iraj maghfouri moghaddam

In order to interpret thebiostratigraphy, facies and depositional environment of the Asmari Formation in the northeast of Ilam, located in the Lorestan zone, a stratigraphic section with a thickness of 215 meters including thin, medium to thick layered limestones was selected. The Asmari Formation conformably overlies the Pabdeh Formation and is overlain the Gachsaran Formation n. The study of communities of large benthic foraminifera in this research led to the identification of 4 biozones of Ruplin- Chattian age: Nummulites vascus, Nاummulites intermedius assemblage zone Lepidocyclina- Operculina- Ditrupa assemblage zone Archaias asmaricus, Archaias hensoni, Miogypsinoides complantus assemblage zone Elphidium sp.14, Miogypsina sp. Peneroplis farsensis assemblage zone Also based on the field observations, petrographic studies and textural characteristics as well as the abundance and distribution of foraminiferal fauna and other components, 10 carbonate microfacies have been identified. These carbonate microfacies were deposited in the inner, middle and outer ramp environments. The co-existence of coral and large benthic foraminifera such as Amphistegina, Archaias and Borelis , is indicative of tropical to subtropical waters under oligotrophic to slightly mesotrophic nutritional conditions.

The Zang Trap Formation is a carbonate unit that is the result of the first transgression of the sea at the beginning of the Cenozoic on the northern and eastern margins of the Lorestan area. This unit is located on the Amiran turbidite Formation and below the clastic and continental deposits of the Kashkan Formation with a discontinuous boundary. The facies and age of the Taleh Zang Formation in different areas of Lorestan area show important differences. In order to study the facies and sedimentary environment of Taleh Zang Formation in the north of Lorestan area, two stratigraphic sections of Qableh and Darabi in the west and north of Kuh Dasht, respectively, were studied. Based on the recognized large foraminifera the age of the Taleh Zang Formation in the study stratigraphic sections is assigned to the Thaetian (late Paleocene). The petrographic analysis and fauna association of the Taleh Zang Formation led us to identify 6 microfacies that are belonged to to the tidal zone, inner and mid ramps.The absence of corals and the low abundance of calcareous algae and the high abundance of benthic foraminifer indicate that the bio assemblage of the Taleh Zang Formation was similar to that of the eastern Tethys.

The carbonate deposits of the Taleh Zang Formation are exposed extensively in the southeastern to northern Lorestan zone, SW Iran. The thickness of the shallow water carbonate Taleh Zang Formation in Ritt Anticline is 84.5 meters. It overlies on top of the turbidity Amiran Formation and it is overlain by the clastic-dominated Kashkan Formation. Petrographic examinations revealed seven facies deposited in tidal flat, lagoon, shoal and open marine. Detailed analysis of sedimentary facies indicates that in the Late Paleocene interval, the depositional system of the Taleh Zangi Formation was a ramp carbonate platform. Changes in the depositional facies and cycle stacking patterns indicate one transgressive-regressive sea-level cycle from the bottom to the top of the section, which is equivalent to the last eustatic sea level rise in the Late Paleocene (Thanetian).  This depositional sequence is separated by type 2 and 1 sequence boundaries at its lower and upper boundaries, respectively. Elemental geochemical evidence indicates a closed to weakly open digenetic system, with low water-rock interaction for carbonates of the Taleh Zang Formation. The relatively open digenesis system in this formation could be due to the influence of meteoric fluids in the erosional discontinuity at the border between the two formations, the Taleh Zang and Kashkan formations.

During the Late Carboniferous-Early-Permian, glaciers covered a large part of Gondwana (Aghanbati, 2009). In the Late Asselian-Early Sakmarian, due to the increase in temperature, glaciers have retreated from all of Gondwana (Aghanbati, 2010) and after that progress has occurred continuously at the beginning of the Permian. during the Early Permian, mostly mixed siliceous sediments Carbonate-debris of Droud formation was mainly deposited in continental and intermediate environment, with increasing depth gradually in the late Permian, Middle Permian and early Permian of Ruteh Formation with carbonate facies and then in the late Permian. Ruteh formation was identified and introduced for the first time by Assereto (Assereto, 1963) in the valley of Ruteh village in the northeast of Tehran. in this study of Ruteh formation based on detailed lithological characteristics (macroscopic and microscopic) and identification of benthic foraminifera in a stratigraphic section 30 km south of Amol in central Alborz, in terms of rocks Stratigraphy and biostratigraphy have been investigated.

