| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 99 === We collected sediments from the Bilutu Lake (43°25''12.0'' N, 113°46''32.5'' E) in the center of Inner Mongolia of China to understand climate and environment changes during Younger Dryas Period in northern China. This area is located at the central Asian, where the climate is controlled predominantly by the interaction between the Siberian High, East Asian monsoons and westerly belt. Therefore, this area is considered as a sensitive response for the climate change, so we drilled and analyzed the lake sediments here. The retrieved core from this lake was 7.52 m in length which covered the age ranging from 8.5 to 13 cal. ka BP by C-14 dating, and the average sedimentation rate was estimated as 0.167cm/yr. The X-ray diffraction (XRD) analyses show that the mineral assemblage is predominantly composed of quartz, feldspar, clay minerals, calcite, dolomite and magnesite. In addition, the abundant aragonites indicates the existing of Ostracodas.
Combining the results of XRD, total carbon content (TOC), grain size analyses, field-emission Scanning Electron Microscopy (SEM) observation and magnetic proxies, we conclude the environmental change between 8.5-13 cal. ka BP in northern China. As global temperature rising in the Bølling-Allerød period globally, there were more coarse sediments deposited in this lake by melting glacier. Several events of extreme climate changes were recorded by highly fluctuated variations of grain size. In the Younger Dryas period, dry climate caused the lake to shrink and magnesite deposited. Moreover, the interbedded muds and silts implied rapid environmental changes, and induced an oxidation condition at that time. During the Holocene, the climate became wetter, and the compositions of pore water changed to more brine than before. Meanwhile, according to the variations of carbonate minerals, the climate displayed high fluctuations of precipitation and evaporation between 8,500-10,200 cal. yr BP.
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