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Luminescence surface exposure dating is a newly developed geochronological technique that allows the age of geological or archaeological rock surfaces to be accurately constrained. This dating method requires measuring and calibrating the depth-dependent luminescence signal below an exposed surface and relies on the assumption that neither the shape of the daylight spectrum nor the light attenuation change significantly with depth into the rock. However, lithologies with mm-scale heterogeneity in their mineral distribution or those lacking high sensitivity quartz present a challenge, partly because light attenuation with depth is not necessarily constant in such samples. Addressing these challenges is important for further development of the luminescence surface exposure dating technique. Here we investigate the shape of luminescence-depth profiles in lithologies revealing complex fabrics such as coarse-grained granitic gneisses or gneisses with distinct planar metamorphic layering. We also present luminescence-depth profiles from quartzite, a lithology that appears – at first glance – highly homogenous. We find that the spatial distribution of opaque mineral phases in the metamorphic samples and precipitation of iron hydroxides in the quartzite strongly influence the 3-dimensional transparency and, consequently, the light attenuation with depth, and are the main cause for the observed scatter in the OSL- and IRSL-depth profiles in our samples. The data suggest that for rocks of heterogeneous lithology (i) close petrographic analysis of luminescence-depth profiles are required to ensure that the cores used for calibration have similar mineralogical composition (and thus light attenuation with depth) to those used to calculate a luminescence rock surface exposure age, and that (ii) RGB depth profiles appear to provide a useful semi-quantitative tool for such analysis.

Intraplate tectonism has produced large-scale folding that steers regional drainage systems, such as the 1600 km-long Cooper Ck, en route to Australia's continental depocentre at Lake Eyre. We apply cosmogenic Be-10 exposure dating in bedrock, and luminescence dating in sediment, to quantify the erosional and depositional response of Cooper Ck where it incises the rising Innamincka Dome. The detachment of bedrock joint-blocks during extreme floods governs the minimum rate of incision (17.4 +/- 6.5 mm/ky) estimated using a numerical model of episodic erosion calibrated with our 10Be measurements. The last big-flood phase occurred no earlier than similar to 112-121 ka. Upstream of the Innamincka Dome long-term rates of alluvial deposition, partly reflecting synclinal-basin subsidence, are estimated from 47 luminescence dates in sediments accumulated since similar to 270 ka. Sequestration of sediment in subsiding basins such as these may account for the lack of Quaternary accumulation in Lake Eyre, and moreover suggests that notions of a single primary depocentre at base-level may poorly represent lowland, arid-zone rivers. Over the period similar to 75-55 ka Cooper Ck changed from a bedload-dominant, laterally-active meandering river to a muddy anabranching channel network up to 60 km wide. We propose that this shift in river pattern was a product of base-level rise linked with the slowly deforming syncline-anticline structure, coupled with a climate-forced reduction in discharge. The uniform valley slope along this subsiding alluvial and rising bedrock system represents an adjustment between the relative rates of deformation and the ability of greatly enhanced flows at times during the Quaternary to incise the rising anticline. Hence, tectonic and climate controls are balanced in the long term., AuthorCount:11

Intraplate tectonism has produced large-scale folding that steers regional drainage systems, such as the 1600 km-long Cooper Ck, en route to Australia's continental depocentre at Lake Eyre. We apply cosmogenic 10Be exposure dating in bedrock, and luminescence dating in sediment, to quantify the erosional and depositional response of Cooper Ck where it incises the rising Innamincka Dome. The detachment of bedrock joint-blocks during extreme floods governs the minimum rate of incision (17.4±6.5 mm/ky) estimated using a numerical model of episodic erosion calibrated with our 10Be measurements. The last big-flood phase occurred no earlier than ∼112–121 ka. Upstream of the Innamincka Dome long-term rates of alluvial deposition, partly reflecting synclinal-basin subsidence, are estimated from 47 luminescence dates in sediments accumulated since ∼270 ka. Sequestration of sediment in subsiding basins such as these may account for the lack of Quaternary accumulation in Lake Eyre, and moreover suggests that notions of a single primary depocentre at base-level may poorly represent lowland, arid-zone rivers. Over the period ∼75–55 ka Cooper Ck changed from a bedload-dominant, laterally-active meandering river to a muddy anabranching channel network up to 60 km wide. We propose that this shift in river pattern was a product of base-level rise linked with the slowly deforming syncline–anticline structure, coupled with a climate-forced reduction in discharge. The uniform valley slope along this subsiding alluvial and rising bedrock system represents an adjustment between the relative rates of deformation and the ability of greatly enhanced flows at times during the Quaternary to incise the rising anticline. Hence, tectonic and climate controls are balanced in the long term.

