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Thermoluminescence and Excess 226Ra Decay Dating of Late Quaternary Fluvial Sands, East Alligator River, Australia

Published online by Cambridge University Press:  20 January 2017

Andrew Murray ,
Ellen Wohl  and
Jon East
Andrew Murray
Affiliation:
Alligator Rivers Region Research Institute, Jabiru East, NT 0886, Australia
Ellen Wohl
Affiliation:
Department of Geosciences, University of Arizona, Tucson, Arizona 85721 USA
Jon East
Affiliation:
Alligator Rivers Region Research Institute, Jabiru East, NT 0886, Australia
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Abstract

Thermoluminescence (TL) dating was applied to seven samples of siliceous fluvial sands from the East Alligator River of Northern Australia, giving ages ranging from modern to 6000 yr B.P. Two methods of estimating the equivalent dose (ED), total bleach and regenerative, were applied to the 90- to 125-μm quartz fraction of the samples in order to determine the reliability and internal consistency of the technique. High-resolution γ and α spectroscopy were used to measure radionuclide contents; these measurements revealed an excess 226Ra activity compared with 230Th. This excess decreased with depth, and was used directly to derive mean sedimentation rates, and thus sediment ages. Both this method and one 14C date confirmed the validity of the TL values, which increased systematically with depth and were consistent with site stratigraphy. TL was of limited use in the dating of these late Holocene deposits because of age uncertainties of 500 to 1600 yr, resulting from a significant residual ED. This residual probably resulted from incomplete bleaching during reworking upstream of the sampling site. For Pleistocene deposits, the residual ED will be less significant because of higher total EDs, and TL dates will be correspondingly more accurate.

Type
Research Article
Information
Quaternary Research , Volume 37 , Issue 1 , January 1992 , pp. 29 - 41
Copyright
University of Washington

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