Australia: The Land Where Time Began

A biography of the Australian continent 

Major Flow Regime Changes in the Middle and Late Quaternary in Eastern Central Australia

The Lake Eyre Basin is a low gradient arid region that extends from the tropics to the temperate zone that has undergone gentle crustal warping in the late Cainozoic that led to substantial alluvial deposition, the deposits now being the repositories of evidence of changes in the palaeoclimate and the palaeohydrology from the Late Tertiary to the Holocene. A chronology of multiple episodes of enhanced flow regime from about 750 ka to the Holocene has been established, based on auger holes and bank exposures along the lower 500 km of Cooper Creek, that is a major contributor to Lake Eyre in the eastern section of the basin from which 85 luminescence dates have been obtained, TL and OSL, that were combined with 142 luminescence dates from northeastern Australia. It has been found that at 250-230 ka,  mean bankfull discharges on Cooper Creek upstream of the Innamincka Dome or oxygen isotope stages (OIS) 7-6, have been estimated to have been 5-7 larger than those of the present, though there has been substantially less reworking during and following the OIS 5 than prior to it, and there appears to have been a decline in lower Cooper Creek. There is evidence in the Tirari Desert, adjacent to the Lake Eyre, of widespread alluvial activity, possibly during, but definitely before the Middle Pleistocene, yet in OIS 7-5 the river became laterally restricted. There has been a general decrease in the magnitude of the wetness episodes to which eastern central Australia has returned periodically, while the Quaternary has been characterised by a climate that oscillated dramatically between wet and dry. The periods of greatest runoff and sand transport in Cooper Creek, during the last full glacial cycle, was later in OIS 5, at a time when the global sea level and temperatures were substantially lower than those of either 5e or the present, and not during the last interglacial maximum of OIS 5e (132-122 ka). In OIS 4 and 3 full activity returned, though to a lesser extent than in mid and late OIS 5, sand being transported by flows that were strongly seasonal, though powerful, feeding the source-bordering dunes in OIS 5 and 3. In the Late Quaternary this fluvial activity chronology coincides broadly with that of southeastern Australia, suggesting that the wet phases in eastern central Australia have been governed by the conditions in the western Pacific close to the east coast, both north and south, and to a lesser extent than by the northern monsoon. Cooper Creek's energy has been amplified  locally by flow confinement within the Innamincka Dome, and there is evidence here of short, high magnitude episodes of flow during the Last Glacial Maximum, and in the early Middle Holocene, conditions that could form large palaeochannels, though were too short-lived to rework the extensive flood plains of the river elsewhere along its length.

Sources & Further reading

Nanson, Gerald C., David M. Price, Brian G. Jones, Jerry C. Maroulis, Maria Coleman, Hugo Bowman, Timothy J. Cohen, Timothy J. Pietsch, and Joshua R. Larsen. "Alluvial Evidence for Major Climate and Flow Regime Changes During the Middle and Late Quaternary in Eastern Central Australia." Geomorphology 101, no. 12 (10/1/ 2008): 109-29.

Author: M. H. Monroe
Last Updated 26/08/2013
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