TANG Ling-Yu, SHEN Cai-Ming, KONG Zhao-Zheng, WANG Fu-Bao, LIU Kam-Biu
The Last Glacial Maximum(LGM)covered a time interval from 25 000 to 15 000 a BP, when the climate was cold and dry, and the Paleovegetation was dominantly dry grasslands or grassland-deserts in the Tibetan Plateau. Despite a large amount of late Quaternary palynology data published in China, there is very limited information available about pollen and vegetation during the LGM, largely because of the scarcity of fossil pollen in sediments at that stage. Only some recent studies have provided detailed palynological data for reconstructing paleovegetation during the LGM, and the pollen diagram from Lake Ren Co in Basu County, eastern Tibet, is one of them. Lake Ren Co(30°43 097′N, 96°40 052′E, 4 450 m a.s.l)is a closed-basin of freshweter lake situated in the subalpine forest-meadow region in the eastern Tibet. Surface pollen samples from the lake are dominated by Artemisia(30%)and contain about 30% tree pollen, mainly from Betula, Picea, Pinus, and Abies. A 4 m long core, predominantly consisting of gyttja, yields two basal dates of 18 250±1 030 and 17 860±340 a BP, although dating control may be complicated by hardwater effect as suggested by a date of 2 090±60 a BP from the core top. The late-glacial pollen assemblages are dominated by Chenopodiaceae(20%～50%)and Artemisia(10～30), and pollen influx values are very low. Betula pollen increased sharply after ca. 13 5ka(unadjusted data), as did Abies and Picea during the early Holocene. The data also suggest that the climate in the eastern Tibet was cold and dry during the LGM and last-glacial time. The mean annual temprature was probably 6 K colder than the present, and the mean annual precipitation was only 250 mm, about 40% of that at present. The vegetation around Lake Ren Co was probably a desert-steppe during the LGM. Similar variations can be seen in the pollen diagrams from the Wasong section and the RM core, Zoige basin, western Sichuan Province, the Gounong Co, the Qinghai lake and the Chaerhan saline lake, Qinghai Province, and the Yuanbao section, Linxia County, Gansu Province.
