جستجوی مقالات مرتبط با کلیدواژه « Qom Formation » در نشریات گروه « علوم پایه »

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.

In this research, the deposits of the Oligocene-Miocene Qom Formation in Kuh-e Charkheh (Natanz), Western Zefreh and Varton sections, northeastern Isfahan were studied. According to the field observations and thin section analysis in Carbonate part of the mentioned sections, 8 microfacies were identified, which were deposited from shallow part of lagoon to open marine and the sedimentary environment of 3 sections due to absence of reef and presence of bioclastic barrier and absence of spillage, the homoclinal carbonate ramp was detected. According to the sequence stratigraphic studies, each of the studied sections has two 3rd sequences. In Kuh-e Charkheh section, both sequences include of TST and HST, which are separated by sequence boundary SB2. In the western Zefreh section, the first sequence includes of TST and HST that is separated from the second sequence (include of LST, TST and HST) with sequence boundary SB1. In the Varton section, the first sequence is aggredation type and separated from the second sequence, which include TST and HST by a sequence boundary SB2.

The Lachinag synformal anticline is located to the northwest of the Mil anticline and the western end of the Dochah Fault in northern central Iran. This synform includes the terminal members of the Qom Formation (members E and G) and the Upper Red and Pliocene conglomerates. Additionally, with an axial surface plunge from the northwest to the southeast, this fold trends toward the southeast, resulting in its asymmetric geometry. In this synform, the deformable marl and gypsum layers of the E and G members of the Qom Formation have contact with the competent conglomerate and sandstone layers from the Upper Red Formation. The juxtaposition of these layers and the occurrence of deformation phases resulted in the migration of ductile layers as well as a significant increase in the thickness of the marl and gypsum deposits of the Qom Formation (particularly in the E member). Due to the migration of these layers towards low pressure areas and their substantial thickening at the hinge of the Lachinag synformal anticline, the layers as well as the limbs of this fold were overturned. Finally, a synformal box fold was formed. Structural investigations have revealed that this fold initially formed as a result of the right-lateral strike-slip shear parallel to the Dochah Fault. This process occurred during the post-Miocene under the influence of counterclockwise left-lateral strike-slip shear forces around a pole axis at approximately 135 degrees from the north. Consequently, the fold acquired a synformal geometry. The left-lateral shear force may be due to the clockwise rotation of the South Caspian basin and the application of left-lateral shear forces on the northern parts of Central Iran, similar to what has been observed in the Kushk-e Nosrat Fault.

The Qom Formation, (Oligocene-early Miocene in age) consists of thick successions of marine marls, limestones, gypsum, and siliciclastics. It is deposited in the Sanandaj–Sirjan fore-arc basin, Urumieh-Dokhtar Magmatic Arc (Intra-arc basin), and Central Iran back-arc basin and it was subdivided into 11 members to date. "Unnamed member" which is identified by Nummulites intermedius and Eulepidina cf. dilatata and attributed to Rupelian, was introduced as the oldest member of the Qom Formation. Recent studies by the current author subdivided the Rupelian stage into “early Rupelian” and “late Rupelian”, based on the first appearances of lepidocyclinids in the latter one. Accordingly, the "unnamed member" is late Rupelian in age. Besides, the early Rupelian strata are characterized by the presence of Nummulites without lepidocyclinids, reported merely from southwestern and southern Kashan. The basal deposits of the Qom Formation sections in SW and S Kashan (composed of marl, limestone and marl limestone) are distinctly different from the “unnamed” member (alternation of silty marl, sandstone and limestone), “a” member (basal limestone) and “b” member (sandy marl) of the Qom Formation, in terms of lithology. Therefore, the mentioned deposits are introduced as a new member and named the "Verkan Member". Accordingly, the number of the Qom Formation members has increased to 12 and the “Varkan Member” (with 108-m thickness in the Varkan section and early Rupelian in age) is introduced as the oldest member of Qom Formation. The “Verkan Member” is present in the Varkan (SW Kashan), Vidoja (SW Kashan) and Ghohroud (S Kashan) sections.

