Crystal structure characteristics and genesis analysis of Ordovician dolomite in North China

Based on the sedimentary background, this study combines petrology and XRD analysis to investigate the types and characteristics of Ordovician dolomite in North China, and discusses their origins, revealing the dolomitization mechanisms of the Ordovician. The results show: ① According to the crystal morphology and grain size of dolomite, five types of dolomite (LD1 ~ LD5) have been identified in the Lower Ordovician Liangjiashan Formation, while three types of dolomite (MD1~ MD3) have been recognized in the Middle Ordovician Majiagou Formation; ② The larger the dolomite crystal grain size, the stronger the degree of dolomitization and the higher the structural order. Meanwhile, a larger cell parameter (c/Å) value suggests a more disordered lattice and a faster dolomite crystallization rate; ③ LD1 and MD1 formed through supratidal evaporative pump dolomitization, while LD2 and MD2 resulted from reflux dolomitization. LD3 through LD5, along with MD3, formed during various stages of burial dolomitization; ④ During the sedimentation stage, a continuous sea-level decline influenced the initial distribution of the Liangjiashan Formation dolomite. Additionally, three regression stages in the Middle Ordovician were the primary periods for the formation of the Majiagou Formation dolomite, which was subsequently altered primarily by burial dolomitization. This study provides a new perspective on the dolomitization process of the Ordovician in North China.