塔里木盆地南缘4kaB.P.以来气候环境演化与古城镇废弃事件关系研究

Paleo-climatic and Environmental Development since about 4 ka B.P. and the Relation with Abandonments of Ancient Cities in Southern Xinjiang

策勒绿洲沉积地层及地球化学元素的研究表明，虽然近４ ｋａ Ｂ．Ｐ．来本地区气候环境的干旱状况持续未变，但期间仍有若干次相对湿润与干旱化加剧时期的波动。结合年代学的研究，以约２ ０００ ａＢ．Ｐ．为界，其以前气候以相对湿润为主，而此以后，则以持续干旱为主要特征，且揭示出４ 次具有突变性质的气候转干时期，即自约１ ５００ａ Ｂ．Ｐ．开始，类似本地区现今气候环境特征已经出现，自约１ ２００ ａ Ｂ．Ｐ．至１ ０００ ａ Ｂ．Ｐ．、１ ０００ ａ Ｂ．Ｐ．至６３０ ａＢ．Ｐ．期间和２００ ａ Ｂ．Ｐ．以后，策勒地区沙漠化进程急剧加强。本研究揭示了４ ｋａ Ｂ．Ｐ．来本地区持续干旱化的特征，并有后期加剧的趋势，而上述气候的转干事件与塔里木盆地古城废弃事件之间具有良好的吻合关系，表明气候环境的自然演化是影响人地关系的重要因素之一。

Generally speaking, the study of paleoenvironmental changes in southern Xinjiang is much more lackward because of the difficulty to obtain an ideal geological record which bears high resolution paleoclimatic information. Recently, a synthetic study on the stratigraphic and geochemical characteristics of the sediment since about 4 ka B.P. in Cele district, southern Xinjiang, has shown that during this period, although the dry state always existed, there were still several variations of relative wet periods and aggravated periods. Combining with the chronological and sedimentary studies, before about 2 000 a B.P., climate was dominated by relative wet, but after this time boundary, it was characterized by consecutive drought, and with four intense desertification periods being revealed, i.e. since about 1 500 a B.P., the climatic characteristics similar to modern climate of this area had basically appeared at about 1 200 a B.P. to 1 000 a B.P., 1 000 a B.P. to 630 a B.P.and after 200 a B.P.. In the aridest southern Xinjiang, natural environmental changes play very important role in affecting the man land relationship, especially in the early historic period. It is of interesting to compare the abandonment of ancient cities in southern Xinjiang with the climatic and environmental changes, for example, these above mentioned abrupt climatic dryness basically coincide well with the periods of intense abandonment of the ancient cities during early 5~6 century, the Song and Yuan dynasty, and the Ming and Qin dynasty respectively. So, in order to further realize the content of man land relationship and its development, we shall pay special attention to the time scales, because during different time scale, the affecting factors of man land relationship would have been changed, but it is undoubtedly, during late period of historic time, the influence of human being had been getting more evidently and importantly.