فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و دوم شماره 4 (پیاپی 65، زمستان 1395)

Introduction According to different paleontological and paleomagnetic studies, Iran was part of the Gondwana during the Permian. The Permian lithostratigraphic units in the Alborz-Azerbaijan are introduced as Doroud, Ruteh and Nesen Formations. The Ruteh Formation, the second depositional cycle of the Permian in the Alborz Basin, have been studied at two stratigraphic sections in the Central Alborz. The Sangsar section located on the south flank of the Central Alborz, 1 km northwest of Mahdishahr city and the Makaroud section located on the north flank of the Central Alborz, about 37 km south of Chalous city. The thickness of the Ruteh Formation at the Sangsar section is 106 m and at the Makaroud section is 222 m. At the Sangsar section the Ruteh Formation is underlain by the Doroud Formation with gradual contact and is overlain by a lateritic horizon. At the Makaroud section the Ruteh Formation disconformably overlies the Doroud Formation and the upper boundary is faulted and the Chalous Formation overlies the Ruteh Formation at this section. The aim of this paper is to analysis microfacies, interpret depositional environments and delineate relative sea level changes of the Ruteh Formation. Other researchers studied the Ruteh Formation at different sections in the Alborz Basin believe that the carbonate sediments of this formation have been deposited in a homoclinal carbonate ramp and consist of two-three 3rd order depositional sequences. But no sedimentological studies have been done at the selected sections in this study.
Material & Methods Two stratigraphic sections of the Ruteh Formation have been selected, measuted and sampled. One hundred sixty three samples (fifty seven samples from Sangsar and one hundred six samples from Makaroud section) were collected and thin sections were prepared from all samples. Afew samples were collected from lower and upper formations. Thin sections were stained with potassium ferricyanide and alizarin-red S solution according to Dickson (1965) method. The grain and matrix percentages were estimated using visual percentage charts of Bacelle and Bosellini (1965). Dunham (1962) classification were used for carbonate facies nomenclature. Based on lithological and textural characteristics, fossil content, abiotic allochems, facies succession and their comparision with well studied environments by Flugel (2010), microfacies and their subenvironments have been identified. In this study investigation of relative sea level changes is on the basis of field observations and facies analysis. Based on the vertical succession of microfacies and sedimentary paleoenvironmental features, Systems tracts and sedimentary sequences have been recognized.
Discussion of Results & Conclusions Field and petrographic studies at the Sangsar and Makaroud sections, indicate that the Ruteh Formation sediments consist of 19 carbonate microfacies and one siliciclastic petrofacies that during the Middle Permian times deposited in tidal flat to open marine facies belts of a bioclastic homoclinal carbonate ramp on the southern passive margin of the Paleotethys located on the northern Gondwana Supercontinent in a tropical region. Tidal flat facies belt includes: Dolomitic mudstone, lime mudstone to sandy lime mudstone, pelloid intraclast packstone and one quartzarenite siliciclastic petrofacies. Lagoon facies belt includes: bioclast mudstone, dasycladacea wackestone, foraminifera pelloid wackestone, bioclast pelloid wackestone, bioclast tubiphytes wackestone, bioclast algal wackestone/packstone. Shoal facies belt includes: ooid pelloid packstone/grainstone, bioclast pelloid packstone/grainstone, pelloid bioclast grainstone and algal packstone/grainstone. Open marine facies belt includes: tubiphytes gymnocodiacea wackestone, gymnocodiacea packstone, bioclast gymnocodiacea wackestone, sponge spicule bioclast wackestone, crinoid mudstone/wackestone and bioclast mudstone.
