دانشگاه اصفهان پژوهش های چینه نگاری و رسوب شناسی 2008-7888 42 3 2026 09 23 Lithostratigraphy and petrofacies of the Middle Triassic (Upper part of the Elika Formation) and the Upper Triassic–Lower Jurassic strata (Basal part of the Shemshak Group, Shamirzad Formation) in the Jajarm Bauxite Mine, NE Iran سنگ‎‍چینه‎‍نگاری و پتروفاسیس نهشته‎‍های تریاس میانی (بخش بالایی سازند الیکا) و تریاس بالایی-ژوراسیک زیرین (بخش قاعده‎‍ای گروه شمشک، سازند شهمیرزاد) در معدن بوکسیت جاجرم 1 22 30392 10.22108/jssr.2026.148175.1326 FA عزیزاله طاهری استاد، گروه زمین‎‍شناسی، دانشکده علوم‌زمین، دانشگاه صنعتی شاهرود، شاهرود، ایران مهدی جعفرزاده دانشیار، گروه زمین‎‍شناسی، دانشکده علوم زمین، دانشگاه صنعتی شاهرود، شاهرود، ایران Journal Article 2026 01 31 Abstract In the northeastern Jajarm region, within the structural zone of the Eastern Alborz, a complete sequence of the Elika Formation (Early–Middle Triassic) and the Shemshak Group (Late Triassic–Middle Jurassic) is exposed. In this study, the upper part of the Elika Formation and the Upper Triassic Shahmirzad Formation of the Shemshak Group were investigated based on lithostratigraphic and petrographic analyses. The upper part of the Elika Formation, approximately 80 m thick, mainly consists of dolomite and dolomitic limestone with stromatolitic structures and lacks fossils, indicating deposition in a tidal environment. The Shemshak Group, with an approximate thickness of 2,050 m, comprises sandstones, silty sandstones, siltstones, shales, and fossiliferous limestones, and is subdivided into the Shahmirzad, Alasht, Shirin-Dasht, Fil-Zamin, and Densrit formations. The Shahmirzad Formation, about 285 m thick, predominantly consists of shale and sandstone and includes fossiliferous marker beds and diverse petrofacies such as litharenite and lithic arkose. The results indicate that the Shemshak Group exhibits significant lateral variations due to deposition in a fluvial–deltaic environment, and the observed litharenites reflect uplifted sequences associated with orogenic activity and foreland basin subsidence. The results of this study provide a detailed lithostratigraphic framework and fundamental data for identifying bauxite horizons and guiding future exploration. Keywords: Jajarm, Shemshak Group, Elika Formation, Shahmirzad Formation, Petrofacies Introduction The Shemshak Group in the Gol-e-Bini section, similar to other exposures of this group, is predominantly composed of siliciclastic deposits, including sandstone, siltstone, and silty sandstone. This succession was previously investigated by Fürsich et al (2009). According to these studies, the total thickness of the Shemshak Group was measured as 2,050 meters, comprising, from base to top, the Shahmirzad, Alasht, Shirindasht, Fil-e-Zamin, and Dansirit formations. In the Gol-e-Bini section, the lower boundary of the Shemshak Group unconformably overlies the dolomitic strata of the Elika Formation, whereas its upper boundary is disconformably overlain by marly limestones and marls of the Dalichai Formation. Both the lower and upper contacts are erosional disconformities associated with two major tectonic phases, namely the Early Cimmerian and Middle Cimmerian tectonic events, respectively. Variations in sedimentary successions among different depositional basins emphasize the importance of stratigraphic investigations, particularly lithostratigraphic subdivision, as one of the fundamental components of regional geological studies. The relatively homogeneous lithological characteristics and the scarcity of key beds have made the recognition of lateral facies variations within the Shemshak Group extremely difficult. Therefore, the present study focuses on a detailed stratigraphic investigation of the upper part of the Elika Formation and the basal formation of the Shemshak Group, including the Shahmirzad Formation. These formations were subdivided into lithological units, and where possible, key beds and marker horizons were identified and introduced. Materials & Methods The study of the Shemshak Group has been carried out in two stages: field and laboratory. Due to the lithological homogeneity of the succession and the absence of distinct key beds, tracing lateral facies variations within the Shemshak Group is inherently difficult. In this research, after a thorough review of previous studies and field surveys, suitable stratigraphic sections were selected for examination. Because