Abstract
Deposits of Lower Carboniferous rocks in Kalmard block are recognized by Gachal informal formation, showing various characteristics in different outcrops. Lower Carboniferous deposits (Gachal formation) are composed chiefly of carbonate, evaporite and siliciclastic rocks. This formation is composed of 198 m sandstone, limestone and dolomite as well as a small amount of shale, marl and gypsum in the Madbeiki section. This formation unconformably underlies Precambrian metamorphic deposits (Kalmard formation) while lateritic soils of lower Permian (Chili formation) are depicted overlying an erosional unconformity above this formation. According to lithologic and microscopic investigations, the deposits of Gachal formation can be divided into 1 siliciclastic petrofacies, 1 evaporite microfacies and 16 carbonate microfacies. Field observations, along with microscopic examinations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the rocks of the studied formation. Vertical changes of microfacies and depth variation curve indicate the high thickness of the microfacies of tidal flat, lagoon and shoal environments and low thickness of the microfacies of open marine environment. The carbonate-evaporite-siliciclastic sequence of Gachal formation is made up of three third-order depositional sequence, separated each other by type 1 sequence boundary (SB1). Siliciclastic and evaporite deposits include LST system tract, and carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. Gachal formation rocks in Madbeiki section are deposited in a low-angle homoclinal ramp, mostly in the inner ramp, located in the southern Paleotethys Ocean. The depositional sequence identified in Gachal formation points to the age of Lower Carboniferous, conforming to upper Kaskaskia super sequence. The upper erosional boundary between Gachal and Chili formations conform to the global-scale sea level fall.
Highlights
Central Iran, shaped like a triangle and as one of the major, largest and most complex geological units in Iran, is located in the center of Iran
The third depositional sequence is like the first one, i.e. is composed of siliciclastic-carbonate deposits. This sequence contains a set of tidal flat to open marine parasequences and its maximum flood surface (MFS) is recognized by dolomitized crinoid bryozoan packstone
Depositional environment and sequence stratigraphy of the deposits of Gachal formation in Madbeiki section, the researchers came up with the following results: Deposits of Lower Carboniferous rocks in Kalmard block are recognized with Gachal informal formation, showing various characteristics in different outcrops
Summary
Central Iran, shaped like a triangle and as one of the major, largest and most complex geological units in Iran, is located in the center of Iran. Structural model of this area consists of separate blocks, separated by deep faults, and enjoy distinct characteristics. Kalmard Block, enjoying a northeastern trend, is situated between Kalmard faults in the east and those of Naein in the west [1]
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