Characteristics and genesis of microbial lumps in the Maozhuang Stage (Cambrian Series 2), Shandong Province, China

Microbial lumps have been found in the Maozhuang Stage (Cambrian Series 2) in the Liangcheng section, Shandong Province, China. Their macro- and micro-scale features distinguish them from other carbonate particles such as intraclasts and oncoids. Most lumps have a coarse sand to pebble size. They were mostly rounded during sedimentation or combined to form irregular shapes. A distinct boundary is present between the lumps and the surrounding cement of sparry calcite. The lumps contain either no core at all or several irregular “cores”, without a distinct inner texture. They are composed mainly of calcified (micritized) microbes, most likely cyanobacteria. The microbes drilled holes in carbonate grains, after which lumps formed by micritization, cementation, and agglutination by an extracellular polymeric substance (EPS) in a high-energy shallow-marine, subtidal environment. As the lumps are directly related to microbes, they should be considered as microbialites.