四川盆地北部剑阁古隆起的厘定及其基本特征

Discovery of the Jiange Paleo-Uplift in North Sichuan Basin and Its Basic Characteristics

古隆起成因机制及其演化的分析,可为探讨大陆陆内构造变形提供基础,古隆起也是重要油气勘探领域之一。地震剖面、钻井资料和野外露头等证据揭示,四川盆地北部须家河组上部地层缺失并非周边造山作用剥蚀形成,而是古隆起活动造成,本文称之为剑阁古隆起,对其进行厘定和描述。通过分析地震剖面和连井剖面的年代地层格架,并结合Bischke曲线分析法,确定古隆起的形成与演化历史。结合区域构造背景,分析古隆起成因。剑阁古隆起相对高部位的边界近似为须家河组缺失尖灭线,分布在江油—剑阁—广元—旺苍一带。它于晚三叠世须三期开始形成,主要发育期为须四期到须六期,持续到早侏罗世后衰亡,经历了一个完整的形成—演化—衰亡的隆起旋回,持续大约21Ma,造成约350m的地层沉积间断,后期改造使古隆起初始形态不复存在。剑阁古隆起的形成受控于勉略洋盆的关闭,大地构造位置属于晚三叠世扬子地块北缘前陆盆地的前隆部分,它的发现对分析扬子地块北缘构造演化和川北地区须家河组油气勘探具有重要意义。

Analysis of the formation mechanism and evolution of paleouplift could provide the basis for studying the inland tectonic movement. Paleouplift is now an important exploration target for hydrocarbon. Seismic profiles, well data and outcrops of North Sichuan Basin indicate that the lack of upper Xujiahe Formation in the study area was not caused by erosion due to surrounding orogeny, but by the formation of a paleouplift, which is named Jiange paleouplift and discussed in this study. Combined with Bischke Plot Analysis, we verified the formation and evolution history of the paleouplift by analyzing the time-strata relationship of seismic profiles and cross well lines. The high altitude boundary of the Jiange Paleouplift is equivalent to missing pinchout line of Xujiahe Formaiton, which distributes around Jiangyou, Jiange, Guangyuan and Wangcang, with its center in Jiange. It began to form during the sedimentation of the 3~h member of Xujiahe Foramtion in late Triassic, developed mainly from the 6th member to 6th member of the Xujiahe Formation, and demised at end of Early Jurassic, experiencing a complete uplifting circle of formation-development-demise and lasting about 21Ma. This uplift resulted in the sedimentation gap of about 350m, and the initial morphology of the uplift does not exist due to the later transformation. The formation of the Jiange Paleouplift was controlled by closure of the Mianlue Ocean, which is tectonically located in the fore-bulge part of the Late Triassic foreland basin in the northern margin of Yangtze Plate. Its discovery is of great significance for analyzing the tectonic evolution history of northern margin of Yangtze Plate and for guiding the hydrocarbon exploration efforts of Xujiahe Formation in North Sichuan Basin.