新疆地区的"中世纪温暖期"——古尔班通古特沙漠四厂湖古环境的再研究

文章依据新疆天山北麓古尔班通古特沙漠东南缘的四厂湖人工剖面进行的孢粉分析、平均粒径、磁化率以及烧失量测定结果,揭示了四厂湖地区最近1000年以来的古环境特征。研究结果表明,在与被称之为"中世纪温暖期(900-1300A.D.)"相当的时段内,淡水的四厂湖湖体周边地区曾经生长着由中旱生的灌木及草本组成的荒漠草原植被,并分布有淡水沼泽隐域植被。当时气候湿润,湖区生物物种多样性增加。结合新疆其他地区的第四纪研究成果,反映出该时期新疆地区气候湿润、湖沼发育、植被生长旺盛,因此本区在中世纪时气候应称之为湿润期或适宜期。而中世纪前后,该区以旱生、超旱生植物花粉占绝对优势,湖区植物种类减少,风沙作用较强,荒漠化景观显著。

"MEDIEVAL WARM PERIOD" IN XINJIANG:REDISCUSSION ON PALEOENVIRONMENT OF THE SICHANGHU PROFILE IN GURBANTUNGGUT DESERT

The so-called 'Medieval Warm Period' (900-1300A. D.) was one of the special climatic phases during the last 2 000 years. Enough evidences have shown that the climate of eastern China was warm during that period, but simultaneous climate of western China was not yet quite clear.Based on a relatively high-resolution pollen record, along with data of grain size, susceptibility, and loss of ignition (LOI) of sediments from the Sichanghu profile, which is located in the southeastern margin of the Gurbantunggut Desert, the northern piedmonts of Tianshan Mountains in Xinjiang, paleoenvironment of the last 1 000 years has been analyzed. Results show that during the last 1 000 years the regional vegetation was desert vegetation, dominated by species of Chenopodiaceae, Ephedra, Artemisia, Gramineae, and Compositae etc. But during the period corresponding to the Medieval Warm Period (900-1300A.D.) , desert-steppe vegetation, which was composed of meso-xerophytic shrubs and grasses with some aquatic intrazonal helophyte, grew around the fresh water Sichanghu Lake which was indicated by gastropods such as Radix acuminate and Gy-raulus found at the second and fourth strata. The LOI value, A/C ( Artemisia/Chenopodiaceae) ratio, total concentration, Simpson Index, and pollen percentage of aquatic plants were very high, whereas the average granularity and susceptibility were low, indicating a humid climate, increased plant diversity and a high biomass during that period. Combined with the results from other areas in Xinjiang, it reveals that during that period the climate was humid, and helophytes grew well. The period in this area, therefore, is named the Humid or Optimum Climatic Period.However, before and after the Humid or Optimum Climatic Period ( Medieval Period ) the number of plant species decreased, and gastropods were not found at any stratum. The LOI value, A/C ratio,total concentration, Simpson Index,and pollen percentage of aquatic plants were very low, indicating that before and after the Medieval Period the climates were dry, and desertification phenomena existed.