Basin-Mountain Coupling Syestem and Its Sedimentary Response in Sichuan Analogous Foreland Basin

According to integrated analysis of the basin tectonic-sedimentary evolutionary history from Upper Triassic Xujiahe period to Cretaceous,it's believed that the Sichuan basin belongs to intracontinental compressional superimposed basin which is developed on the basis of a large peripheral foreland basin and has the features of analogous forland basin.The basin formation and evolution are controlled strictly by polychromic,nonsynchronous and multidirectional thrusting-napping processes of Longmen Mountains,Micang Mountains-Daba Mountains and Xuefeng Mountains.And it can be divided into secondary basin-mountain coupling systems controlled respectively by overthrust on the marginal orogenic belt,which are western Sichuan,northeast Sichuan,and southeast Sichuan.And it has formed a peculiar tectonic-sedimentary pattern,which is called three depressions around one uplift.Corresponding to the multidirectional and alternative thrusting-napping activity in each orogenic belt,the basin-mountain processes can be divided into evolutionary phases,including early peripheral foreland basin(T3m→T3xt),middle analogous forland basin(T3x→J3),and late atrophy phase(K).The sedimentary response to coupling processes between basin and mountain in each evolutionary phase is of particular similiarities and differences.The differences are that different thrusting-napping stress positions in each orogenic belt had different subsidence-sediment center positions,which were moving back and forth among western Sichuan depression,northeast Sichuan depression,and northeast Sichuan depression.The similiarities are that stratigraphic distribution of all the secondary basin-mountain coupling systems has the features of onlap and wedge shape which is become thinner from the front depression,foreland ramp to forebulge zone.They also have similar combinations of sedimentary facies,distribution rules of facies belts,and petroleum geologic characteristics.