MAGNETIC SUSCEPTIBILITY AS INDICATORS OF SEDIMENTARY ENVIRONMENT DURING UPPER JURASSIC AND LOWER CRETACEOUS IN JIANMENGUAN, SICHUAN PROVINCE

It is found that the values of magnetic susceptibility have apparent relations with the size of sedimentary particles based on the study of magnetic susceptibility of Upper Jurassic and Lower Cretaceous in Jianmenguan, Sichuan Province. Sediments with medium or coarse grained particles usually have low values of magnetic susceptibility, while the fine grained sandstone, silt and mudstone often appear to have much higher values. As sedimentary rate has something to do with the size of sedimentary particles, this susceptibility can be used as a quantitative indicator for the variation of sedimentary rate. What's more, the sedimentary rate usually varies in different environments, so the magnetic susceptibility can also be used as reference of sedimentary facies. The study of magnetic susceptibility anisotropy in Jurassic and Cretaceous shows that there exit two maximal axis directions of magnetic susceptibility in the study area of Jianmenguan. The southeastward maximal axis direction corresponds to the direction of paleocurrent in the area. However, the southwestward maximal axis direction is probably caused by tectonism.