| The northeastern margin of the Qinghai-Tibet Plateau is located in the region affected by the modern Asian monsoon and the transition zone between China's arid and semi-arid climate,the sediments here are very sensitive to climate change and record important information on climate evolution.The ideal place to respond to global change.The Jianzha Basin in the study area has a special geographical location.It is not only affected by the uplift of the Qinghai-Tibet Plateau,but also in the spatial distribution of the intersection of the three natural areas and the monsoon convergence zone,so it is very sensitive to climate change.The sediments contain rich structural and paleoenvironment information,which is a good carrier to record the evolution of climate and environment,and provide a new reliable basis for further discussion on the uplift of the Qinghai-Tibet Plateau,the evolution of paleoenvironment and the drought of inland Asia.In this paper,the sedimentary sequence of the Jiarang section in the Jianzha Basin with a time span of 11.8?5.8 Ma is selected as the research object.The environmental magnetism and color are the main research methods.Based on the fine magnetic stratigraphic chronological framework,the sediment The system's environmental magnetism and chromaticity analysis,combined with the evolution characteristics of sedimentary facies in Jiarang section,can get the information of paleoclimatic evolution in this area.Comparing with the trend of deep sea oxygen isotope changes and other global climate change events,the paleoenvironment evolution information and tectonic activity information of Jianzha Basin during 11.8?5.8 Ma were obtained,and the following relevant conclusions were mainly drawn:(1)By studying the environmental magnetism and chromaticity of sediments in the Jianzhan Basin of the Jianzha Basin,combined with the established chronological scale,high-resolution magnetic parameters and chromaticity change curves during the period of about 11.8?5.8 Ma in the Jianzha Basin were obtained.The changes in degree and susceptibility have a good correspondence with the changes in sedimentary lithology andmagnetic minerals,indicating that the susceptibility and chromaticity can truly reflect the climate and environmental conditions at that time,and are two effective climatic substitute indicators.And through the magnetic susceptibility and color reconstruction of the Jianzha Basin precipitation and temperature changes of 11.8?5.8 Ma,revealing the climate change process of the Jianzha Basin.(2)Environmental magnetic parameter changes and correlation studies show that the main magnetic minerals in the sediments of the Jiarang section are single-domain low-coercive ferrimagnetic minerals(magnetite,maghemite),and there is also a certain amount of red Iron ore,the mineral particles are mainly coarse-grained SSD particles,and there are also a certain amount of superparamagnetic particles.(3)According to the test results of environmental magnetism and colorimetry,after comprehensive comparison of the change trends of various parameters,correlation analysis,combined with specific lithology and sedimentary environment changes,the climate evolution between 11.8?5.8 Ma in the study area is divided into the following four variation stages: cold and dry period(about 11.8?9.8 Ma)-warm and wet periods alternate with cold and dry periods(about 9.8?8.6 Ma)-warm and humid period(about 8.6?7.2 Ma)-relatively warm and humid period(about 7.2?6.2 Ma)-dry and cold period(about 6.2?5.8 Ma).After about 8.6 Ma,all parameters of environmental magnetism and redness value show a clear increasing trend,indicating that the summer monsoon was significantly enhanced,revealing the response to the uplift of the Tibetan Plateau.After about 7.2 Ma,the combined effects of climate change plateau uplift,global cooling and Arctic ice sheet expansion in the study area. |
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