University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 Journal of Stratigraphy and Sedimentology Researches , Vol. 39, Issue 3, No. 92, Autumn 2023 Journal of Stratigraphy and Sedimentology Researches , Vol. 39, Issue 3, No. 92, Autumn 2023 28848 10.22108/jssr.2023.28848 FA Journal Article 2024 10 20 https://jssr.ui.ac.ir/article_28848_675c040350ffdb061ec7cad5fe39cdf3.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 Organic facies and organic petrographic characteristics of the Pabdeh Formation in the Kilur-Karim Oilfield, SW Iran Organic facies and organic petrographic characteristics of the Pabdeh Formation in the Kilur-Karim Oilfield, SW Iran 1 14 28056 10.22108/jssr.2023.139363.1270 FA Sara Amiri Department of Petroleum Geology and Sedimentary basins, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Majid Alipour Department of Petroleum Geology and Sedimentary Basins, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Journal Article 2023 10 05 Abstract In this research, the organic matter present in the Pabdeh Formation is investigated using Rock-Eval pyrolysis and organic petrographic techniques. For this purpose, a total of 22 cutting samples were collected at 50-meter intervals from 3 wells in the Kilur-Karim Oilfield. According to hydrogen index (HI) versus maximum temperature (Tmax) diagrams, the Pabdeh Formation in this oilfield contains type II/III kerogen, with thermal maturity corresponding to the early stages of hydrocarbon generation. In general, according to the Rock-Eval pyrolysis data, the middle parts of the Pabdeh Formation show a higher potential for hydrocarbon generation. On the other hand, organic petrography results show that samples from the middle parts of the Pabdeh Formation contain high amounts of amorphous organic matter along with solid bitumen. In addition, the upper and lower parts of this formation contain lower amounts of organic matter and mainly have abundant fossil content. A combination of results from two analytical techniques reveals that the Pabdeh Formation in the Kilur-Karim Oilfield contains a relatively organic-rich zone in the middle, which is surrounded by organic-poor facies above and below. These results can be helpful for a better understanding of the organic facies and palaeodepositional environments of the Pabdeh Formation in the study area. Keywords: Pabdeh Formation, Organic petrography, Organic facies, Kilur-Karim Oilfield Introduction In this study, the organic geochemical characteristics of the Pabdeh Formation in the Kilur-Karim Oilfield have been investigated using the Rock-Eval pyrolysis and organic petrography methods. The Kilur-Karim Oilfield is one of the hydrocarbon fields located in the southern Dezful Embayment, which is located in the vicinity of the Bibi Hakimeh Oilfield about 40 km north of the Persian Gulf. This oilfield generally has a northwest-southeast trend and is separated from the Bibi Hakimeh structure by a thrust from the north side. It is worth mentioning that in previous studies, the organic geochemistry of the Pabdeh Formation has been investigated using different geochemical techniques (such as Rock-Eval pyrolysis and gas chromatography-mass spectrometry analyses) and also modeling techniques (Alizadeh et al. 2012, 2020; Karimi et al. 2016; Vatandoust et al. 2020; Safaei-Farouji et al. 2021). However, microscopic studies have not been conducted on this formation so far. Therefore, the organic petrographic characteristics of the Pabdeh Formation remain largely undocumented in the Zagros Basin. The purpose of the present study is to investigate the organic matter contained in the Pabdeh Formation using organic petrographic techniques in order to better understand its Palaeodepositional environments. In addition, organic petrographic results are used in combination with the Rock-Eval pyrolysis data to throw light on the organic facies of the Pabdeh Formation. Materials & Methods In this study, a total of 22 cutting samples from the Pabdeh Formation were analyzed using a Rock-Eval 6 pyrolysis instrument. The Rock-Eval 6 device is one of the most cost-effective laboratory methods for the geochemical evaluation of hydrocarbon source rocks and for the evaluation of thermal maturity (Lafargue et al. 1998). Among the advantages of this device are raising the analysis temperature to about 850 degrees centigrade, measuring the amount of total organic carbon (TOC) with higher accuracy, as well as distinguishing between organic and inorganic carbon (Behar et al. 2001). In this study, the standard method (Espitalié et al. 1977; Peters 1986) was followed for Rock-Eval pyrolysis. The cutting samples were taken at regular intervals of 50 meters from the studied wells. Since the Pabdeh Formation in the studied wells was drilled with oil-based mud, to remove the effects of contamination, first the samples were washed using a solvent (diluted chloroform) or detergent and placed in the oven for 72 hours. In the next step, the allochthonous organic matter (such as mica pieces and iron shavings) was separated from the samples. The cleaned samples were pulverized into pieces smaller than 80 microns using a mortar and 50 to 70 mg of them were subjected to the Rock-Eval pyrolysis. This analytical method provides valuable data, including numbers of peaks, that enable geochemists to infer the amount, type and maturity of the organic matter. One of the applications of the data derived from the Rock-Eval pyrolysis is to plot HI data either in front of the oxygen index (OI) or Tmax data (Hunt 1996). These diagrams are used to determine the type of organic matter and thermal maturity respectively (Tissot and Welte 1984; Dembicki 2009). In addition, data from the Rock-Eval pyrolysis can be used for drawing geochemical logs, which provide an opportunity to investigate the vertical and lateral changes in geochemical characteristics (Peters and Cassa 1994; Peters 1986). A number of geochemical parameters are calculated based on the raw data provided by the Rock-Eval device. The HI is calculated from the ratio of S2 to the TOC and the OI is calculated from the ratio of S3 to the TOC. Finally, the hydrocarbon generation potential is calculated using the ratio of the S1/(S1+S2) (Behar et al. 2001). In this research, after carefully investigating the results from the Rock-Eval pyrolysis (22 samples of Pabdeh Formation), a total of 10 samples were selected for organic petrographic studies. For this purpose, polished pellets were prepared according to standard methods (Taylor et al. 1998). At first, the cuttings were placed inside the epoxy resin in a way that the resin penetrated into the space between all the particles. Then, an activator was added to the prepared mixture and after hardening, the surface of the samples was polished (Bustin et al. 1983). For organic petrographic inspection, the polished pellets were examined using a Zeiss-AxioPlan-II reflective microscope under 100x magnification and in oil immersion. Discussion of Results & Conclusion We report the results of Rock-Eval pyrolysis and organic petrography of samples related to the Pabdeh Formation in three wells of the Kilur-Karim Oilfield. According to the HI versus OI diagram, this formation contains type II/III kerogen, which is at the beginning of the hydrocarbon generation window. According to diagrams of S1+S2 versus TOC, the hydrocarbon generation potential of the Pabdeh Formation in this oilfield is fair to good. The relatively high values of S2 and TOC in the middle parts of the Pabdeh Formation indicate that these parts are richer than the lower and upper parts. Based on organic petrographic observations, the middle parts of the Pabdeh Formation were deposited under anoxic conditions and contain significant amounts of amorphous organic matter. The upper and lower parts of this formation were deposited under oxic conditions and contain lower concentrations of organic matter. These results support the conclusion that the middle parts of the Pabdeh Formation contain a distinct type of organic facies, which has higher hydrocarbon generation potential. On the other hand, the lower and upper parts of the Pabdeh Formation are characterized by poor organic facies with limited generative potential. Our results suggest that this pattern of organic facies variation within the Pabdeh Formation is mainly controlled by the palaeo-depositional conditions. As a result, it can be concluded that only the middle parts of the Pabdeh Formation in the studied oilfield have hydrocarbon generation potential. These results can be helpful not only for modeling hydrocarbon systems, but they are also very important in reconstructing the palaeodepositional conditions during the deposition of the Pabdeh Formation. Abstract In this research, the organic matter present in the Pabdeh Formation is investigated using Rock-Eval pyrolysis and organic petrographic techniques. For this purpose, a total of 22 cutting samples were collected at 50-meter intervals from 3 wells in the Kilur-Karim Oilfield. According to hydrogen index (HI) versus maximum temperature (Tmax) diagrams, the Pabdeh Formation in this oilfield contains type II/III kerogen, with thermal maturity corresponding to the early stages of hydrocarbon generation. In general, according to the Rock-Eval pyrolysis data, the middle parts of the Pabdeh Formation show a higher potential for hydrocarbon generation. On the other hand, organic petrography results show that samples from the middle parts of the Pabdeh Formation contain high amounts of amorphous organic matter along with solid bitumen. In addition, the upper and lower parts of this formation contain lower amounts of organic matter and mainly have abundant fossil content. A combination of results from two analytical techniques reveals that the Pabdeh Formation in the Kilur-Karim Oilfield contains a relatively organic-rich zone in the middle, which is surrounded by organic-poor facies above and below. These results can be helpful for a better understanding of the organic facies and palaeodepositional environments of the Pabdeh Formation in the study area. Keywords: Pabdeh Formation, Organic petrography, Organic facies, Kilur-Karim Oilfield Introduction In this study, the organic geochemical characteristics of the Pabdeh Formation in the Kilur-Karim Oilfield have been investigated using the Rock-Eval pyrolysis and organic petrography methods. The Kilur-Karim Oilfield is one of the hydrocarbon fields located in the southern Dezful Embayment, which is located in the vicinity of the Bibi Hakimeh Oilfield about 40 km north of the Persian Gulf. This oilfield generally has a northwest-southeast trend and is separated from the Bibi Hakimeh structure by a thrust from the north side. It is worth mentioning that in previous studies, the organic geochemistry of the Pabdeh Formation has been investigated using different geochemical techniques (such as Rock-Eval pyrolysis and gas chromatography-mass spectrometry analyses) and also modeling techniques (Alizadeh et al. 2012, 2020; Karimi et al. 2016; Vatandoust et al. 2020; Safaei-Farouji et al. 2021). However, microscopic studies have not been conducted on this formation so far. Therefore, the organic petrographic characteristics of the Pabdeh Formation remain largely undocumented in the Zagros Basin. The purpose of the present study is to investigate the organic matter contained in the Pabdeh Formation using organic petrographic techniques in order to better understand its Palaeodepositional environments. In addition, organic petrographic results are used in combination with the Rock-Eval pyrolysis data to throw light on the organic facies of the Pabdeh Formation. Materials & Methods In this study, a total of 22 cutting samples from the Pabdeh Formation were analyzed using a Rock-Eval 6 pyrolysis instrument. The Rock-Eval 6 device is one of the most cost-effective laboratory methods for the geochemical evaluation of hydrocarbon source rocks and for the evaluation of thermal maturity (Lafargue et al. 1998). Among the advantages of this device are raising the analysis temperature to about 850 degrees centigrade, measuring the amount of total organic carbon (TOC) with higher accuracy, as well as distinguishing between organic and inorganic carbon (Behar et al. 2001). In this study, the standard method (Espitalié et al. 1977; Peters 1986) was followed for Rock-Eval pyrolysis. The cutting samples were taken at regular intervals of 50 meters from the studied wells. Since the Pabdeh Formation in the studied wells was drilled with oil-based mud, to remove the effects of contamination, first the samples were washed using a solvent (diluted chloroform) or detergent and placed in the oven for 72 hours. In the next step, the allochthonous organic matter (such as mica pieces and iron shavings) was separated from the samples. The cleaned samples were pulverized into pieces smaller than 80 microns using a mortar and 50 to 70 mg of them were subjected to the Rock-Eval pyrolysis. This analytical method provides valuable data, including numbers of peaks, that enable geochemists to infer the amount, type and maturity of the organic matter. One of the applications of the data derived from the Rock-Eval pyrolysis is to plot HI data either in front of the oxygen index (OI) or Tmax data (Hunt 1996). These diagrams are used to determine the type of organic matter and thermal maturity respectively (Tissot and Welte 1984; Dembicki 2009). In addition, data from the Rock-Eval pyrolysis can be used for drawing geochemical logs, which provide an opportunity to investigate the vertical and lateral changes in geochemical characteristics (Peters and Cassa 1994; Peters 1986). A number of geochemical parameters are calculated based on the raw data provided by the Rock-Eval device. The HI is calculated from the ratio of S2 to the TOC and the OI is calculated from the ratio of S3 to the TOC. Finally, the hydrocarbon generation potential is calculated using the ratio of the S1/(S1+S2) (Behar et al. 2001). In this research, after carefully investigating the results from the Rock-Eval pyrolysis (22 samples of Pabdeh Formation), a total of 10 samples were selected for organic petrographic studies. For this purpose, polished pellets were prepared according to standard methods (Taylor et al. 1998). At first, the cuttings were placed inside the epoxy resin in a way that the resin penetrated into the space between all the particles. Then, an activator was added to the prepared mixture and after hardening, the surface of the samples was polished (Bustin et al. 1983). For organic petrographic inspection, the polished pellets were examined using a Zeiss-AxioPlan-II reflective microscope under 100x magnification and in oil immersion. Discussion of Results & Conclusion We report the results of Rock-Eval pyrolysis and organic petrography of samples related to the Pabdeh Formation in three wells of the Kilur-Karim Oilfield. According to the HI versus OI diagram, this formation contains type II/III kerogen, which is at the beginning of the hydrocarbon generation window. According to diagrams of S1+S2 versus TOC, the hydrocarbon generation potential of the Pabdeh Formation in this oilfield is fair to good. The relatively high values of S2 and TOC in the middle parts of the Pabdeh Formation indicate that these parts are richer than the lower and upper parts. Based on organic petrographic observations, the middle parts of the Pabdeh Formation were deposited under anoxic conditions and contain significant amounts of amorphous organic matter. The upper and lower parts of this formation were deposited under oxic conditions and contain lower concentrations of organic matter. These results support the conclusion that the middle parts of the Pabdeh Formation contain a distinct type of organic facies, which has higher hydrocarbon generation potential. On the other hand, the lower and upper parts of the Pabdeh Formation are characterized by poor organic facies with limited generative potential. Our results suggest that this pattern of organic facies variation within the Pabdeh Formation is mainly controlled by the palaeo-depositional conditions. As a result, it can be concluded that only the middle parts of the Pabdeh Formation in the studied oilfield have hydrocarbon generation potential. These results can be helpful not only for modeling hydrocarbon systems, but they are also very important in reconstructing the palaeodepositional conditions during the deposition of the Pabdeh Formation.

