Pabdeh Formation Research Articles

A bulk kinetic, burial history and thermal modeling study of the Albian Kazhdumi and the Eocene-Oligocene Pabdeh formations in the Ahvaz anticline, Dezful Embayment, Iran

The Ahvaz anticline which is located in the middle region of the Dezful Embayment is certainly one of the most important oilfields in Iran. Burial history reconstruction and one-dimensional thermal maturity modeling of the Late Jurassic to Present-day successions have been conducted in the Ahvaz anticline. The petroleum generation bulk kinetic parameters of the Kazhdumi and Pabdeh formations were computed by a non-isothermal open system pyrolysis at different heating rates. Bulk kinetic experiments reveal that a relatively narrow distribution of activation energies, range from 40 to 52kcal/mol for the Kazhdumi samples and from 42 to 54kcal/mol for Pabdeh shales, are directly related to the homogeneity in the organic matter. The principal activation energies of 46kcal/mol and 48kcal/mol, frequency factors of 4.36×10+11s−1 and 1.91×10+12s−1 and hydrogen indexes (HI) of 123 and 351mg/g TOC have been computed for the Kazhdumi and Pabdeh formations, respectively. The lithology composition (percentages of shale, marl, gypsum, limestone and sandstone) of the Late Jurassic-Present formations in the selected wells was determined by using cutting samples and wireline well log data. The computed kinetic parameters and derived lithology composition of strata were applied to thermal maturity modeling. Thermal maturity modeling and burial history reconstruction which is calibrated by vitrinite reflectance data and formation temperature indicate that the palaeo-heat flow ranges from 37mW/m2 to 41mW/m2.The Kazhdumi Formation entered the main stage of oil generation during the Late Miocene (6.5Ma) and the Pabdeh Formation reached early stage of oil window from the Early Pliocene (3.5Ma). Our results provide the bulk petroleum generation kinetic parameters description of the Kazhdumi and Pabdeh formations and demonstrate the thermal maturation state of source rocks, especially the Albian shales, that has been recognized as most important source rock in the Dezful Embayment.

Biostratigraphy and planktonic foraminiferal abundance in the phosphate-bearing Pabdeh Formation of the Lar Mountains (SW Iran)

Biostratigraphy and planktonic foraminiferal abundance in the phosphate-bearing Pabdeh Formation of the Lar Mountains (SW Iran)

Late Paleocene to early Oligocene dinoflagellate cysts of the Zagros basin, west Iran (palaeopalynology and palynostratography)

Palynological investigation about 120 samples from 460m thick outcrop section of late Paleocene to early Oligocene of the Pabdeh Formation, southwestern in Iran yield 55 species of dinoflagellate results to defined 7 biozone. The quantities of marine palynomorph elements are indicated of open marine at this time, but a low increase number of spore and pollen in some of the sample indicated the condition for growth forest are suitable that consequent increase the harm climate and humidity. The species are common with different latitude and most of them cosmopolitan. Thermal maturity index measurement indicates oil prone in most of the samples. Keywords : Pabdeh Formation; Dinoflagellatecyst; Paleogene; Palynostratigraphy; Thermalmaturity.

Paleogene dinoflagellate cysts and thermal maturity from Pabdeh Formation ( Zagros basin, west of Iran)

Palynological investigation on 132 samples from the 428m thick outcrop section of Late Paleocene to Early Oligocene of the Pabdeh Formation in southwestern Iran yielded 55 species of dinoflagellate cysts and allowed establishment of seven biozones. Quantity of marine palynomorph elements indicate an open marine environment at that time interval but, a slight increase in number of spore and pollen grains in some samples indicate suitable conditions for forest development as a consequence of increase in climate humidity. The species are common in various latitudes and most of them are cosmopolitan. Thermal maturity index measurement indicates oil prone nature for majority of the samples. Keyword : Pabdeh Formation, Dinoflagellate cysts, Paleogene, Palynostratigraphy, Thermal maturity

Geochemical characteristics and hydrocarbon generation modeling of the Kazhdumi (Early Cretaceous), Gurpi (Late Cretaceous) and Pabdeh (Paleogene) formations, Iranian sector of the Persian Gulf

