University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 38 3 2022 09 23 Palaeoenvironment reconstruction, diagenetic overprint and geochemistry of the Upper Cretaceous Sarvak Formation in the north of Dezful Embayment, south-west of Iran Palaeoenvironment reconstruction, diagenetic overprint and geochemistry of the Upper Cretaceous Sarvak Formation in the north of Dezful Embayment, south-west of Iran 1 34 26938 10.22108/jssr.2022.134679.1237 FA Umid Kakemem Ph.D. student of Sedimentology and Petrology of Sedimentary Rocks, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran Mohammadhossein Adabi Professor, Department of Petroleum and Sedimentary Basins, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran Abas Sadeghi Professor, Department of Petroleum and Sedimentary Basins, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran 0000-0002-5515-0781 Mahmoud Jalali Exploration Directorate, NIOC, Tehran, Iran Ehsan Dehyadegari Assistant Professor, Department of Petroleum and Sedimentary Basins, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran Journal Article 2022 08 09 Abstract The Sarvak Formation, with a total thickness of 1566 m and major limestone lithology in the Ahvaz and Mansouri oil fields, is studied to determine its palaeoenvironment, diagenetic overprint and geochemistry. In the studied wells, the formation conformably overlies the Kazhdumi Formation and is overlain by the Ilam Formation. The petrographical studies led to identifying twelve facies precipitated in four major sub-environments, including inner-, middle-, and outer ramp and an intra-shelf basin on a homoclinal ramp-type setting. Dissolution, compaction, and cementation are the main diagenetic alterations that changed the primary chemical composition and the reservoir property of the Sarvak Formation. These diagenetic processes occurred in phreatic marine, meteoric, and burial realms. Sedimentary geochemistry of major and trace elements, including Ca, Mg, Fe, Mn, and Sr, along with O and C stable isotopes, reveal aragonite as the original carbonate mineralogy of the Sarvak Formation. The depositional environment in the lower Sarvak with the predominant shallow open marine and stratigraphic succession with no evidence of exposure, change to stratigraphic succession with more shallow sub-environments (lagoon and bioclastic-shoal), and the evidence of exposure such as cementation and extensive dissolution, which led to depletion in Sr, δ18O, and δ13C and enrichment in Fe and Mn during sea level fall in the inner ramp microfacies. The Fe and Mn cross-plot with a positive trend shows the effects of diagenetic phases in minor phreatic marine and mainly meteoric realm, all confirmed by petrography. The Sr/Ca ratio has the most correlation to the modern tropical warm-water shallow marine that could confirm the primary aragonite mineralogy; which is supported by the predominance of carbonate mud in the identified facies, primary isopachous fibrous marine cements, and extensive dissolution evidence. The cross-plot of Fe versus Sr and Mn versus Sr/Mn ratio suggests deposition in mainly an oxygenation state that experienced low to high water/rock interaction during different depositional sequences. The δ18O and δ13C co-variation and their comparison with the other fields of the Sarvak conducted in different regions show precipitation in an isotopic equilibrium in the carbonates with the Upper Cretaceous seawater, since calculating salinity (Z=130) and temperature (T= 26°C) of the Sarvak Formation confirm the above statement. Keywords: Diagenesis, Sedimentary geochemistry, Water/rock interaction, Upper Cretaceous, Sarvak Formation. Introduction: The Albian–Turonian Sarvak Formation (Motiei 1993), which forms a part of the Bangestan Group the second most important reservoir succession in the Zagros Basin and Persian Gulf (Esrafili-Dizaji et al. 2015; Assadi et al. 2016). This succession is equivalent to Mishrif, Ahmadi and Rumaila in Saudi Arabia, Natih in Oman, Derder in Turkey, and Mishrif in Iraq, which was deposited on a shallow carbonate platform along with interashelf basins on the passive margin of the Arabian Plate (Ziegler 2001; Piryaei et al. 2011; Alsharhan 2014). Various studies conducted on the geochemistry of carbonates reveal its adequacy in determining palaeoclimate and original mineralogy, defining the rate and type of diagenetic alteration, distinguishing diagenetic realms and trends as well as the stratigraphic position of depositional sequence stratal surfaces and boundaries (Adabi and Asadi Mehmandosti 2008; Crowe et al. 2013; Fallah-Bagtash et al. 2020; Omidpour et al. 2021). In this study, regarding the oil industry needs for exploration and production and based on petrographical and geochemical analysis, the facies, paloeoenvironment, diagenetic characteristics and geochemistry of the Sarvak Formation are studied in the northern Dezful Embayment, southern Iran. Material & Methods The facies analysis and diagenetic characteristics of the Sarvak Formation in two wells in the Ahvaz and Mansouri oil fields are studied using 900 thin sections obtained mainly from core samples. The nomenclature for carbonate rocks used in this study is the terminology introduced by Dunham (1962) and its modified classification by Embry and Klovan (1971). The facies analysis and interpretation of the depositional environments were conducted using the standard microfacies of Burchette and Wright (1992) and Flügel (2010). All thin sections were stained with potassium ferricyanide and Alizarin Red-S to distinguish carbonate minerals (Dickson 1965). The geochemical studies are done using analyzing trace and major elements including Ca, Mg, Fe, Mn, and Sr along with O and C stable isotopes of carbonate rocks both in the Exter University of England on 57 samples from the Ahvaz Oil Field and 43 samples from the Mansouri Oil Field. The trace and major elements are analyzed using Agilent 5110 VDV Inductively Coupled Optical Emission Spectrometer (ICP-OES) with 0.02 mmol/mol precision for Mg/Ca ratio, 0.4 µmol/mol for Sr/Ca ratio, 0.02 mmol/mol for Fe/Ca ratio and 0.006 mmol/mol for Mn/Ca ratio. For stable isotopes, the analysis is done using SerCon 20-22 Gas Source Isotope Ratio Mass Spectrometer (GS-IRMS) based on the Copenhagen University Standard (LEO, Carrara Marble) and with the precision of ±0.08‰ for δ13C and 0.28‰ for δ18O. Discussion of Results & Conclusion The Sarvak Formation, with dominant limestone lithology and 831 and 735 m thickness, respectively in Ahvaz and Mansuri Oil Fields, conformably overlies the Kazhdumi Formation and is unconformably overlain by the Ilam Formation. The petrographical studies led to determinate five facies association deposited on a low angle ramp type setting along with an intrashelf basin. Diagenetic studies reveal the impact of marine, unconformity-related meteoric, and shallow and deep burial diagenesis that mainly caused intense compaction, dissolution and cementation. These main diagenetic features changed the nature of the associated facies regarding the reservoir property of the Sarvak Formation. The impact of main diagenetic features along the Sarvak succession improved the understanding of the elemental, and O and C stable isotope analyses. The geochemical analysis as well as petrographical evidences such as diversity of fauna and flora and primary marine diagenetic features confirm the original aragonite mineralogy for the Sarvak carbonate, which was formed in a warm and humid condition on a shallow marine platform. The analyzed δ18O and δ13C, along with the variable concentration of Sr, Fe and Mn suggest maintenance of the primary composition along with alteration in burial realm and mainly meteoric diagenesis. The cross-plot of trace element and O and C stable isotopes indicate that the Sarvak carbonate rocks altered in the open to close diagentic system during different depositional stratigraphic sequences depending on the exposure of the carbonate platform and its scale and duration Abstract The Sarvak Formation, with a total thickness of 1566 m and major limestone lithology in the Ahvaz and Mansouri oil fields, is studied to determine its palaeoenvironment, diagenetic overprint and geochemistry. In the studied wells, the formation conformably overlies the Kazhdumi Formation and is overlain by the Ilam Formation. The petrographical studies led to identifying twelve facies precipitated in four major sub-environments, including inner-, middle-, and outer ramp and an intra-shelf basin on a homoclinal ramp-type setting. Dissolution, compaction, and cementation are the main diagenetic alterations that changed the primary chemical composition and the reservoir property of the Sarvak Formation. These diagenetic processes occurred in phreatic marine, meteoric, and burial realms. Sedimentary geochemistry of major and trace elements, including Ca, Mg, Fe, Mn, and Sr, along with O and C stable isotopes, reveal aragonite as the original carbonate mineralogy of the Sarvak Formation. The depositional environment in the lower Sarvak with the predominant shallow open marine and stratigraphic succession with no evidence of exposure, change to stratigraphic succession with more shallow sub-environments (lagoon and bioclastic-shoal), and the evidence of exposure such as cementation and extensive dissolution, which led to depletion in Sr, δ18O, and δ13C and enrichment in Fe and Mn during sea level fall in the inner ramp microfacies. The Fe and Mn cross-plot with a positive trend shows the effects of diagenetic phases in minor phreatic marine and mainly meteoric realm, all confirmed by petrography. The Sr/Ca ratio has the most correlation to the modern tropical warm-water shallow marine that could confirm the primary aragonite mineralogy; which is supported by the predominance of carbonate mud in the identified facies, primary isopachous fibrous marine cements, and extensive dissolution evidence. The cross-plot of Fe versus Sr and Mn versus Sr/Mn ratio suggests deposition in mainly an oxygenation state that experienced low to high water/rock interaction during different depositional sequences. The δ18O and δ13C co-variation and their comparison with the other fields of the Sarvak conducted in different regions show precipitation in an isotopic equilibrium in the carbonates with the Upper Cretaceous seawater, since calculating salinity (Z=130) and temperature (T= 26°C) of the Sarvak Formation confirm the above statement. Keywords: Diagenesis, Sedimentary geochemistry, Water/rock interaction, Upper Cretaceous, Sarvak Formation. Introduction: The Albian–Turonian Sarvak Formation (Motiei 1993), which forms a part of the Bangestan Group the second most important reservoir succession in the Zagros Basin and Persian Gulf (Esrafili-Dizaji et al. 2015; Assadi et al. 2016). This succession is equivalent to Mishrif, Ahmadi and Rumaila in Saudi Arabia, Natih in Oman, Derder in Turkey, and Mishrif in Iraq, which was deposited on a shallow carbonate platform along with interashelf basins on the passive margin of the Arabian Plate (Ziegler 2001; Piryaei et al. 2011; Alsharhan 2014). Various studies conducted on the geochemistry of carbonates reveal its adequacy in determining palaeoclimate and original mineralogy, defining the rate and type of diagenetic alteration, distinguishing diagenetic realms and trends as well as the stratigraphic position of depositional sequence stratal surfaces and boundaries (Adabi and Asadi Mehmandosti 2008; Crowe et al. 2013; Fallah-Bagtash et al. 2020; Omidpour et al. 2021). In this study, regarding the oil industry needs for exploration and production and based on petrographical and geochemical analysis, the facies, paloeoenvironment, diagenetic characteristics and geochemistry of the Sarvak Formation are studied in the northern Dezful Embayment, southern Iran. Material & Methods The facies analysis and diagenetic characteristics of the Sarvak Formation in two wells in the Ahvaz and Mansouri oil fields are studied using 900 thin sections obtained mainly from core samples. The nomenclature for carbonate rocks used in this study is the terminology introduced by Dunham (1962) and its modified classification by Embry and Klovan (1971). The facies analysis and interpretation of the depositional environments were conducted using the standard microfacies of Burchette and Wright (1992) and Flügel (2010). All thin sections were stained with potassium ferricyanide and Alizarin Red-S to distinguish carbonate minerals (Dickson 1965). The geochemical studies are done using analyzing trace and major elements including Ca, Mg, Fe, Mn, and Sr along with O and C stable isotopes of carbonate rocks both in the Exter University of England on 57 samples from the Ahvaz Oil Field and 43 samples from the Mansouri Oil Field. The trace and major elements are analyzed using Agilent 5110 VDV Inductively Coupled Optical Emission Spectrometer (ICP-OES) with 0.02 mmol/mol precision for Mg/Ca ratio, 0.4 µmol/mol for Sr/Ca ratio, 0.02 mmol/mol for Fe/Ca ratio and 0.006 mmol/mol for Mn/Ca ratio. For stable isotopes, the analysis is done using SerCon 20-22 Gas Source Isotope Ratio Mass Spectrometer (GS-IRMS) based on the Copenhagen University Standard (LEO, Carrara Marble) and with the precision of ±0.08‰ for δ13C and 0.28‰ for δ18O. Discussion of Results & Conclusion The Sarvak Formation, with dominant limestone lithology and 831 and 735 m thickness, respectively in Ahvaz and Mansuri Oil Fields, conformably overlies the Kazhdumi Formation and is unconformably overlain by the Ilam Formation. The petrographical studies led to determinate five facies association deposited on a low angle ramp type setting along with an intrashelf basin. Diagenetic studies reveal the impact of marine, unconformity-related meteoric, and shallow and deep burial diagenesis that mainly caused intense compaction, dissolution and cementation. These main diagenetic features changed the nature of the associated facies regarding the reservoir property of the Sarvak Formation. The impact of main diagenetic features along the Sarvak succession improved the understanding of the elemental, and O and C stable isotope analyses. The geochemical analysis as well as petrographical evidences such as diversity of fauna and flora and primary marine diagenetic features confirm the original aragonite mineralogy for the Sarvak carbonate, which was formed in a warm and humid condition on a shallow marine platform. The analyzed δ18O and δ13C, along with the variable concentration of Sr, Fe and Mn suggest maintenance of the primary composition along with alteration in burial realm and mainly meteoric diagenesis. The cross-plot of trace element and O and C stable isotopes indicate that the Sarvak carbonate rocks altered in the open to close diagentic system during different depositional stratigraphic sequences depending on the exposure of the carbonate platform and its scale and duration

