Facies Analysis, Sedimentary Environment and Sequence Stratigraphy of the Carboniferous Deposits of Gachal Formation, Eastern Central Iran (Rahdar Section)

Early carboniferous deposits of the Kalmard block, with various characteristics in different outcrops, are recognized by Gachal Formation. Generally speaking, this formation comprises of four different members (A, B, C and D), consisting of carbonate and evaporative rocks. Gachal Formation is composed chiefly of 55 meters sandstone and limestone interbedded with shale. According to the lithological and microscopic studies, Gachal Formation is deposited in beach, semi-restricted and open lagoon, shoal and open marine environments. Vertical changes of microfacies and the curve of its depth changes account for the high thickness of the facies of shoal and bar sub-environments and the low thickness of the facies of lagoon and open marine sub-environment as well. Gachal Formation rocks in Rahdar section are deposited in a low-angle?homoclinal ramp?located in southern Paleothysis Ocean. The carbonate-sandstone sequence in?Gachal Formation in Rahdar section is composed of a depositional sequence separated from each other by type 1 sequence boundaries. Deposits of this formation are separated from lower deposits by type 2 sequence boundary and from?Khan Group by unconformity. The sedimentary sequence identified in this formation points to the age of late Visean, conforming to Kaskaskia IV. The erosional boundary between Gachal and Khan Formations is relatively compatible with drop in sea level at Late Kaskaskia global scale.

Facies Interpretation, Depositional Environment and Sequence Stratigraphy of the Gachal Formation in the Madbeiki Section, Kalmard Block, East Central Iran

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.

Facies Analysis, Depositional Environment of the Lower Permian Deposits of Chili Formation in Kalmard Block, Eastern Central Iran (Darin Section)

Early Permian deposits in north of Kalmard region recognize with formal group of Khan;they have various features in the different place. This group includes four different formations from lower to the upper part: Chili, Sartakht and Hermez. These formations consist of carbonate rocks. Chili Formation has 104 m, thickness in Darin section and consists of limestone with intermediates of shale and marland sandstone. Lower boundary of this formation is disconformable with Gachal formation. The upper boundary is separated by unconformity from the upper part Sartakht formation according to the lithological characters and microscopic studies, cause identifications of beach, intertidal, open and semi-restricted lagoon, shoals and bar and open marine sub-environ- ments for the Chili Formation. Vertical changes of microfacies and depth changes curve show much more thickness of shoals and bar microfacies, and little thickness of open and semi-re- stricted lagoon and open marine microfacies. Deposits of Chili Formation in Darin section deposited in the gentle gradient Homoclinal ramp in the south of Paleotethys Ocean. Two depositional sequences have been identified in this formation, based on recognized Fusulinid, show age of Sakmarian, which has adaptation with Lower Absaroka III.

Sequence Stratigraphy of Lower Carboniferous Rocks in Bakhshi Section, East-Central Iran

The deposits of Lower Carboniferous rocks in Kalmard Block are characterized by Gachal informal formation, showing various properties in different outcrops. These deposits (in Gachal formation) are composed chiefly of carbonate, evaporite and siliciclastic rocks. This formation commonly hosts 190 m sandstone, limestone, dolomitic limestone and dolomite as well as a small amount of shale and marl in the Bakhshi section. It unconformably underlies Devonian deposits (Rahdar formation) while lateritic soils of lower Permian (Chili formation) are depicted overlying an erosional unconformity above this formation. The mixed carbonate-evaporite-siliciclastic sequence of Gachal formation is made up of three third-order depositional sequences, separated from each other by Type 1 sequence boundary (SB1). Siliciclastic and evaporite deposits include LST system tract, whereas carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. The depositional sequences identified in Gachal formation point to the Lower Carboniferous age, conforming to upper Kaskaskia supersequence. The upper erosional boundary between Gachal and Chili formations complies with the global-scale sea level fall.