شواهد ژئوشيميائي براي تشخيص كاني شناسي اوليه كربنات هاي سازندهاي سروك، سورگاه و ايلام در مقطع شيوند-تاقديس منگشت

Geochemical evidence for recognition of original carbonate mineralogy of the Sarvak, Surgah and Ilam Formations in Shivand section Mongasht anticline

Sarvak, Surgah and Ilam Formations from Bangestan Group with Cenomanian to Santonian age consist of carbonate units and have a total thickness of 679 m in Mongasht Anticline, Shivand area, 45 km southeast of Izeh, in Zagros basin. Recognition of original carbonate mineralogy based on petrographic evidence is difficult, because aragonite and high Mg calcite transformed to low Mg calcite during diagenesis. Major (Ca, Mg) and minor elements (Sr, Na, Fe, Mn) and carbon and oxygen isotope values used to determine carbonate mineralogy in Sarvak, Surgah and Ilam Formations. Bivariate plots of major and minor elements and oxygen and carbon isotopes values indicate that aragonite is the original carbonate mineralogy in studied formations. Major and minor elements, and oxygen and carbon isotopes values , along stratigraphic columns were used to distinguish between Sarvak, Surgah and Ilam Formations . Paleotemperature calculation based on oxygen isotope values of the least altered samples indicate that sea water temperature during precipitations of Sarvak, Surgah and Ilam Formations were 27?C (-3.49 %oPDB), 31?C (-4.40 %oPDB), 261C (-3.21 %oPDB) respectively.