https://jssr.ui.ac.ir/article_26938_0a2e46e9e1a879b950fb4819970b8efa.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 38 3 2022 09 23 Sedimentology, facies and depositional model of the alluvial fan of Abyek, Qazvin Sedimentology, facies and depositional model of the alluvial fan of Abyek, Qazvin 35 58 27112 10.22108/jssr.2022.135308.1242 FA Vida Davoudi PhD Geology, Department of Geology, Faculty of Sciences, Bu-Ali Sina University, Hamedan, Iran Saeed Khodabakhsh Associate Professor, Department of Geology, Faculty of Sciences, Bu-Ali Sina University, Hamedan, Iran Behrouz Bahramabadi Assistant Professor, Department of Geography, Faculty of Sciences, Imam Ali University, Tehran, Iran Journal Article 2022 10 03 Abstract This study was done to describe and interpret the facies, the provenance of sediments, pedogenesis processes, and the model of the Abyek alluvial fan in the northern margin of Qazvin Plain, using 45 sediment samples in the form of nine profiles and nine surface samples. The facies study led to the determination of six facies grouped into two facies associations including coarse-grained lithofacies (Gms, Gcs, Gci, Gcp/Gmp, Gmg, and Glns), and calcrete facies (Plc). This alluvial fan is dominated by the episodic matrix to clast-supported gravel (interbedded with a subordinate) and red, matrix-supported gravel which were deposited by non-cohesive debris flow. The results of granulometry analysis showed that the size of the sediments of the alluvial fan shows wide variations from gravel to clay, and the texture of the sediments of this alluvial fan is mainly gravel and sandy gravel with very poorly sorting and fine skewness. The study of macromorphology and micromorphology of calcrete showed that their occurrence was controlled by pedogenic processes. Micromorphological studies also revealed alpha and beta features such as coated grains, pisoid, laminar crust and strong brecciation. Keywords: Alluvial fan, facies, Calcrete, Qazvin Plain, Abyek. Introduction Alluvial fans are, more often, coarse-grained and serve as an excellent proxy for unrevealing past changes in climate, hinterland tectonics and sea/lake level. Besides tectonics, climate and hinterland lithology exert significant influence on the volume and grain size of sediments received in such systems (Chakraborty and Paul 2013). In this regard, the classification of alluvial fans by Blair and McPherson (1994) based on sedimentary processes strengthens the old hypothesis of dry and wet alluvial fans. Although the validity of this climate-response hypothesis has been questioned. The purposes of this study are 1) to investigate of sedimentary features and description and interpretation of sedimentary facies to identify sedimentary facies and the facies model of the Abyek alluvial fan and 2) to discuss the role of climate, tectonics, and lithology of the source area on the sedimentary facies. Material & Methods In order to study Abyek alluvial fan, 45 samples of different facies were collected in the form of nine sediment profiles and nine surface samples. The characteristics of representative profiles including sedimentary structures, texture, bed geometries, and lithology were used to describe fan facies. In addition, paleocurrent directions were depicted using azimuth measurements of imbricated pebbles. Facies were described following Miall’s (2006) facies classification. Also, in order to study thin sections, 11 samples from the sand-size sediments and 12 calcrete samples were prepared, respectively, in order to determine the provenance of sediments and microscopic characteristics (Carver 1971). Folk’s (1980) classification was used to name gravelly and sandy sediments in terms of composition. Modal analysis for sandstone samples was done by counting more than 250 points in each section based on the Gazzi-Dickinson method (Gazzi 1966; Dickinson 1970). In this study, in order to analyze calcrete samples, six thin section samples and two blocks with dimensions of 1 x 1 cm were prepared and imaged by FESEM electron microscope. Scanning electron microscopy (SEM) was performed on the representative samples at the Beamgostar Laboratory, Iran (Mira3-TESKAN Scanning Electron Microscope, 20KV). Also, five powder samples and three oriented clay samples were analyzed to determine the mineralogy of clay fraction. The mineralogical composition of representative bulk and oriented samples was investigated by X-ray diffraction (XRD) in Malayer University, Iran (Italstructures, 40 Kv, Cukα 30mA). Finally, by combining field, laboratory data, the sedimentary facies, the origin of sediments and the model of the Abyek alluvial fan and the features of diagenesis and pedogenesis of its sediments were identified and analyzed. Discussion of Results & Conclusions The study of facies of Abyek alluvial fan led to the identification of six facies in two groups: the first group includes coarse-grained lithofacies, which includes matrix-supported gravel (Gms), clast-supported gravel (Gcs), inversely graded clast-supported gravel (Gci), rhythmic gravelly and sandy planar couplets (Gcm and Gmm/Sm), graded clast- to matrix-supported gravel (Gmg) and Grain- to ground-supported lenticular gravel (Glns) and the second group includes calcrete (Plc). The debris-flow deposits, red-coloration, interbedded mudflow, polygonal mud cracks, and calcretes of the studied areas are indicative of a generally warm and arid climate (Gile et al. 1965; Hayward 1983; Kraus 1999; Clyde et al. 2010), which also exists in other areas of the Qazvin Plain. Subaerial debris flows require abundant clastic debris, a steep slope, and a high discharge for their initiation. Abundant clastic detritus resulting from mechanical weathering during long dry periods are transported by flash floods, with little vegetation to inhibit run-off (Miall 1977). Also, non-cohesive debris flows are caused by watersheds with a small amount of mud (especially clay). In this study, the granulometry results show that the amount of mud in the analyzed samples is very small (less than 5%). Since the silty and clay fractions are the product of hydrolysis of feldspar and secondary minerals or they were formed through severe tectonic cuts (Blair 1999); therefore, such reactions are very slow in warm and dry climates and lead to an insignificant amount of mud fraction (Blair and McPherson 2009). On the other hand, the presence of ancient soil (red horizons) indicates periodic sedimentation and warm and dry climate conditions (Yan et al. 2007). The presence of calcrete in the alluvium as well as the palygorskite clay mineral, which is a clay mineral specific to calcrete (Zucca et al. 2017), are other clear signs to confirm the warm and dry climate. On the other hand, the composition and analysis of the palaeoflow direction based on the imbrication of pebbles shows that the alluvial sediments were mostly transported from north to south; Therefore, the tectonic uplift caused by the southern Alborz fault has a significant contribution to the formation of alluvial fans on the northern edge of the Qazvin Plain. Stable tectonic conditions and warm and dry climates (Reeves 1983; Wright and Tucker 1991) are the main factors controlling the formation of calcrete in this alluvial fan. According to granulometry, the sediments of this alluvial fan are mainly composed of a wide range of semi-coarse to fine-grain sediments. The percentage of boulders is very low and coarse pebbles are rarely found in the studied samples. In other words, among the gravel clasts larger than 6 cm, the superiority is with gravels with a diameter of 6 to 12 cm (40 to 90 percent). This shows that coarse rock fragments rarely form in the catchment area. The main reason for the formation of relatively fine-grained deposits in the alluvial fan is the watershed lithology, which is mostly limestone (especially marl), fine-grained volcanic rocks, sandstone, siltstone and shale derived that easily have been decomposed and crushed. A small abundance of coarse rock fragments can also occur where strong tectonic shears have pulverized the rocks of the catchment area (Blair 2003). However, according to the watershed lithology in the catchment basin, the lithological composition of the parent rock is the main reason for the formation of such deposits. In addition, the most mature type of calcrete has been found in the Abyek alluvial fan with a calcareous lithological composition, which clearly shows the dominant contribution of calcareous parent rock to the formation of calcrete. Abyek alluvial fan due to specific features such as the frequency (80–95%) of Gms facies, the presence of red horizon, the amount of mud less than 5%, and the small radius (approximately 3.5 km) can be considered as a fan caused by the accumulation of non-cohesive debris flow (Blair and McPherson 2009). This alluvial fan is a special type of fan resulting from non-cohesive deposits (with a very low percentage of clay) that were formed during sudden discharges. The very small abundance (10–15%) of gravelly facies caused by runoff shows that the contribution of floods to the initial accumulation of alluvial fan sediments was very small and only leads to the transportation and redeposition of sediments locally. Abstract This study was done to describe and interpret the facies, the provenance of sediments, pedogenesis processes, and the model of the Abyek alluvial fan in the northern margin of Qazvin Plain, using 45 sediment samples in the form of nine profiles and nine surface samples. The facies study led to the determination of six facies grouped into two facies associations including coarse-grained lithofacies (Gms, Gcs, Gci, Gcp/Gmp, Gmg, and Glns), and calcrete facies (Plc). This alluvial fan is dominated by the episodic matrix to clast-supported gravel (interbedded with a subordinate) and red, matrix-supported gravel which were deposited by non-cohesive debris flow. The results of granulometry analysis showed that the size of the sediments of the alluvial fan shows wide variations from gravel to clay, and the texture of the sediments of this alluvial fan is mainly gravel and sandy gravel with very poorly sorting and fine skewness. The study of macromorphology and micromorphology of calcrete showed that their occurrence was controlled by pedogenic processes. Micromorphological studies also revealed alpha and beta features such as coated grains, pisoid, laminar crust and strong brecciation. Keywords: Alluvial fan, facies, Calcrete, Qazvin Plain, Abyek. Introduction Alluvial fans are, more often, coarse-grained and serve as an excellent proxy for unrevealing past changes in climate, hinterland tectonics and sea/lake level. Besides tectonics, climate and hinterland lithology exert significant influence on the volume and grain size of sediments received in such systems (Chakraborty and Paul 2013). In this regard, the classification of alluvial fans by Blair and McPherson (1994) based on sedimentary processes strengthens the old hypothesis of dry and wet alluvial fans. Although the validity of this climate-response hypothesis has been questioned. The purposes of this study are 1) to investigate of sedimentary features and description and interpretation of sedimentary facies to identify sedimentary facies and the facies model of the Abyek alluvial fan and 2) to discuss the role of climate, tectonics, and lithology of the source area on the sedimentary facies. Material & Methods In order to study Abyek alluvial fan, 45 samples of different facies were collected in the form of nine sediment profiles and nine surface samples. The characteristics of representative profiles including sedimentary structures, texture, bed geometries, and lithology were used to describe fan facies. In addition, paleocurrent directions were