mining activities and tectonic deformation have disrupted parts of the original sedimentary succession, no single complete stratigraphic section could be identified. Consequently, the succession was examined in three separate sections: Gol-e-Bini 4, Gol-e-Bini 6, and Zoo. During field investigations, the sedimentary succession was subdivided into lithological units based on bedding characteristics, sedimentary structures, fossil content, lithology, and both vertical and lateral facies variations. For further description and analysis, samples were collected from certain beds to prepare thin sections. In total, 100 sandstone samples were collected during fieldwork, of which 70 thin sections were prepared and examined using a polarizing microscope. Discussion of Results & Conclusions The upper part of the Elika Formation, with a thickness of about 80 meters, mainly consists of dolomites and dolomitics limestone containing stromatolitic structures and lacking any fossil content, indicating deposition in a tidal flat environment. The considerable thickness and lithological composition of the Shemshak Group suggest sediment accumulation within a shallow basin characterized by a high subsidence rate, most likely within a foreland basin setting. Progressive subsidence of the basin floor resulted in gradual landward transgression and rising relative sea level, eventually leading to the establishment of a carbonate platform upon which the sediments of the Dalichai Formation were deposited. Petrographic and Petrofacies analysis indicates that carbonate and chert rock fragments are abundant in the basal part of the Shemshak Group, whereas metamorphic rock fragments appear in its upper part. These variations in rock fragment composition are related to tectonic conditions and provenance. The carbonate lithic fragments were most likely derived from erosion of the Elika Formation, while the metamorphic fragments were sourced from the Gorgan Schists, which stratigraphically underlie the Elika Formation. The dominant lithology of the Shahmirzad Formation consists of shale interbedded with sandstone layers. A fossiliferous limestone bed in the upper part of the formation constitutes an important marker horizon within this siliciclastic succession. In addition, sandstone beds containing autochthonous calamites in the middle part of the formation represent another distinctive stratigraphic horizon. The predominant petrofacies in the Shahmirzad Formation include siltstone, litharenite with clay cement and matrix, litharenite with carbonate cement, feldspathic litharenite with carbonate cement, feldspathic litharenite with siliceous cement, lithic arkose with carbonate cement, and lithic arkose with clay cement. The Shahmirzad Formation representing the basal unit of the Shemshak Group that was deposited predominantly in a fluvial depositional environment characterized by channel sandstones, floodplain deposits, and swamp sediments. The occurrence of thin coal seams, root horizons, plant fossil remains and wood fragments, collectively indicate deposition under warm and humid climatic conditions. Evidence for a subsequent marine transgression is provided by carbonate beds in the upper part of the formation containing bivalve and echinoid fossils. در شمال ‌شرقی جاجرم، حوضۀ ساختاری البرز خاوری، توالی کاملی از سنگ‌های سازند الیکا (تریاس پیشین–میانی) و گروه شمشک (تریاس پسین–ژوراسیک میانی) رخنمون دارد. در این مطالعه، بخش بالایی سازند الیکا و سازند شهمیرزاد از گروه شمشک، بر‎‍اساس مطالعات سنگ‌چینه‌نگاری و پتروگرافی بررسی شدند. بخش بالایی سازند الیکا با ضخامت حدود ۸۰ متر، عمدتاً شامل دولومیت و آهک دولومیتی با ساخت‌های استروماتولیتی و فاقد فسیل و نشان‌دهندۀ ته‎‍نشست در محیط جزر و مدی است. گروه شمشک با ضخامت تقریبی ۲۰۵۰ متر شامل ماسه‌سنگ، سیلت‌سنگ، شیل و آهک فسیل‌دار است و به سازندهای شهمیرزاد، آلاشت، شیرین‌دشت، فیل‌زمین و دنسریت تفکیک می‌شود. سازند شهمیرزاد با ضخامت حدود ۲۸۵ متر، عمدتاً از شیل و ماسه‌سنگ تشکیل می‎‍شود و شامل لایه‌های شاخص فسیل‌دار و پتروفاسیس‌های متنوع نظیر لیت‌آرنایت و لیتیک آرکوز است. یافته‌ها نشان می‌دهد که سازند شهمیرزاد تحت تأثیر رسوب‌گذاری در محیط رودخانه‌ای–دلتایی، دچار تغییرات جانبی درخور توجه است و لیت‌آرنایت‌های موجود، نمایانگر توالی‌های بالا‎‍آمدۀ ناشی از فعالیت کمربندهای کوهزایی و ته‌نشست‌های مرتبط با حوضه فورلند هستند. نتایج این مطالعه، چارچوب لیتواستراتیگرافی دقیق و اطلاعات پایه‌ای ارزشمندی را برای شناسایی افق‌های بوکسیتی و مطالعات اکتشافی آینده ارائه می‌دهد.

