OSL Dating of Sediment from the Grabben Gullen Creek, Upper Lachlan River Catchment, SE Australia

Kinnaird, T., Sanderson, D. , Bishop, P. and Munoz-Salinas, E. (2011) OSL Dating of Sediment from the Grabben Gullen Creek, Upper Lachlan River Catchment, SE Australia. Technical Report. SUERC, Edinburgh, UK.

Abstract

This report is concerned with optically stimulated luminescence (OSL) investigations on sediment collected from a profile in the upper Lachlan River catchment area in New South Wales, southeast Australia. The samples were collected as part of a larger study that is investigating land-use change in this region, traditionally associated with the arrival of Europeans in SE Australia. Sampling was undertaken by E. Muñoz-Salinas and P. Bishop. Analyses were performed at the Scottish Universities Environmental Research Centre, East Kilbride. In total three dating samples, and five profiling samples were submitted to the laboratory. Field profiling undertaken by E. Muñoz-Salinas and P. Bishop provided a basic assessment of the luminescence characteristics of the section sampled. On the basis of this work three units have been defined (Muñoz-Salinas et al., 2010): a pre-‘Swampy Meadow’ deposit (> 185 cm depth in profile), a ‘Swampy Meadow’ deposit (185 – 61 cm) and the ‘Post-Settlement Alluvium’ (> 61 cm). Profiling and full dating samples were subjected to laboratory preparation of sand-sized quartz (Burbidge et al., 2007; Kinnaird et al., 2007). Laboratory profiling samples were taken from both the ‘pre-Swampy Meadow’ and ‘Swampy Meadow’ deposits. Aliquots of HF etched quartz and polymineral concentrates were subjected to simple single-aliquot dose determinations (calculated relative to a single regenerative dose of 5 Gy, normalised to a 1 Gy test dose), which were used to plot dose-depth and luminescence sensitivity profiles. Stored doses and sensitivities obtained from the quartz separates are consistent across the pre-‘Swampy Meadow’/‘Swampy Meadow’ boundary. Normalised ratios were scaled to account for the test dose change between the profiling (1 Gy) and full SAR (2 Gy) measurements. These normalised values were then fitted to a composite dose response curve generated from the full dating samples. Dose rates for each profiling sample location were estimated from the adjacent full dating locations. Apparent ages were calculated for each profiling sample from base to top these are: 4.56 ± 0.22, 4.48 ± 0.09, 3.87 ± 0.47, 3.36 ± 0.02 and 1.05 ± 0.01 ka. Dose rates for the tube samples (and when available bulk sediment) were obtained by high resolution gamma spectrometry coupled with in-situ field gamma spectrometry and beta dose rate measurement using thick source beta counting. Equivalent doses were determined by OSL from 16 aliquots of quartz per sample using the quartz single-aliquot-regenerative (SAR) procedure. The material exhibited good OSL sensitivity and produced acceptable SAR internal quality control performance. Dose distributions from the aliquots were examined using radial plotting methods. An age estimate of 5.66 ± 0.43 ka (215 cm) was obtained for the ‘pre-Swampy Meadow’ deposit. Age estimates of 5.17 ± 0.30 ka (163 cm) and 2.43 ± 0.14 ka (103 cm) were obtained for the ‘Swampy Meadow’ deposit. The full dating samples analysed in this study do not show excess scatter in their dose distributions which might indicate partial zeroing at time of deposition. The age estimates suggest that sedimentation is continuous across the ‘pre-Swampy Meadow’/’Swampy Meadow’ contact at a rate of 1.1 mm/yr. The hypothesis that ‘enhanced erosion and gullying in the Grabben Cullen Creek region was a result of the introduction of pastoral farming by European settlers’ has been tested in this study. A linear extrapolation through the profiling apparent ages would estimate the age of the ‘Swampy Meadow’/’Post-Settlement Alluvium’ boundary at ~ 390 yrs. The Grabben Creek region of the Southern Tablelands of New South Wales is believed to have been settled by Europeans since the 1820s (Wasson et al., 1998). If the ‘Post-Settlement Alluvium’ was generated as a response to land clearing and the introduction of sheep and cattle associated with settlement, then it should be no older than ~ 200 yrs. We accept that there are a large number of inherent assumptions in projecting an age for the Swampy Meadow’/’Post-Settlement Alluvium’ boundary, however, it is interesting to note that the age constraints presented herein apparently question the accepted hypothesis. This study has highlighted the need for further small-aliquot or single-grain analysis on retained material from the profiling samples in the upper part of the succession, to provide additional information on the section.

• Item Type: Research Reports or Papers (Technical Report)
• Status: Published
• Glasgow Author(s) Enlighten ID: Munoz-Salinas, Dr Esperanza and Kinnaird, Dr Timothy and Sanderson, Professor David and Bishop, Professor Paul
• Authors: Kinnaird, T., Sanderson, D., Bishop, P., and Munoz-Salinas, E.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre; College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences; College of Science and Engineering > School of Geographical and Earth Sciences > Geography
• Publisher: SUERC