Construction model and paleogeographic distribution of Late Pennsylvanian phylloid algal–microbial reefs: A case study in eastern Inner Mongolia, North China

Abstract

The Gzhelian (Late Pennsylvanian) reefs of the Amushan Formation in eastern Inner Mongolia, North China, were formed by filamentous microbes and phylloid algae. Loosely accumulated prostrate phylloid algae provided substrates for growth of filamentous microbes to construct a rigid reef framework. Filamentous microbes grew parallel to the surfaces of phylloid algae, forming micritic encrustations. Subsequent developed stage of the filamentous microbes, growing perpendicularly to the phylloid algae surfaces, produced the peloid-A aggregations (concentrated areas of peloids of A type). The remaining spaces in the phylloid algal–microbial frameworks were filled by microbes that grew perpendicularly to the phylloid algae surfaces, generating peloid-B aggregations (concentrated areas of peloids of B type). Microbial sediment with various proportions of phylloid algae is a significant character of the Gzhelian buildups in the subtropical North China. North China buildups have similar reef-building organisms to the typical Tethyan buildups, but have a different construction model. As such, the subtropical North China buildups are considered as a sub-type of the tropical Tethyan buildups.