The Ruteh Formation at both sections deposited mainly in inner ramp environment but thickness of the sediments deposited in open marine facies belt at the Sangsar section is more than the Makaroud section. The main sediments constituents including algae, foraminifera and metazoans show different distribution in the various subenvironments of the carbonate platform. This studies resulted in identifying two low rank sequences at the Sangsar section and three low rank sequences at the Makaroud section. Sequence boundaries are identified by disconformities, volcanics, paleosol horizons, emergence of tidal flat microfacies and microfacies that are indicative of maximum sea level fall in each sequence. The deepest microfacies are also regarded as maximum flooding surfaces. Deposits of the Ruteh Formation at both sections is part of the Transpecos Supercycle (Absaroka II Subsequence). The most deepening of the sea water occurs in the middle parts of the Ruteh Formation and general trend of the sea level changes in this formation is accordant with the global sea level changes during the Permian.

Introduction The siliciclastic sediments of Kashafrud Formation (Bajocian–Bathonian) in the Kopet-Dagh Basin (Madani, 1977; Afshar-Harb, 1979) are composed of conglomerate, sandstone and shale. It is reported that these sediments were mostly deposited in deep water environment in the eastern Kopet-Dagh basin (Poursoltani et al., 2007; Taheri et al 2009; Poursoltani and Gibling, 2011). The study area is located in west of Bojnurd in the western parts of the basin with a thickness of about 749 m and consists of three units. It covers unconformably the limestone of Triassic Elika Formation and overlaid by carbonate sediments of Chamanbid Formation. The purpose of this research is to interpret depositional environment and sequence stratigraphic analysis of the Kashafrud Formation in order to understand the paleogeography of Middle Jurassic time.
Methods This research is based on field observations of one measured stratigraphic section in Navia area and petrographic studies of 69 samples. Lithofacies are classified, using Miall codes (2000, 2006) and thin sections are used for determination of composition and texture of coarse grain rocks. 10 shale samples have also washed for micro- paleontological study and three samples, including shale and sandstone, have studied with SEM and EDX by LEO-1450 V model in Central Laboratory of Ferdowsi University of Mashhad. We also measured 44 directional structures azimuths for paleocurrent analysis.
Results Based on field studies, three lithofacies are recognized in the study area as follow.
Conglomerate lithofacies are observed in the basal part of the studied section with 7 m thickness and is composed of Gcm, Gt and Gmm lithofacies. They are mostly grain-supported with graded bedded, poorly sorted with rounded pebbles, low sandy matrix and trough cross-beds (Gt). Gmm is identified by increases in sandy matrix, moderate sorting and quartz pebbles content.
Sandstone lithofacies consist of St, Sp, Sm, Se, Sl, Sr, Sh, Sm and St lithofacies. St is the most abundance sandstone lithofacies in unit 1. In this lithofacies grain size decreases upward and changes to thin-bedded and fine grain sandstones. Sp with planar cross bedding has Ophiomorpha trace fossil in unit 2. It has low angle and planar cross bedding that vertically changes to Sr lithofacies. Sr (Rippled lamination and layered sandstone) is present in both units 1 and 2 but it has Palaeophycus and Thalassinoides trace fossils in second unit. Sh lithofacies is recognized by parallel or horizontal bedding and lamination. This lithofacies is less abundant in unit 1 and interbeded with mud rocks lithofacies, while in unit 2 it seen with Sl lithofacies. Sl (Low angle cross-bedded sandstone) and is the most abundant lithofacies in unit 2 and mostly fine grain and associated with Sh and Sr. Se (Erosional scours) is mostly observed at the base of sandstones and associated with Sp and Sm.
The Kashafrud sandstones are mostly sublitharenite and minor amounts of litharenite with mineralogically supermature and textural submature.
Mud rock lithofacies consist of laminated (Fl) and massive (Fm) fine grain rocks. The Fl lithofacies is mainly composed of silt-size grains with Palaeophycus, Planolites and Rhizocorallium trace fossils in unit 3.
Discussion Kashafrud Formation is interpreted to be deposited in fluvial and deltaic environments. Fluvial environmentis supported by fining upward cycles, abundance of sandstone, well-rounded grains, trough cross-bedded and Plant remnants in red shale. They have mostly sublitharenite composition. Calculated chemical weathering index indicated that the rocks at the source area have been highly affected by high weathering condition that can be related to warm and semi-humid climatic conditions (Sarbaz et al., 1395, in press). Paleocurrent analysis also revealed that the probable source of these sediments can be located in south of the Kopet-Dagh basin.