Optically stimulated luminescence (OSL) ages from a relict shoreline on Lake Callabonna record a major pluvial episode in southern central Australia between 1050 70 and 1100 60 Common Era (CE), within the Medieval Climatic Anomaly (MCA). During this pluvial interval Lake Callabonna filled to 10e12 times the volume of the largest historical filling (1974) and reached maximum depths of 4e5 m, compared to the 0.5e1.0 m achieved today. Until now there has been no direct evidence for the MCA in the arid interior of Australia. A multi-proxy, analogue-based atmospheric circulation reconstruction indicates that the pluvial episode was associated with an anomalous meridional atmospheric circulation pattern over the Southern extratropics, with high sea-level pressure ridges in the central Indian Ocean and Tasman Sea, and a trough extending from the Southern Ocean into central Australia. A major decline in the mobility of the Australian aboriginal hunter-gatherer coincides with this MCA period, in southern central Australia.

The elevated temperature infrared stimulated luminescence (IRSL) and post-IR IRSL signals of potassium (K)-feldspars have recently garnered attention for their minimal rates of anomalous fading. The post-IR IRSL signal has been used to obtain age estimates for geological deposits, mostly in Europe. Studies on the behaviour of the IRSL and post-IR IRSL signals of K-feldspars from a wider range of geographic regions and depositional contexts are needed, particularly for regions where the OSL signal from quartz is poorly behaved. Discrepancies in the literature regarding the behaviours of the IRSL and TL signals of K-feldspars also highlight the need to characterise the behaviours of samples from a wide variety of contexts. This paper begins to address this problem by characterising and comparing the IRSL signals of a metamorphic and a volcanic K-feldspar sample from two sites in East Africa, a region in which the OSL signal from quartz has generally proven problematic for dating. We demonstrate that the metamorphic and volcanic K-feldspars have substantially different TL glow curves that respond differently to IR stimulation. The sample of metamorphic K-feldspar from Tanzania (MR9) has a peak at 430 °C that is associated with the IRSL signal and an optically less-sensitive peak at 350 °C, while the sample of volcanic K-feldspar from Ethiopia (MB3) exhibits a single broad TL region centred at ∼230 °C that responds differently to IR stimulation. Differences in the change of IRSL decay curve shape with stimulation temperature suggest that the processes of IRSL production many vary between the two samples. Using dose recovery tests, we demonstrate that the IRSL (50 °C), IRSL (225 °C) and post-IR IRSL (50 °C, 225 °C) signals of sample MR9 are suitable for dose and age estimation using the single-aliquot regenerative-dose procedure, while those of sample MB3 are less suitable. The post-IR IRSL signal of the latter sample performs poorly in tests of SAR suitability and the t

Optically stimulated luminescence (OSL) ages from a relict shoreline on Lake Callabonna record a major pluvial episode in southern central Australia between 1050 ± 70 and 1100 ± 60 Common Era (CE), within the Medieval Climatic Anomaly (MCA). During this pluvial interval Lake Callabonna filled to 10–12 times the volume of the largest historical filling (1974) and reached maximum depths of 4–5 m, compared to the 0.5–1.0 m achieved today. Until now there has been no direct evidence for the MCA in the arid interior of Australia. A multi-proxy, analogue-based atmospheric circulation reconstruction indicates that the pluvial episode was associated with an anomalous meridional atmospheric circulation pattern over the Southern extratropics, with high sea-level pressure ridges in the central Indian Ocean and Tasman Sea, and a trough extending from the Southern Ocean into central Australia. A major decline in the mobility of the Australian aboriginal hunter-gatherer coincides with this MCA period, in southern central Australia.