The marls and argillaceous limestones of the Early Cretaceous Kazhdumi, Late Cretaceous Gurpi and Paleogene Pabdeh formations are considered as potential source rock candidates in this area. The present study characterizes hydrocarbon potential, type of organic matter and thermal maturity of these three formations in the Iranian sector of the Persian Gulf. Also, 1D basin modeling was used to analyse the burial history and timing of hydrocarbon generation in these formations. A total of 179 cutting samples from 25 wells were evaluated through Rock–Eval pyrolysis and organic petrography. Average total organic carbon (TOC) content for the samples of the Kazhdumi, Gurpi and Pabdeh formations that were analyzed for the current study is 1.2, 0.9 and 1 wt.%, respectively. All three formations show lower TOC contents in central part relative to eastern and western parts of the study area. Rock–Eval pyrolysis and organic petrography show that the organic matter in all three formations is mainly composed of Type II and mixed Type II–III kerogen. This study shows that the Kazhdumi, Gurpi and Pabdeh formations in Iranian offshore areas are not as rich as onshore areas, and specifically in the Dezful Embayment, in terms of organic matter quantity and quality. Thermal history modeling indicates that constant heat flow values in the range of 64–73 mW/m2 gives the best fit between measured and calculated vitrinite reflectance and bottom hole temperature. The Rock–Eval Tmax, vitrinite reflectance and the generated models suggested that in the eastern parts of the study area, the Kazhdumi Formation is at the last stage of oil generation and the Gurpi and Pabdeh formations are within the main oil generation window. Hydrocarbon generation began in the Early Eocene, Middle Eocene and Early Miocene in the Kazhdumi, Gurpi and Pabdeh formations, respectively. In the western parts of the Persian Gulf, the Kazhdumi Formation is within the main oil window with hydrocarbon generation took place during the Oligocene and the Gurpi and Pabdeh formations are early mature and immature, respectively. All three formations are thermally immature in the central part of the Persian Gulf. The Kazhdumi Formation shows positive correlation with the crude oils of the Cretaceous and Tertiary reservoirs taken from the northwestern Persian Gulf. The Pabdeh and Gurpi formations show no correlation with crude oils produced in the northwestern and southeastern Persian Gulf.

Preliminary petroleum source rock evaluation of the Asmari–Pabdeh reservoirs, Karanj and Parsi oil fields, Zagros, Iran

Abstract Petroleum source rock evaluation is formed a main part in the oil field study. The present work is focused on the Dezful Embayment, the Karanj and Parsi oil fields, Zagros. To evaluate the source rocks, oil–oil and oil–rock correlation, multidisciplinary methods were used. Rock-Eval pyrolysis data and Illite Crystallinity Index indicated that the Pabdeh Formation is in beginning of oil generation. The kerogen is principally type II. The Gurpi Formation is in the same maturity level as well. Different parameters such as normal alkanes ratios, CPI, Pri/Phy, Pri/n-C17, Phy/n-C18 were determined. These reservoirs seem to be charged partially by the Pabdeh Formation itself. To make the reservoir oils correlation with the possible source rocks, 6 samples were selected and analysed using GC–MS procedure. Ts/Ts+Tm ratio and C29bb/(bb+aa) sterane to C2920S/(20S+20R) sterane variation are showing high maturity of the Asmari oils in these fields. C29/ (C27+C28+C29) diasterane to C29/C30 hopane ratio are the same in all analysed samples. Carbon isotope data (δ13C) are −26.3, −26.7 and −26.7‰ for saturated and −25.6, −25.8, and −26.1‰ for aromatic fractions of Karanj–Parsi oils and Pabdeh bituminous shale, respectively. All geochemical and isotopic data demonstrated that the oil of Pabdeh and Asmari reservoirs in the Karanj and Parsi oil fields have the same source and are belong to paraphinic oils family.

Burial and thermal maturity modeling of the Middle Cretaceous–Early Miocene petroleum system, Iranian sector of the Persian Gulf

The Cretaceous Kazhdumi and Gurpi formations, Ahmadi Member of the Sarvak Formation, and Paleogene Pabdeh Formation are important source rock candidates of the Middle Cretaceous–Early Miocene petroleum system in the Persian Gulf. This study characterizes generation potential, type of organic matter, and thermal maturity of 262 cutting samples (marls and argillaceous limestones) from these rock units taken from 16 fields in the Iranian sector of the Persian Gulf. In addition, the burial and thermal histories of these source rocks were analyzed by one-dimensional basin modeling. Based on the total organic carbon and genetic potential values, fair hydrocarbon generation potential is suggested for the studied samples. Based on T max and vitrinite reflectance values, the studied samples are thermally immature to mature for hydrocarbon generation. The generated models indicate that studied source rocks are immature in central wells. The Gurpi and Pabdeh formations are immature and the Ahmadi Member and Kazhdumi Formation are early mature in the western wells. The Pabdeh Formation is within the main oil window and other source rocks are at the late oil window in the eastern wells. The hydrocarbon expulsion from the source rocks began after deposition of related caprocks which ensures entrapment and preservation of migrated hydrocarbon.