depicted using azimuth measurements of imbricated pebbles. Facies were described following Miall’s (2006) facies classification. Also, in order to study thin sections, 11 samples from the sand-size sediments and 12 calcrete samples were prepared, respectively, in order to determine the provenance of sediments and microscopic characteristics (Carver 1971). Folk’s (1980) classification was used to name gravelly and sandy sediments in terms of composition. Modal analysis for sandstone samples was done by counting more than 250 points in each section based on the Gazzi-Dickinson method (Gazzi 1966; Dickinson 1970). In this study, in order to analyze calcrete samples, six thin section samples and two blocks with dimensions of 1 x 1 cm were prepared and imaged by FESEM electron microscope. Scanning electron microscopy (SEM) was performed on the representative samples at the Beamgostar Laboratory, Iran (Mira3-TESKAN Scanning Electron Microscope, 20KV). Also, five powder samples and three oriented clay samples were analyzed to determine the mineralogy of clay fraction. The mineralogical composition of representative bulk and oriented samples was investigated by X-ray diffraction (XRD) in Malayer University, Iran (Italstructures, 40 Kv, Cukα 30mA). Finally, by combining field, laboratory data, the sedimentary facies, the origin of sediments and the model of the Abyek alluvial fan and the features of diagenesis and pedogenesis of its sediments were identified and analyzed. Discussion of Results & Conclusions The study of facies of Abyek alluvial fan led to the identification of six facies in two groups: the first group includes coarse-grained lithofacies, which includes matrix-supported gravel (Gms), clast-supported gravel (Gcs), inversely graded clast-supported gravel (Gci), rhythmic gravelly and sandy planar couplets (Gcm and Gmm/Sm), graded clast- to matrix-supported gravel (Gmg) and Grain- to ground-supported lenticular gravel (Glns) and the second group includes calcrete (Plc). The debris-flow deposits, red-coloration, interbedded mudflow, polygonal mud cracks, and calcretes of the studied areas are indicative of a generally warm and arid climate (Gile et al. 1965; Hayward 1983; Kraus 1999; Clyde et al. 2010), which also exists in other areas of the Qazvin Plain. Subaerial debris flows require abundant clastic debris, a steep slope, and a high discharge for their initiation. Abundant clastic detritus resulting from mechanical weathering during long dry periods are transported by flash floods, with little vegetation to inhibit run-off (Miall 1977). Also, non-cohesive debris flows are caused by watersheds with a small amount of mud (especially clay). In this study, the granulometry results show that the amount of mud in the analyzed samples is very small (less than 5%). Since the silty and clay fractions are the product of hydrolysis of feldspar and secondary minerals or they were formed through severe tectonic cuts (Blair 1999); therefore, such reactions are very slow in warm and dry climates and lead to an insignificant amount of mud fraction (Blair and McPherson 2009). On the other hand, the presence of ancient soil (red horizons) indicates periodic sedimentation and warm and dry climate conditions (Yan et al. 2007). The presence of calcrete in the alluvium as well as the palygorskite clay mineral, which is a clay mineral specific to calcrete (Zucca et al. 2017), are other clear signs to confirm the warm and dry climate. On the other hand, the composition and analysis of the palaeoflow direction based on the imbrication of pebbles shows that the alluvial sediments were mostly transported from north to south; Therefore, the tectonic uplift caused by the southern Alborz fault has a significant contribution to the formation of alluvial fans on the northern edge of the Qazvin Plain. Stable tectonic conditions and warm and dry climates (Reeves 1983; Wright and Tucker 1991) are the main factors controlling the formation of calcrete in this alluvial fan. According to granulometry, the sediments of this alluvial fan are mainly composed of a wide range of semi-coarse to fine-grain sediments. The percentage of boulders is very low and coarse pebbles are rarely found in the studied samples. In other words, among the gravel clasts larger than 6 cm, the superiority is with gravels with a diameter of 6 to 12 cm (40 to 90 percent). This shows that coarse rock fragments rarely form in the catchment area. The main reason for the formation of relatively fine-grained deposits in the alluvial fan is the watershed lithology, which is mostly limestone (especially marl), fine-grained volcanic rocks, sandstone, siltstone and shale derived that easily have been decomposed and crushed. A small abundance of coarse rock fragments can also occur where strong tectonic shears have pulverized the rocks of the catchment area (Blair 2003). However, according to the watershed lithology in the catchment basin, the lithological composition of the parent rock is the main reason for the formation of such deposits. In addition, the most mature type of calcrete has been found in the Abyek alluvial fan with a calcareous lithological composition, which clearly shows the dominant contribution of calcareous parent rock to the formation of calcrete. Abyek alluvial fan due to specific features such as the frequency (80–95%) of Gms facies, the presence of red horizon, the amount of mud less than 5%, and the small radius (approximately 3.5 km) can be considered as a fan caused by the accumulation of non-cohesive debris flow (Blair and McPherson 2009). This alluvial fan is a special type of fan resulting from non-cohesive deposits (with a very low percentage of clay) that were formed during sudden discharges. The very small abundance (10–15%) of gravelly facies caused by runoff shows that the contribution of floods to the initial accumulation of alluvial fan sediments was very small and only leads to the transportation and redeposition of sediments locally.

https://jssr.ui.ac.ir/article_27112_52f245d4d3a833046780b59a63c813f1.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 38 3 2022 09 23 The effects of Qatar-Arc on the upper part of the K3 Reservoir Unit of the Upper Dalan Formation in the lower part of the Permian–Triassic Boundary: Comparison of two fields in the Central Persian Gulf Basin The effects of Qatar-Arc on the upper part of the K3 Reservoir Unit of the Upper Dalan Formation in the lower part of the Permian–Triassic Boundary: Comparison of two fields in the Central Persian Gulf Basin 59 90 27129 10.22108/jssr.2022.133702.1227 FA Sogand Asadolahi Shad MS student of Sedimentology and Sedimentary Petrology, School of Geology, College of Science, University of Tehran, Iran Vahid Tavakoli Associate Professor, School of Geology, College of Science, University of Tehran, Iran Hossain Rahimpour-Bonab Professor, School of Geology, College of Science, University of Tehran, Iran Journal Article 2022 05 17 Abstract Paleohighs play an important role in increasing the quality and sedimentological characteristics of the reservoirs. The Upper Dalan Formation with Late Permian age in the center of the Persian Gulf Basin is known as a giant gas reservoir. In this paper, 60 meters of the Upper Dalan Formation have been studied in two fields in the center of the Persian Gulf Basin. Petrographic studies of the two fields led to the identification of seven microfacies in field A and six microfacies in field B in the form of four facies belts in the carbonated ramp environment. In order to evaluate the heterogeneity of the reservoir, the determination of rock types was performed by using four standard methods. Examination of the average porosity and permeability shows that the dissolution in field B is more severe than in field A. Study of diagenetic processes, the type of dolomites formed and the average porosity and permeability in the samples of the two fields indicate that the location of field B on the Qatar arc leads to the formation of dolomicrites, increased dissolution and finally higher reservoir quality in microfacies groups in this field in comparison with field A. Keywords: Upper Dalan Formation, Qatar Arc, Permian–Triassic boundary, Microfacies, Heterogeneity Introduction Due to the presence of great hydrocarbon resources and fields in the south and southwest of Iran, the study and investigation of fields and formations in these areas was an important and a significant topic for many researches in recent decades. The Dalan Formation of the Middle–Late Permian age forms the main gas and condensate reservoirs in numerous hydrocarbon fields in the south and southwest of Iran (Alsharhan and Nairn 1994; Ehrenberg et al. 2007; Tavakoli 2015). The Upper Dalan Formation of the Late Permian age has one of the largest gas reservoirs in the world and it is placed on the Faragan Formation of the Early Permian and continues to the Kangan Formation of the Early Triassic. This formation is mainly composed of carbonate-evaporite sequences that developed on a homoclinal carbonate ramp continuously with significant changes in heterogeneity and reservoir quality towards the Late Permian Paleotethys Ocean (Fallah-Bagtash et al. 2020; Ghasemi et al. 2022). Extensive studies have been conducted concerning the investigation and analysis of sedimentological evolution, texture (petrographic analysis), analysis of facies groups, sedimentary environments and sub-environments, diagenetic processes and investigation of heterogeneities in it. The most common pores identified in the formation are interparticle, moldic and connected vuggy types. The main diagenetic processes affecting the upper Dalan Formation in these studies are dolomitization and dissolution which increase the reservoir quality and the formation of anhydrite and calcite cements as well as compaction that reduce the reservoir quality (Amel et al. 2015; Fallah-Bagtash et al. 2020; Ghasemi et al. 2022). There have been limited case studies on paleohighs in the world. For example, concerning the effect of paleohighs on gas reservoirs, we can refer to the research conducted on the Middle Permian Maoko Limestone, which is a main natural gas production reservoir in the southern Sichuan basin of China. The results of these studies state that the presence of ancient elevations causes special changes in hydrocarbon reservoirs. These changes may increase reservoir quality, change the diagenetic processes, and subsequently increase dissolution which makes favorable conditions for the accumulation of hydrocarbon materials in reservoirs. Despite such importance, the influence of the Qatar-Arc on the sedimentological and petrophysical characteristics of the Dalan Formation has not been studied. Therefore, the main goal of this paper is to investigate the effects of the presence of the Qatar-Arc on the reservoir quality (porosity and permeability), diagenetic processes, facies properties, and sedimentological evolution of a part (30 meters in each field) of the Upper Dalan Formation below the Permian–Triassic boundary. This study compares the effects of the presence of the arc in the upper part of the Dalan Formation in two fields A and B in the central part of the Persian Gulf basin. Materials & Methods Data studied in this research was obtained from two exploration wells in two different fields. The data includes information obtained from the study of 30 meters of cores in each field. In X1 well (Field A) and X2 well (Field B), the studied data are related to the amount of porosity, permeability, investigation of facies and sedimentary characteristics. In each meter, four thin sections and a total of 123 thin sections in X1 well and 121 thin sections in t X2 well have been studied and analyzed. The number of plugs taken in X1 well is 93 for porosity and 92 for permeability. In X2 well, 103 plugs have been prepared for porosity and 96 plugs for permeability. The study of thin sections has been done by a polarizing microscope. To accurately determine the lithology of limestone from dolomite, one-third of each thin section was stained with Alizarin Red-S solution according to the common method of Dickson (1965). Boyle's law has been used to determine the porosity and Darcy's law has been used to determine the permeability of core plugs. Blue epoxy impregnation has been used to determine the types of pores (Choquette and Pray 1970). The classification of microfacies analyzed in both fields is based on Dunham classification (Dunham 1962) and the division related to facies belts based on Flugel (2010). To determine the rock types, four common methods, Winland (Winland-Plot; Schmalz and Rahme 1950; Kolodzie 1980; Pitman 1992; Amaefule et al. 1993; Rezaee et al. 2006; Purcell 2013), Lorenz (SML-Plot; Lorenz 1905), Reservoir quality index (RQI-FZI Method; Amaefule et al. 1993) and Lucia's Method (1995) have been used. Discussion of Results & Conclusions Facies analysis led to the identification of seven microfacies in field A and six microfacies in field B belonging to four sub-environments deposited in a carbonate ramp. Micriticization, bioturbation, cementation, dolomization, neomorphism, dissolution, compaction (chemical) and fracturing are observed in the studied succession. These diagenetic processes affected the deposits of the Upper Dalan Formation during different stages of marine, meteoric and