Deltaic sediments are composed of proximal and distal delta front as well as prodelta. Proximal deposits consist of several coarsening upward cycles including shale and fine to coarse grain sandstones with a thickness of about 7 m. Dominant sedimentary structures are horizontal and low angle cross-lamination, wavy ripple cross-lamination, massive beds, hummocky and trough cross-beds as well as plant fragments. These evidences show that sediments may have been affected by interaction of long-shore waves as well as storm events (e.g. Edwards et al., 2005; Hampson, 2010).
Distal delta front form the main parts of sediments including fine-grain black to olive green shale and siltstone with fine sandstones interbeds. Major lithofacies are Fl and Fm with Palaeophycus, Planolites and Rhizocorallium trace fossils. These intervals may have been deposited below wave base under low energy conditions (Einsele 2000; Alvan and Eynatten, 2014).
Prodelta sediments are mostly composed of clayey and silty shale. Based on vertical variations of these sediments to silty and fine to very fine grained sandstones of distal delta front, they may have been deposited in low energy and probably more reduction conditions (Hoir et al., 2002). The study of small foraminifera of deltaic shale led to identification of 14 different species of 12 genera. The community of these microfossils, which is reported for the first time, show that deposition may have taken place in the shallow water near shore environment within about 50m depth (e.g. Murray, 1991).
Sequence stratigraphy Kashafrud Formation in this section is composed of two depositional sequence (DS1 and DS2). The lower boundary of the first sequence (DS1), based on angular unconformity (above Triassic limestone of Elika Formation) and fluvial conglomerate deposits, is type I (SB1). The upper boundary of DS1 is SB2 and is located in proximal delta front deposits with no subaerial exposure evidences. The thickness of the first sequence is about 400 m and consists of LST, TST and HST. The LST is composed of continental sediments (137 m) that is covered by transgressive surface. This surface reveals by massive shale (50 m) of distal delta fronts and maximum flooding surface is located in the upper part of these deposits. HST (215 m) is composed of 12 shallowing and coarsening parasequences. DS2 with thickness of about 349 m is separated from DS1with sequence boundary type 2. This depositional sequence is only composed of TST with Fm and Fl lithofacies that transitionally changes to deeper water black shale that follows by marl and fine grain carbonate sediments of the Chaman-Bid Formation. Therefore, the maximum flooding surface is probably located within the Chaman-Bid Formation. Interpreted sea level fluctuation curve of the study area can be related to regional geological history and sometimes can be relatively correlated with global sea level curve (Haq et al, 1987)

Introduction The Kopet Dagh Sedimentary Basin is located at some parts of Turkmenistan, Afghanistan and NE of Iran (Berberian and King, 1981). This sedimentary basin formed after the closure of Paleotethys Ocean owing to the Middle Triassic Orogenic event and mainly consists of Jurassic to Tertiary deposits (Afshar-Harb, 1994). The Abderaz Formation is various in thickness and consists mainly of brown shales and chalky limestone in its type section which is located in 75 km of east of Mashhad city at Mozduran area (Afshar-Harb, 1994). It unconformably overlies the Aitamir Formation and conformably covers by the Abtalkh Formation (Afshar-Harb, 1994). There are several investigations on the Abderaz Formation biostratigraphy and stratigraphical properties such as Kalantari (1969), Vahidinia (1973), Foroughi (2004), Bakhshandeh et al. (2007, 2008), Shafiee et al. (2011, 2012), Vahidinia et al. (2014). To study the planktonic foraminifera of the Upper Cretaceous deposits in the west of the Kopet Dagh Basin, the Sheikh stratigraphic section in south flank of Sheikh syncline at north east of Bojnurd was selected and investigated.
