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

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

Geochronometria

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2017

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

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

Geochronometria

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2013

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tom 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.

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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

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

Geochronometria

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2014

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tom 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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Analysis of the spatiotemporal land-use/land-cover change and its driving forces in fuxian lake watershed, 1974 to 2014

70%

Li S.-H. , Jin B.-X. , Zhou J.-S. , Wang J.-L. , Pang S.-Y.

Polish Journal of Environmental Studies

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2017

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tom 26

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nr 2

EN

Land-use/land-cover change (LUCC) is an important issue of research into global change. To identify the spatiotemporal change and the driving mechanism of land use at the regional scale is of great significance to environmental preservation and economic development in the whole locality. In order to analyze the spatiotemporal change of land cover in Fuxian Lake watershed for the last four decades, our paper extracted the information of land use and land cover in the area using the method of combining supervised classification with visual interpretation. The process of extraction referred to a total of 10 time series remotesensing images (namely the 1974, 1977, 1987, 1990, 1996, 2000, 2006, 2009, 2012, and 2014 phases) as the main data source, and drew on the achievement data from the China Geography Census as an ancillary source. Accordingly, we obtained the spatiotemporal characteristics of the land-cover type change in Fuxian Lake watershed for the last 40 years. Finally, based on the socioeconomic data in the locality, using principal component analysis and multiple regression analysis, this paper analyzed the driving forces of LUCC in the watershed to acquire the major driving force factors, and built up a corresponding multiple linear regression model. The same kind of model was established for the local cultivated land and its driving force factors. The result shows that: 1) In terms of changing trends, along with the increasing human activities in the socioeconomic domain of the catchment, the last four decades has seen a mounting local number of gardens, building regions (districts), roads, structures, artificial piling and digging of land, as well as wastelands and bare surface. As a contrast, there has been a decreasing trend for cultivated land, woodland, grassland, and water for the same term. 2) The variation degree of land cover was higher during the period 1990-96 and 2000-06, and was the lowest in 1974-77. 3) During 1974-77, 1987-2000, 2006-14, and 1974-2014, there was a noticeable discrepancy between the converted areas of various land-use types, which was higher for woodland, grassland, and arable land, and was lower for water by comparison. 4) The cultivated area in Fuxian Lake watershed was positively correlated with such factors as overall population, natural population growth rate, the production value of the primary industry, the production value of the tertiary industry, industrial production value, GDP, fiscal expenditure, living expenditure per capita, and annual average temperature. It was negatively correlated with some other factors, including agricultural population, agricultural production value, rural income per capita, total retail sales of consumer goods, grain total output, the per unit area yield of grain, the amount of fertilizer used in agriculture, the amount of pesticide used in agriculture, and annual average precipitation.