afshin zohdi

Tozlou Pb-Zn mineralization, ~250-300m long, and ~50m thick, is hosted by limestone units of the Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Mineralization at Tozlou can be divided into five stages. Stage 1 is the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is categorized with dolomitization processes along with minor pyrite. Stage 3 occurred as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 includes late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes. Hydrothermal alterations include decarbonatization, carbonatization ± silicification, and late carbonatization. Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements pattern of ore samples, fresh and altered limestones is similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Characteristics of Tozlou occurrence are comparable with intermediate-sulfidation type of epithermal deposits.

Epithermal deposits are a group of base/precious-metal deposits that are formed by hydrothermal fluids in shallow environments under pressure/temperature changes and fluid-rock interactions (Hedenquist et al., 2000). Based on the host rock, epithermal deposits are divided into volcanic-hosted deposits and sedimentary-hosted deposits. According to the tectonic setting and magma type, they are divided into calc-alkaline magmas (including three subcategories of high-, intermediate-, and low-sulfidation) and alkaline magmas (White and Hedenquist, 1990; Cooke and Simmons, 2000; Hedenquist et al., 2000; Simmons et al., 2005). These types of deposits include a continuous range of deposits formed by magmatic/meteoric fluids and show different geometry, but have the same formation mechanism, especially the hydrothermal fluids circulation (Sillitoe and Hedenquist, 2003; Simmons et al., 2005).
Sedimentary rock-hosted deposits are divided into two groups: Carlin-type and sediment-hosted disseminated deposits. Carlin-type deposits are often formed as strata-bound or replacements at the boundary of rock units and are controlled by faults. They are distinguished by invisible Au in As-rich pyrite and arsenopyrite and do not show compatible spatial relationships to magmatic centers (Kuehn and Rose, 1992). Sediment-hosted disseminated deposits occurred as disseminated ore in sedimentary rocks (Hofstra and Cline, 2000). These deposits are physically and chemically comparable to Carlin-type deposits, but spatially and temporally are related to sub-volcanic porphyry intrusions (Theodore et al., 2000; Hofstra and Cline, 2000).
Tozlou Pb-Zn occurrence is 50km south of Qeydar in Zanjan province. This occurrence was first discovered/explored in 2017. Although general geological characteristics of Tozlou occurrence have been determined (Majidifard and Shafei, 2006), the mineralogy and origin of Tozlou occurrence have not been studied in detail. Here, detailed geology, mineralogy, alteration styles, and geochemistry of Tozlou occurrence are investigated to constrain the genetic model and type of its mineralization system. These results may have implications for future exploration of base-metal mineralization in this region and nearby areas. 

Comprehensive field and laboratory works have been carried out on Tozlou area. During the fieldwork, a detailed stratigraphic section of limestone units of Qom Formation was measured, sampled, and described. Fifty samples were collected from ore zones and limestone host rocks for laboratory analysis. Then, 34 thin and 15 polished-thin sections were prepared for mineralogical studies in the laboratory at the University of Zanjan, Iran. Fourteen typical samples from the ore zones and fresh/altered host limestone were analyzed for geochemical analysis using ICP–MS in Zarazma Analytical Laboratories, Tehran, Iran.

The main rock units exposed in Tozlou occurrence belong to Eocene sequence, Lower Red Formation, Qom Formation, and Quaternary units. Small outcrops of gabbro-gabbro diorite (gb) can also be seen in this region. Eocene strata include brown thin-bedded sandstone (Unit Es), alternating tuff and shale (Unit Etsh), and thin- to medium-bedded tuffs (Unit Et). Lower Red Formation includes a polygenetic conglomerate (Unit Ollrc) of Oligocene age. Qom Formation consists of massive- to medium-bedded cream-to-grey limestones (Unit OMql) and alternating marl and thin-bedded grey limestone (Unit OMqml). Quaternary units include terrigenous sediments.
Pb-Zn mineralization at Tozlou has ~250-300 m leng and ~50 m thick and is hosted by limestone units of Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Decarbonatization, carbonatization±silicic, dolomitization, and late carbonatization are hydrothermal alterations in Tozlou area. Mineralization processes at Tozlou can be divided into five stages. Stage 1 comprises the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is represented by the dolomitization of the limestone host rock, which is accompanied by minor pyrite. Stage 3 occurs as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 is characterized by late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes.
Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements patterns of ore samples, fresh and altered limestones, are similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Despite carbonate host rock, we think that mineralization at Tozlou is similar to the intermediate-sulfidation style of epithermal base metal deposits.

The chronological and paleoenvironmental settings of the Sirenia-bearing strata in the Zagros Basin of Iran were studied in four sections. These sections, located in the Izeh (Asmari Formation), Interior Fars (Gachsaran Formation), and Coastal Fars (Mishan Formation) zones of the Zagros Basin, were investigated for the details of their micropaleontology, biostratigraphy, and microfacies. A total of 113 thin sections were analyzed. Fossils from the Asmari Formation and the Gachsaran Formation were younger (Burdigalian), while those from the Mishan Formation were older (Aquitanian). Thirteen carbonate microfacies were identified in three facies belts; tidal flat, inner ramp, and middle ramp. The tidal flat facies association included mudstone microfacies. Inner ramp facies association consisted of bioclast with porcelaneous tests wackestone, peloid and miliolids packstone to grainstone, bioclast and miliolids wackestone to packstone, benthic foraminifera grainstone, red algae with bryozoan and miliolids wackestone to grainstone, and echinoid and miliolid packstone to grainstone facies. Middle ramp facies association was comprised of red algae and meandrous coral packstone to rudstone, coral floastone, bioclast and bryozoan wackestone to packstone, echinoid and bryozoan packstone, bryozoan and benthic foraminifera wackestone to packstone, and echinoid and bioclast wackestone facies. A shallow carbonate ramp was identified as the habitats of sea cows in the Aquitanian-Burdigalian of the Zagros Basin.

Ghezeljeh deposit is located in the Central Iranian zone, in the Zanjan province and northeast of the Mahneshan city. The rock units in this area belongs to the Oligo-Miocene, which contain Lower Red, Qom and Upper Red formations. The Upper Red Formation in Ghezeljeh region has about 750 m thickness and mainly consists of brown to green marl intercalations with sandstones. In this area, the alternation of marl and sandstone sequences contain sandstone layers with thickness about 2 to 8 meters, which in two horizons, the copper-lead and zinc mineralization has occurred. Copper mineralization, in addition to being observed inside the sandstone unit. In the Ghezeljeh deposit, the host rocks of the copper ores, are gray sandstones and conglomerates which are intercalated with red and gray marl units. According to field and microscopic studies, the main ore mineral consist of pyrite, chalcocite, chalcopyrite, bornite, galena and sphalerite which associated with the secondary minerals such as serosite, malachite, azurite, covellite, smithzonite and goethite. The ore mineral textures consist of disseminate, framboidal pyrite, solution seams, interparticle cement, replacement and relict. Preliminary fieldwork studies in the Ghezeljeh region also show that organic matter including plant remains and diagenetic pyrite are the effective factors to concentrate and mineralization. It is considerable that the grade of lead, zinc and copper, in Ghezeljeh deposit are 6%, 3% and 1%, respectively. Generally, host rock, tectonic setting, sedimentary environment, mineralogy, texture, mineralization control factors all confirm that the studied mineralization has more similarities with Redbed type copper deposits.

