学术
摘 要:
文章对川西甘孜地区甘孜寺剖面进行了系统的磁性地层学研究及石英颗粒表面形态特征分析。磁性地层学研究结果显示，B／M界线出现在S8的顶部，并且在剖面下部12．7-14．0m处出现了松山负向期的贾拉米洛正向极性亚带。本次测试以及结合以前的研究结果表明，甘孜地区典型的风尘堆积形成于约1．15MaB．P．以前。石英颗粒表面形态特征的分析结果说明风尘物质可能经历了风、流水、冰川等多种外动力作用，进一步证明该区的风尘物质主要来源于青藏高原及其周缘地区的冰水沉积。另外，研究结果指示青藏高原及其周缘地区的环境状况大约在1．15MaB．P．发生了很大变化，主要表现为干旱化程度以及高原冬季风的明显增强，而这些变化又与青藏高原在该时期的快速隆升密切相关。磁性地层的研究结果将为在该区进一步开展古环境演化过程的对比分析及阶地地貌发育历史的研究奠定基础。[著者文摘]
文章出处:
《第四纪研究》-2006年26卷2期 -250-256页
栏目信息:
文献标识码:
A
文章编号:
1001-7410（2006）02-250-07
MAGNETOSTRATIGRAPHY AND ITS PALEOCLIMATIC SIGNIFICANCE OF A LOESS-SOIL SEQUENCE FROM GANZI AREA, WEST SICHUAN PLATEAU
Qiao Yansong, Zhao Zhizhong, Wang Yan ,Wang Shubing , Fu Jianli, Li Chaozhu ,Jiang Fuchu（ Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081 ）
Abstract:
Eolian deposit is widely distributed in West Sichuan Plateau. In this paper, a loess-soil sequence near Ganzi Temple in Ganzi County of Sichuan Province is dated using geomagnetic and luminescence methods. The studied section is 15.3m thick and consists of 26 field definable lithological units. 40 oriented paleomagnetic samples were taken at 20 -40cm intervals from the Ganzi Temple section. Measurements were carried out in the Paleomagnetism Laboratory, Institute of Geomechanics, Chinese Academy of Geological Sciences. Stepwise thermal demagnetization up to 620℃ was performed on all 40 samples using a TD - 48 thermal demagnetizer with a temperature step of 20 50℃. Measurements were made using a 2G -755 three-axis cryogenic magnetometer. The reverse boundary between the Brunhes normal zone and the Matuyama reversed zone is recognized at the top of S8 , and the Jaramillo normal subzone occurs in the lower part of this sequence at a depth of 12.7 - 14.0m. Two boundary ages of Jaramillo normal subzone （0.99MaB. P. and 1.07MaB. P. ） suggest an average eolian accumulation rate of about 1. 625cm/ka in this period. Extrapolation with this accumulation rate yields a basal age of about 1.15MaB. P. at the Ganzi Temple section. Eolian deposit older than 1.15MaB. P. has never been reported in West Sichuan Plateau, which indicates that eolian deposition in this region started at about 1.15MaB. P. Morphological features of quartz grains from the Ganzi Temple section indicate that the eolian dust in Ganzi may be from the materials of glaciation and melting ice. The results of magnetostratigraphy and morphology of quartz grains suggest a climatic event at about 1.15MaB. P. in West Sichuan Plateau, which was interpreted as a result of both the reduction of vegetation near Ganzi area and the strengthening of winter monsoon associated with the uplift of the Tibetan Plateau. In addition, the result of magnetostratigraphy is favourable for the studies of climatic change and neotectonic movement in this region.[著者文摘]
Key words:
West Sichuan Plateau, Ganzi Temple section, magnetostratigraphy, morphology of quartz grains
基金资助:
国家自然科学基金项目（批准号：40472088）和中国地质调查局地调项目（批准号：200312300034）联合资助
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