burial diagenesis. The study of the reservoir quality in the upper Dalan in both fields indicates that the reservoir quality is higher in the B field compared to field A. Detection and evaluation of heterogeneity were performed to increase the quality and accuracy of studying reservoirs. Four common methods of determining rock types and evaluating heterogeneity have been used. In the Winland method, plotting the porosity and permeability data related to two fields separately has led to the identification of six rock types in field A and seven rock types in field B. In the A field, most samples have small pore-throats and in field B, a large number of samples have a medium, and particularly large pore-throats (pore-throats between 5 to 15 and 15 to 60 microns). In the hydraulic flow unit method, six rock types have been determined after performing calculations in both fields. The results show that the reservoir quality is higher in the samples of B field compared to field A. In the method, Lucia, based on the standard ranges in both fields A and B, five rock types were determined from the final results. In field A, the amount of non-reservoir samples is more than in field B, the changes in the diagrams are almost uniform, and the samples are distributed in three classes 1 (grain support), 2 (grain support-packstone), and 3 (mud support) of Lucia. In field B, most of the samples are concentrated in classes 1 and 2 of the Lucia classification, respectively. In the Lorenz method, four rock types have been determined in both fields. Distribution patterns are almost the same in both fields. Rock type 1 with the highest reservoir quality has the lowest amount of abundance. The most abundant sedimentary sub-environments in field A are leeward shoal and lagoon while in field B, tidal facies and lagoon are more abundant. In field B, the low depth and high evaporation have caused intolerable conditions for living organisms. Also, the bioturbation process has not been observed near the Permian–Triassic boundary (PTB) of field B. Isopachous cements were not formed in field B because these sediments have not spent a long time in the marine environment and the water depth has decreased rapidly. The abundant dissolution of grains in B field and the lack of observation of this phenomenon in field A is other evidence of the influence of atmospheric diagenesis on the sediments near the boundary in field B. The dolomites formed in B field are fine-grained compared to field A, which indicates the formation in a marine diagenetic environment with a short time for formation. The seepage-reflux dolomitization model has been widely accepted for these fine-grained (dolomicrite) and anhedral dolomites (Tucker 1994; Amel et al. 2015; Fallah-Bagtash et al. 2020; Enayati-Bidgoli and Navidtalab 2020). The model states that dolomites have been formed in an early diagenetic stage in shallow water depth. It can be seen that the presence of the Qatar-Arc and the decrease in water depth have led to strong effects of the evaporation process in field B. It also caused increasing dolomite and anhydrite formation in the lower part of the PTB. An increase in dissolution in the upper part of the boundary is another effect of the Arc. The formation of fine-crystalline dolomites, increased dissolution (moldic and vuggy), formation of anhydrite nodules, and better reservoir quality in field B compared to field A are the results of the presence of the Qatar-Arc in the field B. Abstract Paleohighs play an important role in increasing the quality and sedimentological characteristics of the reservoirs. The Upper Dalan Formation with Late Permian age in the center of the Persian Gulf Basin is known as a giant gas reservoir. In this paper, 60 meters of the Upper Dalan Formation have been studied in two fields in the center of the Persian Gulf Basin. Petrographic studies of the two fields led to the identification of seven microfacies in field A and six microfacies in field B in the form of four facies belts in the carbonated ramp environment. In order to evaluate the heterogeneity of the reservoir, the determination of rock types was performed by using four standard methods. Examination of the average porosity and permeability shows that the dissolution in field B is more severe than in field A. Study of diagenetic processes, the type of dolomites formed and the average porosity and permeability in the samples of the two fields indicate that the location of field B on the Qatar arc leads to the formation of dolomicrites, increased dissolution and finally higher reservoir quality in microfacies groups in this field in comparison with field A. Keywords: Upper Dalan Formation, Qatar Arc, Permian–Triassic boundary, Microfacies, Heterogeneity Introduction Due to the presence of great hydrocarbon resources and fields in the south and southwest of Iran, the study and investigation of fields and formations in these areas was an important and a significant topic for many researches in recent decades. The Dalan Formation of the Middle–Late Permian age forms the main gas and condensate reservoirs in numerous hydrocarbon fields in the south and southwest of Iran (Alsharhan and Nairn 1994; Ehrenberg et al. 2007; Tavakoli 2015). The Upper Dalan Formation of the Late Permian age has one of the largest gas reservoirs in the world and it is placed on the Faragan Formation of the Early Permian and continues to the Kangan Formation of the Early Triassic. This formation is mainly composed of carbonate-evaporite sequences that developed on a homoclinal carbonate ramp continuously with significant changes in heterogeneity and reservoir quality towards the Late Permian Paleotethys Ocean (Fallah-Bagtash et al. 2020; Ghasemi et al. 2022). Extensive studies have been conducted concerning the investigation and analysis of sedimentological evolution, texture (petrographic analysis), analysis of facies groups, sedimentary environments and sub-environments, diagenetic processes and investigation of heterogeneities in it. The most common pores identified in the formation are interparticle, moldic and connected vuggy types. The main diagenetic processes affecting the upper Dalan Formation in these studies are dolomitization and dissolution which increase the reservoir quality and the formation of anhydrite and calcite cements as well as compaction that reduce the reservoir quality (Amel et al. 2015; Fallah-Bagtash et al. 2020; Ghasemi et al. 2022). There have been limited case studies on paleohighs in the world. For example, concerning the effect of paleohighs on gas reservoirs, we can refer to the research conducted on the Middle Permian Maoko Limestone, which is a main natural gas production reservoir in the southern Sichuan basin of China. The results of these studies state that the presence of ancient elevations causes special changes in hydrocarbon reservoirs. These changes may increase reservoir quality, change the diagenetic processes, and subsequently increase dissolution which makes favorable conditions for the accumulation of hydrocarbon materials in reservoirs. Despite such importance, the influence of the Qatar-Arc on the sedimentological and petrophysical characteristics of the Dalan Formation has not been studied. Therefore, the main goal of this paper is to investigate the effects of the presence of the Qatar-Arc on the reservoir quality (porosity and permeability), diagenetic processes, facies properties, and sedimentological evolution of a part (30 meters in each field) of the Upper Dalan Formation below the Permian–Triassic boundary. This study compares the effects of the presence of the arc in the upper part of the Dalan Formation in two fields A and B in the central part of the Persian Gulf basin. Materials & Methods Data studied in this research was obtained from two exploration wells in two different fields. The data includes information obtained from the study of 30 meters of cores in each field. In X1 well (Field A) and X2 well (Field B), the studied data are related to the amount of porosity, permeability, investigation of facies and sedimentary characteristics. In each meter, four thin sections and a total of 123 thin sections in X1 well and 121 thin sections in t X2 well have been studied and analyzed. The number of plugs taken in X1 well is 93 for porosity and 92 for permeability. In X2 well, 103 plugs have been prepared for porosity and 96 plugs for permeability. The study of thin sections has been done by a polarizing microscope. To accurately determine the lithology of limestone from dolomite, one-third of each thin section was stained with Alizarin Red-S solution according to the common method of Dickson (1965). Boyle's law has been used to determine the porosity and Darcy's law has been used to determine the permeability of core plugs. Blue epoxy impregnation has been used to determine the types of pores (Choquette and Pray 1970). The classification of microfacies analyzed in both fields is based on Dunham classification (Dunham 1962) and the division related to facies belts based on Flugel (2010). To determine the rock types, four common methods, Winland (Winland-Plot; Schmalz and Rahme 1950; Kolodzie 1980; Pitman 1992; Amaefule et al. 1993; Rezaee et al. 2006; Purcell 2013), Lorenz (SML-Plot; Lorenz 1905), Reservoir quality index (RQI-FZI Method; Amaefule et al. 1993) and Lucia's Method (1995) have been used. Discussion of Results & Conclusions Facies analysis led to the identification of seven microfacies in field A and six microfacies in field B belonging to four sub-environments deposited in a carbonate ramp. Micriticization, bioturbation, cementation, dolomization, neomorphism, dissolution, compaction (chemical) and fracturing are observed in the studied succession. These diagenetic processes affected the deposits of the Upper Dalan Formation during different stages of marine, meteoric and burial diagenesis. The study of the reservoir quality in the upper Dalan in both fields indicates that the reservoir quality is higher in the B field compared to field A. Detection and evaluation of heterogeneity were performed to increase the quality and accuracy of studying reservoirs. Four common methods of determining rock types and evaluating heterogeneity have been used. In the Winland method, plotting the porosity and permeability data related to two fields separately has led to the identification of six rock types in field A and seven rock types in field B. In the A field, most samples have small pore-throats and in field B, a large number of samples have a medium, and particularly large pore-throats (pore-throats between 5 to 15 and 15 to 60 microns). In the hydraulic flow unit method, six rock types have been determined after performing calculations in both fields. The results show that the reservoir quality is higher in the samples of B field compared to field A. In the method, Lucia, based on the standard ranges in both fields A and B, five rock types were determined from the final results. In field A, the amount of non-reservoir samples is more than in field B, the changes in the diagrams are almost uniform, and the samples are distributed in three classes 1 (grain support), 2 (grain support-packstone), and 3 (mud support) of Lucia. In field B, most of the samples are concentrated in classes 1 and 2 of the Lucia classification, respectively. In the Lorenz method, four rock types have been determined in both fields. Distribution patterns are almost the same in both fields. Rock type 1 with the highest reservoir quality has the lowest amount of abundance. The most abundant sedimentary sub-environments in field A are leeward shoal and lagoon while in field B, tidal facies and lagoon are more abundant. In field B, the low depth and high evaporation have caused intolerable conditions for living organisms. Also, the bioturbation process has not been observed near the Permian–Triassic boundary (PTB) of field B. Isopachous cements were not formed in field B because these sediments have not spent a long time in the marine environment and the water depth has decreased rapidly. The abundant dissolution of grains in B field and the lack of observation of this phenomenon in field A is other evidence of the influence of atmospheric diagenesis on the sediments near the boundary in field B. The dolomites formed in B field are fine-grained compared to field A, which indicates the formation in a marine diagenetic environment with a short time for formation. The seepage-reflux dolomitization model has been widely accepted for these fine-grained (dolomicrite) and anhedral dolomites (Tucker 1994; Amel et al. 2015; Fallah-Bagtash et al. 2020; Enayati-Bidgoli and Navidtalab 2020). The model states that dolomites have been formed in an early diagenetic stage in shallow water depth. It can be seen that the presence of the Qatar-Arc and the decrease in water depth have led to strong effects of the evaporation process in field B. It also caused increasing dolomite and anhydrite formation in the lower part of the PTB. An increase in dissolution in the upper part of the boundary is another effect of the Arc. The formation of fine-crystalline dolomites, increased dissolution (moldic and vuggy), formation of anhydrite nodules, and better reservoir quality in field B compared to field A are the results of the presence of the Qatar-Arc in the field B.