After preparing microscopic thin-sections from all samples, the sections were stained with red alizarin solution according to Dickson's method (Dickson, 1965) to distinguish calcite from dolomite and then studied under a microscope to identify microfossils. After the identification of microfossils, the bio zonation of the sediments of Ruteh Formation was started based on the biozone of Leven and Okay (1996) belonging to the West of Paleo-tethys.

In the biostratigraphic studies of the Ruteh formation in the stratigraphic section of South Amol, whereas 31 genera and 57 species of benthic foraminifera were identified, three local biozones were identified and introduced as described below. Small Foraminifera and Fusulinids together with green and red algae constitute the most important microfossils of Ruteh formation. Neoendothyra bronnimanni-Neoendothyra reicheli assemblage zone This biozone, which is an accumulation type, is defined based on the existing symbiotic community in it, and it occupies 72 meters from the base of the Ruteh formation after the erosion boundary between the Dorud and Ruteh formations. The lower boundary of this biozone is determined by the beginning of the symbiotic complex below and its upper boundary by the appearance of the indicator foraminifera of Midian stage, such as Chusenella sinensis and Codonofusiella erki. The age of this biozone based on its identified species such as various speciesof Neoendothyra and the comparison of this cumulative biozone with Khachik Julfa layers and other areas of the Tethys region such as Afghanistan indicates the late Murgabian age for this zone. Chusenella sinensis - Codonofusiella erki Pachyphloia assemblage zone This cumulative biozone includes 282 meters of the thickness of Ruteh formation after biozone 1. Its lower boundary is determined based on the emergence of the midian Chusenella sinensis, and the upper boundary of this biozone is determined by the emergence of the foraminifera such as Dagmarita chanakchiensis and Paraglobivalvulina mira. The age of this formation is based on the presence of foraminifera such as Chusenella sinensis and the comparison of this accumulation biozone with midian foraminifera of Khuf Formation Paraglobivalvulina mira - Dagmarita chanakchiensis assemblage zone This biozone, which is defined based on the following symbiotic complex, inhabits 288 meters from the top of the Ruteh Formation in the studied section. Based on the symbiont complex, the age of this biozone has been identified as the early Julfian. However, an indicator species such as Pachyphloia iranica is accepted by most of the experts as the indicator species of Julfian stage (Bozorgnia, 1973).

The following results have been obtained in the Lithostratigraphic and biostratigraphic studies of the Ruteh formation in the section of the mansion:The thickness of the sediments of Ruteh formation in this section is 642 meters and in terms of lithology, it mainly consists of thick to medium and thin dark limestone along with dolomitic limestone, limy dolomite, sandy limestone, cherty limestone, shale and sandstone.The lower boundary of Ruteh Formation with Dorud Formation is disconformity, so that the limestones at the base of Ruteh Formation are placed on the eroded surface of the sandstones at the top of Dorud Formation. Its upper border is also with the Nesen Formation, which is discontinuous and eroded along with a laterite horizon. Based on the above biological zones and the set of fossils identified in them, the age of the Late Murgabin-Early Julfian Ruteh formation was determined.

 The Miocene Guri member is characterized as one of the most significant successions in the Zagros basin. The Guri member is composed of carbonate (Limestone and marly limestone) and Marl (calcareous Marl) layers with abundant imperforate and perforate benthic foraminifera. The paleoenvironmental analysis, facies, depositional environment and diagenetic proceses of the Guri Member of Mishan Formation are described from three stratigraphic sections (Milaton, Omidieh and Shahid rajaei) in the Chahar bisheh, Aghajari and Parsi oil fields, south west iran. The petrographic analysis of the Guri member led us to identify 11 microfacies that are belonged to shoal, lagoon, and tidal flat environments. These microfacies deposited on a shallow carbonate ramp (homoclinal ramp) with the gentle slope. Bioturbation, micritization, cementation, neomorphism, physical and chemical compaction, dissolution, replacement and fracturing are the main diagenetic features that are created in the marine, meteoric, burial and uplift diagenetic environments. The sediments of the Guri Member are dominated by Thalassinoides suevicus in the Y, T, question mark and cylindrical shaped burrows. These trace fossils created by the Miocen crabs. The bioturbations in the layers are categorized into five ichnofabric classes which are equal to standard ichnofabric indexes of 1 to 5. The more ichonfabrics in the Omidieh section than in Parsi has been due to the large changes in environmental conditions such as depth, salinity and oxidation rate. Paleoenvironmental investigations of Thalassinoides suevicus indicates a very shallow, warm marine conditions with very high oxygen rate.

