Petrographic and geochemical investigation of the dolomites of the Shabazan Formation NW Semirom: A study of the dolomitization process in the eastern margin of the Foreland Zagros Basin

In order to understand the dolomitization processes in the eastern margin of the foreland Zagros sedimentary basin, the dolomites of Shahbazan Formation in the outcrop, located 6 kilometers north-west of Semirom, were studied by petrography and geochemistry. The Shahbazan Formation with a thickness of 74 m conformably overlaid on the terrigenous rocks of the Kashkan Formation and was covered disconformably by carbonate rocks of the Asmari Formation. Based on field evidence, petrography (including polarizing microscopes and SEM) and geochemistry of major, minor and rare earth elements (REE), four types of dolomites have been identified in the Shahbazan Formation. The results of this research indicate that the formation of very fine to fine crystalline dolomite occurred in tidal flat and other dolomites have been formed in shallow to intermediate deep burial diagenetic environments by moderately saline marine fluids (mean Na 363 ppm), via seepage reflux of evaporate seawater into the Shahbazan Formation platform.The similar distribution of the trace element versus Mg and REE pattern in the three dolomite types indicate that the Shahbazan dolomites formed a single diagenetic fluid with similar origin. The difference between the dolomite crystals size indicate variable water-rock interaction, temperature and depth of burial.