Calcified microorganisms bloom in Furongian of the North China Platform: Evidence from Microbialitic-Bioherm in Qijiayu Section, Hebei

Abstract

In order to study the sedimentological response of the first episode of "cyanobacteria calcification event" in Phanerozoic, we studied the microbialites from Furongian Series in Qijiayu section, Hebei Province, which is located in the central part of the North China Platform. Cambrian Furongian Series is made up of three third-order depositional sequences, Depositional Sequence 1 (DS1) in Changshan Formation and DS2 and DS3 in Fengshan Formation. Two beds of massive limestone of a shallow ramp facies developed in Changshan Formation and the first third-order sequence of Fengshan Formation. Both of them contains many dome-shaped carbonate structures that formed as a result of forced regression. These structures can be described as leiolitic bioherms, with a morphology like string of beads. In the current study, microorganisms such as Epiphyton, Girvanella and Renalcis are reported from the leiolitic bioherms. This provides not only documentation for the model of cyanobacteria calcification, but also describes the genesis of leiolitic bioherms by microbial processes inside cyanobacteria dominated microbial mats. Moreover, the diverse emergence of the calcified microorganisms represents the fossil evidence of calcified microorganisms' blooms in Cambrian Furongian and offers a reference for studying the complex microbial processes in such old carbonate depositions.