The Burdigalian carbonate of the Central Iran contains very well-preserved specimens of Kuphus polythalamius. The tube of Kuphus polythalamius is a calcareous secretion that enables Pelecypoda to live in the mud of shallow seas. This research focusses on the Paleontology and taphonomy of the Kuphus polythalamius of the Member F (Qom Formation) in the southeast of Kashan located in the Central Iran. The Member F is 60 meters thick and composed of medium bedded limestone. The scattering of the larger benthic foraminifera in the study area indicates the existence of the Borelis melo curdica-Borelis melo melo assemblage zone of Burdigalian age. The presence of Kuphus polythalamius among the porcelaneous foraminiferal and green algal assemblage demonstrate that carbonate generation happened in warm tropical to subtropical marine. The surface of some samples contains distinct horizons of beekite, indicating a break in sedimentation, which is expanded as a silica crust on carbonate tubes.

The benthic and planktonic foraminiferal contents of the Bangestan Group (Sarvak, Surgah and Ilam formations) in the Sepid Kuh anticline in the Lorestan Zone, W Iran, were studied. Bangestan Group consists of limestone, argillaceous limestone, dolomitic limestone and marl with thickness of 5400 m. In this section Bangestan Group overlies Garu Formation disconformably and its upper boundary is not exposed. By micropaleontological study on 176 thin sections, 8 genus and 34 species planktonic foraminifera were identified. 400 m of Sarvak Formation has very little fossil diversity that does not indicate a certain age. For this reason, this interval was called the indeterminate zone, which due to its stratigraphic position, is probably of Cenomanian age. Based on the biostratigraphical range of planktonic foraminifera distinguished, four biozones can be identified: Helvetoglobotruncana helvetica Total Rang Zone (Early- Middle Turonian), Marginotruncana schneegansi partial Range Zone (late Turonian), Diacarinella concavata Interval Zone (Coniacian), and Diacarinella asymetrica Total Zone (Santonian).

This study provides a evaluation of the initial carbonate mineralogy, and diagenetic condition of the Ruteh Formation, a middle-late Permian carbonate sequence, in the Emarat section in Central Alborz, northern Iran. 200 samples were examined for petrographical contents and thirty-four samples were collected for geochemical analysis. The high Sr and Na contents, Sr/Na>1, and the presence of dolomites and dissolution fractures are indicative aragonite early mineralogy. The diagenetic process in the Ruteh Fm. are an indication of the marine, meteoric and burial diagenetic environments. The original carbonate texture in the Ruteh Fm. are Severely affected by diagenetic process. The data obtained from the values of the Major (Ca and Mg), minor (Sr, Na, Fe, and Mn), oxygen and carbone isotopes show the initial aragonite composition of the Ruteh Fm. deposited in a subtropical shallow water. An open diagenetic system was indicated by changes in the values of Sr / Ca and δ18O vs. Mn. The shallow burial diagenetic temperature of the Ruteh carbonate was approximate 28.6°C with the maximum diagenetic temperature of 53.4°C.

Seven genera and seventeen species of marine Ostracoda are reported for the first time from the Attari section (Qom Formation), northeast of the Semnan, Central Iran. In this section, the Qom Formation outcrops with 280 m thickness lies on the Eocene volcanic and under the Upper Red formation. According to the distribution of index foraminifera, there is conspicuous similarity between larger bentic foraminifera assemblages of the Qom Formation foraminifera and those of the Zagros basin, such as Borelis melo curdica the age of Qom Formation in the Attari section is Early Miocene (Burdigalian). The Miocene and even Oligocene Ostracoda fauna, relatively similar to the Attari section, have been reported from the Mediterranean area and the Proto- Indo- Pacific Ocean. The presence of one species with Paratethian origin in the Qom Formation is strong evidence that during the Burdigalian stage, the sea way between Central Iran and Paratethys basin still existed.

Lower Miocene deposits in Iran have a significant expansion. In Zagros and Central Iran, these sediments include Asmari and Qom formations, respectively. Due to its economic importance and especially the possibility of reservoir and cap rocks, many studies have been conducted on the Miocene deposits in areas with high hydrocarbon potential. However, in the high Zagros, due to the limited oil reserves, the Miocene deposits have been less studied. According to the geological map of Harsin in the northern parts of the high Zagros zone (Shahidi and Nazari, 1997), the Miocene deposits consist of carbonate and clastic rocks. In terms of lithology, especially the presence of clastic rocks, these deposits are very similar to the Qom Formation, but since they are located in the high Zagros zone, it may not be correct to refer to this formation. On the other hand, the lithology and appearance of these deposits are fundamentally different from the Asmari Formation. Therefore, in this paper, like the geological map of Harsin, they are called Miocene deposits. In this paper, the paleoenvironment and microfacies of Miocene deposits in the high Zagros have been studied.

