نشریه رخساره های رسوبی
سال نهم شماره 1 (پیاپی 16، بهار و تابستان 1395)

Introdaction
Upper Devonian-Lower Carboniferous rocks are widely exposed throughout Kerman Province (Central-East Iran Microplate). They are mainly represented by limestones, sandstones and interbedded shales, of the Bahram and Hutk Formations. The regional geology and stratigraphy of the Kerman area have been described by Huckriede et al. (1962) and Wendt et al. (2002). The Hutk section is located about 35 km north of Kerman in the Khajeh Mountain, where the Precambrian to Jurassic rocks are exposed. The study area is located in the southwestern part of the geological map of Zarand (Vahdati Daneshmand et al., 1995), and structurally belongs to the southwestern part of the Central-East Iran Microplate. This paper is the first study on stratigraphy and biostratigraphy of the Hutk Formation in the Hutk section, providing evidence of a Tournaisian age of the Formation. Nineteen samples (3-4 kg each) were collected from the Hutk Formation in Hutk section, and processed for conodonts. Of these, twelve samples yielded more than 101 conodont elements. In general, the preservation of the conodont elements is good, although a few specimens being broken or incomplete. The identified conodont fauna consists of thirteen species and subspecies of seven genera including: Gnathodus, Protognathodus, Polygnathus, Mehlina, Bispathodus, Clydagnathus, Siphonodella. In the present paper, we follow the standard conodont zonations of the Early Carboniferous, established by Sandberg et al. (1978). The conodont associations found in the 12 productive conodont samples from the Hutk section allows us to subdivide the deposits into three conodont biozones: the duplicata Zone, Upper part of Upper duplicata-Lower crenulata zones and anchoralis-latus Zone
duplicata Zone: Neopolygnathus communis, Polygnathus inornatus, Polygnathus sp. B, Polygnathus longiposticus, Mehlina sp., Clydagnathus cavusformis occur in this interval associated with the Bispathodus aculeatus aculeatus and Bispathodus stabilis. According to Molloy et al., (1997) Polygnathus longiposticus ranges from within the Lower duplicata Zone in to the Lower Crenulata Zone. Co-occurrence of this species with Clydagnathus cavusformis, which ranges from Middle expansa-Upper duplicata zones, defines the interval.
Upper part of Upper duplicata-Lower crenulata zones: An undifferentiated Upper part of Upper duplicata-Lower crenulata zones interval is discriminated from samples A12 to A16 by co-occurences of Neopolygnathus dentatus and Siphonodella obsoleta. Its lower limit is recognized by the first occurrence Siphonodella obsoleta, which ranges from the Upper part of Upper duplicata to the isostica-U. crenulata zones (Sandberg et al., 1978). The upper limit is identified by the last occurrence of Neopolygnathus dentatus, which ranges from the Latest marginifera to the Lower crenulata zones (Barskov et al., 1991; Ji & Ziegler, 1993).
Barren interval: There is a five-meter barren zone intervenes between the lowest sample attributable to anchoralis-latus Zone and the uppermost bed attributable to Upper part of Upper duplicata-Lower crenulata zones which do not yield any conodont specimen, so the age of this bed has been recognized on the basis of stratigraphic position as Upper crenulata-typicus zones.
anchoralis-latus Zone: The assosiation of Gnathodus pseudosemiglaber and Neopolygnathus communis can be seen here. Its lower boundary is defined by FAD of Gnathodus pseudosemiglaber that ranges from anchoralis–latus Zone to texana Zone (Lane et al., 1980). Co-occurences of this species with Neopolygnathus communis which extinct at anchoralis-latus Zone defines the interval.
Biofacies and Paleoecology: During the Early Carboniferous, the lateral distribution of conodonts across the shallow carbonate shelf to the open sea and basinal environments follows a similar pattern as during the Late Devonian time (Schonlaub & Kreutzer, 1993). The basic concept of conodont biofacies introduced by Sandberg (1976) and later completed by others (e.g. Sandberg & Ziegler 1979; Sandberg et al., 1988; Sandberg & Dreesen, 1984, 1987; Pohler and Barnes, 1990 and Savoy & Haris, 1993). The Paleoenvironment and paleoecology were interpreted from field observation and conodont assemblages. Shallow water conodont biofacies (icriodid-polygnathid) in Lower Famennian deposits of the studied section indicates an inner shelf to foreshore depositional environment for this part of section (Ahmadi et al., 2012). This is similar to most Iranian sequences of Central Iran such as Hojedk (Gholamalian & Kebriaei, 2008), Dalmeh (Hairapetian & Yazdi, 2003) and Chahriseh (Gholamalian, 2007). The middle-late Famennian deposits are characterized by clastic sediments which indicates a considerable sea level fall and marine regression at the Latest Devonian time. This situation is different from other sequences of Central Iran. Middle and late Famennian in some sections (eg. Ghale-Kalaghu and Howz-e-Dorah 1, 2) shows predominance an inner shelf environment (Bahrami et al., 2011) whereas in Kale-e-Sardar section (Eastern Tabas) deep marine sediment were deposited (Gholamalian et al., 2009). The duplicata Zone is characterized by 8 conodont taxa. Species of Polygnathus is most abundant followed by those of Clydagnathus and a low number of Bispathodus+Mehlina. The polygnathid biofacies and occurrences of Clydagnathus represent an inner shelf to mid-continental shelf environment. The upper beds (Upper part of Upper duplicata-Lower crenulata zones, anchoralis latus Zone) is characterized by the appearances of Gnathodus and Siphonodella. These genera have low abundance so the statical analysis is impossible but the presence of these genera represents a sea level rise and establishment of deeper environment during the late Tournaisian. From the Early Carboniferous sequences of Hutk section, north of Kerman, thirteen species and subspecies of conodonts were identified. The age of Hutk Formation has been determined as Tournaisian based on its fauna. Three biozones were recognized on the basis of vertical distribution of these taxa along the stratigraphic column. These strata lie unconformably over the Middle-Upper Famennian terrigenous sediments and covered disconformably by dolostones of Jamal Formation.

