نشریه رخساره های رسوبی
سال سیزدهم شماره 2 (پیاپی 25، پاییز و زمستان 1399)

This research has studied calcareous nannofossils of the Baghamshah Formation in Tabas Block (eastern Iran). Calcareous nannofossils are one of the most important fossil groups for biostratigraphical analysis. The earliest paleontological studies on the Baghamshah Formation have focused on ammonites (e.g., Seyed-Emami et al. 1988, 1991, 1997, 2001, 2002; Wilmsen et al., 2009). Kallanxhi et al. (2016) have also considered this formation's ammonites and nannofossil contents. The current study is the first investigation of calcareous nannofossils of the Baghamshah Formation in the Kharvan section and aims to discuss the possibility of using the standard nannofossil zones for the Baghamshah Formation.

The Kharvan section with 239 meters thickness is located 40 km northeast of Tabas near the Kharvan village. The formation has lithologically consisted of green and gray shales and marls. Generally, 75 samples from the Baghamshah Formation have been taken. Samples were prepared via the smear slide method (Bown & Young, 1998). All nannofossils were photographed in both cross-polarized light (XPL) and (PPL) and identified using Perch-Nielsen (1985) and Bown & Young (1998).

46 species belonging to 26 genera were identified in the studied section. Amongst them, 38 species belong to 21 genera of nannoliths and coccoliths, and 8 species from 5 genera belong to Didemnid ascidian spicules. Didemnid ascidian spicules are organisms with soft bodies and rigid spicules, which carbonate-rich seawaters and coral reefs are suitable environments for their colonization (Varol, 2006). The most dominant genera from the Baghamshah Formation are Watznaueria and Nannoconus. Among the nannofossil species, Nannoconus steinmannii, Retecapsa angustiforata, Calcicalathina oblongata, Tubodiscus verenae, Lithraphidites bollii, Cruciellipsis cuvillieri, and Nannoconus abundans are index species, used for biozonation. The Biostratigraphic studies in the Baghamshah Formation is led to the identification of calcareous nannofossils biozones CC1 to CC5 of Sissingh (1977) in the Kharvan section. Determined biozones represent the age of the early Berriasian - late Hauterivian for the investigated strata in the Kharvan section

The nannofossil assemblages of the Baghamshah Formation in the Kharvan section have average to pretty good preservation. In this section, the presence of CC1 at the lower part of the Baghamshah Formation and the presence of CC5 at the upper part of the formation shows that the age of the Baghamshah Formation is Early Berriasian - Late Hauterivian in the Kharvan section.

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.

The Kopet-Dagh sedimentary Basin that crops out from NE Iran to Turkmenistan was formed as an intracontinental Basin due to the southeastern extension of the South Caspian Basin by Neotethyan back-arc rifting after the closure of the Palaeotethys and the early Cimmerian Orogeny (middle Triassic). A thick sedimentary package (10 kilometers) consisting of five transgressive- regressive super-sequences from Jurassic to Miocene time is deposited in the Eastern part of the sedimentary basin that is mainly controlled by NW-SW running major faults. The Cretaceous sequence in the Kopet-Dagh Basin is divided into nine formations, mainly composed of sandstones, conglomerates, mudstones, limestones, and dolomites with minor amounts of evaporates (Afshar-Harb, 1979). The regional trend of the Kopet-Dagh sedimentary basin was northwest-southeast during the Cretaceous. After the deposition of thick, red siliciclastic sediments of the fluvial system during the Early Cretaceous, a suitable condition for the deposition of carbonate sediments (named as Tirgan Formation) was provided as a result of major marine transgression during the Barremian-Aptian stages. The Tirgan Formation is one of the most widespread Upper Cretaceous formations in the eastern Kopet-Dagh that unconformably overlies the fluvial sediments of the Shurijeh Formation and is overlain by a sharp contact of the Sarcheshmeh Formation.

This study is focused on two stratigraphic sections in the Eastern Kopet-Dagh in northern Iran. Ninety thin sections were examined to identify fine-scale physical characteristics (mineralogical composition and fossil contents). Lithology, grain size, and sedimentary structures were recorded.

