Exploring western Thar linear dunes with a portable luminescence reader: Holocene dynamics and also MIS 3-MIS 2 preservation.

The Thar Desert in South Asia contains a vast range of dune morphologies, and linear dunes have increasingly been studied here for their palaeoenvironmental records (Srivastava, 2019; 2023: Srivastava et al., 2020). Mostly recently, the portable optically stimulated luminescence (port-OSL) reader, alongside laboratory dated samples has been used to produce a calibration for samples in the previously unexplored far west of the Thar, covering the last ~12 ka (Nitundil et al., 2023).

Here we present age estimates from the port-OSL reader calibration for 321 samples, collected from five locations along a ~60 km south-north transect in the far western Thar (west of Jaisalmer). We also present 9 new laboratory ages across three of these locations, for targeted samples as guided by the port-OSL age estimates. The port-OSL age estimates, based on the port-OSL calibration, represent 19 shallow dune profiles (~2 m) and five long (~10 m) dune profiles. Together, the port-OSL age estimates indicate the temporal pattern of accumulation between ~12 and 8 ka, known further east in the Thar (Srivastava, 2023). However, one dune flank at the Asu Tar location exceeded our calibrated range, and the subsequent laboratory dating reveals these basal samples to be ~44±3 ka (8.3 m) and ~23±2 (7.8 m). This is the first-time an aeolian unit older than the Holocene has been found in this part of the Thar. In addition, the laboratory ages are not near saturation, which contrasts with saturation at ~48 ka for linear dunes in the Bikaner dunefield region, ~320 km to the northeast (Srivastava et al., 2019).

The low-fidelity port-OSL-derived age estimates are demonstrated to be a powerful approach for understanding the broad pattern of dune accumulation for the last ~12 ka across a large spatial area of the western Thar, and for whole dune depths. This facilitates a rapid and cost-effective exploration of landscape-scale change in dunefields, and in this case has been useful to identify packages of older sediments that can then be selected for laboratory dating.