نشریه رسوب شناسی کاربردی
پیاپی 20 (پاییز و زمستان 1401)

In order to study lithostratigraphy, microfacies, and biostratigraphy of the Pabdeh Formation based on the new biozonation of planktonic foraminifera in the Tethys region, 1 subsurface section in well No. 314 of Gachsaran Oil Field has been studied.The Pabdeh Formation with a thickness of 241m consists mainly of shale, calcareous shales, argillaceous limestones, and cherty limestones. The lower boundary of the Pabdeh Formation with the Gurpi Formation is unconformable and the upper boundary with the Asmari Formation is conformable.Investigation of the stratigraphic distribution of these microfossils in the subsurface section (Gachsaran well No. 314) led to the identification of 52 genera and 21 species of planktonic foraminifera and 17 biozones based on equivalent to new biozone of (Wade et al, 2011) in the global biozonation in this region. These identified biozones include 2 biozones in the Paleocene, 13 biozones in the Eocene, and 2 biozones in the Oligocene in the studied and are well correlated with some biozones in the Tethys region. Based on the foraminiferal assemblages and their biozonation, the age of the Pabdeh Formation in well No. 314 of Gachsaran Oil Field is Middle Paleocene (Selandian) – Early Oligocene (Rupelian). Defined biozones are compared with the other sections presented in the Izeh Zone (Tange Hatti, north flank of Tange Pabdeh, Chahardeh, and Lar Mountains) in the Zagros Basin.Petrography and microscopy studies of the Pabdeh Formation in section imply, these sediments are belonging to microfacies (Deep Shelf) and were deposited part of a carbonate platform.

Jahrom and Asmari Formations in two wells from Nargesi field in the southern part of Dezful Embayment were studied to interpret the sedimentation and diagenesis history of Paleocene-Miocene successions. A total of 14 different microfacies were identified based on the study of 270 m drilling core and 495 microscopic thin sections,which are located in four sets of open marine, shoal, lagoons and tidal flats. The microfacies of the Asmari Formation are include tidal and lagoon sets. The microfacies of the Jahrom Formation are include middle ramp and the open marine, and energetic facies of the shoal sets have been observed in abundance in this formation, and to a lesser extent has lagoon facies. According to the characteristics of the above microsfacies, it is suggested that a shallow carbonate ramp with a gentle slope be used as a sedimentation environment for these Formations in Nargesi field. Asmari Formation is deposited in the shallower parts of this ramp. The paragenetic succession of Jahrom and Asmari Formations has been interpreted based on petrographic evidence in four marine, meteoric, burial and uplifting environments, and have affected sediments, during the three stages of eogenesis, mesogenesis and telogenesis. Dolomitization, cementation, anhydritization, micriticization, neomorphism, compaction, dissolution and fracture are the predominant diagenetic processes in these Formations. Dolomitization and anhydritization processes have been observed throughout the Asmari Formation, but are less intense in the Jahrom Formation. Asmari Formation cements are mostly dolomitic and anhydrite, but Jahrom Formation cements are mostly calcite.

The Najmah Formation is composed of variable microbial build-ups disconformably resting on the dark calcareous shales and limestones of the Sargelu Formation. The transition from the middle Jurassic Sargelu to the upper Jurassic Najmah was associated with a conspicuous change in depositional environment so that the intrashelf basin of the Sargelu with the domination of black calcareous shales and dark pelagic limestones evolved to a shallow-marine ramp with carbonate deposition from mostly microbial origin. This change caused by a regression and a resultant interruption in sedimentation is evidenced by the occurrence of intraclastic breccia, fenestral fabrics, evaporite pseudomorphs as well as various microbial build-ups in the Najmah pointing to the superiority of arid climate and hypersaline conditions with paramount environmental stresses during the deposition of the formation. Facies recognized in the Najmah Formation include five microfacies (MF) and two lithofacies (LF) representing supratidal, intertidal and subtidal sub-environments. Based on microfabric viewpoint, microbialites of the formation can be divided into thrombolite and stromatolite. The formation is dominantly composed of stromatolite, which is subdivided into stratiform and domal stromatolites based on morphoscopic criteria. Moreover, these stromatolites can be microscopically subdivided into five microfabrics among which so-called “planar micrite with sparite laminae” is the most frequent microfabric. Stromatolites of the Najmah developed in a supratidal to intertidal environment. Furthermore, thrombolite with a clotted and non-laminar fabric is another build-up of the formation, deposited in a shallow subtidal zone making the basal part of the cycles of the Najmah following the bottommost red shale.