https://jssr.ui.ac.ir/article_30392_247db6a21f917b419c116120056c7f77.pdf

دانشگاه اصفهان پژوهش های چینه نگاری و رسوب شناسی 2008-7888 42 3 2026 09 23 Miocene deposits of the folded Zagros (Asmari Formation, Lorestan Region) ریزرخساره‎‍ها، محیط رسوبی و توالی‎‍های دیاژنزی نهشته‎‍های الیگوسن- میوسن زاگرس چین‎‍خورده (سازند آسماری، پهنۀ لرستان) 23 52 30376 10.22108/jssr.2026.147601.1323 FA محسن آشنا دانشجوی دکتری گروه زمین‎‍شناسی، واحد خرم‎‍آباد، دانشگاه آزاد اسلامی، خرم‎‍آباد، ایران کبری میربیک سبزواری استادیار گروه زمین‎‍شناسی، واحد خرم‎‍آباد، دانشگاه آزاد اسلامی، خرم‎‍آباد، ایران محمدصادق دهقانیان دانشیار گروه زمین‎‍شناسی، واحد بندرعباس، دانشگاه آزاد اسلامی، بندرعباس، ایران سیدوحید شاهرخی دانشیار گروه زمین‎‍شناسی، واحد خرم‎‍آباد، دانشگاه آزاد اسلامی، خرم‎‍آباد، ایران سیامک بهاروند دانشیار گروه زمین‎‍شناسی، واحد خرم‎‍آباد، دانشگاه آزاد اسلامی، خرم‎‍آباد، ایران Journal Article 2025 12 13 Abstract In this study, the depositional and post-depositional history of carbonate rocks of the Asmari Formation in the Lorestan region was investigated. Three stratigraphic sections were analyzed: the northern Khorramabad section (92.3 m), the southeastern Khorramabad section (90 m), and the southwestern Khorramabad section (190 m). A total of 380 samples were collected for petrographic examination. The lower boundary of the Asmari Formation with the Shahbazan Formation is a conformable contact, while its upper boundary with the Gachsaran Formation represents a conformable unconformity. Thirteen microfacies were identified, including various dolomudstones, wackestones, packstones, grainstones, and rudstones containing different types of foraminifera, echinoderms, bryozoans, coralline algae, and anhydrite. These microfacies represent deposition on a carbonate ramp ranging from inner to mid and outer ramp settings. Several diagenetic processes were recognized, such as micritization, neomorphism, marine, meteoric, and burial cementation, dissolution, development of both fabric-selective and non-fabric-selective porosity, and replacement processes including pyritization, silicification, and dolomitization. Based on petrographic evidence, the paragenetic sequence of the Asmari Formation carbonates was interpreted to have formed in four diagenetic environments: marine, meteoric, burial, and uplift. These environments correspond to stages of early diagenesis (eogenesis), middle diagenesis (mesogenesis), and late diagenesis (telogenesis). Keywords: Asmari Formation, depositional environment, diagenesis, Zagros, Lorestan Introduction The Asmari Formation, with its dominant carbonate lithology, is rich in benthic foraminifera of Oligocene-Miocene age. Therefore, using this valuable fossil content and other skeletal components in this formation, the type of its depositional environment can be determined according to the models presented by Flügel (2010) and Wilson (1986). The Asmari Formation deposits can be considered as the last widespread marine transgression in the Zagros Basin (Amiri Bakhtiar and Noraiyanejad 2022). In terms of age, it begins in the Oligocene and continues up to the Burdigalian of the Early Miocene (Motiei 2000). Based on its fossils and age, the Asmari Formation can be divided into three parts: Lower, Middle, and Upper Asmari (Motiei 2000). In most outcrops in Lorestan, the Lower Asmari limestones are deposited directly over the carbonate rocks of the Shahbazan Formation, which are of Late Eocene age. In more northern areas, the Lower Asmari is absent, and it appears that the interval from the Late Eocene to the Oligocene was subaerial. Toward the southern regions, the Late Eocene–Oligocene limestones of the Lower Asmari grade into the deeper-water shales of the Pabdeh Formation (Paleocene–Oligocene). From Lorestan toward the Dezful Embayment, the Lower Asmari limestones were deposited along the margin of the deeper Pabdeh basin. The study area is situated within the Zagros Fold-Thrust Belt, specifically in the Lorestan sedimentary province. Three stratigraphic sections were selected in this region for detailed analysisThe study of the Asmari Formation in the Lorestan sedimentary basin is highly important, primarily due to its role as one of the most significant carbonate hydrocarbon reservoirs in the Zagros Basin. The primary objective of investigating this formation in this part of the basin is to identify facies variations, reconstruct depositional environments, and understand its diagenetic evolution, thereby enabling the prediction of reservoir quality and porosity distribution across different segments of the basin. A precise analysis of the petrophysical properties and sequence stratigraphy of the Asmari Formation in Lorestan provides a framework to improve reservoir modelling, evaluate the processes controlling hydrocarbon migration and accumulation in the area, and reduce exploration risks during the drilling of development and appraisal wells. Material & Methods In this research, following multiple field visits and the study of the 1:250,000 scale geological maps of Khorramabad and Pol-e Dokhtar, three suitable outcrop sections of the Asmari Formation were selected within the Zagros Fold-Thrust Belt (Lorestan sedimentary basin). Section 1: Located on the northern limb of the Khorramabad َnticline, near Sarab-e Chenar village (Bastam area). The geographical coordinates are 48° 8’ 58" E longitude and 33° 41’ 36" N latitude. Section 2: Located southeast of Khorramabad, along the road to Sepiddasht. The geographical coordinates are 48° 13’ 10" E longitude and 33° 36’ 40" N latitude. Section 3: Located approximately 85 km south of Khorramabad (Varah-Zard village) and 11 km north of Pol-e Dokhtar. The geographical coordinates are 47° 43’ 2" E longitude and 33° 13’ 26" N latitude. These sections were chosen to ensure they exhibit maximum thickness, significant lithological variations, easy accessibility, and minimal cover. A total of 380 rock samples were collected