SW Iran Research Articles

Sedimentology, depositional environment and classification of Karkheh River\u2019s Delta, West of Khuzestan Plain (SW of Iran)

Karkheh river’s Delta is located in the west of Khuzestan Plain and can be divided into two smaller deltas; northern delta named as Karkheh Delta (including Bostan, Sableh and Neisan Deltas) and southern delta named as Karkheh -e- Noor Delta. Based on Galloway7 classification, Karkheh Delta is river-dominated type (type 1). Considering activity, this delta is divided to two parts; an active part in north and an inactive part in south. Based on Orton and Reading 16 classification, Karkheh Delta is placed in fine-grained (muddy) delta category due to prevailing silt and clay. In terms of sediment transportation and deposition process, this delta is a constructive delta. To recognize changes of Karkheh Delta’s area, Landsat images 5, 7 and 8 were studied and compared using 13 satellite images from 1973 to 2016 which shows an increase in the delta’s area particularly in northern part. In order to study sedimentology of this delta, 25 samples were taken. Sediment sizing analysis results show that silt is the most abundant sediment on average in this delta whereas clay, sand and gravel are in next abundance. Due to Shepard 17 classification, in Karkheh delta, silty clay, clay silt, silt, sandy silt and clay-silt-sand were identified. Also, channel, flood plain, crevasse, levee and sabkha depositional environments could be recognized in this delta.

Reservoir gas isotope fingerprinting and mechanism for increased H2S: An example from Middle East Shanul gas field

Hydrogen sulfide (H2S) is an undesirable compound in oil and gas reservoirs, which reduces the economic value of gas reservoirs and has toxic and corrosive effects on reservoir operation equipment. Albeit initial generation mechanisms of hydrogen sulfide in gas reservoirs, increasing its concentration during the production phase may affect project economics. Thus, the determination of causes of increasing hydrogen sulfide concentration is of great importance. This study reports a systematic approach to investigate the possible mechanisms behind increasing H2S concentration in a carbonate gas reservoir after ten years of sweet gas production from an onshore field located in SW of Iran. Initial data during the development phase suggested a sweet gas reservoir fluid and all production and processing facilities were designed based on sweet gas production. Some wells showed increasing H2S concentration in two local sections of the field after ten years. Sampling from gas, water, and rock have been done, and isotope analysis was performed for both contaminated and non-contaminated wells. Geochemical and field data analysis were performed to determine the source of H2S increasing in this field. Results showed that the amount of sulfur isotope in the gas phase ranged from - 7.3 to −11.8‰. A general trend between the concentration of H2S and sulfur isotope was obtained. Sulfur isotope values of rock samples (core, drill cuttings, and outcrop samples), varied between + 8.3% and + 34.9% depending on formation age. Integration of geochemical, geological, and operational data indicated the occurrence and migration of H2S from an anhydrite rich formation at the bottom of the reservoir. All other possible mechanisms was rejected based on isotopic and geological evidence.

Depositional history of the uppermost Albian–Turonian Sarvak Formation in the Izeh Zone (SW Iran)

The uppermost Albian–Turonian interval has been studied in the south of the Izeh Zone (SW Iran) to investigate the depositional history of the Sarvak Formation in this area. This interval in the Middle East is characterized by the presence of very large shallow water carbonate platforms, surrounding the intra-shelf basins. The expansion of up to 90% hemipelagic strata throughout the studied outcrop proposes that it has been deposited in an intra-shelf basin. Three Cenomanian and one Turonian depositional sequences were distinguished in the studied interval based on the alternation of three microfacies associations including oligosteginid-dominated, oligosteginid-free, and platform-top microfacies. The biostratigraphical calibration by means of the planktic foraminifera indicates that these sequences can be well correlated on a global scale. The simultaneous influence of eustatic, tectonic, and environmental factors on the depositional sequences in the Lar Anticline section makes it difficult to identify the dominance of one over the others. The ability to correlate the sequence boundaries in the studied section with the global events suggests the effect of eustasy on the deposition of this interval. However, the tectonic control by the creation of a paleo-depression, subsidence (during the TST of Sequence 3), and uplift (at the Cenomanian/Turonian boundary (SB4) and mid-Turonian (SB5)) overprinted the eustatic factor. The influx of clay and the black shale formation during OAE2 conditions are the environmental factors that cannot be ignored in the deposition of sequence 1 and sequence 3, respectively.