In order to understand the sedimentation history of carbonate rocks of Asmari Formation, a 145 m thick stratigraphic section was selected in the south of Lorestan. The lithology of this periodic formation is from thin-layer, middle-layer limestones, thick to very thick-layered. The samples taken from this section are 145 samples that were examined in terms of sedimentary environment and diagenetic processes based on field evidence and studies of thin microscopic sections and due to the absence of evidence such as the construction of bird eyes. , Stromatactis cavities, Typical structures, Intracellular components, Evaporative minerals and the absence of traces and structures resulting from sediment drying as well as the absence of slippery and sedimentary sediments (turbidites, intraclasts and sections) Finally, it led to the identification of 7 micro-defects related to 4 lagoon facies belts, dam, restricted section (middle ramp) and internal ramp. In this section, several diagenetic processes such as micriticization, morphology (increasing and decreasing), cementation (coaxial cement, fibrous thickness, dimensional, block, joint and kilotopic dynamics), compaction (mechanical and chemical), dissolution (dependent To fabric and non-fabric dependent), substitution (pyritization, silicification and dolomitization) and diagenetic modeling. Based on petrographic evidence, the paragenetic sequence of Asmari Formation deposits in this section has been interpreted in four marine environments, freshwater, burial and uplift. Three stages of diagenesis, namely primary diagenesis (eogenesis), middle diagenesis (mesogenesis) and final diagenesis (telogenesis) have been determined for the studied deposits.

In order to examine the effect of depositional environments on large-test fusulinids in Middle Permian deposits of Iran two stratigraphic sections in Shotori and Bagh-e Vang Mountains in Tabas Block located in east-central Iran and one stratigraphic section in Hambast Valley, Abadeh area situated in west-central Iran were studied. The possible cause of the few occurrences of large-test fusulinids in Middle Permian shallow water carbonates of the Shotori section was high temperature (more than 36° centigrade) of paleo sea indicating unfavorable condition for algal-symbiont large-test fusulinids life. There is no large-test fusulinid in Middle Permian deep-water limestones with cherty interbeds of Bagh-e Vang section. In Hambast Valley section, the Middle Permian shallow-water subtidal limestones of the middle and upper parts of the Unit 1 of Surmaq Formation contain abundant large-test fusulinids. No large-test fusulinid is recorded from the deep-water limestones with cherty interbeds of the Unit 2 of the Surmaq Formation. The presence of cherts in the Middle Permian of Iran in both Bagh-e Vang and Hambast valley sections are related with Middle Permian chert-event and eutrophication also reported in South China and North America which is adverse for the life of large-test fusulinids in oligotrophic shallow water environment. Considering the local disappearance of the large-test fusulinids in the three studied sections before the end-Guadalupian bio-event, it can be concluded that the climate change and the nutrient level input had major role in extinction of these organisms..

The study area is located in the northwest of Chabahar city and south of Sistan and Baluchestan province in the southeast of Iran. This area is part of Makran geological area. In this research, library and documentary studies were performed first. Then, in field studies and field visits, two sediment cores were prepared from Holocene sediments in the shallow coastal area and below the tidal limit in the Gulf of Pazm using the Euger core-catching device. Sedimentary samples from different parts of the sedimentary core (22 samples) were subjected to sedimentological and geochemical analyzes. The results of sediment granulation show that the particle size is often in the range of clay to silt and less amounts of sand and gravel, which in some horizons show particles in the size of sand and gravel. Gravel particles are mainly associated with skeletal fragments and the amount of carbonate in sediments varies between 17 and 84%. The abundance of most elements, especially aluminum, magnesium, manganese, cream, barium are inversely related to changes in sea level and the two elements of calcium and strontium, which represent sediments in the basin, are directly related to changes in sea level. The results of equating the approximate age of the sedimentary sequence show that two important phases of progress and rapid sea level rise occurred in the time range from 2100 to 2800 and also from 4900 to 5800 years ago.

