MAJOR EPISODES OF QUATERNARY ACTIVITY IN THE LOWER NEALES RIVER, NORTHWEST OF LAKE-EYRE, CENTRAL AUSTRALIA

The Lake Eyre Basin, Australia's largest internal drainage system, rep resents a key site in unravelling the complexities of terrestrial clim ate change. The basin, covering one-sixth of the Australian continent, spans a number of climatic zones, including the tropical monsoon syst em to the north and the mid-latitude westerly circulation to the south . This study describes four major episodes of Quaternary fluvial, lacu strine and aeolian activity in the Neales River, a western catchment o f Lake Eyre. The first phase is represented by coarse-grained fluvial aggradation which dates to at least 170 ka. The depocentre of Lake Eyr e is believed to have been located further to the east during this pha se. The second episode is a phase of high lake level lacustrine deposi tion which occurred before 103 ka. The deltaic margin of the lake at t his time was approximately 20 km west of the present playa. The third phase was characterised by significant base level lowering and channel incision after 50 ka but before 31 ka. Lake level lowering induced fl uvial incision of up to 9 m, scouring several metres into the basal si licified Miocene sediments some time after 50 ka. The final phase was a period of aeolian and ephemeral-fluvial deposition which peaked betw een 20 ka and 18 ka, coincident with the Last Glacial Maximum. These e pisodes are compared with chronostratigraphic data from the monsoon do minated catchments of the Cooper and Diamantina Rivers. The nature and record of fluvial and lacustrine deposition are correlated throughout the basin during the penultimate and last interglacial cycles. The la te Quaternary record is more ambiguous and further studies are require d to elucidate the precise nature of climate change in the basin over the last 30 ka.