青藏高原与黄土高原毗邻地区晚更新世以来孢粉植物群及沉积环境

Quaternary Palynoflora and Sedimentary Environment in the Neighbouring Area of Qinghai-Xizang Plateau and Loess Plateau

Among the comtinental deposits, the loess of the loess plateau, due to its continuous deposition and homogeneous structare in substantial composition, is an ideal geological body for studies on the evolutionary process of palaeoclimate, especially on the palaeosoil in loess. Systematic studies on the evolutionary process of palaeoe-nvironments have been carried on by the authors through pollen analysis of pollen samples from 9 natural loess sections and surfece samples of 13 sites, in Qinghai and Gansu provinces . In this region the development of vegetation in the Quaternary period may be divided based on spore pollen assemblages into three stages, which are in transitional relationship from coniferous stage to forest-steppe stage and then to steppe stage. The first stage is marked by the presence of more pinaceous pollen (over 60%), such as Pinus, Picea.Abiesmdicatmg a rather cool climate. The second stage is characterized by the presence of more Pinus and herbaceous pollen with some deciduous broad-leaved tree pollen, indicating a warmer and moister climate than the present climate. In the last stage, however, such xerophilous her bs as Chenopodiaceae, Artemisia, Compositae, Cruciferae, etc., were prevailing in the are, indicating that the climate was rather cool and dry. It has been confirmed that the evolutionary process of the palaeoclimate enviroment revealed by the loess deposites shows a general tendency of rhythmic fluctuation since Pleistocene being in transition from humid forest proirie to arid desert steppe By comparing the spore-pollen assemblages of loess and the palaeosoil in loess, the authors suggest that the palaeoclimate during the deposition of palaeosoil was warmer and wetter than that during the deposition of loess.