几种较特殊的地震成因软变形沉积构造

地震形成的软沉积变形构造是一种重要的沉积构造, 广泛分布于各个时代的各种地层中。近期在对宁夏固原市杨郎镇境内的寺口子下白垩统乃家河组剖面和北京南口林场中元古代剖面考察时发现了几种较特殊软沉积变形构造, 分别是: 软变形褶皱、软变形宽U形构造、软变形宽弧形构造、软变形平卧"V"形构造、软变形"Ω"形构造、球状枕状构造、软双重构造及软窗棂构造。这些构造的共同特征是: 1)大部是一种连续变形, 揭示它们是在未固结的塑性状态下形成的; 2)几何学特征具有突变性, 与正常的沉积构造极度不和谐, 无法从正常沉积和构造变形的角度得到合理解释; 3)都发生在粒度较细的岩层中; 4)整个岩层受扰动强烈, 显得很"杂乱"; 5)尺度相对较大; 6)一般都有一个或两个再作用面(或剪切面)。我们认为它们是被一种强烈的沉积后改造作用形成的, 与地震(诱发)密切相关, 是一种地震成因的软变形沉积构造。

Study on several special sedimentary structures of earthquake-induced soft deformations

Earthquake-induced soft deformation structure is an important sedimentary structure, which is widely distributed in various strata of every phrase. Recently, we found several specific soft sediment deformation structures during the survey at the Sikouzi profile of Naijiahe Formation, Lower Cretaceous in Yanglang Town, Guyuan, Ningxia Province, as well as at the Nankou forest farm profile of Middle Proterozoic in Beijing. Through our preliminary identification, these soft deformation structures can be respectively defined as soft deformation fold, wide U-shaped soft deformation structure, wide arc-shaped soft deformation structure, prostrate V-shaped soft deformation structure, Ω-shaped soft deformation structure, spherical and pillow structure, soft duplex and soft mullion structure. These structures have the following common characteristics: 1)The most are continuous deformations, which reveal they are formed under unconsolidated plastic state. 2)They have mutability in geometric features and are disharmonious with normal sedimentary structures, thus we can't provide reasonable explanations from the perspective of normal sedimentary and tectonic deformations. 3)They all develop in fine-grain strata. 4)The whole strata have intense disturbance and appear extremely "messy". 5)They have relatively large scales. 6)Usually, they have one or two reactivation surface(s)or shear plane(s). Though research, we discover they are formed by a strong external force transformation after deposition, and further they are closely related to earthquakes (earthquake-triggered). Therefore, we regard these structures as a kind of seismic origin soft deformation sedimentary structure.