Shear wave velocity estimation utilizing statistical and multi-intelligent models from petrophysical data in a mixed carbonate-siliciclastic reservoir, SW Iran

The conjugation of two or more Artificial Intelligent (AI) models used to design a single model that has increased in popularity over the recent years for exploration of hydrocarbon reservoirs. In this research, we have successfully predicted shear wave velocity (Vs) with higher accuracy through the integration of statistical and AI models using petrophysical data in a mixed carbonate-siliciclastic heterogeneous reservoir. In the designed code for multi-model, first Multivariate Linear Regression (MLR) is used to select the more relevant input variables from petrophysical data using weight coefficients of a suggested function. The most influential petrophysical data (Vp, NPHI, RHOB) are passed to Ant colony optimization (ACOR) for training and establishing initial connection weights and biases of back propagation (BP) algorithm. Afterward, BP training algorithm is applied for final weights and acceptable prediction of shear wave velocity. This novel methodology is illustrated by using a case study from the mixed carbonate-siliciclastic reservoir from one of the Iranian oilfields. Results show that the proposed integrated modeling can sufficiently improve the performance of Vs estimation, and is a method applicable to mixed heterogeneous intervals with complicated diagenetic overprints. Furthermore, predicted Vs from this model is well correlated with lithology, facies and diagenesis variations in the formation. Meanwhile, the developed AI multi-model can serve as an effective approach for estimation of rock elastic properties. More accurate prediction of rock elastic properties in several wells could reduce uncertainty of exploration and save plenty of time and cost for oil industries.

Geological interpretation using multivariate K-means and robust factor analysis in Dezak area, SW Iran

The Dezak limestone area, located SW Iran, is a potential site for industrial survey project of Precipitated Calcium Carbonate (PCC). Economic geology studies and geochemical implications of the area involve a high-risk level given the high purity of the limestone and the amount of penalty elements in the deposit. Generally, considering the compositional properties of geochemical data and using multivariate methods for a total of 527 composite samples showed that the data can be classified into five classes based on geological characteristics. According to K-means analysis, the grades of CaCO3 and SiO2 were 96.066% and 1.4754% within the second zone, and 94.5914% and 2.3278% within the fifth zone, respectively. Therefore, these zones were recognized as the first and second highest priorities having in common 165 and 133 samples on the specific geological units of Kdl and Kdld, respectively. Geochemical classification confirmed the geological units and variations. The priorities may preferably change depending on the time, place, plant requirements, access position, and the concentration of MgO and SiO2. Results from the robust factor analysis indicated that CaCO3 enrichment was mainly associated with depletion of SiO2 and Fe2O3 as well as P2O5 and, to some extent, MgO. This indicates the suitability of the selected study area, as major penalties are in contrast to CaCO3 enrichment. Geological and geochemical studies suggest different types of crystallized limestone and micritic limestone as the best zones for extraction. Therefore, geological properties were verified using multivariate K-means and factor analysis in the Dezak area.

