寒武纪丝状蓝细菌生物膜主导和诱发的巨型鲕粒:以河南新安县石井剖面苗岭统徐庄组为例

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...

Giant ooids induced and predominated by photosynthetic biofilms of filamentous cyanobacteria:an example from the Miaolingian Xuzhuang Formation at the Shijing section in Xin'an County of Henan Province,North China Platform

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".