青土湖地区9500a BP以来的环境变化研究

通过对青土湖地区ZY剖面的代用指标分析,研究了该区9500aBP以来的气候环境变化.在9500～6700aBP期间,剖面为风成砂沉积,平均粒径、磁化率、碳酸盐含量和C/N代用指标值均出现了的最低值,代表了湖泊干涸状态下强烈的风力搬运堆积,反映为一种暖干的古气候环境;6700～5800aBP期间,为碳酸盐粉砂质粘土沉积,代用指标的值均为高值,指示高水位、暖湿的古气候环境;5800～2700aBP为碳酸盐粉砂沉积,代用指标的值均表现为中等,代表了低水位状态下的碳酸盐沉积,反映夏季风减弱,区域降水量减少;2700～1100aBP期间为沼泽沉积,此时湖泊水量变化是以人为因素为主还是自然因素为主,需要进一步研究.

Environmental Change around the Qingtu Lake since 9 500 a BP

Investigations of geomorphology and sedimentology, and analyses of radiocarbon dates, grain size, susceptibility, content of carbonate and C/N-indicates of the sediment at the present-day closed basin (Qingtu Lake) in the terminal of the Shiyang River in arid region of China were conducted to recover the history of palaelake change since the Holocene. Qingtu Lake lies in Minqin basin in the east of the Hexi Corridor, which is located in the west edge of the East Asia monsoon. Through a field survey, the profile ZY is chosen as study object. Proxies of the Profile ZY, such as grain size, susceptibility, content of carbonate and C/N, reveal the variation of summer monsoon precipitation in the Shiyang River drainage basin during 9500～1100 a BP. An abrupt event happened during 9500～6700 a BP, when climate was droughty and windy, with sands depositing; During 6700～5800 a BP summer monsoon strongly impacted the region, and precipitation was abundant, atmosphere was humid, lakes were deeper; During 5800～2700 a BP summer monsoon became unsteady, so was water level of lakes, with frequently fluctuating climate; During 2700～1100 a BP human activity increased obviously and water level of lakes declined continuously, so it is necessary to study whether the natural factors were the key to control the water level.