Calcifying cyanobacteria in dendrolites of the Cambrian Zhangxia Formation: A case study of the Houziyu section in Ezhuang Town, Zibo City, Shandong Province

Dendrolites develope at the top of the Cambrian Zhangxia Formation in Houziyu section, Ezhuang Town, Zibo, Shandong. According to the sedimentary facies characteristics reflected by the macroscopic lithology changes in the outcrop, the sequence of the Zhangxia Formation in the study area can be divided into three fourth-order sub-sequences. As more and more evidence indicating the microbial influence on the dendrolite formation process continues to accumulate, the widely accepted view of the "CCM mechanism triggering the calcification of cyanobacterial sheaths" is challenged. This paper integrates field exploration sampling and thin-section analysis to identify and subsequently describe the fabrics of the dendrolites under the microscope. Their genetic mechanisms are further analyzed by comparing them with modern examples. The main components of the dendrolites are dark micrite matrix, sparry calcite, and detrital grains. Microscopically, calcified cyanobacteria fossils, including Epiphyton, Hedstroemia, Renalcis, and Bacinella, as well as Lithocodium-like fabrics, are observed within the dendrolites. Through the study of various types of calcified cyanobacteria and their calcified microbial membrane residues in the dendrolites of the study area, a detailed supplement has been made to the diversity of calcified microorganisms found in dendrolites. It is clear that the dendrolites are the product of the calcification of microbial films or mats dominated by cyanobacteria such as Epiphyton. Extracellular polymeric substances (EPS) play a crucial role in the development and mineral precipitation of dendrolites, providing a typical example for the "microbial influence" genesis of dendrolites.