Clayminerals Characteristics And Environmental Indicative Significance Of Gypsum Salt-bearing Strata In Gongjue Formation,Nangqian Basin

The Qinghai-Tibet Plateau has always been one of the hotspots studied by scholars at home and abroad.The main research contents include plateau uplift,sedimentary environment,climate change,etc.During the geological history evolution,a set of the Nangqian Basin in the northeastern part of the Qinghai-Tibet Plateau developed.The Cenozoic continental red clastic rocks and the gypsum-bearing rock formations are good materials for studying the paleo-Paleocene paleoclimatic evolution and the deposition of the salt-bearing salt in the Qinghai-Tibet Plateau.On the basis of summarizing the research results of the predecessors,from the perspective of clay mineralogy and elemental geochemistry,I collected the clastic sediments of the 257m salt-bearing salt formation in the Gongjue Formation of the Nangqian Basin at a distance of 6m,and analyzed the clay minerals.Composition and combination characteristics to study climate and sedimentary environment changes.The results showed that the clay minerals were mainly illite?52.1%?,followed by chlorite?8.1%?and kaolinite?3.5%?.According to lithological characteristics and changes in clay mineral composition,the profile can be divided into three stages from bottom to top,indicating warm and humid,low salinity,cold dry-high salinity,warmer wet-low salinity climate and sedimentation.surroundings.The geochemical macroelements Sr,Ba,V,and Ni reflect the sedimentary environment and source area of the basin.The changes of chemical element ions Ca²⁺,SO₄^2-,and Sr²⁺reflect the sedimentary relationship of the mudstone-gypsum cycle,Na⁺and Cl^-The trend of content change is related to the migration and occurrence of rock salt.Based on the analysis of clay mineral combination characteristics and geochemical elements,the lithology and sedimentary environment of the salt-salt profile of the Gongjue Formation in the Nangqian Basin were discussed,and the climatic conditions during the formation of the red mudstone-gypsum deposit were inferred.During the Cenozoic period,in the mid-latitude arid region,most of the basins in the northern and northeastern Tibetan Plateau were dominated by lacustrine sediments,indicating that the Central Asia region is dominated by semi-humid climate during this period.The formation of the red mudstone-gypsum deposit in the Gongjue Formation of the study area is a response to the dry and wet climate of the Qinghai-Tibet Plateau and the entire mid-latitude arid region.