Understanding the origin of ancient carbonate ooids: recent findings
Muhammad Riaz, Santanu Banerjee, Khalid Latif, Ziliang Liu, Mohamed S. Ahmed, Douaa Fathy
Abstract
The origin and micro-texture of ooids remain controversial. This study presents a review of microstructure of ooids and explains the origin of microstructures in Cambrian ooids in the North China Platform. Factors controlling the morphology and mineral composition of ooid are very complex. Ooids form by a combination of physical, chemical and biological processes, in various environments. Recent studies on modern Bahamian ooids and laboratory experiments with microbial cultures highlight the formation of ooids without detailed explanation of the role of amorphous calcium carbonate (ACC). This review reinforces the biochemical hypothesis for the origin of ooids and proposes the sequence of microbial activities that involves the active and stationary stages in its formation. Microbes, particularly the filamentous fossils of calcified sheath of cyanobacteria, excrete extracellular polymeric substances (EPS) that act as a template for the formation of ACC. The dark micrite bands, dominated by filamentous cyanobacteria within the cortex and the core of the Cambrian pelagic and benthic ooids of the North China Platform supports the biochemical origin of ooid formation.