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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

2017

Vol. 44, no. 1

175--187

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.

Coarse versus fine-grain quartz optical dating of the sediments related to the 1985 Ms7.1 Wuqia earthquake, northeastern margin of the Pamir salient, China

Yang H., Chen J., Porat N., Li T., Li W., Xiao W.

Geochronometria

2017

Vol. 44, no. 1

299--306

Optical dating of earthquake related sediments were investigated including one modern sample and three samples from a trench excavated across the 1985 Ms7.4 Wuqia Earthquake surface rupture. The results indicated that equivalent dose (De) values vary with grain size and the method used for De determination. The residual dose of the modern sample is 0.1 ka ( 0.2+0.2−0.1 Gy) for the quartz single grain measurements. Only 1.5–3.6% of the grains have a detectable OSL signal. Single grain quartz ages are similar to the expected ages. Fine grain quartz results overestimate the De values and are much older than single grain quartz and coarse grain quartz small aliquot standardized growth curve (SA-SGC) ages. Single grain quartz OSL dating may be optimal for dating earthquake related deposits, but SA-SGC can save measurement time and has potential for dating some poorly bleaching samples.