Preliminary Study Of Palaeoclimatic And Palaeoenvironmental Evolution Since Late Pleistocene In Zabuye And Qiulinanmu Lakes, Tibet

This thesis pays attention to the climatic changes of 2.415-27.5ka B.P. in the Zabuye and Qiulinanmu Lakes of Tibet. The sudden climatic change from warm-wet climate to cold-arid one was clear in Qiulinanmu Lake that not appeared in another lake. The amplification of cold climate by Tibet was distinct in the area. The conclusions are as follows.Ulexite was first found in Qiulinanmu Lake. Alternate clay and particulate borax and mirabilite meant climatic changes of warm to cold climate suddenly.The clays consisted of illite and chlorite, indicating weathering was weak and physical weathering dominant. Carbonate mainly includes dolomite, aragonite and gaylussite in Huangyangtan, calcite and aragonite in high terrace of Zabuye Lake, and dolomite in Qiulinanmu Lake. Pollens of herb (>80%) and arbor and less fern meant half desert-steppe and half shrubby meadow. Most ostracodes of the two lakes could be lived in far-ranging salinity and temperature.In the whole, the climate was cold and arid and changed frequently. Zabuye Lake was a freshwater lake in the time of 142.2±7.4 ka B.P. and 60.3±2.7 ka B.P. And the salinity was higher, the local depth was not more than 15m, the climate was more wetter and colder at 60.3±2.7 ka B.P.. The climate was warm and a little wet during 27.5-20.6 ka B.P.; and cold in 20.6-10.9 ka B.P.. The Last Glacial Maximum was at 20.6-15.9 ka B.P.. The Dryas Events were clear and the Younger Dryas was ended at 10.9ka B.P. The cold climate of 10.1-7.2 ka B.P. was the result of global cold events in early Holocene (or"8.2 ka B.P. cold events"). The finest climate appeared at 7.2-4.3 ka B.P., and during the time of 6.67-4.83 ka B.P., the lake water was alkaline to weak alkaline and the consistence of brine was low in Qiulinanmu Lake. There were 3 alternate changes of warm-wet and dry-cold climates in the time of 4.72-4.56 ka B.P., and the lake water was freshwater in the margin of the Zabuye Lake in 4.67-4.5 ka B.P.. The cold climate appeared at 4.56-3.7 ka B.P. with the changes of 5 cold-dry climates and 4 warm-wet ones, and the climate was dry-warm and changed frequently in 3.7-2.4 kaB.P.. The reasons of the climates above were that Qinghai-Tibet Plateau itself made any cold climate larger, west-wind circumfluence was dominate in the place and the third reason is the maculae action of 22a, 80-90a and 200a periods, the fourth was foehn wind (5-2.4ka B.P.) and Indian monsoon.The climatic model of salt minerals was first given on the basis of physicochemical theory and much research work, that's△_rG_m(T)=△_rH_m^?(298.15K)-T△_rS_m^?(298.15K)+αβRTlnγJ. The fractual model of high terrace gravel in Zabuye Lake was follows that N(r)=103.2245r-2.4429, D=2.4429.