In order to reconstruction of sedimentary conditions and paleogeography of Qom Formation, one stratigraphic outcrop in the Northeast of Mahneshan has been studied. In this study, microfacies analysis and microfossil investigations have been carried out on Forty-seven samples from one hundred sixty-two meters of sedimentary rock layers. Qom Formation in this section, is composed of carbonate, clastic and volcanoclastic layers that covers the andesitic strata of the Karaj Formation with a disconformity boundary and overlayed by clastic strata of the Upper Red Formation with gradual boundary. Microfacies analysis led to identification of one lithofacies (grain supported conglomerate) and three microfacies (1- Algal coral bioclast packstone, 2- Carbonate volcaniclastic and 3-Pelagic wack/packstone) that are related to the open carbonate shelf, submarine channels and submarine volcano in this section. Fossil investigations lead to identification if seventeen species of foraminifera fossils and two biostratigraphical zones. Based on foraminiferal index fossils (Borelis melo curdica, Meandropsina iranica, Praeorbulina glomerosa), Burdigalian-Langhian have been proposed as relative age for these strata. Facies change throw the stratigraphic column show deepening upward trend (during Langhian) in this study that can be correlated with paleogeographic events and relative sea level rise in Langhian age in this area.

Brittleness which is of great significance in rock engineering properties is one of the most important properties of rock. The evaluation of brittleness indexes is a helpful method for the estimation of rock brittleness. However, there is still much uncertainty about the relation between rock brittleness and rock failures (i.e. Hydraulic fracture, Rock blasting in coal mines and tunnels). This fact can be attributed to the lack of a concept of universally accepted brittleness and brittleness index. In this paper, the relationship between rock brittleness is investigated by using the ratio of point index to porosity (PMP) in the sandstones of the Qom Formation. In addition, the available estimation methods for the rock brittleness index are summarized and their application is briefly discussed. In order to estimate of brittleness index and the ratio of point load index, 15 blocks from Latgah sandstones in northern Hamedan have been selected. Lithological characteristics, physical and mechanical properties of these sandstones have been determined. The samples have been tested under point load strength index uniaxial compressive strength (UCS), and Brazilian tensile strength experimentals. Then, the ratio of point load index to porosity (PMP) has been calculated. To achieve the desired target, the most appropriate and meaningful relationships between brittleness rock and the ratio of point load index to porosity (PMP) have been presented by the regression method. The relationships between point load index, porosity, and brittleness indexes (B1, B2, B3, B4, and BI) have been evaluated by simple regression (SR) techniques using Minitab 16 software. The statistical analyses revealed the existence of powerful correlations between the ratio point load index to porosity (PMP) with brittleness indexes (B3, B4)in the dry state and also, the powerful correlations between the ratio point load index to porosity (PMP) with brittleness indexes (B1, B2) in the saturated state.

Qom formation in type section in the South of Qom city (Dobaradar, Dochah, Mil, Naraghi, Khorabad and Shorab areas) has been divided to six members (a-f) (Furer and Soder, 1955). Lower Miocene age and carbonate shelf as sedimentary environment have been proposed for these strata in the previous studies (Alipour et al, 1395). Moreover, carbonate shelf as sedimentary environment has been proposed for marly strata in the upper parts of this section (Rabbani et al, 1399).

Studied section is located in the Southwest of Zanjan provience (near Qamchoghai village). We can use Zanjan to Halab main road (about 40km) to access this area at the right of the road near the Zarrinabad factory. Forty-two samples from one hundred and forty-three meters of strata have been studied. All samples have been documented in Paleontology Laboratory in the University of Zanjan.

Thick bedded limestones are cropping out at the base of the section that overlay the red bedded strata (lower red Formation equivalent) (Alipour et al, 1395) by disconformity boundary. Theses thick bedded strata are overlayed by marl and argillaceous limestone strata (the most upper parts of Qom Formation) by conformity boundary that gradually turned to the lower most parts of the Upper Red Formation (gypsum) in the upper parts of the section. Microfacies analysis and field studies proposed open carbonate shelf as sedimentary environment for these strata (Rabbani et al, 1399). Also, Alipour et al. (1395) believes that carbonate shelf can be consider as sedimentary environment for the f member of Qom Formation in this section.

