TITLE:
Facies Interpretation, Depositional Environment and Sequence Stratigraphy of the Gachal Formation in the Madbeiki Section, Kalmard Block, East Central Iran
AUTHORS:
Soheil Erfani, Mohammad Hossein Adabi, Mahmood Reza Majidifard, Nader Kohansal Ghadimvand
KEYWORDS:
Lower Carboniferous, Kalmard Block, Gachal Formation, Depositional Environment, Sequence Stratigraphy
JOURNAL NAME:
Open Journal of Geology,
Vol.6 No.6,
June
27,
2016
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.