摘要：

巨鲕的产出时代多见于新元古代和早三叠世,而寒武纪的巨鲕却鲜见报道。近期,笔者在重庆石柱地区下寒武统天河板组中发现厚约35cm的透镜状巨鲕灰岩。在该层巨鲕灰岩中,巨鲕粒径一般为5～7mm,最大可达9mm,约占岩石组分的55％,与大量强烈重结晶的正常鲕粒伴生。钙质生物壳体较常见,颗粒间见亮晶方解石胶结物。研究区巨鲕最外圈纹层上常见蓝细菌化石,形成发育不完全的突起状“夭折的纹层”;巨鲕内的暗色纹层中亦见杂乱交错的、有一定重结晶的蓝细菌等微生物化石。故推测其为微生物成因形成的,且早寒武世频繁的强风暴背景和蓝细菌等微生物的积极参与是该层巨鲕形成的必备条件。

关键词: 巨鲕, 蓝细菌, 早寒武世, 风暴, 微生物成因, 巨鲕, 蓝细菌, 早寒武世, 风暴, 微生物成因

Abstract:

Giant ooids are commonly seen in the Precambrian and Lower Triassic,while they are hardly reported in the Cambrian. Recently,we found giant ooid limestone with about 35 cm thick in the Lower Cambrian Tianheban Formation at the Shiliu section in Shizhu area,Chongqing. The diameter of these giant ooids is generally 5-7mm,with a maximum diameter of 9mm. The giant ooids make up 55％ of rock components. Meanwhile,the recrystallized normal ooids and calcareous shells are relatively common in the limestone. The cements of sparry calcites can be found between the grains. Abundant Cyanobacteria fossils found in the outermost laminae of a giant ooid,form a sort of protruberance-shaped laminae named as “abortive laminae”,with which the microbial cause of giant ooids is clearly revealed. The recrystallized inner dark laminae of giant ooids similarly contain messy girvanell fossils. So it is thought that the active involvement of microorganisms and frequent strong storms are the necessary conditions for the formation of giant ooids.

Key words: giant ooid, Cyanobacteria, Early Cambrian, storm, microbial cause, giant ooid, Cyanobacteria, Early Cambrian, storm, microbial cause

中图分类号: 

• P588.24＋5