University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 olume 36, Issue 4 - Serial Number 81, Winter 2021 olume 36, Issue 4 - Serial Number 81, Winter 2021 26247 FA Journal Article 2022 01 11 https://jssr.ui.ac.ir/article_26247_3e22143227304843f8aaaf22ba83384a.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 Biostratigraphy of the Oligocene deposits of Pabdeh Formation based on planktonic foraminifera in Bandar Abbas area Biostratigraphy of the Oligocene deposits of Pabdeh Formation based on planktonic foraminifera in Bandar Abbas area 1 26 24852 10.22108/jssr.2020.121426.1152 FA Jahanbakhash Daneshian Kharazmi University, Tehran, Iran Mahboobeh Sadat Tabatabaei Kharazmi University, iran Alireza Tahmasbi National Iranian Oil Company, Tehran, Iran Journal Article 2020 03 05 Abstract In this research, the biostratigraphy of Oligocene deposits of the Pabdeh Formation in Bandar Abbas region is considered. For this purpose, the planktonic foraminifera was studied and identified. Based on the index forms of these microfossils, biozones were recognized and compared to global biozonation. Investigation of the stratigraphic distribution of these microfossils in the four studied surface and subsurface sections (Champeh, Safid, Band-e Lengeh, and Taftan) led us to the identification of the Eocene/Oligocene boundary and four biozones of planktonic foraminifera (Zone E16, Hantkenina alabamensis Highest-occurrence Zone, Zone O1, Pseudohastigerina naguewichiensis Highest-occurrence Zone, Zone O2, Turborotalia ampliapertura Highest-occurrence Zone, Zone O3, Dentoglobigerina sellii Partial-range Zone) in this region. Based on the foraminiferal assemblages and their biozonation, the age of Oligocene deposits of the Pabdeh Formation is Rupelian. Also, the lateral extension of Oligocene deposits of the Pabdeh Formation in the studied area has been considered. Keywords: Pabdeh Formation, Biozonation, Oligocene, Planktonic foraminifera, Bandar Abbas Hinterland. Introduction Folded Zagros with about 2,000 km long is divided into Lurestan, Dezful Embayment, Izeh Zone, Abadan Plain, Fars, and Bandar Abbas hinterland. ThePabdeh Formation mainly is composed of shales and marls with a marine origin, comprises alternation of dark to light gray shale beds and thin to thick limestones with good preservation of planktonic foraminifera, developed in southwest Lorestan, Khuzestan and Fars Provinces (Aghanabati 2011). James and Wynd (1965) introduced a type section of this formation in Tang-e Pabdeh and Wynd (1965) presented biofacies and biostratigraphic zonations of this formation for the first time. In this research, the Oligocene deposit of Pabdeh Formation has been studied in terms of biostratigraphy and standard biozonation. Material & Methods In order to study of planktonic foraminifera in Bandar Abbas hinterland, four stratigraphic sections including Champeh outcrop section and Safid, Taftan and Band-e Lengeh wells were investigated. In total, 938 samples were studied for foraminiferal biostratigraphy. Planktonic foraminiferal taxa were identified from the washed residues of 53 marl samples in the Champeh section. Other samples were studied in thin sections. Identification of planktonic foraminifera and standard biozonation carried out based on Berggren et al. (1995), Berggren and Pearson (2005), Wade et al. (2011), and Berggren et al. (2018). Discussion of Results & Conclusions In studied sections, the stratigraphic distribution of planktonic foraminifera permitted us to recognize the Eocene/Oligocene boundary and four planktonic foraminiferal biozones (E16 to O3). We recognized the Eocene/Oligocene boundary and Hantkenina alabamensis Highest-occurrence Zone (E16) in studied sections according to the extinction of hantkeninids. Pseudohastigerina naguewichiensis Highest-occurrence Zone (O1): The lower boundary of this Zone is the latest occurrence of Hantkenina alabamensis and the upper boundary is based on the last occurrence of Pseudohastigerina naguewichiensis. Turborotalia ampliapertura Highest-occurrence Zone (O2): The lower boundary of this zone is the last occurrence of Pseudohastigerina naguewichiensis and the upper boundary is the highest occurrence of Turborotalia ampliapertura. Globigerina sellii Partial-range Zone (O3): The lower boundary of this biozone is the highest occurrence of Turborotalia ampliapertura but the upper boundary is not observed in the studied sections. In Taftan well, the Eocene/Oligocene boundary was defined based on the extinction of Turborotalia cerroazulensis because of the absence of hantkeninids. Therefore, P17 is introduced for upper Eocene instead of E16. Also, the key species Pseudohastigerina naguewichiensis was not observed in Band-e Lengeh and Taftan wells. This species shows the upper boundary of O1 and the lower boundary of O2 zones. Thus, no distinction can be made between the O1 and O2. These two biozones are comparable with Small globigerinids-Haplophragmium slingeri-Zeauvigerina assemblage zone of Wynd (1965). The study area is located in Lengeh trough. In shallow parts, the Asmari Formation was deposited on the Pabdeh Formation (Champeh section and Safid well), while at the same time, sedimentation of Pabdeh Formation continued in the deeper parts of the basin (Band-e Lengeh and Taftan wells). In Bandar Abbas hinterland, the thickness of Oligocene deposits of the Pabdeh Formation has increased relatively from northwest to southeast, so there is the lowest thickness in the Safid well and the highest thickness in the Band-e Lengeh well. Generally, the Oligocene deposits of Pabdeh Formation are thicker and belong to Rupelian in Bandar Abbas hinterland. Towards the Fars area, these deposits are the same in age but their thicknesses are reduced. Towards the Izeh area, the deposits are younger and continued until Chattian, but the thickness is less than the study area. Abstract In this research, the biostratigraphy of Oligocene deposits of the Pabdeh Formation in Bandar Abbas region is considered. For this purpose, the planktonic foraminifera was studied and identified. Based on the index forms of these microfossils, biozones were recognized and compared to global biozonation. Investigation of the stratigraphic distribution of these microfossils in the four studied surface and subsurface sections (Champeh, Safid, Band-e Lengeh, and Taftan) led us to the identification of the Eocene/Oligocene boundary and four biozones of planktonic foraminifera (Zone E16, Hantkenina alabamensis Highest-occurrence Zone, Zone O1, Pseudohastigerina naguewichiensis Highest-occurrence Zone, Zone O2, Turborotalia ampliapertura Highest-occurrence Zone, Zone O3, Dentoglobigerina sellii Partial-range Zone) in this region. Based on the foraminiferal assemblages and their biozonation, the age of Oligocene deposits of the Pabdeh Formation is Rupelian. Also, the lateral extension of Oligocene deposits of the Pabdeh Formation in the studied area has been considered. Keywords: Pabdeh Formation, Biozonation, Oligocene, Planktonic foraminifera, Bandar Abbas Hinterland. Introduction Folded Zagros with about 2,000 km long is divided into Lurestan, Dezful Embayment, Izeh Zone, Abadan Plain, Fars, and Bandar Abbas hinterland. ThePabdeh Formation mainly is composed of shales and marls with a marine origin, comprises alternation of dark to light gray shale beds and thin to thick limestones with good preservation of planktonic foraminifera, developed in southwest Lorestan, Khuzestan and Fars Provinces (Aghanabati 2011). James and Wynd (1965) introduced a type section of this formation in Tang-e Pabdeh and Wynd (1965) presented biofacies and biostratigraphic zonations of this formation for the first time. In this research, the Oligocene deposit of Pabdeh Formation has been studied in terms of biostratigraphy and standard biozonation. Material & Methods In order to study of planktonic foraminifera in Bandar Abbas hinterland, four stratigraphic sections including Champeh outcrop section and Safid, Taftan and Band-e Lengeh wells were investigated. In total, 938 samples were studied for foraminiferal biostratigraphy. Planktonic foraminiferal taxa were identified from the washed residues of 53 marl samples in the Champeh section. Other samples were studied in thin sections. Identification of planktonic foraminifera and standard biozonation carried out based on Berggren et al. (1995), Berggren and Pearson (2005), Wade et al. (2011), and Berggren et al. (2018). Discussion of Results & Conclusions In studied sections, the stratigraphic distribution of planktonic foraminifera permitted us to recognize the Eocene/Oligocene boundary and four planktonic foraminiferal biozones (E16 to O3). We recognized the Eocene/Oligocene boundary and Hantkenina alabamensis Highest-occurrence Zone (E16) in studied sections according to the extinction of hantkeninids. Pseudohastigerina naguewichiensis Highest-occurrence Zone (O1): The lower boundary of this Zone is the latest occurrence of Hantkenina alabamensis and the upper boundary is based on the last occurrence of Pseudohastigerina naguewichiensis. Turborotalia ampliapertura Highest-occurrence Zone (O2): The lower boundary of this zone is the last occurrence of Pseudohastigerina naguewichiensis and the upper boundary is the highest occurrence of Turborotalia ampliapertura. Globigerina sellii Partial-range Zone (O3): The lower boundary of this biozone is the highest occurrence of Turborotalia ampliapertura but the upper boundary is not observed in the studied sections. In Taftan well, the Eocene/Oligocene boundary was defined based on the extinction of Turborotalia cerroazulensis because of the absence of hantkeninids. Therefore, P17 is introduced for upper Eocene instead of E16. Also, the key species Pseudohastigerina naguewichiensis was not observed in Band-e Lengeh and Taftan wells. This species shows the upper boundary of O1 and the lower boundary of O2 zones. Thus, no distinction can be made between the O1 and O2. These two biozones are comparable with Small globigerinids-Haplophragmium slingeri-Zeauvigerina assemblage zone of Wynd (1965). The study area is located in Lengeh trough. In shallow parts, the Asmari Formation was deposited on the Pabdeh Formation (Champeh section and Safid well), while at the same time, sedimentation of Pabdeh Formation continued in the deeper parts of the basin (Band-e Lengeh and Taftan wells). In Bandar Abbas hinterland, the thickness of Oligocene deposits of the Pabdeh Formation has increased relatively from northwest to southeast, so there is the lowest thickness in the Safid well and the highest thickness in the Band-e Lengeh well. Generally, the Oligocene deposits of Pabdeh Formation are thicker and belong to Rupelian in Bandar Abbas hinterland. Towards the Fars area, these deposits are the same in age but their thicknesses are reduced. Towards the Izeh area, the deposits are younger and continued until Chattian, but the thickness is less than the study area.