Geochemical investigation, oil–oil and oil–source rock correlation in the Dezful Embayment, Marun Oilfield, Zagros, Iran

Geochemical analysis of crude oils from Bangestan and Khami reservoirs, and potential source and reservoirs rocks from the Marun Field in the Dezful Embayment, Zagros Fold Belt Iran show that the Kazhdumi Formation (Fm.) is likely to be thermally mature (at least in the oil window) across the entirety of the Marun field, and that it has excellent generative potential as a source rock. Geochemical data also suggest the Pabdeh Formation has remarkable generative potential but is not thermally mature at the crest of the Marun field, although it is likely to be thermally mature in synclinal regions to the NE and SW. The Gurpi Formation, while thermally mature (early oil window) has marginal generative potential. It is notable, therefore, that oils from the Bangestan and Khami reservoirs have biomarker characteristics that do not match bitumen obtained from the Kazhdumi Formation. Examples of this include the ratio of diasteranes to steranes, the proportions of different carbon numbered hopane homologues and the ubiquitous occurrence of alkylated-trimethyl-benzenes. These biomarker characteristics could only have been imparted to the Bangestan and Khami oils by a source rock other than the Kazhdumi Formation. This contrasts with the stable isotope composition of the Bangestan and Khami oils which suggest correlation to the Kazhdumi Formation. Biomarkers are a quantitatively minor fraction of oil, thus it is possible that the biomarker characteristics of the oils was created by mixing Kazhdumi-bitumen with other petroleum from the Gurpi and Pabdeh formations. This could happen if 1) multiple oil charges from different source kitchens filled the same reservoir, or 2) if oil migrated vertically from the flanks and crossed the Gurpi and Pabdeh formations – both of which have been considered regional seals. Both scenario 1) or 2) would point to a filling history more complicated than previously conceived.

Biostratigraphy and Geochemistry of Upper Paleocene - lower Eocene Oceanic Red Beds from the Zagros Mountains, SW Iran

Oceanic Red Beds studied are well known in the upper Cretaceous (CORBs, i.e. Cretaceous Oceanic Red Beds), but their presence and genesis have hitherto not been intensively discussed for equivalent Paleogene deposits. We describe a red to purple shale interval from the Pabdeh Formation, Zagros basin, Iran, which can be assigned to Late Paleocene to Early Eocene age, nannofossil zones NP9-NP12. Parts of the purple marl interval within NP9/NP10 coincide with the PETM (Paleocene-Eocene Thermal Maximum) interval. Coccolithus pelagicus, Sphenolithus moriformis, Sphenolithus orphanknollensis, and Toweius ssp. are dominant in nannofossil assemblages in this interval, and PETM event taxa such as Discoaster araneus appear. Based on whole rock geochemistry and microfossil assemblages, the red to purple marls were deposited in an oligotrophic environment with low nutrient (Ba) values, and were accompanied by a shift to more oxic conditions and low amount of TOC in an oceanic basin. Low amount of major elements like Si, Al and Fe indicates low terrestrial input and relatively high amount of CaO (biogenic element) emphasizes the open sea and pelagic deposition of the shale. Warm deep water can be inferred by the presence of the dinoflagellate taxa Impagidinium and nannoplankton taxa, Discoaster. As a result, the purple shale can be considered as typical Paleogene ORBs in the Zagros basin deposited under very similar conditions as well studied Tethyan Cretaceous oceanic red beds.

Folding Mechanism in the Asmari Anticline, Zagros, Iran

Asmari anticline is a NW-SE fold in the Dezful Embayment sub-basin of Zagros. Fars group (Late Moicene-Quaternary) is cropping out in the cores of anticlines in this area, but Pabdeh and Asmari formations (Oligocene-Early Miocene) have cropped out only in Asmari anticline in the Dezful Embayment. Therefore, it has formed a unique exposure for above formations. In order to this situation, folding mechanism of Asmari anticline has investigated in this research. According to our results, Asmari anticline has two mechanisms: flexural-slip in post-Cretaceous sequences (Khami-Quaternary) and fault-bend folding in pre-Cretaceous sequences. So, there is a hybrid folding mechanism that has introduced for the first time in this paper.