Based on sedimentological features, sixteen facies are recognized that grouped within five facies associations consist of deep and shallow open marine (FA), shoal (FB), lagoon (FC), and Tidal flat (FD). Deep open marine facies include green-gray fissile (sandy-silty) shale and shallow open marine facies are mainly consist of bioclastic wackestone, ooid/peloid bioclastic floatstone, sandy intraclastic floatstone, sandy intraclastic bioclastic float-rudstone, and sandy peloid bioclastic grainstone. The main constituents in this association are brachiopods, bryozoans, echinoderms, oysters, orbitolinids, intraclasts, ooids, and peloids. Micrite envelopes and borings are the common features in this association. The skeletal elements display high fragmentation, preferentially horizontal orientation, and fining up-ward fabrics. Green-gray fissile shale is deposited in a low energy depositional setting below weather wave base (SWWB), periodically affected by storm waves, suggested by the presence of the siliciclastic grains. The skeletal elements of the shallow open marine facies offer a shallow full open marine setting between SWWB and fair-weather wave base (FWWB) (Bovar-Arnal et al., 2009). High fragmentation, preferentially horizontal orientation, and fining upward skeletal elements suggest the storm-generated shell concentrations. Low energy periods of the sedimentary environment (post- and pre-storm phase) are indicated by micrite envelopes and borings. Shoal association consists of ooid grainstone and sandy ooid grainstone facies with predominantly well-sorted fabric. The main sedimentary structures in this association are sigmoidal cross-beds, wave ripples, cross lamination, and planar cross-beds with the erosional surface. These sediments are deposited in medium-high energy shoal settings above FWWB in the inner ramp environment suggested by well sorting of the elements and predominantly grainstone facies (Bachmann & Hirsch, 2006; Brandano et al., 2012). The sedimentary structures clearly show that tidal currents controlled the association's deposition in a sandy shoal environment. Lagoon association includes sandy mudstone, bioclastic wack-packstone, sandy ooid wackestone, sandy peloid packstone, intraclast, ooid float-rudstone, ooid/peloid pack-grainstone, ooidal bioclastic float-rudstone with main ooids, peloids, benthic foraminifers, echinoderms, and minor content of green algae, bivalves, brachiopods as well as siliciclastic grains that are commonly floated in the micritic matrix. These sediments are mainly deposited in a semi-restricted to restricted (sandy mudstone) lagoon setting above FWWB. The periodical water circulation suggested by the mixture of the open marine (echinoderm, brachiopods) to more restricted and brackish water elements (ostracodes, benthic forams), floated within the micritic matrix (Colombie & Strasser, 2005; Bachmann & Hirsch, 2006; Bovar-Arnal et al., 2009). The tidal flat association mainly consists of peloids, benthic foraminifers, and ostracods surrounded by flat microbial laminations. The flat geometry of the microbial lamination and the presence of the peloids and benthic foraminifers as the main elements in this association demonstrate a flat substrate in a tidal flat setting of the most internal part of the carbonate platform.

In a general view, petrography and field observations, facies associations relationship, and vertical trend of the studied successions suggest Tirgan sediments in the Kopet-Dagh basin are deposited in shallow to the deep marine environment with tidal flat, lagoon, shoal, and shallow to deep marine facies zones. These sediments were deposited in a homoclinal ramp characterized by gradationally vertical changes in the facies associations and abundant storm deposits. This carbonate system was influenced by storm (shallow marine zone) and tidal (shoal zone) currents suggested by the storm-generated shell concentrations, wave ripples, cross laminations, and sigmoidal cross-beds.

The relationship between the composition of siliciclastic sediments, tectonic setting, and the source rocks has been studied by many researchers. The siliciclastic deposits are always affected by the composition of source rock, chemical weathering, transport distance, and diagenetic changes after deposition. It is possible to determine the paleoclimatic conditions of siliciclastic rocks, particularly sandstones, using different methods such as petrography and geochemistry. Interpretation of paleoclimatic conditions has a significant impact on the reconstruction of paleogeography (Garzanti & Resentini, 2016). Due to their fine-grain and low permeability, shale can preserve the composition of source rock minerals and, therefore, are very important in interpreting the source rocks (Khanehbad et al., 2012). In this study, the distribution of the major elements in the sandstones and shales of the Shurijeh Formation is compared with the standard values, and the paleoclimatic conditions have been interpreted.