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

The Shahdad Kaluts include a series of longitudinal dunes with a northwest-southeast trend that are located in the north of Shahdad (East of Kerman) and southwest of the Lut desert. The succession of Kaluts consists of hetrolithic layers of sand and mud sediments that deposited in a temporary lake environment. In addition to physical sedimentary structures, in this s successions, various soft-sediment deformation structures observed, which are formed under the influence of liquidization process in two stages of liquefaction and fluidization. One of the most important deformed structures during liquefaction stage are load and flam structures, folding and convolute bedding and tepee structures. In the fluidization stage, ball and pillow structures, water-escape and sediment-injection structures were formed. Autoclastic breccias and microfaults also formed shortly after consolidate of sediments. The triggers and main formation factors of these structures are divided into two categories: endogenic (sedimentary process and depositional setting) and exogenic (earthquake activity) triggers.

The studied section is located at the Tange-Neyzar, 115 km NE Mashhad. The upper part of the Neyzar Formation consists of shale and marl, while the basal parts of Kalat Formatiom is composed of sandstone unit with interbedded shale. An oxisol type has been identified at the boundary between these formations. There are characteristics macromorphological and micromorphological features in this oxisol unit. The occurrence of beta microfabric indicates the role of micro-organisms activities in the formation of the palaeosol. The geochemical studies indicate that the average paleotemperature is 11˚ C. The paleo-rainfall varies from 818.66 to 1563 mm (with an average 1200 mm). The pressure of CO2 was measured from 2237.10 to 2981.08, which is 7.99 to 10.65 times the current value. It corresponds to the modeled values for that geological time in the other areas of the world. In addition, the fluctuation of water-stable (falling at sea level) played a critical role in the development of palaeosol in this section.

In northern region of Khorramabad city in Lurestan province, Asmari Formation is mainly composed of limestone with some interbeds of marl. The studied Formation, is late Oligocene-Early Miocene in age. In this study, petrographic studies as well as stable isotopes of oxygen and carbon have been used to make an understanding of after sedimentation conditions. We also have identified and distinguished some evidence from each diagenetic stage. Consideration of the cements, which have been deposited in cavities and fractures of carbonate rocks shows that sometimes there are differences in the isotopic oxygen content and carbon content of the edge and central parts. However, these changes in many cases are slight. Numerous diagenetic processes such as calcite cementation (syntaxial overgrowth cement, isopachous fibrous, spar mosaic cement, blocky cement, and granular cement), iron oxide cement, pyrite, limited dolomitization, micritiization, bioturbation, fractures and fillings and dissolution, incremental neomorphism, physical and chemical compaction (stylolite and stilomotel) have been affected the limestone successions of Asmari Formation in the study area. Some of these processes may occur in several diagenetic environments. In order to differentiate them, we have used cathodoluminescence and isotope study techniques. We have been utilized the oxygen and carbon stable isotopes track each diagenetic phase. In this study, we have used cathodoluminescence images to make a map for isotopic analysis. Finally, by integrating petrographic, cathoduminescence, and isotopic data, different diagenetic environments have been identified and distinguished. We hope this information make a more accurate picture of after sedimentation conditions of the sedimentary Basin.

In this study, the quality assessment of the Ilam Formation reservoir in an oil field of the Abadan plain has been investigated using wireline logs and core data. To determine permeability in core study laboratories, gas, especially dry air, is usually used because of its convenience, time consuming and very low cost. This can lead to errors and inadequate validity of absolute permeability in the evaluation and simulation of oil and gas production from reservoirs. In this paper, the corrected permeability of Klinkenberg is used in the permeability study of the reservoir section of the Ilam Formation. In addition, the reservoir quality index and porosity method based on the pore throat size distribution have been used to determine the type of petrophysical rock typing. The study shows that rock types 3 and 4, which have been identified as the best petrophysical rock typing in the reservoir of Ilam Formation, have interconnected and interparticle pores that have been obtained by dissolution. Identified rock types 1 and 2 of the studied reservoir are introduced as low quality petrophysical rock types due to the diagenetic process of cementation. The obtained results have helped to determine the best reservoir production horizons of Ilam Formation in the studied well in exploratory studies.

In this research, the Asmari Formation in the Mansourabad Oilfield in the southern part of the Dezful Embayment has been studied in order to determine the age, study and identify microfacies and depositional environment. The biostratigraphy study was based on benthic foraminifera and recognition of microfacies and depositional environment carried on the thin sections prepared from core and cutting samples of two wells from the studied oilfield. The lower boundaries of this formation are conformable and gradually with the Pabdeh Formation, but sharp with the Gachsaran Formation, respectively. According to the study, four assemblage zones were identified in the Asmari Formation. Lepidocyclina-Operculina-Ditrupa zone indicates the age of Rupelian/Chattian, Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus zone indicates the age of Chattian, Indeterminat zone indicates the age of Aquitanian, and Borelis melo curdica-Borelis melo melo zone indicates the age of Burdigalian. Based on petrographic analysis nine microfacies related to tidal flat, lagoon and open marine sub-environment were identified that were deposited on a carbonate ramp environment extended from inner to outer ramp. This study led to better understanding of the stratigraphy and depositional environment of this reservoir formation.

