青海湖盆地35万年来的植被演化及环境变迁

VEGETATIONAL AND ENVIRONMENTAL CHANGES IN THE LAST 350ka IN ERLANGJIAN, QINGHAI LAKE

本文依据青海湖南岸二郎剑阶地QH-86孔(深155m)中200余个孢粉样品的分析资料,将该孔深78m以上的孢粉图式,从下至上划分出七个区域性孢粉带,并结合铀系法测年数据,论述了350ka B.P.来的湖区植被和环境演变。其气候曲线与毗邻的柴达木盆地,甚至与深海钻孔及洛川黄土,具有可对比性。

Qinghai Lake is situated in the northeastern margin of the Qinghai-Xizang Plateau, i. e. a boundary area of East Asia monsoon with very sensitive climatic and vegetational changes. In accord with cold and semiarid climate, the vegetation zone of Qinghai Lake region belongs to high cold shrub steppe and meadow. In the provious papers based on the information of sporo-pollen assemblages by radioearbar dating, the authors (Duet al. 1989, Kong et al. 1990) preliminary have pictured the vegetational and climatic changes in the last 11000 a. Unfortunately, vegetational and climatic succession was so short that only a little is known about the environmental changes since pleistocene. The pollen analytical investigation of 155m-deep-QH86 core from Erlongjian terrace in Qinghai Lake has been carried out. (Fig. 1) For sporo-pollen analysis on 200 samples collected from core-QH86, 90 samples are qualified for statistics. Based on the characteristics of QH86 core sporo-pollen assemblage along with ^(230)Th dating, seven pollen zones may be subdivided in an ascending order as follows: (Fig. 2) In zone Ⅰ(342--275ka B. P.), zone Ⅲ(230--175ka B. P.) and zone Ⅴ_c(83—63ka B. P.) the vegetation belongs to temperate steppe mixed by a few trees. During those periods some hydrophytes, such as Typha, myriophyllum, pediastrum boryanum and ferns apparently increased. The climate was relatively warm and wet. It is emphasized that the vegetation and natural environment changed violently in Qinghai Lake region between 39 and 26 ka B. P. (pollen zone Ⅵ) the vegetation was dominant in a subalpine conifer forest consisting of picea, pinus Abies and etc. Such broad-leaved deciduous trees as Betula, Ulmus Quercus meight grow in conifer forest. Lakes and bogs were well developed. In contrast with zone Ⅶ, zone Ⅱ (275—230ka B. P.), zone Ⅳ (175—120ka B. P.) and zone Ⅵ (63—39ka B. P.) the vegetation was represented by temperate shrub, semi-shrub and steppe, consisting of predominant Chenopodiaceae, Artemisia, Ephedra, Nitraria and Gramineae. In those periods trees, ferns and algae were obviously reduced due to dry and cold climate. It is pointed out that palynalagical evidence is still shot for some layers during 730-350ka B. P. in QH86 core. So it is necessary to make further investigations.