https://jssr.ui.ac.ir/article_27129_e2df4d6add2918db3e1a8fd6359aa3cc.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 38 3 2022 09 23 Revision in nomenclature and classification of the Neogene marl deposits: A case study from south and southeast of Tehran Revision in nomenclature and classification of the Neogene marl deposits: A case study from south and southeast of Tehran 91 112 27107 10.22108/jssr.2022.135225.1240 FA Hamid Reza Peyrowan Associate Professor of Agricultural Research, Education and Extension Organization, Soil Conservation and Watershed Research Institute, Tehran, Iran 0000-0002-1335-1219 Kourosh Shirani Associate Professor of Agricultural Research, Education and Extension Organization, Soil Conservation and Watershed Research Institute, Tehran, Iran Journal Article 2022 09 26 Abstract Marl is a type of mixed carbonate–silicate sediment and contains clay and carbonate minerals deposited in different environments. The terms marl and marlstone are still imprecisely used in geology. I n this study, to revise the nomenclature and sedimentary classification of marl deposits, 99 samples were taken from different terrestrial and marine marl formations. The texture and percentage of carbonate and salt contents in the marls were measured. According to Folk's classification, the majority of the samples are in the range of sandy silt, sandy mud, silt, muddy sand, and silty sand. Based on the electric conductivity parameter (EC), all samples have a high content of salt and are classified in saline and very saline classes. The results based on the classification method of Haldar and Tisljar also confirm that most of the samples are in the category of "calcite clayey siltstone", clayey calcite siltstone, and “calcite-silt clay” and a few examples are "calcite – silt clay” and clayey- silt limestone, except for one sample of the Kond Formation, which is within the marl field. The main samples are not classified by the Pettijohn method and samples are mostly silty, and muddy and the name chalk-salt siltstone and mudstone were found to be more suitable for the terrestrial marl deposits under investigation in this research. Keywords: Continental marl, Carbonate content, Marine marl, Marl Classification, Salinity Introduction In geology, the term marl refers to chemical-detrital sediments, which have between 35% to 65% carbonate or clay content. Various definitions have been presented by different researchers about marl, despite relatively different descriptions in all of them, and marl nomenclature has been established on carbonate and clay contents. There is no unanimity regarding the nomenclature of marl sediments and many of the definitions are not precise, and in some of them, different origins are mentioned for marl, such as Terzaghi and Peck (1967), exclusively considered marine origin for marl sediments. Mitchell (1993) related these sediments to the biochemical process, while there is a wide range of marl deposits from terrestrial to marine in nature. Investigating the sedimentary characteristics and granulometry of evaporite marl samples in Iran by Farzami et al. (2014), Hatmian Zarami et al. (2014), Shaban et al. (2015), Haqiqhat et al. (2006) Abazade Chavandarqh et.al. (2006) and Samadi Tabrizi et al. (2013) all point to the fact that among the components of clay, silt and sand, the dominant texture of the samples is silty; in addition, carbonate is not the major chemical component of these samples and instead chalk and salt minerals are dominant. All of them have preferred the terms chalky and salty siltstone and mudstone rocks rather than marl. Marls of Iran can be divided into two categories: terrestrial and marine marls. Terrestrial marls have evaporite particles consisting of silt and clay and chemical substances such as calcite, halite, carbonate and sulfate salts, gypsum and anhydrite or one of these minerals. Marl deposits belong to two groups of Paleogene and Neogene marls in Iran. The origin of these marls are mostly salty lakes and they do not contain marine fossils. They are often red to reddish and pea colored. The surface of the soil has the effects of salt particles, salt crust and the effects of puffiness (Puffy Soil). These marls are often younger and belong to the Neogene period. From a geochemical point of view, they have harmful substances for plant growth, and for this reason, they show great sensitivity to various forms of surface, rill, gully and tunnel erosion (Peyrowan et al. 2014). Marine marls consist of clay and silt and calcite chemical substances. They have little or no evaporite minerals with high solubility such as halite, carbonate and sulfate salts, gypsum and anhydrite. Their origin is an ancient marine environment with normal salinity. They are often green in color. These marls in Iran are pre-Neogeneic in terms of age, i.e., Paleozoic and Mesozoic eras with more vegetation, and erosion mainly surfaces and shallow rills (Peyrowan et al. 2014). The terms marl and marlstone are still used imprecisely in geology (Donovan 2006). According to Donovan and Pickerill (2013), more precise lithological terms should be used for these deposits attributed to marl. This point is noticed by Picard (2010) and Alvarez (2009) stating that the interchangeable use of the terms "marl" and "marlstone" has continued into the 21st century. Picard (1953) has been concerned about the imprecise use of the term marl since almost seven decades ago. Prominent authors such as Alvarez (2009) and Tucker (2011) have also faced certain inaccuracies in the definition of marl or marlstones, and this problem still continues with its effects on published texts of geosciences. The two words "marl" and "marl stone" belong to the past, and surely it is time to be more careful in using such words. These terms have had more of an economic aspect than a precise geological scientific term and have been used for the remedial uses of agricultural soils that have been faced with carbonate deficiency (Neuendorf et al. 2005). As such, the nomenclature of marl sediments in Iran and other countries does not have a correct scientific classification, and this problem is clearly visible even in the maps produced by the Geological Survey and Mineral Exploration of Iran. The problems in the nomenclature of marls in previous research and studies are based on the fact that the amount of carbonate and clay are the classification criterion, while many of these deposits, which are among the marls of the detrital kind, have a silty and muddy texture instead of a clay texture. Also, they have a low amount of carbonate; instead, they have a lot of gypsum and salts. Even marls of marine origin, such as the Qom Formation, do not have the range of marl in terms of the amount of carbonate and clay, except for a few cases. The present research was conducted in the marl areas of Tehran province to determine the sedimentological characteristics of the marls in the study area in order to provide a suitable classification method regarding the sedimentological nomenclature of these deposits. Materials & Methods The studied area is located in the south and east of Tehran city, which includes Pakdasht, Varamin, Ivanki and Hassanabad. In general, the region has a dry semi-desert (desert) climate with little annual rainfall. Marl deposits are exposed in the form of hills at the foot of the Alborz highlands and in the southern parts of Tehran and Varamin plains. Due to their high erodibility, these deposits have different forms of surface, rill and gully erosion. Also, they are exposed in the form of single and witness hills during the severe erosion cycle. On the surface of the slopes of these sediments, there are many gypsum crystals, salt crust and sodium fatty stains (slicken slide). Due to the severe soil erosion of these slopes, vegetation is difficult to establish. In the parts where these slopes are covered by Quaternary gravel cover, erosion is less and plant establishment is improved. In this research, different marl units including Pliocene marls, Qom Formation marl and three Upper Red marl members and two Lower Red chalk and salt members were selected for investigation and the following steps were done: 1- Sampling of 99 samples from Varamin, south of Varamin, south of Hassanabad, Ivanki and Pakdasht from Upper Red marl members (M1, M2, M3, Lower Red members (OLg, OLS), Eocene marl units of Kond Formation (Ek), marl unit Pliocene (PlM), marl unit of Qom Formation (OlM) and marl alluviums (QtM); 2- Determining physical characteristics including granulometry through three steps: Sieve analysis, hydrometer and a combination of both; 3- Determining the percentage of carbonate content in marls of the region by acid neutralization method; 4- Determining the rate of salinity of the samples based on the electrical conductivity (EC) criterion. Discussion of Results & Conclusion In this research, with the aim of revising the nomenclature and sedimentary classification of marl deposits from South Varamin, South Hassan Abad, Ivanki and Pakdasht areas, samples were taken from different continental and marine marl units. Granulometry, carbonate percentage and salinity were measured. Sediment classification (Folk 1974) has been used to name the marl deposits of the study area. The samples are plotted in six fields of Folk's triangle, which show predominantly sandy silt, sandy mud, silt, mud, muddy sand and silty sand respectively. The examination of marl samples in the present research shows that the amount of carbonate in the marl samples of marine formations such as the Qom Formation is higher than the continental marl formations and even reaches 68.53%, but in the Neogene continental marl formations of the region including the Lower and Upper Red formations, it ranges from 5.1 to 33.34%, with an average of 20.98%. In these formations, the amount of clay varies in the range of 2.5 to 49%, and the average clay in all samples is 25.49%. The chemical part is not limited to carbonate; chalk and salt are also present in addition to carbonate. Therefore, most of the samples are not classified as marl sediments. The results of the classification method (Haldar and Tisljar 2014) also confirm that the application of marl nomenclature to the studied fine-grained deposits does not have scientific precision and accuracy. Except for one sample of the Kond Formation, which is within the marl class, most of the samples are in the category of "calcite clayey siltstone", clayey calcite siltstone, and “calcite-silt clay” and a few examples are "calcite – silt clay” and clayey- silt limestone. The salinity of the samples was estimated by measuring the electrical conductivity (EC) of an extracted solution. The salinity of the studied marl samples showed that all the mentioned samples have high degrees of EC, which indicates the presence of high salts. The presence of abundant gypsum crystals, white salt crust on the surface of marl, dark spots of sodium fatty color and puffiness of the soil surface (Puffy Soil) are the field evidence of the presence of salts in the chemical composition of the samples. Since the samples are more silty and muddy in terms of texture and have a percentage of carbonate content less than 35% (the threshold for naming marl in the Pettijohn classification) and on the other hand, they are rich in salts, thus the names of “chalky – Salty” siltstone and mudstone is more suitable for the studied marl deposits. Based on the results of the present study, the studied marls physically have more silt than clay, and chemically, more gypsum and salt content than carbonate. This is in line with the findings of other researchers including Abbasi and Amini (2008), Hatmian Zarmi et al. (2012), Shaban et al. (2012) and Farzami et al. (2015). The results of this research are also in line with other researchers including Alvarez (2009) and Neuendorf et al. (2005), Picard (2010), Donovan and Pickerill (2013). Based on the results, it is suggested to revise the nomenclature and classification of the deposits attributed to the marly formations of Iran. The texture of the sediment, the type of mineral composition present in terms of the abundance of calcite or evaporite minerals, as well as the color and marine or continental origin, should be used as criteria, and naming should be done based on the two destructive and chemical components of the sediments with accurate measurements. Abstract Marl is a type of mixed carbonate–silicate sediment and contains clay and carbonate minerals deposited in different environments. The terms marl and marlstone are still imprecisely used in geology. I n this study, to revise the nomenclature and sedimentary classification of marl deposits, 99 samples were taken from different terrestrial and marine marl formations. The texture and percentage of carbonate and salt contents in the marls were measured. According to Folk's classification, the majority of the samples are in the range of sandy silt, sandy mud, silt, muddy sand, and silty sand. Based on the electric conductivity parameter (EC), all samples have a high content of salt and are classified in saline and very saline classes. The results based on the classification method of Haldar and Tisljar also confirm that