Abstract
Middle Triassic carbonate sequences of Shotori Formation have a thickness of 70 m and are deposited Robat-e-Kalmard region of Tabas city in Central Iran basin. Gradationally and conformably overlying Sorkh shale Formation, Shotori Formation, mostly composed 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-coarsely crystalline dolomites. According to petrographic (fabric and grain size) and geochemical (elemental analysis of Ca, Mg, Na, Sr, Fe, Mn) evidence, five various types of dolomites were recognized in Shotori Formation. This variety results from early and late diagenetic processes, triggering a change in dolomitizing fluids and thereby forming various dolomites. Geochemical studies have revealed that the dolomites of Shotori Formation have formed under meteoric diagenesis and reducing conditions. Various dolomitization mechanisms are proposed for various types of dolomites; that is to say, Sabkha model is considered for type 1 dolomite, mixing zone model for type 2 and 3 dolomites and burial model for type 4 and 5 dolomites.
Highlights
IntroductionShotori Formation, with age of Middle Triassic (Anisian-Ladinian), is a thick-bedded
Geochemical studies have revealed that the dolomites of Shotori Formation have formed under meteoric diagenesis and reducing conditions
Various dolomitization mechanisms are proposed for various types of dolomites; that is to say, Sabkha model is considered for type 1 dolomite, mixing zone model for type 2 and 3 dolomites and burial model for type 4 and 5 dolomites
Summary
Shotori Formation, with age of Middle Triassic (Anisian-Ladinian), is a thick-bedded. Dolomite, coming in different types and shapes, is the major component of Shotori Formation. It can be found either in early or late forms, according to which the late dolomite forms immediately or short after deposition. This study employs a combination of petrographic and geochemical methods like main and trace elements to describe the dolomitic texture of Shotori Formation, their types and diagenesis process. This can assist in the determination of the origin of dolomites [1]-[8]
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