https://jssr.ui.ac.ir/article_28056_86ef4f851094d743a5b27c70b17d328a.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 An Analysis of the organic geochemistry and environmental geochemistry of the Sargelu and Garau formations in the Qalikuh region, Lorestan An Analysis of the organic geochemistry and environmental geochemistry of the Sargelu and Garau formations in the Qalikuh region, Lorestan 15 40 28068 10.22108/jssr.2023.138481.1263 FA Amirsaeid Hosseini National Iranian Oil Company, Tehran, Iran Mehrab Rashidi National Iranian Oil Company, Tehran, Iran Manouchehr Daryabandeh National Iranian Oil Company, Tehran, Iran Journal Article 2023 08 08 Abstract Sargelu and Garau formations are significant geological units in the Zagros, which are known for having the most important unconventional hydrocarbon resources in Iran. This study aimed to evaluate the hydrocarbon generation potential of two formations by analyzing 15 oil-shale samples collected from the Gashun-G and Pirbadush sections along the Qolyan River in the Qalikuh area, Lorestan. The analysis method used was Rock-Eval pyrolysis. To determine the scatter pattern of heavy elements, a total of 15 samples of river sediments and water were analyzed using ICP-MS. The average values for total organic carbon (TOC) and most hydrocarbon production indicators in Garau oil shales exceed the values observed in Sargelu oil shales. Based on the findings of the elemental analysis and pollution index calculations conducted on sediments, it can be seen that Sargelu shows a higher presence of heavy elements, a higher contamination factor (CF) and average pollution load index (PLI) compared to Garau samples. This difference can be attributed to the physical and chemical characteristics of the sediments. Conversely, Garau samples show a higher average Contamination Degree (CD) in its water, which may be attributed to environmental factors such as temperature and pH of water. The results of the statistical analysis demonstrate a wide range of heavy element formation factors within the sediments and waterways of the Garau route. As a result, despite the lack of human activity in this area, in addition to the amount of organic matter in the oil-shale, the geo-genic activity causes natural environmental pollution that is influenced by various factors, including oxidation-reduction potential, reactive processes, type of bedrock, clay minerals, sediment texture and environmental conditions. Keywords: Heavy elements, Pollution Indicators, Oil shales, Qalikuh, Sargelu and Garau Introduction Hydrocarbon sources can be classified into two categories (i.e. conventional and unconventional). The Qalikuh region of Lorestan in southwestern Iran is known for its significant unconventional resources, specifically the dark-colored oil-shale found in the Sargelu and Garau formations. These formations are known to have the largest reserves of such resources in the country. The majority of conventional oil and gas fields are situated in the Khuzestan Plain and the folded belt of Zagros. However, the Qalikuh region, which contains unconventional hydrocarbon resources, is located in the high Zagros, or crush zone. The oil-shale of the Sargelu and Garau formations serves as the source rocks for these resources. Black shale has a significant effect on the accumulation of heavy and toxic metals in the environment (Derkowski and Marynowski 2018). These rocks show geochemical indicators such as sedimentation in anaerobic environments, high concentrations of sulfides, clays, and organic substances, as well as the formation of complex metal compounds. Consequently, these rocks are susceptible to heightened levels of heavy metal toxicity. The concentration of heavy elements in sediments may be influenced by various physical-chemical properties of the sediment such as ion exchange capacity, chemical composition, and organic matter content. The initial stage in the management of environmental pollution related to the accumulation of heavy elements in sediments and water surrounding oil-shale involves the assessment of regions containing these resources and the evaluation of the extent of pollution. The purpose of this study is to investigate the hydrocarbon generation potential of oil-shale found in the Sargelu and Garau formations, as well as the relationship between this potential and the distribution of heavy elements in river sediments and waterways along these formations. The findings of this study conducted in the Qalikuh region, which is characterized by a significant distance from anthropogenic activities, could have the potential to help formulate strategies for the future exploration and utilization of unconventional oil-shale reserves. Material & Methods In this study, following the identification of oil-shale outcrops and permanent waterways in the Gashun (G) and Pirbadush (P) sections of the Qolyan River, which are situated along the Sargelu and Garau formations, a random sampling approach was employed to collect sediments, water, and oil-shale. The sediment samples were collected by Tucker's (1998) established standards for sedimentology sampling. A shovel was used to extract the samples from a depth of 10–30 cm. Subsequently, the samples were carefully transferred into plastic bags. Water samples were collected from the river according to the established standard (ISO, 1985). The temperature (ºC) of the water was measured, and the samples were collected using 1.5-liter dark polyethylene containers. These containers were treated beforehand with a solution of 10% nitric acid and distilled water in a 1:1 ratio. The containers were washed, utilized, and positioned at the center of the river flow. Within a time frame of less than 24 hours and while being kept away from direct light and heat, the samples were analysed by the laboratory of the Research Institute of Petroleum Industry (RIPI). The pyrolysis Rock-Eval analysis laboratory was utilized to assess the total organic carbon TOC content of oil-shale samples. In addition, inductively coupled plasma mass spectrometry (ICP-MS) was performed on sediment and water samples to quantify elemental contamination levels. This study included a comparison between the polluting elements present in sediments and the global average shale (GAS), as well as an assessment of the toxicity equivalent (TE) of these elements. Besides, the researchers examined the environmental indicators of sediments, specifically the CF and PLI. The CF (1) is used to quantify the amount of environmental pollution in the case of a specific element. PLI (2), a measure used to assess the amount of pollution in an area, serves as a means of quantifying pollution levels in a given area. The levels of water pollutant elements were evaluated by comparing them to the standards set by the World Health Organization (WHO-2011) and the national standard of Iran (IRISI-1053). Based on these comparisons, the amount of water pollution was determined and the CD for water was used, which is a measure to evaluate the cumulative effect of various quality factors that may negatively affect the quality of drinking water, which is calculated from the equation (3). 2) PLI= , Subsequently, the present study used statistical techniques, namely Pearson's correlation coefficient and principal component analysis (PCA) to investigate the association between organic matter content in oil shale and the number of heavy elements in sediments and passing water from the Sargelu and Garau formations. The primary goal was to determine the source of heavy elements in the region. Discussion of Results & Conclusion Based on determining Tmax in Rock-Ewell pyrolysis analysis of oil shale samples, the shale samples from the Sargelu Formation exhibited higher maturity levels than those from the Garau Formation. Through the elemental analysis performed on the sediments, it was found that the Sargelu Formation has a higher abundance of heavy elements and a higher average CF than the Garau Formation. The PLI of Sargelu sediments (0.66) shows a higher value than that of Garau (0.52). Station P2 shows the PLI (1.56), followed by stations P1 and P3, all of which are located inside the Sargelu Formation. Additionally, oil shale samples (6–8) in the vicinity of these stations show different characteristics compared to other oil shale samples and the content of total organic matter has higher values (20.2, 22.4 and 23.9). However, the Garau Formation shales have a higher average total organic matter (14.5) than the Sargelu Formation shales (13.3). In addition, the potential correlation coefficient between heavy elements in sediments and the TOC is higher in the shales of Sargelu Formation. Consequently, the sediment contamination may be attributed to the widespread occurrence of hydrocarbon oil shale and dominant reduction conditions. The Pearson's correlation coefficient was used to evaluate the relationship between the content of organic matter in oil shale and heavy elements in sediments. The analysis showed a positive correlation at the mean level of significance for Zn, V, Ni, Cu and Cd in sediments with TOC. Moreover, the analysis of water samples indicated a significant positive relationship between heavy element concentrations, including Mo, V, and Ni, and the TOC of oil shale. The application of principal component analysis was conducted on heavy elements in conjunction with the organic matter content of oil shale and heavy elements in transient water, both derived from the Sargelu Formation. This analysis led to the identification of two distinct factors. Through the evaluation of pollution indicators and statistical analyses, it has been determined that the primary contributors to pollution in Sargelu sediments are the amount of organic matter in the oil shales within the area as well as the oxidation-reduction potential. Similarly, the key factors influencing water pollution along the trajectory of this formation are the quantity of organic matter in the oil shales of the region and the environmental pH. The findings from the Rock-Eval pyrolysis analysis show that the shale samples obtained from the Garau Formation show a higher average TOC compared to the Sergelu samples. In addition, most of the hydrocarbon production indices (except S1, S2/S3, PI and Tmax) in the Garau Formation show higher values than Sargelu Formation. Through conducting elemental analysis on water samples, it was determined that the Garau Formation exhibits a greater abundance and diversity of heavy elements compared to the Sargelu Formation. Meanwhile, the average CD of water in the Garau Formation was observed to be higher than in the Sargelu Formation. The average CD of water in the Garau Formation (0.92) shows a higher value than the Sargelu Formation (0.72). Stations G7 and P7 have been identified as having the highest level of water pollution in the region, followed by station P3. Stations G7 and P7 are located in the Garau Formation, and station P3 is located in the Sargelu Formation. The fluctuations of this index can be attributed to the amount of organic matter in the oil shale in the region, as well as the prevailing environmental conditions such as pH and temperature. The presence of natural environmental pollution in the sediments and water of this remote area, which has not been affected by human activities, depends on other factors except the organic compounds in the oil shale. These factors include oxidation-reduction potential, reactive and replacement processes, distribution of shale-clay bedrock, sedimentary texture and environmental conditions. The Pearson correlation coefficient was computed to evaluate and assess the relationship between the amount of the quantity of organic matter present in oil shale and the heavy elements found in sediments. The analysis showed that TOC shows a positive correlation only with Pb at a moderate level of significance. In addition, this correlation was observed exclusively with Ni in the water passing through the Garau Formation. PCA was used to investigate heavy elements and organic matter content of shale and oil sediments as well as water samples obtained from the Garau Formation. The analysis showed the presence of four distinct factors in the sediments and three factors in the passing waters in the Garau Formation. Through the assessment of pollution indicators and statistical analyses, it was found that the primary factors of pollution in the sediments of the Garau Formation are the amount of organic matter in the oil shale, reactive and substitution processes occurring in the sediments, shale-clay bedrock, minor-minerals of the shale. Similarly, the key factors affecting the pollution of the passing waters in this formation are the amount of organic matter in the oil shale of the region as well as the environmental pH and oxidation-reduction reactions. The comparison between the Pirbadush and Gashun sections shows that the TOC of oil shale is higher in the Pirbadush, as well as the CD of water and PLI in sediments. These changes can be attributed to the presence of more hydrocarbon oil shale and more expansion of the Garau and Sargelu formations in Pirbadush section. It is worth mentioning that the organic matter in oil shales had the greatest effect on the levels of Mo, V and Cd in fluvial sediments and Mo, V and Ni in the water of the region. Environmental management resulting from the exploitation of unconventional shales contains elements such as Mo and V require hydrological and ecological knowledge and a strong management framework. In order to manage possible risks, several management methods should be considered. These methods should be supported by environmental