Australia: The Land Where Time Began

A biography of the Australian continent 

The Last Interglacial – The Arid Rivers

It is indicated by the rivers feeding Lake Eyre that during the last interglacial stream flows where stronger until 85 ka after which activity of the flows waned.

The best-known arid river systems in Australia are the Diamantina River and Cooper Creek, both of which are rivers on an immense scale. The catchment of the Georgina-Diamantina-Warburton and the Thompson-Barcoo-Cooper drainages have their headwaters in northern Australia and extend into central Australia, a distance of more than 1,000 km, and carry flood waters from the northern monsoon into Lake Eyre. At least whenever the monsoon drops enough water to reach the Lake before it soaks into the parched river beds of evaporates in dry heat of central Australia. Another layer of environmental variability, over and above that resulting from precipitation fluctuations, is added by the dynamics of the slow movement of floodwater into the heart of the continent.

According to Smith the fluvial history of the Cooper and Diamantina is now known in some detail. Along the middle and lower reaches of these rivers the major phase of fluvial activity peaked about 110-109 ka, leaving a series of palaeochannels that have since been buried by dunes of the desert and more recent floodplains of the present (Wells & Callen, 1986; Nanson, Price and Short, 1992; Magee, 1997; Nanson et al., 2008). A broad meandering channel system that was up 4 times the width of the floodplain of the present was formed by these ancestral rivers. A wide range of fossil fauna has been found in the palaeochannels, which attracted the attention of J.W. Gregory in 1901-1902) and filled with fine cross-bended white sand, which indicates that at the time of deposition discharge rates were higher than in the mud-dominated channels of the present. The Katapiri Formation is the collective name for these channel deposits, and it is usually divided into the Upper Katapiri Last Interglacial and the Lower Katapiri (260-220 ka). The deposits have been shown by OSL dating of the Upper Katapiri to range in age from 120 to 60 ka. In the Channel Country, higher in the catchment it is indicated by sand-dominated bed-loads that around 120 ka discharges were higher (Nanson et al., 1988), though from 85 ka these were replaced by the low-energy network of anastomosing muddy streams for which the area has its present name ‘The Channel Country’.

Towards the close of MIS 5 Cooper Creek stream flows appear to have become strongly seasonal. Source-bordering dunes were formed as channel sands were blown from the seasonally dry beds by the prevailing winds, the large, meandering channels having been formed by 85 ka. It has been found by OSL dating of several of these source-bordering dunes that the dunes can be separated into several clusters based on age ranging from 120 to 100 ka and from 85 – 40 ka (Maroulis et al., 2007; Cohen et al., 2010). The channels and floodplains were inundated with mud after a switch to increasingly low-energy flows from 40 ka. Cooper Creek, a major Australian inland river, had been greatly diminished by increasing aridity by about 40-35 ka (Nanson et al., 2008: 126).

Detailed histories of other arid zone rivers are not known. Along the Finke River in Central Australia major alluviation occurred around 100-90 ka, and the next evidence of major activity was in the Holocene (Nanson, Chen & Price, 1995). From 75 to 20 ka the Todd River was active, though not much is known of its flow regime during the last interglacial (Hollands et al., 2006). Smith suggests it is possible the Sandover River may have been a more energetic fluvial system during           MIS 5, though the limitations of thermoluminescence (TL) and U/Th dating of palaeochannels and alluvial terraces in the region of Central Australia means there is no solid chronology for the system during the Quaternary (Tooth, 1997).

It is suggested by the balance of evidence that even the largest of these inland river systems had switched to flows that were strongly seasonal by 85 ka, and that they were operating primarily as arid fluvial systems by the close of the Katapiri at 60 ka. High-magnitude, short-lived flows occurred in Central Australia and along Cooper Creek throughout the Pleistocene (Bourke, 1998; English et al., 2001; Nanson et al., 2008), though these are probably a reflection of the interdecadal variability that is a characteristic of these arid rivers at the present.

Sources & Further reading

  1. Smith, Mike, 2013, The Archaeology of Australia’s Deserts, Cambridge University Press


Author: M. H. Monroe
Last updated: 10/04/2014
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