Dolomite distribution's study of the Lower Miocene deposits (Qom Formation), southeastern Tehran, Central Iran

The sequence of Lower Miocene (Aquitanian-Burdigalian) of the Qom Formation is a significant formation in the Central basin of Iran, which is equivalent to the oil-bearing Asmari Formation in southwestern Iran. Petrographic studies of this sequence in the Yortshah anticline have studied and revealed that dolomitization is one of the most important diagenetic processes, which was affected carbonates of the Qom Formation. Various studies have shown the existence of nine types of dolomite in this anticline, of which dolomicrosparite is the main type of dolomite. The dolomites of this formation formed in four mechanisms, including sabkha, reflux, burial, and mixing zones. The dolomites of the Qom Formation are not large-scale layered, and the limestones are incompletely dolomitized, due to the many burial effects and the longtime of this stage of diagenetic processes, the burial model is likely to have the biggest impact on the dolomitization process of the Qom Formation. The existence of a high percentage of evaporative minerals in the Upper Red Formation, which is located over the Qom Formation, also the presence of clay and marly layers inside of Qom Formation could be the main sources of Mg supply for burial dolomitization, however, may be Mg be provided from brine water in deep sediment. Based on geochemical study aragonite is the main composition of preexisting limestone from which dolomites were formed in the Yortshah anticline.