The Study On Change Of Palaeoenvironment In Muli Permafrost Aera Of Tianjun County Of Qinghai Provincesince Mid-last Glacial Age

This paper seclected the quaternary stratigraphic in Muli permafrost aera of Tianjun county of Qinghai Province as research object, which is in the northeast of Qinghai-Tibet Plateau and adjacent to the south of Mid-Qilian Mountain. On the base of previous studies, this paper took some analysis about particle size, magnetic susceptibility and paleo temperature and compared the characteristics of them with the paleo oxygen isotope stages in Guliya Ice Core since 50 ka BP Then this paper rehabilitates the process and evolution of climate changing in research area since midlast glacial age of Late Pleistocene. And the main conclusions are as follows:1. The quaternary stratigraphic in research area includes the upper Ledu formation of Late Pleistocene stratigraphic and all the Holocene stratigraphic. The age of the boundary between the upper Ledu formation and the bedrock which is below it is about 44.84 ka BP And the age of the boundary between the upper Ledu formation and the Holocene stratigraphic in which lies a gray-brown clay containing gravel isabout 11.37 ka BP2. The paleo climate and sedimentary environment of research area have three stages since mid-last glacial age. The most old and warm stage is a interglacial age of mid-last glacial age between the age 44.84 ka BP and 31.54 ka BP In this stage, the foremost sedimentary facies is outwash and flood depositions. The particle size is thicker, and the value of magnetic susceptibility and paleo temperature is greater than the others’ s. During this stage, climate fluctuated and had a abnormal warm event, which leaded to a greater speed of sedimentary. Then it came the coldest stage which is called the Last Glacial Maximum and Late Glacial, dating age is between 31.54 ka BP and 11.32 ka BP The foremost sedimentary facies is outwash with some characteristics of fluvial deposits, meaning that this stage had a weak and unstable transportation power. Fine particles composition increases with a significant reduction of the value of magnetic susceptibility and paleo temperature. But during the later period of Late Glacial, the paleo temperature incressed gradually with some sudden and short cold events, such as YD event. The newest stage is Holocene from 11.32 ka BP to nowadays, The foremost sedimentary facies is outwash and alluvium-flood depositions. The the value of magnetic susceptibility and paleo temperature is greater than the prior’s. this stage has gone through cold dry- Megathermal-cool minor stages, which of the middle is a relatively long warm period, which is called Megathermal. Although the weather is warm and wet in general, it also has some minor intense and frequent fluctuations between warm and cold.3. The analysis show that the paleo temperature which is calculated and based on the Iron oxide ratio can be used as climate index of the cold plateau in some degree, because of its good correlation with particle size, magnetic susceptibility. And the climate change characteristics since mid-last glacial age in research area could be corresponding well to the different stages of the paleo oxygen isotope stages in Guliya Ice Core since 50 ka BP respectively, such as OIS1, OIS2, OIS3 a, OIS3 b. In addition, the peaks and valleysof the climate change characteristics could also be corresponding well to the sudden cold events, such as Heinrich event(from H1 to H5), Younger Dryas event(about 11 ka BP), or the warm event, such as Allerod-Bolling event(shortly before YD event).