One of the best techniques to major elements values in the siliciclastic sediments is the analysis of rock by the XRF method. Petrographic studies on seven samples of sandstones were done using a polarizing microscope and classified based on Folk's (1980) classification scheme. Also, six shale samples with the lowest calcium carbonate content are selected. Fresh shale and sandstone samples were chosen for geochemical analysis and then were powdered to the size of fewer than 63 microns using Agate mortar. The presence of calcium carbonate on cement can cause an error in Ca contents, so the samples were washed with 10% hydrochloric acid to remove the CaCO3. The residual powders (IR) were analyzed using Philips Panalytical Model X-ray Fluorescence (XRF) to determine the major oxides and trace elements of siliciclastic particles in the Taban Gostar laboratory in Tehran.

The Suttner & Dutta (1986) binary diagram determines the paleoclimatic conditions and paleoweathering at the source area. In this diagram, the plotted values of the Shurijeh Formation sandstone samples show the semi-humid climatic condition. In contrast, the plotted values of shale samples in this diagram show different results. They indicate the semi-arid climatic conditions, which are entirely different from the results of the sandstone samples. Various statements can be presented for this difference. First, shale samples usually have higher K2O and Al2O3 than SiO2 due to the presence of higher amounts of clay minerals. However, in the sandstones (due to the presence of quartz and chert minerals), silica is higher than the shale samples (Gateneh, 2000). Therefore, these differences in the values of SiO2, Al2O3, and K2O cause the differences in the shale and sandstone samples in the binary diagram (Suttner and Dutta, 1986). By comparing this chart with the "A-CN-K" ternary chart, better results can be obtained. This indicates that it is better to select the sandstone samples which are least affected by diagenetic processes based on detailed petrography studied.Calculation of the CIA index values in the studied sandstone and shale samples shows high weathering conditions in the source rock area within the semi-humid climatic conditions. The use of binary diagrams for sandstone samples confirms this subject, and the results are the same as the triangular diagram "A-CN-K" for the sandstones. However, in the case of shale samples containing clay minerals, the binary diagram shows completely different results, indicating cold and dry climatic conditions. One of the main reasons for this difference is the increase of the SiO2/Al2O3 ratio in shale samples. Therefore, binary diagram is not recommended for the shale samples, including clay minerals. Instead, it is better to use only the triangular diagram "A-CN-K", which shows the wet conditions and semi-humid climate. Small changes in the amount of Al2O3 due to diagenesis, on the one hand, and large changes in the amounts of Na2O, CaO, K2O, and SiO2 in the diagenetic condition, on the other hand, can even exacerbate the error of using the triangular diagram A-CN-K. Because the values of these elements, based on the geochemical analysis data, are less than the original values; therefore, it causes analytical errors in the interpretation of the data. For this reason, it is recommended to select the least affected sandstone samples by diagenetic processes after a detailed petrographic study.

The extent of the Shemshak group with Late Triassic-Middle Jurassic age in Iran can be divided into two structural-sedimentary zones of Iran and Zagros, which are separated by the main thrust of Zagros. The first zone is divided into two areas of Alborz and Central Iran (Moin-o-Sadat & Zade-Kabir, 1991). After the Early Cimmerian orogeny, a sedimentary sequence consisting of marl, sandstone, and reef limestone was deposited in Central Iran, called Nayband Formation. The Nayband Formation type section is located near the Naybandan village, 220 km south of Tabas city (Douglas, 1929). Its thickness reaches 3000 m in type locality (Kluyver et al., 1983; Seyed-Emami, 2003; Fürsich et al., 2005). The study area of the current research is located 74 km northeast of Isfahan, 15 km northwest of Chahriseh village (33°04’10’’N, 52°01’40’’E). This region is located in the western margin of the central Iran zone and south of Kashan. The thickness of the Nayband Formation in the north and northeast of Isfahan reaches a maximum of 660 meters, divided into five members (Mannani & Yazdi, 2009).

