Alluvial evidence for major climate and flow regime changes during the middle and late Quaternary for eastern central Australia

As a low-gradient arid region spanning the tropics to the temperate zone, the Lake Eyre basin has undergone gentle

late Cenozoic crustalwarping leading to substantial alluvial deposition, thereby forming repositories of evidence for

palaeoclimatic and palaeohydrological changes from the Late Tertiary to the Holocene. Auger holes and bank

exposures at five locations along the lower 500 kmof Cooper Creek, a major contributor to Lake Eyre in the eastern

part of the basin, yielded 85 luminescence dates (TL and OSL) that, combinedwit a further 142 luminescence dates

from northeastern Australia, have established a chronology of multiple episodes of enhanced flow regime from

about 750 ka to the Holocene. Mean bankfull discharges on Cooper Creek upstream of the Innamincka Dome at

250–230 ka or oxygen isotope stages (OIS) 7–6 are estimated to have been 5 to 7 times larger than those of today,

however, substantially less reworking has occurred during and afterOIS 5 than before. Lower Cooper Creek appears

to have similarly declined. In the TirariDesert adjacent to Lake Eyre there is evidence of widespread alluvial activity,

perhaps during but certainly before the Middle Pleistocene, yet the river became laterally restricted in OIS 7 to 5.

While the Quaternary has been characterised by a dramatically oscillating wet–dry climate, since oxygen isotope

stage OIS 7 or 6 there has been a general decline in the magnitude of the episodes ofwetness towhich the eastern

part of centralAustralia has periodically returned. During the last full glacial cycle, Cooper Creek'speriods of greatest

runoff and sand transport were not during the last interglacial maximumof OIS 5e (132–122 ka) but later in OIS 5

when sea levels and global temperatureswere substantially below those of 5e or today. Fluvial activity returned in

OIS 4 and 3, but not to the extent of mid and late OIS 5; strongly seasonal but still powerful flows transported sand

and fed source-bordering dunes in OIS 5 and 3. This chronology of fluvial activity in the late Quaternary broadly

coincideswith that for rivers of southeastern Australia and suggests that thewet phases in eastern central Australia

have not been governed asmuch by the northern monsoon as by conditions in thewestern Pacific close to the east

coast both north and south. Flow confinement within the Innamincka Dome has locally amplified Cooper Creek's

energy, and here evidence exists for short but high-magnitude episodes of flow during the Last Glacial Maximum

and in the early tomiddleHolocene, conditions thatwere capable of forming large palaeochannels but thatwere not

long-lived enough to rework the river's extensive floodplains elsewhere along its length.