  The Paleocene- Early Eocene Sachun Formation in southeast Zagros basin of Iran (Fars sub-basin) is composed of marl, carbonates and evaporates facies (Amiri Bakhtiyar, 2007). The first Cenozoic evaporate succession of Zagros basin in Iran is present in the Sachun Formation. This formation is at type section is composed of marl, carbonate and evaporite (Motiie, 2003; Amiri Bakhtiar, 2007). According to Heydari (2008), during this period Arabian plate and Zagros basin were at the 300 N latitude, so temperature condition was suitable for the formation of evaporate and these deposits have formed along with shallow marine carbonates of Umm er Radhuma (Paleocene), Rus (Early Eocene) and Dihban (Paleocene-Eocene) Formations (Zigler, 2001; Alavi, 2004; Ghazban, 2007). The Sachun Formation has not been studied in detail and can only been refer to works of Arzaghi et al. (2012) and Shabafrooz et al (2013). The aim of this study is to investigate depositional history and diagenetic evolution of evaporite deposits of the Sachun Formation in Siyah anticline section located about 12 kilometers south east of Sarvestan city. After identification of the lower and upper boundaries of this formation, 300 samples were colocted for petrographic studies with sampling interval of 1-2 meters. In order to identify evaporate minerals and intensity of evaporation, ten samples were selected to analyze by XRD (Sw 1800). Additional studies of diagenetic processes heve been performed by Su 3500 scanning electron microscope (SEM) on ten samples at central laboratory of Shahid Beheshti University. Ten Polished section were prepared in central laboratory of National Iranin South Oil Company (NISOC) to study carbonate-evaporite alternation. In this study, structure and structural classification of evaporate have been performed according to Maiklam et al. (1969) and Warren (2006) works. Discussion and Evaporates deposits of the Sachun Formation in Siyah anticline have formed as three types: primary, secondary and tertiary. Primary evaporates are beds and laminates that have formed in sabaqoues environment (salina) due to evaporation. Along with primary evaporates, carbonate also deposited in lagoonal and sabkha environments. Secondary evaporates formed during eogenetic and mesogenetic stages. Nodules sulphates (anhydrite & gypsum) have displaced in marl-carbonate matrix as enterolithic and chicken wire structures. Transformation of gypsum to anhydrite have taken placed in mesogenetic stage due to incrassation of pressure and temperature. Tertiary evaporates or telogenetic evaporites formed in meteoric environment. The most important diagenetic processes in this stage include hydration of anhydrite and formation of bassanite along with secondary gypsum with granoblastic, porphyroblastic and alabastrian textures. Gypsum viens in evaporate and carbonate sediments have been filled by satinspare and sigmoidal gypsum cements. Besides, gypsum cements have formed in carbonate facies. Another diagenetic processes are calcification, dissolution and dissolution breccia. Keywords: Siyah Anticline; Sachun Formation; Gypsum; Anhydrite; Bssanite.
Reference
Alavi, M., 2004. Regional stratigraphy of the Zagros fold-thrust belt of Iran and proforland evolution. American Journal of Sciences, 304:1-20.
Amiri-Bakhtiar, H., 2007. Lithostratigraphy and biostratigraphy of the Tarbur Formation in Fars region. PhD Dissertation, Shahid Beheshti University,Tehran, 439 p.
Arzaghi, S., Khosrow-Tehrani, K., & Afghah, M., 2012. Sedimentology and petrography of Paleocene–Eocene evaporites: the Sachun Formation, Zagros Basin, Iran. Carbonates and Evaporites, 27:43–53.
Ghazban, F., 2007. Petroleum Geology of the Persian Gulf. Tehran University Press, Iran, 707 p.
Maiklem, W.R., Bebout, D.G., & Glaister, R.P., 1969. Classification of anhydrite-a practical approach. Bulletin of Canadian Petroleum Geology, 17:194-233.