Late paleocene to early oligocene dinoflagellate cysts from the zagros basin, West Of Iran

Palynological investigation on 132 samples from the 428m thick outcrop section of Late Paleocene to Early Oligocene of the Pabdeh Formation in southwestern Iran yielded 55 species of dinoflagellate cysts and allowed establishment of seven biozones. Quantity of marine palynomorph elements indicate an open marine environment at that time interval but, a slight increase in number of spore and pollen grains in some samples indicate suitable conditions for forest development as a consequence of increase in climate humidity. The species are common in various latitudes and most of them are cosmopolitan. Thermal maturity index measurement indicate oil prone nature for majority of the samples.

Correlation of Oils and Source Rocks in Marun Oil Field in the South West of Iran: Using Biomarkers

Biomarkers study is one useful tool for oil-oil and oil-source correlations in any petroleum field. Molecular markers were used together with stable carbon isotopes to constrain genetic relationships between oils and potential source rocks in the Marun oil field. The Marun oil field is one of the giant oil fields in south west of Iran. It consists of two oil reservoirs named Asmari and Bangestan. This article presents the correlation of Asmari and Bangestan oil reservoirs with probable source rocks named Pabdeh, Kazhdomi, and Garau formations. Distribution patterns of different biomarkers, such as Hopanes and Steranes (obtained by gas chromatography-mass spectrometry), were used to correlate oils and source rocks. The results show that there is an obvious similarity in distribution patterns of all biomarkers between Kazhdomi formation and oil samples as compared with Pabdeh and Garau formations. Furthermore, stable carbon isotope shows that in contrast to Pabdeh and Garau formations, the carbon isotope range of Kazhdomi formation had a good overlaying with Asmari and Bangestan oil reservoirs. The result of this study shows Kazhdomi formation as a proper source rock of oil in the Marun oil field.

Sequence stratigraphy of the Gurpi Formation (Campanian–Paleocene) in southwest of Zagros, Iran, based on palynomorphs and foraminifera

The Gurpi Formation is a well-known source rock in the Zagros basin, which stretches from northeast to southwest Iran. Sequence stratigraphy was done based on the integration of evidence derived from palynological proxies and foraminiferal data. According to sequence stratigraphy, seven time lines including four sequence boundaries of type II and three maximum flooding surfaces with a resolution varying from 1 to 5 MY and three complete third-order sequences and one transgressive systems tract (TST) were differentiated. Maximum flooding surface of the first sequence in middle Campanian probably equates the 70-Ma maximum flooding surface (MFS) K175 of Sharland et al. (GeoArabia P: 371, 2001), and MFS of the second sequence in early Maastrichtian is correlated with the marked 68-Ma MFS (MFS K180) of Sharland et al. (GeoArabia P: 371, 2001) that is recorded in many parts of the Arabian Plate. Correlation with the Haq global eustatic curve, though uncertain because of the effect of local tectonics over the relative sea level changes, however, could be possible with the 69.5 Ma. Also, purple shales of the base of the Pabdeh Formation with a Thanetian age are defined as a MFS, correlation of which with the marked 58-Ma MFS (MFS Pg10) of Sharland et al. (GeoArabia P: 371, 2001) and with 56.5-Ma MFS of Haq seems likely. The relative sea level curve resulted in this study is not well in accord with the existing eustasy curves for the middle Campanian-late Paleocene indicating effect of tectonic on relative sea level changes during this period.

Facies analysis and depositional environment study of the mixed carbonate–evaporite Asmari Formation (Oligo-Miocene) in the sequence stratigraphic framework, NW Zagros, Iran

The carbonate–evaporite mixed Asmari Formation was investigated on the three representative outcrops (these of Zarrin-abad, Abhar, and Darreh-shahr, corresponding to three sections) of the Lurestan Zone in NW Zagros, where the sedimentary facies of the Asmari Formation shows significant differences to those in other parts of Zagros. In the light of study results from the field observation and laboratory measurements, 16 facies have been recognized and differentiated, which are grouped into 5 facies associations, representing 6 sub-environments on a carbonate ramp. The sub-environments include peritidal area, lagoon, platform margin high-energy belts, middle ramp, outer ramp and evaporitic saltern. The evaporitic saltern points to such a condition, during which there occurred periodic change from carbonate to evaporitic settings. The alternation of carbonate with evaporitic settings appeared on a carbonate ramp connected with a hydrographically isolated intrashelf basin. The development of evaporite-dominated deposits of the Kalhur Member of Asmari Formation is related to the restriction of the basin during sea-level falls. This restriction led to succeeding evaporation of seawater and precipitation of evaporites. In times of sea-level rising, the basin was well reconnected to open ocean and thus the carbonate factory was reestablished over the basin. From sequence stratigraphic points of view, the formation is composed of two second-order regressive sequences, representing transitional conditions from deep-marine facies underlying Pabdeh Formation to shallow evaporitic facies overlying Gachsaran Formation. Each sequence is composed of a unit of evaporites at bottom displaying a falling-stage systems tract followed by thick carbonate strata, representing transgressive and highstand systems tracts. It is obvious that the major relative sea-level fall of the first second-order sequence was recorded by the facies development of the upper Kalhur gypsum of the Asmari Formation in the Zarrin-abad section, and there developed the paleokarst facies located at the sequence boundary in the Abhar, and Darreh-shahr sections.

