摘要
通过对吉木萨尔县大龙口非海相二叠系—三叠系界线上下地层磁性特征的研究,在梧桐沟组—锅底坑组共发现78个极性异常,其中以负极性为主,间隔了一系列的正极性和过渡极性。梧桐沟组上部以负极性为主,间隔了2个正极性和过渡极性。这可与巴基斯坦盐岭和四川广元上寺的大隆组下部对比,即相当于Da段。梧桐沟组顶部和锅底坑组底部,正、负极性变化频繁,极性特征可与巴基斯坦盐岭和四川广元上寺大隆组中部对比,即相当于Db段。锅底坑组下部以负极性为主,间隔了2个正极性段,可与四川广元上寺大隆组中上部对比,即相当于Dc段。锅底坑组中下部以负极性为主,上部夹1个正极性段,可与四川广元上寺大隆组上部磁性特征对比,即相当于Dd段。锅底坑组中上部以负极性为主,间隔了4个正极性段,可与四川广元上寺飞仙关组下部对比,即相当于Fa段。根据磁性段的划分对比,将二叠系—三叠系界线置于Fa和Dd之间,即本次研究测制剖面的41层和42层之间。根据各岩组的古地磁特征求得岩组形成时的古地磁极:梧桐沟组79.1°N,238.1°;锅底坑组72.3°N,322.2°;下三叠统77.5°N,320.8°。古纬度基本一致,为32°～35°N。
Paleomagnetic investigation on the non-marine Permo-Triassic transitional succession of the Dalongkou section in Jimsar, Xinjiang reveals that there are 78 polarity intervals in the upper part of the Wutonggou Formation and the Guodikeng Formation; and they are mainly reversed polarity intervals intercalated with some normal and transitional intervals. The upper part of the Wutonggou Formation is dominated by reversed intervals, intercalating 2 normal and transitional intervals. It can be correlated with of the lower part, i. e. the Da member of the Dalong Formation of the Shangsi section, Guangyuan, Sichuan. The top part of the Wutonggou Formation and the basal part of the Guodikeng Formation are characterized by frequent change of normal and reversed intervals, and can be correlated with the middle part, i. e. the Db member of the Dalong formation. The lower part of the Guodikeng Formation is represented mainly by reversed intervals, intercalated with 2 normal intervals, and can be correlated with the middle-upper part, i. e. the DC member of the Dalong Formation. The lower-middle part of the Guodikeng Formation comprises mainly reversed intervals, intercalating 2 normal intervals, and can be correlated with the upper part, i. e. the Dd member of the Dalong Formation. The middle-upper part of the Guodikeng Formation is also characterized by reversed intervals with some normal intervals, and can be correlated with the lower part, i. e. the Fa member of the Feixianguan Formation of the Shangsi section. Based a on classification and correlation of magnetic polarity zones, the Permo-Triassic boundary is placed between the Fa and Dd, that is to say, between bed 41 and 42 of the Dalongkou section.
出处
《地质论评》
CAS
CSCD
北大核心
2003年第5期525-536,共12页
Geological Review
基金
科技部基础研究项目(编号 G99-A-05a和2001DEA20020-11)
