activity at that time. However, it is clear that the northwest Australian monsoon was active, albeit for possibly a short period of time during the very latest Pleistocene. The indications from our paleohydrological findings are that the monsoon regime of northwestern Australia has remained relatively stable since the middle Holocene.

Luminescence dates have also been obtained from desert dunes located along the northern margins of the Great Sandy Desert. These indicate that significant dune mobility occurred at various times during the middle and late Pleistocene. However, better stratigraphic control is required before the full significance of the dates can be realised.

There may be some suggestion that Milankovitch insolation variations play a role in controlling the activity of the northwest Australian monsoon. However, these are tentative indications and any attempts to explain variations in monsoon activity must be placed within the context of the details of hydrometeorological controls.}