OSL And Its Sedimentation Rate Of The Qarhan Salt Lake Since The Holocene

Qarhan Salt Lake,located in the Qaidam Basin in the northern part of the Qinghai-Tibet Plateau,is the largest salt lake in China and the catchment center of the Qaidam Basin since the late Pleistocene.The sedimentary sequence of Qarhan Salt Lake is relatively continuous,and the environmental evolution information recorded is relatively complete,which is an ideal place to study the environmental evolution since the late Pleistocene in the Qaidam Basin.Although a large number of research works have been carried out on the salt lake deposit,salt forming source,salt element migration,salt age and process,etc.for the Qarhan salt lake.However,due to various factors such as low carbonate and organic matter content in salt lake sediments,less aeolian debris,and unclosed geochemical systems,it is difficult to date.On the other hand,the chronology of Qarhan Salt Lake mainly focuses on the late Pleistocene to Early Holocene（deep salt lake sediments）,and there is little chronological research on Middle and Late Holocene sediments（shallow salt lake sediments）,and some of the existing chronological data have the problem of chronological inversion,which hinders the understanding of the environmental evolution process of Qarhan Salt Lake.Therefore,this paper takes the Holocene sediments of the Qarhan Salt Lake as the research object,through the three-dimensional study of the eastern part of the Bieletan section（BLT）,the western part of the Bieletan section（BLTW）and the eastern part of the Dabuson section（DBX）.Since the relatively small influence of salt lake sedimentation and input of exogenous material on the selected sediment profile,the optically stimulated luminescence（OSL）method was used to determine the Holocene age of shallow sediments in Qarhan Salt Lake,establish a chronology framework for Qarhan Salt Lake since the Holocene,and provide new evidence and understanding of the paleoenvironmental evolution of Qarhan Salt Lake since the Holocene,in combination with X-ray diffraction（XRD）and particle size analysis.The main contents are as follows:（1）The OSL dating results of the sediment profile of the Qarhan Salt Lake show that the two clastic layers of the DBX profile were formed at 6.2 ka（8.9 m）and 2.8 ka（5.5 m）,respectively,indicating that the formation age of the surface salt in the eastern section of the Dabuson section was 2.8 ka.The two clastic layers of the BLT profile were formed at 2.9 ka（3.1 m）and 0.9 ka（1.5 m）,respectively,and the two clastic layers of the BLTW profile were formed at 2.4 ka（3.2 m）and 0.7 ka（1.4 m）,respectively,indicating that the formation age of the surface salt of the east and west sections of the Bieletan section was 0.7-0.9 ka.These results are smaller than the age（8-9 ka,1-2 m）of the surface salt of Qarhan Salt Lake obtained by previous U-Th and ¹⁴C dating.（2）Based on the OSL dating results of clastic layers measured at three sections of the Qarhan Salt Lake and its burial depth,the sedimentation rates of each area were calculated,and the results showed that the deposition rates in the eastern part of the Dabuson section and the eastern part of the Bile Beach section were relatively large,respectively 1.43 m/ka,1.29 m/ka,and the sedimentation rate in the west of the Bieletan section section is relatively small,1.10 m/ka.The deposition rate in the eastern part of the Dabuson section increased from 1.00 m/ka to 1.96 m/ka,that in the eastern part of the Bieletan section increased from 0.94 m/ka to 2.14 m/ka,and that in the west of the Bieletan section increased from 0.90 m/ka to 2.14 m/ka.m/ka increased to 1.56 m/ka,indicating that the east of the Dabuson section,the east and west of the Bieletan section received stronger river recharge,resulting in an increase in sedimentation rate.In addition,the formation age of the S4 layer salt in the Qarhan Salt Lake is estimated to be 14.4-24.4 ka（east of the Dabuson section）,27.1 ka（east of the Bieletan section）and21.0-27.6 ka（west of the Bieletan section）.（3）The eastern and western sections of the Bieletan section and the eastern section of the Dabuson section were all stone salt layers,and debris layers of about 0.3 m,0.4m and 0.4 m thick were formed at 1.5 m and 3.1 m,1.4 m and 3.2 m,5.5 m and 8.9 m,respectively,indicating that there were at least two wetting events in the three profiles.Combined with OSL dating results,mineralogy and sedimentary characteristics,it is indicated that the wetting events of the three sections of Qarhan Salt Lake are flood events,which is consistent with the paleoenvironmental research results of the previous people through the shoreline of Qarhan Salt Lake and the Kunlun Mountain Water System.