南疆尼雅地区4000a来的地化元素分布特征与古气候环境演化的初步研究

Study on the Characters of the Geochemical Elements and Changes of Paleoclimate since about 4 000 a B.P. in Niya Section

通过应用因子分析法对尼雅剖面中的多种地化元素和氧化物的分析 ,在R、Q型因子分析的基础上 ,提取出古气候信息。初步的研究表明 :近 40 0 0a来 ,尼雅地区气候环境仍以干旱化为主 ,但此期间出现过多次不同程度的干湿变化 ,大致可分为 5个气候期 :4 0～ 3 0kaB P .相对暖干期 ;3 0～ 2 2kaB .P .相对冷湿期 ;2 2～ 1 6kaB .P .相对暖干期 ;1 6～ 1 0kaB .P .相对冷湿期 ;1 0kaB .P .

Niya relics lie in south Xinjiang, north of Kunlun Mountains and in south edge of Taklimakan desert, 100 km north away from county town. It was the important post of south route of ancient “Silk Road”. In the article, we select about 300 cm natural profile on the right bank of Niya river, collect 22 samples, and analyze them with radiocarbon \{\}\+\{14\}C dating and X fluorescent spectrum analysis of geochemical elements. By applying the factor analyzing method to deal with various geochemical elements and oxides in section of Niya, the results of Q\|type factors and R\|type factors are obtained, which we use as a proxy to extract the information of paleoclimate and resume the features of paleoclimate in Niya. Since \{4 000\} a B.P., climate in Niya region has a trend of drought, although the area of Niya has experienced alternations of relative cold\|moisture and warm\|dry period. The pattern of paleoclimatic evolution of this area not only has its regional characters and coincides with that of others areas in Xinjiang, but also corresponds to the global climatic changes. During the period, the history of paleoclimatic changes is reconstructed as follows:\;(1) 4.0～3.0 ka B.P., it was dry in climate mainly, although several little cold\|moisture and warm\|dry fluctuation appeared, showing no difference with the results obtained in Aibi Lake in north Xinjiang (that is, in 6.4～3.5 ka B.P.,drier in climate and fluctuating frequently). In 3.5 ka B.P., a warm peak value appeared, consistent with the second high temperature event of Dunde ice core(3.0～2.9 ka B.P.) in Holocene.\;(2) 3.0～2.2 ka B.P., relative cold\|moisture in climate. Around 2.7 ka B.P., a short dry period in climate appeared, consistent with the cold\|moisture period(3.0～2.0 ka B.P.) in Boston Lake area basically, also consistent with the third Neo\|glacial epoch in north hemisphere and relative cold\|moisture in climate (2.5 ka B.P.) in south Zhili.\; (3) 2.2～1.6 ka B.P., relative warm\|dry period in climate. During the period, it was getting drier in climate obviously. Large scale drought lasting for several years appeared in south and east Xinjiang. Jinjue (relics of Niya) and Yumi, which were small countries in the west region in West\|Han Dynasty, disappeared in desert, and the Silk Road moved toward south, according to the apparent warm\|dry period in Boston Lake of Tarim Basin, also according to the fifth severe cold period in east China and sub\|Atlantic period in climate in south Zhili.\;(4) 1.6～1.0 ka B.P., it grew colder and went into cold\|moisture period. A warm\|dry change appeared at about 1.2 ka B.P., according to the warm period appearing around 7 century found in Guliya ice core.\;(5) 1.0 ka B.P. to present. There was a warm\|dry trend again in 1.0 ka B.P., consistent with the record of Guliya ice core. After that, for about \{1 000\} years, warm\|dry appeared in climate on the whole.