monitoring programs to provide reliable scientific information for the development and implementation of regulations. Some of these methods include: Planning land use and environmental risk assessment, accurate monitoring systems in functional equipment, and collecting environmental data of clear and accessible to the public. Abstract Sargelu and Garau formations are significant geological units in the Zagros, which are known for having the most important unconventional hydrocarbon resources in Iran. This study aimed to evaluate the hydrocarbon generation potential of two formations by analyzing 15 oil-shale samples collected from the Gashun-G and Pirbadush sections along the Qolyan River in the Qalikuh area, Lorestan. The analysis method used was Rock-Eval pyrolysis. To determine the scatter pattern of heavy elements, a total of 15 samples of river sediments and water were analyzed using ICP-MS. The average values for total organic carbon (TOC) and most hydrocarbon production indicators in Garau oil shales exceed the values observed in Sargelu oil shales. Based on the findings of the elemental analysis and pollution index calculations conducted on sediments, it can be seen that Sargelu shows a higher presence of heavy elements, a higher contamination factor (CF) and average pollution load index (PLI) compared to Garau samples. This difference can be attributed to the physical and chemical characteristics of the sediments. Conversely, Garau samples show a higher average Contamination Degree (CD) in its water, which may be attributed to environmental factors such as temperature and pH of water. The results of the statistical analysis demonstrate a wide range of heavy element formation factors within the sediments and waterways of the Garau route. As a result, despite the lack of human activity in this area, in addition to the amount of organic matter in the oil-shale, the geo-genic activity causes natural environmental pollution that is influenced by various factors, including oxidation-reduction potential, reactive processes, type of bedrock, clay minerals, sediment texture and environmental conditions. Keywords: Heavy elements, Pollution Indicators, Oil shales, Qalikuh, Sargelu and Garau Introduction Hydrocarbon sources can be classified into two categories (i.e. conventional and unconventional). The Qalikuh region of Lorestan in southwestern Iran is known for its significant unconventional resources, specifically the dark-colored oil-shale found in the Sargelu and Garau formations. These formations are known to have the largest reserves of such resources in the country. The majority of conventional oil and gas fields are situated in the Khuzestan Plain and the folded belt of Zagros. However, the Qalikuh region, which contains unconventional hydrocarbon resources, is located in the high Zagros, or crush zone. The oil-shale of the Sargelu and Garau formations serves as the source rocks for these resources. Black shale has a significant effect on the accumulation of heavy and toxic metals in the environment (Derkowski and Marynowski 2018). These rocks show geochemical indicators such as sedimentation in anaerobic environments, high concentrations of sulfides, clays, and organic substances, as well as the formation of complex metal compounds. Consequently, these rocks are susceptible to heightened levels of heavy metal toxicity. The concentration of heavy elements in sediments may be influenced by various physical-chemical properties of the sediment such as ion exchange capacity, chemical composition, and organic matter content. The initial stage in the management of environmental pollution related to the accumulation of heavy elements in sediments and water surrounding oil-shale involves the assessment of regions containing these resources and the evaluation of the extent of pollution. The purpose of this study is to investigate the hydrocarbon generation potential of oil-shale found in the Sargelu and Garau formations, as well as the relationship between this potential and the distribution of heavy elements in river sediments and waterways along these formations. The findings of this study conducted in the Qalikuh region, which is characterized by a significant distance from anthropogenic activities, could have the potential to help formulate strategies for the future exploration and utilization of unconventional oil-shale reserves. Material & Methods In this study, following the identification of oil-shale outcrops and permanent waterways in the Gashun (G) and Pirbadush (P) sections of the Qolyan River, which are situated along the Sargelu and Garau formations, a random sampling approach was employed to collect sediments, water, and oil-shale. The sediment samples were collected by Tucker's (1998) established standards for sedimentology sampling. A shovel was used to extract the samples from a depth of 10–30 cm. Subsequently, the samples were carefully transferred into plastic bags. Water samples were collected from the river according to the established standard (ISO, 1985). The temperature (ºC) of the water was measured, and the samples were collected using 1.5-liter dark polyethylene containers. These containers were treated beforehand with a solution of 10% nitric acid and distilled water in a 1:1 ratio. The containers were washed, utilized, and positioned at the center of the river flow. Within a time frame of less than 24 hours and while being kept away from direct light and heat, the samples were analysed by the laboratory of the Research Institute of Petroleum Industry (RIPI). The pyrolysis Rock-Eval analysis laboratory was utilized to assess the total organic carbon TOC content of oil-shale samples. In addition, inductively coupled plasma mass spectrometry (ICP-MS) was performed on sediment and water samples to quantify elemental contamination levels. This study included a comparison between the polluting elements present in sediments and the global average shale (GAS), as well as an assessment of the toxicity equivalent (TE) of these elements. Besides, the researchers examined the environmental indicators of sediments, specifically the CF and PLI. The CF (1) is used to quantify the amount of environmental pollution in the case of a specific element. PLI (2), a measure used to assess the amount of pollution in an area, serves as a means of quantifying pollution levels in a given area. The levels of water pollutant elements were evaluated by comparing them to the standards set by the World Health Organization (WHO-2011) and the national standard of Iran (IRISI-1053). Based on these comparisons, the amount of water pollution was determined and the CD for water was used, which is a measure to evaluate the cumulative effect of various quality factors that may negatively affect the quality of drinking water, which is calculated from the equation (3). 2) PLI= , Subsequently, the present study used statistical techniques, namely Pearson's correlation coefficient and principal component analysis (PCA) to investigate the association between organic matter content in oil shale and the number of heavy elements in sediments and passing water from the Sargelu and Garau formations. The primary goal was to determine the source of heavy elements in the region. Discussion of Results & Conclusion Based on determining Tmax in Rock-Ewell pyrolysis analysis of oil shale samples, the shale samples from the Sargelu Formation exhibited higher maturity levels than those from the Garau Formation. Through the elemental analysis performed on the sediments, it was found that the Sargelu Formation has a higher abundance of heavy elements and a higher average CF than the Garau Formation. The PLI of Sargelu sediments (0.66) shows a higher value than that of Garau (0.52). Station P2 shows the PLI (1.56), followed by stations P1 and P3, all of which are located inside the Sargelu Formation. Additionally, oil shale samples (6–8) in the vicinity of these stations show different characteristics compared to other oil shale samples and the content of total organic matter has higher values (20.2, 22.4 and 23.9). However, the Garau Formation shales have a higher average total organic matter (14.5) than the Sargelu Formation shales (13.3). In addition, the potential correlation coefficient between heavy elements in sediments and the TOC is higher in the shales of Sargelu Formation. Consequently, the sediment contamination may be attributed to the widespread occurrence of hydrocarbon oil shale and dominant reduction conditions. The Pearson's correlation coefficient was used to evaluate the relationship between the content of organic matter in oil shale and heavy elements in sediments. The analysis showed a positive correlation at the mean level of significance for Zn, V, Ni, Cu and Cd in sediments with TOC. Moreover, the analysis of water samples indicated a significant positive relationship between heavy element concentrations, including Mo, V, and Ni, and the TOC of oil shale. The application of principal component analysis was conducted on heavy elements in conjunction with the organic matter content of oil shale and heavy elements in transient water, both derived from the Sargelu Formation. This analysis led to the identification of two distinct factors. Through the evaluation of pollution indicators and statistical analyses, it has been determined that the primary contributors to pollution in Sargelu sediments are the amount of organic matter in the oil shales within the area as well as the oxidation-reduction potential. Similarly, the key factors influencing water pollution along the trajectory of this formation are the quantity of organic matter in the oil shales of the region and the environmental pH. The findings from the Rock-Eval pyrolysis analysis show that the shale samples obtained from the Garau Formation show a higher average TOC compared to the Sergelu samples. In addition, most of the hydrocarbon production indices (except S1, S2/S3, PI and Tmax) in the Garau Formation show higher values than Sargelu Formation. Through conducting elemental analysis on water samples, it was determined that the Garau Formation exhibits a greater abundance and diversity of heavy elements compared to the Sargelu Formation. Meanwhile, the average CD of water in the Garau Formation was observed to be higher than in the Sargelu Formation. The average CD of water in the Garau Formation (0.92) shows a higher value than the Sargelu Formation (0.72). Stations G7 and P7 have been identified as having the highest level of water pollution in the region, followed by station P3. Stations G7 and P7 are located in the Garau Formation, and station P3 is located in the Sargelu Formation. The fluctuations of this index can be attributed to the amount of organic matter in the oil shale in the region, as well as the prevailing environmental conditions such as pH and temperature. The presence of natural environmental pollution in the sediments and water of this remote area, which has not been affected by human activities, depends on other factors except the organic compounds in the oil shale. These factors include oxidation-reduction potential, reactive and replacement processes, distribution of shale-clay bedrock, sedimentary texture and environmental conditions. The Pearson correlation coefficient was computed to evaluate and assess the relationship between the amount of the quantity of organic matter present in oil shale and the heavy elements found in sediments. The analysis showed that TOC shows a positive correlation only with Pb at a moderate level of significance. In addition, this correlation was observed exclusively with Ni in the water passing through the Garau Formation. PCA was used to investigate heavy elements and organic matter content of shale and oil sediments as well as water samples obtained from the Garau Formation. The analysis showed the presence of four distinct factors in the sediments and three factors in the passing waters in the Garau Formation. Through the assessment of pollution indicators and statistical analyses, it was found that the primary factors of pollution in the sediments of the Garau Formation are the amount of organic matter in the oil shale, reactive and substitution processes occurring in the sediments, shale-clay bedrock, minor-minerals of the shale. Similarly, the key factors affecting the pollution of the passing waters in this formation are the amount of organic matter in the oil shale of the region as well as the environmental pH and oxidation-reduction reactions. The comparison between the Pirbadush and Gashun sections shows that the TOC of oil shale is higher in the Pirbadush, as well as the CD of water and PLI in sediments. These changes can be attributed to the presence of more hydrocarbon oil shale and more expansion of the Garau and Sargelu formations in Pirbadush section. It is worth mentioning that the organic matter in oil shales had the greatest effect on the levels of Mo, V and Cd in fluvial sediments and Mo, V and Ni in the water of the region. Environmental management resulting from the exploitation of unconventional shales contains elements such as Mo and V require hydrological and ecological knowledge and a strong management framework. In order to manage possible risks, several management methods should be considered. These methods should be supported by environmental monitoring programs to provide reliable scientific information for the development and implementation of regulations. Some of these methods include: Planning land use and environmental risk assessment, accurate monitoring systems in functional equipment, and collecting environmental data of clear and accessible to the public.

