渭河平原全新世气候与季风强度变化

HOLOCENE CLIMATE AND MONSOON INTENSITY CHANGE IN WEIHE PLAIN

为探讨渭河平原全新世黄土沉积时期的气候、土壤与季风变化,本研究以2.15 m厚度的宝鸡宝陵剖面为研究对象,选取了化学元素、碳酸钙以及土壤微结构作为研究指标,对全新世气候特征、土壤类型以及季风降水与强度变化进行探讨。实验结果表明,S_(0)发育时期表现为中等化学风化,CaCO_(3)含量在S_(0)中下部小于1%,在全新世黄土层中的平均含量为12.14%。S_(0)以发育新生红色粘土胶膜的致密块状微结构为主要特征,L以孔隙发育的团块结构为主要特征。主要结论如下:1)晚全新世L黄土堆积时气候相对冷干,年均降水量为500~600 mm,冬季风增强,冬季风与夏季风强度相近,并非冬季风占主导地位;2)晚全新世L发育时夏季风带来的降水量占当时年降水量的50%左右,与其他来源的降水量基本相同;3)晚全新世发育的L黄土受成壤作用较弱,具有碱性褐色土的特征。中全新世的成壤作用较强,发育的S_(0)古土壤为湿润条件下的亚热带黄棕壤;4)中全新世气候温暖湿润,当时年均降水量为800 mm左右,夏季风带来的降水量明显多于其他来源的降水量,表明中全新世时期,夏季风确实占主导地位。

In order to explore the climate, soil and monsoon changes during the Holocene loess deposition period in the Weihe Plain, the loess-paleosol profile with a thickness of 2.15 m is selected as the study object, which is named as BL profile(34° 25′04″N, 107° 06′29″E), and 44 loess samples are collected. BL profile is located in Baoling village, Baoji City, Shaanxi Province, in the west of Weihe Plain. The chemical elements, calcium carbonate and soil microstructure are selected as study indicators to discuss the Holocene climate characteristics, soil types, monsoon precipitation and intensity. The experimental results show that Spaleosol formation stage has moderate chemical weathering degree, the average CIA of S_(0)is 66.95, the content of CaCO_(3)in the middle and lower part of Sis less than 1%, and the average content in the Holocene loess layer is 12.14%. Sis mainly characterized by the dense block microstructure of the newly developed red clay film, and Lis mainly characterized by the block structure of the pores. The main conclusions are as follows:(1)In the Late Holocene Lloess accumulation period, the climate was relatively cold and dry, with an average annual precipitation of 500~600 mm, and with the enhancement of winter monsoon, the intensity of winter monsoon was similar to that of summer monsoon, but winter monsoon was not dominant.(2)During the development of Lin the Late Holocene, the precipitation brought by the summer monsoon accounted for about 50% of the annual precipitation at that time, which was basically the same as that from other sources.(3)Lloess in Late Holocene was weakly pedogenesis and had the characteristics of alkaline brown soil. Spaleosol in Middle Holocene had strong pedogenesis, and S_(0)paleosol was subtropical yellow-brown soil under humid conditions.(4)The climate of the Middle Holocene was warm and humid. At that time, the average annual precipitation was about 800 mm. The precipitation brought by the summer monsoon was significantly more than that from other sources, indicating that the summer monsoon did dominated during the Middle Holocene.