This study aims to investigate the use of hydraulic fracturing in the Bangestan reservoir in one of the major fields, which is in southwest Iran. It is a tight reservoir with natural fractures. Because hydraulic fracturing is one of the reservoir development techniques, it is extremely critical to determine the in situ stresses in order to assess the effectiveness of this technique in enhancing the reservoir’s production. For this purpose, a one-dimensional geomechanical model of the reservoir was developed. Geomechanical modeling was created based on the data available from the studied oil field wells as well as pre-existing experimental and mathematical correlations. The following criteria were determined for the candidate layer for hydraulic fracturing operations in the second stage of the research after determining the required geomechanical parameters: (1) appropriate porosity, (2) low in situ stress, (3) low water saturation, (4) low uniaxial compressive strength, and (5) high difference between the minimum and maximum horizontal stresses. The results of this study led to the selection of layer 3 of the reservoir as the target layer for hydraulic fracturing.

Stratigraphic and sedimentology studies have been carried out on sixty-nine rock samples related to the one hundred fifteen meters thickness of the Dalichai and Lar formations in the southeast of Zanjan. The carbonate layers of the Dalichai Formation with seventy-eight meters thickness overlay the strata of the Shemshak Group/Formation (the boundary has been covered) and are overlaid by thirty-seven meters thickness of carbonate layers of the Lar Formation with gradual boundary in this area. There are some sedimentological changes in the succession across the Dalichai-Lar formations boundary such as color changes, bedding thickness changes from medium to thick, disappearance of Thalassinoides facies, chert nodules, and Ammonite/Belemnite facies and finally changes in microfacies from mudstone to the wackestone/packstone (deeper to the shallower). The Lar Formation is the youngest formation in this area that has been covered by the Quaternary sediments. Five lithofacies have been identified based on field and microscopic studies: 1- Pelloidal packstone with intraclasts, 2- Pellet/oncoid wackestone/packstone, 3- Mudstone with Thalassinoides, 4- Bositra buchi pelagic packstone and 5- Pelagic mudstone that shows basin and outer ramp as depositional environments for the Dalichai and Lar formations in this section. Field and facies studies show a deepening upward trend to the middle parts of the section (upper parts of the Dalichai Formation) and followed by shallowing upward trend to the upper parts (Lar Formation) of the section.

In this study, by integrating sedimentologic data with geochemical data, the sequence stratigraphy framework of the Sargelu and Najmah formations in the Hawraman region of NW Kermanshah were studied. Three depositional sequences of the type “T/R facies cycles” including TR1–TR3 were recognized in the Sargelu Formation. The occurrenceof dark, organic-rich shale and bituminous limestone in these sequences together with depleted δ13C values with some striking negative excursionsin intervals with outer shelf/basin facies indicates a rapidly enhancing accommodationspace during the development of these depositional sequences leading to the prevalenceof deep marine deposition, particularly during the transgressive systems tracts (TSTs). In addition, three other T/R facies cycles were recognized in the Najmah Formation. Facies stacking patterns and internal architecture of these depositional sequences along with the existence of peaks in the δ13C to heavier values suggests their deposition during limited accommodationspace. At the contact between the Sargelu and Najmah formations, there occurreda positive peak in δ18O, which most likely is an indication of a local climate change at the Middle-Late Jurassic interface. The correlation of depositional trends of the TST and RST with that of δ13C may show that eustatic acted as the main control on the variations of δ13C.

The study of the effect of global regression on the Middle Miocene (upper parts of the Qom Formation and Lower parts of the Upper Red Formation) strata has been carried out on two stratigraphic sections in the Zanjan area, northwest Iran. Lithological and microfacies analysis shows that these carbonate strata gradually turn to clastic (sandstone and conglomerate) and, in some regions, turn to evaporate deposits. Microfacies studies also confirm this sedimentary facies changes. Thus, the pelagic wack/packstone microfacies gradually change to sandy bioclast pelagic wack/packstone and finally, at the top of the section changes to the continental sandstone. Facies and lithological changes confirm the shoreline regression that can be correlated with the eustatic sea-level curve. Evaporitic strata in some parts of this area show small restricted basins because of this event. The eustatic sea-level curve in the Langhian and Serravallian ages shows global sea-level fall that can be correlated with the global oxygen isotope changes and glaciation events at this time. Therefore, we can conclude that the Middle Miocene strata have been affected by this global regression in the Zanjan area.

