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Dolomitization Mechanism Based on Petrography and Geochemistry in the Shotori Formation (Middle Triassic), Central Iran

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Document pages: 20 pages

Abstract: MiddleTriassic carbonate sequences of Shotori Formation have a thickness of 70 m andare deposited Robat-e-Kalmard region of Tabas city in Central Iran basin. Gradationallyand conformably overlying Sorkh shale Formation, Shotori Formation, mostlycomposed of medium to thick dolomites (50 m), interbeded with thin lime and sandstones,is disconformable by a laterite horizon at its upper boundary. This Formation mainly consists of fine-to-coarselycrystalline dolomites. According to petrographic (fabric and grain size) andgeochemical (elemental analysis of Ca, Mg, Na, Sr, Fe, Mn) evidence, fivevarious types of dolomites were recognized in Shotori Formation. This varietyresults from early and late diagenetic processes, triggering a change in dolomitizingfluids and thereby forming various dolomites. Geochemical studies have revealedthat the dolomites of Shotori Formation have formed under meteoric diagenesisand reducing conditions. Various dolomitization mechanisms are proposed forvarious types of dolomites; that isto say, Sabkhamodel is considered for type 1 dolomite, mixing zone model for type 2 and 3 dolomites and burial model for type 4 and 5 dolomites.

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