Deposits of Permian rocks in Kalmard Block are recognized with Khan Group, showing various characteristics in different outcrops. This group is made up of three informal formations, namely Chili, Sartakht and Hermez. Upper Permian deposits (Hermez Formation) are composed chiefly of lateritic and carbonate rocks. This formation is composed of 65.5 m lateritic soils, lateritic sandstone, limestone, dolomite and dolomitic limestone in the Darin section. This formation unconformably overlies middle Permian siliciclastic and evaporite deposits (Sartakht Formation), where as it is depicted underlying an erosional unconformity above lateritic deposits of lower Triassic (Sorkh Shale Formation). According to lithologic and microscopic investigations, the deposits of Hermez Formation can be divided into 1 siliciclastic petrofacies and 14 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 point to the high thickness of the microfacies of lagoon, tidal flat and shoal environments and low thickness of open marine microfacies. Hermez Formation rocks in Darin section are deposited in a low-angle homoclinal ramp, mostly in the inner ramp, located in the southern Paleo-Tethys Ocean.
Central Iran zone, 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, thereby exhibiting distinct characteristics. Kalmard Block, enjoying a northeastern trend, is situated between Kalmard faults in the east and those of Naein in the west [
This section is located in the west of Tabas (at 1:250000 scale) [
To determine the facies characteristics and depositional environment conditions
in this section, the geological maps of Tabas (at 1:250000 scale) [
Upper Permian deposits (Dzhulfian-Dorashamian stages), composed of sandstone, limestone, dolomite and dolomitic limestone, are recognized by Hermez informal formation in Kalmard Block. One of the most comprehensive outcrops of Hermez Formation is situated in Darin section, in which deposits of Hermez Formation rocks have strike N18E, Dip 61NW and 65.5 m thickness. The lithology of Hermez Formation in Darin section is composed chiefly of sandstone, limestone, dolomite and dolomitic limestone, and, based on morphologic and lithologic characteristics, can be divided into six units including: a sequence of reddish, old lateritic soils and lateritic sandstone with 6 m in thickness (unit 1), which has unconformably overlain carbonate and siliciclastic deposits of Chili Formation (lower Permian), medium-to-thick, gray dolomitic limestone with 8.5 m in thickness (unit 2), medium-to-thin, yellow dolomitic limestone with 6 m in thickness (unit 3), a sequence of dolomitic limestone and thick-to-medium, light gray lime dolomite with 30 m in thickness (unit 4), thick-to-medium, reddish yellow dolomite with a thickness of 4 m (unit 5) and 11-meter, thick-to-medium, dark gray limestones (unit 6). The unit unconformably underlies medium-to- thin, reddish sequence of shale and lateritic and oxidized siltstone belonging to Sorkh Shale Formation (Lower Triassic).
Lithologic and microscopic studies reveal that this sequence consists of one siliciclastic petrofacies and fourteen carbonate microfacies. These siliciclastic petrofacies and carbonate microfacies of Hermez Formation are deposited on four facies belts including Tidal flat environment (A), Lagoon environment (B), Shoal environment (C) and Open marine environment (D). These facies belts, facing sea from the coast, include:
This facies belt includes one petrofacies and five microfacies. A1 is a siliciclastic petrofacies while A2 to A5 are carbonate microfacies. These petrofacies and microfacies are deposited in the supertidal and intertidal subenvironments, described as follow:
A1: Sublitharenite Petrofacies
This petrofacies involves 45% immature, well-sorted but relatively poor- rounded quartz, together with 10% rock fragments with 2 mm in size. The average size of grains ranges from 0.3 mm to 2 mm (
A2: Dolomitized Fenestral Gypsiferous Mudstone Microfacies
This facies is composed of 20% gypsum crystals in 0.2 mm size and fenestral fabric or bird’s eyes, lying within a lime mud matrix. This facies has undergone dolomitization process (
A3: Oxidized Dolomudstone Microfacies
This microfacies consists of microcrystalline dolomite or dolomicrite, oxidized by Fe (
A4: Fenestral Bioclast Mudstone/Wackstone Microfacies
This microfacies is completely covered by 5% to 10% microcrystalline lime mud and fenestral fabric or bird’s eye, intraclast and skeletal fragments (algae, benthic foraminifera, gastropod) (
A5: Fenestral Bioclast Intraclast Wackstone Microfacies
The analysis of the structure of this microfacies shows a composition of intraclast, 10% to 15% skeletal fragments and fenestral fabric or bird’s eye together with calcimicrobe algae, located within a lime mud matrix (
A6: Fenestral Benthic Foraminifera Intraclast Pelecypod Algal Wackstone/Packstone Microfacies
This microfacies hosts benthic foraminifera with 5% 0.2-mm-sized Globivavulina sp., 5% intraclast fragments with 0.2 mm in size, 5% pelecypoda with a size of 0.3 mm, 5% dasycladaceae algae with 0.3 mm in size and fenestral fabric and bird’s eye, situated in a lime mud matrix (
Interpretation
Petrofacies and microfacies of this group are formed in the semi-arid to arid supratidal and intertidal environments. Petrofacies A1 is a sublitharenite petrofacies, formed in the supratidal subenvironment and a warm and humid climateas a result of intense chemical weathering [
