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| Earthquake-induced soft-sediment deformation structures in the Mesoproterozoic Wumishan Formation,North China,and their geologic implications | |
| 作者单位： | ZHANG ChuanHeng1，2，3，WU ZhengJie3，GAO LinZhi4，WANG Wei3，TIAN YanLin3 & MA Chao3 1 State Key Laboratory of Geological Processes and Mineral Resources，China University of Geosciences，Beijing 100083，China; 2 Key Laboratory of Lithospheric Tectonics and Lithoprobing Technology，Ministry of Education，China University of Geosciences，Beijing 100083，China; 3 School of Geosciences and Resources，China University of Geosciences，Beijing 100083，China; 4 Institute of Geology，Chinese Academy of Geological Sciences，Beijing 100037，China |
| 基金项目： | 中国地质调查局勘测项目 |
| 摘 要： | Soft-sediment structures are key to defining seismites. Two soft-sediment deformation horizons, bounded by undeformed carbonate strata, have been found in the Wumishan Formation in the Jumahe region, 175 km southwest of Beijing. One is in the lowest part of Wumishan Formation; and the other is in the uppermost part of Litho-member I. The soft-sediment structures in these two horizons fall into three categories: mould-and-sag structures, hydraulic shatterings and liquefaction dikes. The mould-and-sag structures are divided into two types: one developed in tidal-flat sediments, accompa-nied by many liquefaction-related structures and characterized by autochthonous post-earthquake sediments in sags, and the other type developed in deep-water environments, is not associated with liquefaction structures, and is overlain immediately by seismogenic tsunamites. The hydraulic shat-terings are composed of pockets of fluidization conglomerate, sand intrusions, and syndepositional faults. The liquefaction dikes fall into two categories: hydraulic-fracturing dikes and lateral-spreading dikes. The former are steep, planar, and pinch out upwards. The latter are snake-like and characterized by no diapir-related drag structures in surrounding rocks. Examination of the attitudes and strati-graphic positions of these structures suggests that these soft-sediment structures are seismogenic, and consequently, are seismites. Most seismites in the Wumishan Formation are developed near the former western, margin fault of Yanliao rift. This occurrence suggests that they could be related to movements on this fault. Other geological implications are discussed. |
| 收稿时间： | 26 September 2005 |
| 修稿时间： | 20 January 2006 |
Earthquake-induced soft-sediment deformation structures in the Mesoproterozoic Wumishan Formation,North China,and their geologic implications |
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| Authors: | Zhang ChuanHeng Wu ZhengJie Gao LinZhi Wang Wei Tian YanLin Ma Chao |
| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;Key Laboratory of Lithospheric Tectonics and Lithoprobing Technology, Ministry of Education, China University of Geosciences, Beijing 1000037, China;School of Geosciences and Resources, China University of Geosciences, Beijing 100083, China 2. School of Geosciences and Resources, China University of Geosciences, Beijing 100083, China 3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
| Abstract: | Soft-sediment structures are key to defining seismites. Two soft-sediment deformation horizons, bounded by undeformed carbonate strata, have been found in the Wumishan Formation in the Jumahe region, 175 km southwest of Beijing. One is in the lowest part of Wumishan Formation; and the other is in the uppermost part of Litho-member I. The soft-sediment structures in these two horizons fall into three categories: mould-and-sag structures, hydraulic shatterings and liquefaction dikes. The mould-and-sag structures are divided into two types: one developed in tidal-flat sediments, accompa- nied by many liquefaction-related structures and characterized by autochthonous post-earthquake sediments in sags, and the other type developed in deep-water environments, is not associated with liquefaction structures, and is overlain immediately by seismogenic tsunamites. The hydraulic shat- terings are composed of pockets of fluidization conglomerate, sand intrusions, and syndepositional faults. The liquefaction dikes fall into two categories: hydraulic-fracturing dikes and lateral-spreading dikes. The former are steep, planar, and pinch out upwards. The latter are snake-like and characterized by no diapir-related drag structures in surrounding rocks. Examination of the attitudes and strati- graphic positions of these structures suggests that these soft-sediment structures are seismogenic, and consequently, are seismites. Most seismites in the Wumishan Formation are developed near the former western, margin fault of Yanliao rift. This occurrence suggests that they could be related to movements on this fault. Other geological implications are discussed. |
| Keywords: | Mesoproterozoic Wumishan Formation soft-sediment structures paleo-earthquakes seismites Yanliao rift |
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