from these sections: 90 samples from the northern Khorramabad section, 90 samples from the southeastern Khorramabad section, and 200 samples from the southern Khorramabad section. Thin sections were prepared from all samples for petrographic analysis. These thin sections were prepared at Lorestan University and studied and photographed using an Olympus BH2 polarizing microscope equipped with a Nikon D70 camera. Carbonate rock nomenclature followed the method proposed by Dunham (1962) and the modified scheme from Embry and Klovan (1971). The interpretation of microfacies and depositional environments was conducted based on the works of Flügel (2010) and Wilson (1975). Discussion of Results & Conclusions In the three studied sections, 13 carbonate microfacies have been identified. These include: Anhydrite microfacies, fenestral dolomudstone, nodular dolomudstone, wackestone/packstone with extraclasts, mudstone to wackestone with bioturbation, wackestone/packstone with imperforate foraminifera, wackestone/packstone with imperforate and perforate foraminifera, wackestone/packstone with perforate foraminifera, bioclastic grainstone containing foraminifera, packstone to grainstone with echinoderms, bryozoans, and coralline algae, rudstone/floatstone containing foraminifera and coralline algae, floatstone/rudstone with coralline red algae, mudstone to wackestone with planktonic foraminifera. These microfacies were deposited within three distinct facies belts corresponding to a carbonate ramp: the tidal flat, lagoon, and open marine environments. Based on field evidence and the identified microfacies in the studied stratigraphic sections, the depositional environment of the Asmari Formation exhibits a continuous and gradual transition from the mudstone, wackestone, and packstone microfacies of the low-energy lagoonal environment associated with the inner ramp, to the grainstone facies of the high-energy lagoon at the beginning of the mid-ramp. This is followed by a gradual transition to packstone facies with elongated foraminifera and hyaline tests, and floatstone and rudstone microfacies of the distal mid-ramp, eventually leading to mudstone facies containing planktonic foraminifera characteristic of the open marine environment at the beginning of the outer ramp. The presence of evidence such as the abundance of non-porous benthic foraminifera with porcelains shells in a texture ranging from wackestone to packstone, red algae, weak to moderate sorting of allochems and supporting mud texture, the depositional environment of the Asmari Formation deposits in the stratigraphic sections is considered as a homoclinal carbonate ramp. Among the most important diagenetic processes in the studied sections are compaction, cementation, dissolution, porosity and replacement. Based on petrography evidence, the diagenetic sequence of the Asmari Formation occurred during three stages (eogenesis, mesogenesis, and telogenesis) and in four diagenetic environments (marine, burial, freshwater, and uplift). Early Diagenesis (Eogenesis): This stage includes some diagenetic processes, such as micritization and syntaxial rim cement, which are characteristic of early diagenesis in marine environments, have been identified in the studied sections, confirming the initial diagenesis stage. Freshwater Diagenesis: In the freshwater phreatic environment, intergranular pores are continuously filled with water, which can lead to the dissolution of metastable minerals like aragonite and high-magnesium calcite (Heydari and Wade 2014). Intermediate Diagenesis (Mesogenesis): During this stage, sediments are subjected to pressure and temperature resulting from burial at various depths, continuing until the threshold of diagenesis is reached. Processes occurring in this stage include physical and chemical compaction, blocky and drusy cements, dolomitization, and pyritization, all of which have been identified in the studied samples. Chemical compaction leads to the formation of features resulting from pressure dissolution, such as stylolites. Late Diagenesis (Telogenesis): During uplift, iron ions are introduced into the sediments by meteoric waters through fractures, forming hydrated iron oxides (oxidizing conditions), which gradually convert to hematite. Fractures and joints identified in the studied sections formed during this stage and are filled with freshwater cements. در این پژوهش، تاریخچۀ رسوب‎‍گذاری و پس از رسوب‎‍گذاری سنگ‎‍های کربناتۀ سازند آسماری در پهنۀ لرستان مطالعه شده است. سه برش چینه‎‍شناسی (برش شمال خرم‎‍آباد 3/92 متر، برش جنوب شرق خرم‎‍آباد 90 متر و برش جنوب غرب خرم‎‍آباد 190 متر) در راستای این هدف انتخاب و در‎‍مجموع 380 نمونه از این برش‎‍ها برای مطالعات سنگ‎‍شناسی برداشت شد. در این برش‎‍ها مرز زیرین سازند آسماری با سازند شهبازان به‎‍صورت ناپیوستگی هم‌شیب و مرز بالایی آن با سازند گچساران همساز است. در این توالی‎‍ها 13 ریزرخساره، شامل ریزرخساره‎‍های انیدریت، دولومادستون فنسترال، دولومادستون ندولار، وکستون/پکستون داری اکستراکلست، مادستون تا وکستون دارای آشفتگی زیستی، وکستون/پکستون دارای روزن‌داران بدون منفذ، وکستون/پکستون دارای روزن‌داران بدون منفذ و منفذدار، وکستون/پکستون دارای روزن‌داران منفذدار، گرینستون بایوکلستی حاوی روزن‌دار، پکستون تا گرینستون دارای روزن‌داران، اکینودرم، بریوزوئر و کورالین، رودستون/فلوتستون حاوی روزن‌دار و جلبک کورالیناسه‎‍آ، فلوتستون/رودستون بایوکلستی حاوی جلبک قرمز کورالین و ریزرخسارۀ مادستون تا وکستون داری روزن‌داران پلانکتونیک شناسایی شد که بیانگر محیط رسوبی از نوع رمپ کربناته‎‍اند. در این برش‎‍ها چندین فرآیند دیاژنزی ازجمله میکریتی‎‍شدن، نوریختی، سیمانی‎‍شدن (نوع دریایی، آب شیرین و تدفینی)، انحلال و تخلخل (وابسته به فابریک سنگ و غیر وابسته فابریک)‎‍ و جانشینی (پیریتی‎‍شدن، سیلیسی‎‍شدن و دولومیتی‎‍شدن) رخ داده است. براساس شواهد پتروگرافی، توالی پاراژنتیکی نهشته‎‍های سازند آسماری در این برش‎‍ها در چهار محیط دریایی، آب شیرین، تدفینی و بالاآمدگی تفسیر شده است. این فرآیندها مراحل دیاژنزی اولیه (ائوژنز)‎‍، دیاژنز میانی (مزوژنز) و دیاژنز نهایی (تلوژنز) را پشت سر گذاشته‎‍اند.