https://jssr.ui.ac.ir/article_28068_f286745ae9b72b2f3bd82f1b0c468c68.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 Environmental geochemistry of water, sediments and slimes of Semnan Spas Environmental geochemistry of water, sediments and slimes of Semnan Spas 41 60 28086 10.22108/jssr.2024.139770.1273 FA Giti Forghani Tehrani Associate professor, Hydrogeology and Environmental Geology Department, Faculty of Earth Sciences, Shahrood University of technology, Shahrood, Iran Rahim Bagheri Associate Professor, Hydrogeology and Environmental Geology Department, Faculty of Earth Sciences - Shahrood University of Technology-Shahrood-Iran Journal Article 2023 11 12 Abstract In order to study the environmental characteristics of Semnan spas, water, sediment, and slime samples were collected. The concentration of Ag, As, Cd, Pb and Zn (0.7, 33, 0.4, 128.5, and 297 mg/kg, respectively) in the sediment samples are much higher than their respective values in mean crust and mean sediment compositions. The sediments are not enriched in Mo, Ni, Th, Co, Cr, Mn, Fe and U, while moderately enriched in Sb and Cu, significantly enriched in Cd, As, Zn and Pb, and highly enriched in Ag. The Bioconcentration Factor (BCF) values of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high (1286, 2863, 2340, 1053, 1236, and 976, respectively). The water samples are classified as neutral-high-metal, and the concentrations of B, Li, Ba, Zn, Pb, Se, Cu, As, Ni and Mn in all samples are higher than their mean concentrations in unpolluted natural waters. The values of Contamination Degree (Cd) and Heavy Metal Pollution Index (HPI) in all samples are higher than 3 and 75, respectively, confirming the high level of pollution in the samples. The Water Hazard Index (WHI) values of the studied samples are lower than 5, indicating the non-toxicity of the target elements. The high concentration of potentially toxic elements in water, sediments and slime samples of Semnan Spa should be taken into account by people who use the Semnan spas for therapeutic purposes. Keywords: Pollution, Balneology, Spa, Semnan Introduction Balneology is considered a simple, pleasant and safe cure for some health issues, and usually is regarded as a treatment with no side impacts. This treatment is based on the probable positive biological impacts of mineral waters and hot springs on the health status (Mirhosseini et al. 2015). A wide range of diseases including rheumatism, gout, high levels of blood lipids, premature aging, chronic spine pain, osteoarthritis, and skin problems can be improved using this method. The therapeutic mechanisms of mineral waters are still not well known, but probably a combination of chemical, thermal, mechanical, immunological and psychological effects are involved (Toth et al. 2015). Semnan Spa complex, 21 Km northwest of Semnan, is located in the Alborz structural zone of Iran. The oldest rock unit exposed in the study area is the Lower to Middle Triassic limestone-dolomite of the Elica Formation, which is overlaid by the shale, marl and sandstone strata of the Upper Triassic-Middle Jurassic Shemshak Group/Formation. This succession is covered by the Middle to Upper Jurassic Lar Formation which consists of limestone-dolomite rock units, and is underlined by conglomerate and red sandstone of the Paleocene-Eocene Fajan Formation as well as the Quaternary alluvial deposits. The Elika and Lar formations are exposed at high altitudes and are considered optimal sources for groundwater recharge (Karimi et al. 2017). Because the impermeable Shemshak Group/Formation is located between the Elika and Lar formations, there is no hydraulic connection between these two carbonate aquifers. Moreover, the main aquifer of the area, which is located in thick dolomite layers of the Lar Formation, is covered by thick and impermeable layers of the Fajan Formation; thus, the aquifer is confined. The present study aims to investigate the geochemistry of water, sediment and slime of the Semnan spas. For this purpose, the concentration of major ions in the water samples and the contents of potentially toxic elements in water, sediment and slime samples were measured. Considering the possible negative impacts of human exposure to excessive amounts of toxic elements, this study deems of crucial importance. Material & Methods To study the hydrogeochemical characteristics of the Semnan spas, water samples were collected from five spas in the study area in the wet (February 2019) and dry (September 2019) seasons. In each sampling site, two polyethylene bottles were filled with water samples (one for major ion concentrations and the other for potentially toxic element contents). pH, temperature and electrical conductivity (EC) of the samples were recorded in the field using a calibrated YK-2001CT pH-EC meter. Five sediment and slime samples were also collected using a stainless steel shovel. The collected samples were stored in polyethylene bags and were kept at 4°C until chemical analyses. The concentration of Na and K was determined using flame photometry, the concentration of HCO3, Cl, Ca and Mg was measured by titration method, and the content of SO4 was obtained using a spectrophotometer. Total Dissolved Solid (TDS) values were measured using the filtration method. The concentration of potentially toxic elements was measured after passing the water samples through a 0.45 μm filter. The filtered water samples were acidified (pH 2) using a few drops of concentrated nitric acid. The concentration of potentially toxic elements was measured using the ICP-MS device. After drying at room temperature, the sediment samples were passed through a 63 μm sieve. The slime samples were oven-dried at 37°C and then were powdered using a ceramic mortar. In the next step, the slime samples were then passed through a 63 μm sieve. The sediment and slime samples were digested by the mixtures of concentrated (HF+HClO4+HNO3+HCl) and (HNO3+HClO4) mixtures, respectively. The concentration of major and trace elements in sediment and slime samples was measured using an ICP-MS device at the Isfahan University of Technology. Discussion of Results & Conclusions EC values of the water samples vary between 17230 (SP3 in the wet season) and 23460 μS/cm (SP4 in the wet season). TDS of the water samples changes in the range of 11100 mg/L (SP2 in the dry season) to 16200 mg/L (SP5 in the wet season). The pH of the water samples varies between 6.4 (SP4 in the wet season) and 7.9 (SP1 in the dry season) and the temperature is between 21.5°C (SP3 in the wet season) and 41°C (SP4 in the dry season). While there is no noticeable variation in the values of EC and TDS in the dry and wet seasons, the recorded temperature and pH values of the water samples collected in dry season are higher, which is probably due to the release of acidic gases (carbon dioxide) in high-temperature conditions of the dry season. Based on the hydrochemical data, Cl and Na are the most dominant ions in the studied samples. On the basis of the average values, the order of abundance of major cations and anions follows the order of Na > Ca > Mg > K and Cl > SO4 > HCO3, respectively. There is a clear difference in the concentration of Cl and Na in dry and wet seasons, which is probably due to the increase in water temperature in the dry season. Plotting the major ion values on the Piper diagram indicates that the studied samples are of Cl type and Na facies. The presence of strong acids (chlorine ions) may enhance the solubility of metals in water samples. In all samples, the predominance of Na and K over Ca, and the predominance of Mg over Ca is evident. The predominance of Na over Ca and Mg indicates that sodium originates from halite dissolution or silicate hydrolysis (Hounslow 1995). The predominance of Cl in the studied samples confirms the dissolution of evaporative minerals. Considering the presence of sulfate ions and the predominance of Mg compared to Ca, the possible origin of these ions in water samples is the dissolution of magnesium sulfates or the hydrolysis of silicates. Karimi et al. (2017) showed that the Cl and Na ions in Semnan spas originate from the dissolution of minerals from the Lar Formation, and hydrolysis of Na-feldspar of the Fajan Formation. They indicated that SO4 and Ca originate from gypsum layers of the Fajan Formation. Based on the Cl-SO4-HCO3 diagram (Giggenback 1988), the studied samples are mature and rich in Cl; therefore, the water samples were not probably affected by surficial processes such as mixing with underground water (Singh et al. 2015). RK-RMg diagram (Giggenback and Glover 1992) shows that the chemistry of water samples is controlled by rock dissolution. The Saturation Index (SI) values of different minerals in the studied samples are the same, showing a common source of the springs. Moreover, there is no obvious change in the SI values of minerals in dry and wet seasons. According to the average values, the mineral SI values decline in the order of dolomite > calcite/aragonite > gypsum > anhydrite > halite. SI values show that the studied water samples are supersaturated in dolomite, saturated in calcite and aragonite, and undersaturated in halite, gypsum, and anhydrite, which is in accordance with the dolomite lithology of the aquifer. Based on average values, the concentration of potentially toxic elements in water samples decreases as follows: B > Zn > Mn > Al > Li > Cu > Fe > Ba > As > Ni > Pb > Se. The concentration of B, Li, Zn, Ba, Pb, Mn, Se, Cu, As and Ni in water samples is much higher than their average values in unpolluted waters (Markert 1994). The high concentration of B, Li, Zn, Mn, Se and Cu in Semnan spas may induce positive health impacts (Jurowski et al. 2014; Maret 2017), while high amounts of Ba, Pb, Ni and As in water may lead to negative health effects (USEPA 2013). Calculation of contamination degree (Cd) and HPI shows that all samples are contaminated with potentially toxic elements, and SP4 is the most polluted spring in the study area. Plotting the obtained data on the Ficklin diagram indicates that the waters of the studied area are in near-neutral-high metal class. The concentrations of Ag, As, Cd, Pb and Zn in the studied sediment samples are much higher than the mean sediment and mean crust composition. On the basis of EF values, sediments are not enriched in Mo, Ni, Th, Co, Cr, Mn, Fe and U, moderately enriched in Sb and Cu, significantly enriched in Cd, As, Zn and Pb, and highly enriched in Ag. Compared to the reference values, the concentration of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn is much higher in slime samples. The BCF values of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high (1286, 2863, 2340, 1053, 1236, and 976, respectively), indicating the high potential of toxic elements to be bioaccumulated in living organisms. Cd, As, Ni, and Pb are toxic elements with no known positive impacts on the human body. On the other hand, although Zn, Cu and Mn are considered essential micronutrients, excessive exposure to these elements may impose negative health impacts. Therefore, the negative impacts of potentially toxic elements should be considered along with the positive therapeutic properties of sediments and slime of the studied spa. Supersaturation of water samples in dolomite and their saturation in calcite and aragonite, as well as the position of the samples on the RK-RMg diagram, confirm the occurrence of dissolution process as the main factor controlling the hydrochemistry of the samples. High amounts of acidic ions (i.e., Cl and SO4) as well as the high temperature of water can be considered as the main reasons for elevated concentration of potentially toxic elements (e.g., B, Li, Zn, Ba, Pb, Se, Cu, As, Ni and Mn) in water samples. Based on the pollution indices, all water samples are enriched in potentially toxic elements, and SP4 shows the highest level of pollution. Sediment samples are enriched in Ag, Pb, Sb, Zn, Cd and As, and the concentration of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high. Although B, Li, Se, Zn, Cu, Mn and Fe have been known as essential micronutrients in certain uptake values, there is no known positive function for Ni, As, Pb, Ba and Cd in the human body. Therefore, during the use of hot springs for therapeutic purposes, the adverse impacts of excessive exposure to these elements through dermal contact, ingestion and inhalation must be taken into account Abstract In order to study the environmental characteristics of Semnan spas, water, sediment, and slime samples were collected. The concentration of Ag, As, Cd, Pb and Zn (0.7, 33, 0.4, 128.5, and 297 mg/kg, respectively) in the sediment samples are much higher than their respective values in mean crust and mean sediment compositions. The sediments are not enriched in Mo, Ni, Th, Co, Cr, Mn, Fe and U, while moderately enriched in Sb and Cu, significantly enriched in Cd, As, Zn and Pb, and highly enriched in Ag. The Bioconcentration Factor (BCF) values of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high (1286, 2863, 2340, 1053, 1236, and 976, respectively). The water samples are classified as neutral-high-metal, and the concentrations of B, Li, Ba, Zn, Pb, Se, Cu, As, Ni and Mn in all samples are higher than their mean concentrations in unpolluted natural waters. The values of Contamination Degree (Cd) and Heavy Metal Pollution Index (HPI) in all samples are higher than 3 and 75, respectively, confirming the high level of pollution in the samples. The Water Hazard Index (WHI) values of the studied samples are lower than 5, indicating the non-toxicity of the target elements. The high concentration of potentially toxic elements in water, sediments and slime samples of Semnan Spa should be taken into account by people who use the Semnan spas for therapeutic purposes. Keywords: