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Preserving the palaeoenvironmental record in Drylands: Bioturbation\ud and its significance for luminescence-derived chronologies

By M.D. Bateman, C.H. Boulter, A.S. Carr, C.D. Frederick, D. Peter and M. Wilder

Abstract

Luminescence (OSL) dating has revolutionised the understanding of Late Pleistocene dryland activity. However,\ud one of the key assumptions for this sort of palaeoenvironmental work is that sedimentary sequences have been\ud preserved intact, enabling their use as proxy indicators of past changes. This relies on stabilisation or burial\ud soon after deposition and a mechanism to prevent any subsequent re-mobilisation. As well as a dating\ud technique OSL, especially at the single grain level, can be used to gain an insight into post-depositional\ud processes that may distort or invalidate the palaeoenvironmental record of geological sediment sequences.\ud This paper explores the possible impact of bioturbation (the movement of sediment by flora and fauna) on\ud luminescence derived chronologies from Quaternary sedimentary deposits in Texas and Florida (USA) which\ud have both independent radiocarbon chronologies and archaeological evidence. These sites clearly illustrate the\ud ability of bioturbation to rejuvenate ancient weathered sandy bedrock and/or to alter depositional stratigraphies\ud through the processes of exhumation and sub-surface mixing of sediment. The use of multiple OSL replicate\ud measurements is advocated as a strategy for checking for bioturbated sediment. Where significant OSL\ud heterogeneity is found, caution should be taken with the derived OSL ages and further measurements at the\ud single grain level are recommended. Observations from the linear dunes of the Kalahari show them to have no\ud bedding structure and to have OSL heterogeneity similar to that shown from the bioturbated Texan and Florida\ud sites. The Kalahari linear dunes could have therefore undergone hitherto undetected post-depositional sediment\ud disturbance which would have implications for the established OSL chronology for the region

Publisher: Elsevier
Year: 2007
OAI identifier: oai:eprints.whiterose.ac.uk:2264

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