Heydari, E., 2008. Tectonics versus eustatic control on supersequences of the Zagros Mountains of Iran. Tectonophysics, 451:56–70
Motiei, H., 2003. Stratigraphy of Zagros, Treatise on the Geology of Iran. Ministry of Mines and Metals, Geological Survey of Iran, Tehran, 539 p
Shabafrooz, R., Mahboubi, A., Moussavi-Harami, R., & Amiri Bakhtiar, H., 2013. Facies analysis and sequence stratigraphy of the evaporite bearing Sachun Formation at the type locality, South East Zagros Basin, Iran. Carbonates and Evaporites, 28: 457-574.
Warren, J.k., 2006. Evaporates: Sediments, Resources and Hydrocarbons. Springer-Verlag Berlin, 1035p.
Ziegler, M.A., 2001. Late Permian to Holocene paleofacies evolution of the Arabian Plate and its hydrocarbon occurrences. Geo Arabia, 6: 445-503

  The Surmeh Formation, with the age of Late Jurassic, is one of the geographically widespread formations in the Zagros and Persian Gulf (Zigler, 2001), The major part of the Salman Oil Field, about two thirds, lies within Iranian waters, while one third is located in territorial waters of Abu Dhabi (Figure 1). As it is one of the most important oil reservoirs in the region, the Surmeh Formation contains gigantic oil reserves. The Surmeh Formation in the Salman Oil Field comprises mainly limestone and dolomite. It is equivalent to the Arab Formation of Saudi Arabia and other Arab countries (Al-Shahran & Narin, 2003). Surmeh Formation in Salman Oil Field is one of the most important oil tanks in the southeast of the Persian Gulf. The Salman oil field has different oil and gas reservoirs from different periods of Permian to Jurassic (James & Wynd, 1965). The main objective of this research is to identify sedimentary conditions and reservoir characteristics of Surmeh Formation. 223 thin sections (with a maximum distance of 30 cm) were prepared and most of them stained with Alizarin Red-S solution and ferricyanide potassium using the Dickson method (1965) in order to recognize calcite from dolomite. The carbonate microfacies were classified according to Dunham (1962) classification and a sedimentary model was proposed using Flugel (2010) scheme. The textures of dolomites were described following Sibley and Gregg (1987). Data gained from aforementioned sources were gathered in order to build and define facies, a depositional model, different diagenetic stages and reservoir quality. The present study is based on laboratory studies of microscopic thin sections
made from core samples. Results and This semi-circular shape of the Salman Oil Field structure reflects its origin as a salt dome.The ten identified microfacies include massive, nodular and laminated anhydrite with chicken-wire fabric, dolomudstone, mudstone with crystals and anhydrite nodules, wavy to laminated dolostromatolite boundstone, bioclast dolopackstone/dolowackestone, peloid-bioclastic dolopackstone/ dolowackestone, peloid-bioclastic dolograinstone, ooid-peloid dolograinstone, ooid dolograinstone, and bioclastic intraclast dolograinstone implying that the Surmeh Formation was deposited in four different environments from sabkha to marine shoal in a homoclinal carbonate ramp setting. The marine and meteoric diagenetic settings were susceptible to produce a variety of features from different types and phases of dolomitization, anhydritization, via cements from early marine to late diagentic cements to micritization, neomorphism, compaction and dissolution. Between all processes affected the Surmeh reservoir, dolomitization, in most cases, enhanced reservoir quality whereas anhydritization reduced reservoir quality.
Porosity variations along the Upper and Lower Arab units in Salman field is directly related to the amount of dolomitization. It also should be stated that, moderate to good reservoir quality is seen in facies belong to moderate to high energy zones of leeward to seaward shoal environments, whereas shallower facies of the inner ramp has the lowest amount of porosity and permeability. In these environments, pores have been filled with the secondary cements. The most important pore types are intergranular, intragranular, vuggy and moldic which are mostly seen in grain-dominated facies. Four types of dolomite in mud-dominated and two kinds of dolomite in grain-dominated textures have been recognized. Mud-dominated dolomites include dolomicrite, dolomicrosparite, dolosparite and scattered dolomites in a limestone matrix. Grain-dominated dolomites are known as fabric retentive and fabric destructive. Sabkha and seepage-reflux models are proposed for the formation of these dolomites. According to these models, it should be mentioned that the type 1 dolomites formed in sabkha environment, while types 2, 3 and 4 are formed under the influence of recrystallization of dolomicrites in a shallow burial environment. In addition, dolomitization in grain-dominated textures occurred from seepage-reflux processes in shoals adjacent to the limited and hypersaline lagoons. Acknowledgment
The authors are greatly acknowleged the Department of Geology, Islamic Azad University, North Tehran Branch and IOOC for providing all the data and logestic support for this study. We are also grateful to anonymous reviewers for their critical review and suggestions that improved our manuscript significantly. Keywords: Sedimentary environment; Diagenesis; Microfacies; Surmeh Formation; Salman Oil Field. References
Alsharhan, A.S., & Narin, A.E.M., 2003. Sedimentary basins and petroleum geology of the Middle East. Elsevier Science, Netherland, 843 p.
