Microbially-dominated Cambrian (Miaolingian) carbonate reef of the North China

Abstract

The Miaolingian Series is a distinctive lithostratigraphic unit within the Cambrian System, characterized by the abundance of non-laminated dendrolites relative to stromatolites. During the Miaolingian Epoch, the North China Platform was marked by a pervasive development of ooid banks (more than one million km²) along with large and small bioherms associated mainly with sea-level fall. The North China Platform, exemplified by the Huolianzhai section, serves as a paradigm for deciphering the microbial composition and the sedimentary architecture of microbial carbonates that developed in the normal regression phase of third-order sea level changes. Carbonate reefs (biohermal-type structures) in this section comprise a high density of calcified sheaths of filamentous cyanobacteria together with Epiphyton. The microbial carbonate may result from sophisticated calcification of extracellular polymeric substances (EPS) that form multiple biofilms in relatively thick microbial mats dominated by cyanobacteria. The presence of the dolomitic crystals within dense micrite of microbial carbonates, such as thrombolite, leiolite, stromatolite along with potential fossilized cyanobacterial spores embedded within clotted micrite of the thrombolitic leiolites, has sparked both interest and intrigue. These findings underscore the complex and enigmatic origins of microbial carbonates which are interpreted to have been predominantly influenced by cyanobacterial activity. This study provides valuable insights into the formation of microbial carbonates, with implications for similar geological settings worldwide.