Oolitic Limestone Induced by Photosynthetic Biofilms in the Xuzhuang Formation of Nangao Section, North China

Abstract

The role of biofilms in the formation of ooids is a focal point of current research. This study synthesizes macroscopic data with microscopic observations to analyze the depositional environment and genesis of oolitic limestone within the Xuzhuang Formation at the Nangao section. Notably, cerebroid ooids with unique cortical morphologies have been discovered. Within the nucleus, cortex, and the lumps among the ooids, a high-density preservation of Girvanella has been identified. Clotted micrite structures have also been observed within the filler content. The findings suggest that phototrophic biofilms have facilitated the formation of oolitic limestone in this profile, offering direct evidence for the connection between the festooned cortical morphologies and biofilms. This study further questions the interpretation of clotted micrite structures as sponge remains. These insights significantly enhance our understanding of the causal factors behind ooid formation.