汉中下志留统放射虫硅质岩的岩石学特征及其地质意义

汉中梁山地区的放射虫硅质岩成层性好，层次多，厚度较大，分布面积较广，主要同充填石英的放射虫铸型与隐晶质、微晶质的玉髓、石英及少量伊利石泥质基质构成。岩石中ＳｉＯ_２的平均含量在９０%以上。从岩石学碱性条件下转变和分解，析出ＳｉＯ_２，造成有利于硅质生物大量繁殖的条件。本区下志留统龙马溪组的放射虫硅质岩形成在水深相对较浅的深水陆棚与大陆坡过渡带上，水深约在２００ｍ左右。

Petrological Characteristics of Radiolarian Silicalite and Its Geological Significance of Lower Silurian in the Hanzhong Region

The well stratificatied and widespread radiolarian silicalite with a fairly great thickness in the Liangshan region,Hanzhong,is mainly composed.of quartz filling radiolarian cast,aphanitic or microcrystalline chert and quartz as well as a little illite matrix.The average content of SiO 2 in the rock is above 90%.By analysis of petrological characteristics,the origin of radiolarian silicalite in this region is explained that the distal volcanic product provided SiO 2,for volcanic product changes,dissolved and released out SiO 2 into sea water where formed a favorable environment for the growth of siliceous organism.The radiolarian silicalite of the Lower Silurian Longmaxi Formation in this region was formed in the transitive zone between the deepwater continental shelf where the water depth is relatively shallow and the continental slope,in which the sea water depth is about 200 m.