四川盆地上二叠统吴家坪组条带状硅质岩分布广泛,所含生物主要为体小壳薄的有孔虫、介形虫、腕足类、双壳类等,缺乏放射虫,偶见海绵骨针.显微薄片显示,生物屑多被硅化,见残余方解石碎屑.MnO/TiO2值平均为4.5,Al-FeMn判别图解多数样品落干Ⅰ区,Co/Ni值平均为0.127,稀土元素总量平均为1.4778×10-6,轻稀土元素总量/重稀土元素总量的值皆小于1,重稀土元素有富集趋势,这些特征均表明硅质岩中的硅来源于热水沉积.综合分析认为,所研究的硅质岩为沉积-交代的综合产物,由石灰岩发生交代作用所形成;沉积物中的硅来自同沉积火山活动、海底热泉及上升洋流等;硅质岩形成时主要为较深水的斜坡,部分为开阔台地,与碳酸盐岩原岩具有相同的沉积环境.

Late Permian Wujiaping banding siliceous rock is widely distributed in the upper Yangtze area. Small foraminifera, ostracoda, brachiopod and dissoconch are common but radiolaria is Lack of and calthrop is rare. The observation of microscopic sections has shown that pioclasts are most silicated and residual calcites can be found. Average ratio of MnO/TiO2 is 4.5. There are 4 specimens that fall in domainⅠin the Al-Fe-Mn discrimination diagram. The ratios of Co/Ni are less than 0.5 with the average of 0.127. Total volume of the rare-earth element is 1.4778×10-6. The values of∑LREE/∑HREE are less than 1. The HREE has a concentration tendency. All of these characteristics indicate that the Si in the silica rock derives from the hydrothermal deposits. It is believed that the silica rock isa deposition-alternation product, which was caused by metasomatosis of limestone. The silica rock is commonly built up in the deepwater slope and partly in the open platform so that it formed in the same depositional environment with carbonate rock.