https://jssr.ui.ac.ir/article_30376_ed41fb34491c2698d275684f26ec6494.pdf

دانشگاه اصفهان پژوهش های چینه نگاری و رسوب شناسی 2008-7888 42 3 2026 09 23 Lithostratigraphy and biostratigraphy of Permian strata in the south of the Sanandaj–Sirjan Zone, western Kerman Province, based on foraminifera مطالعۀ سنگ چینه‌نگاری و زیست چینه‌نگاری نهشته‌های پرمین در جنوب کمربند دگرگونی سنندج-سیرجان، غرب استان کرمان بر‌اساس روزنبران 53 78 30464 10.22108/jssr.2026.148208.1327 FA محمدجواد حسنی استادیار، گروه اکولوژی، پژوهشگاه علوم و فناوری پیشرفته و علوم محیطی، دانشگاه تحصیلات تکمیلی صنعتی و فناوری پیشرفته، کرمان، ایران Journal Article 2026 02 01 Abstract This study investigates the lithostratigraphy and biostratigraphy of the Permian strata in the west of Sirjan City, within the southern metamorphic Sanandaj–Sirjan Zone (SSZ). The measured section is bounded by faults at its base and top. The studied strata unconformably overlie the metamorphosed Permian–Carboniferous sedimentary deposits and are overlain primarily by the dolomitized and recrystallized Permian–Triassic metamorphic rocks. Fourteen lithostratigraphic units were identified, their characteristics shaped by both original sedimentary basin fluctuations and post-diagenetic metamorphism. The microfossil assemblage is notably distinct from those of adjacent structural zones, comprising 11 fusulinid and 29 smaller foraminifera species. This unique fauna suggests that during the Permian, the SSZ constituted an independent basin situated on the northern margin of the Neo-Tethys Ocean and the southern margin of the Cimmerian Superterrane. Based on the identified smaller foraminifera and fusulinids, the age of the studied section is constrained to the Bolorian through Murgabian (Middle to Late Permian). Keywords: Permian, Sanandaj–Sirjan, lithostratigraphy, Biostratigraphy, smaller foraminifera Introduction The Sanandaj–Sirjan Zone (SSZ), extending 1500 km in length and 150–250 km in width, is one of the major structural zones of Iran (Aghanbati 2004). This zone contains sedimentary and igneous rocks ranging from Precambrian to Late Cretaceous, which have been intensely overprinted by multi‑stage regional metamorphism under various metamorphic facies (Nadimi and Konon 2012; Mehdipour Ghazi and Moazzen 2015; Hassanzadeh & Wernicke 2016; Gharibnejad et al. 2022). A prominent stratigraphic feature distinguishing this zone from Central Iran and the Zagros is the widespread outcrops of the Permian marine strata, particularly in the Sirjan area. The study of the Permian deposits in the SSZ is complicated because they record the breakup of the Cimmerian supercontinent from the northern margin of Gondwana at the end of the Paleozoic and the subsequent birth of the Neo-Tethys Ocean. Field evidence indicates that from the latest Carboniferous to the Early Permian, a marine basin formed in the southern part of the SSZ, and its extent and depth increased progressively throughout the Permian. The occurrence of shelf deposits and diverse marine fossils points to the formation and development of a marine environment that later evolved into the Neo-Tethys Ocean during the Mesozoic. Despite the necessity of detailed stratigraphic investigations to resolve palaeogeographic uncertainties, the intense folding, fault displacements and regional metamorphism in this belt have largely destroyed original fossil content, texture, and sedimentary structures, rendering conventional stratigraphic studies impossible in most areas. Nevertheless, these difficulties should not preclude stratigraphic efforts where feasible. Therefore, the present study focuses on the lithostratigraphy and biostratigraphy of the relatively undeformed and weakly metamorphosed Permian strata in the Sirjan area, located in the southern part of the SSZ. The aim is to determine the age of these deposits and to compare their faunal content (particularly small foraminifers and fusulinids) with other regions of Iran. Material & Methods The Permian deposit outcrop studied in this research is located in western Kerman Province, west of Sirjan city, within the SSZ (Fig. 1A). The outcrop lies west of the Sirjan salt marsh and northwest of the village of Kheyrabad, accessible via the Sirjan–Kheyrabad road and unpaved roads west of Kheyrabad (Fig. 1B). The measured section is on the eastern slope of Mount Hezarchil at 55°11′57.41″E and 29°31′6.03″N. The study area is in the southern part of the SSZ. According to the 1:100,000 