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Optical dating of sediments from manas lake in northwestern china: Paleoenvironmental and neotectonic implications

Tse Y.-Y., Li S.-H.

Geochronometria

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2017

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Vol. 44, no. 1

175--187

EN

Manas Lake is a closed lake basin in northern Xinjiang Province of China, with its current lake bed at 244 m a.s.l. Sediments from the lake area provide valuable information about the paleoenvironmental changes in the Westerlies-dominated arid region. To obtain a chronological constraint on the past changes, optically stimulated luminescence dating was conducted on sediments from the lake beaches. The results show that lacustrine episodes dated at ~80–73 ka ago were recorded in northwestern side of the lake at 270 m a.s.l., while paleoshoreline to near-shore environments during ~80–90 ka ago were recorded in the opposite side of the lake at 262 m a.s.l. The ~80 ka old sedimentary layers are overlain by paleoshoreline sediments formed within the last ~1 ka, separated by a large age gap. From this study and the results from previous studies, it is concluded that breaks in sedimentary records are common in the lake area at elevation > 260 m a.s.l. When comparing sedimentary environments at different times from different sites in this study and previous studies, it is suggested that a small amount of uplift of the northwestern side of Manas Lake relative to the southeastern side may have occurred in the last 80 ka.

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Review and assessment of the potential of post-IR IRSL dating methods to circumvent the problem of anomalous fading in feldspar luminescence

Li B., Jacobs Z., Roberts R. G., Li S.-H.

Geochronometria

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2014

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Vol. 41, no. 3

178--201

EN

Quartz has been the main mineral used for optically stimulated luminescence (OSL) dating of sediments over the last decade. The quartz OSL signal, however, has been shown to saturate at rel-atively low doses of ~200–400 Gy, making it difficult to be used for dating beyond about 200 thou-sand years (ka), unless the environmental dose rate is low. The infrared stimulated luminescence (IRSL) from feldspars has been shown to continue to grow to higher dose levels than quartz OSL. The application of IRSL dating of feldspars, however, has long been hampered by the anomalous fading effect. Recent progress in understanding anomalous fading of the infrared stimulated luminescence (IRSL) signals in potassium-feldspar has led to the development of post-IR IRSL (pIRIR) protocols and also a multiple elevated temperature (MET) stimulation (MET-pIRIR) protocol. These procedures have raised the prospect of isolating a non-fading IRSL component for dating Quaternary deposits containing feldspars. In this study, we review the recent progress made on (1) overcoming anomalous fading of feldspar, and (2) the development of pIRIR dating techniques for feldspar. The potential and problems associated with these methods are discussed.

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Residual doses and sensitivity change of post IR IRSL signals from potassium feldspar under different bleaching conditions

Chen Y., Li S.-H., Li B.

Geochronometria

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2013

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Vol. 40, no. 4

229--238

EN

The residual doses and sensitivity change for potassium-rich feldspar (K-feldspar) have been studied using the post-infrared infrared stimulated luminescence (pIRIR) and multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocols. Laboratory simulated poorly-bleached and well-bleached samples were those K-feldspar grains bleached using a solar simulator for 10 minutes and 8 hours, respectively. The residual doses rise with stimulation temperature and time. The poorly-bleached sample has larger residual doses than the well-bleached sample, especially at high stimula-tion temperatures. The high-temperature pIRIR signals contain a large amount of hard-to-bleach sig-nals. A decrease of luminescence sensitivity was observed after conducting a high-temperature-treatment in the measurement cycles. The sensitivity decreases significantly between the first and the second cycle. The extent of decrease in sensitivity shows a clear temperature trend. The higher the stimulation temperature of pIRIR signals is, the larger the sensitivity decreases. This decrease is more severe for the poorly-bleached sample than for the well-bleached sample, and could possibly lead to problems in sensitivity correction.