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University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 Reservoir quality of the Jahrum carbonate succession; a case study from the Fars region of Zagros Basin, SW Iran Reservoir quality of the Jahrum carbonate succession; a case study from the Fars region of Zagros Basin, SW Iran 27 58 24872 10.22108/jssr.2020.119638.1168 FA Roghayeh Fallah Bagtash Shahid Beheshti University, Tehran, Iran Mohammadhossein Adabi Shahid Beheshti University, Tehran, Iran Abbas Sadeghi Shahid Beheshti University, Tehran, Iran 0000-0002-5515-0781 Ehsan Dehyadegari Shahid Beheshti University, Tehran, Iran Journal Article 2020 06 14 Abstract Eocene to Oligocene–Miocene carbonates of Jahrum and Asmari formations form the reservoirs of the Khesht Field in the Fars Province, the Zagros Foreland basin. In this study, the reservoir characteristics of the upper parts Jahrum Formation in the Khesht Oil Field have been investigated based on the combination of facies analysis and diagenetic features of samples in the porosity-permeability framework. The Jahrum Formation in the Fars Province is mainly composed of limestones that formed on a laterally continuous carbonate ramp with significant variations in reservoir heterogeneity and quality. Petrographic studies led to the identification of five carbonate microfacies. Five petrophysical rock types (RT) in KH-02 well are recognized by considering primary and secondary controls on pore type and size distribution. From RT1 with no reservoir property toward RT5 reservoir quality is enhanced. Diagenetic features have significantly affected reservoir properties by both enhancing and destroying porosity and permeability. Bivariate plots of porosity and permeability, combined with thin-section petrography indicate that pervasive anhydrite cement and compaction had the greatest negative impact on reservoir quality, whereas, dolomitization, fracturing, and dissolution of Nummulites played the most positive role. Therefore, the general characteristics of the Jahrum reservoir in the Khesht Field are mainly shaped by diagenetic features. Using CycloLog software in the two studied wells led to the identification of two sedimentary cycles within the Jahrum Formation. The negative trend of the INPEFA log (sea-level fall) in the second sedimentary cycle includes the upper part of the Jahrum Formation which has medium to high reservoir quality. Keywords: Reservoir zonation, Rock types, Diagenesis, Cyclolog Software, Jahrum Formation. Introduction Carbonate reservoirs are difficult to describe and produce a realistic picture of reservoir properties due to the vertical and lateral heterogeneity in various categories including lateral distribution of facies (Alsharhan 2006; Dou et al. 2011) and complex diagenetic evolution of carbonates (Lucia 2007; Ahr 2008; Rong et al. 2012; Moore 2013). Carbonates of the Jahrum Formation in Fars province together with the Asmari Formation form the main part of reservoirs in SW Iran. So far, no study has been conducted to investigate the reservoir characteristics of the Jahrum Formation in the Khesht oil field. These carbonates are generally deposited in a shallow marine environment, and the estimated porosity from thin-section petrographic studies show that due to the abundance of lime mud and low textural maturity, their reservoir capacity was low in the time of deposition (Hassanvand 2016). Therefore, due to the low primary porosity in most parts of the Jahrum Formation, it seems that the reservoir quality of this formation largely depends on the development of secondary porosity as a result of the performance of various diagenetic processes such as dolomitization (Azomani et al. 2013), fracturing and dissolution. Due to the importance of reservoir studies and the investigation of the distribution of reservoir properties, the combination of facies analysis and diagenetic characteristics of the Jahrum Formation samples in the framework of porosity and permeability were used for reservoir zonation in Khesht-2 well and the studied rocks were divided into different rock types. Also, the identifying sedimentary cycles of the Jahrum carbonate succession and reservoir correlation in KH-02 and KH-03 wells were performed using Cyclolog software. Material and Methods Petrographic analysis of thin sections together with petrophysical wire logs, porperm data, and core descriptions were used for Jahrum reservoir zonation in the Khesht oil field. In this way, 40 m of cores and 80 thin sections from KH-02 well were used to investigate facies distribution and diagenetic processes in the studied interval. All thin sections stained for dolomite identification using Dickson (1965) method and limestone classification has been done according to Dunham's (1962) and Embry and Klovan (1971) schemes. Facies analysis and interpretation of the depositional environment was performed using the standard microfacies classification by Wilson (1975) and Flügel (2010). We followed Lucia (1995, 2007) for reservoir quality characterization and identification of rock types. Determination of sedimentary cycles and reservoir correlation between the studied wells has been done by using CycloLog software and gamma-ray log. Discussion of Results & Conclusion The Late Eocene Jahrum Formation in the Khesht oil field, SW Iran has mainly composed of limestones lithology. Petrographical studies led to identifying five carbonate microfacies in the Jahrum succession which have been deposited on a homoclinal carbonate ramp. These microfacies are consists of F1) Echinoid Orbitolites Nummulites wacke/pack/rudstone - inner ramp (restricted lagoon); F2) Nummulites Echinoid packstone to grainstone - inner ramp (shoal); F3) coral boundstone - inner to mid ramp; F4) Echinoid Nummulites wackestone - mid ramp (open marine); F5) Bioclast dolostone (shallow burial environment). The Jahrum carbonates have been subjected to a variety of diagenetic processes including micritization, dolomitization, cementation, dissolution, fracturing, and styloliteration in the three diagenetic realms including marine, meteoric, and shallow to deep burial. The wide range of porosity and permeability values in most facies of the Jahrum Formation shows that the sedimentary texture of the studied samples alone did not control the reservoir quality. The reservoir quality of the studied succession is mainly controlled by different diagenetic processes. Petrographic studies along with porosity and permeability cross plots for the studied samples show that the combination of the dolomitization, dissolution, and fracture processes played the greatest role in improving the reservoir quality of the studied formation, but calcite and anhydrite cementation; especially pervasive dolomitization type and compaction, have reduced the reservoir quality of the studied succession. The INPEFA stratigraphy approach has identified two sedimentary cycles within the Jahrum succession with good correlation in both KH-02 and KH-03 wells. Reservoir quality is significantly better during sea-level fall than when sea level was high in both sedimentary cycles. Overall, the Jahrum Formation is deposited in a regression cycle that begins with the deposition of open marine microfacies on the Pabdeh Formation and ends with the deposition of echinoid Orbitolites Nummulites wackestone/packstone (F1) at the end of the sequence in a lagoonal environment at the boundary of the Asmari Formation. Using CycloLog software and correlation between the reservoir zones of the Jahrum Formation in Khesht Oil Field and the identified timelines reveals that some reservoir zones show good compatibility. However, some of these zones do not correspond to the timelines. By considering other cyclo-stratigraphic factors along with lithology, porosity, and permeability data, revision in Jahrum reservoir zonation in the Khesht Oil Field is needed. Abstract Eocene to Oligocene–Miocene carbonates of Jahrum and Asmari formations form the reservoirs of the Khesht Field in the Fars Province, the Zagros Foreland basin. In this study, the reservoir characteristics of the upper parts Jahrum Formation in the Khesht Oil Field have been investigated based on the combination of facies analysis and diagenetic features of samples in the porosity-permeability framework. The Jahrum Formation in the Fars Province is mainly composed of limestones that formed on a laterally continuous carbonate ramp with significant variations in reservoir heterogeneity and quality. Petrographic studies led to the identification of five carbonate microfacies. Five petrophysical rock types (RT) in KH-02 well are recognized by considering primary and secondary controls on pore type and size distribution. From RT1 with no reservoir property toward RT5 reservoir quality is enhanced. Diagenetic features have significantly affected reservoir properties by both enhancing and destroying porosity and permeability. Bivariate plots of porosity and permeability, combined with thin-section petrography indicate that pervasive anhydrite cement and compaction had the greatest negative impact on reservoir quality, whereas, dolomitization, fracturing, and dissolution of Nummulites played the most