Abstract
A comparative study using quartz optically stimulated luminescence (OSL) and feldspar post-infrared infrared stimulated luminescence (post-IR IRSL) was undertaken on Quaternary fluvial sediments from an unnamed tributary of the Moopetsi River in South Africa. The aim is to assess whether the post-IR IRSL signal can be used to date incompletely bleached sediments. Several post-IR IRSL signals using varying stimulation and preheat temperatures were investigated; of these the post-IR IRSL225 signal was deemed most appropriate for dating because it bleached most rapidly. The feldspar post-IR IRSL225 equivalent dose (De) values from this site are consistently larger than those from quartz OSL, probably due to differences in the bleaching characteristics of the two signals. Additionally, the post-IR IRSL225 De values within a sample showed less variation in precision than the quartz De data, possibly due to greater averaging between grains in the feldspar small aliquots. The agreement between ages based on the OSL and post-IR IRSL225 signals was better for younger samples (<20 ka) than for older ones (>50 ka); the cause of this variation is unclear.
Highlights
Across the South African interior, numerous dongas have formed within Quaternary colluvium and alluvium
After 10 s of bleaching, the quartz optically stimulated luminescence (OSL) signal was reduced to 5% of the original signal whilst the post-IR IRSL225 signal was only reduced to ~86%, and the post-IR
Laboratory characterisation of the post-IR IRSL225 signal from feldspars from an unnamed tributary of the Moopetsi River has shown that this signal is suitable for dating but the signal is slow to bleach, taking ~4 days in the SOL-2 to reach
Summary
Across the South African interior, numerous dongas (gullies and badland-type environments) have formed within Quaternary colluvium and alluvium Within these dongas, exposures of up to 30 m in thickness reveal multiple phases of sedimentation, palaeosol formation and erosion. The aim of this paper is to assess whether the post-IR IRSL signal from feldspars can be used to date poorly bleached fluvial sediments, and to extend the age range of luminescence dating beyond that which is possible using the OSL signal from quartz. A site in north-eastern South Africa comprised of fluvial sediments is used in this study; a suite of 10 luminescence ages based upon the OSL signal from quartz already exists (Lyons, 2012) and can be compared with new data obtained using feldspar post-IR IRSL signals
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