Materials and methods In order to biostratigraphic analysis of the Abderaz Formation, one stratigraphic section in south flank of Sheikh syncline were studied. The thickness of the Abderaz Formation in the studied section is 252 m and a total of 235 thin sections were prepared and analyzed. The identification of species and classification of genera follows that of Postuma (1971), Wonders (1980), Loeblich and Tappan (1988), Bolli et al. (1989), Robaszynski et al. (1984), Robaszynski and Caron (1979) and Premoli Silva and Verga (2004).
Lithostratigraphy The Kalat Formation in the Sheikh section is 252 m in thickness and it conformably overlies the sandy limestones of the Aitamir Formation and conformably covers by argillaceous limestones of the Abtalkh Formation. Lithostratigraphically, the Abderaz Formation are divided into three parts. Generally, these parts are mainly composed of thick bedded to massive limestone, chalky limestone, argillaceous limestone and marly limestone.
Biostratigraphy The biostratigraphic analysis of the Abderaz Formation in Sheikh section led to recognition of 44 species belonging to 14 genera of planktonic foraminifera, 4 species belonging to 12 genera of benthic foraminifera and 4 species belonging to 2 genera of oligosteginids and then 7 biozones are identified based on biozonation scheme of Premoli Silva and Verga (2004). These biozones are briefly described below: 1: Helvetoglobotruncana helvetica Total range Zone: This biozone is characterized by first appearance to last appearance of Helvetoglobotruncana helvetica. The foraminifera content of this biozone include Helvetoglobotruncana helvetica, Marginotruncana coronata, Marginotruncana pseudolinneiana, Marginotruncana marginata, Marginotruncana schneegansi, Marginotruncana renzi, Whiteinella archaeocretacea, Whiteinella baltica, Whiteinella aprica, Whiteinella praehelvetica, Whiteinella paradubia, Praeglobotruncana cf. stephani, Archaeoglobigerina cretacea, Archaeoglobigerina blowi, Dicarinella algeriana and Dicarinella imbricata.
Age: Early to Middle Turonian
2: Dicarinella primitiva-Marginotruncana sigali Partial range Zone: This biozone is marked between the last appearance of Helvetoglobotruncana helvetica and the first appearance of Dicarinella concavata. The associating foraminifera in this biozone include Dicarinella primitiva, Marginotruncana sigali, Marginotruncana marginata, Marginotruncana pseudolinneiana, Whiteinella baltica, Whiteinella paradubia, Whiteinella inornata, Dicarinella algeriana, Archaeoglobigerina cretacea and Archaeoglobigerina blowi.
Age: Middle to Late Turonian
3: Dicarinella concavata Interval Zone: This biozone is characterized by first appearance of Dicarinella concavata and the last appearance of Dicarinella asymetrica.The foraminifera content of this biozone consist of Dicarinella concavata, Dicarinella primitiva, Marginotruncana marginata, Marginotruncana pseudolinneiana, Marginotruncana schneegansi, Marginotruncana sigali, Marginotruncana sinuosa, Marginotruncana paraconcavata, Whiteinella baltica and Archaeoglobigerina cretacea.
Age: Late Turonian-Lowermost Santonian
4: Dicarinella asymetrica Total range Zone: This biozone is characterized by total range of Dicarinella asymetrica. The foraminifera content of this biozone include Dicarinella asymetrica, Dicarinella concavata, Marginotruncana pseudolinneiana, Marginotruncana sigali, Marginotruncana sinuosa, Marginotruncana paraconcavata, Contusotruncana fornicata, Globotruncanita elevata, Globotruncana bulloides, Globotruncana lapparenti and Globotruncana linneiana.
Age: Early Santonian-Lowermost Campanian
5: Globotruncanita elevata Partial range Zone: This biozone is marked between the last appearance of Dicarinella asymetrica and the first appearance of Globotruncana ventricosa. The associating foraminifera in this biozone include Globotruncanita elevata, Globotruncanita stuartiformis, Contusotruncana fornicata, Globotruncana bulloides, Globotruncana lapparenti, Globotruncana hilli, Globotruncana linneiana, Macroglobigerinelloides bollii, Macroglobigerinelloides prairiehilensis, Macroglobigerinelloides messinae and Archaeoglobigerina cretacea.