Thermal evolution of the Kuh-e-Asmari and Sim anticlines in the Zagros fold-and-thrust belt: Implications for hydrocarbon generation

Mixed layer clay minerals, vitrinite reflectance and geochemical data from Rock-Eval pyrolysis were used to constrain the burial evolution of the Mesozoic–Cenozoic successions exposed at the Kuh-e-Asmari (Dezful Embayment) and Sim anticlines (Fars province) in the Zagros fold-and-thrust belt. In both areas, Late Cretaceous to Pliocene rocks, show low levels of thermal maturity in the immature stages of hydrocarbon generation and early diagenetic conditions (R0 I–S and Ro% values < 0.5). At depths of 2–4 km, Tmax values (435–450 °C) from organic-rich layers of the Sargelu, Garau and Kazhdumi source rocks in the Kuh-e-Asmari anticline indicate mid to late mature stages of hydrocarbon generation. One dimensional thermal models allowed us to define the onset of oil generation for the Middle Jurassic to Eocene source rocks and pointed out that sedimentary burial is the main factor responsible for measured levels of thermal maturity. Specifically, the Sargelu and Garau Formations entered the oil window prior to Zagros folding in Late Cretaceous times, the Kazhdumi Formation during middle Miocene (syn-folding stage), and the Pabdeh Formation in the Late Miocene–Pliocene after the Zagros folding. In the end, the present-day distribution of oil fields in the Dezful Embayment and gas fields in the Fars region is primarily controlled by lithofacies changes and organic matter preservation at the time of source rock sedimentation. Burial conditions during Zagros folding had minor to negligible influence.

Using Rock Eval Pyrolysis for Studying the Hydrocarbon Potential of the Pabdeh Formation in Ziluee Oilfield, South West of Iran

The author discusses the hydrocarbon potential of Pabdeh formation in Ziluee oilfield, in southwest Iran. The research was focused on characterization of this formation based on Rock-Eval (RE) pyrolysis, which is an effective instrument for analyzing probable source rock. Various diagrams were employed for interpreting the raw outputs of RE. The results revealed that kerogen type II and III are mainly distributed in understudied cuttings; therefore, Pabdeh can produce oil and gas in Ziluee oilfield, while its genetic potential is fair to good and maturation level is high enough. Based on RE data and lithological studies, Pabdeh was divided into three important zones, A, B, and C. Zone B is the most effective zone for producing oil, whereas zones A and C mainly produced gas in the proposed oilfield. Jones diagram showed that different intervals of this formation were not deposited in a singular environment. Some intervals belonged to a reducing lacustrine marine and some of them deposited in terrigenous oxidizing condition. Finally, the effect of mineral matrix and amounts of inert carbon in the samples was calculated. The small value of mineral matrix effect indicates that small amount of hydrocarbon was absorbed by minerals during pyrolysis. In addition, amount of inert carbon is negligible in studied samples of Pabdeh formation.

Larger benthic foraminifera: a tool for biostratigraphy, facies analysis and paleoenvironmental interpretations of the Oligo-Miocene carbonates, NW Central Zagros Basin, Iran

