Formation Environment and Genesis of the Oncolite in Lower Cretaceous Liupanshan Group of Liupan Mountain Area
Oncolites were found in Lower Cretaceous Naijiahe Formation of Liupanshan Group in a tunnel of Sikouzi Reservoir in the Liupan Mountain. A study of their external core and lamination characteristics suggests that they were formed mainly in a turbulent and high-energy water-environment. CaO content of concolites reaches 48.18%, indicating obvious effect of the capturing and adhesion of calcium carbonate particles. Calcified algae itself and in situ precipitation of micro-organisms might also have been the causes for the formation of these concolites. In the study area concolites were formed in a high salinity, high temperature, hot and strong evaporation arid environment. A study of the formation environment of these oncolites in Liupanshan area shows that their formation environment was consistent with the tectonic setting at that time.