Luminescence Profile Measurements on Samples from Vietnam Submitted by P. Carling

Cresswell, A.J. , Sanderson, D.C.W. and Carling, P.A. (2018) Luminescence Profile Measurements on Samples from Vietnam Submitted by P. Carling. Technical Report. SUERC, East Kilbride, UK.

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Luminescence measurements have been conducted on small samples from a stratigraphic horizon in Vietnam overlaying a regionally extensive gravel layer containing tektites and shocked quartz that are evidence for a meteorite impact dated to approximately 700 ka. The lower part of this stratigraphic horizon contains coarser grains and smashed granules which may also be associated with the impact event. Profiling measurements of the same sedimentary feature in Thailand showed an inverted luminescence profile. The measurements conducted here show that these materials had been very well bleached prior to deposition, with bright rapidly depleting OSL signals from quartz grains. These samples do not reproduce the inverted sequence observed in Thailand. The OSL measurements suggest three distinct zones within the sedimentary sequence; the youngest 6-7 samples showing a steady increase in stored dose estimates, the middle 7-8 samples show approximately constant dose estimates, with a discontinuity in dose estimate above the oldest 7-8 samples which also show a higher OSL depletion rate and IRSL:OSL ratio. It is suggested that the data represent a history of rapid sedimentation depositing the lower zone, followed by an erosional event removing the upper part of this sequence, before a second period of rapid sedimentation with material potentially from a different source, and finally a more recent period of lower sedimentation rate. These samples appear to be very suitable for quantitative dating with sufficient material for dose rate determination in some instances, and could be considered for establishing a chronology for this stratigraphic sequence. Quantitative SAR OSL analysis has been conducted on three samples, one from each of the three zones, where control samples had been collected providing sufficient material for dose rate calculation. There are differences between the three samples in both dose rate (upper sample with the lowest dose rate and the lower sample the highest) and luminescence sensitivity (with the lowest sample being less sensitive), suggestive of differences in the source materials for each of the three zones. The SAR ages for the upper two samples are inverted and significantly different from the profiling apparent ages (16.0 ± 2.3 ka for the upper and 5.4 ± 0.7 ka for the middle sample). The lowest sample, just above the gravel layer containing shocked quartz and tektites, has an equivalent dose distribution with a broad peak corresponding to an age of 14 ± 2 ka, with several aliquots with equivalent doses that correspond to ages significantly in excess of 50 ka. The 14 ± 2 ka age is consistent with previous OSL ages for the corresponding sedimentary layer in Thailand (8 and 19 ka), which is significantly younger than the impact date and suggest that these layers are not associated with the impact. However, the significantly older ages for some samples may suggest an earlier deposition with subsequent disturbance introducing the younger material. Alternative quartz analysis methods would be needed to extend the range of measurement to explore the age of these older components.

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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