The 9 April 2013 Kaki earthquake (Mw 6.3) in SW Iran occurred along a blind backthrust in the Fars geological province of the Zagros Fold and Thrust Belt

Abstract The Zagros Fold and Thrust Belt (ZFTB) in southern Iran is a seismically active tectonic zone, where SW-vergent thrust faults and NW–SE- and NE–SW-oriented strike-slip fault systems accommodate crustal shortening, resulting from the active Arabia–Eurasia collision. The majority of earthquakes in Iran occur within the ZFTB, posing a major hazard for society. The 9 April 2013 Kaki Earthquake (Mw 6.3) in the southern part of the ZFTB took place along a fault that was previously unknown regarding its surface expression, geometry and kinematics. We have used surface–subsurface distributions and focal mechanism solutions of the Kaki Earthquake aftershocks to characterize the fault system responsible for the quake. Our results indicate that it was a NE-vergent thrust fault with a minor dextral component that slipped c. 7–17 km at depth, causing the Kaki Earthquake. There were no surface ruptures, although some surface fissures developed in fluvial terraces during the main shock. We interpret this fault as a blind backthrust, which probably represents a reactivated Mesozoic basement fault emanating from the Zagros detachment surface. An upper shallow décollement zone within the Miocene Gachsaran Salt facilitated its upward propagation on the back-limb of an overturned syncline.

Contamination factor and pollution load index to estimate source apportionment of selected heavy metals in soils around a cement factory, SW Iran

ABSTRACT The present study was carried out aimed at characterizing the spatial distribution and source apportionment of heavy metals (HMs), including lead (Pb), cadmium (Cd), nickel (Ni) and manganese (Mn), in the soils around the Yasouj cement factory. A total of 61 surface soil samples (0–30 cm) were collected, and after measuring the near-total concentration of selected HMs, contamination factor (CF) and pollution load index (PLI) were calculated. Comparing the observed concentrations of the studied HMs with their global permissible limits revealed that the whole area was severely polluted to Ni (average: 243.53 mg kg−1). The spatial distribution of selected HMs in the studied soils indicated that the distance to the cement factory is not necessarily a factor of influence. CF analyses revealed that Pb and Mn caused an ‘extremely polluted’ class for most of the sampling sites. Accordingly, preventing the adverse impacts of cement production in the area requires further precautions. The PLI numeric values ranged from 1.0 to 2.3, suggesting that both bedrock weathering and industrial activities might equally contribute to spreading HMs in the area. It can be concluded that calculating and interpreting PLI may provide valuable information about the possible sources of HMs.

Correction to: Biostratigraphy of the Kazhdumi Formation (Albian), northeast of Shiraz, Zagros Basin (SW of Iran)

The article Biostratigraphy of the Kazhdumi Formation (Albian), northeast of Shiraz, Zagros Basin (SW of Iran)”.

Correction to: Biostratigraphy, facies analysis and sequence stratigraphy of the Sachun Formation (Interior Fars, Zagros, SW of Iran)

The article “Biostratigraphy, facies analysis and sequence stratigraphy of the Sachun Formation (Interior Fars, Zagros, SW of Iran)”, written by Kamal Karimi,Massih Afghah, Seyyed Hossein Ghetmiri and Mohammad Bahrami was originally published online on 09 October 2020 with Open Access under a Creative Commons Attribution 4.0 International License.

A novel and efficient chemometric approach to identifying oil families by saturate biomarker data and FTIR spectroscopy of asphaltene subfractions

The genetic classification is commonly performed by the utilization of a few interpretive biomarker ratios (e.g., 14 peak ratios) in chemometric methods. In this paper, a novel workflow with higher efficiency in revealing subtle differences between samples was suggested to solve the limitations of traditional methods. The peak areas of selected source related biomarker compounds were employed to generate 342 peak ratios. The use of higher peak ratios in the comparisons provides higher sensitivity regarding dissimilarities among studied samples. These peak ratios were utilized as an input in PCA and HCA techniques. Also, a new similarity coefficient measurement was suggested for the HCA technique. In this procedure, the moving window correlation coefficient technique was implemented on generated data series. The dissimilarity matrix for each pair of samples was constructed by the calculated minimum correlation coefficient in all moving windows. A complete linkage algorithm was then exerted on the dissimilarity matrix to relate different samples and define oil families. This new procedure provides higher efficiency regarding commonly used procedures in the PCA and HCA techniques for disclosing dissimilarities between samples. Furthermore, structural characteristics of asphaltenes due to their similarity with the precursor kerogen were applied to complement GC-MS data. Asphaltenes were fractionated into three subfractions for comprehensive comparison among studied samples. The proposed technique was carried out on the 18 oil samples from the Dezful Embayment, SW Iran. The studied oils comprise three distinct oil families, including group I (Rag-e Sefid and Shadegan samples), group II (Ahvaz samples), and group III (Qale Nar samples). Both FTIR and GC-MS corroborate these three oil families.

