科研之友
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摘要
The Xitaijinair Salt Lake, located in the middle of the Qaidam Basin, Qinghai Province, China, is rich in resources of Li, K, B and Mg. For the tremendous economic value, previous studies mainly focused on the hydrology and hydrochemical characteristics of brine. However, the formation and evolution of the salt lake is still controversial and the chronology of the Xitaijinair Salt Lake is absent. In this paper, two cores from the middle and east edge of the salt lake were dated with the methods of Optically Stimulated Luminescence (OSL) and radiocarbon dating (AMS 14C), the condition experiments of OSL dating were conducted and the feasibility of the two methods was also discussed. The sedimentary sequence of the two cores showed that the sediments both in the top and bottom are dominated by silty clay, while the middle of the cores are dominated by halite with several layers of silty clay. The sedimentary facies also revealed that the Xitaijinair Salt Lake has been desalted at least twice. Based on 5 AMS C and 4 OSL chronologies, the chronological framework of the Xitaijinair Salt Lake was preliminary discussed. In the middle of the cores, the OSL dating materials are scarce and only obtained AMS C chronologies. Thus, we calculated the reservoir effect offset by comparing the OSL chronologies with AMS C chronologies from the same layer. The ages of silty clay layer from the middle of the cores were obtained by deducting reservoir effect offset from the measured AMS 14C ages. The results showed as follows: (1) In AMS 14C dating method, samples older than 30 ka were obviously underestimated. While for the younger samples, a ~4. 0 ka reservoir effect offset was calculated by comparing with the OSL ages. Relatively, the OSL dating results are more reasonable. (2) In both of the two cores, the top silty clay layer was formed about 0. 3 ka BP: the silty clay layer in the middle, about 4. 0 ka BP, and the bottom silty clay layer, at least 70 ka BP. (3) It seems the Bagayawur anticline in the northeast of the salt lake controlled the formation of the basin, and the blind fault between the anticline and basin controlled the depth of the basin. However, more details are needed to reveal the specific process between the lake evolution and tectonic activity.
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