Three sections of Miocene deposits are studied, located 23 km south of Harsin (Figure 1). Fig. 1. Locality map of the studied area. In the present study, a total of 130 sections were taken. Thin sections were prepared from rock samples and isolated fossils were isolated from soft samples. Texture properties and fossil assemblages in thin sections were examined and identified by a polarizing microscope.BiostratigraphyBased on foraminiferal distribution, the following assemblage zones are recognized:1) Indeterminate Zone I: In view of the fact that we unable to find any index microfossils, comments on the age of this zone are difficult, which explains why this is here referred to as an indeterminate zone.2) SBZ25: Larger benthic foraminiferal zone SBZ 25 can be divided into two subzones; those of M. globulina and M. intermedia.2-a) M. globulina Subzone: This is defined by the FO of M. globulina at the base and the FO of M. intermedia at the top. It is regarded as a common global index for the Burdigalian Stage.2-b) M. intermedia Subzone: This is defined by the stratigraphical range of M. intermedia, which is considered to be a characteristic form for the middle-upper Burdigalian (Cahuzac & Poignant, 1997). 1) Indeterminate Zone II: In view of the fact that we could not find any index microfossils in this zone, we here refer to it as indeterminate zone. As to its stratigraphical position, we prefer an early Langhian date for this zone.2) Orbulina suturalis Interval Zone: Planktonic foraminifera are frequent to dominant in the upper part of the Sayl Cheshmeh section. Based on their vertical distribution, a single biozone has been recognized. This is defined by the FO of O. suturalis (Brönnimann, 1951) and ends right below the conglomerate/sandstone levels of Pliocene age

Depositional model:

Based on the field observations, petrographic studies and textural characteristics as well as the abundance and distribution of foraminiferal fauna and other components, 7 carbonate microfacies have been identified. These carbonate microfacies were deposited in4 facies belts including lagoon, margin facies, upper slope facies and lower slope facies (Fig. 2). Fig. 2. Depositional model for the platform carbonate of the Miocene deposits in the Harsin area, High Zagros Zone The stratigraphical position and vertical and lateral dispersion of different facies along with textural features and skeletal composition, and the presence of coral reef reefs and sudden change of facies and the absence of large tidal zones of Miocene deposars in Harsin area indicate that this sequence deposited on a rimmed carbonate platform.

A stratigraphic section was selected in East Garkan in order to study the paleontology of the Qom Formation ostracods in Urumieh -Dokhtar Zone. In this section, Qom Formation is gradually located on the clastic rocks of the Lower Red Formation and with disconformity under the Upper Red Formation. A total of 10 species of 14 ostracods genera were identified. The common stratigraphic range of these ostracods and the presence of accompanying foraminifera confirm the Late Oligocene (Chattin) age for the desired layers. The ostracod and foraminiferal assemblage from the studied section shows that the Qom Formation has accumulated in a warm and oxygen-rich environment. Based on the study of 60 samples found from the studied section, two sedimentary environments of the estuary (including alluvial channels, barrier; central basin and intertidal) and shelf (including inner, middle and outer shelf) were identified. The ostracods are spread in the middle of the side bay and the outer ramp.

In order to study, biostratigraphy, Sedimentary environment and biogeochemistry of Garau Formation studied at one stratigraphical section at the KhorramAbad anticline. This section has a thickness of 137.5 meters. Study of microfacies sections of the Early Cretaceous Formation of the Garau Formation and study of paleontological and histological characteristics of specimens including abundance of skeletal and non-skeletal alocomas, cement, detrital particles and matrix resulted in the identification of 8 microfacies in the deep-sea region in the study area. Also the proposed sedimentary model of the Garau Formation is based on carbonate platform microfacies determined by ramp type. In this research, the geochemical characteristics of the Garau Formation in the Khorramabad anticline were done by Rock-eval method. Based on the analysis of existing data, type III kerogen was studied. The TOC of samples from this rock unit is relatively weak and varies from about 0.24 to 1.28 . Garau Formation samples in Khorramabad anticline have low potential for hydrocarbon production. Since the hydrogen index of the Garau Formation samples is between 50-250 mgHc/gRock, so the potential of the Garau Formation in these samples seems to be more focused on the production of light (gas) hydrocarbons.

