| The arid regions responded sensitively to the large-scale climate change, they have become a hot spot in global climate research. Different geological carrier has recorded regional palaeoclimate evolution during Holocene. Inland lakes are the sensitive indicators of regional climate change. As the large freshwater lake in southern Xinjiang, Bosten Lake provided an ideal place to carry out the regional response of the global climate change. Primary researches were mostly focused on the sediment core drilled from the lake. However, few studies concentrated on lakeshore deposits. The lakeshore sedimentary facies and their magnetic characteristics recorded rich information of the change process of hydrodynamic condition, sedimentary environment and paleoclimate. In this paper, we selected a continuous depositional sequence derived from Bosten lakeshore as a study object. With a chronological support of 5 radiocarbon dates, the environmental magnetic properties of the sediments have been systematically analyzed by the detailed analysis of environmental magnetism. Together with non-magnetic means of grain size, carbonate content, organic matter content and X-ray diffraction, the evolution of Holocene climate and the depositional environment were discussed and predicted in this region. The results are as follows:(1) In general, the magnetism of BST11C3 lakeshore sediments was weak. The sediments were dominated by ferrimagnetic minerals with low coercivity and relatively coarse particle size. Magnetite was the main controlling magnetic mineral. In different lithologic facies, the magnetic properties showed distinct differences. In the lakeshore facies and limnetic shallow-water facies, the magnetism was higher and the particle size was coarser. In addition, the sediments carried a small amount of hard magnetic particles, to some extent caused by the frequent hydrodynamic actions. However, in the shallow lake facies, the content of magnetic minerals decreased and the fine magnetic particles increased, which positively indicated the change of sedimentary environment.(2) The magnetic minerals in the sediments were dominated by exogenous clastic inputs. In upper and middle sediments, the exogenous clastic power was stronger and brought a small amount of wind substances. And authigenic iron sulphides and biogenetic minerals have little or no effect on their magnetic properties. Through the response of environmental magnetism indicators and other environmental indicators to regional sedimentary fluctuations, we could infer the site has experienced a frequently hydrological process of alternative occurrence of shallow delta facies, shallow lake facies, lacustrine-bog facies and shore-lacustrine facies.(3) The Holocene climate change of Southern Xinjiang followed "the westerlies evolution"mode:Early Holocene stage (10500-7700cal a BP) was dominated by relatively arid climate and the sedimentary environment started to evolve into the lacustrine facies after 8200 cal a BP. In Mid-Holocene, the climate of earlier stage (7700-5500cal a BP) was humid and the sedimentary environment entered into stable lacustrine facies deposits, with a drought event at around 6000cal a BP. The climate of later stage (5500～4200cal a BP) was relatively wet with dramatic and frequent oscillations, but the wetting degree was lower. The humid and unstable climate caused magnetic differences of the sediments under the specific hydrodynamic conditions. As a whole, the climate experienced a cold-wet, warm-dry and cold-wet alternation change. In the Late Holocene (4200cal a BP-the present), the climate became relatively humid and it was fluctuant since 2700 cal a BP. |
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