A Geomechanical Evaluation of Fault Reactivation Using Analytical Methods and Numerical Simulation

One of the main problems related to mature oilfields is the decreased pore pressure due to hydrocarbon production. Therefore, to maintain the production rate of a reservoir, the lost pressure must be compensated. A very traditional method to increase the pressure is to inject natural gas into the reservoir. This technique is widely used in SW Iranian reservoirs because of the readily available supply of this type of gas. Reactivation of pre-existing faults and inducing new fractures into the reservoir and cap rock are some of the potential risks regarding gas injection. In this article, using data such as well logs, pore pressure estimates, and rock mechanical test results, the geomechanical simulation of the Asmari reservoir in the Gachsaran oilfield, SW Iran has been carried out. For this purpose, the current stress field was determined using elastic moduli of reservoir rocks and formation integrity test (FIT) results. Then, by applying analytical methods such as Mohr diagrams and slip tendency, the reactivation possibility of four faults in the field was analyzed, and the maximum sustainable pore pressures were estimated. In the next step, numerical simulations were conducted using ABAQUS software to investigate the injected gas flow path, leakage potential through the cap rock, possible fault reactivation due to gas injection, and shear stress build-up and plastic strain development in different parts of the reservoir. Results of Mohr diagrams and slip tendency showed that all the faults are stable in the current stress state, and fault F2 has the potential to sustain a maximum pore pressure of 55 MPa in the field. On the other hand, fault F3 has the proper conditions (i.e., strike and dip referring to σHmax orientation) for reactivation. Results of numerical simulations suggested that an injection pressure of 30 MPa would not induce any new fracture or fault slip within 5 years of injection. In this period, the injected gas plume moves upward through the damage zone and reaches the shallower parts of the cap rock. It was also shown that by applying an injection pressure of 60 MPa, slip would occur on fault F4 after 10 days of injection.

Vegetation history of the Maharlou Lake basin (SW Iran) with special reference to the Achaemenid period (550\u2013330 bc)

This study presents the results of a palynological investigation on a sediment core from the seasonal and saline Lake Maharlou in the Zagros Mountains in southwest Iran. We emphasised studying the role of man in modifying the vegetation of the area and the dominant agricultural practices during the Imperial Persia period (2,500–1,299 cal bp; 550 bc-ad 651), particularly the Achaemenid Empire (2,500–2,280 cal bp; 550–330 bc). Scattered pistachio-almond scrub combined with Quercus brantii was the main vegetation type of the basin during the period studied. The present study depicts a significant increase in agriculture, suggesting urban development during the Late Antiquity and early Islamic Iranian dynasties. The inferred chronology of arboricultural activities is compatible with historical evidence showing that Fars Province witnessed economic and agricultural flourishing during these periods. The presence of the ‘Persian gardens’ is supported by the co-increase of cypress tree pollen frequencies with pollen of other cultivated trees, especially Platanus; both trees were cultivated for their shade and symbolic values. This study also provides pollen evidence of Punica granatum during the Achaemenid period and Phoenix dactylifera cultivation during the early post-Sasanian era. The variations in indicator pollen ratios among Poaceae, Artemisia, and Amaranthaceae appear compatible with the palaeohydrology of the basin and show periods of aridity followed by higher moisture availability. We suggest that anthropogenic activities played the leading role in vegetation change in the Maharlou Lake basin enhanced by climatic changes during the last ~4,000 years.

