The present paper deals with the sedimentary sequences and sedimentary facies types in the Upper Triassic Xujiahe Formation in the northeastern Sichuan foreland basin in terms of field outcrops and well data. Eight types of sedimentary facies are discriminated, including alluvial fan, braided stream, meandering stream, fan delta, braided delta, meandering delta, lake and marine delta facies. The palaeogeography went through the evolution from the marine facies to the transitional facies and continental facies, suggesting the basin-mountain coupling and sedimentary responses in the northeastern Sichuan foreland basin during the Late Triassic. During the deposition of the first member of the Xujiahe Formation (i. e. , the Xiaotangzian), the bulk of the study area was uplifted and developed into the continent under the influence of the Indosinian movement. The marine delta deposits were developed only in Guangyuan and Jiange. During the deposition of the second member of the Xujiahe Formation, the highly overthrusting in the Micangshan-Dabashan tectonic zone resulted in the gradual subsidence of the northeastern Sichuan foreland basin. The braided delta deposits were organized in the frontal part of the Micangshan-Dabashan zone. The shallow lake deposits appeared in the southwestern part of the basin. During the deposition of the third member of the Xujiahe Formation, the gradually decrease of tectonism in the Micangshan-Dabashan zone led to the decrease of sediment supply. The braided delta deposits occurred in the frontal part of the Micangshan-Dabashan zone. The shallow lake deposits prograded from the marginal part to the central part of the basin. Till the deposition of the fourth to sixth members of the Xujiahe Formation, the highly overthrusting and tectonic uplifting in the Micangshan-Dabashan zone permitted the rapid subsidence of the northeastern Sichuan foreland basin, and the sudden increase of abundant sediment supply. From the the marginal part to the central part of the basin, there occurred the alluvial fan, fan delta, braided delta, meandering stream, meandering delta and shallow lake deposits.%在对川东北前陆盆地上三叠统须家河组露头剖面野外实测和钻井等资料综合研究的基础上,对该区上三叠统须家河组层序及沉积相类型、沉积特征进行了详细的研究.结果表明:研究区内主要发育冲积扇、辫状河、曲流河、扇三角洲、辫状河三角洲、曲流河三角洲、湖泊、海相三角洲等八种主要的沉积相类型.古地理演化经历了由海相环境—海陆过渡相环境—陆相环境的转变.反映了川东北前陆盆地晚三叠世须家河期盆-山耦合过程及其沉积响应.须一段(即小塘子期)发育时期,受印支期构造运动的影响,本区大部分隆升成陆,仅在研究区北西部广元、剑阁等地发育海相三角洲相沉积.须二段发育时期,米仓山-大巴山构造山系的逆冲推覆构造作用较为强烈,川东北前陆盆地坳陷幅度加大,沉积物供给充分,沿米仓山-大巴山前缘地带主要发育辫状河三角洲沉积,而盆地西南部主要发育浅湖沉积.在须三段发育时期,米仓山-大巴山构造山系构造活动逐渐减弱,处于低幅稳定隆升状态,碎屑物供给量减少,沿米仓山-大巴山前缘地带主要发育辫状河三角洲沉积；从盆地前缘地带向中心地带则主要发育浅湖沉积.须四-须六段发育时期,米仓山-大巴山开始进入强烈逆冲推覆和构造隆升阶段,川东北前陆盆地坳陷幅度急剧加大,碎屑物供给量骤然增多,从盆地前缘地带向中心地带主要发育冲积扇-扇三角洲-辫状河三角洲、曲流河、曲流河三角洲相到浅湖相沉积.
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