Diagenetic implications for the oolitic limestone in the Miaolingian Zhangxia Formation, Beijing (North China Platform)

The Cambrian Miaolingian in the North China Platform is characterized by wide-stretched deposition of oolitic grainstones within the Xuzhuang, Zhangxia and Gushan formations. Appraisal of ooid fabric and diagenesis provides significant information about the depositional environment and post-depositional features of the oolitic limestone in the Miaolingian Zhangxia Formation. Ooids are investigated for depositional environments, which contribute to several types of ooids that can be broadly grouped into two types, i.e., ooids preserving syn-depositional fabrics and diagenetically altered ooids. Microscopic examination revealed that the radial ooid surpasses other ooid types, accounting for 90% of the total grains. An insight into the diagenetic attributes by integrating the surficial diagenetic environments to several zones of the burial diagenetic regions preserved within calcite cementation provides instances for reconstruction of diagenetic history. Five diagenetic processes recognized through the ooids in the Zhangxia Formation are micritization, cementation, neomorphism, compaction and dolomitization. Most commonly observed cement types include syntaxial overgrowth, blocky, acicular, granular and radiaxial–fibrous cements, which demonstrate that a mixed marine to meteoric phreatic environment is the potential site for extensive porosity destruction.