most of the samples are in the category of "calcite clayey siltstone", clayey calcite siltstone, and “calcite-silt clay” and a few examples are "calcite – silt clay” and clayey- silt limestone, except for one sample of the Kond Formation, which is within the marl field. The main samples are not classified by the Pettijohn method and samples are mostly silty, and muddy and the name chalk-salt siltstone and mudstone were found to be more suitable for the terrestrial marl deposits under investigation in this research. Keywords: Continental marl, Carbonate content, Marine marl, Marl Classification, Salinity Introduction In geology, the term marl refers to chemical-detrital sediments, which have between 35% to 65% carbonate or clay content. Various definitions have been presented by different researchers about marl, despite relatively different descriptions in all of them, and marl nomenclature has been established on carbonate and clay contents. There is no unanimity regarding the nomenclature of marl sediments and many of the definitions are not precise, and in some of them, different origins are mentioned for marl, such as Terzaghi and Peck (1967), exclusively considered marine origin for marl sediments. Mitchell (1993) related these sediments to the biochemical process, while there is a wide range of marl deposits from terrestrial to marine in nature. Investigating the sedimentary characteristics and granulometry of evaporite marl samples in Iran by Farzami et al. (2014), Hatmian Zarami et al. (2014), Shaban et al. (2015), Haqiqhat et al. (2006) Abazade Chavandarqh et.al. (2006) and Samadi Tabrizi et al. (2013) all point to the fact that among the components of clay, silt and sand, the dominant texture of the samples is silty; in addition, carbonate is not the major chemical component of these samples and instead chalk and salt minerals are dominant. All of them have preferred the terms chalky and salty siltstone and mudstone rocks rather than marl. Marls of Iran can be divided into two categories: terrestrial and marine marls. Terrestrial marls have evaporite particles consisting of silt and clay and chemical substances such as calcite, halite, carbonate and sulfate salts, gypsum and anhydrite or one of these minerals. Marl deposits belong to two groups of Paleogene and Neogene marls in Iran. The origin of these marls are mostly salty lakes and they do not contain marine fossils. They are often red to reddish and pea colored. The surface of the soil has the effects of salt particles, salt crust and the effects of puffiness (Puffy Soil). These marls are often younger and belong to the Neogene period. From a geochemical point of view, they have harmful substances for plant growth, and for this reason, they show great sensitivity to various forms of surface, rill, gully and tunnel erosion (Peyrowan et al. 2014). Marine marls consist of clay and silt and calcite chemical substances. They have little or no evaporite minerals with high solubility such as halite, carbonate and sulfate salts, gypsum and anhydrite. Their origin is an ancient marine environment with normal salinity. They are often green in color. These marls in Iran are pre-Neogeneic in terms of age, i.e., Paleozoic and Mesozoic eras with more vegetation, and erosion mainly surfaces and shallow rills (Peyrowan et al. 2014). The terms marl and marlstone are still used imprecisely in geology (Donovan 2006). According to Donovan and Pickerill (2013), more precise lithological terms should be used for these deposits attributed to marl. This point is noticed by Picard (2010) and Alvarez (2009) stating that the interchangeable use of the terms "marl" and "marlstone" has continued into the 21st century. Picard (1953) has been concerned about the imprecise use of the term marl since almost seven decades ago. Prominent authors such as Alvarez (2009) and Tucker (2011) have also faced certain inaccuracies in the definition of marl or marlstones, and this problem still continues with its effects on published texts of geosciences. The two words "marl" and "marl stone" belong to the past, and surely it is time to be more careful in using such words. These terms have had more of an economic aspect than a precise geological scientific term and have been used for the remedial uses of agricultural soils that have been faced with carbonate deficiency (Neuendorf et al. 2005). As such, the nomenclature of marl sediments in Iran and other countries does not have a correct scientific classification, and this problem is clearly visible even in the maps produced by the Geological Survey and Mineral Exploration of Iran. The problems in the nomenclature of marls in previous research and studies are based on the fact that the amount of carbonate and clay are the classification criterion, while many of these deposits, which are among the marls of the detrital kind, have a silty and muddy texture instead of a clay texture. Also, they have a low amount of carbonate; instead, they have a lot of gypsum and salts. Even marls of marine origin, such as the Qom Formation, do not have the range of marl in terms of the amount of carbonate and clay, except for a few cases. The present research was conducted in the marl areas of Tehran province to determine the sedimentological characteristics of the marls in the study area in order to provide a suitable classification method regarding the sedimentological nomenclature of these deposits. Materials & Methods The studied area is located in the south and east of Tehran city, which includes Pakdasht, Varamin, Ivanki and Hassanabad. In general, the region has a dry semi-desert (desert) climate with little annual rainfall. Marl deposits are exposed in the form of hills at the foot of the Alborz highlands and in the southern parts of Tehran and Varamin plains. Due to their high erodibility, these deposits have different forms of surface, rill and gully erosion. Also, they are exposed in the form of single and witness hills during the severe erosion cycle. On the surface of the slopes of these sediments, there are many gypsum crystals, salt crust and sodium fatty stains (slicken slide). Due to the severe soil erosion of these slopes, vegetation is difficult to establish. In the parts where these slopes are covered by Quaternary gravel cover, erosion is less and plant establishment is improved. In this research, different marl units including Pliocene marls, Qom Formation marl and three Upper Red marl members and two Lower Red chalk and salt members were selected for investigation and the following steps were done: 1- Sampling of 99 samples from Varamin, south of Varamin, south of Hassanabad, Ivanki and Pakdasht from Upper Red marl members (M1, M2, M3, Lower Red members (OLg, OLS), Eocene marl units of Kond Formation (Ek), marl unit Pliocene (PlM), marl unit of Qom Formation (OlM) and marl alluviums (QtM); 2- Determining physical characteristics including granulometry through three steps: Sieve analysis, hydrometer and a combination of both; 3- Determining the percentage of carbonate content in marls of the region by acid neutralization method; 4- Determining the rate of salinity of the samples based on the electrical conductivity (EC) criterion. Discussion of Results & Conclusion In this research, with the aim of revising the nomenclature and sedimentary classification of marl deposits from South Varamin, South Hassan Abad, Ivanki and Pakdasht areas, samples were taken from different continental and marine marl units. Granulometry, carbonate percentage and salinity were measured. Sediment classification (Folk 1974) has been used to name the marl deposits of the study area. The samples are plotted in six fields of Folk's triangle, which show predominantly sandy silt, sandy mud, silt, mud, muddy sand and silty sand respectively. The examination of marl samples in the present research shows that the amount of carbonate in the marl samples of marine formations such as the Qom Formation is higher than the continental marl formations and even reaches 68.53%, but in the Neogene continental marl formations of the region including the Lower and Upper Red formations, it ranges from 5.1 to 33.34%, with an average of 20.98%. In these formations, the amount of clay varies in the range of 2.5 to 49%, and the average clay in all samples is 25.49%. The chemical part is not limited to carbonate; chalk and salt are also present in addition to carbonate. Therefore, most of the samples are not classified as marl sediments. The results of the classification method (Haldar and Tisljar 2014) also confirm that the application of marl nomenclature to the studied fine-grained deposits does not have scientific precision and accuracy. Except for one sample of the Kond Formation, which is within the marl class, most of the samples are in the category of "calcite clayey siltstone", clayey calcite siltstone, and “calcite-silt clay” and a few examples are "calcite – silt clay” and clayey- silt limestone. The salinity of the samples was estimated by measuring the electrical conductivity (EC) of an extracted solution. The salinity of the studied marl samples showed that all the mentioned samples have high degrees of EC, which indicates the presence of high salts. The presence of abundant gypsum crystals, white salt crust on the surface of marl, dark spots of sodium fatty color and puffiness of the soil surface (Puffy Soil) are the field evidence of the presence of salts in the chemical composition of the samples. Since the samples are more silty and muddy in terms of texture and have a percentage of carbonate content less than 35% (the threshold for naming marl in the Pettijohn classification) and on the other hand, they are rich in salts, thus the names of “chalky – Salty” siltstone and mudstone is more suitable for the studied marl deposits. Based on the results of the present study, the studied marls physically have more silt than clay, and chemically, more gypsum and salt content than carbonate. This is in line with the findings of other researchers including Abbasi and Amini (2008), Hatmian Zarmi et al. (2012), Shaban et al. (2012) and Farzami et al. (2015). The results of this research are also in line with other researchers including Alvarez (2009) and Neuendorf et al. (2005), Picard (2010), Donovan and Pickerill (2013). Based on the results, it is suggested to revise the nomenclature and classification of the deposits attributed to the marly formations of Iran. The texture of the sediment, the type of mineral composition present in terms of the abundance of calcite or evaporite minerals, as well as the color and marine or continental origin, should be used as criteria, and naming should be done based on the two destructive and chemical components of the sediments with accurate measurements.

https://jssr.ui.ac.ir/article_27107_63ed50370182837eb8c004f42b6d77e4.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 38 3 2022 09 23 A workflow to the identification of key sequence stratigraphic surfaces from GR log interpretation; Case studies of the Sarvak and Fahliyan formations in the Abadan Plain and Northwest of the Persian Gulf A workflow to the identification of key sequence stratigraphic surfaces from GR log interpretation; Case studies of the Sarvak and Fahliyan formations in the Abadan Plain and Northwest of the Persian Gulf 113 144 27151 10.22108/jssr.2022.135581.1246 FA Ali Imandoust MSc in Stratigraphy and Paleontology, Department of Geosciences, Kish Petroleum Engineering, Tehran, Iran Omid Reza Salmian MSc in Petroleum Exploration Engineering, Faculty of Mining Engineering, University of Tehran, Tehran, Iran Ali Asaadi Ph.D. in Petroleum Geology, Tehran Energy Consultants (TEC), Tehran, Iran Journal Article 2022 11 02 Abstract Gamma Ray (GR) log is widely used to overcome the lack of continuous core samples and thin sections in many subsurface reservoirs, significantly reducing the uncertainty of presenting a robust sequence stratigraphic framework. The Lower Cretaceous Fahliyan Formation and Late Cretaceous Sarvak carbonates host important hydrocarbon accumulations in SW Iran and the Persian Gulf. This study addresses the application of Gamma Ray Dynamic Integrated Prediction Error Filter Analysis (GR D-INPEFA) and Normalized Cumulative Gamma Deviation Log (NCGDL) curves to discriminate and correlate sequences of the studied carbonates in two giant oil fields in the Abadan Plain and Northwestern Persian Gulf. In the first stage, depositional sequences were differentiated using the results from the core description and petrographic analysis. In this respect, four and three third-order depositional sequences were identified in the Sarvak and Fahliyan formations respectively. In the second stage, according to the turning points of the D-INPEFA and NCGDL curves, they were picked as positive or negative breaks in all studied wells. Based on calibrating the results from the analysis of D-INPEFA curve with the identified depositional sequences, positive changes (PB) occur at sequence boundaries (SB) and negative trend (NB) changes are associated with maximum flooding surface (MFS). The trend of changes in the NCGDL curve compared to the D-INPEFA curve is quite opposite. In other words, Positive Surfaces (PS) correspond