An integrated approach to distribute carbonate reservoir properties, using lithofacies and seismic attributes: a case study from SW of Iran

Complexity and heterogeneity of carbonate deposits make the understanding of the reservoir quality challenging. This study is a contribution to the understanding of the distribution of carbonate–evaporite reservoir property of the Permo–Triassic Kangan–Dalan succession in one of the giant gas fields in the southwest of Iran. To capture and describe the complexity and heterogeneity of the carbonate reservoir, we defined different rock properties approach to the management of quantitative data on carbonate reservoir which is based on well and seismic data with an integrated sedimentological investigation, petrophysical evaluation, and seismic analysis to determine the new reservoir lithofacies classification. A lithofacies-based reservoir characterization study was conducted carbonate reservoir to build a numerical 3-dimensional (3D) geological model including reservoir property prediction for reservoir flow simulation. To do this, full suite of logs from six wells, core from four wells in the studied interval and 3D seismic volume across the studied interval have been involved and investigated. Five lithofacies were identified from detailed analysis, and the relationship between lithofacies and reservoir property was considered and geostatistically propagated in the studied area. This study shows that an integrated study using seismic data and well logs can be used to basically divide the reservoir into relatively homogeneous zones based on core and petrophysical analysis, and then evaluate each zone to distinguish high-quality zones. This approach provides useful insight to Permo–Triassic carbonate reservoir and other similar reservoirs and can also be effectively used in areas which lack well or outcrop data.

Origin, geochemical characteristics and filling pathways in the Shadegan oil field, Dezful Embayment, SW Iran

The Shadegan oil field is one of the fields in the central part of the Dezful Embayment. Little or no geochemical studies have been performed previously in this field. This paper provides valuable information to answer most of the geochemistry ambiguities and issues in this field. Different techniques were used to investigate the genetic types of Asmari and Bangestan reservoirs. Structural characteristics of asphaltenes, biomarker fingerprints, and V/Ni ratio indicates that all oils in the Shadegan field have similar source rock(s) and belong to one oil family. The homologous series of normal alkanes distribution and the absence of 17α(H) 25-hopane reveals that biodegradation has not affected oil samples and planktons/algal or higher plants are dominating organic matters, proved by hopanes/steranes ratio. The Pr/Ph < 1, 0.49 < V/(V + Ni) < 0.81, and homohopanes distribution implied an anoxic condition during source rock deposition. The DBT/Ph, C24/C23 tricyclic terpanes, C22/C21 tricyclic terpanes, C29/C30 hopane, diasterane/sterane ratios suggest that the contribution of clay to source rock was insignificant and source rock has composed of a mix shale and carbonate. Steranes show C29 > C27 > C28 pattern, and the ternary diagram of steranes confirmed that the source rock deposited in the open marine environment and oil samples originated from marine organic matters. All samples have been sourced from a source rock(s) older than the Upper Cretaceous, as shown by the oleanane ratio. The Kazhdumi Formation is the primary source rock in this field, and some contributions from other source rocks might have occurred. In general, samples indicate maturity before the peak of the oil window in which the Bangestan samples have lower maturity regarding the Asmari samples based on aromatic and saturate maturity parameters. The tracing of oil filling pathways by isopleth maps of 4-/1-MDBT and C29 sterane 20S/(20S + 20R) ratios revealed that each reservoir had been charged from several directions. Although the Upper Asmari and Bangestan reservoirs have been charged laterally, the Lower Asmari has been charged vertically and laterally.

