四川盆地晚震旦世—早寒武世德阳—安岳裂陷槽南段地质特征

Geological characteristics of the southern segment of the Late Sinian–Early Cambrian Deyang-Anyue rift trough in Sichuan Basin,SW China

基于最新钻井、地震和野外露头资料,对四川盆地德阳—安岳裂陷槽南段的地层发育与沉积充填演化等地质特征进行深入研究。结果表明:(1)四川盆地晚震旦世—早寒武世裂陷南段地层发育较全,灯一+灯二段厚度较稳定,为400~550 m;灯三+灯四段槽缘与槽内厚度差异较大,厚度差最大可达250 m;川南寒武系麦地坪组和筇竹寺组厚度相对较薄,且地层厚度变化较大,厚薄变化频繁。(2)灯四段沉积期德阳—安岳裂陷槽向南延伸,影响至川南地区。与裂陷槽中段和北段相比,南段总体具有宽、缓、浅的特征,且存在多个台阶,隆凹相间,呈指状展布。(3)川南地区灯一—灯二段沉积期以碳酸盐台地为主,沉积分异不明显;而灯四段沉积期存在较明显沉积分异,由槽内向槽缘发育盆地—斜坡—次级斜坡—斜坡—次级斜坡—台地边缘—局限台地。(4)川南地区裂陷槽的演化经历了灯一—灯二段沉积稳定期、灯三—灯四段开启期、麦地坪组—筇竹寺组充填期以及沧浪铺组消亡期等4个关键阶段。

Based on the latest drilling,seismic and field outcrop data,the geological characteristics(e.g.strata,development and sedimentary evolution)of the southern segment of the Late Sinian–Early Cambrian Deyang–Anyue rift trough in the Sichuan Basin are analyzed.First,the strata in the southern segment are complete.The first to second members of Dengying Formation(Deng 1+Deng 2)are found with relatively stable thickness(400–550 m),and the third to fourth members(Deng 3+Deng 4)show great thickness difference between the marginal trough and the inner trough,which is up to 250 m.The Cambrian Maidiping Formation and Qiongzhusi Formation in southern Sichuan Basin are relatively thin,with the thickness changing greatly and frequently.Second,the Deyang–Anyue rift trough extended southward during the Deng 4 period,affecting southern Sichuan Basin.Compared with the middle and northern segments of the rift trough,the southern segment is generally wide,gentle and shallow,with multiple steps,and alternating uplifts and sags,which are distributed in finger shape.Third,the Deng 1+Deng 2 in southern Sichuan Basin records the dominance of carbonate platform and unobvious sedimentary differentiation,and the Deng 4 exhibits obvious sedimentary differentiation,namely,basin–slope–secondary slope–slope–secondary slope–platform margin–restricted platform,from the inner trough to the marginal trough.Fourth,the rift trough in southern Sichuan Basin has evolved in four stages:stabilization of Deng 1–Deng 2,initialization of Deng 3–Deng 4,filling of Maidiping–Qiongzhusi,and extinction of Canglangpu Formation.