Pollution, Balneology, Spa, Semnan Introduction Balneology is considered a simple, pleasant and safe cure for some health issues, and usually is regarded as a treatment with no side impacts. This treatment is based on the probable positive biological impacts of mineral waters and hot springs on the health status (Mirhosseini et al. 2015). A wide range of diseases including rheumatism, gout, high levels of blood lipids, premature aging, chronic spine pain, osteoarthritis, and skin problems can be improved using this method. The therapeutic mechanisms of mineral waters are still not well known, but probably a combination of chemical, thermal, mechanical, immunological and psychological effects are involved (Toth et al. 2015). Semnan Spa complex, 21 Km northwest of Semnan, is located in the Alborz structural zone of Iran. The oldest rock unit exposed in the study area is the Lower to Middle Triassic limestone-dolomite of the Elica Formation, which is overlaid by the shale, marl and sandstone strata of the Upper Triassic-Middle Jurassic Shemshak Group/Formation. This succession is covered by the Middle to Upper Jurassic Lar Formation which consists of limestone-dolomite rock units, and is underlined by conglomerate and red sandstone of the Paleocene-Eocene Fajan Formation as well as the Quaternary alluvial deposits. The Elika and Lar formations are exposed at high altitudes and are considered optimal sources for groundwater recharge (Karimi et al. 2017). Because the impermeable Shemshak Group/Formation is located between the Elika and Lar formations, there is no hydraulic connection between these two carbonate aquifers. Moreover, the main aquifer of the area, which is located in thick dolomite layers of the Lar Formation, is covered by thick and impermeable layers of the Fajan Formation; thus, the aquifer is confined. The present study aims to investigate the geochemistry of water, sediment and slime of the Semnan spas. For this purpose, the concentration of major ions in the water samples and the contents of potentially toxic elements in water, sediment and slime samples were measured. Considering the possible negative impacts of human exposure to excessive amounts of toxic elements, this study deems of crucial importance. Material & Methods To study the hydrogeochemical characteristics of the Semnan spas, water samples were collected from five spas in the study area in the wet (February 2019) and dry (September 2019) seasons. In each sampling site, two polyethylene bottles were filled with water samples (one for major ion concentrations and the other for potentially toxic element contents). pH, temperature and electrical conductivity (EC) of the samples were recorded in the field using a calibrated YK-2001CT pH-EC meter. Five sediment and slime samples were also collected using a stainless steel shovel. The collected samples were stored in polyethylene bags and were kept at 4°C until chemical analyses. The concentration of Na and K was determined using flame photometry, the concentration of HCO3, Cl, Ca and Mg was measured by titration method, and the content of SO4 was obtained using a spectrophotometer. Total Dissolved Solid (TDS) values were measured using the filtration method. The concentration of potentially toxic elements was measured after passing the water samples through a 0.45 μm filter. The filtered water samples were acidified (pH 2) using a few drops of concentrated nitric acid. The concentration of potentially toxic elements was measured using the ICP-MS device. After drying at room temperature, the sediment samples were passed through a 63 μm sieve. The slime samples were oven-dried at 37°C and then were powdered using a ceramic mortar. In the next step, the slime samples were then passed through a 63 μm sieve. The sediment and slime samples were digested by the mixtures of concentrated (HF+HClO4+HNO3+HCl) and (HNO3+HClO4) mixtures, respectively. The concentration of major and trace elements in sediment and slime samples was measured using an ICP-MS device at the Isfahan University of Technology. Discussion of Results & Conclusions EC values of the water samples vary between 17230 (SP3 in the wet season) and 23460 μS/cm (SP4 in the wet season). TDS of the water samples changes in the range of 11100 mg/L (SP2 in the dry season) to 16200 mg/L (SP5 in the wet season). The pH of the water samples varies between 6.4 (SP4 in the wet season) and 7.9 (SP1 in the dry season) and the temperature is between 21.5°C (SP3 in the wet season) and 41°C (SP4 in the dry season). While there is no noticeable variation in the values of EC and TDS in the dry and wet seasons, the recorded temperature and pH values of the water samples collected in dry season are higher, which is probably due to the release of acidic gases (carbon dioxide) in high-temperature conditions of the dry season. Based on the hydrochemical data, Cl and Na are the most dominant ions in the studied samples. On the basis of the average values, the order of abundance of major cations and anions follows the order of Na > Ca > Mg > K and Cl > SO4 > HCO3, respectively. There is a clear difference in the concentration of Cl and Na in dry and wet seasons, which is probably due to the increase in water temperature in the dry season. Plotting the major ion values on the Piper diagram indicates that the studied samples are of Cl type and Na facies. The presence of strong acids (chlorine ions) may enhance the solubility of metals in water samples. In all samples, the predominance of Na and K over Ca, and the predominance of Mg over Ca is evident. The predominance of Na over Ca and Mg indicates that sodium originates from halite dissolution or silicate hydrolysis (Hounslow 1995). The predominance of Cl in the studied samples confirms the dissolution of evaporative minerals. Considering the presence of sulfate ions and the predominance of Mg compared to Ca, the possible origin of these ions in water samples is the dissolution of magnesium sulfates or the hydrolysis of silicates. Karimi et al. (2017) showed that the Cl and Na ions in Semnan spas originate from the dissolution of minerals from the Lar Formation, and hydrolysis of Na-feldspar of the Fajan Formation. They indicated that SO4 and Ca originate from gypsum layers of the Fajan Formation. Based on the Cl-SO4-HCO3 diagram (Giggenback 1988), the studied samples are mature and rich in Cl; therefore, the water samples were not probably affected by surficial processes such as mixing with underground water (Singh et al. 2015). RK-RMg diagram (Giggenback and Glover 1992) shows that the chemistry of water samples is controlled by rock dissolution. The Saturation Index (SI) values of different minerals in the studied samples are the same, showing a common source of the springs. Moreover, there is no obvious change in the SI values of minerals in dry and wet seasons. According to the average values, the mineral SI values decline in the order of dolomite > calcite/aragonite > gypsum > anhydrite > halite. SI values show that the studied water samples are supersaturated in dolomite, saturated in calcite and aragonite, and undersaturated in halite, gypsum, and anhydrite, which is in accordance with the dolomite lithology of the aquifer. Based on average values, the concentration of potentially toxic elements in water samples decreases as follows: B > Zn > Mn > Al > Li > Cu > Fe > Ba > As > Ni > Pb > Se. The concentration of B, Li, Zn, Ba, Pb, Mn, Se, Cu, As and Ni in water samples is much higher than their average values in unpolluted waters (Markert 1994). The high concentration of B, Li, Zn, Mn, Se and Cu in Semnan spas may induce positive health impacts (Jurowski et al. 2014; Maret 2017), while high amounts of Ba, Pb, Ni and As in water may lead to negative health effects (USEPA 2013). Calculation of contamination degree (Cd) and HPI shows that all samples are contaminated with potentially toxic elements, and SP4 is the most polluted spring in the study area. Plotting the obtained data on the Ficklin diagram indicates that the waters of the studied area are in near-neutral-high metal class. The concentrations of Ag, As, Cd, Pb and Zn in the studied sediment samples are much higher than the mean sediment and mean crust composition. On the basis of EF values, sediments are not enriched in Mo, Ni, Th, Co, Cr, Mn, Fe and U, moderately enriched in Sb and Cu, significantly enriched in Cd, As, Zn and Pb, and highly enriched in Ag. Compared to the reference values, the concentration of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn is much higher in slime samples. The BCF values of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high (1286, 2863, 2340, 1053, 1236, and 976, respectively), indicating the high potential of toxic elements to be bioaccumulated in living organisms. Cd, As, Ni, and Pb are toxic elements with no known positive impacts on the human body. On the other hand, although Zn, Cu and Mn are considered essential micronutrients, excessive exposure to these elements may impose negative health impacts. Therefore, the negative impacts of potentially toxic elements should be considered along with the positive therapeutic properties of sediments and slime of the studied spa. Supersaturation of water samples in dolomite and their saturation in calcite and aragonite, as well as the position of the samples on the RK-RMg diagram, confirm the occurrence of dissolution process as the main factor controlling the hydrochemistry of the samples. High amounts of acidic ions (i.e., Cl and SO4) as well as the high temperature of water can be considered as the main reasons for elevated concentration of potentially toxic elements (e.g., B, Li, Zn, Ba, Pb, Se, Cu, As, Ni and Mn) in water samples. Based on the pollution indices, all water samples are enriched in potentially toxic elements, and SP4 shows the highest level of pollution. Sediment samples are enriched in Ag, Pb, Sb, Zn, Cd and As, and the concentration of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high. Although B, Li, Se, Zn, Cu, Mn and Fe have been known as essential micronutrients in certain uptake values, there is no known positive function for Ni, As, Pb, Ba and Cd in the human body. Therefore, during the use of hot springs for therapeutic purposes, the adverse impacts of excessive exposure to these elements through dermal contact, ingestion and inhalation must be taken into account

https://jssr.ui.ac.ir/article_28086_efd68ff52447f01f8861c77aeaeff58a.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 One and two-dimensional modeling of petroleum systems in the internal Fars region One and two-dimensional modeling of petroleum systems in the internal Fars region 61 78 28099 10.22108/jssr.2024.138467.1262 FA Ali Soleimani MSc, Department of Sedimentary Basins and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran Ehsan Dehyadegari Assistant Professor, Department of Sedimentary Basins and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran Mahboubeh Hosseini-Barzi Associate Professor, Department of Sedimentary Basins and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran Mehrab Rashidi PhD, National Iranian Oil Company Exploration Directorate, Tehran, Iran Mohammad Hassan Jazayeri MSc, National Iranian Oil Company Exploration Directorate, Tehran, Iran 0009-0008-0015-0429 Journal Article 2023 07 20 Abstract In this study, one and two-dimensional models of petroleum systems were constructed in the internal part of the Fars region. Based on the results obtained from one-dimensional modeling and the study of thermal maturation history, the Sarchahan Formation is considered the main source rock of the Paleozoic petroleum system, which started hydrocarbon generation about 130 to 140 million years ago. The liquid hydrocarbon content in wells A and B is estimated to be 720 and 5100 (Kg/m2) respectively, and the gas hydrocarbon content is estimated to be 70 and 600 (Kg/m2). Furthermore, based on the results of two-dimensional modeling, the younger petroleum system source rocks such as the Cretaceous and younger source rocks are thermally immature and have not entered into the oil window. According to the migration modeling results, the most important factor in the movement of hydrocarbon fluids prior to the Zagros orogeny is vertical migration in the career layers, but after this orogeny and tectonic compression, the horizontal migration component has also become active. Keywords: Petroleum system Modeling, Burial history, Source rock, Fars internal region Introduction The petroleum system modeling functions as a powerful tool in the process of hydrocarbon exploration, where regional studies and simulation of subsurface processes can significantly assist in identifying traps and exploration targets. A petroleum system consists of various elements including source, reservoir and cap rocks, hydrocarbon traps, and processes such as generation, migration, and hydrocarbon accumulation. Modeling of petroleum systems is divided into one-, two-, and three-dimensional (1–3D) based on the specific objectives and available data. One-dimensional modeling, nowadays, is used as a computational method based on measured data to indirectly evaluate the maturity of source rocks and determine the oil and gas generation window. For a better understanding of the petroleum system, especially during hydrocarbon generation in the source rock and subsequent expulsion of hydrocarbon molecules, one-dimensional modeling has special applications. The purpose of this study is to construct 1D and 2D models of the petroleum system of two fields located in the Internal Fars with the use of data from two exploration wells and a 2D structural section in order to determine the liquid and gas hydrocarbon content generated from the source rock, as well as the migration pathways of various hydrocarbons over geological timescales. Material & Methods The first step in one-dimensional modeling is to create a well and input relevant data such as well name, geographical coordinates (longitude and latitude), final depth, and rotary table height in the dedicated section. The next step is to input data related to different layers, including information such as layer name, depth, thickness, and age of the layers, palaeo water depth, erosion rate or non-deposition time, lithology related to each formation, the role of each layer in the regional petroleum system, temperature data, and finally, geochemical data such as total organic carbon (TOC) and kinetic data related to potential source rocks. =The TOC and hydrogen index values should be considered initially to ensure calculations are performed with minimal error. In order to simulate a sedimentary basin, the following parameters need to be defined for each event or geological layer. After constructing and running the one-dimensional model, calculations related to temperature and maturity are calibrated using measured data, and then the modeling results are extracted. These results include the burial history plot of strata at the well location and time plots of various parameters of source rock such as vitrinite reflectance, hydrocarbon generation and expulsion rates for potential source rocks in the study area. The first step in the two-dimensional modeling of the hydrocarbon system is to input the structural pattern (2D structural interpretation from seismic sections) into the software. To do this, depth lines representing layers with structural interpretations in the cross-sectional direction are first inputted into the software, and other layers are defined using the lithological pattern and isopach maps. In the software Open-Flow, it is necessary to reconstruct the layers up to the basement, so all successions and studied formations should be included in the model, from the surface and topographic layer to the basement. In this study, information on sedimentology, lithology, thickness and erosion rates of layers, palaeo-water depth, and organic geochemistry of two wells located in two gas fields was utilized. On the other hand, for determining the structural pattern of the study area, a 2D structural cross-section interpretation prepared perpendicular to the Zagros thrust trend was used. By constructing a 1D model in two selected wells, the maturity and hydrocarbon generation history of the source rocks were evaluated. Additionally, the heat flow of each well was calibrated with measured temperature data, and based on these data, a heat flow map was designed in the 2D models. Discussion of Results & Conclusions To achieve more accurate results in modeling, hypothetical layers from the bottom of each well to the top of the basement were considered. On the other hand, a layer reconstruction process was carried out for a portion of the Aghajari Formation which had partially eroded. Based on the data and various tested models, the thermal flow of the basin with a good match to the current well temperature was assumed to be a constant of 55 mw/m2. Considering the very good match between the measured temperature in the well and the calculated temperature in the model, the modeling results can be reliable. The obtained results showed that the Sarchahan Formation began hydrocarbon generation approximately 130 to 140 million years ago, with liquid hydrocarbon amounts of 720 and 5100 (Kg/m2) in wells A and B, respectively, and gas hydrocarbon amounts of 70 and 600 (Kg/m2) respectively. By constructing a 2D model in the selected structural section (perpendicular to the Zagros fold-thrust trend), migration and accumulation paths of hydrocarbons were identified. The results obtained from the 2D model indicate that the Paleozoic oil system was formed with the Sarchahan Formation as the source rock, the Dalan and Kangan formations as reservoir rocks, and the Dashtak Formation as the cap rock. The Sarchahan Formation is the most important source rock that charges the regional reservoirs, and the Cretaceous source rocks had a minimal role in hydrocarbon accumulation due to low maturity. The thermal maturity of the Sarchahan Formation is currently in the late oil window at the top parts of the anticlines and in the wet and dry gas window in the base of the synclines. According to the migration model results, hydrocarbon migration to the reservoirs has started from the Late Cretaceous. Prior to the Zagros orogeny and considering the results of structural reconstruction, there was no folding in the sediments, and throughout the section, the layers were stacked on top of each other like a Layer Cake. Therefore, before the orogeny, the most important factor in the movement of hydrocarbon fluid migration was vertical migration in the career layers. After the orogeny and folding, in addition to vertical migration, the horizontal migration component became active. Abstract In this study, one and two-dimensional models of petroleum systems were constructed in the internal part of the Fars region. Based on the results obtained from one-dimensional modeling and the study of thermal maturation history, the Sarchahan Formation is considered the main source rock of the Paleozoic petroleum system, which started hydrocarbon generation about 130 to 140 million years ago. The liquid hydrocarbon content in wells A and B is estimated to be 720 and 5100 (Kg/m2) respectively, and the gas hydrocarbon content is estimated to be 70 and 600 (Kg/m2). Furthermore, based on the results of two-dimensional modeling, the younger petroleum system source rocks such as the Cretaceous and younger source rocks are thermally immature and have not entered into the oil window. According to the migration modeling results, the most important factor in the movement of hydrocarbon fluids prior to the Zagros orogeny is vertical migration in the career layers, but after this orogeny and tectonic compression, the horizontal migration component has also become active. Keywords: Petroleum system Modeling, Burial history, Source rock, Fars internal region Introduction The petroleum system modeling functions as a powerful tool in the process of hydrocarbon exploration, where regional studies and simulation of subsurface processes can significantly assist in identifying traps and exploration targets. A petroleum system consists of various elements including source, reservoir and cap rocks, hydrocarbon traps, and processes such as generation, migration, and hydrocarbon accumulation. Modeling of petroleum systems is divided into one-, two-, and three-dimensional (1–3D) based on the specific objectives and available data. One-dimensional modeling, nowadays, is used as a computational method based on measured data to indirectly evaluate the maturity of source rocks and determine the oil and gas generation window. For a better understanding of the petroleum system, especially during hydrocarbon generation in the source rock and subsequent expulsion of hydrocarbon molecules, one-dimensional modeling has special applications. The purpose of this study is to construct 1D and 2D models of the petroleum system of two fields located in the Internal Fars with the use of data from two exploration wells and a 2D structural section in order to determine the liquid and gas hydrocarbon content generated from the source rock, as well as the migration pathways of various hydrocarbons over geological timescales. Material & Methods The first step in one-dimensional modeling is to create a well and input relevant data such as well name, geographical coordinates (longitude and latitude), final depth, and rotary table height in the dedicated section. The next step is to input data related to different layers, including information such as layer name, depth, thickness, and age of the layers, palaeo water depth, erosion rate or non-deposition time, lithology related to each formation, the role of each layer in the regional petroleum system, temperature data, and finally, geochemical data such as total organic carbon (TOC) and kinetic data related to potential source rocks. =The TOC and hydrogen index values should be considered initially to ensure calculations are performed with minimal error. In order to simulate a sedimentary basin, the following parameters need to be defined for each event or geological layer. After constructing and running the one-dimensional model, calculations related to temperature and maturity are calibrated using measured data, and then the modeling results are extracted. These results include the burial history plot of strata at the well location and time plots of various parameters of source rock such as vitrinite reflectance, hydrocarbon generation and expulsion rates for potential source rocks in the study area. The first step in the two-dimensional modeling of the hydrocarbon system is to input the structural pattern (2D structural interpretation from seismic sections) into the software. To do this, depth lines representing layers with structural interpretations in the cross-sectional direction are first inputted into the software, and other layers are defined using the lithological pattern and isopach maps. In the software Open-Flow, it is necessary to reconstruct the layers up to the basement, so all successions and studied formations should be included in the model, from the surface and topographic layer to the basement. In this study, information on sedimentology, lithology, thickness and erosion rates of layers, palaeo-water depth, and organic geochemistry of two wells located in two gas fields was utilized. On the other hand, for determining the structural pattern of the study area, a 2D structural cross-section interpretation prepared perpendicular to the Zagros thrust trend was used. By constructing a 1D model in two selected wells, the maturity and hydrocarbon generation history of the source rocks were evaluated. Additionally, the heat flow of each well was calibrated with measured temperature data, and based on these data, a heat flow map was designed in the 2D models. Discussion of Results & Conclusions To achieve more accurate results in modeling, hypothetical layers from the bottom of each well to the top of the basement were considered. On the other hand, a layer reconstruction process was carried out for a portion of the Aghajari Formation which had partially eroded. Based on the data and various tested models, the thermal flow of the basin with a good match to the current well temperature was assumed to be a constant of 55 mw/m2. Considering the very good match between the measured temperature in the well and the calculated temperature in the model, the modeling results can be reliable. The obtained results showed that the Sarchahan Formation began hydrocarbon generation approximately 130 to 140 million years ago, with liquid hydrocarbon amounts of 720 and 5100 (Kg/m2) in wells A and B, respectively, and gas hydrocarbon amounts of 70 and 600 (Kg/m2) respectively. By constructing a 2D model in the selected structural section (perpendicular to the Zagros fold-thrust trend), migration and accumulation paths of hydrocarbons were identified. The results obtained from the 2D model indicate that the Paleozoic oil system was formed with the Sarchahan Formation as the source rock, the Dalan and Kangan formations as reservoir rocks, and the Dashtak Formation as the cap rock. The Sarchahan Formation is the most important source rock that charges the regional reservoirs, and the Cretaceous source rocks had a minimal role in hydrocarbon accumulation due to low maturity. The thermal maturity of the Sarchahan Formation is currently in the late oil window at the top parts of the anticlines and in the wet and dry gas window in the base of the synclines. According to the migration model results, hydrocarbon migration to the reservoirs has started from the Late Cretaceous. Prior to the Zagros orogeny and considering the results of structural reconstruction, there was no folding in the sediments, and throughout the section, the layers were stacked on top of each other like a Layer Cake. Therefore, before the orogeny, the most important factor in the movement of hydrocarbon fluid migration was vertical migration in the career layers. After the orogeny and folding, in addition to vertical migration, the horizontal migration component became active.