Zardu geological map (Sabzehei 1994), rock exposures near the section consist mainly of metamorphosed limestone and shale units of Late Paleozoic (Carboniferous–Permian) to Early Mesozoic (Triassic) age (Fig. 1C). These rocks have undergone intense folding and multiple fault displacements and appear dark (light brown to black) on satellite imagery (Fig. 1D). Forty‑five samples were collected from the Permian outcrop. Due to faulted lower and upper boundaries, the outcrop limits were clearly distinguishable in the field (Fig. 2). During sampling, efforts were made to select samples with minimal recrystallization, stylolites, and other diagenetic or metamorphic effects. Sampling intervals were measured by tape, with denser and more regular sampling in fossiliferous, non‑metamorphosed layers. The true thickness of the section is 195 m. Most samples showed fusulinid remains, but in many cases, the fusulinid tests were destroyed, leaving only recrystallized or replaced molds. Therefore, three thin sections were prepared from each fossiliferous sample and one thin section from each non‑fossiliferous sample. Thin sections were studied using binocular and polarizing microscopes, and fossil content and petrographic features were photographed with a 10‑megapixel camera. Microfossil identification followed multiple references, cited in the biostratigraphy section. Finally, the identified fossil content was plotted on the measured stratigraphic column, and the range of each fossil along the section was delineated. The fossil assemblage from the studied section was compared with those from other structural zones of Iran to establish the relationship between the study area and other geological domains. Discussing of Results & Conclusion The lower boundary of the studied section rests upon strongly deformed metamorphic sedimentary units due to fault activity. These units include fault breccia, metaconglomerate, and metaquartzite with interbeds of schists and marbles. Intense shearing in the underlying unit and brecciation at the base of the section confirm a faulted lower boundary (Fig. 2). Fifteen lithological units are distinguishable above the basal fault contact as follows (Fig. 2): Unit 1 – Recrystallized and stylolitic limestone, 8 m thick (Fig. A3), with abundant calcite veins. Fusulinid remains occur as dissolved and calcite‑replaced molds (Fig. B3, C3), most of which are unidentifiable. Unit 2 –Fossiliferous limestone, 17 m thick (Fig. A3), with much better-preserved texture and fossil content than the underlying layers. Unit 3 –Sandstone (litharenite/quartzarenite), 6m thick, in sharp contact with the previous unit, showing cross‑bedding (Fig. A3). Unit 4 –Uniformly thick‑bedded fossiliferous limestone, 27 m thick (Fig. A3), where most identified species appear. Unit 5 –Thick‑bedded, unfossiliferous, recrystallized dolomitic limestone, 11 m thick (Fig. A3). Unit 6 –Litharenitic sandstone, 3.5 m thick (Fig. A3). Unit 7 –Highly fossiliferous limestone, 3.8 m thick (Fig. A3). Unit 8 –Massive recrystallized limestone, 6.5 m thick (Fig. A3, A4), with dissolved/replaced fusulinid traces. Unit 9 –Medium‑ to thick‑bedded fossiliferous limestone, 6 m thick (Fig. A4, B4) with lower fusulinid diversity compared to other microfossils. Unit 10 –Slightly metamorphosed shale, 3 m thick (Fig. B4). Unit 11 –Recrystallized calcareous sandstone, 5 m thick (Fig. B4, A5). Unit 12 –Intensely recrystallized and fractured massive limestone, 23 m thick (Fig. A5, B5). Unit 13 –Fossiliferous limestone succession, 54.7 m thick: Lower part medium‑ to thick‑bedded, middle part thick‑bedded to massive and the upper part medium‑ to thick‑bedded limestones (Fig. B5). Unit 14 –Recrystallized, stylolitic dolomitic limestone with calcite veins, 14.5 m thick (Fig. B5, A6, B6). Unit 15 –Medium‑ to thick‑bedded fossiliferous limestone, 6 m thick (Fig. B6), terminated upward by a fault contact. This unit is relatively rich in fossils, containing large fusulinids. Above the upper fault, thick‑bedded to massive dolomitic succession (Fig. B6) with intense fracturing and abundant calcite veins are present. Microscopic studies revealed two main foraminiferal groups: fusulinids and non‑fusulinids. Fusulinids assemblage includes 11 genera and 11 species as Afghanella sp., Cancellina ovalis, Codonofusiella cf. nana, Dunbarula sp., Eopolydiexodina persica, Grovesella sp., Mesoschubertella thompsoni, Misellina ovalis, Polydiexodina sp., Skinnerella