对前寒武纪一些沉积构造成因的思考:以天津蓟县剖面为例  

Discussion on Genesis of Some Sedimentary Structures from Precambrian:Taking Jixian Section in Tianjin as an Example

作　　者：刘贺娟[1] 孙晓岭[2,3] 王德海[4] 

机构地区：[1]克劳斯塔尔工业大学石油工程研究所 [2]太原理工大学矿业工程学院,山西太原030024 [3]鄂尔多斯职业学院矿业系,内蒙古鄂尔多斯017000 [4]吉林大学地球科学学院,吉林长春130061

出　　处：《地球科学与环境学报》2013年第3期44-54,共11页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(49802012;40472065);鄂尔多斯市科技计划项目(EKJ1225)

摘　　要：天津蓟县剖面元古界地层中发育一类特殊的沉积构造。通过对蓟县剖面发育的砂脉构造和臼齿构造(微亮晶集合体)进行对比研究,分别从宏观、微观特征以及发育的层序地层位置等角度归纳两者的异同,包括外观形态、与底基质接触关系、与层理关系、组成矿物成分、沉积环境、成岩特征、孔隙系统的扩展方式、分布时限、成因模式等。此外,通过与宏观藻类化石共生的臼齿构造微观特征研究,揭示臼齿构造微生物作用的影响。结果表明:砂脉构造在海进期—高水位早期形成,臼齿构造形成于最大海泛期以后的深水环境,风暴浪基面附近更发育,并受风暴流和原孔隙流体的对流渗流作用影响;由于广泛的海进造成微生物群落异常繁殖,在沉积底基质上发育微生物席,微生物席暴露后脱水干裂,而后在水动力作用下充填碎屑颗粒形成砂脉构造,这属于物理地质作用过程引起的再沉积作用结果;相比而言,臼齿构造的形成更复杂,元古代时期大气中CO2分压几次大的波动是控制微亮晶形成的主因,致使海水中碳酸钙过饱和度很大,风暴流和孔隙流体快速渗流混合作用带来了微亮晶成核的原始微粒碎屑,微生物的共同作用导致微亮晶在先存裂隙或底基质孔隙空间中快速成核和结晶生长;伴随微亮晶的生长,孔隙流体从孔隙中排出并向周围孔隙介质运移扩散,使得孔隙流体压力在附近基质中积累,导致裂隙进一步发展和臼齿构造的形态复杂性,这属于风暴作用诱导的化学地质作用过程引起的再沉积结果,涉及微生物-化学-流体力学耦合作用影响。砂脉构造和臼齿构造都经历过微生物席发育-埋藏-脱水脱气作用,都可以归为微生物引起的原生沉积构造范畴。The special sedimentary structures develop in Proterozoic of Jixian section. Sand dyke structure and molar-tooth structure （microsparite aggregate） developed in Jixian section werecontrasted through three aspects, such as macroscopic, microscopic features and the location of sequence stratigraphic development, the difference and similarity of these structures were summarized, including appearance, contact relationship with substrate, relationship with bedding, mineral composition, sedimentary environment, diagenetic characteristic, expanded mode of pore system, distribution time limit, genetic model and so on. Furthermore, according to the microscopic characteristic of molar-tooth structure intergrowthing with macro algae fossil, the microbial effect of molar-tooth structure was explained. Sand dyke structure develops from the transgressive period to the early stage of high water level period, but molar-tooth structure forms in the deep water environment after the maximum flooding period, develops frequently around the storm wave base, and is affected by convection and infiltration of storm flow and original pore fluid. The extensive transgression of sea causes the multiplication of microbe community. The microbial mats develop above the sedimentary substrate, dehydrate and split after the exposure. Sand dyke structure forms for the filling of the splitting fractures by the elastic particles under the hydrodynamic action, which belongs to the redeposition caused by physical geological function. By comparison, the formation of molar-tooth structure is more complicated, the several waves of CO2 partial pressure in the atmosphere of Proterozoic are the main factors controlling the formation of microsparite and results in higher supersaturation of calcite in the sea. The initial elastic particle of microsparite nucleation is found under the mixing action of storm flow and rapid seepage of pore fluid, and the participant of microbe causes microsparite nucleates rapidly and grows crystally in the existent crack or

关 键 词：砂脉构造 臼齿构造 微生物席 沉积构造 还原环境 蓟县剖面 孔隙流体 

分 类 号：P588.21[天文地球—岩石学]