Biostratigraphy:

In order to relative dating of these strata, formainifera and macrofossils content have been studied. Sixteen species of foraminifera and one species of echinoderms have been identified. Some sponges have been reported for the first time from this section. Based on index fossils (specifically Borelis melo curdica and Pericosmus latus), Burdigalian age can be proposed for these strata.

Paleontological studies on thin section samples lead to identify sixteen species of foraminifera fossil that based on occurrence of Borelis melo curdica (as index foraminifera fossil), one biostratigraphic zone has been identified that proposed Burdigalian age for the studied strata. Also, presence of Pericosmus latus (as index echinoid fossil) confirm the Lower/Middle Miocene age for these strata. Some of sponges fossils related to the Hexactinellidea have been reported from the Qom Formation in this section for the first time.

Sequence stratigraphy is a branch of stratigraphy that can enable us to correlate deposits with considerable accuracy. This research aims to investigate the role of fossils in the recognition of system tracts and sequence boundaries along succession using microfacies features. To achieve this aim, we studied the Qom Formation at the Qasr-e-Bahram section located in the south of Garmsar. This formation is mainly composed of argillaceous limestones, limestones, and marls, overlies the Lower Red Formation, and lies under the Upper Red Formation disconformably. Based on paleontological studies, the suggested age is the Late Aquitanian to Burdigalian (Early Miocene). The microfacies analysis indicates a variety of facies and environments (lagoon, carbonate barrier, and open marine). The significant presence of red algal with other reef-forming elements within microfacies as well as the presence of turbidite facies probably implies a shelf carbonate platform. According to geological field and laboratory studies, deposits of the Qom Formation include four third-order depositional sequences, and the presence and abundance of fossils such as foraminifera, algae, bryozoans, and corals were useful tools in identifying the systems tracts and their boundaries.

This article is the first published example of the application of (tephra) event stratigraphy in the Qom Formation as well as the temporal and spatial distribution of the Qom Formation pyroclastic deposits. The presence of igneous (volcanic) associations is the most obvious facies change of the Qom Formation. The tuffaceous limestones and tuff units of both Bozdan and Kagharaki sections (in the southeast of Kerman province) are late Rupelian in age, indicating the occurrence of a volcanic event in NW Jazmourian at the same time. The pyroclastic deposits of the Qom Formation have a significant and regular extent in different areas of the formation realm (from Jazmourian to Mako). In general, it can be said that the pyroclastic units of the Qom Formation are mainly distributed in the following three areas: 1) Jazmourian–Jiroft–Sirjan (fore-arc); 2) Southwest of the Natanz–Kashan–Qom–Saveh belt (mainly in intra-arc); and 3) Zanjan region (SE, S, SW, W, and NW of Zanjan). The thickness and age of these deposits vary in different sections.

The Qom Formation with Oligocene-Miocene age which is important due to its hydrocarbon reservoirs in some areas, is outcropped with a 330 meters thick mixed siliciclastic-carbonate sequence in Dastjerd area that uncomfortably overlain the Lower Red Formation and is conformably underlained by Upper Red Formation. In this study, the deposits were studied for petrography, microfacies and sedimentary environment, sea-level changes and mixing mechanism. Based on the frequency and distribution of the skeletal and other constituents of the carbonate deposits of Qom Formation in the studied section, six microfacies associated with three facies belt (open marine, shoal & lagoon) were identified related to a carbonate ramp. Mixing and hybridization of carbonate deposits of Qom Formation with different amounts of siliciclastic inputs in sand, silt size in through the thickness and laterally in the depositional basin of this sediments, is related to the tectonic activity and erosion of older rocks such as the Lower Red Formation and associated Paleogene volcanic rocks, deposited in the backarc basin of a subduction system. According to the microfacies analysis of the studied sediments, two cycles of sea level changes were recognized. The first cycle is associated with unstability of the basin floor and fluctuations in the relative sea-level, which leads to the deposition of a thick layer of sandstone regarded to the high tectonic activity and the second cycle is coincident with more stability of the basin which ultimately tends to a shallowing condition.