Age: Early Campanian
6: Globotruncana ventricosa Interval Zone: This biozone is marked between the first appearance of Globotruncana ventricosa and the first appearance of Radotruncana calcarata.The foraminifera content of this biozone include Globotruncana ventricosa, Contusotruncana patelliformis, Contusotruncana plummerae, Contusotruncana fornicata, Globotruncanita elevata, Globotruncana stuarti, Globotruncana lapparenti, Globotruncana bulloides, Globotruncana hilli, Globotruncana linneiana and Globotruncana mariei.
Age: Middle to Late Campanian
7: Radotruncana calcarata Total range Zone: This biozone is characterized by total range of Radotruncana calcarata. The foraminifera content of this biozone include Radotruncana calcarata, Globotruncana ventricosa, Contusotruncana patelliformis, Contusotruncana fornicata, Globotruncanita stuartiformis, Globotruncanita elevata, Globotruncana stuarti, Globotruncana lapparenti, Globotruncana bulloides, Globotruncana linneiana and Globotruncana mariei.
Age: Late Campanian
Finally, according to the recognized planktonic foraminifera and indicated biozones, the Early Turonian to Late Campanian age for deposits of the Abderaz Formation in the Sheikh stratigraphic section at north east of Bojnurd is proposed

Introduction The Cretaceous successions of the Arabian plate host main hydrocarbon reserves of the world and the Middle East. The Arabian plate had experienced particular sedimentary circumstances in the early Cretaceous so that the shape of sedimentary basin had drastically changed by salt diapirs movements and basement tectonics. However, these conditions caused creation and development of intrashelf basins in this time interval. The two main and well-known intrashelf basins are Bob basin and Kazhdumi basin which are respectively located in the northeast and the east of the Arabian plate. This study has focused on the Aptian sediments which are known by the term "Dariyan Formation" in the northern of the Persian Gulf. The study outlines the extension of the Aptian intrashelf basin in northern Fars platform within the structural Zagros zone.
Material and Methods The Dariyan Formation was studied in detail by using thin sections which are prepared from cores and cuttings of two wells (Sarvestan and Ahmadi wells) in the northern Fars area. In addition data from a neighbor well (Qutbabad) are used to complete the data set for the study. Petrographic studies were carried out on more than 300 thin sections using Dunham classification. Various microfacies and facies sets are determined based on grain and texture content, energy index and other sedimentary factors in comparing recent and ancient environments. A southeast-northwest transect (AA' transect) was selected in order for better investigation of lateral facies and environmental changes in the studied area during the Aptian.

Discussion of Results and Conclusions Facies analysis led to the identification of 8 microfacies into 4 facies sets: lagoon, shoal, open marine and basin facies sets. In the stratigraphic studies of the Dariyan Formation, three biozones (16, 17 and 18) are common which are introduced by Wynd 1965. Changes in fossil content of the Dariyan Formation mostly help to identify these biozones. In the lower parts of the Dariyan Formation, presence of Palorbitolina (early Aptian) in companied with Hensonella and Lithocodium aggregatum are marker of biozone 16 while in the upper Dariyan Formation, presence of Mesorbitolina (late Aptian) with conical Orbitolina and other small benthic foraminifera are sign of biozone 18. Biozone 17 could be identified by presence of pelagic fauna such as Globigerina.
The Dariyan Formation is divided into two parts in the Ahmadi well and three parts in the Sarvestan well. In the Ahmadi well, sediments of the rock unit 1 belong to biozone 16 which starts by open marine mudstone to wackestone facies and continues by thick layered alternations of Orbitolina Hensonella wackestone, bioclast mudstone and bioclast pelloid wackestone/packstone facies. The rock unit 2 (biozone 18) includes Orbitolina bioclast pelloid grainstone (lagoon facies) in alternation of open marine wackestone/ mudstone. In the Sarvestan well, the lower Dariyan Formation is composed of sediments which belong to biozone 16. These sediments are just like the rock unit 1 in the Ahmadi well which include lagoonal microfacies set and they suddenly change to deep pelagic facies (biozone 17) of the middle Dariyan Formation. In the Sarvestan well, the upper Dariyan Formation is just like rock unit 2 in the Ahmadi well. It is composed of sediments belonging to biozone 18. Paleontological data from Iranian National Oil Company are representative of the presence and extension of biozone 17 towards the Kolah Qazi mountain. This pelagic set disappears towards the Qutbabad well (southeast of the studied area).
