四川盆地盆-山耦合系统和沉积响应特征

依据四川盆地晚三叠世须家河期至白垩纪盆地构造和沉积演化史的综合分析结果,认为该盆地属于发育在大型周缘前陆盆地基础上的陆内压性叠合盆地,具类前陆盆地性质。盆地形成和演化受周边龙门山、米仓山-大巴山和雪峰山3个造山带多期次非同步异方位的逆冲推覆活动控制,可划分为受盆缘造山带逆冲推覆作用控制的川西、川东北和川东南3个盆-山耦合次系统,区域上构成了独具特色的"三坳围一隆"构造-沉积格局。对应各造山带异方位的交替逆冲推覆活动,盆-山耦合过程又可划分为早期周缘前陆盆地(T3m→T3xt)、中期类前陆盆地(T3x→J3)、晚期萎缩衰亡(K)3个演化阶段。各演化阶段盆-山耦合过程的沉积学响应具有特征的异同性:差异性为对应各造山带逆冲推覆应力方位的变化,各亚阶段沉降-沉积中心位置各异,往复迁移于川西、川东北和川东南3个坳陷带;相似性为各次系统地层分布都呈自前缘坳陷带向前陆斜坡带和前陆隆起带上超减薄变细的楔状体,具有相似的沉积组合、相带展布和油气地质特征。

Sedimentary Response to the Coupling Process Between Basin and Mountain of Sichuan 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 three 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 three 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.