IntroductionThere are several carbonate-hosted Pb–Zn (F–Ba) deposits in the central Alborz zone hosted by upper part of Elika Formation. From an economic point of view, the most important deposits discovered to date are Sheshroudbar, Pachi Miana, Kamarposht and Era. It makes the central Alborz zone as one of the most important Pb–Zn (F–Ba) districts in Iran. In this district, Elika Formation is restricted by NE–SW-trending reverse faults, and thrusted over the Shemshak Formation. The main orebodies occurred in open spaces which formed due to angles between normal and reverse faults in the carbonate rocks of Elika Formation (Tabasi, 1997). Some of these deposits have been studied, and various models such as syn-diagenesis to epigenetic are presented for ore genesis (Alirezaei, 1989; Gorjizad, 1996; Rastad and Shariatmadar, 2002; Rajabi et al., 2013; Vahabzadeh et al., 2014; Nabiloo et al., 2018).Sarcheleshk is an abandoned mine of Pb–Zn (F–Ba) mineralization in the central Alborz zone. Except for small-scale geological maps of the area, i.e., 1:100,000 geological map of Pol-e-Sefid (Vahdati Daneshmand and Karimi, 2004) and Semnan (Nabavi, 1988), previous studies of Pb–Zn (F–Ba) mineralization at Sarcheleshk was limited and include Mohammadi Lisehroudi (2019). In this contribution, we provide the first detailed geological, mineralogical and geochemical studies in the Sarcheleshk deposit to reveal more details of the type and genetic model of ore formation. Materials and methodsDetailed field work has been carried out at different scales in the Sarcheleshk area. A total of 60 samples were collected from various parts of orebodies, host carbonate and mafic igneous rocks. The samples prepared for thin (n=32) and polished-thin (n=12) sections in the laboratory of University of Zanjan, Zanjan, Iran. Representative 8 samples from the ore zone, 1 sample from barren dolomitic limestone and 3 samples from mafic igneous rocks, were analyzed for major, trace and rare earth elements using XRF and ICP–MS in the Zarazma Analytical Laboratories, Tehran, Iran. Discussion and conclusionThe Sarcheleshk Pb–Zn (F–Ba) deposit is located 20 km southwest of Pol-e-Sefid, Mazandaran province. The most important rock units exposed in this area include early to middle Triassic dolomitic limestone (Elika Fm.), late Triassic gypsum, dolomitic limestone and marl (Paland Fm.), late Triassic mafic igneous rocks, late Triassic to early Jurassic shale, siltstone and sandstone (Shemshak Fm.), middle Jurassic ammonite-bearing marl, calcareous marl and marly limestone (Dalichay Fm.), late Jurassic cherty limestone and dolomitic limestone (Lar Fm.), and early Eocene Alveolina–Nummulitic limestone (Ziarat Fm.).Mineralization at Sarcheleshk occurs as strata-bound orebodies hosted by dolomitic limestone of Elika Formation, and controlled structurally by faults, fractures and dissolution collapse breccias. The ore veins have a varying width from 0.5 to 1.5 m. Detailed field geology and petrographic studies indicate that wall-rock alterations developed at the Sarcheleshk deposit include dolomitization, silicification, and calcitization. The ores at Sarcheleshk are dominated by galena, sphalerite, pyrite, fluorite, and barite, with lesser, chalcopyrite, and tetrahedrite, all of which are hosted by a dolomite, calcite, and quartz gangue assemblage. The ore minerals show vein-veinlets, open space filling, brecciated, rhythmic, disseminated, replacement, and relict textures. The mineralization process at Sarcheleshk can be divided into three stages. Stage 1 is diagenesis stage represented by rhythmic texture of fluorite, galena, sphalerite, and calcite bands. Stage 2 (epigenetic stage), volumetrically most important, is marked by fluorite-sphalerite-galena-pyrite-chalcopyrite, barite-pyrite and barite-calcite, and late stage calcite veins and veinlets. Stage 3 is the supergene mineral assemblages consisting of smithsonite, cerussite, chalcocite, covellite, azurite, and goethite. The ore samples and mafic igneous rocks show different Chondrite-normalized trace and REE patterns, indicating that they are genetically unconnected. It is declined syn-sedimentary and/or hydrothermal igneous origins for the Sarcheleshk deposit, and specify that basinal brines may have played a role in Pb–Zn (F–Ba) mineralization at Sarcheleshk deposit.Our data suggests that Sarcheleshk deposit is a F–Ba-rich MVT deposit and is comparable with other Pb–Zn (F–Ba) deposits of central Alborz zone.

Toryan area is located in the Central Iranian zone, about 120 km northwest of Zanjan. In this area, the exposed rock units belong to the Upper Red Formation (URF). The thickness of the URF at Toryan is 1010 m, and consist of four main parts. These parts, from bottom to top, consist of: 1-alternation of gypsiferous (locally salt) green marls (300 m), 2-alternation of red marls and grey to red sandstones (275 m), 3-alternation of red and green marls intercalated with sandstone (210 m), and 4-green marls with interbedded green siltstones (225 m). Based on microscopic studies, average particle size of sandstones in the Toryan area is about 0.2 mm. These sandstones also display poor orientation, poor to moderate sorting, and mainly are angular to semi-angular. Based on component types and results of point counting, the studied sandstones contains 16% quartz (included mono and poly-crystalline with both straight and wavy extinction), different types of rock fragments (sedimentary, metamorphic and volcanic) and 10% feldspar (mainly ortoz). According to Folk (1980) classification, it can be stated that the studied sandstones are litharenite to feldspathic litharenite with calcite and evaporitic cements. Based on the main components and the results of petrographic, major and minor elements geochemical analyses, the tectonic setting of these sandstones is related to foreland and collision basins. These data represent an intermediate to felsic source rock for these sandstones, which were affected by semi-arid to arid climate.

Early to Middle Triassic carbonate sequences of Elika formation in Zal Section (South of Julfa, NW Iran), consist of two different lithology: limestone and dolomite. The thickness of this formation is about 377 m and contains nine different units. The two upper units (8 and 9) are mainly dolomites with thickness of 78 m. The transition between limestone and thick-bedded dolomite in this formation is gradual with the presence of medium-bedded dolomitic limestone lithology. Petrographic results and geochemical analysis clearly show that these dolomites are mainly type I (dolomicrite). Dolomite crystals formed in shallow burial environment (reduction conditions), which affected by marine fluids with little chemical change during dolomitization. The result of XRD analysis in different types of dolomites shows that most of the dolomites of the Elika formation are so close to stoichiometric state and the amount of Mol/Percent of MgCO3 in these dolomites are between 46.7 to 50.4. The Elika dolomites deposited in shallow marine environments (supratidal to intertidal) with high rate of evaporation and salinity, which led to form very fine dolomite along with some silt-sized quartz. The presence of ooid, primary sedimentary structures such as lamination, along with low amount of Fe and Mn and high amount of Na and Sr prove mentioned sedimentation situation. High amount of Na in these dolomites possibly indicate the presence of clay minerals, which identified by SEM and XRD studies.

According to facies analysis and sedimentological data integrated with statistical analysis, five microfacies (MF) and two lithofacies (LF) are identified in the Sargelu Formation (Middle Jurassic), exposed in the Lurestan sub-basin. The facies associations indicate the presence of three sunenvironments including the basin / shelf, slope and middle shelf facies belts with pelagic/hemipelagic sedimentation, periodically influenced by depositions of turbidites and tempestites. The sequence of identified sedimentary facies shows that among the main factors controlling the facies character, two factors of oxygen content and intra-basinal flows are the most important ones affecting the deposits of the Sargelu Formation. Statistical investigation on the distribution of size and skewness of Posidonia-containing microfacies, especially Posidonia Wackestone – Packstone (MF-G) also confirms that the Sargelu Formation deposited in a low-energy basin–outer shelf setting and high energy slope and middle shelf facies belts. The widespread occurrence of intervals containing Posidonia species was linked to nutrient supply and oxygen supply by marine currents. Differences in the Posidonia distribution pattern in the Wackestone – Packstone microfacies (MF-G) led to the decomposition of this microfacies into four subfacies (MF-G1, MF-G2, MF-G3, MF-G4), which differ in the patterns of statistical skewness and the position of sub-facies along the depositional profile. In this regard, the left-skewed distribution points toward the slope, whereas the right-skewed distribution points to the middle shelf, and the bimodal-skewed distribution indicates the outer basin/shelf subenvironment.

