Geochemical and petrographical research on dolomites in Lower Cretaceous rocks, Esfahan province

The study area is located to the south، west and north Esfahan province. this research is geochemical and petrographic study of Lower cretaceous dolomites. Five dolomite type have been identified. The first type is very fine-fine crystalline dolomite formed in near surface conditions and in early stages of diagenesis، in tidal flat to lagoonal environments. The Sr content is high (2537ppm) and Fe (8861ppm) and Mn (852ppm) is low. The second type is fine-medium-grained، subhedral to euhedral، crystalline dolomites. Compared to the first type، Sr content is lower and Fe and Mn content is higher. This type of dolomites is most likely formed in early burial diagenesis. The third type is medium-coarse-grained، euhedral and subhedral، crystalline dolomite and show clear rim and cloudy center. Compared to the type1 and type2، this type of dolomite contains higher Fe and Mn and lower Sr. They are likely formed in deeper burial diagenesis and by dolomitization of earlier calcareous deposits or recrystalization of first- and second- type dolomites. The medium-coarse-grained، crystalline dolomite fill in pores and fractures، and are called «four-type» in this study. This type of dolomite is likely formed during late diagenesis and under conditions of medium pressure and temperatures less than 60-80 °C. In this dolomite values of Fe and Mn increase from the fringes of pores and fractures to the center. The fifth dolomite type is coarse، crystalline، saddle dolomite filling pores and fractures. This dolomite