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

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.

Lower Cambrian facies architecture and sequence stratigraphy, NW France: framework for evaluation of basin-wide processes of sedimentation

“…2). This is common in carbonate platforms, with various models available to explain the systematic distribution of dolomite and limestone (Rahimi et al 2016). A terrestrial source of high-Mg waters is favoured in this case, which promoted dolomitization of limestone close to shore and/or close to the unconformity.…”

“…A terrestrial source of high-Mg waters is favoured in this case, which promoted dolomitization of limestone close to shore and/or close to the unconformity. Dolomitization is interpreted to have occurred during early diagenesis and shallow burial as high-Mg meteoric pore waters mixed with those of marine phreatic origin (Humphrey & Quinn, 1989;Rahimi et al 2016).…”

Dolomite genesis in bioturbated marine zones of an early-middle Miocene coastal mud volcano outcrop (Kuwait)

“…Interestingly, a nanoscale in-situ observation using atomic force microscopy (AFM) has shown that the precipitation of gypsum is coupled with dolomite dissolution 59 . The absence of fossils in MV1 can be related to dolomitization in the upper tidal flat environment 60 . MV1 is possibly a re-worked carbonate material from the vents during sediment extrusion thereby abrading pre-existing earlier dolomite of spheroidal nature.…”

Dolomitization Mechanism in the Chorgali Formation (Eocene), Pakistan: Evidences from Field observations, Petrography, Mineralogical and SEM analysis

“…Thus, hypersaline fluids, usually produced by high rates of evaporation, resulting in the precipitation of dolomites along with gypsum and anhydrite (Mckenzie, 1981). During petrographic examinations, fine crystalline dolomite (Df) exhibited small crystal size and planar intercrystalline boundaries with fabric retentive character are the possibilities of the dolomites formed in supratidal and intertidal realms in the early stage of diagenesis near-surface lowtemperature conditions (Figure 3a-d;Saller, 1984;Gregg and Sibley, 1984;Land, 1985;Sibley and Gregg, 1987;Mitchell et al, 1987;Gregg and Shelton, 1990;Rahimi et al, 2016). According to Shah, (2009) the epeirogenesis experienced resultant emergence in various areas of Pakistan, and this caused unconformities of varying magnitude.…”