positive role. Therefore, the general characteristics of the Jahrum reservoir in the Khesht Field are mainly shaped by diagenetic features. Using CycloLog software in the two studied wells led to the identification of two sedimentary cycles within the Jahrum Formation. The negative trend of the INPEFA log (sea-level fall) in the second sedimentary cycle includes the upper part of the Jahrum Formation which has medium to high reservoir quality. Keywords: Reservoir zonation, Rock types, Diagenesis, Cyclolog Software, Jahrum Formation. Introduction Carbonate reservoirs are difficult to describe and produce a realistic picture of reservoir properties due to the vertical and lateral heterogeneity in various categories including lateral distribution of facies (Alsharhan 2006; Dou et al. 2011) and complex diagenetic evolution of carbonates (Lucia 2007; Ahr 2008; Rong et al. 2012; Moore 2013). Carbonates of the Jahrum Formation in Fars province together with the Asmari Formation form the main part of reservoirs in SW Iran. So far, no study has been conducted to investigate the reservoir characteristics of the Jahrum Formation in the Khesht oil field. These carbonates are generally deposited in a shallow marine environment, and the estimated porosity from thin-section petrographic studies show that due to the abundance of lime mud and low textural maturity, their reservoir capacity was low in the time of deposition (Hassanvand 2016). Therefore, due to the low primary porosity in most parts of the Jahrum Formation, it seems that the reservoir quality of this formation largely depends on the development of secondary porosity as a result of the performance of various diagenetic processes such as dolomitization (Azomani et al. 2013), fracturing and dissolution. Due to the importance of reservoir studies and the investigation of the distribution of reservoir properties, the combination of facies analysis and diagenetic characteristics of the Jahrum Formation samples in the framework of porosity and permeability were used for reservoir zonation in Khesht-2 well and the studied rocks were divided into different rock types. Also, the identifying sedimentary cycles of the Jahrum carbonate succession and reservoir correlation in KH-02 and KH-03 wells were performed using Cyclolog software. Material and Methods Petrographic analysis of thin sections together with petrophysical wire logs, porperm data, and core descriptions were used for Jahrum reservoir zonation in the Khesht oil field. In this way, 40 m of cores and 80 thin sections from KH-02 well were used to investigate facies distribution and diagenetic processes in the studied interval. All thin sections stained for dolomite identification using Dickson (1965) method and limestone classification has been done according to Dunham's (1962) and Embry and Klovan (1971) schemes. Facies analysis and interpretation of the depositional environment was performed using the standard microfacies classification by Wilson (1975) and Flügel (2010). We followed Lucia (1995, 2007) for reservoir quality characterization and identification of rock types. Determination of sedimentary cycles and reservoir correlation between the studied wells has been done by using CycloLog software and gamma-ray log. Discussion of Results & Conclusion The Late Eocene Jahrum Formation in the Khesht oil field, SW Iran has mainly composed of limestones lithology. Petrographical studies led to identifying five carbonate microfacies in the Jahrum succession which have been deposited on a homoclinal carbonate ramp. These microfacies are consists of F1) Echinoid Orbitolites Nummulites wacke/pack/rudstone - inner ramp (restricted lagoon); F2) Nummulites Echinoid packstone to grainstone - inner ramp (shoal); F3) coral boundstone - inner to mid ramp; F4) Echinoid Nummulites wackestone - mid ramp (open marine); F5) Bioclast dolostone (shallow burial environment). The Jahrum carbonates have been subjected to a variety of diagenetic processes including micritization, dolomitization, cementation, dissolution, fracturing, and styloliteration in the three diagenetic realms including marine, meteoric, and shallow to deep burial. The wide range of porosity and permeability values in most facies of the Jahrum Formation shows that the sedimentary texture of the studied samples alone did not control the reservoir quality. The reservoir quality of the studied succession is mainly controlled by different diagenetic processes. Petrographic studies along with porosity and permeability cross plots for the studied samples show that the combination of the dolomitization, dissolution, and fracture processes played the greatest role in improving the reservoir quality of the studied formation, but calcite and anhydrite cementation; especially pervasive dolomitization type and compaction, have reduced the reservoir quality of the studied succession. The INPEFA stratigraphy approach has identified two sedimentary cycles within the Jahrum succession with good correlation in both KH-02 and KH-03 wells. Reservoir quality is significantly better during sea-level fall than when sea level was high in both sedimentary cycles. Overall, the Jahrum Formation is deposited in a regression cycle that begins with the deposition of open marine microfacies on the Pabdeh Formation and ends with the deposition of echinoid Orbitolites Nummulites wackestone/packstone (F1) at the end of the sequence in a lagoonal environment at the boundary of the Asmari Formation. Using CycloLog software and correlation between the reservoir zones of the Jahrum Formation in Khesht Oil Field and the identified timelines reveals that some reservoir zones show good compatibility. However, some of these zones do not correspond to the timelines. By considering other cyclo-stratigraphic factors along with lithology, porosity, and permeability data, revision in Jahrum reservoir zonation in the Khesht Oil Field is needed.

https://jssr.ui.ac.ir/article_24872_5d2f21b4e0fc22a74073b6b094e68d07.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 Conodont biostratigraphy and biofacies of Late Devonian-Early Carboniferous deposits at Chelcheli section, Northwest Shahrud (Eastern Alborz) Conodont biostratigraphy and biofacies of Late Devonian-Early Carboniferous deposits at Chelcheli section, Northwest Shahrud (Eastern Alborz) 59 86 24914 10.22108/jssr.2020.123445.1167 FA Ali Bahrami Department of Geology, Faculty of Sciences, University of Isfahan Mehdi Yazdi Department of Geology, Faculty of Sciences. University of Isfahan. Seyed Mahmood Hosseini-Nejad School of earth science, Damghan University Journal Article 2020 06 09 Abstract Chelcheli section (397m thick) about 70 km northwest of Shahroud on the Shahroud-Gorgan road (Tuskistan route), about 5 km east of the Chahar-Bagh village is sampled and studied to investigate the DC transition and the conodont facies changes during the Global Hangenberg Crisis. The measurement of one hundred eighty two meters of the upper part of Khoshyilagh formation and 215 meters of the Lowermost Mobarak formation led to the discrimination of 11 rock units with different sedimentary features. In total, forty limestone samples, about 4-5 kgs were systematically collected and treated with conventional preparation methods. Three hundred forty conodont elements were obtained, which led to the identification of 47 species and subspecies belonging to 16 genera that allowed the separation of 15 conodont bio-zones from the early Famennian to the Late Tournasian. Keywords: Biostratigraphy; Late Devonian; Mississippian; Devonian – Carboniferous boundary, Hangenberg Crisis; Chelcheli; Eastern Alborz. Introduction In Iran, Devonian-Carboniferous sequences are found in limited areas, but their spread is more extensive in eastern and central Alborz and central Iran (Wendt et al. 2005). However, these deposits are located in different structural units and prevailing geological setting have caused different sedimentary facies and sequences (Ashuri 1990, 1997, 1998, 2001, 2002, 2004, 2006; Bahrami et al. 2011; Habibi et al. 2008; Sardar Abadi et al. 2015; Yazdi 1999, Yazdi and Turner 2000; Wendt et al. 2002, 2005). The Alborz range in northern Iran is an active fold-and-thrust belt (Alavi, 1996; Berberian, 1983) and is situated about 200 – 500 kms to the north of the Neo-Tethyan suture. The closure of the Palaeotethys between the Iran Plate as a part of Gondwana and the Turan Plate (Laurussia) occurred in the early Late Triassic and was accomplished during the Early/earliest Mid Jurassic (Golonka 2002). During the Palaeozoic, Iran was situated at the northern margin of Gondwana (Berberian and King 1981; Scotese 2001). In the mid-Palaeozoic, most of Iran was located about 20°–25° south of the palaeoequator. During the Mississippian, the Alborz Basin was positioned at a palaeolatitude of approximately 45–50°S (Muttoni et al. 2009; Torsvik & Cocks 2004, 2013; Vachard 1996). Most of the D/C sections from central and eastern Alborz Mountains have been deposited in a shallow-water, carbonate ramp setting (Königshof et al. 2020 in press). However, in contrast to other D/C sections in Iran (Bahrami et al. 2011; Habibi et al. 2008), the Chelcheli section exhibits “characteristic