AEOLIAN AND FLUVIAL EVIDENCE OF CHANGING CLIMATE AND WIND PATTERNS DURING THE PAST 100 KA IN THE WESTERN SIMPSON DESERT, AUSTRALIA

Sediments near Finke in central Australia provide evidence of late Quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western Simpson Desert. Thermoluminescence (TL) dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance. Quaternary alluviation in the Finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the Holocene. In contrast to rivers in the eastern part of the Lake Eyre basin, substantial alluviation took place here in the early to mid-Holocene, probably due to reactivation of the northern monsoon and its partial penetration into central Australia. The regional dunefield near Finke consists of linear dunes largely reworked and aligned during the last glacial (30-12 ka) as part of the great anticlockwise whorl of dunes in central Australia. The oldest dated source-bordering dunes from the Finke River are bright red in colour, were deposited at c 100 ka and are now buried beneath paler source-bordering dunes. The latter consist of two exposed units; a lower one of unknown orientation that dates at 17-9 ka, and an upper unit, aligned to the northwest and parallel to the prevailing winds, that dates at 5-0 ka. The TL signature and sediment texture of the oldest source-bordering dunes show them to have probably been derived from weathered alluvial red-beds of similar or greater age nearby, and to have contributed abundant sand to the regional dunefield immediately north of the river. In contrast, sand from the younger, paler source-bordering dunes appears to be from a different source and to have only recently extended into the regional field. The Finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified Australia's whorl of continental dunes. The 30-18 ka regional Linear-dunes near Finke are oriented almost due north. Their cross-sectional asymmetry (steeper eastern slopes) suggests a response to southwesterly or westerly sand-transporting winds between 18 and 10 ka; these winds appear to have shifted to their present southeast orientation during the past 5 ka. From dune ages, alignments and asymmetry, it is proposed here that there was a northward shift in the wind pattern al Finke by about 100-150 km (1-1.5 degrees of latitude) during the last glacial, but that through this period the regional dune pattern has remained remarkably stable.