Oligo-Miocene rocks are deposited between Pyrenean and Pasadenian orogenic phases. This rocks in central Iran back arc deposits are named Qom formation. There are well developed outcrops of Qom formation at the North of Central Iran zone. In order to study microbiostratigraphy of the formation, Three sections, north west of Darjazin town , Bonak mount and Arvaneh were selected. In these sections Qom formation with discontinuity overlays the Lower Red formation and with the same quality under the Late Miocene Conglomerate with intercalations of Sandstone, which is equivalent to the Upper Red Formation is placed. The main lithological composition of the Qom Formation in the study area alternates between layers of limestone and Marl with intercalations of siliciclastic rocks. Members and submembers of the Qom formation type area are not visible in this area and can only based on the lithological characteristics divide to local units. Based on bentic foraminifera and other microbiostratigraphical data, Qom Formation age in north west-west of Semnan (Darjazin-After zone), which is located in the Central Alborz structural- sedimentary zone, is early Miocene epoch and Burdigalian stage, which is the equivalent of Borelis melo curdica-Borelis melo biozone.

The Ruteh Formation with a thickness of 642 m, mainly consisting limestone, dolomitic limestone and shale, disconformably lied on Sandstone and underlied disconformably by Nessen Formation. Based on petrographic studies of 200 thin-sections and sedimentary structures of the Ruteh Formation Identified and separated 18 carbonate microfacies and one clastic facies that deposited 4 facies belt of tidal flat, lagoon, shoal and open marine. The sedimentary environment of middle and late Permian deposits in the Alborz area is very similar to the recent carbonate environments in the Persian Gulf. The sediments are formed in shallow environments in the epicontinental platforms. The sedimentary environment of the Ruteh Formation is identified as a homoclinal ramp. Sequence stratigraphy studies have been carried out based on the accurate determination of sedimentary environments and field studies. From sequence stratigraphy point of view, a third-order sequence of the late morghabin age, three third-order sequences to the early, middle and late midian age and two third-order sequences to early and late Julfian age is determined

The Gurpi Formation constitutes the source rock for petroleum in the oil-rich South Iranian Basin.Gurpi Formations is well distributed along Zagros Foreland Basin particularly in the north west of the Zagros (Lorestan Province). For Microbiostratigraphy and Paleobathymetric studies of the Gurpi Formation in the central part of Lorestan two stratigraphic sections including Sultan and Amiran sections were selected. In this study, 48 foraminiferal species belonging to 25 genera were identified, and 7 biozones were recognized; Globotruncanita elevata Zone, Globotruncana ventricosa Zone, Radotruncana calcarata Zone, Globotruncanella havanensis Zone, Globotruncana aegyptiaca Zone, Gansserina gansseri Zone, Contusotruncana contusa Zone.Planktonic foraminiferal morphology was studied in order to assign paleobathymetry and the changes through sedimentation course of the Gurpi Formation.Three third-order sequences were identified,on the basis of deepening and shallowing patterns in the morphological changes and the distribution of the Gurpi Formation planktonic foraminifers and planktonic/ benthic ratio.

In this research, microbiostratigraphy and depositional environmental implications related to the Surgah Formation at the northern flank of Sepid kuh anticline, Lorestan Basin, is discussed. A study of small planktonic foraminifera from the 101m-thick Surgah Formation led to the identification of three Turonain- Santonian biozones: 1-Helvetoglobotruncana helvitica, 2-Marginotruncana sigali,3-Dicarinella concavata. The age of Surgah Formation in the study area is determined as Turonian- Santonian. The Surgah Formation overlies the Sarvak Formation and underlies Ilam Formation in the studied stratigraphic section. Based on analysis of pelagic foraminiferal assemblages and microfacies features 7 different microfacies have been recognized, which can be grouped into three depositional environments: inner, middle and outer ramp.

This research focusses on the biostratigraphy and paleoecological implications of the carbonatesof the Asmari Formation. The Asmari Formation is located in the Siah Kuhanticline of Izeh, Zagros Basin, SW Iran. It is of Late Oligocene (Chattian) - Early Miocene (Burdigalian) age. In this stratigraphic section, the Asmari Formation overlies the Pabdeh Formation and underlies the Gachsaran Formation. It consists of cream-colored limestone intercalated with marl. 182 thin sections were prepared and the benthic foraminifera distribution analyzed. Examination of large benthic foraminifera from the 228 m-thick Asmari Formation led to the identification of 3 biozones: the Lepidocyclina- Operculina- Ditrupa Assemblage Zone, Miogypsina-Elphidium sp. Assemblage Zone and the Borelis melocurdica- Meandropsina iranica Assemblage Zone.