rock” types around the D/C boundary such as black shale and sandstone. In this study, we have sampled conodonts from the Khoshyeilagh Formation and the overlying Mobarak Formation of the Chelcheli section with a special focus on the D/C boundary. Material and Methods In total, forty limestone samples, about 4-5 kgs were systematically collected and treated with conventional preparation methods. The samples were processed with diluted acetic/formic acid (20%). The conodonts were extracted from residues by hand picking and heavy liquid technique at the University of Isfahan, I.R. Iran. Discussion of Results and Conclusions Discriminated conodont species: Alternognathus, Bispathodus, Branmehla, Clydagnathus, Gnathodus, Icriodus, Mehlina, Palmatolepis, Polygnathus, Neoplygnathus, Protognthodus, Pseudopolygnathus, Scaliognathus, Doliognathus, Siphonodella and Scaphignathus are amongst the cosmopolitan species, the index and indicator spacies in the study of DC boundary. The upper Palmatolepis triangularis Zone to Bispathodus ultimus Zone (early-late Famennian) were assigned to the uppermost portion of the Khoshyeilagh formation within 12 conodont zones. Protognathodus kockeli Zone to Scaliognathus anchoralis-Doliognathus latus zone was also assigned to the Tournasian part of Mobarak formation classified in 3 distinct conodont zones. The presence of tiny black shale horizons just bellow the DC boundary and its association with offshore conodont species such as bispatotides and palmatolpids indicates an increase in the sea level to the highest level into near the end of the latest Famennian. Subsequently 8-10 meters of quartzitic sandstone unit with cross-stratification and no conjunctival fauna due to lowering of sea level show the evidence of biological and sedimentological changes during the Hangenbeg Crisis in the Chelcheli section. Gradual and recurrent increase in polygnathids, protognathids, and Siphonodellis, which are subsequently replaced by offshore Gnathoids also indicates that water levels are re-emerging into the Upper Tournasian Abstract Chelcheli section (397m thick) about 70 km northwest of Shahroud on the Shahroud-Gorgan road (Tuskistan route), about 5 km east of the Chahar-Bagh village is sampled and studied to investigate the DC transition and the conodont facies changes during the Global Hangenberg Crisis. The measurement of one hundred eighty two meters of the upper part of Khoshyilagh formation and 215 meters of the Lowermost Mobarak formation led to the discrimination of 11 rock units with different sedimentary features. In total, forty limestone samples, about 4-5 kgs were systematically collected and treated with conventional preparation methods. Three hundred forty conodont elements were obtained, which led to the identification of 47 species and subspecies belonging to 16 genera that allowed the separation of 15 conodont bio-zones from the early Famennian to the Late Tournasian. Keywords: Biostratigraphy; Late Devonian; Mississippian; Devonian – Carboniferous boundary, Hangenberg Crisis; Chelcheli; Eastern Alborz. Introduction In Iran, Devonian-Carboniferous sequences are found in limited areas, but their spread is more extensive in eastern and central Alborz and central Iran (Wendt et al. 2005). However, these deposits are located in different structural units and prevailing geological setting have caused different sedimentary facies and sequences (Ashuri 1990, 1997, 1998, 2001, 2002, 2004, 2006; Bahrami et al. 2011; Habibi et al. 2008; Sardar Abadi et al. 2015; Yazdi 1999, Yazdi and Turner 2000; Wendt et al. 2002, 2005). The Alborz range in northern Iran is an active fold-and-thrust belt (Alavi, 1996; Berberian, 1983) and is situated about 200 – 500 kms to the north of the Neo-Tethyan suture. The closure of the Palaeotethys between the Iran Plate as a part of Gondwana and the Turan Plate (Laurussia) occurred in the early Late Triassic and was accomplished during the Early/earliest Mid Jurassic (Golonka 2002). During the Palaeozoic, Iran was situated at the northern margin of Gondwana (Berberian and King 1981; Scotese 2001). In the mid-Palaeozoic, most of Iran was located about 20°–25° south of the palaeoequator. During the Mississippian, the Alborz Basin was positioned at a palaeolatitude of approximately 45–50°S (Muttoni et al. 2009; Torsvik & Cocks 2004, 2013; Vachard 1996). Most of the D/C sections from central and eastern Alborz Mountains have been deposited in a shallow-water, carbonate ramp setting (Königshof et al. 2020 in press). However, in contrast to other D/C sections in Iran (Bahrami et al. 2011; Habibi et al. 2008), the Chelcheli section exhibits “characteristic rock” types around the D/C boundary such as black shale and sandstone. In this study, we have sampled conodonts from the Khoshyeilagh Formation and the overlying Mobarak Formation of the Chelcheli section with a special focus on the D/C boundary. Material and Methods In total, forty limestone samples, about 4-5 kgs were systematically collected and treated with conventional preparation methods. The samples were processed with diluted acetic/formic acid (20%). The conodonts were extracted from residues by hand picking and heavy liquid technique at the University of Isfahan, I.R. Iran. Discussion of Results and Conclusions Discriminated conodont species: Alternognathus, Bispathodus, Branmehla, Clydagnathus, Gnathodus, Icriodus, Mehlina, Palmatolepis, Polygnathus, Neoplygnathus, Protognthodus, Pseudopolygnathus, Scaliognathus, Doliognathus, Siphonodella and Scaphignathus are amongst the cosmopolitan species, the index and indicator spacies in the study of DC boundary. The upper Palmatolepis triangularis Zone to Bispathodus ultimus Zone (early-late Famennian) were assigned to the uppermost portion of the Khoshyeilagh formation within 12 conodont zones. Protognathodus kockeli Zone to Scaliognathus anchoralis-Doliognathus latus zone was also assigned to the Tournasian part of Mobarak formation classified in 3 distinct conodont zones. The presence of tiny black shale horizons just bellow the DC boundary and its association with offshore conodont species such as bispatotides and palmatolpids indicates an increase in the sea level to the highest level into near the end of the latest Famennian. Subsequently 8-10 meters of quartzitic sandstone unit with cross-stratification and no conjunctival fauna due to lowering of sea level show the evidence of biological and sedimentological changes during the Hangenbeg Crisis in the Chelcheli section. Gradual and recurrent increase in polygnathids, protognathids, and Siphonodellis, which are subsequently replaced by offshore Gnathoids also indicates that water levels are re-emerging into the Upper Tournasian

https://jssr.ui.ac.ir/article_24914_dc9d2eb6ad325e60d0a82870a40622ed.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 Lithostratigraphy, petrography, and geochemistry of sandstone in the middle part of the Upper Red Formation, Ghezeljeh area, NW Zanjan Lithostratigraphy, petrography, and geochemistry of sandstone in the middle part of the Upper Red Formation, Ghezeljeh area, NW Zanjan 87 108 24882 10.22108/jssr.2020.122844.1163 FA Seyedeh Aliyeh Mir Hosseini MSc student in economic geology, University of Zanjan, Zanjan, Iran Ghasem Nabatian Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran Afshin Zohdi Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran Armin Salsani Department of Geology, Science and Research Branch, Islamic Azad University, Tehran, Iran 0000-0002-7692-2955 Journal Article 2020 05 04 Ghezeljeh area is located in the northeastern part of Mahneshan at 70 km northwest of Zanjan. The rock units exposed in the area are including the Lower Red, Qom, and Upper Red formations which the Upper Red Formation is the purpose of current research. According to field studies, the Upper Red Formation with 750 meters thickness includes 250 meters of evaporative units with intercalations of marls at the bottom and 500 meters of alternation of marls and sandstones intercalations at the top. According to microscopic studies, the grain size of the studied samples ranging from very fine sandstone to gravel. These sandstones show poorly orientation and well to poor sorted and are angular to sub-angular. The sorting and roundness parameters as well clay content show that these sandstones are immature and in some cases are sub mature. Based on a high percent of components and the Folk classification, the middle part of the Upper Red Formation displays lithic-arenite (sed-arenite) and feldspathic-lithic-arenite with an average composition of Q38F15Rf47. Geochemical studies show that these sandstones sourced from intermediate to felsic igneous rocks and deposited on the active continental margin. Furthermore, the weathering index shows an arid and semi-arid climatic condition during their deposition. Keywords: Stratigraphy, Geochemistry, Upper Red Formation, Ghezeljeh, Zanjan. Introduction Sedimentary rocks are the main source of information about past conditions. According to the chemical composition of sediments and sedimentary rocks, the origin and other depositional processes such as weathering, transportation, and diagenesis can be evaluated (Mclennan et al. 