Biohermal complex dominated by microbial carbonates from the early Miaolingian (lower Cambrian) Maozhuang Formation, North China

The depositional period of the early Miaolingian Maozhuang Formation in the North China Platform (NCP) is characterized by sediments of a restricted tidal-flat facies zone, i.e., transgressive red bed (sabkha facies) and highstand dolostone, and by sediments of an open tidal-flat facies zone, i.e., transgressive red bed and highstand limestone. The Maozhuang Formation at the Jinzhouwan section is composed of sediments of an open tidal-flat facies in which highstand limestone is marked by a set of bioherms that represent rare examples of microbial carbonates in the NCP. They consist of stromatolites and leiolites with intercalations of oolitic grainstones that can be categorized into four units: Unit [1] encompasses large-scale columnar stromatolites, small quartz grains and trilobite fragments; Unit [2] consists of structureless leiolites that contain trilobite fragments, quartz grains, and few dark and dense clumps of micrite dominated by calcified sheaths of filamentous cyanobacteria which probably grew in relatively thick cyanobacterial mats; Unit [3] comprises radial ooids that contain abundant fossils of calcified sheaths of filamentous cyanobacteria that might be genetically involved in the formation of ooids; Unit [4] contains small columnar stromatolites and small-scale micritic clumps dominated by filamentous cyanobacteria. The filamentous fossils in units [3] and [4] provide useful information regarding the origin of radial ooids and stromatolites in normal marine environment. Further, the large and small columnar stromatolites of early Miaolingian age in units [1] and [4] represent a unique example because they belong to the first episode of cyanbacterial calcification at the base of Phanerozoic.