Rock physics analysis and modelling using well logs and seismic data for characterising a heterogeneous sandstone reservoir in SW of Iran

Rock physics aims to link geological and reservoir properties to the elastic and seismic parameters. By analysing well logs and seismic data in a rock physics framework, reservoir conditions and key reservoir properties such as lithology and fluid saturations could be understood and/or predicted more precisely. In this study, we have conducted a detailed rock physics study on a heterogeneous sandstone reservoir located in south-west of Iran. First, we carried out Rock Physics Diagnostic (RPD) analysis on the data obtained from the wells based on the contact or granular-medium models and Gassmann’s fluid substitution relations. Then, by using constant-cement model that was identified as the most acceptable model in the RPD analysis, P- and S-wave velocities were predicted in several wells of the studied reservoir. Due to heterogeneous nature of the reservoir, we used various cement percentages (2–9%) for estimating seismic velocities at different subzones of the studied interval. The generated error logs show that the constant-cement model (with its optimised parameters) provides suitable approximation of velocities along the reservoir interval. In addition, by generating a Rock Physics Template (RPT) using well logs, we have evaluated the lithological and fluid saturation changes. In order to integrate the available 3D seismic data of the studied field in our rock physics study, we first performed pre-stack stochastic seismic inversion. The inversion results was then superimposed on the constructed RPT to have a first look identification of the hydrocarbon content in the whole 3D area of the reservoir framework.

Deep-T-platform responses to the global sea-level fluctuations, Oligocene Asmari and Pabdeh Formations of the Zagros foredeep Kalhur sub-basin, SW Iran

A sequence stratigraphic analysis of the Asmari and Pabdeh Formations (Oligocene) carbonate factory in the Kalhur sub-basin of the Zagros foredeep in SW Iran established the depositional attributes and facies patterns of the abnormally deep-T-platforms in response to global sea-level fluctuations. The paleoecology, paleogeography and hydrodynamic properties affected symbiotic large benthic foraminifers (SLBF) to determine the carbonate generation window and steepened ramp systems building from gravel-producing biota within the oligophotic zone. Four facies belts, containing five lithofacies and ten microfacies like those of C-platforms, were identified from grain associations and standard depositional criteria. Highstand systems tracts formed of uncemented and unconsolidated close-cluster reefs developed in the lower mid-ramp to upper part of the outer ramp and prograded below storm wave base (SWB). Portions of the reefs above SWB were eroded and transported downslope to the distal portion of the outer ramp and the proximal part of the basin as tempestites, created by periodic storms. In the subsequent sea-level fall, these platforms were eroded during periodic storms, shedding large volumes of calciturbidites, just as they do in C-platforms. The Rupelian succession consists of three third-order sequences, namely Ru. 1, Ru. 2 and Ru. 3. Further comparison of sea-level and onlap curves in the study area with global and Arabian platform sea-level and onlap curves, provides an exact chronostratigraphic framework, revealing a close correlation with eustatic events in the Zagros foredeep.

Sequence stratigraphy study of the Dariyan Formation in the Gadvan and Zana sections in the northeast and northwest of Shiraz, Zagros Basin, SW Iran

In the present paper, sequence stratigraphy and microfacies of the Dariyan Formation in the two sections of the Gadvan and Zana Mountains located were studied in NE and NW of Shiraz (Fars province, SW Iran). An area of 429.5 m of the Dariyan Formation sediments was studied through 187 thin sections. Also, the index microfacies were closely identified. Generally, index microfacies of the studied thin section were mudstone, wackestone, packstone, and grainstone microfacies. Received paleontological data confirm Aptian–lower Albian age of the Dariyan Formation. According to the lithostratigraphic aspect, the lower contact of Dariyan Formation with the Gadvan Formation in the Gadvan Mountain was described as a gradual type and in Zana Mountain; disconformity was found due to the sign of water withdrawal. Given the upper contact of the Dariyan Formation concerning the formation percentage, contact disconformity was observed due to the changes in the Allochem element and the situation of the entity from water and also according to the high percentage of iron nodules and Gluconate. According to the sequence, stratigraphic studies in the section of Gadvan Mountain, the lower border of the Dariyan Formation with Gadvan Formation was in the gradual form [type 2 Sequence Boundary (SB2)] and there was a disconformity in the upper border of this formation with Kazhdumi Formation [type 1 Sequence Boundary (SB1)]. Dariyan Formation included the system tracts (transgressive system tract, early highstand system tract, and late highstand system tract). There was a disconformity in its lower of the Gadvan Formation and disconformity in its upper boundary with the lower of the part Kazhdumi Formation (SB1) and it included the system tracts (highstand system tract, transgressive system tract, and lowstand system tract). Overall, lap sequence grade3 was seen in the two sections.

