内蒙古阿尔山地区下寒武统苏中组混合沉积特征及形成环境研究

Depositional Characteristics and Environment of Mixing Sediments of Lower Cambrian Suzhong Formation in Aershan Area,Inner Mongolia

以内蒙古阿尔山地区下寒武统苏中组为研究对象,综合区域地层、岩石结构、剖面特征、粒度分布特征,对苏中组碳酸盐岩夹碎屑岩的沉积环境进行了深入分析。从粒度分布特征来看,苏中组砂岩粒度分布表现出双峰和多峰不对称,偏度以正偏为主,峰度数值多且比较低,分选性差,以粗粒物质为主等特征;运用萨胡图解投点、判别函数计算确定内蒙古阿尔山地区下寒武统苏中组砂岩形成于海成三角洲沉积环境。但由于碎屑沉积物粒度普遍偏粗,而且粒度分布与浅海波浪带砂类似,但悬浮组分相对浅海波浪砂偏高,砂岩与灰岩构成透镜状层理和韵律层理,综合认为砂岩是在潮控三角洲的混合坪沉积的。从灰岩特征来看,灰岩主要表现为灰白色细晶灰岩、白云质灰岩、砂质灰岩,表面呈蜂窝状,具重结晶,显示水平层理,综合分析其形成于灰坪环境。

Depositional characteristics and environment of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are analyzed through integrating areal stratum,lithology,section characteristics,and distribution of the grain size.Grain size of the sandstone in the Suzhong Formation presents the following characters： with double or multimodal anisomerous peaks in grain size distribution frequency curves;mainly in positive skewed distribution;numerous but low peak values;poor sorting and most of the grain consists of those of coarse materials.Based on the size parameters,we located in the Sahu diagram and calculated with discriminate function,it is ascertained that the sandstone in the Lower Cambrian Suzhong Formation which lies in Aershan area of Inner Mongolia are deposited in marine delta environment.Nevertheless,most clastic deposits of the Suzhong Formation is macrograin materials with their grain size distribution similar to wave sand of neritic,and with larger suspension population as well;the mixing deposited sandstone and limestone appears lenticular bedding and rhythmic bedding;so we conclude that the sandstone of this area is deposited in the mixed flat of tide dominate delta.The limestone in the area studied mainly are Greyish white sandy limestone,dolomitic limestone,being recrystallized,with honeycombed surface and horizontal bedding,through these,we draw the following conclusion that limestone of the Lower Cambrian Suzhong Formation in Aershan area of Inner Mongolia are deposited in limemud flat.