太原西山上二叠统陆相地层的磁组构学研究

A MAGNETIC FABRIC STUDY OF THE UPPER PERMIAN TERRESTRIAL STRATA IN XISHAN OF TAIYUAN, SHANXI

对太原西山剖面上石盒子组 1段至孙家沟组的 111块定向标本所进行的磁组构学研究表明 ,其磁化率各向异性参数的主体特征为 :磁化率介于 2 0 0— 35 0 ( 10 - 6 SI)之间 ;各向异性度≥ 1.0 3,各向异性明显 ;压扁率 >1,磁化率各向异性数值椭球呈弱压扁型 ;磁面理度 >磁线理度 ,磁面理发育 ;磁面理倾角∠ 2 4°,倾向多变 ,但沿纵向具向南趋势 ;磁面理置信角∠ 2 5°。上述磁化率各向异性参数的沉积地层学意义为 :自上石盒子组 1段至孙家沟组 ,沉积相为水流方向自由迂回摆动的曲流河相 ,沉积环境为地势平坦的冲积平原 ;孙家沟组成岩之末 ,地形略呈北高南低之势 ,当时最近的海岸线位于太原之南。

The characteristics of magnetic fabrics of 111 directional samples from the fist sect of Upper Shihezi Formation to Sunjiagou Formation in Xishan section, Taiyuan have been studied. The values of magnetic susceptibility are between 200*10 -6SI and 350*10 -6SI. Most of the anisotropy degrees of magnetic susceptibility (AMS) are significant (the degree of anisotropy≥1.03), and all of the susceptibility ellipsoids are slightly oblate (the flattening>1). In addition, the foliation planes are prominent with inclinations smaller than 24° and directions diverse in every formation, but they trend southward. The confident angles of foliation planes are smaller than 25°. From the AMS characteristics mentioned above, it can be deduced that the stratigraphy, from the fist sect of Upper Shihezi Formation to Sunjiagou Formation, was formed by meandering rivers with the current swinging freely, and that the sedimentary environment was a smooth alluvial plain. It is also inferred that at the end of the Sunjiagou age the landform in the northern part is higher than that in the southern part, and that the nearest seashore at that time lay south of the Taiyuan city.