Petrographic and geochemical studies of dolomites of Ghorban member of the Sachun Formation in Ghareh anticline section, Southeast Shiraz

Dolomitic limestone and dolomite comprise the most part of Ghorban member of the Sachun Formation (Paleocene-early Eocene) in Ghareh Anticline section in southeast Shiraz. Geochemical and petrographic studies of these deposits indicate that these dolomites have formed in marine, meteoric and burial diagenetic environments. According to these studies, three types of dolomites have been recognized including dolomicrite (less than 16 µm), dolomicrosparite (16-62 µm) and dolosparite (more than 62µm). Evidences such as fenestral porosity, evaporate minerals (gypsum and anhydrite), intraclast and lack of fossil show that dolomicites have been deposited in supratidal environment. Dolomicrosparites which been formed due to recrystalization of dolomicrites and replacement of micrite, have higher amount of Fe and Mn, and lower amounts of Na, Sr and Mg. Quantities and contributions of the above mentioned elements are related to more diagenetic effect on dolomicrites and formation of these dolomites in medium to deep burial diagenesis environment. Dolosparites have been seen in three forms. The first form includes euhedral crystals of dolomite that have been replacement of red algae and micrite. Second form of dolosparites that consist of crystals with syntexial overgrowth, luminescence with zones consisting of light and dull bands and fluids inclusion are pore filling cements which form in burial diagenetic environment. Euhedral-subhedral, porous, destructive fabric with sucrose texture Dolosparites (the third form) in Sachun-Jahrum formations boundary have been interpreted as meteoric-marine mixing zone environment product.