Considering to low frequency of shallow high energy facies such as grain dominated grainstone and packstone facies besides lack of reefs and reefal biota, turbidities, and sedimentary structures such as slides, slumps and debris flows, there are not enough evidences to attribute a rimed carbonate shelf environment for the Dariyan Formation. In contrast regarding to lateral facies changes in the north Fars area and sudden changes of shallow facies sets into pelagic facies sets, it seems a homoclinal carbonate ramp to intrashelf basin could be the best model for the Dariyan formation in the studied area. The term “Sarvestan intrashelf” is proposed for this basin. Extension of the Sarvestan intrashelf can be defined by tracing changes in the lateral facies of the Dariyan Formation.
Therefore despite previous visions, the Fars platform was not a monolith shallow platform. In addition, except Kazhdumi intrashelf basin, there were other deep and local intrashelf basins which were developed within the Fars platform.

The siliciclastic Padeha Strata (Middle Devonian), in the Binalud, 108 metres thick, in the Bujhan area, rests unconformably on Ordovisian basalts. This strata conformably overlain by carbonate rocks of the Sibzar Formation (Middle Devonian). The one stratigraphic section was logged graphically, and 98 fresh sandstone samples were systematically collected, from which 63 thin sections were made. Petrographic modal analyses were made using a Nikon E400 Pol microscope, with 500 point counts on 63 selected samples using the Gazzi-Dickinson method to identify grain and cement types and proportions. Porosity was estimated from counts of 500 points in each of 22 thin sections prepared separately with blue epoxy. Six 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. Luminescence characteristics of the same sandstone suite were studied using a conventional hot-cathode cathodoluminescence (HCL) microscope (model HC4-LM).
Discussion and Based on field and Laboratory studies, 3 association facies, sandstone, dolostone 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 and sedimentary. Dense-minerals include opaques, zircon and tourmaline, dispersed. The sandstones have a compositional range from quartzarenite, subarkose and little bit of arkose.
The Padeha sandstones experienced diagenetic events that included cementation, alteration, compaction and fracturing, dissolution and replacement and porosity. The predominant cement is silica and carbonate (dolomite, calcite, ankerite and siderite), iron oxide, clay minerals (kaolinite, illite and chlorite), with minor authigenic minerals such as appetite. 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. 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 Padeha sandstones as an alteration product and cement. Clay minerals are less than other type of cements, but illite and kaolinite are the main clay minerals cement in Padeha sandstones. Authigenic minerals mainly fill fracturs and pores. The sandstones show variable degrees of mechanical and chemical compaction, which is particularly prominent where early cements are lacking. 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. This was evident using SEM and CL techniques, which show that the majority of grains contain fractures. Dissolution is prominent in the sandstones. Detrital K-feldspar, quartzand 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.
Based on two-dimensional estimates from thin sections, the mean porosity is 4.7%, and maximum 14.4% for 22 samples from the formation as a whole, with little apparent upward change. The bulk of the porosity is secondary. Pores formed mainly through dissolution of K-feldspar and carbonate cement, and as open fractures within grains.