1993). Meanwhile, the study of trace elements has more reliable results than the major oxide elements because these elements are immobile against processes such as transport, diagenesis, and metamorphism (Whitmore 2004; Von Eynatten 2004). So in the current study, in addition to petrographic studies, information obtained from rare earth elements was used to find out the origin of rocks, determine of tectonic setting, and palaeoclimate. The Upper Red Formation, which is the subject of this study, consists of three parts. In the current research, we investigated the middle part (M2) of Upper Red Formation, because it has potential as a cap-rock in gas fields and also a suitable host rock of ore deposits. Therefore, a detailed study of litho-stratigraphy, petrography, and geochemistry of different parts of this formation in Central Iran and Alborz sedimentary basins is very important. This study aims to investigate the tectonic setting, ancient climatic conditions, and the origin of these sandstones in the Ghezeljeh area, NW Zanjan. Material & Methods In the current research, a suitable section was selected by using the Mahneshan geological map with a scale of 1:100000 (Lotfi 2001). In the second step, the stratigraphic column and profiles associated with the geological map (scale: 1:20000) of the study area were prepared. Besides, 30 thin-section fine- to medium-grained samples were prepared and carefully studied for sedimentary aspects and point counting. Furthermore, eight sandstone samples from the Upper Red Formation with minimum alteration and the least amount of carbonate cements, calcareous matrix, and bioclast were selected for whole-rock geochemical analysis. The whole rock geochemical analysis was done in the Zarazma Laboratory, Tehran. Several discriminatory plots of the trace elements were used to determine the provenance and tectonic setting of the studied sandstone of the Upper Red Formation. Discussion of Results & Conclusions The study area is located in the central Iranian zone which is part of the Alpine‒Himalayan orogenic belt. The Upper Red Formation is the main outcropped rock unit in the study area which mainly consists of marls and sandstones. The investigated sandstones are mainly composed of sedimentary and metamorphic rock fragments. Additionally, there are some bioclasts in the studied sandstones that indicate that the carbonate and calcareous fragments in the Upper Red Formation may originate from older carbonate succession such as Qom Formation which has extensive outcrop in the study area. The studied sandstones are generally poor to well-sorted as seen in the thin sections. Petrographic studies revealed that sandstones of Upper Red Formation in the Ghezeljeh area are mainly lithic-arenite (sed-arenite) and feldspathic-lithic-arenite with an average composition of Q38F15Rf47. The grain size and particle geometry, as well as the degree of sorting of the studied sandstones, indicate that they are texturally immature to sub-mature in terms of textural maturity. The petrographic and geochemical studies of sandstones in the middle part of the Upper Red Formation indicate that the active tectonic setting and recycled orogeny for the investigated sediments which is consistent with the earlier studies. Moreover, the results of the modal analysis show that the climatic condition was dry to semi-humid during the deposition of this formation. According to geochemical analyzes, the investigated sandstones originated from acidic to intermediate igneous rocks. Furthermore, geochemical diagrams show that the studied sandstones formed in an active continental margin setting. These studies generally indicate that the investigated sediments were deposited probably in a foreland basin during the Arabia‒Eurasia collision. Ghezeljeh area is located in the northeastern part of Mahneshan at 70 km northwest of Zanjan. The rock units exposed in the area are including the Lower Red, Qom, and Upper Red formations which the Upper Red Formation is the purpose of current research. According to field studies, the Upper Red Formation with 750 meters thickness includes 250 meters of evaporative units with intercalations of marls at the bottom and 500 meters of alternation of marls and sandstones intercalations at the top. According to microscopic studies, the grain size of the studied samples ranging from very fine sandstone to gravel. These sandstones show poorly orientation and well to poor sorted and are angular to sub-angular. The sorting and roundness parameters as well clay content show that these sandstones are immature and in some cases are sub mature. Based on a high percent of components and the Folk classification, the middle part of the Upper Red Formation displays lithic-arenite (sed-arenite) and feldspathic-lithic-arenite with an average composition of Q38F15Rf47. Geochemical studies show that these sandstones sourced from intermediate to felsic igneous rocks and deposited on the active continental margin. Furthermore, the weathering index shows an arid and semi-arid climatic condition during their deposition. Keywords: Stratigraphy, Geochemistry, Upper Red Formation, Ghezeljeh, Zanjan. Introduction Sedimentary rocks are the main source of information about past conditions. According to the chemical composition of sediments and sedimentary rocks, the origin and other depositional processes such as weathering, transportation, and diagenesis can be evaluated (Mclennan et al. 1993). Meanwhile, the study of trace elements has more reliable results than the major oxide elements because these elements are immobile against processes such as transport, diagenesis, and metamorphism (Whitmore 2004; Von Eynatten 2004). So in the current study, in addition to petrographic studies, information obtained from rare earth elements was used to find out the origin of rocks, determine of tectonic setting, and palaeoclimate. The Upper Red Formation, which is the subject of this study, consists of three parts. In the current research, we investigated the middle part (M2) of Upper Red Formation, because it has potential as a cap-rock in gas fields and also a suitable host rock of ore deposits. Therefore, a detailed study of litho-stratigraphy, petrography, and geochemistry of different parts of this formation in Central Iran and Alborz sedimentary basins is very important. This study aims to investigate the tectonic setting, ancient climatic conditions, and the origin of these sandstones in the Ghezeljeh area, NW Zanjan. Material & Methods In the current research, a suitable section was selected by using the Mahneshan geological map with a scale of 1:100000 (Lotfi 2001). In the second step, the stratigraphic column and profiles associated with the geological map (scale: 1:20000) of the study area were prepared. Besides, 30 thin-section fine- to medium-grained samples were prepared and carefully studied for sedimentary aspects and point counting. Furthermore, eight sandstone samples from the Upper Red Formation with minimum alteration and the least amount of carbonate cements, calcareous matrix, and bioclast were selected for whole-rock geochemical analysis. The whole rock geochemical analysis was done in the Zarazma Laboratory, Tehran. Several discriminatory plots of the trace elements were used to determine the provenance and tectonic setting of the studied sandstone of the Upper Red Formation. Discussion of Results & Conclusions The study area is located in the central Iranian zone which is part of the Alpine‒Himalayan orogenic belt. The Upper Red Formation is the main outcropped rock unit in the study area which mainly consists of marls and sandstones. The investigated sandstones are mainly composed of sedimentary and metamorphic rock fragments. Additionally, there are some bioclasts in the studied sandstones that indicate that the carbonate and calcareous fragments in the Upper Red Formation may originate from older carbonate succession such as Qom Formation which has extensive outcrop in the study area. The studied sandstones are generally poor to well-sorted as seen in the thin sections. Petrographic studies revealed that sandstones of Upper Red Formation in the Ghezeljeh area are mainly lithic-arenite (sed-arenite) and feldspathic-lithic-arenite with an average composition of Q38F15Rf47. The grain size and particle geometry, as well as the degree of sorting of the studied sandstones, indicate that they are texturally immature to sub-mature in terms of textural maturity. The petrographic and geochemical studies of sandstones in the middle part of the Upper Red Formation indicate that the active tectonic setting and recycled orogeny for the investigated sediments which is consistent with the earlier studies. Moreover, the results of the modal analysis show that the climatic condition was dry to semi-humid during the deposition of this formation. According to geochemical analyzes, the investigated sandstones originated from acidic to intermediate igneous rocks. Furthermore, geochemical diagrams show that the studied sandstones formed in an active continental margin setting. These studies generally indicate that the investigated sediments were deposited probably in a foreland basin during the Arabia‒Eurasia collision.

