Doctor of Philosophy
School of Geosciences
Coleman, Maria, Alluvial, aeolian and lacustrine evidence for climatic and flow regime changes over the past 250 ka, Cooper Creek near Innamincka, South Australia, Doctor of Philosophy thesis, School of Geosciences, University of Wollongong, 2002. http://ro.uow.edu.au/theses/1963
Cooper Creek at Innamincka in South Australia is one of very few places where evidence of palaeoclimatic history from the Quaternary Period is preserved in at least three stratigraphic settings; fluvial, aeolian and lacustrine. The significance of this study location is enhanced firstly because here this semi-arid to arid partly tropical catchment has a drainage area of nearly 237 000 km2 and therefore constitutes a very significant portion of the 1.3 million km2 Lake Eyre basin, Australia's largest dryland drainage system. Secondly, and very unusually for such a large river system, the flow of the Cooper at Innamincka bifurcates; north to Coongie Lakes, west towards Lake Eyre, and south down Strzelecki Creek and into the Lake Frome basin.
This study attempts to reconstruct the palaeoenvironmental Quaternary history of a complex system of dividing drainage. Sixty nine thermoluminescence dates and numerous stratigraphic and sedimentological analyses, including particle size, mineral content, and petrographic and scanning electron microscopy, reveal interacting depositional conditions in alluvial (channel and overbank), aeolian (source-bordering and longitudinal dune) and lacustrine (lunette) environments, information that provides an improved understanding of Australian Quaternary climatic and flow-regime changes in central Australia. These results point to a progressive but probably oscillating drying trend on Cooper Creek during the Mid to Late Quaternary. The oldest dated alluvium near Innamincka suggests extensive fluvial activity at about 250 ka to 230 ka (OI Stages 7/8), some of it well away from the existing channel. In agreement with work done by others further upstream on Cooper Creek, there appears after this to have been a period of reduced fluvial activity until extensive channels operated again along both Cooper and Strzelecki Creeks during the middle of OI Stage 6. This was followed by another probable hiatus until OI Stage 5 when significant fluvial activity was this time associated with the development of source-bordering dunes adjacent to palaeochannels on Cooper Creek, and with the formation lunettes in the Coongie Lakes region. Pronounced fluvial activity appears to have continued through to OI Stage 4, ceasing at locations other than near the existing channel of Cooper Creek by about 60 ka to 52 ka. While Cooper Creek had sufficient power to continue to slowly migrate in the vicinity of its present channel from about 55 ka until the LGM , the region was clearly significantly drier and less fluvially active from early OI Stage 3 to the present.
Source-bordering dunes dating at 40 ka to 25 ka do not correspond to older adjacent palaeochannels on Cooper Creek (the youngest dating at ~52 ka) and therefore suggest substantial aeolian reworking in OI Stages 3 and 2. Cooper Creek beyond the Innamincka D o m e ceased to transport any significant sand at around the L G M . Only within the flow-confining and thereby stream-power amplifying effect of the D o m e is there evidence on Cooper Creek of a final period of enhanced fluvial activity in the Early to Mid Holocene. However, it appears that Strzelecki Creek remained fluvially active even after the LGM , transporting clean channel sands at 15 ka to 10 ka.
The accumulated dune ages from this study indicate a pronounced period of aeolian activity from the L G M to the present, initially with the reworking of existing source-bordering dunes but then, particularly during the Holocene, with the extension northwards of derivative longitudinal dunes. There appears to have been two stages of longitudinal dune formation in the Strzelecki dunefield: 16 ka to 9 ka and 5 ka to 1 ka, probably signifying two periods of local dryness and windiness. Lacustrine lunettes were reworked from older lunettes in the Coongie Lakes region during the Holocene providing further evidence for the region as a whole becoming drier. Cooper Creek and Strzelecki Creek near Innamincka became a low-energy largely mud-transporting system from the Mid Holocene, vastly different to their Mid to Late Pleistocene precursors.