The Qom Formation is considered as one of the most important reservoir formations in Central Iran. This study was conducted to identify the facies and sedimentary environment of this formation in Sarajeh gas field and Yurtshah aquifer which are located in the southeast and northeast of Qom, respectively. 15 sedimentary facies were identified after examining the Qom formation-related thin sections and cores in the study area, which can be divided into 9 belts or facies groups according to standard models. According to the characteristics of the studied samples, the expansion of turbidite deposits and the frequency of reef / shoal facies, the paleoenvironment of Qom Formation in Sarajeh Field and Yurt-e-shah Aquifer is a carbonate shelf. Facies related to deep sections are less frequent, so the paleo-position of the two fields under study has been shallow sections of the platform.There are three main features in the facies identified in the study areas that have not been introduced in other sections and other studies of the Qom Formation, including the presence of supratidal facies (especially anhydrite facies), the continuous reef sequences and the existence of facies has planktonic foraminifera. The most complete sequence of the Qom Formation is related to Sarajeh field, but in Yurtshah Square this sequence is not complete and also shows less thickness. The ancient position of Sarajeh field was an depression and the Yurtshah anticline was an paleohigh. These conditions have led to thickness changes in the the Qom Formation even in the regional dimension.

In order to study of the Oligocene depositional sequences, a stratigraphic section of the equivalent deposits of the Qom Formation (for convenience in the continuation of the article, Qom Formation is mentioned) which is 330 meters in thickness has been nominated in northwest of the Hamedan. Facies analysis has produced eight microfacies related to the four facies belts of tidal flat, reef, slope and open marine. Base on lacking the sediment gravity flows, turbidity facies, and abundance in reef facies deposits, a carbonate shelf is proposed for Qom formation. In this research, two depositional sequences and three-sequence surfaces have been separated based on sequence stratigraphic studies (the first and third sequence surfaces being of the first type). A comparison of the relative sea-level change curve in the study area with the Oligocene-Miocene global sea-level change curve shows that sequences of the Qom Formation have acceptable compatibility with global changes in seawater level. Also, the comparison of the sequence boundaries of this study with the Zagros and European basins indicates that the Oligocene sequence levels of the Qom Formation which are identified in the Zagros basin, are well corresponded with the results of this study compare to the European one.

The present study is the first study aimed at biostratigraphy based on calcareous nannoplankton that has been performed on all succession exposed from the Oligo-Miocene marine deposits (members a to f of the Qom Formation). The studied deposits are located in the middle part of the Central Iran Zone and more precisely in the Navab anticline (northeast of Kashan city), which has a thickness of 417 meters. Due to the location and expansion of all members in this section, it has been a very suitable area for biostratigraphic assessments comparable to world standard models. In this study, a total of 370 microscopic slides prepared from rock samples were studied to the determination of the calcareous nannoplankton and accurately separate world standard biological zones, which led to the identification of 72 species belonging to 18 genera of this valuable group of the planktonic micro-organisms. According to the identified index species, standard nannoplankton biozones of the NP25 and NN1-NN4 were separated from this surface section of the Qom Formation. In addition, the equivalent biozones such as CNO5-6, CNM1- CNM6 as well as zones and subzones CP19b, CN1a, b, c, CN2- CN3, which belonging to the newest biozonation patterns, were also separated in this study. Therefore, based on the geological time value of the separated biozones, the age of late Chattian to late Burdigalian-early Langhian was proposed for the Qom Formation in the Navab anticline section. In this study, for the first time, the important chronostratigraphic boundaries such as the Paleogene-Neogene system boundary (or Chattian-Aquitanian stage boundary) in the upper parts of sub-member "c1", the Aquitanian- Burdigalian stage boundary at the base of member "e" and Burdigalian- Langhian in the upper part of member "f", were disaggregated based on biostratigraphic criteria.