sp. and Yangchienia sp. Non‑fusulinid foraminifers include: Climacammina cf. aljutovica, Climacammina elegans, Climacammina cf. procera, Climacammina sp., Climacammina cf. tudiola, Climacammina valvulinoides, Cribrogenerina gigas, Cribrogenerina major, Cribrogenerina sumatrana, Cribrostomum sp., Cryptoseptida sp., Deckerella sp., Deckerella composita, Deckerella geyeri, Deckerella cf. quadrata, Deckerella cf. tenuissima, Diplosphaerina inaequalis, Geinitzina sp., Langella conica, Langella cf. perforate, lunucammina sp., Nodosinelloides camerta, Pachyphloia sp., Padangia sp., Palaeotextularia sp., Palaeotextularia consobrina, Palaeotextularia bella and Palaeotextularia longiseptata. The fossil assemblage of the studied section was compared with those reported from the Alborz, east-central Iran, and Zagros basins. The assemblage of the SSZ is almost unique and does not fully resemble neighboring zones. The Yazd Block (east-central Iran) – No fusulinid‑bearing Permian strata; the Permian consists of dolomites of the Jamal Formation. Tabas Block (east-central Iran) – Fusulinids such as Armenina spp., Misellina spp., etc., show partial similarity up to the middle Kubergandian, but younger strata are unfossiliferous. Alborz (Ruteh Formation, Murgabian–Midian) – Fusulinids like Dunbarula mathieui, Yangchienia haydeni, and Neoschwagerina margaritae were reported but are absent in our section (likely because the Ruteh Formation is younger). Zagros (Dalan Formation) – Eopolydiexodina persica from Murgabian deposits matches the occurrence of the same species at the base of the Murgabian in our study. Thus, the studied assemblage shows the greatest similarity with east-central Iran (Tabas Block) and the Zagros, indicating a palaeogeographic affinity of the southern SSZ with these areas. During the Permian, the SSZ was part of the Cimmerian supercontinent (bordered by Paleo-Tethys to the north and Neo-Tethys to the south). The greater similarity with southern east-central Iran and the Zagros suggests that the studied section lay on the southern margin of the Cimmerian supercontinent, within the northern waters of the Neo-Tethys Ocean (Fig. 7). Based on fusulinid ranges and correlation with previous studies (Leven 2003; Leven & Gorgij 2008, 2011a, b; Fassihi et al. 2019, 2020, 2023; Hosseinipour 2024, among others), two biozones are recognized in the studied section (Figs. 8, 9): Eopolydiexodina persica Zone – Murgabian age: This zone begins at 131 m above the base of the measured section. The Kubergandian–Murgabian transition is marked by the first appearance of Eopolydiexodina persica, Afghanella sp., and Polydiexodina sp., and the last occurrence of Codonofusiella cf. nana and Cancellina ovalis. Immediately before and after this transition, Skinnerella sp. becomes more abundant. At this level, various Deckerella species (formerly common) disappear, while diversity and abundance of Cribrogenerina increase. Cancellina ovalis‑Codonofusiella nana Assemblage Zone – middle–upper Kubergandian age: This biozone is recorded from 77 m above the base of the measured section. Within this zone, various species of Deckerella and Palaeotextularia are present in most samples. At the base of the section, the Bolorian sediments exist, but due to a lithological change (fossiliferous limestone passing into sandstone) and the absence of fusulinids, the precise Bolorian–Kubergandian boundary cannot be determined. Therefore, this boundary is placed below the first sandstone unit, consistent with the last occurrence of Misellina ovali (Leven 2003; Wang et al. 2018). در این مطالعه، سنگ چینه نگاری و زیست چینه نگاری نهشته های پرمین در غرب شهر سیرجان، واقع در جنوب زون ساختاری کمربند دگرگونی سنندج-سیرجان بررسی شده است. برش بررسی شده با مرزهایی گسله بر نهشته های دگرگون شده و در هم ریختۀ پرموکربنیفر و در زیر نهشته های عمدتاً دولومیتی و ریکریستالیزۀ پرمو-تریاس قرار گرفته است. تعداد 14 واحد سنگ چینه شناسی در برش تشخیص داده شده است که حاصل تغییرات سنگ شناسی ناشی از دگرگونی و نوسانات حوضۀ رسوبی اند. مجموعه روزنبران شناسایی شده در برش، شامل 11 گونه از فوززولینها و 29 گونه از روزنبران کوچک است که در مقایسه با مطالعات انجام شده در دیگر زونهای ساختاری مجاور منحصر به فرد است و نشان می دهد که زون ساختاری کمربند دگرگونی سنندج-سیرجان در زمان پرمین به صورت حوضۀ رسوبی مستقلی در شمال اقیانوس نئوتتیس و حاشۀ جنوبی ابر خشکی سیمرین قرار داشته است. محدودۀ سنی برش مطالعه شده نیز براساس روزنبران کوچک و فوزوزلینهای شناسایی شده، Bolorian تا Murgabian پیشنهاد می شود.