Dickson, J.A.D., 1965. A modified staining technique for carbonate in thin section. Nature, 205: 587.
Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. American Association of Petroleum Geologists Memoir, 1: 108-121.
Flugel, E., 2010. Microfacies of Carbonate Rocks: Analysis, Interpretation and Application. Springer Verlag, New York, 996 p.
James, G.A., & Wynd J.G., 1965. Stratigraphic nomenclature of Iranian oil consortium agreement area. American Association of Petroleum Geologists Bulletin, 49 (12): 2182-2245.
Sibley, D.F., & Gregg, J.M., 1987. Classification of dolomite rock textures. Journal of Sedimentary Petrology, 57 (5): 967-975.
Zeigler, M.A., 2001. Late Permian to Holocene paleofacies evolution of the Arabian plate and its hydrocarbon occurrences. GeoArabia, 6(3): 445-504

  In this study, the Upper Jurassic carbonate strata in the Kopet-Dagh sedimentary basin (Mozduran Formation) has been investigated in the Gonbad plain in the west of Golestan Forest National Park. Mozduran Formation in the studied section is composed of muddy limestone containing chert nodules with interbeds of marl and shale that is conformably covered the shale beds of Kashaf-Rud Formation with a sharp boundary. The aim of this study is to interpret the diagenetic history of the Mozduran Formation and to interpret the relation between dolomitization and sequence stratigraphy. One of the most important applications of geochemical studies in carbonate rocks is to determine the composition of primary mineralogy, interpret sedimentary environment and depositional conditions, the palaeo temperature, alteration, differentiation of different diagenetic environments and determination of diagenetic trends (Adabi & Asadi Mehmandosti, 2008). Material and In this study, samples collected from surface section in south of Cheshmeh-Khan village and the data of Qezel-Tapeh well #2 have been used. 130 samples of limestone and dolomite and 8 samples of sandstone from Cheshmeh-Khan section (with thickness of 236 meters) and 103 samples from Qezel-Tapeh well #2 were analyzed and studied. Thin-sections stained with Alizarin Red-S, using Dickson (1965) method to differentiate calcite from dolomite. Global sea level curves presented by Haq et al. (1987) were used and compared with interpreted sea level curve for the sequence stratigraphic analysis. 4 samples of dolomite and 2 samples of pyrite were studied by scanning electron microscopy (SEM) and also analyzed by EDX. In order to study the geochemistry of Mozduran Formation in the Cheshmeh-Khan section, 20 samples (10 samples of micrite and 10 samples of dolomite) were selected for determination of the major elements (Mg and Ca) in terms of percentage and minor elements (Fe, Mn, Sr) in terms of ppm, samples were analyzed by atomic absorption (AAS). Results and Diagenetic studies indicate that the most important diagenetic processes affected these sediments are dolomitization, cementation, micritization, dissolution, physical and chemical compaction and neomorphism. These processes have affected sediments in three meteoric, marine and burial environments. In general, early diagenetic peocesses in marine environment include micritization, formation of isopachous cement and primary dolomite. Formation of isopachous, syntaxial and drusy cements, dissolution (formation of vugy porosity) and neomorphism have occurred at the stage of meteoric diagenesis. Last diagenetic processes (in shallow and deep burial stages) include dolomitization, mechanical compaction, stylolization and formation of fractures.
Neomorphism has seen to operate in three different processes: conversion of calcareous mud to coarse calcite crystals in mud-supported facies, replacement of calcite in aragonite grains, and converting fine-crystalline to coarse-crystalline dolomites. Based on the size and boundaries of crystals (Warren, 2000), four types of dolomite have been identified in the Mozduran Formation, including very fine-crystalline dolomite, mosaic microcrystalline dolomite, medium-crystalline dolomite and coarse- crystalline dolomite. Dolomites formed as primary and replacement in matrix and allochems. The presence of dolomite along dissolution veins and stylolite as well as coarse crystal dolomites indicate that shallow burial processes probably played an important role in the formation of these dolomites. Microcrystalline dolomite (D1) is perfectly indicative of surface conditions, low temperature and probably supratidal environment, due to very small size of crystals, the absence of fossils and the preservation of the primary sedimentary texture (Adabi, 2009). Super saturated alkaline condition with high pH are also suitable for the formation of these primary dolomite (Deng, et al., 2010).
