Sequence stratigraphy characteristics and coal accumulation law in Mid-Lower Jurassic in southwest Tarim

In order to clarify coal accumulation law in Mid-lower Jurassic in southwest Tarim, through the procedures of comprehensive analysis of previous studies, using profiles, drilling, well logging, core materials, by facies changes directions, identifying sedimentary facies and establishing sequence framework, fan, fan delta, delta, lakes and swamps sedimentary facies were identified. By systematic analysis the types of sedimentary facie, sedimentary boundary characteristics and distribution, two sequence boundaries and four sequence boundaries were recognized. Combining sedimentary and evolution characteristics, stabilized settlement expansion stage was benefitial for coal accumulation, corresponding to the transgressive and high deposition system. Finally, according to the theory of sequence structure type of coal and the characteristics of coal seam thickness distribution, the coal accumulation law in Kizilayao depression, Yecheng-Hetian depression and Hetianbuya depression was identified.