to MFS and Negative Surfaces (NS) occur at SB. The results demonstrate that the proposed integrated method is feasible and effective to identify sequence stratigraphic key surfaces in similar carbonate and siliciclastic reservoirs of Iran. Keywords: Sarvak, Fahliyan, Gamma Ray Log, Sequence Stratigraphy, Stratigraphic Key Surfaces Introduction The distribution of various components of the petroleum systems (source, reservoir and cap rocks), generally has a close relationship with the sequence stratigraphy pattern (Parvin et al. 2019; Makled et al. 2020). Data from various sources with different scales, such as microscopic thin sections study, cores interpretation, petrophysical log signature, and seismic sections, can be employed in sequence stratigraphic investigations (Van Buchem et al. 2011; Kadkhodaie and Rezaee 2017; Tavakoli 2017; Guo et al. 2021; Yong et al. 2021; Hassan et al. 2022). The identification of key sequence stratigraphic surfaces is typically done accurately by information and results provided by cores and microscopic thin sections study. Nevertheless, cores are only available in limited and sparse wells as a discontinuous nature due to the high cost, lengthy process, and limited cores preparation (Hassan et al. 2022). Hence, it is crucial to identify a method that, in conjunction with the core data, can provide a precise and continuous comprehension of the sequence stratigraphic framework at the well scale. Petrophysical well log data especially GR log has long been used in sequence stratigraphic interpretation (Catuneanu 2006; 2017). Due to its low impact from environmental factors, stability against diagenesis processes, and availability in the majority of drilled wells in a field, the GR log is effectively used in identifying sequences and interpreting key sequence stratigraphic surfaces (Moghaddasi et al. 2020; Falahatkhah et al. 2021). The possibility of a comprehensive understanding of the relationship between key sequence stratigraphic surfaces, and a numerical interpretation of the GR log in recent studies is highlighted (Falahatkhah et al. 2021). The curve of D-INPEFA and NCGDL are effective in identifying and matching key sequence stratigraphic surfaces (Behdad 2019; Mayhoub et al. 2019; De Jong et al. 2020; Moghaddasi et al. 2020; Khalili et al. 2021; Yong et al. 2021; Kassem et al. 2022). In this study, the application of GR D-INPEFA and NCGDL curves to discriminate and correlate the sequence surfaces of the Sarvak and Fahliyan formations in two giant oil fields in the Abadan plain and Northwestern Persian Gulf was investigated. This study was conducted to reveal the response of GR D-INPEFA and NCGDL curves to key sequence stratigraphic surfaces including SB, MFS, and systems tracts. Material & Methods By integrating the results of core intervals description, thin sections study and GR well log data from the Sarvak and Fahliyan formations in two giant oil fields in the Abadan Plain and Northwestern Persian Gulf, it was possible to identify and present sequence stratigraphic framework. For sequence stratigraphic analysis in this study, we employed the van Wagoner model (Van Wagoner et al. 1990). In this model, a depositional sequence is discriminated by identifying two key surfaces including SB and MFS, as well as the transgressive system tract (TST) and high-stand system tract (HST). The integration of petrography analysis and core descriptions was employed to identify the main facies in the studied carbonate succession. Afterward, SB and MFS have been interpreted by integrating interpreted facies and main diagenesis features related to disconformity surfaces. Finally, the identified depositional sequences based on geological studies were compared to the discriminated turning point in cyclostratigraphy via INPEFA and NCGDL curves. Ultimately, the efficiency of this numerical method was determined based on correspondence and agreement of the results with the discriminating of the depositional sequences via geological interpretation. Discussion of Results & Conclusion In the D-INPEFA curves, the upward trend is called the PB and the downward trend is called NB. The positive trend represents transgressive and the negative trend represents regressive. The positive changes in PB occur at SB and negative trend changes in NB show MSF. On the other hand, the trend of the NCGDL curve completely shows the opposite trend of the D-INPEFA curve. The turning points of the NCGDL curve, including PS and NS, correspond to some levels of maximum inundation and SBs, respectively. The following findings were obtained after investigating the sequence stratigraphic framework of the Sarvak and Fahliyan formations in two giants of fields: 1- Four and three third-order sequences were identified in the Sarvak and Fahliyan formations respectively, based on facies interpretation and the pattern of shallowing and deepening facies trends. The disconformity surfaces which are recognized as an SB are discriminated by some evidence, including karstification and brecciation. 2- In general, GR log interpretation and calculating INPEFA and NCGDL curves show that PB and NS occur at SB, NB and PS show MFS. As a result, such picked breaks and surfaces are timelines that can be calibrated with facies changes and key sequence stratigraphic surfaces and correlation in the field scale. 3- The relationship between the turning points of the D-INPEFA and NCGDL curves with sequence stratigraphic surfaces is not absolute, and in some cases, this relationship can be ambiguous, inverse, or unrelated. In other words, to reduce the uncertainty in the presenting sequence stratigraphy correlation with these curves, the sequences should first be identified through the results of the direct data including core and thin section, and use these curves for correlation after presenting the sequence framework. Abstract Gamma Ray (GR) log is widely used to overcome the lack of continuous core samples and thin sections in many subsurface reservoirs, significantly reducing the uncertainty of presenting a robust sequence stratigraphic framework. The Lower Cretaceous Fahliyan Formation and Late Cretaceous Sarvak carbonates host important hydrocarbon accumulations in SW Iran and the Persian Gulf. This study addresses the application of Gamma Ray Dynamic Integrated Prediction Error Filter Analysis (GR D-INPEFA) and Normalized Cumulative Gamma Deviation Log (NCGDL) curves to discriminate and correlate sequences of the studied carbonates in two giant oil fields in the Abadan Plain and Northwestern Persian Gulf. In the first stage, depositional sequences were differentiated using the results from the core description and petrographic analysis. In this respect, four and three third-order depositional sequences were identified in the Sarvak and Fahliyan formations respectively. In the second stage, according to the turning points of the D-INPEFA and NCGDL curves, they were picked as positive or negative breaks in all studied wells. Based on calibrating the results from the analysis of D-INPEFA curve with the identified depositional sequences, positive changes (PB) occur at sequence boundaries (SB) and negative trend (NB) changes are associated with maximum flooding surface (MFS). The trend of changes in the NCGDL curve compared to the D-INPEFA curve is quite opposite. In other words, Positive Surfaces (PS) correspond to MFS and Negative Surfaces (NS) occur at SB. The results demonstrate that the proposed integrated method is feasible and effective to identify sequence stratigraphic key surfaces in similar carbonate and siliciclastic reservoirs of Iran. Keywords: Sarvak, Fahliyan, Gamma Ray Log, Sequence Stratigraphy, Stratigraphic Key Surfaces Introduction The distribution of various components of the petroleum systems (source, reservoir and cap rocks), generally has a close relationship with the sequence stratigraphy pattern (Parvin et al. 2019; Makled et al. 2020). Data from various sources with different scales, such as microscopic thin sections study, cores interpretation, petrophysical log signature, and seismic sections, can be employed in sequence stratigraphic investigations (Van Buchem et al. 2011; Kadkhodaie and Rezaee 2017; Tavakoli 2017; Guo et al. 2021; Yong et al. 2021; Hassan et al. 2022). The identification of key sequence stratigraphic surfaces is typically done accurately by information and results provided by cores and microscopic thin sections study. Nevertheless, cores are only available in limited and sparse wells as a discontinuous nature due to the high cost, lengthy process, and limited cores preparation (Hassan et al. 2022). Hence, it is crucial to identify a method that, in conjunction with the core data, can provide a precise and continuous comprehension of the sequence stratigraphic framework at the well scale. Petrophysical well log data especially GR log has long been used in sequence stratigraphic interpretation (Catuneanu 2006; 2017). Due to its low impact from environmental factors, stability against diagenesis processes, and availability in the majority of drilled wells in a field, the GR log is effectively used in identifying sequences and interpreting key sequence stratigraphic surfaces (Moghaddasi et al. 2020; Falahatkhah et al. 2021). The possibility of a comprehensive understanding of the relationship between key sequence stratigraphic surfaces, and a numerical interpretation of the GR log in recent studies is highlighted (Falahatkhah et al. 2021). The curve of D-INPEFA and NCGDL are effective in identifying and matching key sequence stratigraphic surfaces (Behdad 2019; Mayhoub et al. 2019; De Jong et al. 2020; Moghaddasi et al. 2020; Khalili et al. 2021; Yong et al. 2021; Kassem et al. 2022). In this study, the application of GR D-INPEFA and NCGDL curves to discriminate and correlate the sequence surfaces of the Sarvak and Fahliyan formations in two giant oil fields in the Abadan plain and Northwestern Persian Gulf was investigated. This study was conducted to reveal the response of GR D-INPEFA and NCGDL curves to key sequence stratigraphic surfaces including SB, MFS, and systems tracts. Material & Methods By integrating the results of core intervals description, thin sections study and GR well log data from the Sarvak and Fahliyan formations in two giant oil fields in the Abadan Plain and Northwestern Persian Gulf, it was possible to identify and present sequence stratigraphic framework. For sequence stratigraphic analysis in this study, we employed the van Wagoner model (Van Wagoner et al. 1990). In this model, a depositional sequence is discriminated by identifying two key surfaces including SB and MFS, as well as the transgressive system tract (TST) and high-stand system tract (HST). The integration of petrography analysis and core descriptions was employed to identify the main facies in the studied carbonate succession. Afterward, SB and MFS have been interpreted by integrating interpreted facies and main diagenesis features related to disconformity surfaces. Finally, the identified depositional sequences based on geological studies were compared to the discriminated turning point in cyclostratigraphy via INPEFA and NCGDL curves. Ultimately, the efficiency of this numerical method was determined based on correspondence and agreement of the results with the discriminating of the depositional sequences via geological interpretation. Discussion of Results & Conclusion In the D-INPEFA curves, the upward trend is called the PB and the downward trend is called NB. The positive trend represents transgressive and the negative trend represents regressive. The positive changes in PB occur at SB and negative trend changes in NB show MSF. On the other hand, the trend of the NCGDL curve completely shows the opposite trend of the D-INPEFA curve. The turning points of the NCGDL curve, including PS and NS, correspond to some levels of maximum inundation and SBs, respectively. The following findings were obtained after investigating the sequence stratigraphic framework of the Sarvak and Fahliyan formations in two giants of fields: 1- Four and three third-order sequences were identified in the Sarvak and Fahliyan formations respectively, based on facies interpretation and the pattern of shallowing and deepening facies trends. The disconformity surfaces which are recognized as an SB are discriminated by some evidence, including karstification and brecciation. 2- In general, GR log interpretation and calculating INPEFA and NCGDL curves show that PB and NS occur at SB, NB and PS show MFS. As a result, such picked breaks and surfaces are timelines that can be calibrated with facies changes and key sequence stratigraphic surfaces and correlation in the field scale. 3- The relationship between the turning points of the D-INPEFA and NCGDL curves with sequence stratigraphic surfaces is not absolute, and in some cases, this relationship can be ambiguous, inverse, or unrelated. In other words, to reduce the uncertainty in the presenting sequence stratigraphy correlation with these curves, the sequences should first be identified through the results of the direct data including core and thin section, and use these curves for correlation after presenting the sequence framework.