Microfacies, depositional environment and paleoecology of the Asmari Formation in the Karanj oil field, norhtern Dezful embayment, SW Iran

Microfacies, depositional environment and paleoecology of the Asmari Formation in the Karanj oil field, norhtern Dezful embayment, SW Iran

Biostratigraphy, facies analysis and sequence stratigraphy of the Sachun Formation (Interior Fars, Zagros, SW of Iran)

AbstractTwo sections of the Maastrichtian–Lower Eocene Sachun Formation, crossing Interior Fars zone, Zagros basin in SW Iran, were selected. To biostratigraphy, facies analysis, paleoenvironment and sequence stratigraphy, foraminifers and lithofacies were studied. Three foraminifer assemblage zones were observed in the studied areas. According to stratigraphic distribution of the identified foraminifers, the Sachun Formation is assigned to Upper Cretaceous (Maastrichtian)—Lower Eocene (Ypersian) age. The sedimentation of the Sachun Formation was controlled by the sea-level fluctuation. According to the sedimentary records, Sachun Formation has been deposited in a tectonically unstable basin. Microscopic investigation confirms the presence of seven microfacies, which can be grouped into four depositional environments: tidal flat, lagoon, shoal, and open marine. A carbonate shallow shelf is suggested for the depositional environment of the Sachun Formation, with the depth of sedimentary basin of the Sachun Formation decreasing from the study area to the south of Fars zone. Sachun Formation facies have been deposited in a shallow depositional basin characterized by permanent sea level changes. The vertical distribution of the investigated lithofacies supports two third-order cyclic sequences in the Sachun Formation, based on shallowing upward patterns in the determined lithofacies.

Biostratigraphy correlation, of Cretaceous successions in Kuh-e-Rahmat and Kuh-e-Sabz sections, NE Shiraz, Zagros (SW Iran)

Two stratigraphic sections (Kuh-e-Rahmat and Kuh-e-Sabz) of Upper Cretaceous strata in the Interior Fars region (SW of Iran) were selected. Lower Cretaceous succession of Kuh-e-Rahmat was consisted of Dariyan, Kazhdumi Sarvak and Ilam Formations. The lower contact of the Sarvak Formation with Kazhdumi Formation is described as a transitional type whereas the upper contact of Sarvak Formation was not clear. Stratigraphic distribution of microfossils reveals three biozones in this section: 1: Palorbitolina lenticularis (Aptian), 2: Orbitolina concava and Hemicyclamina sigali (late Albian-early Cenomanian), 3: Stomiosphaera conoidea (Late Cenomanian-Early Turonian). Kuh-e-Sabz lithologic aspect consists of two rock units such as: Sarvak Formation and thin-bedded limestone of lower part of Ilam Formation. The lower contact of the Sarvak Formation was not clear whereas the upper contact with Ilam Fm. was exposed as an erosional disconformity including oxidized zone. Vertical distribution of investigated taxa supports three biozones: 1: Taberina bingistani zone (middle Cenomanian), 2: Praelveolina cretacea zone (late Cenomanian), 3: Dicyclina schlumbergeri zone (Santonian-Campanian). The Sarvak Formation of Kuh-e-Rahmat was deposited in an inner shelf paleoenvironment (as open marine facies) because of well distributed of pelagic fauna, while Kuh-e-Sabz section mostly shows reef facies (back reef-fore) along the platform including agglutinated and porcelaneous foraminifera which reflects an inner shallow platform (0-50m).