Investigating arid Australia’s sedimentary history using deep floodplain cores from the Lake Eyre Basin

Arid Australia’s landscape and environmental history is unique on a global scale, with the Lake Eyre Basin (LEB) covering one seventh of the Australian continent. The extensive river systems within the LEB are also unique in their morphology. Of these Cooper Creek and the Diamantina River, the two main feeder rivers to Kati-Thanda- Lake Eyre are investigated within this thesis using Optically Stimulated Luminescence (OSL), sedimentological analyses to understand the chrono-stratigraphy and sedimentation rates of these two dominant tributaries. These rivers were once meandering systems transporting bedload but due to either climate, tectonics or both have shifted to anabranching mud-dominated river systems. Cooper Creek has had extensive research whereas the Diamantina River has had little to no research done on the Quaternary fluvial successions. Both systems are influenced by low amplitude tectonic structures impacting stream gradients and channel patterns. This thesis set out to test the influence of such structures on sedimentation rates using single grain OSL. Four cores (two from each river system) were investigated, and all represent the most complete cores from Quaternary fluvial successions in the LEB. Three dominant fluvial facies were classified; channel, channel marginal and overbank. Twenty-eight samples were analysed with 26,100 grains of quartz measured. Two dominant types of palaeodose (De) distributions were encountered well-bleached and overdispersed. For well-bleached distributions the normal median absolute deviation (nMAD) was applied to two thirds of the of the single grain De distributions and for the overdispersed samples the Finite Mixture Model (FMM) was applied to the other third. Ages on the Cooper range from 5.6 ± 0.5 to 438.4 ± 59.7 ka; ages on the Diamantina were 1.1 ± 0.1 to \u3e214.5 ± 24.5. Some samples were near saturation, using the conventional Single Aliquot Regenerative (SAR) protocol underestimating the full De distributions. Calculated sedimentation rates on Cooper Creek show that it decreases downstream of the structural Innamincka Dome supporting earlier work that Innamincka Dome is producing a measurable impact on upstream sedimentation rates. Average sedimentation rates on the Cooper range from 75.8 ± 10.4 mm/ka to 71.0 ± 8.0 mm/ka. In contrast, sedimentation rates on the Diamantina River show that the most downstream core had the highest sedimentation rate of 90.9 ± 11.3 mm/ka and, in an area, where stream gradients are the lowest at 85mm/km. In this location the role of tectonics is less clear and the location of the Gason Dome appears to be driving a record of past channel migration in what is now an anabranching system