Qishan Holocene Loess And Environmental Evolution

In Guanzhong Basin there are some Holocene loess Profiles withseveral layers of palaeosol. They provide detailed information about enviromentChange. The profile studied in this paper is located at Wulipu, Qishan County,Shaanxi. In this profile, the S₀ is seperated into two layers: S_o¹ and S₀². And thereare one loess layer between the two.From it, 160 samples were gathered andanalyzed in laboratory, such as magnetic susceptibility, grain-size, TOC, total Feand carbonate. The field investigations and analysis above have revealed thecharacteristics of climatic change during the Iast 11500 years:(l) 11500-8500aB.P., temperature went high and precipitation got much,summer monsoon got strong. During this period, the annual temperature wasabout l2.2℃, the precipitation was about 730mm.(2) 8500-6000aB.P., summer monsoon reached its maximum in the Holocene.In this time, the highest annual temperature was about l4.3℃, and the rainfalls800mm. But at about 7000aB.P.,there is a short arid phase.(3) 6000-5000aB.P., summer monsoon got weak, and winter monsoon Strong.In this time, the annual lowest temperature was about 4℃ and rainfall 320mm.(4) 5000-3100aB.P., it got warm and wet. Its highest temperature was about14℃ and the rainfall 760mm. But at about 4000aB.P., there is a short arid phase.(5) ＜3100aB.P., Winter monsoon got strong. The temperature declined, andfluctuated at l2℃. The rainfall decreased to about 650mm.