Variations of Thermally and Optically Stimulated Luminescence Sensitivity of Loess and Pedocomplex Samples from Southern Tajikistan, Central Asia

Abstract

To better understand the factors controlling the quartz luminescence sensitivity in loess deposits, samples from two loess sections in southern Tajikistan are investigated. Both pattern and amplitude in the variations of quartz luminescence sensitivity of these two sections are similar, showing higher values in pedocomplex units and lower values in the loess units. Similar trends of variation are found between the quartz luminescence sensitivity and climate proxies, including frequency-dependent magnetic susceptibility, median grain size and IRSL/[post-IR] OSL ratio. Laboratory experiments involving thermal activation and repeated bleaching/irradiation cycles reveal much larger sensitivity enhancement for samples with initial lower sensitivity from loess units than those from pedocomplex units with higher sensitivity. The observed systematic contrast in quartz luminescence sensitivity between the loess and pedocomplex units are interpreted as resulting from the differentiation of the weathering products from the source area and subsequent sensitization during the sedimentary transfer prior to deposition.

Luminescence Sensitivity of Rhine Valley Loess: Indicators of Source Variability?

“…We therefore do not consider these further, although we note that these trends do not contradict the statistically significant trends in the IR 50 data. Our observed trend is the inverse of that previously observed for quartz in other LPS across Eurasia [42,43]. 50 Sensitivity down Core REM3B: Implications for Source Variability?…”

“…Approaches include cathodoluminescence signal spectra deriving from crystalline impurities, which relate to source rock formation [33,34]; electron spin resonance (ESR) signal intensity of luminescence centres, which are thought to reflect source rock age [34,35]; ratios of linearly-modulated optically stimulated luminescence (OSL) components as proxies for formation age [36,37]; and OSL sensitivity measurements as a qualitative indicator of source lithology and transport history [38][39][40][41]. Among these approaches, OSL sensitivity is the quickest to measure and has therefore been favoured in loess studies as a means to rapidly assess potential changes in sediment source down LPS profiles [42][43][44].…”

“…Consequently, shifts in sediment provenance may be observed through variations in OSL sensitivity down LPS [43]. Additional luminescence characteristics such as dose recovery [44] and infrared stimulated luminescence (IRSL)/OSL ratios [42] have also been observed to change in parallel, but require additional measurements. OSL sensitivity profiles have so far been generated for LPS sites on the Chinese Loess Plateau [43,44] and in Central Asia [42].…”

“…Additional luminescence characteristics such as dose recovery [44] and infrared stimulated luminescence (IRSL)/OSL ratios [42] have also been observed to change in parallel, but require additional measurements. OSL sensitivity profiles have so far been generated for LPS sites on the Chinese Loess Plateau [43,44] and in Central Asia [42]. Despite the presence of thick loess deposits across Europe [3,[46][47][48], however, this approach has yet to be tested on that continent.…”

Luminescence Sensitivity of Quartz From Rocks Under in situ Chemical Weathering Conditions

“…Meanwhile, studies focused on the effects of sedimentary transport processes and the characterization of source materials on the QLS have been developed. Aiming to discover and understand the relationships between QLS and the petrological background of quartz, studies have been undertaken in the following areas: the age of intrusive granite (Rink, 1994), crystallization temperature (Sawakuchi et al, 2011b), inclusions (Chauhan and Singhvi, 2019), thermal and sedimentary history (Preusser et al, 2006;Pietsch et al, 2008;Zheng et al, 2009;Fitzsimmons, 2011;Sawakuchi et al, 2011a;Lü and Sun, 2017;Sawakuchi et al, 2018;Chang and Zhou, 2019;Nian et al, 2019;Li and Zhou, 2020;Sawakuchi et al, 2020;Bartyik et al, 2021;del Río et al, 2021). These exploratory efforts have enhanced our understanding of QLS and expanded its application scenarios.…”