https://jssr.ui.ac.ir/article_24882_beda19834ca63f76f5e0fa78531a3336.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 Microfacies analysis, sedimentary environment and sequence stratigraphy of the Ilam Formation (Coniacian? - Santonian) in the northwestern part of the Abadan Plain Microfacies analysis, sedimentary environment and sequence stratigraphy of the Ilam Formation (Coniacian? - Santonian) in the northwestern part of the Abadan Plain 109 134 24590 10.22108/jssr.2020.120331.1131 FA Navab Khodaei Student of Geology, Faculty of Basic Sciences, University of Hormozgan, Iran Peyman Rezaee Geology Department, Hormozgan University, Iran 0000-0002-5148-491X Javad Honarmand Assistant Professor, Department of Petroleum Geology, Institute of Earth Sciences, RIPI, Iran Iraj Abdollahi-Fard Exploration Directorate, NIOC, Iran Journal Article 2019 12 05 Abstract The Ilam Formation (Coniacian? –Santonian), is among the most important oil reservoirs of the Abadan Plain, SW Iran. Despite its reservoir significance, there is no comprehensive knowledge about the geological characteristics and factors controlling reservoir quality. In this study, the Ilam Formation is investigated using detailed core description, thin section study, and conventional petrophysical well log data to explain facies characteristics, sedimentary environment, and presenting the sequence stratigraphic framework. Accordingly, a total of 280 m of cores in four key wells from three oil fields as well as 620 thin sections were described and studied. The results of facies analysis lead to the recognition of 12 microfacies grouped in four facies belts including lagoon, shoal, shallow and deep open marine and two siliciclastic petrofacies (shales) related to brackish water and shallow lagoonal environment, which deposited in a carbonate ramp. Frequency analyses of facies associations and petrophysical well log signature indicate that the sedimentary basin was deepening to the east. Based on the identified sequence boundaries and maximum flooding surfaces, one third-order sequence in the studied interval was recognized and correlated by using the petrophysical well log data in all studied wells. The maximum flooding surfaces are discriminated by the development of deep-marine facies and also high gamma-ray responses on the well logs. Keywords: Ilam Formation, Abadan Plain, Facies, Sedimentary Environment, Sequence Stratigraphy Introduction Sedimentary facies, along with the distribution of diagenetic processes and fractures, are the three most important factors controlling the pores system and the reservoir characteristics of carbonates (Lucia 2007; Ahr 2008; Moore and Wade 2013). Despite the high impact of diagenetic processes on carbonate sequences, facies analysis and reconstruction of the ancient sedimentary environment is one of the most important and primary steps in the comprehensive geological studies of the reservoir (Ahr 2008). The sequence stratigraphic framework can provide an interconnection between the characteristics of the facies associations as components of a sequence and reservoir characteristics and also facilitate reservoir evaluation (Morad et al. 2012). To identify the key sequence boundaries, the integration of microfacies and core study results is applied (Tucker 1993; Taghavi et al. 2006). In other words, by using this framework, the pattern of facies distribution and the diagenetic processes trend related to facies could be examined (Mazzullo 1994). The focus of sequence stratigraphy is on the stacking pattern of sediments in space and time framework, which is formed by the contrast of the parameters of accommodation space and sediment supply (Catuneanu 2006; Catuneanu et al. 2012). Reservoir study in the sequence stratigraphy framework can lead to the identification, description, and study of the distribution of reservoir zones (Taghavi et al. 2006). To separate the sequences, it is important to identify the two key surfaces of maximum flooding surfaces and the sequence boundaries. The carbonate rocks of the Bangestan Group include the Sarvak and Ilam formations, where they are important reservoir rocks in many oil fields in the Zagros Basin and the Persian Gulf. The Ilam Formation in the Lorestan Basin is characterized by pelagic facies whereas in the Dezful Embayment and Fars appeared with neritic facies (James and Wynd 1965). In the type section in the northwest of Kabir-Kuh anticline, the lower boundary of this formation with Surgah Formation is conformable, while from the Lorestan Basin to the southeast, the Surgah Formation was disappeared and the Ilam Formation is placed on the Sarvak Formation disconformably. The purpose of this research is to identify and introduce microfacies and determine the geometry of the Ilam Formation platform along with determining the position of the studied wells in the sedimentary model. Also, we seek to identify the third-order depositional sequences and correlate them through petrophysical logs in other studied wells. Material & Methods In this study, four key wells in three oil fields of the Abadan Plain were used to identify microfacies, sedimentary environments and determine the depositional sequences of the Ilam Formation, by describing 280 meters of cores and studying 620 thin sections. Thin sections were stained by Alizarin Red S to differentiate calcite from dolomite (Dickson 1966). To identify microfacies and sedimentary environment, integration of core descriptions and thin section petrography studies have been used. In petrographical study of microscopic thin sections, mineralogy, texture, grain size, sorting, skeletal and non-skeletal components, and fossil content in each sample were identified and described quantitatively. The Dunham classification (Dunham 1962) has been used to describe and name microfacies. Standard facies models were used for facies analysis and nomenclature (Flügel 2010). Besides, based on the pattern of facies distribution, and also the frequency of facies, the location of the studied wells and palaeogeographical directions in the carbonate platform was determined. In order to determine the general time framework of the studied interval, based on identifying and investigating the distribution of fossil associations, especially planktonic and benthic foraminifera, biozones were compared with Wynd biozones (Wynd 1965) and to provide sequence stratigraphic framework, sequence boundaries, and maximum flooding surfaces were determined based on the pattern of facies changes as well as the determination of discontinuity surfaces (Hunt and Tucker 1992; Catuneanu 2006). Finally, using petrophysical logs (GR, RHOB, NPHI, and PHIE), the identified depositional sequences in studied wells are correlated. Discussion of Results & Conclusions Based on the integration of core description results, petrographic studies, and petrophysical logs, the Ilam Formation in some fields located in the northwestern part of Abadan plain were examined from several points of view such as facies features, sedimentary environment, platform geometry, biostratigraphy, and sequence stratigraphy framework. Facies studies led to the identification of two siliciclastic (shales) petrofacies PF1 and PF2, belonging to the estuary and shallow lagoon environment, respectively, and the 12 carbonate microfacies (MF1 to MF12) belonging to the four facies belts lagoon, shoal, shallow and deep open marine which are deposited in a carbonate ramp. An examination of the facies frequency showed that deep open marine facies, with the major abundance of planktonic foraminifera in a distinct trend from west to east, showed an increased thickness. Based on this, it seems that the west of the studied transect is the landward margin of the carbonate ramp, and by moving towards the high Zagros, in the east of transect, we approach the deep parts of this carbonate platform. Examination of the available cores and microfacies changes indicate that the only identified sequence boundaries are the lower contact (base of the Laffan Member) and the upper contact (the boundary between Ilam and Gurpi formations) in the studied succession, which both of them show evidence of subaerial exposure and brecciation (Sequence Boundary type 1); Therefore, the whole studied interval was identified as a third-order depositional sequence. The shaly Laffan Member was considered as Lowstand System Tract (LST) that mainly consisted of charophyte algal facies in the continental and estuary environment. The Maximum Flooding Surface (MFS) has corresponded to the deepest carbonate microfacies whereas Regressive Surface (RS) was considered by the continental fine-grained siliciclastic sediment supply and the increasing of lagoonal carbonate facies frequency. Transgressive Systems Tract (TST) is characterized by deep open marine microfacies, Highstand Systems Tract (HST) with shallow open marine microfacies, and Falling Stage Systems Tract (FSST) is characterized by the predominance of lagoonal microfacies with continental fine-grained siliciclastic sediments supply, and finally, correlation of sequence boundaries was performed in the studied wells by petrophysical logs. The thickness of HST and FSST facies show a reverse ratio in comparison with the whole thickness of the Ilam Formation. The maximum thickness of HST facies was observed in the east of the study area (Well D), whereas the maximum thickness of FSST was observed in the west of the studied transect (Well A). This confirms that the source of the continental siliciclastic sediments was closed to the west of the study area during the relative sea-level fall. The thickness changes observed for the Ilam Formation, along with the lateral facies change, could be attributed to tectonic activities and the beginning of collision and the closure of the Neo-Tethys. Abstract The Ilam Formation (Coniacian? –Santonian), is among the most important oil reservoirs of the Abadan Plain, SW Iran. Despite its reservoir significance, there is no comprehensive knowledge about the geological characteristics and factors controlling reservoir quality. In this study, the Ilam Formation is investigated using detailed core description, thin section study, and conventional petrophysical well log data to explain facies characteristics, sedimentary environment, and presenting the sequence stratigraphic framework. Accordingly, a total of 280 m of cores in four key wells from three oil fields as well as 620 thin sections were described and studied. The results of facies