PRELIMINARY RESEARCHES ON LICHENOMETRIC CHRONOLOGY OF HOLOCENE GLACIAL FLUCTUATIONS AND ON OTHER TOPICS IN THE HEADWATER OF URUMQI RIVER, TIAN-SHAN MOUNTAINS
CHEN JI-YANG Lanzhou Institute of Glaciology and Geocryology. Academia Sinica, Lonzhou 730000, PRC
This paper introduced briefly the research results on lichenometry of the Holocene glacial fluctuations in the headwater of the Urumqi River, in the central Tianshan Mountains and discussed the histories of the Holocene glaciers and the climate. It is considered that lichenometry is one applicable method for dating the mid- and late- Holocene deposits in the cold and mountainous regions. Rhizocarpon geographicum (L.)DC and Xanthoria elegans (Link.) Th. Fr. could be used for dating the deposits of about 4500 and 500 a B.P. respectively. There existed at least four periods of glacial advances which occurred before about 5700, 4100, 2800 and 403- 74 a B. P. respectively with the first period the longest. Little Ice Age includes three stages of glacial advances which ended before about 403, 208 and 74 a B. P. respectively with the second stage the maximum. During the general Holocene warming processes, there existed at least four cold peri- ods which ended before about 5700, 4100, 2800 and 420- 91 a B.P. respectively, the average air temperatures of which were about 1.5, 1.25, 0.9 and 0.65℃ higher than the present one respectively with the warm periods in between. The amplitude of air temperature changes is about 2.5℃.