四川盆地晚二叠世克拉通内裂陷作用背景下的盐亭—潼南海槽沉积充填特征

Sedimentary filling configuration of Yanting-Tongnan trough under the background of intracratonic rift in Later Permain,Sichuan Basin

四川盆地晚二叠世经历了克拉通内裂陷作用以及基底断裂活动,在区域大缓坡背景下,形成"三隆三凹"的古地理格局,发育鄂西—城口海槽、开江—梁平海槽以及盐亭—潼南海槽。在区域背景及动力学分析的基础上,利用钻井、露头、地震资料等论证了盐亭—潼南海槽的几何形态,盐亭—潼南海槽发育在川中地区,整体呈北西-南东向近平行于开江—梁平海槽展布,向西北部广海开口,向东南台地区逐渐变浅并与鄂西—城口海槽连通。利用地震、地质结合的方法,探讨了盐亭—潼南海槽的沉积格局,其以细粒沉积为主,地层厚度薄,其西侧磨溪—中江台缘带以发育生屑滩为主,东侧广安—公山庙台缘带以发育生物礁为主;生物礁滩的分布随着海平面变化具有明显的迁移特征,整体上可以分为两期,并逐渐由两侧台缘带向海槽内迁移。盐亭—潼南海槽的形成、发展及消亡主要受勉略洋扩张-收缩的影响;晚二叠世勉略洋扩张期,四川盆地NW向基底断裂活动,导致川中地区正断活动,形成断陷海槽,即盐亭—潼南海槽。

Previous research shows that Sichuan Basin underwent intracratonic rift and basement fault activities in the Late Permian,developing apaleogeographic framework of＂three uplifts and three depressions＂under the background of the regional large ramp,including Exi-Chengkou trough,Kaijiang-Liangping trough and Yanting-Tongnan trough.Based on geological background and tectonic dynamics analysis and using data of drillings,outcrops and seismos,Yanting-Tongnan trough has been researched in Central Sichuan Basin in our study,which extends in NW-SE nearly paralleling to Kaijiang-Liangping trough,opening to the sea northwestward,and gradually becoming shallower to the east platform and conneted to Exi-Chengkou trough.According to the comprehensive analysis of geology and seismism,sedimentary configuration of YantingTongnan trough has been discussed,which mainly filled with fine grained sediment,and platform margin reef belt distributes around the trough.Organic banks distribute on the west margin of the trough and reefs on the east margin of the trough.The formation,evolution,filling and extinction processes of the Yanting-Tongnan trough was controlled by the expansion of Mianlüe ancient ocean;in the extensional tectonic environment,due to Emei Taphrogenesis,the NW basement faulting inside Sichuan Basin caused tenso-shear activities and thus resulted in tectonic differential settlement of cratonic basin and a series of uplifts and troughs.