北京西山地区雾迷山组风暴硅岩沉积序列

Depositional Sequence of Storm Siliceous Rock in Wumishan Formation,West Mountain,Beijing,China

北京西山地区雾迷山组发育硅质条带白云岩，在硅质条带中发育典型的风暴硅岩沉积。风暴硅岩砾屑具菊花状构造和底模构造，与上下围岩形成典型的风暴序列。该序列从底部至顶部可划分为五个单元。每个单元分别代表正常天气至风暴天气再至正常天气的沉积特征。研究认为，风暴硅岩为在风暴流的影响下近源快速堆积的产物，并建立了风暴硅岩的沉积模式。

Siliceous rock can be defined as sedimentary rock which contains about 70￣80 percent authigenic silica rock with the exception of quartz in sandstone and quartzite.This paper mainly describes the characteristics and vertical sequences of storm siliceous of Wumishan Formation in Beijing west mountain.The thichness of Wumishan Formation about 2 168.55 m.It mainly consists of dolomite interbeded with siliceous rock.Research shows that there doveloped storm siliceous rock in this area.Its vertical sequence consists of bottom unit,lower unit,intermediate unit,upper unit and top unit,i.e.,(a)The bottom unit: 50 cm in thickness,gray black shaly dolomite,normal shallow sea environment,(b)The lower unit:25￣30 cm in thickness,dolorudite with scoured base,which consists of two sedimentary cycles showing coarse upward seqence,result from early tempestuous current,(c)Intermediate unit:20 cm in thickness,storm siliceous rock with surface of scour,siliceous gravel arranged as daisy,which are formed in strom surge,(d)Upper unit:40 cm in thickness,black shaly dolomite,resulting from the last stage of tempestuous current,and (e)Top unit:stromatolithic dolomite interbeded with siliceous strip,wich are formed in normal weather deposit.From bottom unit to top unit,which shows complete process of storm deposit,it can be regarded as typical sequence.At last,their sedimentary models have been developed.