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

Key words: 
• siliceous rock /
• storm deposit sequence /
• Wumishan formation

Abstract: Siliceous rock can be defined as sedimentary rock which contains about 70 ～ 80 percent authigenicsilica rock with the exception of quartz in sandstone and quartzite. This paper mainly describes the char-acteristics 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 withsiliceous rock. Research shows that there doveloped storm siliceous rock in this area. Its vertical sequenceconsists 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 showingcoarse 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 stromsurge, ( d) Upper unit: 40 cm in thickness, black shaly dolomite, resulting from the last stage of tempestu-ous current, and ( e) Top unit: stromatolithic dolomite interbeded with siliceous strip, wich are formed innormal weather deposit. From bottom unit to top unit, which shows complete process of storm deposit, itcan be regarded as typical sequence. At last, their sedimentary models have been developed.