Upper Triassic succession in the northeast of Isfahan (Chahriseh section) was studied using Kashan's quadrangular geological map (Zahedi et al., 1991). Characteristics of sedimentary sequences such as stratification, lateral expansion and sedimentary structures were recorded. Sampling was taken systematically and regularly at one-meter intervals. Twenty-two plant macrofossils of Nayband Formation from the Qadir member have been collected.

A key bed of gray sandstone with plant macrofossils, up to 15 m thick, is identified in the Qadir member. Two genera and four species have been found in the section, include Clathropteris meniscoides (Brongniart 1825) Brongniart 1828 (Age: Carnian- Early Lias), Clathropteris obovata Oishi 1932, emend. Harris 1961 (Age: Norian- Middle Jurassic), Nilssonia pseudobrevis (Barnard 1967b) Corsin & Stampfli 1977 (Age: Norian- Rhaetian) and Nilssonia sp.Based on the Clathropteris meniscoides, Clathropteris obovata, and Nilssonia pseudobrevis in Qadir member (Nayband Formation) and their in situ stratigraphic position, these strata are deposited in Rhaetian. In this study, Clathropteris obovata is reported from Late Triassic age in Iran for the first time. Before this, Clathropteris obovata in Iran has been reported from only Jurassic (Late Liassic-Early Dugger); however, this species has a wider range from Late Triassic to Late Dugger succession in the other parts of the world. So, its record in the Nayband Formation (Late Triassic) is not unexpected. Moreover, the record of Clathropteris in the northeast of Isfahan is its first occurrence in an area outside of Kerman in Central Iran. Due to the low presence of plant macrofossils and the abundant presence of Clathropteris in the northeastern region of Isfahan, high humidity and warm weather of the Late Triassic may be suggested.

Asmari Formation is a thick succession of Oligocene-Miocene sedimentary rocks, the leading crude oil reservoir in the Zagros structural-sedimentary zone, and one of the largest oil reserves in the world (Alavi, 2004). Due to its economic significance, this formation has long been considered in recent decades. The presence of large benthic foraminifera as the most important fossil group in the Asmari Formation is essential for the biostratigraphic studies of this formation. This study aims to study the Asmari Formation in Gachsaran oil field in southwestern Iran, 200 km southeast of Ahvaz. In order to identify lithological changes and the biostratigraphic studies, three wells were selected from the Gachsaran oil field, including wells A, B, and C.

In the mentioned three wells of the Gachsaran oil field, the Asmari Formation has 590 m thickness in well A, 336 m in well B, and 382 m in well C. In this study, 3235 microscopic thin sections were prepared from the Asmari Formation, 1572 thin sections from well A, 809 from well B, and 854 from well C. Identification of microfossils have been done based on the Adams & Bourgeois (1967), Loeblish & Tappan (1988), and Hottinger (1997), and Biostratigraphic studies according to the Laursen et al. (2009) and Van Bochem et al. (2010).

