浙江桐村寒武系大陈岭组地震驱动的软沉积变形构造特征分析

Analysis on Earthquake-Induced Soft-Sediment Deformation Structures in the Cambrian Dachenling Formation in the Tongcun Village,Zhejiang Province

软沉积变形构造是确立古地震是否发育的关键证据之一。在浙江桐村寒武系大陈岭组剖面确立的三个地震驱动的软沉积变形事件层中,主要软沉积变形有地震微断裂、微褶皱、液化构造,它们反映出沉积物遭受地震作用时,流体压力改变的程度以及发生液化的强度。其中,微褶皱构造主要包括微褶皱纹层和与液化脉有关的褶皱;液化构造包括泄水构造和液化脉构造。通过对软沉积变形构造的形态特征、产状观察和统计,与其它非地震成因的类似构造相区分,进一步确立地震是它们最有可能的驱动机制,统计出三个事件层中地震扰动层的厚度和震中距,估算事件层Ⅱ和事件层Ⅲ的震级为6～7级和6级左右,并初步认为在大陈岭组地震带以外的地层中,存在臼齿构造。从而,完善了震积岩的识别标志和岩相序列,深化了对浙西寒武系大陈岭组地震事件沉积的认识。

Abstract： Soft sediment deformation is one of the key indicators identifying the on the standard as the sediments suffer the earthquake, fliud pressure changing existence of paleo-earthquake. Based degree and the strength of the lique- fled. Through three horizons of soft sediment deformation events with earthquake-driven on the Cambrian Dachenling Formation in the Tongcun village in Zhejiang province, the abundant soft sediment deformation are seismic micro-frac- tures, micro-folding and liquefied structures. They reflect the extent of the fliud pressure changing and the strength of the liquefaction, when the sediments suffer from the earthquake. The micro-foldings in the profile of Tongcun village always place there, and are symmetrical folds and uniform liquid layer. Its tectonic features do not match significantly to, the landslide deformation, and the author and other measure the micro-folding axial plane randomly in the profile of Tongcun village, and get total of 39 sets of data, and then correct in level for statistical analysis. After all the work, the author rules out the possibility of landslide. Liquefied structure is a kind of the geological phenomenon of conservation of matter and transfer of form, and it shows the flow structure when liquefaction invades. The formation of liquefied form caused by three reasons, which re- present the diffferent stages of devolatilization. The auther researchs by contrasting among the liquefied structures by means of four aspects of section characteristics, surface features, contrasting with surrrounding rock, and symbiotic construction. By observing and counting about special characteristics and properties of event horizons of the soft sediment de- formation, and distinguishing the similar structures without earthquake-driven, these indicate that earthquake was the driven force. The discovery of three seismite events layers indicated that the deposition period of Dachenling formation is the period of paleoseimic occuring frequently. Paleoseismic induces the formation of Kaihua-Chunan major desloca- tion, so the author and other consider deposition time of the event layer 11 is the strong activing period of the forma- tion of Kaihua-Chun＇ an major deslocation. Counting the seismic disturbance and epicentral distance in the three e- vents layer estimate the layer I1 and layer m magnitude are 6-7 level and about 6 level, and the autherand other pre- liminary view that the layers without the earthquake zone maybe exist molan tooth. So, the identification mark and li- thological sequence of seismite get perfect, the understanding get deepening about the sedinentation of cambrian Dachenling formation resulting from seismic events in the west of Zhejiang province.