Sibley and Gregg (1987) are believed that semi-shaped straight fabric of coarse-crystalline dolomite (D4) are the result of the slow growth of crystals at low temperatures during shallow burial and formed from recrystallization of finer crystals. Elemental analysis of the studied rocks shows that the effect of diagenic processes, specially diagenetic alteration on a semi-closed system with high water-to-rock exchange on Mozduran Formation was high and the low Sr/Mn ratio shows a high dissolution rate in the formation of dolomites (Rao & Amini, 1995). Very fine crystals of dolomite (the first type) formed in a supratidal environment (Blendinger, 2004), therefore they can form at the end of some shallowing upward sequences (third, fourth, and fifth sequences). The dispersion and abundance of fine crystals of dolomites in the upper parts of sequences represent sea level fluctuation during sedimentation (Khalifa, 2005)

  The siliciclastic Lalun Strata (Early Cambrian), in the Binalud zone, with thickness of 70 metres in the Chenar area, rests with an fault contact on the Early Cambrian sedimentary rocks (Soltaniyeh dolomite). This strata overlain with erosional surface by Eocene conglomerates. The upper part of this strata contains sandstone that compare with upper sandstone unit of other parts (Porsoltani et al., 2014; Poursoltani and Ghotbi Ravandi, 2015). This formation is red to reddish-brown in color, and mostly purple. The one stratigraphic section was logged graphically, and 67 fresh sandstone samples were systematically collected, and 50 thin sections were made. Petrographic modal analyses were done using a Nikon Eclipse E400 Pol microscope, with 500 point counts on 20 samples. Four polished thin sections were studied to determine the composition of mineral components. The Scanning Electron Microscope (SEM) used was a LEO 1450 VP at an acceleration voltage of 30.00 kv. Based on field and laboratory studies, two facies association including sandstone and shale have been identified. The sandstones are fine- to medium-grained and grain-supported, with some coarse-grained and well-rounded components. Based on angularity, sorting, and matrix content, most sandstones are mature and submature. Detrital grains are quartz, predominantly monocrystalline quartz with subordinate polycrystalline quartz, K-feldspar and plagioclase, lithic grains, and accessory minerals and micas. Lithic grains are mainly metamorphic (quartzite) and sedimentary (sandstone and chert), with a few volcanic grains. Heavy minerals include opaques, zircon and tourmaline, scattered or present as a thin laminae. The sandstones have a compositional range from quartzarenite to subarkose and sublitharenite (Folk, 1980). The Lalun sandstones experienced diagenetic events that included compaction, fracturing and cementation. The predominant cement is silica, but some samples contain considerable proportions of carbonate, iron oxides and clays cements, with minor authigenic minerals. The silica is typically non-luminescent, and mainly occurs as syntaxial overgrowths on detrital quartz grains; reddish rims of very fine-grained material that probably include clay and iron oxides mark the contacts between authigenic and detrital quartz. Silica also forms pore-filling cement in primary pores, and large volumes of cement lie along primary and secondary fractures (McBride, 1989; Friis et al., 2010). The cements occupy inter- and intragranular spaces, form veins and fill fractures, and vary from microcrystalline to coarsely crystalline in the case of calcite. Iron oxide cement is present throughout the Lalun Formation as an alteration product and cement. Clay minerals present less than other type of cements, but illite and kaolinite are the main clay minerals cement in Lalun sandstones (Ketzer et al., 2005). Dissolution is prominent in the sandstones. Detrital K-feldspar, quartz, volcanic rock fragments, and carbonate cement all show evidence of partial to complete dissolution. In feldspars, the proportion of voids is variable, with dissolution prominent along cleavages and fractures. The sandstones show variable degrees of mechanical and chemical compaction, which is particularly prominent where early cements are lacking (Mansurbeg et al., 2008). Grain contacts include elongate and concavo-convex, point contacts in rare cases, and sutured contacts that indicate intergranular pressure solution and deformation at a more advanced stage. Quartz and feldspar grains have been intensively fractured but the fractures have been largely healed through silica cementation, allowing the grains to maintain their integrity (Milliken, 1989; Dickinson and Milliken, 1995). This was evident using SEM and CL techniques, which show that the majority of grains contain fractures. Based on petrological and geochemical studies, it is interpreted that diagenetic history of the Lalun sandstones can be related to early, deep burial and late stages (Abdel Wahab, 1998; Salem et al., 2005). Based on petrogragpic studies of upper sandstone units of the Lalun Formation, in Binalud Zone, compaction, fracturing and cementation (mainly silica) are the most important diagentic events of these sandstones. The cements occupy inter- and intragranular spaces, form veins and fill fractures, and vary from microcrystalline to coarsely crystalline. The sandstones show variable degrees of mechanical and chemical compaction, which is particularly prominent where early cements are lacking. Quartz and feldspar grains have been intensively fractured but the fractures have been largely healed through silica cementation, allowing the grains to maintain their integrity. According to diagenetic events, diagenetic history for the Lalun sandstones, in study area, is related to early, deep burial and late stages. Keywords: Diagenesis; Lalun Formation; Early Cambrian; Binalud. Reference
Abdel Wahab, A., 1998. Diagenetic history of Cambrian quartzarenites, Ras Dib-Zeit Bay area, Gulf of Suez, eastern desert, Egypt. Sedimentary Geology, 121: 121-140.