analysis lead to the recognition of 12 microfacies grouped in four facies belts including lagoon, shoal, shallow and deep open marine and two siliciclastic petrofacies (shales) related to brackish water and shallow lagoonal environment, which deposited in a carbonate ramp. Frequency analyses of facies associations and petrophysical well log signature indicate that the sedimentary basin was deepening to the east. Based on the identified sequence boundaries and maximum flooding surfaces, one third-order sequence in the studied interval was recognized and correlated by using the petrophysical well log data in all studied wells. The maximum flooding surfaces are discriminated by the development of deep-marine facies and also high gamma-ray responses on the well logs. Keywords: Ilam Formation, Abadan Plain, Facies, Sedimentary Environment, Sequence Stratigraphy Introduction Sedimentary facies, along with the distribution of diagenetic processes and fractures, are the three most important factors controlling the pores system and the reservoir characteristics of carbonates (Lucia 2007; Ahr 2008; Moore and Wade 2013). Despite the high impact of diagenetic processes on carbonate sequences, facies analysis and reconstruction of the ancient sedimentary environment is one of the most important and primary steps in the comprehensive geological studies of the reservoir (Ahr 2008). The sequence stratigraphic framework can provide an interconnection between the characteristics of the facies associations as components of a sequence and reservoir characteristics and also facilitate reservoir evaluation (Morad et al. 2012). To identify the key sequence boundaries, the integration of microfacies and core study results is applied (Tucker 1993; Taghavi et al. 2006). In other words, by using this framework, the pattern of facies distribution and the diagenetic processes trend related to facies could be examined (Mazzullo 1994). The focus of sequence stratigraphy is on the stacking pattern of sediments in space and time framework, which is formed by the contrast of the parameters of accommodation space and sediment supply (Catuneanu 2006; Catuneanu et al. 2012). Reservoir study in the sequence stratigraphy framework can lead to the identification, description, and study of the distribution of reservoir zones (Taghavi et al. 2006). To separate the sequences, it is important to identify the two key surfaces of maximum flooding surfaces and the sequence boundaries. The carbonate rocks of the Bangestan Group include the Sarvak and Ilam formations, where they are important reservoir rocks in many oil fields in the Zagros Basin and the Persian Gulf. The Ilam Formation in the Lorestan Basin is characterized by pelagic facies whereas in the Dezful Embayment and Fars appeared with neritic facies (James and Wynd 1965). In the type section in the northwest of Kabir-Kuh anticline, the lower boundary of this formation with Surgah Formation is conformable, while from the Lorestan Basin to the southeast, the Surgah Formation was disappeared and the Ilam Formation is placed on the Sarvak Formation disconformably. The purpose of this research is to identify and introduce microfacies and determine the geometry of the Ilam Formation platform along with determining the position of the studied wells in the sedimentary model. Also, we seek to identify the third-order depositional sequences and correlate them through petrophysical logs in other studied wells. Material & Methods In this study, four key wells in three oil fields of the Abadan Plain were used to identify microfacies, sedimentary environments and determine the depositional sequences of the Ilam Formation, by describing 280 meters of cores and studying 620 thin sections. Thin sections were stained by Alizarin Red S to differentiate calcite from dolomite (Dickson 1966). To identify microfacies and sedimentary environment, integration of core descriptions and thin section petrography studies have been used. In petrographical study of microscopic thin sections, mineralogy, texture, grain size, sorting, skeletal and non-skeletal components, and fossil content in each sample were identified and described quantitatively. The Dunham classification (Dunham 1962) has been used to describe and name microfacies. Standard facies models were used for facies analysis and nomenclature (Flügel 2010). Besides, based on the pattern of facies distribution, and also the frequency of facies, the location of the studied wells and palaeogeographical directions in the carbonate platform was determined. In order to determine the general time framework of the studied interval, based on identifying and investigating the distribution of fossil associations, especially planktonic and benthic foraminifera, biozones were compared with Wynd biozones (Wynd 1965) and to provide sequence stratigraphic framework, sequence boundaries, and maximum flooding surfaces were determined based on the pattern of facies changes as well as the determination of discontinuity surfaces (Hunt and Tucker 1992; Catuneanu 2006). Finally, using petrophysical logs (GR, RHOB, NPHI, and PHIE), the identified depositional sequences in studied wells are correlated. Discussion of Results & Conclusions Based on the integration of core description results, petrographic studies, and petrophysical logs, the Ilam Formation in some fields located in the northwestern part of Abadan plain were examined from several points of view such as facies features, sedimentary environment, platform geometry, biostratigraphy, and sequence stratigraphy framework. Facies studies led to the identification of two siliciclastic (shales) petrofacies PF1 and PF2, belonging to the estuary and shallow lagoon environment, respectively, and the 12 carbonate microfacies (MF1 to MF12) belonging to the four facies belts lagoon, shoal, shallow and deep open marine which are deposited in a carbonate ramp. An examination of the facies frequency showed that deep open marine facies, with the major abundance of planktonic foraminifera in a distinct trend from west to east, showed an increased thickness. Based on this, it seems that the west of the studied transect is the landward margin of the carbonate ramp, and by moving towards the high Zagros, in the east of transect, we approach the deep parts of this carbonate platform. Examination of the available cores and microfacies changes indicate that the only identified sequence boundaries are the lower contact (base of the Laffan Member) and the upper contact (the boundary between Ilam and Gurpi formations) in the studied succession, which both of them show evidence of subaerial exposure and brecciation (Sequence Boundary type 1); Therefore, the whole studied interval was identified as a third-order depositional sequence. The shaly Laffan Member was considered as Lowstand System Tract (LST) that mainly consisted of charophyte algal facies in the continental and estuary environment. The Maximum Flooding Surface (MFS) has corresponded to the deepest carbonate microfacies whereas Regressive Surface (RS) was considered by the continental fine-grained siliciclastic sediment supply and the increasing of lagoonal carbonate facies frequency. Transgressive Systems Tract (TST) is characterized by deep open marine microfacies, Highstand Systems Tract (HST) with shallow open marine microfacies, and Falling Stage Systems Tract (FSST) is characterized by the predominance of lagoonal microfacies with continental fine-grained siliciclastic sediments supply, and finally, correlation of sequence boundaries was performed in the studied wells by petrophysical logs. The thickness of HST and FSST facies show a reverse ratio in comparison with the whole thickness of the Ilam Formation. The maximum thickness of HST facies was observed in the east of the study area (Well D), whereas the maximum thickness of FSST was observed in the west of the studied transect (Well A). This confirms that the source of the continental siliciclastic sediments was closed to the west of the study area during the relative sea-level fall. The thickness changes observed for the Ilam Formation, along with the lateral facies change, could be attributed to tectonic activities and the beginning of collision and the closure of the Neo-Tethys.

https://jssr.ui.ac.ir/article_24590_2e28b377581a003a577709a4b79f94ed.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 36 4 2020 12 21 Investigating bio-events and time expansion of Calcareous nannofossils in the upper part of the Gurpi Formation and lower part of the Pabdeh Formation, northwestern Shiraz Investigating bio-events and time expansion of Calcareous nannofossils in the upper part of the Gurpi Formation and lower part of the Pabdeh Formation, northwestern Shiraz 135 147 25046 10.22108/jssr.2020.123093.1165 FA Saeedeh Senemari Associate Professor, Department of mining, Faculty of Engineering, Imam Khomeini International University (IKIU), Qazvin, Iran Behzad Saeedi Razavi 2Research Assistant Professor, Institute of Technology and Engineering, Standard Research Institute, Karaj Journal Article 2020 05 19 Abstract In this study, calcareous nannofossils are investigated in the upper part of the Gurpi Formation and lower part of the Pabdeh Formation at the Par-e Nobar section located in the northwest of Shiraz. The thickness of the studied section is about 41 m. The upper part of the Gurpi Formation is mainly composed of shales and pelagic limestones while the lower part of the Pabdeh Formation consists of shale facies. As a result, 32 species and 22 genera of calcareous nannofossils were detected. According to the first and last occurrence of index species and fossil assemblages, two bio-zones including Nephrolithus frequens Zone (CC26/ UC20dTp ) and Markalius inversus Zone (NP1) are recognized in the upper part of the Gurpi Formation, respectively. Fasciculithus tympaniformis Zone (NP5) and Heliolithus kleinpellii Zone (NP6) are reported for the first time from the lower part of the Pabdeh Formation, respectively. Based on the identified calcareous nannofossils zones, the age of the upper part of the Gurpi Formation is the latest Maastrichtian–early Danian, and the lower part of the Pabdeh Formation is the middle Paleocene/Selandian. Therefore, according to the nannofossil data, the boundary between the two formations is unconformable. Keywords: Paleogene, Bio-event, Zagros, Cretaceous, Calcareous nannofossil. Type text or a website address or translate a document. Showing translation for مقطع تیپ سازند در