Continental High-resolution Sequence Stratigraphic Framework of the Middle Jurassic System in the Middle Yangtze Region and Tectonic Controls

The middle Jurassic System of the Middle Yangtze region is mainly distributed in some sub-basins of the Middle Yangtze foreland basin.This work is based on principles of modern sedimentology and high-resolution sequence stratigraphy in combination with analysis of outcrop lothology,paleontology and sedimentary facies.The result shows that this System is characterized by braided river,braided-river delta,fan delta,and shallow lake sediments,and has named as the Huajiahu Formation,Shaximiao Formation and Qianfuya Formation for varied areas.Sequence stratigraphic characteristics of different regions exhibit both differences and similarities.Based on the theory of high-resolution sequence stratigraphy,the Huajiahu Formation,Shaximiao Formation and Qianfuya Formation can be respectively divided into 4,4 and 2 third-order sequences.Furthermore,fourth-order sequences can be subdivided in local areas.The whole Middle Jurassic System is roughly equivalent to a second-order sequence.The formation of this sequence stratigraphic framework is primarily controlled by the tectonic factors,i.e.the intensive tectonic deformation and movement since the Indosinian period,which resulted in a complicated basin-mountain coupling system that made the sequences distributed laterally and superimposed longitudinally in the foreland basin.