塔里木盆地南缘沉积物磁化率变化与历史时期环境演化

HISTORIC PALEOENVIRONMENTAL CHANGES REFLECTED BY SUSCEPTIBILITY IN THE SEDIMENT, SOUTHERN MARGIN OF TARIM BASIN

磁化率作为一种重要的环境指标 ,在恢复气候环境演变方面得到了较为广泛的应用。本研究表明 ,塔克拉玛干沙漠南缘沉积物的低频磁化率对于本地区环境的演变反映较为敏感 ,因此本文以低频磁化率为主导指标 ,结合其它地质记录 ,对尼雅地区的古气候环境进行了恢复 ,研究结果表明 :近 40 0 0年来尼雅地区的气候环境以干旱化为主 ,但期间仍有几次相对干湿的波动 ,共经历了 3次相对湿润期和 3次相对干旱期。据此恢复出的古气候环境与其它环境指标恢复出的结果具有较好的吻合性 ,不仅具有鲜明的区域性特征 ,同时也具全球性的一致性。

Based on the low frequence susceptibility analyses of Niya section, which locates at the southern margin of Tarim basin, this paper has probe into the paleoenvironmental evolution during historic time (since about 4000a BP) in this district. The paleoenvironmental information reflected by low frequence susceptibility coincides with that revealed by other geologic indices, such as the geo-chemical dry-wet index C, pollen A/C value and δ 13 C. During the last 4000 years, the area of the southern Taklimakan desert has experienced alternations of relative cold -moisture and relative warm-dry periods indicated by susceptibility of sediment, three evident cold-moisture periods and three warm-dry periods are identified, which are coincident with historic records: (1)Relative cold-moisture period (4000～3450a BP). Muti-geologic index and pollen composition in the layer of Niya profile shows the characters of aridity. (2)Relative warm-dry period(3450～2500a BP).The period corresponds to the Zhou Dynasty, the result of study shows that this period is a relative warm-dry period. (3)Relative cold-moisture(2500～1900a BP).The phase likely corresponds to the Qin-Han Dynasties. The peaks of the curves of geochemical element ratios,δ 13 C and Xlf, A/C all indicated a relative wet characters, and coincides with the research of others areas in Xinjiang. (4)Relative warm-dry period inclimate(1900～1400a BP).The phase corresponds to the later part of the Western Han Dynasty and the mostly part of the Wei-Jin and Northern and Southern Dynasties. The changes of the geochemical element ratios, δ 13 C and Xlf all display the evident warm-dry characters. (5) Relative cold-moisture in climate(1400～1000a BP).The period include the Sui to Tang Dynasty (581～907A.D)and the early of Song Dynasty, although several little cold-moisture and warm-dry fluctuation appeared, it was cold-moisture in climate mainly, the paleoclimate become drier in later period. (6) Relative warm-dry period in climate(1000a BP～present). The research of this paper also reflect that susceptibility of arid area is an very ideal proxy to provide useful information of paleoenvironmental changes, the study shows as well that the human activities have an intimate relation with the evolution of paleoclimate in the southern Xinjiang. Paleoclimate has played very important role in influenced in the history of the rise and decline of the Silk Road, abandon of ancient cities and human being's agricultural activities.