Based on petrological and geochemical studies, minor diagenetic events in the eodiagenetic stage include cementation (calcite, dolomite and iron oxide) and rarely fracturing. Mesodiagenetic events were dominated by cementation (silica, dolomite, calcite, iron oxide components, clay minerals), compaction, intra-grain microfractures, alteration of unstable clasts, dissolution and replacement, pressure solution, and rarely formation of apatite. Minor telodiagenetic events include dissolution and cementation (dolomite, ankerite, siderite, iron oxide and rarely kaolinite). The bulk of the porosity is secondary, with an average of 4.7%, which is the result of dissolution and fractures

The Oligocene-Miocene shallow marine limestone, Asmari Formation, from the Zagros Basin, SW Iran, constitutes one of the main hydrocarbon reservoirs in the world. This succession shows a variety of facies patterns and depositional architectures. Also these strata contain a rich fauna of planktonic and benthic foraminifera. Larger benthic foraminifera are considered to be good indicators of shallow marine environments. Distribution of this group in addition to other biogenic components (mollusk, echinoid, bryozoan, coral, corralinacean, brachiopod, worm tube, etc.) and sedimentary structure, along the stratigraphic sequence of the Asmari Formation is used in this research as a tool for introducing the biostratigraphic correlation and foraminiferal associations. In order to study the foraminiferal associations and biostratigraphic correlation of the Asmari Formation in the Fars Basin, four stratigraphic sections were selected, include: Shool, Kaftarak, Darengoon, and Noorabad sections. This study is based on more than 270 thin sections derived from surface outcrops.
According to the distribution of planktonic and benthic foraminifera, three assemblage zones were recognized I-Nummulites vascus-Nummulites fichteli, II- Lepidocyclina-Operculina-Ditrupa and, III-Archaias asmaricus/hensoni-Miogypsinoides complanatus. The oldest recognized biozone (biozone no. I, which is determined according to the presence and absence of Nummulites spp.) is reported from Shool and Kaftarak sections. Biozone no.II is recognised at Noorabad Section and represents undifferentiated Rupelin-Chattian time. Biozone no.III which represents Chattian time is reported from Noorabad and Darengoon sections. The Asmari Formation is time equivalent to Oligocene-Miocene in different parts of the Zagros Basin. The recognised biozones in the Fars Basin confirm the age of Rupelian onto Chattian for the Asmari Formation, in the study area.
Three foraminiferal associations are recognized in the investigated sections according to the test shape of the larger benthic foraminifera and sedimentary texture. The identified foraminiferal associations represent the middle and inner parts of a homoclinal ramp. The association no. 1 consists of planktonic foraminifera together with thin and thick tests of perforate larger benthic foraminifera. Perforate tests are apparent as nummulitid (Nummulites, Operculina and Heterostrgina) and lepidocyclinid (Eulepidina and Nephrolepidina). The association of planktonic foraminifera and thin and flat test of nummulitid and lepodocyclinid representing the deeper part (about 150 m) of the Asmari platform in the study area. Increasing in the thickness ratio to the diameter of the test is the sign of proximal middle ramp. This foraminiferal association is presented thorough the Rupelian-Chattian time in the Noorabad Section and indicated salinity value of 34 to 40 psu. The shallowest depth (40 m) of the proximal middle ramp is coinciding with the presence of thick rotallid tests. The association no. 2 is composed of the mix of perforate and imperforate tests of larger foraminifera (Operculina, Heterostegina, Eulepidina, Nephrolepidina, Neorotalia, Sphaerogypsina, Planorbulina, Archaias, Peneroplis, Austrotrillina, Borelis, Triloculina, Praearchaias, Sivasina, and milliolid). This is formed in the semi-restricted lagoon in the inner ramp and is reported from the Noorabad Section (Rupelian-Chattian), Kaftarak Section (Rupelian) and Darengoon Section (Chattian). The presence of the Borelis genus confirms the salinity value of 40-50 psu for this association. High diversity imperforate tests of larger foraminifera are the main maker of the third association. This indicates the hypersaline-restricted lagoon and salinity value higher than 50 psu. The association no. 3 is the sign of shallowest depth of sedimentary basin. The dominance of Peneroplis, Austrotrillina tests is the indicator of depth lower than 30m. This is formed throughout Late Rupelian and Chattian in the Shool, Noorabad, and Darengoon sections. The end Chattian sea level falling controls the formation of the association no. 3 in these sections. This is resulted in the deposition of the clastic and evaporate sediments of the Razak and Gachsaran formations over the Asmari Formation.