The Toryan occurrence is located in the Central Iran zone, 120 km northwest of Zanjan. Pb–Zn mineralization at Toryan occurred as laminated and lens-shaped parallel to lamination of grey sandstone units of the Upper Red Formation. Mineralization often formed around and within the fragments of the plant fossils, and shows disseminated, replacement, solution seems, intergranoular cement, framboidal, and vein-veinlet textures. At Toryan, ore horizon has 1 m thickness and approximately 350 m length and contains three zones include the red oxidized zone, the bleached zone and the mineralized reduced zone. Galena, sphalerite, pyrite and arsenopyrite are the main ore minerals at Toryan occurrence. Cerussite and goethite are formed during supergene and wethering processes. Comparison of trace elements and REE patterns of barren red and grey host sandstones and mineralized samples indicate that mineralized samples show lower concentrations of trace elements and REE. Based on tectonic setting, sedimentary environment, host rock, presence of plant fossils, geometry, ore texture and mineralogy and alteration, Toryan occurrence can be classified as sediment-hosted Cu deposits of Redbed type, and is comparable with another Redbed type of Cu and Pb–Zn deposits in the Avaj-Zanjan-Tabriz-Khoy belt.

In this study, the Late Paleocene Taleh Zang Formation in the southwest of Kermanshah hasbeeninvestigatedfor elemental geochemistry and effective diagenetic processes during burial. The thickness of the studied section is 282 meters that mainly composed of shallow marine limestones with interbedded of marl and dolomite. The main diagenetic processes affecting the TalehZangFormation include micritization, various types of porosity, cementation, dolomitization and compaction. Due to the texture and the abundance of unstable skeletal particles (green algae and bivalve), porosity and cementation aremorecommon among the identified processes. Microscopic and geochemical studies have shown that these processes have taken place in eogenesis and early mesogenesis stages in marine, meteoric and shallow burial environments. Evidences indicate that the carbonates of the TalehZangFormation didnot tolerate deep burial after the deposition during diagenesis. Fluids that affected the lower parts of the formation during burial were mainly marine. Moreover, tothetop ofthe sequence in addition to seawater less meteoric fluids have affected the marine carbonates of the Taleh Zang Formation during diagenesis. The high amounts of Sr/Mn (mean27/51) and Sr/Ca (mean 1/61) and also low Mn (mean 27ppm) and Fe (mean 78ppm) values indicate close digenetic system with low water/rock interaction for the carbonate samples of the TalehZangFormation.

Understanding the cyclical nature of changes in sea-level regime leads to awareness of historical land events. In the functional basin, it leads to predictions about the presence of source rocks and hydrocarbon reservoirs in sedimentary sequences. Cycles are formed during a process of falling to rising sea level. The study of sedimentary cycles and understanding the causes of their formation is done in the form of cyclic stratigraphy. Relative changes in sea level were the first active mechanism for the formation of marine sedimentary cycles and sequences. In general, cyclic sedimentary patterns are the product of tectonic and climatic processes, followed by global and local changes in sea level.

 The study of cycles and their formation controlling factors in this article has been done using qualitative studies such as field and laboratory evidence of carbonate deposits of Mobarak Formation. In order to achieve the types of cycles and processes affecting their formation, facies and facies association, depositional environment, isotopic geochemistry and relative sensors were determined using benthic foraminifera as well as sequence stratigraphy.
Discussions and

Studies on field evidence such as sediment erosion pattern, lateral continuity of layers, sedimentary and biological structures, as well as petrographic studies of facies and facies association obtained in this formation, four third-order sedimentary sequences of S1 to S4 were identified. The sequences did not have a low- stand systems tract (LST) and were identified by a highstand systems tract (HST) and transgressive systems tract (TST) that could be controlled by the interaction between eustatic sea-level changes and climate conditions. Depositional sequences show retro-gradational (transgressive systems tract) and prograditional (high-stand systems tract) stacking patterns. Together, these sequences cover a large regressive cycle from the basins / open marine facies to the tidal zone. The distribution and geometry of the Tournaisian-Visean Mobarak Formation imply deposition on a low-angle, relatively low-energy homoclinal carbonate ramp. This interpretation is based on the characteristics of the constituting facies and their gradual lateral and vertical changes. Based on the facies analysis and their associations, four facies’ belts (associations) can be recognized, i.e., basinal environments, outer ramp (deep subtidal associations), mid ramp (shallow subtidal associations), and inner ramp. The study of fossils in sedimentary deposits is one of the oldest and most common methods for determining the relative age of sediments.  By examining the distribution of fossils in stratigraphic units and organizing stratigraphy in units based on their fossil content, the age of the units can be determined. According to this, the bio-stratigraphic investigation shows 9 biozones (MFZ1- MFZ9) belonging to the Hastarian, Ivorian, and Moliniacian sub-stages based on the classification of Mississippian Foraminiferal Zones (MFZ). A good agreement between TSTs and HSTs, and δ13C chemo-stratigraphy implies that sea level fluctuations are the main mechanism that control the δ13C fluctuations in the Mobarak Formation.  Integration of these data indicates that the sequences has been driven by the eustatic sea-level changes and suggests a basic for the regional sequence stratigraphic correlations. The relative ages of the studied calcareous strata were obtained in the Kalariz sections. They are related to the three sub-stage of Hastarian, Ivorian, and Moliniacian. In addition, the study of oxygen and carbon isotopes, which was performed in the Kalariz section, was used to determine the sequence levels and the long-term temperature of the Lower Carboniferous deposits. Therefore, by studying the isotopic values of oxygen and carbon, it is found that the analyzed samples of this formation experienced the least amount of alteration and diagenesis and were close to the waters of the lower Carboniferous Sea.

In this study, 12 main facies were identified and classified into 5 facies association. These facies association are spread on a homoclinal ramp carbonate platform. Examining the field and laboratory evidence, four third-order sedimentary sequences S1, S2, S3 and S4 were identified by the high-stand systems tract (HST) and transgressive systems tract (TST) categories. According to the subdivision of Mississippian foraminiferal zones (MFZ), 9 biozones (MFZ1- MFZ9) were identified in this study, which belong to the subgroups of Hastarian, Ivorian and Moliniacian. In addition, by studying the isotopic values ​​of oxygen and carbon, it was found that the analyzed samples of this formation experienced the least amount of alteration and diagenesis and were close to the waters of the lower Carboniferous Sea. Finally, the studies showed that the main mechanism controlling the fluctuations of isotopic values, cycles and sequences of the third order are the Eustatic fluctuations of the water surface.

