早白垩世义县盆地义县组顶部金刚山层沉积相及其古环境意义

辽西义县盆地内近东西走向的马神庙—刀把地—三百垄—金刚山一带为义县组标准地层剖面出露地,义县组建阶标准地层剖面枣茨山金刚山层为一套古湖盆相沉积组合。野外详细的沉积学和地层学研究将金刚山层自下而上划分为湖缘碎屑浊流相、浅水湖坪相和半深湖相3个沉积亚相。金刚山层下部湖缘碎屑浊流相包括3个粗—细粒序递变沉积韵律。粗粒岩石单元为灰绿色含长石岩屑凝灰质砂砾岩、杂色砾岩、灰白色含砾凝灰岩;细粒岩石单元由灰白色含砾凝灰岩、灰绿色致密凝灰岩、质纯膨润土组成。韵律沉积底部粗粒岩石单元为浊流头部沉积产物,其中常形成弥散式正粒序递变层理,细粒岩石单元为浊流体部、尾部逐渐稀释的沉积结果,其中常发育水平层理。中部浅水湖

The Sedimentary Facies and Palaeoenvironment of Jingangshan Layer of Early Cretaceous Yixian Formation in Zaocishan Area,Yixian Basin

The Yixian stage standard section crops along Mashenmiao-Daobadi-Sanbailong-Jingangshan area strikingly from the west to the east in Yixian basin,they are upwardly Mashenmiao layer,Laogonggou layer,Yenangou layer,Zhuanchengzi layer,Dakangpu layer,Zhujiagou layer and Jingangshan layer.As the upper part of Yixian formation,Jingangshan layer is a set of lacustrine deposit in Zaocishan area.Based on sedimentary petrology and stratigraphic studies,these sedimentary strata could be divided into lake margin clastic turbidity facies,shallow water flat facies and semi-deep lake facies(in ascending order).The turbidity facies consists of three coarse-fine grading sedimentary rhythms.The coarse petrologic units are mottled,grey-green feldspar and lithic tuffaceous glutenite and grey-white gravel bearing tuff;the fine units are made of grey-white gravel bearing tuff,grey-green compact tuff,purified bentonite and slightly bentonitic siltstone.The coarse turbidity facies is product of the head of turbidity current,distribution normal grading usually develops in this petrology unit.As the result of the body and tail parts of turbidity current,the finer turbidity facies present themselves with horizontal bedding.In the middle part of Jingangshan layer,the shallow water flat facies is composed of five bentonitic siltstone(purified bentonite and /or shale)-marl rhythms.In lake flat facies,the thickness ratios of carbonate deposit and underlying volcanic clastic deposit range from 0.11 to 0.47,it indicates that lacustrine margin experiences five stages of equal interval lake flat sedimentation.The upper part of Jingangshan layer is the association of pale paper-sheeted shale and silty shale.The coarser petrologic unites of lake margin clastic facies in lower part of Jingangshan layer indicate that they are proximal deposite,the finer unites show the polycylic volcanism during the forming process of lake margin clastic facies.The five bentonitic siltstone marl sedimentary rhythms of middle part lake flat facies may indicate the lake water level survived at least five shoaling changes.Under the regional arid climate,the marl deposit was formed in the lake flat facies.And the deeper area of central lake basin may receive a great volume of suspensive fine-grained materials to form the hydrostatic deposits of semi-deep lake facies.