Morphogroup analysis, due to independence of species level taxonomy, as wel as permit to comparison of assemblages of differing ages, is a useful tool for ecological and palaeoecological interpretation. Foramniferal study of the Qom Formation in the Natanz (with Rupelin-Chattian?-Aquitanian in age and 330 m thickness) and Khorabad (southeastern Qom; with Rupelin-Burdigalian in age and 260 m thickness) sections resulted in identification of 8 morphogroups. The morphogroups were distinguished according to test/shell morphology and architecture (general shape, mode of coiling, and arrangement and number of chambers), inferred life habitat either living on the surface of the sediments or within the sediments (epifaunal and infaunal), and feeding strategy. Generaly, epifaunal morphogroups were dominated in both study sections. The lower 200 m of the Natanz section, are dominated by calcareous porcelaneous morphogroups; while the upper layers are dominated by hyaline morphogroups, which indicates the lower and upper parts were deposited in inner ramp (lagoonal environments) and open sea, respectively. This significant change through time reffers to gradual increasing of the basin depth, decreasing the light intensity, reducing the salinity and decreacing the nutrient level. The distribution of morphogroups in the Khorabad section follows a reverse pattern; so that, despite the minor fluctuations, the lower 200 m of the Khorabad section, are dominated by hyaline morphogroups; while the upper layers are dominated by porcelaneous morphogroups, which indicates the lower and upper parts were deposited in open sea and inner ramp (lagoonal environments), respectively.

The Qom Formation deposits in northern Abadeh (Sanandaj–Sirjan fore-arc basin) studied in order to analyze microfacies, depositional environment and depositional model. Outcrops of the Qom Formation in northern Abadeh, with Rupelian- Chattian in age and 85-m thickness, consist mainly of massive and bedded limestone, shale and conglomerate. The Qom Formation in northern Abadeh conformably overlies the LRF, and its upper boundary covered with quaternary alluvium. Foraminifera, coralline red algae and corals dominate biogenic components of the Qom Formation. Based on field investigations and microscopic studies, nine microfacies (six carbonate microfacies plus three terrigenous facies) were recognized. The conglomerate facies is deposited in braided streams; while, other facies are deposited in marine environment and on a ramp type platform. This ramp is generally dividable into two depositional environments including inner ramp (lagoon) and middle ramp (open marine). However, outer ramp deposits are not observed in the study area. The high abundance of larger benthic foraminifera, coral and corallinacea red algae indicates that deposition took place in tropical warm water.

Rock units in the Madabad celestite deposit are composed of medium to thick-bedded and massive limestone interlayered with marly limestone and marl units of the Qom Formation (lower Miocene). Mineralization occurs as lens-shaped orebody, hosted by limestone units of member of the Qom Formation usually crosscutting bedding of the host rocks. Three stages of mineralization occurred in the Madabad deposit. The first stage is characterized by calcite formation during syn-depositional to syn-diagenesis processes. The second stage is related to hydrothermal processes that are distinguished by formation of fine-grained and sugary crystals of massive stage-1 celestite, vein-veinlets of coarse-grained stage-2 celestite along with minor strontianite and barite, coarse-grained euhedral crystals of stage-3 celestite with vug infilling texture, and finally late-stage quartz and calcite vein-veinlets. Stage three includes supergene processes. Hydrothermal alteration includes dolomitization, calcitization and silicification. Celestite along with minor strontianite and barite are ore minerals, and calcite, dolomite, quartz and iron oxides-hydroxides are gangue minerals at Madabad. The ore minerals show vein-veinlets, vug infilling, brecciated and cataclastic textures. Microthermometric measurements of two-phase liquid-rich fluid inclusions hosted in celestite II indicate that salinities values range from 6 to 18 wt.% NaCl equiv. (avg. 10.6 wt.% NaCl equiv.). These inclusions have homogenization temperatures range from 248 to 365 °C, with an average of 278 °C. These data indicate a minimum trapping depth of 510 m for the Madabad deposit. Sr was originated from evaporate units within the marly parts of the Qom Formation and volcanic units of the Karaj Formation. Characteristics of the Madabad deposit are similar to epigenetic replacement celestite deposits.