In order to study petrography, sedimentary environment, sequence stratigraphy and reservoir potential of Asmari Formation in Kilurkarim oil field, 5 wells from this field were analyzed. Based on the study of 800 thin sections prepared from cutting and cores, 15 carbonate microfacies were identified, which were deposited in a homoclinal carbonate ramp. Major diagenetic processes that have affected the Asmari Formation include, micritization, dolomitization, dissolution, cementation, compaction, pyritization, hematitation, and fracture. The identified diagenetic processes are the product of shallow to deep marine and meteoric diagenesis. The sum of petrographic and petrophysical studies showed that Asmari reservoir can be divided into 5 reservoir zones in the study area. Among the reservoir zones introduced, only zones No. 1 and to some extent zone No. 4 show acceptable reservoir potential. According to lithological changes, gamma log changes, vertical changes of microfacies, sequence stratigraphy of Asmari reservoir in wells No. 1 and 5 of the field was evaluated and 5 third order depositional sequences were detected. In general, the TST systems tract in the studied sequence is characterized by a slight increase in the amount of gamma log in every 5 sequences. The HST systems tract is characterized by the reduction or persistence of gamma log values along the reservoir thickness in all five separated depositional sequences. The important thing about this systems tract is the equivalence of this systems tract with the increase of reservoir potential along the reservoir.

In order to evaluate the hydrocarbon potential of Garau Formation in Aligudarz section, organic petrography analysis and Rock Eval pyrolysis were performed on samples. In this research totally, 15 samples were studied by transmitted, reflected and fluorescence light and also 12 samples using Rock-Eval pyrolysis device. The existence of bituminite was detected in the transmitted light of amorphous organic matter group and their equivalent in reflected light. Also, the fluorescence of all samples was low, which indicates presence of type II kerogen in the Garau Formation. Since the paleo depositional environment of Garau Formation was pelagic (deep marine) with no terrestrial organic matter input so was no chances of existence of vitrinite macerals for reflectance analysis. Hence, in order to evaluate the thermal maturity, the parameter of thermal alteration index (TAI) and solid bitumen reflection (BRo%) were used, which indicate the early to middle stage of thermal maturity (oil window) of samples in the Garau Formation. According to the parameters obtained from Rock Eval pyrolysis and related diagrams, the quantity of organic matter in samples ranged from good to very good and in terms of quality, show type II and II / III kerogen. Finally, the calculated source potential index (SPI) in the studied section is 19.38 m ton / m2 which shows a high source potential index.

The most prominent events in the Early Permian history of Tethys were the early Early Permian (Sakmarian) regression and the subsequent late Early Permian (Yakhtashian – Bolorian) transgression. Like the other region of Thetys, transgression in Iran begins at the time of Yakhtashian – Bolorian, which carbonate platforms began to form. These carbonate rocks have been named the Jamal Formation in the Tabas Block, where the basal section of the Jamal Formation is designated as the Bagh Vang Formation. In order to investigate and determine the exact conditions of the sedimentary environment, in addition to the sections of the Bagh Formation, the Sardar Formation in the lower part and Jamal Formation in the upper part have also been briefly studied. Thin-section analysis in two sections (Bagh-e-Vang and Shesh Angosht ) makes it possible to distinguish 8 microfacies and tow petrofacies, Bioclast grainstone and Intraclast grainstone within the barriers and Fusulinid grainstones/packstone, Bioclast packstone, Intraclast bioclast packstone and Bioclastic wackstone represent the facies of lagoon. Also, characterized that bar separated a lagoonal area from the open-marine environment. The microfacies of Mudstone and Dolomudstone have been identified in the Mudflats area and Lithic arkose and Arkose petrofacies related to peritidal environment. Among the fossils identified in is study, Calcareous algae are one of the most important shallow water fossil groups of upper Paleozoic deposites, which have been introduced in three groups: Dacycoladasean, Gymnocodiacean and Problematica and Also, increasing their diversity and abundance is related to greenhouse conditions and high sea levels.