河北涉县巨鲕粒灰岩的成因及地质意义

Causes and geological significance of the giant ooids in Shexian,Hebei

鲕粒,一直存在化学成因和生物成因的争论,其实这两种成因都客观存在,而且存在两种成因都有的混合成因。对涉县寒武系张夏组地层中发现的巨型鲕粒,通过手标本和薄片观察,发现鲕粒形成前期属于化学成因,受水动力条件的限制,化学成因的鲕层最大生长直径5mm左右。后期鲕粒圈层通过与核形石和藻叠层的微观对比,确定属于生物成因,且生物有一个从繁盛到消亡的过程。鲕粒的生长终止于一层泥质薄膜,被含骨屑和泥质的泥晶方解石所胶结。

There have been controversies about chemical and biological origins of ooids.In fact,both of these causes exist objectively,and there are exist the mixing causes.The giant ooids found in the Zhangxia Formation of the Cambrian in Shexian county were researched by observing samples and thin sections.The ooids were found that their early stage forming were chemical cause.Due to the limitation of the hydrodynamic conditions,the chemical layers of ooids were grown to a maximum diameter of about 5 mm.The later stage of ooids forming was identified as a biological cause by comparing microscopically with oncolite and stromatolite,and the organism had a process from prosperity to demise.The growth of ooids terminated in a layer of argillaceous film,that was cemented by micritic calcite containing biological debris and clay.