Study on several special sedimentary structures of earthquake-induced soft deformations
Zhong Jianhua1, Ni Liangtian1, Shao Zhufu2, Li Yong1, Liu Xuan1, Zhong Fuping3, Chen Bin1, Mao Cui1, Wei Ting1, Meng Wei1, Wang Jinhua1
1. Earth Science and Technology Institute, University of Petroleum, Qingdao, Shandong 266580;
2. Qingdao Institute of Marine Geology, Qingdao, Shandong 266071;
3. Henan University of Science and Technology, Jiaozuo, Henan 454000
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.