Dickinson, W.W., & Milliken, K.L., 1995. The diagenetic role of brittle deformation in compaction and pressure solution, Etjo sandstone, Nomibia. The Journal of Geology, 103: 339-347.
Folk, R.L., 1980. Petrology of Sedimentary Rock. Hemphill Publishing Co., Texas, 182 p.
Friis, H., Sylvestersen, R.L., Nebel, L.N., Poulsen, M.L.K., & Svendsen, J.B., 2010. Hydrothermally influenced cementation of sandstone-An example from deeply buried Cambrian sandstones from Bornholm, Denmark. Sedimentary Geology, 227: 11-19.
Ketzer, J.M., De Ross, L.F., & Norberto, D., 2005. Kaolinitic meniscus bridges as an indicator of early diagenesis in Nubian sandstone, Sinai, Egypt-discussion. Sedimentology, 52: 3213-217.
Mansurbega, H., Morada, S., Salemc, A., Marfild, R., El-ghalie, M.A.K., Nystuenf, J.P., Cajad, M.A., Amorosig, A., Garciah, D., & La Iglesia, A., 2008. Diagenesis and reservoir quality evolution of palaeocene deep-water, marine sandstones, the Shetland-Faroes Basin, British continental shelf. Marine and Petroleum Geology, 25: 514-543.
McBride, E.F., 1989. Quartz cement in sandstones: A review. Earth–Science Reviews, 26: 69-112.
McBbride, E.F., Land, L.S., & Mack, L.E., 1987. Diagenesis, Norphler Formation (Upper Jurassic), Rankin County, Mississippi, and Mobile County, Alabama. American Association of Petroleum Geologists Bulletin, 71: 1019-1034.
Milliken, K.L., 1989. Petrography and composition of authigenic feldspars, Oligocene Frio Formation, South Tesax. Journal of Sedimentary Petrology, 59: 361-374.
Poursoltani, M.R., Gibling, M.R., & Pe-Piper, G., 2014. Petrography analyses of Lower Cambrian sandstones from central Iran. The Atlantic Geoscience Society, 40th Colloquium and Annual Meeting, Canada, 38-39.
Poursoltani, M.R., & Ghotbi Ravandi, M.R., 2015. Diagenetic history of Early Cambrian sandstones, at Gazouieyeh outcrop, Central Iran. Stratigraphy and Sedimentology Researches, 4: 103-125
Salem, A.M., Ketzer, J.M., Morad, S., Rizk, R.R., & Al-Aasm, I. S., 2005. Diagenesis and Reservoir-Quality evolution of incised-valley sandstones: Evidence from the Abu Madi Gas Reservoirs (Upper Miocene), The Nile Delta Basin, Egypt. Journal of Sedimentary Research, 75: 572-584

 

The Garau Formation is one of the Lower Cretaceous source rocks in Zagros sedimentary basin. This formation has been a great target for many studies due to its stratigraphic and economic importance as it has been acting as a source and sometimes as a reservoir in Zagros Basin. This formation in well A in central Lurestan has a thickness of 794 m and lithologically consists of ‎argillaceous limestone, shale and marl. The formation in this well is overlain by the Surgah ‎Formation and disconformably rests on the evaporites of the Gotnia Formation. ‎In order to establish the age and biozonation of the Garau Formation in this well, ‎foraminiferal contents of 528 thin sections have been studied and a biozonation has been established. Material and

Thin sections were studied under a light microscope and based on the FOD and LOD of the index species of foraminifera presented in a range chart a biozonation has been established based on Wynd (1965) and Premoli Silva and Verga (2004). Discussion and

The Garau Formation is 794 meters thick in a well A in central Lurestan and for the confidentiality reason, it is named here as well A. The formation here is confined between the Gotnia Formation at the base and the Surgah Formation at the top. This well situated about a few Km west of Kermanshah and a few Km northeast of Eslam-Abad in the Central Lurestan Province. From the viewpoint of lithology, the Garau Formation in this well is divided into three intervals; the basal interbeds of marl and shale, limestone and shaly limestone units at the middle part and finally upper shaly beds.
A total of 528 thin sections from the cutting samples and 40 thin sections from the core samples of the formation were prepared and studied for age dating and biozonation. Fifteen genera and 48 species of planktonic foraminifera were identified leading to differentiation of 14 planktonic foraminiferal biozones from the Berriasian to middle Cenomanian in age. These established biozones correspond to Radiolaria Flood Zone #12, Assemblage subzsone #13 and Assemblage zone #20 of Wynd (1965).
Also paleoenvironmental investigations were performed on the samples; the identified microfacies and planktonic foraminifera depth morphotypes suggested that the strata of this rock unit deposited in a deep marine setting.
Sixty seven samples were also prepared and studied for their palynological contents. All prepared samples were barren of palynomorphs however, percentage of main groups of palynological elements were calculated for palynofacies studies. Using Tyson diagram (1993), led to the recognition of two types of palynofacies (IX and VI) and proved domination of an anoxic deep marine condition during depositional course of the formation in this well.
