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《Quaternary Sciences》 2006-02
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AGE AND PALEOENVIRONMENT OF XIGEDA FORMATION IN LUDING,SICHUAN

Wang Shubing Zhao Zhizhong Qiao Yansong Jiang Fuchu(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing100081)  
A detailed re-study of the paleomagnetic polarity stratigraphy of Xigeda Formation with an approximate thickness of 400m in Haiziping,Luding,Sichuan suggests that the upper and lower parts separated at a depth of 360m from the surface belong to the Gauss normal polarity chron and the Gilbert reverse polarity chron respectively.According to the Cande's polarity time scale,the age of the Xigeda Formation ranges from 4.2MaB.P.to 2.6MaB.P.,assigned to the Middle and the Late Pliocene,which is consistent with our previous result.This series is known to be the earliest in the Xigeda lacustrine deposition.Based on the  value of the median size,the sedimentation in Haiziping displays five cycles from coarse to fine including fifteen sedimentary stages.Furthermore,the low  value indicating strong hydropower infers a queasy sedimentary environment;while the high  value infers a stale sedimentary environment.The sediments records indicates that the strongest rising of the Tibetan Plateau begins at about 2.8MaB.P.,and ends at 2.6MaB.P.,consisting with the result from the obvious change of the eolian sedimentary environment in the Loess Plateau.The high TOC value corresponds to the high  value and the low TOC value the low  value,showing that the content of the organic matter in lacustrine sediments of the Xigeda Formation is mainly controlled by the lithology.
【Fund】: 中国地质调查局地质调查项目(批准号:200312300034);; 国家自然科学基金重点项目(批准号:90211019)共同资助
【CateGory Index】: P539.3;P531
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