Sedimentary environment and sequence stratigraphic studies of the Qom Formation as a reservoir rock is of utmost importance in terms of the potential for hydrocarbon resources. Bozorgnia (1966) divided the Qom Formation into nine members (a, b, c1, c2, c3, c4, d, e, f) in the age of Rupelian to Burdigalian, which the National Stratigraphic Committee of Iran accepted. This research is focused on paleoenvironmental interpretations and sequence stratigraphy of the Qom Formation in the Goylar stratigraphic section, which is located northwest of the structural zone of Central Iran.

A total of 64 thin sections of hard samples of Qom Formation in the Goylar section have been prepared. Due to the similarity of foraminifera in the Qom and Asmari formations, the biozonation of the Asmari Formation, which is documented by Wynd (1965), Adams & Bourgeois (1967), and Laursen et al. (2009), has been used in this research. Determination of planktonic foraminifera has been done only by studying thin sections. To recognition of the facies and sedimentary model of the Qom Formation, studies of Reed (1995) and Flugel (2010) have been used, and to undertake sequence stratigraphy, the model of Hunt & Tucker (1993, 1995) is used.

Qom Formation in the Goylar section is 155 meters in thickness. Qom Formation includes thick-bedded limestone, thin to medium bedded sandstone, shale and marl, reef-coral limestone, and green marl and argillaceous limestone alternation. According to the lithological characteristics, Qom Formation in this area can be equivalent to member f. A total of 24 genera and 18 species, including 17 genera and species of Benthic foraminifera: Borelis melocurdica, Psuedoilthonella richelli, Peneroplis evolutus, Peneroplis thomasi, Heterolopa dutemplei, Asterigerina rotula, Valvulina sp.1, Valvulina sp.2, Pyrgo sp.1., Amphistegina spp., Spiroloculina sp., Quinqueloculina sp., Austrotrillina sp., Miogypsina sp., Lenticulina sp., Elphidium sp.1., Rotalia sp., Nodosaria sp., Textularia sp.; and 7 genera and 13 species of planktonic foraminifera with an axial incision in thin sections including Globigerinoides primordius, Globigerinoides subquadratus, Globigerinoides triloba, Globigerinoides immaturus, Paragloborotalia mayeri, Paragloborotalia spp., Globigerina praebulloides, Globigerina sp., Globigerinella obesa, Globorotalia archeomenardii, Globorotalia sp., Praeorbulina transitoria, Bolivina sp.According to paleontological studies and based on the stratigraphic distribution of foraminifera, Borelis melocurdica-Borelis melo melo Assemblage Zone (Burdigalian, Early Miocene) has been recognized certainty for the Qom Formation. Facies analysis, including variety in fauna features, facies geometry, and sedimentary textures, has produced seven microfacies related to the four facies belts of the lagoon, reef, slope, and open marine. Deep Shelf/Slope Facies Belt: Mf.1. Planktonic foraminifera wackestone-packstone, Mf.2. Bioclast Miogypsina packstone, and Mf.3. Amphistegina coral corallinacea packstone; Shoal/ Reef deposits facies Belt: Mf.4. Coral Boundstone, and Mf.5. Bioclast bryozoan corallinacea Packstone, and Lagoonal facies Belt: Mf.6. Bioclast Packstone, and Mf.7. Porcelaneous foraminifera Packstone.Consequently, of lacking the sediment gravity flows, turbidity facies, and presence of the reef facies deposits (25 percent of the Qom deposits (including coral boundstone, algae, and bryozoan, sedimentation of the Qom formation occurred likely on an open shelf. Facies distribution chart demonstrates that the beginning and closure of the Qom Formation sedimentation occurred significantly in the continental slope environment (without considering the possible erosion phenomenon). Based on sequence stratigraphic studies, five depositional sequences and six-sequence surfaces have been separated (the first and sixth sequence surfaces being of the type-1). Comparing the sequence levels of this study with the sequences identified in other regions of the Central Iran Basin and the European Basin shows a good correlation.