摘要： 多样化的产出环境和30×10⁸年的分布历史表明,鲕粒成因一直是一个谜一样的沉积学难题,争论的关键问题是其究竟是有机(微生物)成因还是无机成因。来自于华北地台寒武系苗岭统徐庄组鲕粒滩相灰岩顶部的方解石巨鲕表现出同心状、放射—同心状和泥晶质的沉积组构,在鲕粒核心和鲕粒皮层中保存着精美的葛万菌(Girvanella)化石所主导的光合作用生物膜的钙化作用残余物,这为研究鲕粒形成与光合作用生物膜之间复杂的成因联系提供了一个较为直接的微生物证据,因为葛万菌可相对较为肯定地类比于近代的钙化织线菌(Plectonema)丝状蓝细菌化石。所以说,在伴随着后生动物辐射的寒武纪蓝细菌繁盛的方解石海中,尽管形成放射状鲕粒皮层的放射纤维状方解石的沉淀作用机理还没有得到完全彻底的了解,但是这些巨鲕确实表现出光合作用生物膜诱发、滋养并促进了鲕粒形成的直接证据,进一步支持了“鲕粒沉积可以作为一种不同的微生物岩体系新类型”的重要科学理念。

关键词: 鲕粒, 光合作用生物膜, 徐庄组, 寒武系, 华北地台

Abstract: Diversified forming environments and 3000 million years of history clearly express that ooid is an enchanting depositional grain whose origin remains a dilemma,and its formation is still actively debated that is reflected as the strongly difference between the organic and inorganic origins of ooids. Giant ooids from the top part of the Miaolingian Xuzhuang Formation at the Shijing section in Xin'an County of Henan Province are made of calcite and show concentric,radial-concentric,and micritic fabrics. Within both the core and the cortex of these ooids there are excellent calcified residues of photosynthetic biofilms reflected as the high-density preservation of the Girvanella,which provide a relative direct evidence of ooid formation that is genetically related to the photosynthetic biofilm,since it is relatively certain that Girvanella resembles closely recent calcified Plectonema. Therefore,although the exact forming mechanism of radial-fibrous calcites making up the cortex of radial ooids in the calcite sea of the Cambrian that is marked by cayanobacterial blooms and is coincided with metazoan radiation is not wholly understand,direct evidences of that the formation of these giant ooids is dominated,nourished and promoted by photosynthetic biofilms further support an important scientific idea,i.e. ooid deposits can be understood as a new differentiated type of microbialite system. Ultimately,our finding and study provide an important example for the further understanding and elucidating of the “ooid dilemma”.

Key words: ooid, photosynthetic biofilm, Xuzhuang Formation, Cambrian, North China Platform

中图分类号: 

• P534