Middle Ordovician multi-stage penecontemporaneous karstification in North China: Implications for reservoir genesis and sea level fluctuations

•Multi-stages of penecontemporaneous karstification in the Middle Ordovician occurred in North China.•The karstification was closely related to the upward shallowing sequences and generally stacked vertically.•Subaerial exposures and associated karstification strongly controlled the formation and heterogeneity of reservoirs.•The karstification indicates high-frequency relative sea level fluctuations and promotes cyclic carbonate reservoir prediction.