Stoichiometry, structure and ordering of dolomite crystal based on petrography, XRD and XRF data, (a case study of dolomites of Shahbazan Formation dolomits, SW of Kermanshah)

In this research, dolomites of Shahbazan Formation (Eocene) in southwest Kermanshah were studied. Two surface sections were measwred and 98 samples were collected. Four types of dolomites were identified based on petrographic examinations. XRD results were used for determination of stoichiometry, degree of ordering and proportion of dolomite in samples. Results suggest that dolomicrites and dolomicrosparites formed during (early marine diagenesis) in tidal flat setting. The dolosparites formed during late stage dolomitization from recrystallization and evolution of dolomicrite and dolomicrosparite precursor. Dolosparites exhibit better stoichiometry (ave. 52.98 mole% CaCO3) than their precursors (ave. 57.69 mole% CaCO3). Degree of ordering in dolosparites is also higher than dolomicrites and dolomicrosparites (ave. 0.95 and o.68 respectively). Average Mg2+/Ca2+ ratio in studied samples is 0.73. Hence it was concluded that dolomicrites and dolomicrosparites evolved into dolosparites during recrystallization and diagenetic alteration. These evidences along with lack of any evaporates suggest these dolomites formed from dolomitizing fluids with relatively low Mg2+/Ca2+ ratio (probably less 1) in humid climate.