On the base of gamma log and microscopic kerogen analysis result, shaly intervals of the formation, especially the basal shales, can be counted as a source rock. For this reason, three samples were selected for rock eval pyrolysis and the obtained results showed the Kerogen is type III which cannot produce enough petroleum. Although, the Garau Formation in well A has high content of organic matters and it is at mature stage, but due to the low values of hydrogen index (HI), the formation has no potential to act as a source rock. Acknowledgement
The authors wish to thank the exploration directorate authorities of the NIOC for providing data such as thin sections and allow to publish these data. Keywords: Garau Formation; Biostratigraphy; Planktonic foraminifera; Well A; ‎Microfacies; Palynofacies References
Premoli-Silva, I., & Verga, D., (Eds.), 2004. Practical manual of Cretaceous planktonic foraminifera, International School on Planktonic foraminifera, Cretaceous. Universities of Perugia and Milan, Tipografia Pontefelcino, Prugia (Italy), 248 p.
Tyson R.V., 1993. Palynofacies analysis. Applied Micropaleontology, 153-191.
Wynd, J.G., 1965. Biofacies of the Iranian consortium-agreement area. Iranian Offshore Oil Company, Tehran, Report 1082.

Intoduction
Mud cracks are primary polygonal structures that are formed by extension strains during drying period. Major factor in the formation of cracks are humidity and temperature. Quality and quantity of clay minerals, topoghraphy, sediments size, depth of cracks, water salinity and bioturbation are also important in crack,s distribution patterns. Studies have shown that cracks are lattice type in gentle slope areas and rectangular type in elevated slopes. Crack,s width and length, components size, and fractal characteristics are environmental factors in cracks distribution patterns. Fifty samples were collected from four studied regions of Voshmgir dam reservoir, north of Gorgan (S1-S4). Geometrical characteristics of cracks were determined. Samples analyized for granoulometry aspect, using hydrometry method, liquid limit identifying and plastic limit dentifying in the lab. After identification of mud cracks and processing, geometrical parameters such as drawing polygonal geometrical shapes between cracks, number of polygonal shapes between cracks, polygonal shapes area and their internal angels and angels between crossed cracks were measured and analysed statistically in four studied regions and other regions. In general, photos were taken in 45 spots in 4 studied regions from mud cracks and suitable scale were dedicated to the photos in order to determine geometrical parameters. Then, using image,s analysis software, geometrical parameters of each crack were measured and the average were computed Discussion and Textural characteristics of samples collected from four regions in Voshmgir dam reservoirs have shown that sediments are classified in clay and silty clay zones in triangular textural diagram and CL clay in unified classification of soils and were formed in diagenetic phase. Clay mineralogy of sediments include 10% cholorite, 40% illite, 30 % vermiculite and 20% kaolinite. Clay minerals of samples were originated in east of Golestan loesses.
From geometric point of view, cracks had an average of 6.7 sides, 10 cm length of each sides and 307 cm2 area. Mean internal angle was 125 ° and total internal angles 836 °. From superficial aspect, there is a good correlation between studied mud cracks polygones and an ordered polygon. Heterogeneity in angles relations was due to curve forming in sides crossed areas after forming cracks which were related to crack age so the older the cracks become, the angel between sides is more similar to a curve.
Comparing mean geometric parameters in four studied regions have shown that first generation cracks are different from each other in geometric aspects. Due to F.distribution, P.Value and means diagram, cracks parameters and polygons in S1, S2 and S3 areas were the same but S4 characteristic parameters especially total internal angle and each sides length have meaningful difference to the other regions due to low plastic limit and high depth of sediments in S4 area.
Studies of angels between mud cracks have shown that there are two patterns of mud cracks. Some of them are T- shaped in which the crossed angle is approximately 90 °. The other group, by creating hexagonal shapes, are Y- shaped and the angle between them are approximately 120 °. Studied samples are more similar to Y- shaped pattern with a mean angle of 114 °. Keywords: Mud crack; Fine grain facies; Geometric; Voshmgir Dam reservoir; Golestan. References
Amini,A ., Rezaei, H., Parsaee, R.,Teymori, J., 2006. Possiblity of clay materials in produce of type 1 and 2 irrigation channel in Golestan province, Golestan water distrrbution co.
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Goehring, L., 2013. Evolving fracture patterns: columnar joints, mud cracks, and polygonal terrain. Applied Clay Science, 40 (3):103-118.
Goehring, L., Conroy, R., Akhter, A., William, J., Clegg, W.J., & Routh, A.F., 2010. Evolution of mud-crack patterns during repeated drying cycles. Applied Clay Sciences, 37: 89-97.
Velde, M., 1999. Structure of surface cracks in soil and muds. Geoderma, 93: 101-124.
