Developing luminescence chronometers to establish the timing of late Quaternary environmental changes in South Africa

Abstract

The predominantly dryland climate of interior South Africa precludes the widespread preservation of organic proxy records. Various potential geoproxy records exist, but their exploitation requires accurately constrained chronologies. This study investigates the development of two luminescence chronometers, quartz OSL and K-feldspar post-IR IRSL. At four sites across the eastern interior (Moopetsi, Voordrag, St Paul's and Goedgedacht), these chronometers are used to constrain the timing of: (i) the late Quaternary initiation of deposition; (ii) intervening phases of erosion, deposition andpedogenesis; and (iii) the current deep erosional phase. The value of using paired ages (i.e. determining quartz and K-feldspar ages from the same sample) becomes apparent, particularly at Voordrag where quartz OSL reaches saturation within the limit of radiocarbon dating. Paired chronologies show good agreement for younger samples (<24 ka) but systematic underestimation of quartz ages for older samples. Investigation of the post-IR IRSL protocol showed that signal transfer between the Lx and Tx measurements caused systematic underestimation of older feldspar ages. Dose recovery tests showed that it was not possible to recover a large given dose (400 Gy) when using a small (5 Gy) test dose.Two solutions were investigated, specifically increasing the size of the test dose to ~30 % of the De value and increasing the IR stimulation time. This led to the development of a `modified' post-IR IRSL protocol.The derived quartz and K-feldspar single grain chronologies show that the initiation of deposition was not synchronous at the four study sites, and ranges from ~153 { 65 ka. Intervening phases of erosion, deposition and pedogenesis remain difficult to constrain but broad inferences regarding climatic and geomorphic drivers can be made. The current phase of deep erosion appears to be linked to two periods of abrupt climate change, the 3.8 { 4.2 ka arid event and the Little Ice Age

Date of Award	2017
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Geoff Duller (Supervisor) & Stephen Tooth (Supervisor)