Qom Formation carbonate succession unconformably deposited over the red clastic layers of Lower Red Formation after the Eocene tectonic movements in Iran (Berberian & King, 1981; Rahimzadeh, 1994). The type area of the Qom Formation is located in the South East of Qom city. Qom Formation has been divided into six members in the type area (Furrer & Soder, 1955). Based on biostratigraphic studies, Eocene to Middle Miocene age has been proposed for the Qom Formation (Bozorgnia, 1966; Dozy, 1944; Furrer & Soder, 1955; Jaafari, 1963; Zhu et al., 2007). Later studies by (Daneshian & Aftabi, 2010; Daneshian et al., 2008; Ruter et al., 2009) show Oligocene – Miocene age for this Formation. Sedimentological studies in different sections show carbonate shelves and ramps in different locations. So, to biostratigraphy and sedimentary environment reconstruction of Qom Formation, one stratigraphic section has been sampled in the North West of Zanjan. Geological setting  The studied section is located in the North West of Zanjan near And-Abad village. To access the area, we can follow the main road of Zanjan to the Mahneshan. Geological coordination of the studied section is: E 47O 59՜ 10.77     N 36O 48՜ 08.54 . In the studied section, we can see the F member of the Qom formation that created the heights of the area. The And-Abad village is located on the Upper Red Formation in this area. Qom Formation in this area overlies the Lower Red Formation (with the angular unconformity boundary) and underlies the Upper Red formation (with the sharp stratigraphic boundary).

Fifty-three thin sections have been prepared from 168 meters of carbonate layer related to the Qom Formation. We used Adams & Bourgeois (1967) and Leoblich & Tappan (1988) for our biostratigraphic studies. The microfacies studies and reconstruction of the sedimentary environment have been done based on Flugel (2010), and sequence stratigraphy studies carried out according to Van Wagoner et al. (1988). 23 species of foraminifera and 6 microfacies groups have been identified using a transmitted light microscope.

Biostratigraphic studies lead to the identification of 23 foraminifera species: Borelis melo curdica, Textularia sp., Amphistegina sp., Schelumbergerina sp., Quinquloculina sp., Sphaaerogypsina globulus, Pyrgo sp., Dendritina rangi, Ammonia beccarii, peneroplis thomasi, Meandropsina anahensis, Meandropsina irnica, Triloculina trigonula, Orbulina sp., Bolivina sp., Operculina complanata , Globigerinoides sp., Globigerina praebulloides, Triloculina tricarinata, Elphidium sp., Rotalia viennotti, Asterigerina rotula, Archaias kirkukensis. The total range zone of the Borelis melo curdica index species shows Burdigalian age in many studies such as (Adams & Bourgeois, 1967; Ehrenberg et al., 2007; Laursen et al., 2009). In this study, the first occurrence datum (FOD) of this species can be seen at the base of the section from the lowermost part of the Qom Formation layers and the last occurrence datum of this species is located at the top of the section. So we can propose the Burdigalian age for all studies layers of the Qom Formation in this section. Microfacies analysis leads to the identification of 6 different microfacies as follow: 1- Grainestone-packstone with small benthic foraminifera, 2- Floatstone-rudestone with benthic foraminifera and red algae, 3- Wackstone-packstone with peloid, small benthic foraminifera, and sand particles, 4- Boundstone with coral, 5- Wackstone with planktonic foraminifer, 6- Packstone-grainstone with benthic foraminifera. These facies are related to the platform interior, platform margin, and slope and toe of slope parts of the carbonate shelf. Sequence stratigraphic studies is led to identifying one depositional sequence (3rd order) with one sequence boundary type I and one sequence boundary type II. Relative sea-level changes curve and the stratigraphic log show one transgressive-regressive trend during all sections.

To biostratigraphy, microfacies, sedimentary environment, and sequence stratigraphy analysis, one stratigraphic section related to the Qom Formation has been sampled in the North West of the Zanjan. All 53 thin sections have been investigated based on microfacies and fossil contents. 23 foraminifera species have been identified. Based on the total range zone of the Borelis melo curdica index species, Bourdigalian age has been proposed for the studied layers. 6 different microfacies have been identified that show interior platform to lower slope areas of a carbonate platform as a sedimentary environment of the studied samples. On depositional sequence has been determined based on microfacies analysis that shows one transgressive-regressive trend during all sections.

Geotourism is relatively a new form of sustainable tourism and has been developing rapidly over the past two decades. Tourism land is a new concept in recognizing the aesthetic value and the nature of the economic heritage of geology, which is presented by researchers and in a range of definitions. Some have concealed it from geographical, social, economic, and cultural concepts, and they are considered as a subset of geographic tourism, which is scientifically the concept of geoparks.

The city of Mahneshan is a typical example of the diversity and complexity of processes and events occurring in the province and due to its diverse and attractive ecotourism and geotourism capabilities, as well as its historical and ancient features, it has the potential and potential to become a geopark of inter- International. Therefore, our aim is to evaluate the capabilities and capabilities of our city to create a geopark.

the present research is a practical and, in terms of its nature, the dominant approach to analytic descriptive space. Data gathering in this research is based on library and field method, using Comansko models and GIS software for drawing maps. In the present research, the questionnaires are based on the Comanescu model.

In the overall assessment of the data obtained from the mean sum (total value) ‌ for each of the geosites based on the five Comanescu values, it was concluded that the scientific value score in the geocytes was different, the highest and lowest The highest score is for the castle of Behestan and Anguran mines.

According to the evaluations obtained from the geosites, the scientific and aesthetic value indices have the highest scores indicating the potential of geosites in these two fields. In the final ranking for each of the geosites, castle of Behestan and Madabad were ranked first to second, respectively. In addition to their high abilities, factors such as having a fairly accessible access point Having landscapes, the Ghezel uzan River near the castle of Behestan, and more advertising by the tourism organizations are involved in these rankings.

Sea cows are exceptional fossil vertebrates recently discovered in the deposits of the Qom Formation. Yet, the Sirenia-bearing limestones are still poorly understood in terms of detail paleoenvironmental and micropaleontological investigations. In order to distinguish the temporal and paleoenvironmental context of the Sirenia (sea cow) bearing deposits of the Qom Formation in central Iran, three stratigraphic sections were studied in Hamedan (Ivak and Shirinsu) and Isfahan (Chahriseh) provinces. A total number of 47 thin sections were studied for micropaleontology, biozonation and carbonate microfacies analysis, as well as sedimentary environment recounstruction. Biostratigraphical investigations suggest that the Sirenia-bearing deposits are Aquitanian/Burdigalian in age, which implies restriction of sea cows remains to the Lower Miocene. We recognized nine microfacies (n=8 correspond to carbonate; n=1 correspond to siliciclastic) in the study areas. They are systematically grouped into two microfacies settings, representing inner and middle ramp environments. This is based on the facies associations and the distribution of skeletal components and rock textures.  The Sirenia-bearing limestone consists of peloid/algae bearing wackstone/packstone/floatstone. A carbonate (inner) ramp system under shallow water conditions is interpreted as the habitats of the Sirenian mammals during the Aquitanian/Burdigalian in Central Iran. This paleoenvironmental setting could be utilized for further exploration of Qom Formation deposits for discovering sea cows.