Microfacies of this group are recognized with abundant limemud. Bird’s eye or fenestral pores within the carbonate microfacies suggest deposition in tidal environment [
This facies belt is composed of three microfacies as follow:
B1: Intraclast Benthic Foraminifera Wackstone Microfacies
The most abundant allochem of this microfacies is 8% Globivavulina, Textularia, Earlandias, as a benthic foraminiferal species, with 0.3 mm in size together with 5% 0.2-mm-sized intraclast fragments, all located within a micritic matrix (
B2: Bioclast Intraclast Dasycladacea Packstone Microfacies
This microfacies hosts 30% dasycladacea algae, 30% intraclast fragments, 20% benthic foraminifera and 10% pelecypoda fragments with 0.3 mm in size, all of which are located in a micritic matrix. The grain size varies from 0.2 to 1.5 mm in size (
B3: Gastropod Pelecypoda Wackstone Microfacies
This microfacies shows a composition of 8% pelecypoda and 5% gastropod, all scattered within a micritic matrix. The average size of grains is 0.4 mm (
Interpretation
Microfacies of this facies belt share such characteristics as presence of lime mud, non-skeletal grains including intraclast and lagoonal bioclasts such as benthic foraminifera, dasycladacea algae, pelecypoda and gastropod, capable of surviving in restricted and semi-restricted conditions [
This facies belt consists of three microfacies as follow:
C1: Ooid Grainstone Microfacies
The major allochem in this microfacies is ooid, which constitutes 75% of the total sample and is 0.5 mm in diameter. The core of some ooids is composed of crinoid (
C2: Sandy Bioclast Ooid Extraclast Grainstone Microfacies
This microfacies is composed chiefly of 35% intraclast. 15% concentric ooids, 5% bioclast fragments and 10% quartz grains are among other allochems of this microfacies. The average size of the grains ranges from 0.2 to 3.5 mm (
C3: Bioclast Bryozoan Grainstone Microfacies
This microfacies hosts various bioclast fragments including 40% crinoids with 1 mm in size, 10% intraclast with 0.4 mm in size and 15% medium-sorted and rounded quarts grains, located in a micritic matrix (
Interpretation
This facies belt is formed in high-energy shoal setting and below the wave effect due to the presence of non-skeletal fragments such as ooid, intraclast and extraclast and lack of limemud [
This facies belt is composed of three microfacies as follow:
D1: Ostracod Wackstone Microfacies
This microfacies includes 10% 0.1 to 0.2-mm-sized ostracod and 3% 0.1-mm- sized radiolarian, located in a dark micritic matrix (
D2: Dolomitized Archaeodiscus Radiolarian Wackstone/Packstone Mi- crofacies
This microfacies contains 30% radiolarian with 0.1 mm in size and 10% archaediscus with 0.3 mm in size, all scattered within a micritic matrix. It is noteworthy that dolomitization has influenced this microfacies (
D3: Sandy Intraclast Bioclast Packstone Microfacies
The composition of this microfacies shows various bioclast fragments including 40% 1-mm-sized crinoid, 10% 0.4-mm-sized intraclast and 15% medium- sorted and rounded quartz grains, located in a micritic matrix (
Interpretation
The intergranular muddy matrix [
tracod [
According to the microscopic and field observations, vertical relationship between microfacies and the comparison made between microfacies of Hermez Formation and current depositional microfacies, the depositional model of Hermez Formation in Darin section is presented in
These microscopic microfacies consists of orthochem and allochem components, the type of matrix or cement and the type of skeletal and non-skeletal. The frequency percentage of allochem is computed by polarizing microscope and depicted separately for each allochem. It is noteworthy that only two samples of unit1 are studied due to their lateritic and nonremovable nature (
Having analyzed the facies, depositional environment and sequence stratigraphy of the deposits of Khan Group (Hermez Formation) in Darin section, the researchers came up with the following results:
Upper Permian rocks (Dzhulfian-Dorashamian stages) are recognized by Hermez informal formation and consist of sandstone, limestone and dolomitic limestone. One of the most comprehensive outcrops of Hermez Formation is situated in Darin section and is 65.5 m thick. According to the carbonate composition of the rocks in this formation, accompanied by siliciclastic deposits (sandstone of unite 1), deposits of this formation are formed in a warm and humid climate and close to the siliciclastic deposits supply. Investigating the lithofacies of the deposits of Hermez Formation in Darin section resulted in identifying 1 siliciclastic petrofacies and 14 carbonate microfacies. Regarding microscopic and field observations, siliciclastic petrofacies and carbonate microfacies of this section, facing sea from the coast, include: tidal flat environment, lagoon environment, shoal environment and open marine environment. The vertical and lateral changes of microfacies and comparing them with late and early depositional environments indicate that lack of calciturbidite deposits, slumps, barrier reef and oncolite and presence of gradational facies have caused the mentioned deposits to be formed in a low-angle homoclinal ramp, mostly in the inner ramp, located in the passive margin of southern Paleo-Tethys Ocean.
Emraninasab, B.H., Adabi, M.H., Majidifard, M.R., Ghadimvand, N.K. and Erfani, S. (2017) Facies Analysis and Depositional Environment of Upper Permian Rocks in Darin Section, East-Central Iran. Open Journal of Geology, 7, 242-256. https://doi.org/10.4236/ojg.2017.73017