The facies distribution and the biogenic components of the study carbonates in the Ghale Nar oil field in the central part of the Zagros basin were used to reconstruct and interpret the depositional environment of the Asmari Formation. The sediments of the formation consist mainly of limestone, dolomite, dolomitic limestone and are dominated by larger benthic foraminifers (LBF) and corallinacean assemblages. Based on the LBFs, the Asmari formation in the study section is Oligocene (Rupelian–Chattian) to Early Miocene (Burdigalian) in age. Fourteen facies representing upward gradual shallowing trend of an open marine (F1 (the Pabdeh Formation) to 3), shoal (F4–5), semi-restricted and restricted lagoon (F6–12) and near-shore lagoon (F13–14) environments were identified. The facies analysis and the paleoenvironmental interpretations revealed that the carbonate sediments of the Asmari Formation were deposited in a homoclinal ramp consisting of inner, middle and outer zones. The F1 facies (top of the Pabdeh Formation) with planktonic foraminifers represents an outer ramp. The F2–3 facies with planktonic, large and small hyaline benthic foraminifers and corallin algal indicate a distal to proximal middle ramp setting. The F 4–14 facies were characterized by the occurrence of porcelaneous benthic foraminifers representing a shallow-water setting of distal to proximal inner ramp influenced by wave and tide processes. The carbonate ramp developed in tropical waters, under oligotrophic to slightly mesotrophic conditions. Our results from the facies and paleoecological analysis revealed that the Asmari Formation was deposited on a carbonate open ramp dominated by heterozoan and subordinate photozoan skeletal assemblages.

Sedimentary Environments and Correlative Sequence Stratigraphy of Upper Cretaceous—Paleogene Succession in Shiraz Area, Fars, SW IRAN

Sequence stratigraphic evidences have been used in this research to investigate the stratigraphic correlation of cretaceous paleogene succession in Shiraz area, Fars, SW Iran. For this purpose, 4 stratigraphic sections have been chosen and provided. According to petrographic study and field evidences, 4 depositional sequences were identified including the Tarbur, Sachun and Jahrum formations in the east and the Gurpi, Pabadeh and Asmari formations in the west of study area. After identifying the boundaries and systems tract facies, it has been found that the mentioned formations have been deposited among the continuous/discontinuous boundaries in an equivalent manner. In this case, the purple shale (between the Gurpi and Pabdeh formations) could be considered equivalent to the upper part of the Sachun formation. From the point of Paleogeography, the plat-form sedimentary environment covered almost the whole area during the Oligo-Miocene age, so that the Asmari formation would have been deposited, which is marked by sharp contact as disconformity on Jahrum formation in the east of the basin and with continuous contact (C.C) on the Pabdeh formation in the west and southwest.

Biostratigraphy and Paleoecological Study of Pabdeh Formation in Interior Fars, Zagros Basin, Iran

The Zagros basin, which trends NW-SE, is covered by a sea during the Paleogene, resulting in deposition of the Pabdeh Formation in the deeper parts of the basin. The thickness of the Pabdeh Formation in Tang-e-Abolhayat is about 221 m and it consists of purple shale at the base, gray shale, marl and marly limestone with a few horizons of nodular limestone toward the top. Seventy-two samples were collected and processed for nannofossil studies. Based on the identified nannofossil zones the age of the formation in Tang-e-Abolhayat is Late Paleocene-Late Oligocene (NP9-NP24). Changes in the abundance of different genera over the studied interval have resulted in identification of three ecozones: Ecozone 1 is characterized by oligotrophic conditions with an abundance of warm water taxa; Ecozone 2 marks when conditions became more eutrophic and the abundance of temperate taxa increased; Ecozone 3 represents a return to oligotrophic conditions with an increase in warm water taxa.

Facies analysis and sequence stratigraphy of the Asmari Formation in the northern area of Dezful Embayment, south-west Iran

This paper concerns the sequence stratigraphy of the Oligocene (Rupelian–Chattian)–Early Miocene (Burdigalian) Asmari Formation based on microfacies analysis of the sediments in the Ghale Nar Oilfield, central area of Zagros fold-thrust belt. Fourteen facies types typical for upward shallowing trend from open marine (MF 1–3), to shoal (MF 4-5), semi-restricted and restricted lagoon (MF 6–12) and finally to near-shore lagoon (MF 13-14) depositional environments were identified. Based on the environmental interpretations, we reconstructed a homoclinal ramp mainly represented by its inner and middle sectors. Facies types MF 4–14 are characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp influenced by wave and tide processes. MF1 (Pabdeh Formation), and 2 -3 with planktonic, large and small hyaline benthic foraminifera represent between FWWB and SWB. Four third-order depositional sequences were recognized. In this study, in order to better correlate the identified sequences with pre-defined sequences of the Asmari Formation in the Dezful Embayment and the Izeh zone that are chronologically well-defined, we use their number instead of their name. Sequence 2 mainly consists of an open marine environment in the base, followed by semi-restricted to restricted lagoonal facies. Sequences 36 are characterized by semi-restricted to restricted lagoonal facies. Moreover, the regional relative sea-level change curves correlate well with the global sea-level change curves.