In this paper, the biological evolution of the carbonate platform of the Taleh Zang Formation with Paleocene age in the Kermanshah region has been investigated in two stages (time interval) concentrating on fossil debris (such as algae, corals, and benthic foraminifera). For this purpose, two suitable stratigraphic of this formation in the south (Kaboutar Bala section) and southwest (Barikeh section) of Kermanshah were selected, sampled, and studied. For a broader view, the results of this study have been compared with other parts of Tethys basin around the world. The depositional environment of the studied deposits of the Taleh Zang Formation is a carbonate ramp and is probably a form a low gradient ramp due to underdeveloped coral constructions. The gradient of this platform increases from the northwest (Barikeh section) to the southwest (Kaboutar Bala section). Four biofacies were recognized in the studied successions, which include green algae, coral, green algae and benthic foraminifera as well as benthic foraminifera and green algal biofacies. In the lower parts of the Taleh Zang Formation, the presence of algal and coral biofacies (patch reefs) indicates the first stage of carbonate biological evolution of this formation, in that such biofacies has been identified in the Paleocene sequences of other Tethys sectors. Throughout the time and in the upper parts of the Taleh Zang Formation, corals have disappeared and the abundance of green algae is greatly reduced. By the presence of benthic foraminifera with low amounts of green algae, the second stage of the biological evolution of the carbonate platform of the Taleh Zang Formation in the Kermanshah region is formed. In the Early Eocene in Kermanshah region and in the studied successions, due to the seawater regression, the production of carbonates in the Taleh Zang Formation stopped and the detrital red sediments of the Kashkan Formation replaced the carbonates of the Taleh Zang Formation. However, the carbonate production of this formation continued in other areas of the Zagros sedimentary basin (Lorestan province) until the Middle Eocene.

Soltanieh Formation comprises seven informal submembers as alternation of dolomites and shales, more than 1110 meters in thickness, was surveyed in the Seyedkandi section, 32 km southwest of Zanjan, northwest Iran. These submembers were subdivided as lower dolomite, lower shale, second dolomite, second shale, third dolomite, upper shale and upper dolomite, respectively. Based on ichnological data from 109 specimens, 23 ichnogenera and 42 ichnospecies have been recognised. The abundance of trace fossils is very high in the second shale submember, so that 99 specimens were collected from this rock unit. Ichnofossil data from the studied section showsthat the Neoproterozoic-Cambrian boundary is located in the 8 m above the base of second dolomite submember in the studied section, where the first occurrence of Treptichnus pedum was been recorded.

Ghezeljeh area is located in the northeastern part of Mahneshan at 70 km northwest of Zanjan. The rock units exposed in the area are including the Lower Red, Qom, and Upper Red formations which the Upper Red Formation is the purpose of current research. According to field studies, the Upper Red Formation with 750 meters thickness includes 250 meters of evaporative units with intercalations of marls at the bottom and 500 meters of alternation of marls and sandstones intercalations at the top. According to microscopic studies, the grain size of the studied samples ranging from very fine sandstone to gravel. These sandstones show poorly orientation and well to poor sorted and are angular to sub-angular. The sorting and roundness parameters as well clay content show that these sandstones are immature and in some cases are sub mature. Based on a high percent of components and the Folk classification, the middle part of the Upper Red Formation displays lithic-arenite (sed-arenite) and feldspathic-lithic-arenite with an average composition of Q38F15Rf47. Geochemical studies show that these sandstones sourced from intermediate to felsic igneous rocks and deposited on the active continental margin. Furthermore, the weathering index shows an arid and semi-arid climatic condition during their deposition.

The composition, texture and microstructure of rocks affect their physical and mechanical properties such as dry unit weight, porosity, p-wave velocity and Brazilian tensile strength. The aim of this study was to investigate the effect of mineralogy sandstone characteristics on physical and mechanical properties of sandstone in three groups with low mean quartz (less than 65%), moderate (65 to 80%) and high (more than 80% ) and 26 samples were collected from southern province of Zanjan city Then, a comprehensive program of rock mechanic tests are planned and mineralogical properties and engineering parameters such as dry unit weight, porosity, P-wave velocity and Brazilian tensile strength were determined and their relationship was investigated using linear regression analysis. The results show that the mineral composition is effective on the strength properties and increasing the quartz mineral content in the samples, two physical parameters of dry unit weight and P-wave velocity and a mechanical parameter Brazilian tensile strength increase. Also, due to the correlation between physical parameters, P-wave velocity can be predicted with appropriate approximation using porosity parameter for sandstone in studied regions and the results can be used in geomechanical studies.

In this study, petrography and major and minor elements geochemical data are presented for sandstone layers of the Upper Red Formation (URF) in the Chehrabad Pb-Zn deposit (NW Zanjan) to investigate sandstone composition, tectonic setting and their source rock. In this area, URF has 980 m thickness and is conformably overlies the Qom Formation limestones. Based on the microscopic studies, these sandstones mainly composed of fine- to coarse-grained clastic fragments including sedimentary and metamorphic rock fragments (45 %), quartz (38 %) and feldspar (17 %). Based on petrographic studies, these sandstones are feldspathic litharenite and litharenite (mainly chertarenite). Based on the main components and major and minor elements geochemical data, the tectonic setting of these sandstones is an active continental margins and foreland basins. These data represent an intermediate to felsic source rock for these sandstones which was affected by the semi-humid to semi-arid climate and a low chemical weathering.