Vogel, H.J., Hoffmann, H., Leopold, A., & Roth, K., 2005. Studies of crack dynamics in clay soil: II. A physically based model for crack formation. Geoderma, 125: 213–223.
Zhao, Z., Guo, Y., Wang, Y., Liu, H., & Zhang, Q., 2014. Growth patterns and dynamics of mud cracks at different digenetic stages and its geological significance. International Journal of Sediment Research, 29: 82-98

  Parvadeh Formation is the first rock unit of second sedimentary cycle of Jurassic sedimentary deposits in Central Iran. At the type locality, Parvadeh Formation is overlain and underlain by sandstones of the Hojedk and the marls of Baghamshah formations (Seyed-Emami et al., 1991; Aghanabati, 1996; Valipoori Godarzi et al., 2014). Lithologically, this sequence sttarts with a siliciclastic at the base and continues with almost uniform gray limestones. This formation is completely different with the lower shale and sandstone deposits and also upper green gray marl that separates these two rock units. Based on biostratigraphic studies of this section, Middle to Late Bathonian age has been suggested for this sequence (Aghanabati, 1996). The studied section is located at Kamar-Mahdi area, 68 Km southwest of Tabas city, that contain sandstone and siltstone rock units and thin to medium bedded carbonate rocks that continues to sandstone-coal layers of Hojedk Formation (Valipoori Godarzi et al., 2014; Zarrin, 2014). For performance of laboratory studies, totally 86 rock samples were collected from Parvadeh Formation in Kamar-Mahdi section (eleven siliciclastic and seventy-five carbonate samples). All of the carbonate samples were stained using Dickson method (1965) for recognition of calcite from dolomite. Then, the stained microscopic samples were studied and photographed in detail at the laboratories of the department of Geology/University of Birjand. For the purpose of geochemical analysis of major and minor elements, totally 14 suitable micritic samples with low amount of insoluble residues (El-Hefnawi et al., 2010) were selected for atomic absorption spectrometery (AAS) analysis. This method is applied for determination of the amounts of Ca and Mg major elements and Sr, Fe, Mn and Na minor elements in carbonate rock samples. The AAS analyses were carried out using Shimadzu 670 device in analytical chemistry laboratory at the Ferdowsi University of Mashhad. Based on the obtained results from microscopic studies of thin sections, two siliciclastic lithofacies and eight carbonate microfacies were identified as follows: calclithite sandstone (C1), sandy bioclastic packstone (L1), siltstone (L2), extraclastic/peloidal packstone (L3), bioclastic/peloidal wackestone/packstone (L4), bioclastic/oncoidal packstone (L5), coral/sponge framestone (B1), oolithic/bioclastic grainstone (B2), bioclastic floatstone (M1) and bioclastic/oolithic packstone (M2). These lithofacies and microfacies were classified within four beach, lagoon, barrier and open marine facies belts. Based on the position of facies belts and compared with similar models, the suggested depositional environment for Parvadeh Formation in Kamar-Mahdi section is a rimmed shelf type carbonate platform. According to the petrography studies of thin section, the most significant diagenetic processes affecting on the carbonate samples of Parvadeh Formation in Kamar-Mahdi section are: micritization, dissolution and formation of intraparticle and interparticle porosities and incomplete bladed cement during marine diagenetic stage, physical and chemical compaction, creation of moldic and fracture porosities by dissolution, neomorphism, forming of equal mosaic and granular and syntaxial overgrowth cements, dolomitization and incomplete stylolitization in shallow burial diagenetic environment and formation of non-ferroan drusy mosaic and granular cements in phreatic meteoric diagenetic environment.
The analysis of major elements of carbonate samples reveals that the samples are composed of limestone, dolomite and dolomitized limestone. Also, based on the amounts of minor elements, primary mineralogical composition of the studied carbonate samples is aragonite. The Sr-Na crossplot diagram for the studied carbonate samples show a primary mineralogical composition similar to aragonite samples of Mozduran Formation. In addition, comparison of the obtained results with the previously published works (e.g. Brand & Veizer, 1981) indicates an open system geochemically for the studied carbonate samples. Furthermore, based on the amounts of minor elements, it has been concluded that the studied samples have been affected mostly within burial and meteoric diagenetic environments. Finally, based on Na/Sr ratio versus Mn values crossplot, paleoenvironmental conditions for this sequence have had similar to recent tropical environments. Based on the microscopic studies of thin sections and microfacies analysis, four different facies belts including coastal, lagoon, barrier and open marine belts have been identified and a rimmed shelf type carbonate platform depositional environment has been suggested for this sequence. Based on the study of thin sections and also results of geochemical analysis, diagenetic processes on the carbonate samples are mostly operated within burial and meteoric diagenetic environments. Geochemical analysis of the major elements revealed that the studied carbonate samples are composed of limestone, dolomite and dolomitized limestone. The results of geochemical analyses indicate an open geochemical system, aragonitic primary mineralogy and tropical paleoenvironmental conditions for the studied sequence