Dose Extension of a Sample at the Base of a Sedimentary Sequence in Vietnam

Cresswell, A.J. , Sanderson, D.C.W. and Carling, P.A. (2018) Dose Extension of a Sample at the Base of a Sedimentary Sequence in Vietnam. Technical Report. SUERC, East Kilbride, UK.

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Previous optically stimulated luminescence (OSL) dating measurements conducted on samples collected from a sedimentary cover sands sequence in Vietnam indicated basal ages of 14.4 ± 2.1 ka from aliquots yielding finite age estimates. However, some aliquots were beyond the saturation point of the OSL dose response curve (>100Gy, or c. 50 ka). This implies the presence of older material within the deposits. Further investigations have therefore been under taken to investigate luminescence signals associated with deeper traps in these quartzes to extend the range of the dose response. Investigation using aliquots previously measured for OSL has shown that: • Thermally transferred OSL (TT-OSL) produces signals at 1% or lower intensities than the OSL signals. For these quartzes the resulting signal intensities are too low to yield precise dose estimates. • However both the thermoluminescence (TL) during the heating ramp to thermal transfer temperatures (TL-ramp) and isothermal decay (ID) during the thermal transfer period produce large signals whose dose response continues to beyond 500Gy. Since these signals also originate from deep traps following OSL stimulation and grow to high doses they were investigated further. Using freshly dispensed aliquots of the quartz from the basal sample a new SAR dating run was performed, combined OSL, TL-ramp, I-Decay, and TT-OSL readout. As before TT-OSL intensities were low. However the other signals were measured at dose up to 1 kGy. It was possible to obtain finite dose estimates in the range of 200-250 Gy using TL-ramp and I-Decay signals. These correspond to ages of 100-125ka. This confirms the presence of older material in the basal samples. Since the basal samples may also be associated with microtektites of even greater age, a short kinetic analysis of the thermal activation energy and frequency factors associated with these signals was undertaken to evaluate their likely stability over a range of environmental temperatures. The outcome suggests thermal mean lives of 105-106 years at ambient temperatures in the 20-30°C region, with a strong dependence on environmental temperatures. Further work to extend the data sets to other cover sands in the region would potentially be useful.

Item Type:Research Reports or Papers (Technical Report)
Glasgow Author(s) Enlighten ID:Sanderson, Professor David and Cresswell, Dr Alan
Authors: Cresswell, A.J., Sanderson, D.C.W., and Carling, P.A.
Subjects:G Geography. Anthropology. Recreation > GB Physical geography
G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > QC Physics
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Copyright Holders:Copyright © 2018 Scottish Universities Environmental Research Centre
Publisher Policy:Reproduced with the permission of the Authors

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