试论川东北地区下二叠统孤峰组燧石(硅质岩)的沉积环境

引言华南某些地区下二叠统茅口组与上二叠统龙潭组(或吴家坪组)之间,有一套以含层状燧石(硅质岩)及含菊石、放射虫、牙形刺等浮游生物化石的地层,层位属下二叠统顶部,与茅口组上部呈相变关系。这套地层前人一般称孤峰组,湖南则称当冲组,贵州称白泥塘组等。近年来对孤峰组燧石(即茅口组硅质岩)的成因众说纷纭、争论较大。大多数人认,燧石为沉积成因,形成于低能环境,二氧化硅来自陆源化学风化。马忠魏等(1981)认为孤峰组燧石形成于海水深度大于60m的台沟;童玉明等(1985)则认为形成环境应属于深海

SEDIMENTARY ENVIRONMENTS OF THE CHERT(SILICEOUS ROCKS)FROM THE LOWER PERMIAN GUFENG FORMATION IN NORTHEASTERN SICHUAN

There is considerable debate concerning the genesis of the chert (i.e. siliceous rocks from the Maokou Formation) from the Lower Permian Gufeng Formation in northeastern Sichuan in recent years. It is notorious that it is formed in an intraplatform trench environment with a water depth of more than 60 m, or in a deep-sea basin to deep-sea trench environments. The authors feel instead that the siliceous rocks in the Gufeng Formation should be interpreted as having formed in the shallow-water lagoon gulf and restricted platform with a water depth of only several metres in terms of the study of the Permian petrographic sections in Nanjiang and Wangcang coupled with plentiful geological data from northeastern Sichuan.