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The suitability of a low temperature post-IR IRSL signal for dating alluvial and colluvial “cut and fill” sequences in the Great Karoo, South Africa

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journal contribution
posted on 17.03.2020, 14:53 by CJ Oldknow, Andrew Carr, JM Hooke, Z Shen
Alluvial and colluvial “cut and fill” deposits preserved in valleys of the Karoo, South Africa, reflect basin-scale adjustments in fluvial process-regime. Such deposits in the Wilgerbosch catchment have previously proven difficult to date using radiocarbon (14C) and optically stimulated luminescence (OSL) methods. In this paper, we test the suitability of K-feldspar post-IR infrared (pIRIR) methods on 19 samples from Africanders Kloof, a low-order tributary of the Sundays River. Using three carefully screened quartz OSL ages, radiocarbon dating and site stratigraphic considerations we argue that the pIRIR170 protocol can be used to produce reliable age estimates. Fading rates for the pIRIR170 signal are consistently low (average g2days: 0.81 ± 0.58). The pIRIR170 residuals are dose dependent (r2=0.58); but are consistently low as a proportion (e.g. 1-4%) of sample equivalent dose (De). Despite the water-lain depositional context, single aliquot De distributions tend toward normality (for 11/19 samples) irrespective of aliquot size (2 mm or micro-aliquots containing 2-30 grains) with only a few statistical outliers per sample (max. n=3) and overdispersion (OD) ranging from 1.6-30% excluding the two youngest (late Holocene) samples (OD: 37-87%). The resulting pIRIR170 ages are in the correct stratigraphic order and illustrate the potential of pIRIR170 luminescence dating to investigate the timing, processes and drivers of fluvial system adjustments across the Karoo.

History

Citation

Quaternary Geochronology (2020), 101064

Version

AM (Accepted Manuscript)

Published in

Quaternary Geochronology

Publisher

Elsevier

issn

1871-1014

Acceptance date

06/03/2020

Copyright date

2020

Available date

14/03/2020

Publisher version

https://www.sciencedirect.com/science/article/pii/S1871101420300133

Language

en

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