https://jssr.ui.ac.ir/article_28099_0b84a2d719d0ca673ee49acfd3189d75.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 Petrographic and geochemical evidence of diagenetic alterations in the Sarvak Formation in an oilfield from the Abadan Plain, west of Iran Petrographic and geochemical evidence of diagenetic alterations in the Sarvak Formation in an oilfield from the Abadan Plain, west of Iran 79 102 28166 10.22108/jssr.2024.139935.1274 FA Ramin Abbasi M.Sc. Student, Soft-Rock Department, School of Geology, College of Science, University of Tehran, Tehran, Iran Hamzeh Mehrabi Assistant Professor, Soft-Rock Department, School of Geology, College of Science, University of Tehran, Tehran, Iran 0000-0002-2211-4899 Emad Yahyaei M.Sc. Student, Soft-Rock Department, School of Geology, College of Science, University of Tehran, Tehran, Iran Hossein Rahimpor Professor, Soft-Rock Department, School of Geology, College of Science, University of Tehran, Tehran, Iran Journal Article 2023 11 29 Abstract The Sarvak Formation, the second important oil reservoir in the Zagros Basin, has a complicated diagenetic history. This study focuses on the diagenetic processes of this formation in the Abadan Plain. To achieve this goal, petrographic investigations of core samples, thin sections, X-ray diffraction, and scanning electron microscopy are integrated with the results of elemental geochemical data. Intensive meteoric dissolution (karstification), paleosol formation, dissolution-collapsed brecciation, meteoric cementation, and silicification are major meteoric diagenetic processes. Such intensive meteoric diagenesis along with the dominance of kaolinite and montmorillonite, as predominant clay types within the paleosol, all indicate a warm and humid paleoclimatic condition at the time of exposure. These diagenetic alterations provided special trends of variations in the elemental contents of altered carbonates. They include a clear increase in Na, Mn, Fe, and Rb along with the decrease in Sr contents recorded below the Cenomanian–Turonian and mid-Turonian disconformities. The variations in Mg contents depend on the original mineralogy of carbonates that can result in variable trends in response to the meteoric diagenesis. Below the mid-Turonian disconformity, the development of mud-dominated facies hampered the free fluid circulation and, consequently, diagenetic alterations and their related geochemical trends are limited within the Turonian sequence. Keywords: Sarvak Formation, Trace elements, Palaeoclimate, Meteoric diagenesis, Abadan Plain Introduction The Sarvak Formation, as a member of the Bangestan Group, is an important oil reservoir in Iran, especially in the Abadan Plain (Motiei 1993). It is mainly composed of carbonate rocks deposited on the northeast margin of the Arabian Plate (Fard et al. 2006). In carbonate successions, complex diagenesis history is strongly influenced by the combined effects of tectonics, eustacy, and palaeoclimate (Ahr 2008). The Zagros Basin has experienced an active tectonic setting and a warm and humid palaeoclimatic condition, during the Late Cretaceous (Mehrabi 2023). At this time, subaerial exposure of carbonate successions has resulted in the development of disconformities at the Cenomanian–Turonian boundary (CT-ES) and middle Turonian (mT-ES) (Rahimpour-Bonab et al. 2013). This study focuses on the petrographic and geochemical investigations of diagenetic features in the Sarvak Formation in an oilfield in the Abadan Plain. Material & Methods In this study, elemental geochemical analyses of 27 samples taken from the Sarvak Formation are integrated with a petrographic study of 831 thin sections in a well, located in the Abadan Plain. Bulk rock and micrite samples were taken for geochemical analyses. After macro- and microscopic studies, 1.5 to 2 mg of powder was prepared using a dental bit (tungsten carbide). This powder was cleaned to remove the organic matter and oil staining and, then, reacted with pure phosphoric acid to produce the carbon dioxide gas. A Kiel III Thermo Finnigan 252 mass spectrometer is used at the Arak University for elemental analysis. Discussion of Results & Conclusions The main results of this study are as follows: Dissolution and Karstification: Intensive meteoric dissolution in the forms of the vuggy, channel, and moldic pores are frequently recorded in the upper parts of the Sarvak Formation. These pores are subsequently filled by meteoric or burial cements or remain unfilled to provide high reservoir potential beneath the palaeoexposure surfaces. Silicification and Brecciation: Replacement of silica within the skeletal fragments (mostly rudists) or in the form of cement filling the burrows and intra-skeletal pores are recorded at the topmost parts of the Sarvak Formation. It shows close association with other meteoric diagenetic features including dissolution, meteoric cementation, and paleosols. Brecciation is also recorded in microscopic studies. A clay-rich matrix filled between these breccias. Development of paleosols: Bauxite and laterite are common paleosols recorded at the topmost parts of the Sarvak Formation. High Fe and Al contents are measured from these horizons. Fe-oxide staining is distinguished within the weathered and karstified units of this formation, below the disconformable surfaces. Moreover, kaolinite and montmorillonite are common clay minerals within these paleosols that indicate a warm and humid climatic condition at the time of exposure. Trace Elements: Elemental contents of Sr, Rb, Fe, Na, Ca, Mn, and Mg are measured from the Sarvak Formation. Manganese (Mn): Mn values of analyzed samples range from 5 to 809 ppm, with an average of 407 ppm. It shows a uniform trend across the Cenomanian sequence, with a sharp increase at the beginning of Turonian as 809 ppm. Sodium (Na): This element varies from 791 to 15439 ppm in the analyzed samples. An increase in Na is recorded at the base of the Cenomanian that changes to lower values in the upper Cenomanian. Two peaks of Na are recorded around the Cenomanian–Turonian boundary. Lower values of Na are measured from the Turonian sequence. Strontium (Sr): The Sr content of the studied well changes from 28 to 604 ppm, with a mean of 367 ppm. Decreased Sr contents are recorded in the lower part of the Cenomanian sequence that changes to higher concentrations in the upper part of this sequence. Generally, the Sr content of the Cenomanian sequence is low. Around the C-T boundary, perturbations in Sr concentrations are recorded with sharp decreases below the disconformities. Paragenetic Sequence: The paragenetic sequence of the Sarvak Formation includes its deposition in the marine realm, experiencing two stages of meteoric diagenesis, and passing through shallow to deep burial realms. Elemental Evidence: The effects of meteoric waters on marine carbonates commonly result in an increase in Mn concentrations in the altered carbonates (Brand and Veizer, 1980). Such an increase in Mn content is recorded at the C–T and mT paleoexposures. The variations in Na concentrations are strongly facies dependent. Sharp increasing peaks of Na are recorded at disconformable surfaces indicating a meteoric diagenetic effect (Brand and Veizer 1980). Decreased values of Sr are expected within the meteorically-altered carbonates, because the Sr concentration in meteoric waters (0.1–0.01 ppm) is much lower than the marine carbonates (1000–9400 ppm) (Brand and Veizer 1980). In the Sarvak Formation, sharp decreases in Sr are measured from the karstified intervals below the paleoexposure surfaces. Geochemical Correlation: The geochemical profile of the Sarvak Formation in the studied well is correlated with a previous study in the Dezful Embayment (Mehrabi et al. 2022). As shown, there is a close correlation between these sections, especially regarding the trace elemental concentrations. Both C–T and mT disconformities are distinguished across the Zagros Basin, including the Abadan Plain, Dezful Embayment, Izeh, and Fars zones. Consequently, similar geochemical trends are formed as a result of intensive meteoric diagenetic alterations below these disconformable surfaces. Abstract The Sarvak Formation, the second important oil reservoir in the Zagros Basin, has a complicated diagenetic history. This study focuses on the diagenetic processes of this formation in the Abadan Plain. To achieve this goal, petrographic investigations of core samples, thin sections, X-ray diffraction, and scanning electron microscopy are integrated with the results of elemental geochemical data. Intensive meteoric dissolution (karstification), paleosol formation, dissolution-collapsed brecciation, meteoric cementation, and silicification are major meteoric diagenetic processes. Such intensive meteoric diagenesis along with the dominance of kaolinite and montmorillonite, as predominant clay types within the paleosol, all indicate a warm and humid paleoclimatic condition at the time of exposure. These diagenetic alterations provided special trends of variations in the elemental contents of altered carbonates. They include a clear increase in Na, Mn, Fe, and Rb along with the decrease in Sr contents recorded below the Cenomanian–Turonian and mid-Turonian disconformities. The variations in Mg contents depend on the original mineralogy of carbonates that can result in variable trends in response to the meteoric diagenesis. Below the mid-Turonian disconformity, the development of mud-dominated facies hampered the free fluid circulation and, consequently, diagenetic alterations and their related geochemical trends are limited within the Turonian sequence. Keywords: Sarvak Formation, Trace elements, Palaeoclimate, Meteoric diagenesis, Abadan Plain Introduction The Sarvak Formation, as a member of the Bangestan Group, is an important oil reservoir in Iran, especially in the Abadan Plain (Motiei 1993). It is mainly composed of carbonate rocks deposited on the northeast margin of the Arabian Plate (Fard et al. 2006). In carbonate successions, complex diagenesis history is strongly influenced by the combined effects of tectonics, eustacy, and palaeoclimate (Ahr 2008). The Zagros Basin has experienced an active tectonic setting and a warm and humid palaeoclimatic condition, during the Late Cretaceous (Mehrabi 2023). At this time, subaerial exposure of carbonate successions has resulted in the development of disconformities at the Cenomanian–Turonian boundary (CT-ES) and middle Turonian (mT-ES) (Rahimpour-Bonab et al. 2013). This study focuses on the petrographic and geochemical investigations of diagenetic features in the Sarvak Formation in an oilfield in the Abadan Plain. Material & Methods In this study, elemental geochemical analyses of 27 samples taken from the Sarvak Formation are integrated with a petrographic study of 831 thin sections in a well, located in the Abadan Plain. Bulk rock and micrite samples were taken for geochemical analyses. After macro- and microscopic studies, 1.5 to 2 mg of powder was prepared using a dental bit (tungsten carbide). This powder was cleaned to remove the organic matter and oil staining and, then, reacted with pure phosphoric acid to produce the carbon dioxide gas. A Kiel III Thermo Finnigan 252 mass spectrometer is used at the Arak University for elemental analysis. Discussion of Results & Conclusions The main results of this study are as follows: Dissolution and Karstification: Intensive meteoric dissolution in the forms of the vuggy, channel, and moldic pores are frequently recorded in the upper parts of the Sarvak Formation. These pores are subsequently filled by meteoric or burial cements or remain unfilled to provide high reservoir potential beneath the palaeoexposure surfaces. Silicification and Brecciation: Replacement of silica within the skeletal fragments (mostly rudists) or in the form of cement filling the burrows and intra-skeletal pores are recorded at the topmost parts of the Sarvak Formation. It shows close association with other meteoric diagenetic features including dissolution, meteoric cementation, and paleosols. Brecciation is also recorded in microscopic studies. A clay-rich matrix filled between these breccias. Development of paleosols: Bauxite and laterite are common paleosols recorded at the topmost parts of the Sarvak Formation. High Fe and Al contents are measured from these horizons. Fe-oxide staining is distinguished within the weathered and karstified units of this formation, below the disconformable surfaces. Moreover, kaolinite and montmorillonite are common clay minerals within these paleosols that indicate a warm and humid climatic condition at the time of exposure. Trace Elements: Elemental contents of Sr, Rb, Fe, Na, Ca, Mn, and Mg are measured from the Sarvak Formation. Manganese (Mn): Mn values of analyzed samples range from 5 to 809 ppm, with an average of 407 ppm. It shows a uniform trend across the Cenomanian sequence, with a sharp increase at the beginning of Turonian as 809 ppm. Sodium (Na): This element varies from 791 to 15439 ppm in the analyzed samples. An increase in Na is recorded at the base of the Cenomanian that changes to lower values in the upper Cenomanian. Two peaks of Na are recorded around the Cenomanian–Turonian boundary. Lower values of Na are measured from the Turonian sequence. Strontium (Sr): The Sr content of the studied well changes from 28 to 604 ppm, with a mean of 367 ppm. Decreased Sr contents are recorded in the lower part of the Cenomanian sequence that changes to higher concentrations in the upper part of this sequence. Generally, the Sr content of the Cenomanian sequence is low. Around the C-T boundary, perturbations in Sr concentrations are recorded with sharp decreases below the disconformities. Paragenetic Sequence: The paragenetic sequence of the Sarvak Formation includes its deposition in the marine realm, experiencing two stages of meteoric diagenesis, and passing through shallow to deep burial realms. Elemental Evidence: The effects of meteoric waters on marine carbonates commonly result in an increase in Mn concentrations in the altered carbonates (Brand and Veizer, 1980). Such an increase in Mn content is recorded at the C–T and mT paleoexposures. The variations in Na concentrations are strongly facies dependent. Sharp increasing peaks of Na are recorded at disconformable surfaces indicating a meteoric diagenetic effect (Brand and Veizer 1980). Decreased values of Sr are expected within the meteorically-altered carbonates, because the Sr concentration in meteoric waters (0.1–0.01 ppm) is much lower than the marine carbonates (1000–9400 ppm) (Brand and Veizer 1980). In the Sarvak Formation, sharp decreases in Sr are measured from the karstified intervals below the paleoexposure surfaces. Geochemical Correlation: The geochemical profile of the Sarvak Formation in the studied well is correlated with a previous study in the Dezful Embayment (Mehrabi et al. 2022). As shown, there is a close correlation between these sections, especially regarding the trace elemental concentrations. Both C–T and mT disconformities are distinguished across the Zagros Basin, including the Abadan Plain, Dezful Embayment, Izeh, and Fars zones. Consequently, similar geochemical trends are formed as a result of intensive meteoric diagenetic alterations below these disconformable surfaces.