The Asmari Formation in the Gachsaran oil field consists of limestone, dolomitic limestone, and dolomite. Based on the distribution of benthic foraminifera in the studied wells, four faunal assemblages equivalent to those introduced by Laursen et al. (2009) and Van Bochem et al. (2010) have been recognized in the Asmari Formation. They are as follows:1- Nummulites vascus - Nummulites fichteli Assemblage zone 2- Archaias asmaricus-Archaias hensoni - Miogypsinoides complanatus Assemblage zone 3- Miogypsina - Elphidium sp. 14- Peneroplis farsensis Assemblage Zone 4- Borelis melo curdica- Borelis melo melo Assemblage Zone Assemblage zone 1 is equal to zone No. 2 of Laursen et al. (2009) and Van Bochem et al. (2010) (Nummulites vascus - Nummulites fichteli Assemblage zone) and contains index nummulitids such as Nummulites vascus, Nummulites fichteli, Nummulites intermedius with Rupelian in age. This biozone has been recorded in all three wells. Assemblage zone 2 is equivalent to zone No. 4 in Laursen et al. (2009) and Van Bochem et al. (2010) (Archaias asmaricus-Archaias hensoni - Miogypsinoides complanatus Assemblage zone). This assemblage contains index fossils such as Miogypsinoides complanatus, Archaias kirkukensis, Archaias hensoni. The appearance, abundance, and extinction of Archaias are occurred in this zone and represent the Chattian. This zone has also been recognized in all three wells. Assemblage zone 3 which is again present in all three wells, corresponds to zone No. 5 of Laursen et al. (2009) and Van Bochem et al. (2010) (Miogypsina - Elphidium sp. 14- Peneroplis farsensis Assemblage Zone). It has significant fossils such as Miogypsina, Elphidium sp. 14, and Peneroplis farsensis. Due to the presence of these index fossils as well as the disappearance of the genus Archaias at the end of the Chattian, even the absence of Borelis melo curdica (Burdigalian index), this zone belongs to Aquitanian. Assemblage zone 4 is comparable to biozone No. 7 in Laursen et al. (2009) and Van Bochem et al. (2010) (Borelis melo curdica- Borelis melo melo Assemblage Zone). Due to the index species Borelis melo curdica, this part of the sequence belongs to the Early Miocene (Burdigalian). This biozone has been identified only in wells A and C. Therefore, biostratigraphically, the most complete sequence of Oligocene - Early Miocene Asmari Formation in this study is recorded in wells A and C.

Devonian-Carboniferous boundary is an exciting issue for researchers all over the world. In this boundary, significant events have occurred on marine organisms (specially conodonts elements) and terrestrial organisms, consisting of weather and sea-level changes, and relative coincidence with the Hangenberg bio-event (Mc. Ghee, 1998; Sandberg et al., 2002; Caplan & Bustin, 1999; Kaiser et al., 2006, 2011, Bahrami et al., 2011, 2019; Konigshof et al., 2021; Sattari et al., 2021). According to ICS, the Devonian-Carboniferous boundary, as defined by the first Appearance Datum (FAD) of the conodont species Siphonodella sulcata within the Siphonodella praesulcata- Siphonodella sulcata lineage and the GSSP is located in the La Serre Trench E’ section in France (Paproth et al. 1991). Khoshyeilagh Formation in Zoo section consists of shallow marine deposits attributed to the Late Devonian (Frasnian-Famennin) (Najjarzadeh, 1997). This study focuses on identifying and reviewing the Devonian-Carboniferous boundary in a part of the Eastern Alborz area and study the biostratigraphy of deposits near this boundary based on conodont fauna.

58 carbonate and 11 non-carbonate samples (3-4 kg/each) were collected and processed for conodonts. The samples were processed with the conventional acetic acid technique, but formic acid 10% with 10 hours was also used for some silty samples and compacted limestones. Then picked remaining deposits with the handpicking method. The following steps include pasting the conodont specimens on stab, photographing them under an SEM microscope, and naming conodonts elements based on available references (e.g., Branson & Mehl, 1934; …). Accordingly, the biozonation of the studied sequence using the global standard zonings of Ziegler & Sandberg (1990), Sommervile (2008), Poty et al. (2006), Spalletta et al. (2017).

Khoushyeilagh and Mobarak formations Late Devonian-Carboniferous conodonts fauna of Zoo section, (NE Jajarm), led to identifying 10 conodont genera, 23 species, and 8 subspecies. The conodont faunas which be obtained in this research indicate the presence of these biozones: Bispathodus ultimus Zone (Latest Famennian), From the base of Siphonodella duplicata to within Siphonodella crenulata interval (Tournaisian), and Pseudopolygnathos multistriatus Zone (Visean). According to this study, the Fm/T boundary is located at the end of Khoushyeilagh formation, 6m above the diabase layer. The conodonts, as mentioned above, are indicators for Polygnathid biofacies. These sequences are similar to other Famennian-Tournaisian deposits in the east Alborz, both in the litho-facies and bio-facies peculiarities. The conodont Color Alteration Index in the Carboniferous conodonts element increased compared to the Late Devonian elements.

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.