Sediment-hosted stratabound copper (SSC) deposits are bodies of disseminated, cementing, and lesser veinlet hosted copper minerals that are peneconformable with their sedi mentary or metasedimentary host rocks (Hayes et al., 2015). These deposits have been termed sediment hosted stratiform Cu, sedimentary rock-hosted stratiform Cu, Cu shale, Cu sandstone, cupriferous sandstones, sandstone Cu, red-bed Cu, Kupferschiefer type Cu, marine paralic type Cu, reduced-facies Cu, or Revett Cu deposits (Cox et al., 2003, 2007; Hitzman et al., 2005; Hayes et al., 2015). SSC deposits occur in three subtypes divided by host lithology and the corresponding type of reductant that precipitated sulfur and Cu from warm, oxidized, metals-transporting, sedimentary brines. These types are as follows: (1) reduced-facies type; (2) sandstone-type (Revett); and (3) red-bed type. These deposits have been formed during the middle-late Paleoproterozoic to Tertiary.There are several SSC deposits in the Avaj Zanjan Tabriz Khoy area in the northwestern Iran that are hosted by grey sandstone units of the Upper Red Formation (URF). The Tasouj, Tazekand, Nahand Ivand, Ortasou, Chehrabad, Halab, Zagelou and Avaj are the main important deposits in this area. These deposits predominantly consist of bedding-parallel replacement and disseminated Cu–Pb–Zn sulfides, roughly concordant with the stratification. The average Cu, Pb and Zn content of these deposits are ~1.5, 2 and ~1 wt.%, respectively.Apart from small scale geological maps of the area, i.e., 1:250,000 geological maps of Takab (Alavi and Omidi, 1976), 1:100,000 geological maps of Mahneshan (Lotfi, 2001) and a number of unpublished Pb–Zn–Cu exploration reports, no other work has been reported prior to this research study on Pb–Zn–Cu mineralization at Chehrabad. The present paper provides an overview of the geological framework and the mineralization characteristics of the Chehrabad deposit with an application to ore genesis. Identification of these characteristics can be used as an exploration model for this type of Pb–Zn–Cu mineralization in this area and elsewhere.

Detailed field work has been carried out at different scales in the Chehrabad area. During the field works, detailed stratigraphic sections were measured, sampled and described. In addition, the color of the sandstone layers and the presence of fossil woods were scanned during the field work. About 23 polished thin and thin sections from host rocks and mineralized layers were studied by conventional petrographic and mineralogic methods at the University of Zanjan in Iran.

The Pb–Zn–Cu deposit at Chehrabad, 75 km northwest of Zanjan, is located in the Central Iranian zone. Rock units exposed in this area belong to the URF, and consist of alternations of red and green marl intercalated with red to grey, medium- to thick-bedded sandstone. In this area, URF has 980 m thickness and consists of four main parts. These parts, from bottom to top, consist of 1- alternation of gypsiferous green marls along with gypsium and salt layers (235 m), 2- red marls intercalated with grey and red sandstones (445 m), 3- alternation of red and green marls intercalated with sandstones (145 m), and 4- alternation of green marls and green siltstones (155 m). The Pb–Zn and Cu mineralization in the Chehrabad deposit has occurred in grey sandstone units of the second part of the URF. Mineralization has often been formed around and within the fragments of the plant fossils, in the form of disseminated and the solution seems to have been sulfides. Based on field studies, mineralization at the Chehrabad deposit has occurred in two horizons of reduced-grey sandstones, H-A and H-B, with about 4 and 6 m thickness and about 200 and 1000 m length, respectively. These horizons contain red oxidized zone, bleached zone and mineralized reduced zone with the latter being located within the bleached zone.The red oxidized zone consists of red marl and sandstone layers containing iron oxides which are located adjacent to the reduced horizons. The red color of this zone has been caused by the presence of iron oxides around the grains. The oxidized pyrite crystals are the main important minerals in this zone. The bleached zone is a part of sandstone sequences that have undergone changes in their color due to the alteration processes. Grey and green colors in this zone have occurred due to the presence of organic materials and diagenetic pyrites. Mineralization in the reduced zone has occurred within the organic materials bearing bleached zones. Plant debris, plant fossils, diagenetic pyrites and permeability of host rocks have the most important roles for the Pb-Zn and Cu mineralization at the Chehrabad deposit.Galena, sphalerite, chalcocite, pyrite and chalcopyrite along with minor Ag-bearing sulfides (mckinstryite, stromeyrite) are the main ore minerals at the Chehrabad deposit. Cerussite, malachite, azurite, covellite, atacamite, vanadinite, and goethite are formed during supergene processes. Disseminated and cemented textures along with lens-shaped, solution seems, replacement, vein-veinlet, and framboidal are the main ore textures at the Chehrabad deposit. Based on the tectonic setting, host rock, geometry, presence of plant fossils, ore structure and texture and mineralogy, it can be concluded that the Chehrabad deposit is a sediment-hosted Redbed type Cu deposit.

The Upper Red Formation (URF), with the age of Miocene, is mainly composed of clastic sediment including interbedded marl, sandstones and slightly conglomerate layers as well as some evaporate layers mostly in lower parts of the formation. The lithology, color and thickness of this formation are variable in a different locality (Aghanabati, 2004). This formation is the only cap rock for the Qum Formation in the Central Iran zone especially into the Sarajeh and Alborz gas-fields (e.g., Morley et al., 2008). The URF has significant distribution in the northwestern of Iran and hosts significant Cu and Pb-Zn deposits (e.g.; Sadati et al., 2016). The constituents of this formation, particularly in the sandstone layers, provide valuable information in relation to the sedimentary environment and the geodynamic location of this formation (Rieser et al., 2005). In this research, based on the facies analysis (Miall, 1996, 2000), modal analysis and geochemical data, sedimentary environment and tectonic setting of these clastic layers in the Chehrabad deposit section, northwest of Zanjan, are interpreted.

This research is based on a detailed study of lithology, sedimentology and geochemical data of the URF. During field observations, the thickness of sandstone layers and their colors were clearly defined. In order to interpret the sedimentary environments of this formation, a detailed lithofacies have been analyzed during this study. Lateral and vertical variations in all layers have been considered. About 23 thin sections from collected samples are studied by polarizing microscope at the University of Zanjan. In each thin section, the 250-points, based on the Gazzi-Dickinson method, were counted. To investigate the tectonic setting of these sandstones, 9 samples with the least amount of weathering and calcium carbonate were selected for geochemical analyses by XRF methods.

Chehrabad area is located in the northeast of Mahneshan, approximately 75 km, northwest of Zanjan. Rock units exposed in this area belong to the Lower Red, Qom and Upper Red formations. The thickness of the URF in this area is about 980 m and consists mainly of three main units. These units, from bottom to top, consist of evaporate layers, alternation of mudstone and grey to red sandstone and finally mudstone with interbedded gypsum layers with a thickness of 235, 590, and 155 m respectively. The studied sequence is a part of the middle portion of the URF, with 231 m thickness and has the highest amounts of sandstone layers. Based on the field observation, the middle parts of the formation including 7 gray to red color sandstone, which is alternate with the red mudstones. The sandstones in the Chehrabad area are grey to red and have poor imbrication. According to the sorting and roundness parameters of the grains and also the low amounts of clay matrix (less than 5%), these sandstones are perhaps to be mature in terms of texture maturity. Based on the types of sandstone grains and the Folk (1980) classification, the URF sandstones in the study area is classified as feldspathic litharenite to litharenite. Facies analyses, the color of layers, presence of cross-bedding and plant fragments, lack of gravel grains, all represent an oxidized continental environment, such as a fluvial system with a highly sinuous channel (meandering river). Also, the presence of symmetric ripple marks and marine trace fossils indicate that the sedimentation of some parts of this formation has taken place to a tidal condition and most likely close to the coastal environment. In addition, based on field studies and facies analysis, identified lithofacies in Chehrabad area include Fl, Sm, Sh, Sr, Sp, St and Fm. According to the characteristics of each facies and based on the method of Miall (1996), these sandstones were deposited in fluvial and tidal depositional systems. The results of petrography and geochemical studies have been used to interpret the tectonic setting of sandstones in the middle parts of the URF. Based on triangular diagrams of Dickinson and Suczek (1979) (Qt-F-L) and Ingersoll and Suczek (1979) (Qp-Lvm-Lsm and Lv-Lm-Ls), also using binary variables graphs of Bhatia (1983) and Roser and Korsch (1986), the tectonic setting of these sandstones is active continental margins and probably foreland basin.