https://jssr.ui.ac.ir/article_28166_06d9da7836a750463c800febe065e695.pdf

University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 39 3 2023 09 23 Palynostratigraphy of the Upper Cretaceous deposits (K3) in the Central Alborz Basin (Dare-zar section) Palynostratigraphy of the Upper Cretaceous deposits (K3) in the Central Alborz Basin (Dare-zar section) 103 122 28259 10.22108/jssr.2024.139477.1271 FA Elahe Zarei Assistant Professor, School of Geology, Damghan University, Damghan, Iran Fariba Foroughi Assistant Professor, School of Geology, College of science, University of Tehran, Tehran, Iran Farahnaz Akbarzade MSC in School of Geology, College of science, University of Tehran, Tehran, Iran Journal Article 2023 10 17 Abstract To investigate the Upper Cretaceous deposits in the Central Alborz Basin, a 100-meter thick stratigraphic section was chosen in the southwest of Dareh Zar village in the east of Tehran. In this study, a total of 75 species, belonging to 44 dinocyst genera, and 10 species from seven spore genera were identified. Consequently, two biozones—Dinogymnium acuminatum and Carpatella cornuta—have been determined. The association of the Dinogymnium acuminatum biozone with index planktonic foraminifers such as Contusotruncana contusa, Globotruncana arca, and Globotruncana ventricosa at the base of the studied section confirms the Late Cretaceous age. Furthermore, the presence and abundance of the Carpatella cornuta biozone in sample 44 indicate the beginning of the Paleocene. The presence of this biozone with typical dinocysts such as Damassadinium californicum, Thalassiphora delicate, and Tectatodinium sp. suggests the upper Paleocene age range for the end of the stratigraphic section. The presented biozones based on dinocysts are consistent with those in eastern Europe and northwestern Tethys, indicating a marine connection between these regions in the Late Cretaceous. Keywords: Palynostratigraphy, Dinocyst, Upper Cretaceous, Central Alborz Introduction Cretaceous strata in the Alborz region have long fascinated paleontologists, prompting investigations by European geologists who have documented their findings in geological maps. To further explore the Upper Cretaceous strata of the Alborz basin, address existing uncertainties, and precisely map the Cretaceous outcrops and their stratigraphy, a specific stratigraphic section was chosen in the southwest of Dareh Zar village, located in the central Alborz basin. Notably, this area had not been previously studied for palynomorphs. Therefore, efforts were made to conduct palynostratigraphic studies and age determination of these deposits by examining marine palynomorphs noted for their significant diversity and abundance in the selected section. Material & Methods The section under examination is located to the southwest of Dere Zar village, which is situated 80 km from Tehran and 13 km south of Mehrabad city. The geographical coordinates of the area being studied are 35°36'52.1"N and 51°53'31.5"E (Fig 1). This stratigarphic section, with a thickness of approximately 100 meters, consists of grey to olive green marls with interspersed layers of cream-colored argillaceous limestones. These layers are discontinuously overlaying the limestones of the K2 unit. Towards the end of the section, the red polymictic conglomerate of the Fajan Formation, indicating a mix of origins, was observed. For palynostratigraphic study in this section, 89 samples were collected from various parts of the succesion, and palynological slides were prepared using the Travers method (Travers 2007). These prepared slides were then examined under an optical microscope using 40x and 60x magnification lenses. Discussion of Results & Conclusions The study section contains a variety of palynoflora, including dinocysts, spores, pollen, acritarchs, scolecodonts, and foraminifera test lining. A total of about 75 species of 44 dinocyst genera and 10 species of seven spore genera were identified. Upon examination of the slides from this section, it was observed that dinocysts exhibit relatively higher diversity, abundance, and preservation compared to other palynomorphic groups. Consequently, the palynostratigraphic analysis in this section was primarily based on dinocysts. To determine the exact age, charts from Williams et al. (2004), Williams (1978), and Williams and Bujak (1985) were utilized. Dinogymnium acuminatum Interval zone The Dinogymnium acuminatum Interval zone is delineated from the first occurrence of Dinogymnium acuminatum to the initial appearance of the indicator species Carpatella cornuta. This particular species is recognized as one of the most significant Late Cretaceous dinoflagellate species found in marine sediments globally, a distinction introduced by William et al. in 2004. Powell (1992a) classified this species as a Late Cretaceous (early Maastrichtian) dinocyst. Furthermore, various researchers have positioned the genus within the middle Maastrichtian age range (Wilson 1971; Schrank 1987; Marcheinecke 1992; Schiøler & Wilson 1993; Williams et al. 2004). This biozone has also been identified as a local biozone in the Zagros region, specifically in Ilam (Rabani et al. 2009) and Khuzestan (Zarei 2005). Associated dinocysts include: Spiniferites ramosus, Conifera tabulasa, Hystrichodinium pucherum, Trithyrodinium castanea, Odontochitina costat, Odotochitina spp., Trithyrodinium suspectum, spiniferites echinodinum, Phelodinium tricupsus, senegalium bicavatum, Deflandera galeata, Trithyrodinium evittii, Cannosphaeropsis utinensis, Fibrocysta ovalis, Hystrichokolpoma bulbosum, Xenasus ceratiopsis Carpatella cornuta Taxon range zone The Carpatella cornuta Taxon range zone encompasses the occurrence range of Carpatella cornuta, signifying the Paleocene age range. This biozone has been documented in the Gurpi Formation located in the northeast of Khuzestan, with a Late Paleocene age (Zarei 2005), and in the Gurpi Formation in the southeast of Ilam, spanning from the early Danian to the early Selandian (Rabani et al. 2009). The appearance of this species in New Zealand has been assigned to the Early Paleocene (Willumsen 2006), in Morocco (Mancini et al. 1996) and Georgia (Frith 1987), it has been documented in the Early Paleocene. The Lower Paleocene and its last appearance have been correlated with the Lower Paleocene-Upper Paleocene (Danian) boundary. However, in the northern hemisphere, the appearance of this species at mid-latitudes is considered Danian, with its last occurrence in the Selandian (Williams et al. 2004). The presence and abundance of Carpatella cornuta in sample 44 of the studied section indicate the onset of the Paleocene. Associated fossils in this zone include: Cannosphaeropsis utinensis, Spiniferites ramosus, Manumella seelandica, Araucariacites australis, Dinogodinium sp, Manumella drugii, Sentusidinium sp., Dinogymnium wetzelli, Kleithriasphaeridium sp, Operculidinium sp., Phelodinium magnificum, Carpatella cornuta, Hystrichosphaeridium sp., Impagidium sp., Achomosphaera sp., Deflandrea magnifica, Coronifera oceanica. The presence of typical dinocysts such as Damassadinium californicum, Talassiphora delicate, and Tectatodinium spp. in this biozone suggests a Late Paleocene age range. However, due to the poor preservation of palynomorphs in the final 37 meters of the studied section, it's challenging to precisely determine the age of these sections. To address this issue and refine age determination, planktonic foraminifers present in the sediments were analyzed. Studies have revealed the appearance of key foraminifers such as Contusotruncana fornicata, Globotruncana arca, Globotruncana ventricosa, and Hedbergella spp. at the base of the studied section, confirming a Late Cretaceous age (Postuma 1971). To sum up, the study of dinocysts has led to the identification of two distinct biozones, Dinogymnium acuminatum and Carpatella cornuta. Consequently, the age of the studied unit in the Dere Zar Valley section is estimated to span from the Maestrichtian to the end of the Danian/Titanian, with the Cretaceous–Paleocene boundary positioned within the gray marls of sample No. 44. These biozones, as determined in the studied section, align with those established from the Late Cretaceous and Paleocene epochs in various regions of Iran and globally. Notably, the proposed biozones in the central Alborz basin demonstrate the highest compatibility with biozones observed in eastern Europe and Australia. Furthermore, a comparison of the diversity, abundance, and characteristics of biozones across different parts of Iran reveals a significant similarity between the studied region and samples from the Zagros area. Abstract To investigate the Upper Cretaceous deposits in the Central Alborz Basin, a 100-meter thick stratigraphic section was chosen in the southwest of Dareh Zar village in the east of Tehran. In this study, a total of 75 species, belonging to 44 dinocyst genera, and 10 species from seven spore genera were identified. Consequently, two biozones—Dinogymnium acuminatum and Carpatella cornuta—have been determined. The association of the Dinogymnium acuminatum biozone with index planktonic foraminifers such as Contusotruncana contusa, Globotruncana arca, and Globotruncana ventricosa at the base of the studied section confirms the Late Cretaceous age. Furthermore, the presence and abundance of the Carpatella cornuta biozone in sample 44 indicate the beginning of the Paleocene. The presence of this biozone with typical dinocysts such as Damassadinium californicum, Thalassiphora delicate, and Tectatodinium sp. suggests the upper Paleocene age range for the end of the stratigraphic section. The presented biozones based on dinocysts are consistent with those in eastern Europe and northwestern Tethys, indicating a marine connection between these regions in the Late Cretaceous. Keywords: Palynostratigraphy, Dinocyst, Upper Cretaceous, Central Alborz Introduction Cretaceous strata in the Alborz region have long fascinated paleontologists, prompting investigations by European geologists who have documented their findings in geological maps. To further explore the Upper Cretaceous strata of the Alborz basin, address existing uncertainties, and precisely map the Cretaceous outcrops and their stratigraphy, a specific stratigraphic section was chosen in the southwest of Dareh Zar village, located in the central Alborz basin. Notably, this area had not been previously studied for palynomorphs. Therefore, efforts were made to conduct palynostratigraphic studies and age determination of these deposits by examining marine palynomorphs noted for their significant diversity and abundance in the selected section. Material & Methods The section under examination is located to the southwest of Dere Zar village, which is situated 80 km from Tehran and 13 km south of Mehrabad city. The geographical coordinates of the area being studied are 35°36'52.1"N and 51°53'31.5"E (Fig 1). This stratigarphic section, with a thickness of approximately 100 meters, consists of grey to olive green marls with interspersed layers of cream-colored argillaceous limestones. These layers are discontinuously overlaying the limestones of the K2 unit. Towards the end of the section, the red polymictic conglomerate of the Fajan Formation, indicating a mix of origins, was observed. For palynostratigraphic study in this section, 89 samples were collected from various parts of the succesion, and palynological slides were prepared using the Travers method (Travers 2007). These prepared slides were then examined under an optical microscope using 40x and 60x magnification lenses. Discussion of Results & Conclusions The study section contains a variety of palynoflora, including dinocysts, spores, pollen, acritarchs, scolecodonts, and foraminifera test lining. A total of about 75 species of 44 dinocyst genera and 10 species of seven spore genera were identified. Upon examination of the slides from this section, it was observed that dinocysts exhibit relatively higher diversity, abundance, and preservation compared to other palynomorphic groups. Consequently, the palynostratigraphic analysis in this section was primarily based on dinocysts. To determine the exact age, charts from Williams et al. (2004), Williams (1978), and Williams and Bujak (1985) were utilized. Dinogymnium acuminatum Interval zone The Dinogymnium acuminatum Interval zone is delineated from the first occurrence of Dinogymnium acuminatum to the initial appearance of the indicator species Carpatella cornuta. This particular species is recognized as one of the most significant Late Cretaceous dinoflagellate species found in marine sediments globally, a distinction introduced by William et al. in 2004. Powell (1992a) classified this species as a Late Cretaceous (early Maastrichtian) dinocyst. Furthermore, various researchers have positioned the genus within the middle Maastrichtian age range (Wilson 1971; Schrank 1987; Marcheinecke 1992; Schiøler & Wilson 1993; Williams et al. 2004). This biozone has also been identified as a local biozone in the Zagros region, specifically in Ilam (Rabani et al. 2009) and Khuzestan (Zarei 2005). Associated dinocysts include: Spiniferites ramosus, Conifera tabulasa, Hystrichodinium pucherum, Trithyrodinium castanea, Odontochitina costat, Odotochitina spp., Trithyrodinium suspectum, spiniferites echinodinum, Phelodinium tricupsus, senegalium bicavatum, Deflandera galeata, Trithyrodinium evittii, Cannosphaeropsis utinensis, Fibrocysta ovalis, Hystrichokolpoma bulbosum, Xenasus ceratiopsis Carpatella cornuta Taxon range zone The Carpatella cornuta Taxon range zone encompasses the occurrence range of Carpatella cornuta, signifying the Paleocene age range. This biozone has been documented in the Gurpi Formation located in the northeast of Khuzestan, with a Late Paleocene age (Zarei 2005), and in the Gurpi Formation in the southeast of Ilam, spanning from the early Danian to the early Selandian (Rabani et al. 2009). The appearance of this species in New Zealand has been assigned to the Early Paleocene (Willumsen 2006), in Morocco (Mancini et al. 1996) and Georgia (Frith 1987), it has been documented in the Early Paleocene. The Lower Paleocene and its last appearance have been correlated with the Lower Paleocene-Upper Paleocene (Danian) boundary. However, in the northern hemisphere, the appearance of this species at mid-latitudes is considered Danian, with its last occurrence in the Selandian (Williams et al. 2004). The presence and abundance of Carpatella cornuta in sample 44 of the studied section indicate the onset of the Paleocene. Associated fossils in this zone include: Cannosphaeropsis utinensis, Spiniferites ramosus, Manumella seelandica, Araucariacites australis, Dinogodinium sp, Manumella drugii, Sentusidinium sp., Dinogymnium wetzelli, Kleithriasphaeridium sp, Operculidinium sp., Phelodinium magnificum, Carpatella cornuta, Hystrichosphaeridium sp., Impagidium sp., Achomosphaera sp., Deflandrea magnifica, Coronifera oceanica. The presence of typical dinocysts such as Damassadinium californicum, Talassiphora delicate, and Tectatodinium spp. in this biozone suggests a Late Paleocene age range. However, due to the poor preservation of palynomorphs in the final 37 meters of the studied section, it's challenging to precisely determine the age of these sections. To address this issue and refine age determination, planktonic foraminifers present in the sediments were analyzed. Studies have revealed the appearance of key foraminifers such as Contusotruncana fornicata, Globotruncana arca, Globotruncana ventricosa, and Hedbergella spp. at the base of the studied section, confirming a Late Cretaceous age (Postuma 1971). To sum up, the study of dinocysts has led to the identification of two distinct biozones, Dinogymnium acuminatum and Carpatella cornuta. Consequently, the age of the studied unit in the Dere Zar Valley section is estimated to span from the Maestrichtian to the end of the Danian/Titanian, with the Cretaceous–Paleocene boundary positioned within the gray marls of sample No. 44. These biozones, as determined in the studied section, align with those established from the Late Cretaceous and Paleocene epochs in various regions of Iran and globally. Notably, the proposed biozones in the central Alborz basin demonstrate the highest compatibility with biozones observed in eastern Europe and Australia. Furthermore, a comparison of the diversity, abundance, and characteristics of biozones across different parts of Iran reveals a significant similarity between the studied region and samples from the Zagros area.

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