https://jssr.ui.ac.ir/article_27151_414cbc13c350e86c08189b75160c520a.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 38 3 2022 09 23 Identification and description of the upper Neogene palustrine sediments in the east of Damghan Identification and description of the upper Neogene palustrine sediments in the east of Damghan 145 162 27234 10.22108/jssr.2023.136090.1249 FA Kosar Fathalizadeh Master of Science, School of Earth Sciences, Damghan University, Damghan, Iran Elahe Zarei Assistant Professor, School of Earth Sciences, Damghan University, Damghan, Iran Mehdi Sarfi Assistant Professor, School of Earth Sciences, Damghan University, Damghan, Iran Journal Article 2022 12 17 Abstract The studied area is a silty-clayey sedimentary landform, which is located on the border of Alborz and Central Iran sedimentary-structural units. It has 13 km long in the vicinity of the road Damghan to Shahroud. An integration of sedimentological and palynological studies is used for palaeoenvironmental interpretation, origin investigation, and age dating of the landform sediments. The presence of transparent and angular quartzes and unstable minerals and the abundance of organic matter in the landform sediments indicate an aquatic environment in which a series of erosion events to sedimentation has taken place in a short period of time. A combination of sedimentological investigations and palynological studies such as the organic matter preservation factors and the presence of index dinocysts such as Operculodinium cf. eiricianum and Bitectatodinium tepikiense which are characteristic of the shallow aqueous environment, a palustrine environment with brackish water in with an age of Late Neogene is assigned for the studied sediments. This relatively vast aqueous environment was related to the Haj Ali Qoli salt playa (Chah Jam playa) in the south of the studied region. These sediments were developed on a mud flat zone on the northern margin of this playa. Uplifting and exposure of this sedimentary landform could be due to the tectonic activity of the region and the movement of the left-lateral strike-slip of the eastern part of the Damghan Fault. Keywords: Palaeoenvironment condition, Palustrine, Palynomorph, Late Neogene Introduction Palynology and sedimentology are common and applied methods for paleoenvironment interpretation, especially for Neogene and younger sediments. From the combination of palynological and sedimentology studies, useful information on palaeoclimate and palaeoenvironment is available to researchers in the fields of archaeology, palaeogeography, etc. (Asikainen et al. 2007; Head 1996). The main aim of this study is to identify depositional palaeoenvironments in detail and investigate the origin and age of landform sediments. The studied area is located on the border between Alborz structural state and Central Iran, approximately 30 km east of Damghan (coordinates with E 54° 36΄09 ˝ to 54° 45΄37˝ and N 36° 15΄43 ˝ to N 36° 16΄ 26 ˝). Material & Methods Field and laboratory methods were used in this research. After the field studies, samples were collected from three study stations for palynological, sedimentological and microfacies studies. These samples were prepared in the palynology laboratory. The preparation method of Traverse (2007) was used. Cold hydrochloric (20 %) and hydrofluoric acids were used to dissolve carbonate sand silicates, respectively. The residue was neutralized and centrifuged in ZnCl2 with specific gravity (1.9 g/cm3). The remaining residue was then sieved through a 20 µm nylon sieve prior to mounting on slides. A count of 500 particles was recorded for each sample using transmitted light microscopy as is necessary for the differentiation of palyofacies type and the palaeoenvironmental interpretations (Tyson 1995). Discussion of Results & Conclusions A combined investigation of sedimentary and palynology was performed on a silty-clayey sedimentary landform, which is located on the border between the Alborz structural state and central Iran to define its palaeoenvironment and investigation of the origin as well as the age of landform sediments. Sedimentology results: The presence of transparent and angular quartzes, unstable minerals such as feldspar, muscovite and the abundance of organic matter in the landform sediments indicate an aquatic environment in which a series of erosion events to sedimentation has taken place in a short period of time. The vertical fresh profiles were mostly composed of a mixture of distal alluvial and palustrine facies (the latter is particularly dominated by mottling colors and the dominance of carbonate muds) (Mángano et al. 1994). Palynology results: Organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come from the feces and remains of organisms such as plants and animals. Terrestrial palynomorphs are the most abundant and diverse group of palynomorphs in the study area, and the largest percentage of them are pollens. Among the studied pollens, the most pollen belongs to Poaceae (55%), Pinus (25%), Quercoide (15%), Salix (3%) and Glochidion (2%). Based on the presence of some index dinoflagellate species such as Operculodinium cf. eiricianum and Bitectatodinium tepikiense and comparing it with the world standard biozones of Williams et al. (2004), the age range of Late Miocene to Pliocene can be considered for the landform sediments (Head 1996; Hennissen et al. 2014). The presence of marine dinoflagellate cysts such as Bitectatodinium tepikiense is most probably because of the erosion of extensive outcrops of the Late Miocene to Pliocene marine deposits (Head 1994). Dinocysts maybe were simply reworked from older formations. But it is not impossible that during exceptional short-lived episodes of highstands lake in the Pliocene, we could have some of these dinoflagellates (Operculodinium sp.) because the hypersaline lake water or brine groundwater could have been diluted into the brackish water conditions. Organic matter preservation (Lability) factors; palynomacerals derived from higher plants and generally become less abundant, smaller, and more oxidized in a distal direction. Palynomacerals are mostly transported the same way as silt or sand and are thus preferentially deposited in such sediments (nearshore, higher energy or turbidites) (Waveren and Vischer 1994; Zonneveld and Lange 1997). Palynomacerals can be translucent or opaque. A higher percentage of brown palynomacerals is usually found close to the fluvial source, prodelta facies or estuaries may be very dark in color due to oxidation or selective degradation (Van der Zwan 1990; Batten 1996; Bombardiere and Gorin 2000). Opaque palynomacerals can be produced by either the oxidation of brown phytoclasts during prolonged transport or even post-depositionally. Therefore, the ratio of brown to opaque palynomacerals decreases in section number one and two because the brown palynomacerals is lost by selective degradation in distal alluvial and palustrine facies (Waveren and Vischer 1994; Zonneveld and Lange 1997). The ratio of transparent to opaque amorphous organic matter (TAOM/OPAOM); The Amorphous organic matter consists of all particulate organic components that appear structureless at the scale of light microscopy. The main sources of AOM are the degradation of phytoplankton and terrestrial organic matter by heterotrophic bacteria (Tyson 1995; Mendonça Filho et al. 2010). Amorphous materials are divided into two categories: transparent and opaque. The fluorescent intensity of the AOM is controlled by the redox conditions under which it was deposited (Waveren and Vischer 1994; Zonneveld and Lange 1997). An increase in the brown palynomacerals and fluorescent amorphous organic matter in section 3, indicated the proximity of the depositional site to a coastal conditions in a stagnant environment in the palustrine. Combining all information mentioned above, the depositional environment is most probably a transitional fluvial-hypersaline lake environment. The modern analog of such deposits is currently found in the vicinity of the active playas of central Iran including the Haj Ali Qoli playa in the south of Damghan. This interpretation is supported by sedimentological and paleontological data. But the most important question arises where was the studied area located in this palaeolake and why did it rise. The Alborz Mountains in the north of the Iranian Plateau are an active tectonic region with numerous faults. The activity of faults in the region has been studied and investigated by various researchers in the field of geosciences (Berberian 1976; Krinsley 1970). Fault analysis in the region shows that the studied landform is located exactly on the eastern section of the North Damghan Fault. This fault is located ten kilometers north of Damghan city and it represents a Pleistocene to Holocene fault due to the cutting of the same age deposits. The studied landform has been uplifted due to the tectonic activity of the region and the movement of the left-lateral strike-slip of the eastern part of the Damghan Fault (Berberian 1976; Krinsley 1970). The neotectonic activity caused the later upward displacement of those older fluvial-lacustrine/wetland facies to current altitudes creating those beautiful outcrops. Abstract The studied area is a silty-clayey sedimentary landform, which is located on the border of Alborz and Central Iran sedimentary-structural units. It has 13 km long in the vicinity of the road Damghan to Shahroud. An integration of sedimentological and palynological studies is used for palaeoenvironmental interpretation, origin investigation, and age dating of the landform sediments. The presence of transparent and angular quartzes and unstable minerals and the abundance of organic matter in the landform sediments indicate an aquatic environment in which a series of erosion events to sedimentation has taken place in a short period of time. A combination of sedimentological investigations and palynological studies such as the organic matter preservation factors and the presence of index dinocysts such as Operculodinium cf. eiricianum and Bitectatodinium tepikiense which are characteristic of the shallow aqueous environment, a palustrine environment with brackish water in with an age of Late Neogene is assigned for the studied sediments. This relatively vast aqueous environment was related to the Haj Ali Qoli salt playa (Chah Jam playa) in the south of the studied region. These sediments were developed on a mud flat zone on the northern margin of this playa. Uplifting and exposure of this sedimentary landform could be due to the tectonic activity of the region and the movement of the left-lateral strike-slip of the eastern part of the Damghan Fault. Keywords: Palaeoenvironment condition, Palustrine, Palynomorph, Late Neogene Introduction Palynology and sedimentology are common and applied methods for paleoenvironment interpretation, especially for Neogene and younger sediments. From the combination of palynological and sedimentology studies, useful information on palaeoclimate and palaeoenvironment is available to researchers in the fields of archaeology, palaeogeography, etc. (Asikainen et al. 2007; Head 1996). The main aim of this study is to identify depositional palaeoenvironments in detail and investigate the origin and age of landform sediments. The studied area is located on the border between Alborz structural state and Central Iran, approximately 30 km east of Damghan (coordinates with E 54° 36΄09 ˝ to 54° 45΄37˝ and N 36° 15΄43 ˝ to N 36° 16΄ 26 ˝). Material & Methods Field and laboratory methods were used in this research. After the field studies, samples were collected from three study stations for palynological, sedimentological and microfacies studies. These samples were prepared in the palynology laboratory. The preparation method of Traverse (2007) was used. Cold hydrochloric (20 %) and hydrofluoric acids were used to dissolve carbonate sand silicates, respectively. The residue was neutralized and centrifuged in ZnCl2 with specific gravity (1.9 g/cm3). The remaining residue was then sieved through a 20 µm nylon sieve prior to mounting on slides. A count of 500 particles was recorded for each sample using transmitted light microscopy as is necessary for the differentiation of palyofacies type and the palaeoenvironmental interpretations (Tyson 1995). Discussion of Results & Conclusions A combined investigation of sedimentary and palynology was performed on a silty-clayey sedimentary landform, which is located on the border between the Alborz structural state and central Iran to define its palaeoenvironment and investigation of the origin as well as the age of landform sediments. Sedimentology results: The presence of transparent and angular quartzes, unstable minerals such as feldspar, muscovite and the abundance of organic matter in the landform sediments indicate an aquatic environment in which a series of erosion events to sedimentation has taken place in a short period of time. The vertical fresh profiles were mostly composed of a mixture of distal alluvial and palustrine facies (the latter is particularly dominated by mottling colors and the dominance of carbonate muds) (Mángano et al. 1994). Palynology results: Organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come from the feces and remains of organisms such as plants and animals. Terrestrial palynomorphs are the most abundant and diverse group of palynomorphs in the study area, and the largest percentage of them are pollens. Among the studied pollens, the most pollen belongs to Poaceae (55%), Pinus (25%), Quercoide (15%), Salix (3%) and Glochidion (2%). Based on the presence of some index dinoflagellate species such as Operculodinium cf. eiricianum and Bitectatodinium tepikiense and comparing it with the world standard biozones of Williams et al. (2004), the age range of Late Miocene to Pliocene can be considered for the landform sediments (Head 1996; Hennissen et al. 2014). The presence of marine dinoflagellate cysts such as Bitectatodinium tepikiense is most probably because of the erosion of extensive outcrops of the Late Miocene to Pliocene marine deposits (Head 1994). Dinocysts maybe were simply reworked from older formations. But it is not impossible that during exceptional short-lived episodes of highstands lake in the Pliocene, we could have some of these dinoflagellates (Operculodinium sp.) because the hypersaline lake water or brine groundwater could have been diluted into the brackish water conditions. Organic matter preservation (Lability) factors; palynomacerals derived from higher plants and generally become less abundant, smaller, and more oxidized in a distal direction. Palynomacerals are mostly transported the same way as silt or sand and are thus preferentially deposited in such sediments (nearshore, higher energy or turbidites) (Waveren and Vischer 1994; Zonneveld and Lange 1997). Palynomacerals can be translucent or opaque. A higher percentage of brown palynomacerals is usually found close to the fluvial source, prodelta facies or estuaries may be very dark in color due to oxidation or selective degradation (Van der Zwan 1990; Batten 1996; Bombardiere and Gorin 2000). Opaque palynomacerals can be produced by either the oxidation of brown phytoclasts during prolonged transport or even post-depositionally. Therefore, the ratio of brown to opaque palynomacerals decreases in section number one and two because the brown palynomacerals is lost by selective degradation in distal alluvial and palustrine facies (Waveren and Vischer 1994; Zonneveld and Lange 1997). The ratio of transparent to opaque amorphous organic matter (TAOM/OPAOM); The Amorphous organic matter consists of all particulate organic components that appear structureless at the scale of light microscopy. The main sources of AOM are the degradation of phytoplankton and terrestrial organic matter by heterotrophic bacteria (Tyson 1995; Mendonça Filho et al. 2010). Amorphous materials are divided into two categories: transparent and opaque. The fluorescent intensity of the AOM is controlled by the redox conditions under which it was deposited (Waveren and Vischer 1994; Zonneveld and Lange 1997). An increase in the brown palynomacerals and fluorescent amorphous organic matter in section 3, indicated the proximity of the depositional site to a coastal conditions in a stagnant environment in the palustrine. Combining all information mentioned above, the depositional environment is most probably a transitional fluvial-hypersaline lake environment. The modern analog of such deposits is currently found in the vicinity of the active playas of central Iran including the Haj Ali Qoli playa in the south of Damghan. This interpretation is supported by sedimentological and paleontological data. But the most important question arises where was the studied area located in this palaeolake and why did it rise. The Alborz Mountains in the north of the Iranian Plateau are an active tectonic region with numerous faults. The activity of faults in the region has been studied and investigated by various researchers in the field of geosciences (Berberian 1976; Krinsley 1970). Fault analysis in the region shows that the studied landform is located exactly on the eastern section of the North Damghan Fault. This fault is located ten kilometers north of Damghan city and it represents a Pleistocene to Holocene fault due to the cutting of the same age deposits. The studied landform has been uplifted due to the tectonic activity of the region and the movement of the left-lateral strike-slip of the eastern part of the Damghan Fault (Berberian 1976; Krinsley 1970). The neotectonic activity caused the later upward displacement of those older fluvial-lacustrine/wetland facies to current altitudes creating those beautiful outcrops.

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