重庆云阳地区沙溪庙组软沉积物变形构造及其地质意义

Soft sediment deformation structures in Shaximiao Formation and its geological significance in Yunyang area,Chongqing,China

探讨重庆市云阳县普安乡沙溪庙组下段恐龙化石埋藏成因。通过野外观察及室内薄片分析,对化石围岩及上下岩层展开研究。化石围岩为紫红色泥质粉砂岩,其中见大量泥砾及软沉积物变形构造,具稀性泥流沉积特征。化石层上下大量发育以负荷构造、火焰构造、液化砂岩脉等为代表的软沉积物变形构造,与地震活动相关的同沉积断裂、砂球(枕)以及地裂缝伴生发育,表明研究区液化软沉积物变形可能是受古地震事件影响形成。化石墙附近发育管状钙质结核,是区内存在大量甲烷并发生运移及排放的证据,可能是深部液化含水沉积物与甲烷上涌形成的通道。沉积物的液化与甲烷聚集是研究区泥火山发育的先决条件,经地震触发,液化沉积物以泥火山形式溢流喷出,“化石墙”则是喷出泥流对恐龙快速埋藏的结果。

Study of macroscopic phenomena in the field and microscopic thin sections in the laboratory from the Lower Shaximiao Formation and its upper and lower strata is carried out in order to explore the origin of dinosaur-fossils buried strata in Pu'an Township of Yunyang County,Chongqing.The results show that the dinosaur fossil containing rock is composed of purplish red argillaceous siltstone with numerous argillaceous breccias and soft-sediment deformation structures,characteristic of diluted mudflow deposition.Soft-sedimentary deformation products of load structures,flame structures and liquefied sandstone veins are developed above and below the fossil layer.Also,synsedimentary fractures,sand balls(pillows)and cracks resulted from seismic activities are recognized in the study area,which were probably caused by paleo-seismic activity.Tubular calcareous concretions are developed near the Fossil Wall,which is the evidence of the presence,migration and emission of large amounts of methane in this region,and may be the channel formed by upwelling of liquefied water-bearing sediments and methane.The liquefaction of sediments and accumulation of methane are the prerequisites for the development of mud volcanoes in the study area and the liquefied sediments gushed out in the form of mud volcanoes which is triggered by earthquake,and the Fossil Wall was resulted from the rapid burial of dinosaur fossils by erupted mud stream.