Petrography and study of dolomitization model of Shahbazan Formation using elemental analysis(Zagros sedimentary basin, south of Lorestan)

Shahbazan Formation with Eocene age is widely developed in Lorestan basin. In the study section, this formation with a thickness of 62 meters is located on the Kashkan Formation and is discontinuously below the Asmari Formation. The lithology of Shahbazan Formation in the study area includes dolomitic carbonate rocks. In order to study micro-facies, 60 samples of this section were collected and 20 samples were selected for elemental analysis. Based on field observations, lithographic and geochemical evidences based on elemental analysis by (EPMA) and (EDS) methods, two groups of dolomite were identified. Primary dolomites include dolomicrites in size between 4 to 10 microns that represent the formation of a tidal zone environment. Secondary dolomites include dolomicrosparite in size between 10 to 20 microns, dolosparites larger than 50 microns that is formed in a shallow to medium burial diagenesis environment due to the seepage of evaporated basin floor brines in to the carbonate platform on Shahbazan Formation in the study area. Low values of Fe versus high values of Sr and Na in dolomicrites, and high concentration of Fe in dolomicrosparite and dolosparite with some evidence such as intraclast, fenestral prosity and lack of evaporative minerals, indicate that these dolomites have been formed from the tidal model, seepage and then shallow to moderate burial. Geochemical evidence showed that the studied dolomites are non- stoichiometric, which can be explained the age of Shahbazan Formation.