Genesis And Climate Response Of The Late Quaternary Salt Deposits In The Kumishi Basin,Xinjiang

The Kumishi basin is located in the southern margin of East Tianshan,adjacent to Lop Nur area and Tu-Ha area of Tarim Basin.It is an inter mountain basin in Tianshan.Since Late Quaternary,its sedimentary environment has undergone different evolution processes,and a large number of the salt deposits have been deposited under the unique climate,provenance and structural conditions.At present,the research mainly focuses on the characteristics of strata and deposits There are still some scientific problems to be solved,such as:where is the source of the salt deposits enriched in this area?What kind of sedimentary environment changes did it experience in the process of salt formation?The late Quaternary experienced multiple climatic changes.What is the relationship between the use of salt deposits and climate?Therefore,in-depth study and analysis of the above problems is of great scientific significance for the improvement of salt mineralization theory in Northwest China and the evolution of climate and environment in Late Quaternary.Based on AMS14C dating,detrital zircon U-Pb dating,element geochemistry,isotope geochemistry and climatic environmental indicators,the chronostratigraphic framework is established,and the metallogenic environment and genesis of salt deposits are further analyzed,and the related climatic environment and coupling relationship between salinization and climate are studied and analyzed in depth.Based on the above analysis and research,the following understandings are obtained.1.Using AMS14C dating,the chronostratigraphic framework of the Kumishi Basin since Late Pleistocene is established.According to the analysis,about 35000a B.P.chemical deposition began in the Kumishi Basin.Since 14860a B.P.?up to now,it is mainly composed of two layers of halite,i.e.14860a B.P.?8150a B.P.granular rock salt layer and surface salt crust of 8150a B.P.?up to now.2.The Late Quaternary detrital materials in the Kumishi basin mainly come from collision events and magmatic activities in the Late Carboniferous and Early Permian around the basin.The detrital zircon U-Pb dating is used to analyze the provenance.The results show that the detrital zircon is mainly magmatic zircon,and the zircon age is mainly Caledonian and Hercynian.By comparing with the peripheral tectonic events,the detrital zircon of Hercynian is indicated The source is controlled by the Carboniferous Permian collision orogenic events in the South Tianshan,which is the main source of clastic materials in the Kumishi basin.3.From Late Pleistocene to the present,the study area has been a process of gradual drought since late Pleistocene;paleoclimate and paleoenvironmental indicators reveal that although there is a cold and humid climate between the lower granular salt layer and the surface salt crust,the overall process is a gradual drought,and evaporation and concentration is further intensified;on this basis,combined with rare earth elements,it is speculated that the study area has recorded aeolian deposits,which provides evidence for aridity.4.Salt enrichment in the study area is controlled by regional climate,structure,provenance and other conditions;comprehensive analysis of the genesis of salt deposits shows that in the early stage of salt formation,salt minerals around the basin migrated to the low-lying areas of the basin and began to enrich under the conditions of cold,wet and dry climate.In the later stage,salt materials were continuously enriched and mineralized under the strong evaporation and drought climate environment.5.Through the above analysis,it can be recognized that the salinization in the study area is inseparable from the late Pleistocene Holocene and the dry climate(interglacial period)after the late Quaternary glaciation;generally speaking,from 14860 to 8150a B.P.During the Holocene,the climate rapidly warmed and tended to be dry.The lower heavy sulfur isotope and saline water environment may be the response to the rapid rise of temperature after the cold and humid climate.