The URF in the Chehrabad area consists of 3 parts and the thickness of the middle part of this formation is about 231 m, with 7 sandstone layers, which alternation with red mudstone beds. Based on microscopic studies, these sandstones are classified as feldspathic litharenite to litharenite. Based on field evidence and the presence of cross-bedding, plant fragments, lack of gravel grains, symmetric ripple marks, presence of trace fossils and also the type of facies, seven lithofacies (including Fl, Sm, Sh, Sr, Sp, St, and Fm) are recognized. The data obtained from point-count and geochemical studies clearly show that the tectonic setting of these sandstones in the Chehrabad area is an active continental margin.

The Qom Formation was deposited at the north-eastern coast of the Tethyan Seaway, in the Oligocene - Miocene, during the final sea transgression, in Central Iran (Reuter et al., 2009). Although the Mohammadi et al. (2013) believe that above 35˚N (including the study area in this research) deposition of the Qom Formation started during the Miocene. It is essential and important to study different properties of the oil-bearing Qom Formation because of economic importance and communicative role between Eastern Tethys (the proto-Indian Ocean) and the Western Tethys region (the proto-Mediterranean Sea) in the Iranian Plate at the same time (Mohammadi et al., 2013). Furrer & Soder (1955) subdivided the Oligocene-Miocene marine strata of the Qom Formation in the type locality of the formation near the town of Qom, into six members (a-f members: a-member basal limestone, b-member sandy marls, c-member alternating marls and limestones, d-member evaporites, e-member green marls and f-member top limestone). In the Zanjan area, only f-member of the Qom Formation has been deposited (Aghanabati, 2004). In general, the f-member consists of light colored, porous, in part chalky and in part cemented limestone. Although many studies have carried out for nearly four decades on the f-member of the Qom Formation outcrops in Central Iran back-arc basin (which they are listed in Mohammadi et al., 2013), stratigraphical, microfacies analysis and sedimentary environments studies of the f-member of the Qom Formation deposits of the Zanjan area has been the subject of only a few studies. So, here for the first time, we document and discuss the results of detailed fieldwork and microfacies analysis from the early Miocene carbonate platform succession in the south of Zanjan (f-member of the Qom Formation).

This study involves one stratigraphic section that was measured bed by bed and investigated sedimentologically.During the fieldwork study, detailed stratigraphic sections were measured, sampled and described with respect to carbonate facies and biota. The petrographic description is based on approximately 73 thin sections. Thin sections were stained using the method of Dickson (1965) to distinguish ferron and non-ferron calcite from dolomite. The petrographic classification for carbonates is based on Dunham limestone classification (Dunham, 1962). Flügel (2010) facies belts and sedimentary models were also used. The composition of associated fauna (presence of red-algae, coral, benthic foraminifer and echinoderm) and non-skeletal grains (e.g. intraclasts and peloids) was considered. Sedimentologic texture and structure (e.g. crossbedding, dolomitization, presence of silt-size quartz grains, boring and burrowing) have been considered qualitatively.

The Qom Formation in the Madabad celestite deposit (south of Zanjan), lithologically composed of 190 m of medium to thick-bedded and massive limestone and marly limestone. In this area, the Qom Formation is conformably overlies the clastic rocks of the Lower Red Formation and is in turn conformably overlain by the Upper Red Formation. In detail, the Qom Formation in the study area consist of 7 lithostratigraphic units as follow from base to top of the formation: 1) thin to medium-bedded limestone with interbedded of thin-bedded argillaceous limestone, 2) thick-bedded coral-bearing limestone, 3) thick-bedded limestone with interlayers of marly limestone, 4) thin-bedded marly limestone, 5)  thick-bedded echinoderm-bearing limestone with interlayers of marly limestone, 6) thin-bedded marly limestone and finally  and 7) thick-bedded to massive limestone with interlayers of marly limestone.The main components of the Qom Formation contain benthic foraminifera with hyaline test, coral, red algae with less frequency of planktonic foraminifera. Due to the abundance of red-algae, larger benthic foraminifera and micrite, the Qom Formation platform facies is referred to as “red algae foraminifera dominated packstone”. Field and microscopic studies led to identification of five microfacies in the limestone units of the Qom Formation in the Madabad area. These microfacies, ordered from shallower to deeper environments, include: A) red algae coral packstone, B) red algae bioclast packstone to wackestone, C) perforate benthic foraminifera packstone to wackestone, D) red algae echinoderm wackestone and E) planktonic foraminifera red algae bioclast wackestone.In general, microanalysis and paleoenviornmental interpretation of the Qom Formation show that this formation was deposited in a variable depositional system. The Qom Formation facies are dividable to four facies as follow: alluvial-deltaic facies carbonate platform-evaporatic facies, slope facies and basin facies (deep sea facies) (Rahimzadeh, 1994). Microfacies analysis including abundant hyaline-test benthic foraminifera as well as the lack of restricted lagoon microfacies show that in the Madabad section, the Qom Formation was deposited in open marine environment. According to recognized microfacies and absences of gravity deposits (turbidites), real and continuous reef, barrier and storm structures, carbonate platform of the Qom Formation developed on an open shelf without effective barriers separating it from the sea. In detail, the distribution of foraminifera and other components, in addition to the vertical microfacies relationships indicate that facies model of the Qom Formation in this section was distal-inner to middle shelf. The distal inner shelf including only the (A) microfacies and the other recognized microfacies (B-E) deposited through the proximal to distal parts of the middle shelf. Proximal middle shelf is characterized by larger benthic foraminifera with hyaline wall in addition to red algae and distal middle shelf is dominated by planktonic foraminifera and red algae.

The Qom Formation in the Madabad celestite deposit (south of Zanjan), lithologically composed of 190 m limestone and marly limestone. Field and microscopic studies led to identification of five microfacies. Distribution of foraminifera and other components, in addition to the vertical microfacies relationships indicate that facies model of the Qom Formation in this section was distal-inner to middle shelf platform.