龙门山前陆盆地南段乐地1井须家河组震积岩特征及地质意义

Characteristics and geological significance of Xujiahe Formation seismites in Well Ledi-1 in the southern section of the Longmenshan foreland basin, China

通过对龙门山前陆盆地南段乐地1井上三叠统须家河组岩心的系统观察和描述,以前人对震积岩的研究为基础,探讨震积岩的分布特征以及与盆地构造活动的关系。震积岩主要分布在须家河组第二、第三和第四段,发育典型的由地震导致的软沉积物液化变形和脆性变形构造,包括液化砂岩脉、液化卷曲变形与混滑层、负载构造及球枕状构造、环形层理、震裂岩和微断层。认为这些软沉积物液化变形和脆性变形构造是由龙门山隆升构造引起的地震作用形成的。乐地1井中地震岩的分布特征表明龙门山前陆盆地南段在须家河组第二、第三和第四段时期构造活动强烈,并快速向南东方向推进。

Based on the previous study,the distribution characteristics of seismite in Well Ledi-1 and its relation with basin tectonic activities are discussed through systematic observation and description of the cores of the Upper Triassic Xujiahe Formation in the southern section of the Longmenshan foreland basin.The seismites in Well Ledi-1 are mainly occurred in the second,third and fourth Member of the Xujiahe Formation.In the 3 members,earthquake-induced typical liquefaction of soft sediments and brittle deformation structures,such as liquefied sand-veins,liquefied curled deformation structures and mixed layer,load structures and ball-and-pillow structures,loop beddings,shatter breccias and micro-faults are recognized.It is considered that above mentioned liquefaction deformation of soft sediments and brittle deformation are caused by the seismic activity during the uplift of Longmenshan.The distribution characteristics of seismic rocks in Well Ledi-1 indicate that the southern section of Longmenshan foreland basin experienced strong tectonic activity in the second,third and fourth Member of the Xujiahe Formation and the tectonic activity extended rapidly toward the southeast direction,made strong influence on the Longmenshan foreland basin.