اطراف قم مطالعه شده است Translate instead مقطع تیپاین سازند در اطراف قم مطالعه شده است Introduction One of the most extensive Cretaceous and Cenozoic deposits are the Gurpi and Pabdeh formations in the Zagros Basin, which are studied in this research based on calcareous nannofossils. The type section of the Gurpi and Pabdeh formations is located in the southwestern Tang-e Pabdeh, North of Lali oilfield (Jams & Wynd, 1965). The important goals of studying the upper part of the Gurpi Formation and lower part of the Pabdeh Formation is the evaluationof boundaryand biostratigraphy. Material & Methods In this study, 33 samples from the upper part of the Gurpi Formation and lower part of the Pabdeh Formation have been studied. Samples were prepared following the standard smear slide method (Bown and Young 1998). All slides were studied under a polarized light microscope at × 1000 magnification. The nomenclature of calcareous nannofossils follows the taxonomic schemes of Perch-Nielsen (1985). Discussion of Results & Conclusions To study biostratigraphy of the succession based on calcareous nannofossils, the boundary of the Gurpi and Pabdeh formations in the Par-e Nobar section located in the northwest of Shiraz was selected. In this section, the upper part of the Gurpi Formation with 22.2 m thickness mainly consists of shales and argillaceous limestones and the lower part of the Pabdeh Formation with 18.8 m thickness is consists of shale facies. For introducing index species, calcareous nannofossil assemblages, and bio-zones, slides have been studied at the Gurpi/Pabdeh formations boundary which led to the recognition of 32 species and 22 genera of calcareous nannofossils. According to the first and last occurrence of index species and recording bio-events, two bio-zones include Nephrolithus frequens Zone (CC26/ UC20dTp ) and Markalius inversus Zone (NP1) has been recognizedin the upper part of the Gurpi Formation. The Fasciculithus tympaniformis Zone (NP5) and Heliolithus kleinpellii Zone (NP6) are reported for the first time from the lower part of the Pabdeh Formation in the studied section, respectively. The bio-zones identified in the upper part of the Gurpi Formation with a thickness of 22.2 m at the Cretaceous to Paleogene boundary are as follows: Nephrolithus frequens Zone (CC26) / (UC20bTP, UC20d Tp ): The first zone in the upper part of the Gurpi Formation is recorded from the FO to LO of Nephrolithus frequens. The age of this zone is late Late Maastrichtian. The thickness of this zone is 14.8 m. Markalius inversus Zone (NP1) / (CNP1): This zone spans the interval from the last occurrence of Cretaceous taxa to the FO of Cruciplacolithus tenuis. The age of this zone is early Paleocene (early Danian). The thickness of this zone is 7.4 m. Bio-zones introduced in the lower part of the Pabdeh Formation are as follows: These bio-zones in the studied section are 18.4 m thickness from the lower part of the Pabdeh Formation. Fasciculithus tympaniformis Zone (NP5): The first nannofossil unit recorded in the lower part of the Pabdeh Formation is theNP5. This zone spans the interval from the FO ofFasciculithus tympaniformisto the FO ofHeliolithus kleinpellii. The age of this zone is Paleocene (Selandian). The thickness of this zone was measured at about 7.4 m. Heliolithus kleinpellii Zone (NP6): The last bio-zone recorded is NP6. This zone is from the lower part of the Pabdeh Formation.This zone spans the interval from the FO of Heliolithus kleinpellii to the FO of Discoaster mohleri. The age of this zone is Paleocene (Selandian). The thickness of this zone was measured at about 11 m. Thus, based on the identified calcareous nannofossils zones, the age of the upper part of the Gurpi Formation is the latest Maastrichtian–early Danian, and thelower part of the Pabdeh Formation is the middle Paleocene/Selandian. Therefore, according to the nannofossil data, the boundary between the two formations is unconformable. In addition, the Cretaceous–Paleogene boundary is continuously at the top of the Gurpi Formation. This interval was recorded by a significant decrease in Cretaceous nannofossil species, along with an increase in Thoracosphaera operculata and the appearance of the Paleocene species. Also, the conditions of the basin that is part of the eastern Tethys were identified by determining the index species calcareous nannofossils. Therefore, the presence of these species confirms warm climate conditions during the sedimentation of mentioned deposits in this part of Zagros. Abstract In this study, calcareous nannofossils are investigated in the upper part of the Gurpi Formation and lower part of the Pabdeh Formation at the Par-e Nobar section located in the northwest of Shiraz. The thickness of the studied section is about 41 m. The upper part of the Gurpi Formation is mainly composed of shales and pelagic limestones while the lower part of the Pabdeh Formation consists of shale facies. As a result, 32 species and 22 genera of calcareous nannofossils were detected. According to the first and last occurrence of index species and fossil assemblages, two bio-zones including Nephrolithus frequens Zone (CC26/ UC20dTp ) and Markalius inversus Zone (NP1) are recognized in the upper part of the Gurpi Formation, respectively. Fasciculithus tympaniformis Zone (NP5) and Heliolithus kleinpellii Zone (NP6) are reported for the first time from the lower part of the Pabdeh Formation, respectively. Based on the identified calcareous nannofossils zones, the age of the upper part of the Gurpi Formation is the latest Maastrichtian–early Danian, and the lower part of the Pabdeh Formation is the middle Paleocene/Selandian. Therefore, according to the nannofossil data, the boundary between the two formations is unconformable. Keywords: Paleogene, Bio-event, Zagros, Cretaceous, Calcareous nannofossil. Type text or a website address or translate a document. Showing translation for مقطع تیپ سازند در اطراف قم مطالعه شده است Translate instead مقطع تیپاین سازند در اطراف قم مطالعه شده است Introduction One of the most extensive Cretaceous and Cenozoic deposits are the Gurpi and Pabdeh formations in the Zagros Basin, which are studied in this research based on calcareous nannofossils. The type section of the Gurpi and Pabdeh formations is located in the southwestern Tang-e Pabdeh, North of Lali oilfield (Jams & Wynd, 1965). The important goals of studying the upper part of the Gurpi Formation and lower part of the Pabdeh Formation is the evaluationof boundaryand biostratigraphy. Material & Methods In this study, 33 samples from the upper part of the Gurpi Formation and lower part of the Pabdeh Formation have been studied. Samples were prepared following the standard smear slide method (Bown and Young 1998). All slides were studied under a polarized light microscope at × 1000 magnification. The nomenclature of calcareous nannofossils follows the taxonomic schemes of Perch-Nielsen (1985). Discussion of Results & Conclusions To study biostratigraphy of the succession based on calcareous nannofossils, the boundary of the Gurpi and Pabdeh formations in the Par-e Nobar section located in the northwest of Shiraz was selected. In this section, the upper part of the Gurpi Formation with 22.2 m thickness mainly consists of shales and argillaceous limestones and the lower part of the Pabdeh Formation with 18.8 m thickness is consists of shale facies. For introducing index species, calcareous nannofossil assemblages, and bio-zones, slides have been studied at the Gurpi/Pabdeh formations boundary which led to the recognition of 32 species and 22 genera of calcareous nannofossils. According to the first and last occurrence of index species and recording bio-events, two bio-zones include Nephrolithus frequens Zone (CC26/ UC20dTp ) and Markalius inversus Zone (NP1) has been recognizedin the upper part of the Gurpi Formation. The Fasciculithus tympaniformis Zone (NP5) and Heliolithus kleinpellii Zone (NP6) are reported for the first time from the lower part of the Pabdeh Formation in the studied section, respectively. The bio-zones identified in the upper part of the Gurpi Formation with a thickness of 22.2 m at the Cretaceous to Paleogene boundary are as follows: Nephrolithus frequens Zone (CC26) / (UC20bTP, UC20d Tp ): The first zone in the upper part of the Gurpi Formation is recorded from the FO to LO of Nephrolithus frequens. The age of this zone is late Late Maastrichtian. The thickness of this zone is 14.8 m. Markalius inversus Zone (NP1) / (CNP1): This zone spans the interval from the last occurrence of Cretaceous taxa to the FO of Cruciplacolithus tenuis. The age of this zone is early Paleocene (early Danian). The thickness of this zone is 7.4 m. Bio-zones introduced in the lower part of the Pabdeh Formation are as follows: These bio-zones in the studied section are 18.4 m thickness from the lower part of the Pabdeh Formation. Fasciculithus tympaniformis Zone (NP5): The first nannofossil unit recorded in the lower part of the Pabdeh Formation is theNP5. This zone spans the interval from the FO ofFasciculithus tympaniformisto the FO ofHeliolithus kleinpellii. The age of this zone is Paleocene (Selandian). The thickness of this zone was measured at about 7.4 m. Heliolithus kleinpellii Zone (NP6): The last bio-zone recorded is NP6. This zone is from the lower part of the Pabdeh Formation.This zone spans the interval from the FO of Heliolithus kleinpellii to the FO of Discoaster mohleri. The age of this zone is Paleocene (Selandian). The thickness of this zone was measured at about 11 m. Thus, based on the identified calcareous nannofossils zones, the age of the upper part of the Gurpi Formation is the latest Maastrichtian–early Danian, and thelower part of the Pabdeh Formation is the middle Paleocene/Selandian. Therefore, according to the nannofossil data, the boundary between the two formations is unconformable. In addition, the Cretaceous–Paleogene boundary is continuously at the top of the Gurpi Formation. This interval was recorded by a significant decrease in Cretaceous nannofossil species, along with an increase in Thoracosphaera operculata and the appearance of the Paleocene species. Also, the conditions of the basin that is part of the eastern Tethys were identified by determining the index species calcareous nannofossils. Therefore, the presence of these species confirms warm climate conditions during the sedimentation of mentioned deposits in this part of Zagros.

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