https://jssr.ui.ac.ir/article_30464_0e394fec99f53a8b8f19379b55cbb7e2.pdf

دانشگاه اصفهان پژوهش های چینه نگاری و رسوب شناسی 2008-7888 42 3 2026 09 23 Reconstruction of the depositional conditions of the Eocene siliciclastic deposits in the Zagros (Kashkan Formation, south of Lorestan) بازسازی شرایط ته‎‍نهشت نهشته‎‍های آواری ائوسن زاگرس (سازند کشکان، جنوب لرستان 79 113 30406 10.22108/jssr.2026.148437.1328 FA یعقوب نصیری استادیار، گروه زمین‎‍شناسی، دانشکدۀ علوم، مجتمع آموزش عالی گناباد، گناباد، ایران سمیرا تقدیسی نیک بخت استادیار، گروه زمین‎‍شناسی، دانشکدۀ علوم، مجتمع آموزش عالی گناباد، گناباد، ایران مصطفی صداقت نیا دانش‎‍آموختۀ مقطع دکتری، کارشناس آزمایشگاه مرکزی دانشگاه لرستان، خرم‎‍آباد، ایران Journal Article 2026 02 22 Abstract The aim of this research is to investigation the lithofacies and sedimentary environment of the Kashkan Formation (middle Eocene) in the Lorestan sedimentary basin. In this regard, four stratigraphic sections were selected. The Kashkan Formation in the studied area has a variable thickness of 150 to 200 meters. It is mainly composed of conglomerate and sandstone strata, with lesser amounts of fine-grained lithofacies including mudstone, siltstone, and shale. Field studies on the four sections led to the identification of 12 lithofacies, which include five conglomeratic lithofacies (Gm, Gms, Gp, Gh, Gt), five sandstone lithofacies (Sp, St, Sm, Sh, Sr), and two mudstone lithofacies (Fm, Fl). Based on the vertical and lateral changes of facies, the depositional environment of these deposits was a braided river system with a gravelly and sandy bed in proximal areas. The clastic sequences of the Kashkan Formation overlie the marine carbonates of the Taleh Zang Formation, which indicates a sea regression and the progradation of braided rivers toward the basin. A decrease in accommodation space relative to sediment supply caused the progradation of braided river facies within the LST facies suite for the Kashkan Formation. Keywords: Sedimentary environment, Kashkan Formation, Zagros, Lorestan. Introduction Terrigenous rocks in the Zagros region of Iran have received relatively little attention. These rocks (e.g., the Amiran, Kashkan, Aghajari, and Bakhtiari formations) have mostly been studied only from the perspectives of lithostratigraphy or stratigraphic position (Motiei 1993). The Kashkan Formation is most extensively distributed in the Lorestan region, and its main facies include conglomerate, sandstone, and siltstone. This formation is situated between the carbonate Telezang Formation below and the Shahbazan Formation above. Where the Telezang Formation is absent, the Kashkan Formation rests directly on the Amiran Formation. The type section of the Kashkan Formation was introduced by James and Wynd (1965) in the Amiran Anticline near the city of Mamulan. Terrigenous formations are of great importance in the Zagros in terms of tectonics, sedimentary environment, climatic changes, and hydrocarbon generation and storage. The Kashkan Formation is essentially a terrigenous unit and is widely exposed in Lorestan. This formation is named after the Kashkan River that flows through this province. Among the few studies conducted on the Kashkan Formation, Yousefi Yeganeh et al. (2012) investigated the sedimentary environment and trace fossils of this formation within the Lorestan sedimentary basin, focusing on the northern, southeastern, and northwestern parts of Lorestan Province. The main goal of this research is to identify and describe the outcrops of the Kashkan Formation along the Khorramabad–Pol-e Zal Freeway (southern and southwestern Lorestan)—an area that has remained largely understudied. Through detailed analysis of lithological units and sedimentary environments in four selected sections, the depositional processes of this formation will be better understood. Finally, by integrating these findings with previous research, a comprehensive understanding of the depositional history of the Kashkan Formation in the Zagros sedimentary basin will be completed and enhanced. Materials & Methods The sections were selected to maximize thickness, facies diversity, and accessibility while minimizing cover. In this regard, four stratigraphic sections were chosen along the Khorramabad–Pol-e Zal Freeway. In these sections, field characteristics—including grain size, bedding, geometric form of beds, sedimentary structures, contact types between beds, and sediment stacking patterns—were carefully examined and recorded. The thickness of the formation was measured using a Jacob staff and compass. Gravels within conglomeratic units were studied using the ribbon method (Tucker 2003). This method involves dividing conglomeratic outcrops into sequential lateral or longitudinal ribbons; within each ribbon, the size, roundness, sorting, lithology of clasts, and their percentages are systematically recorded to document lateral and vertical depositional changes in a regular, comparable manner. The orientation of the foresets of current ripples was used to determine paleocurrent direction. Sandstone samples were collected based on facies variations using a point-sampling method from the middle part of the beds. Clastic facies were classified according to Miall's (2006) codes, and sandstone classification followed Folk (1980). By integrating data from microscopic and field studies, lithofacies and facies associations representative of sub-environments within a sedimentary system were identified and differentiated. Finally, the sedimentary model of the Kashkan Formation was interpreted. Discussion of Results & Conclusions Field studies on the examined sections led to the identification of 12 lithofacies. These include coarse-grained conglomeratic lithofacies (Gm, Gms, Gp, Gh, Gt), medium-grained sandstone lithofacies (Sp, St, Sm, Sh, Sr), and fine-grained mudstone lithofacies (Fm, Fl). The architectural elements identified in the four studied sections include channel elements (CH), overbank fines (OF), gravelly bar elements (GB), sandy bar elements (SB), and sediment gravity flow elements (SG). The SG (sediment gravity flow) element is introduced as the main and dominant element in proximal braided rivers with debris-laden flows, which is entirely consistent with the high percentage of conglomeratic facies in the studied deposits. This element primarily consists of massive conglomerates with very poor bedding, a lack of large-scale sedimentary structures, and poor sorting. The formation of the SG element is attributed to high-energy fluvial flows, particularly debris flows and hyperconcentrated flows. These flows typically develop under conditions of sudden discharge increases, bank instability, or intense bedload activity within braided river channels, leading to the rapid deposition of coarse-grained sediment. In terms of depositional setting, the SG element is interpreted mainly as a fill of main and subsidiary channels within a braided river system, representing peak flow energy phases. The abundance of this architectural element indicates the predominance of high-energy conditions, a relatively steep channel gradient, and a continuous supply of coarse-grained sediment to the sedimentary basin. Therefore, the SG element in the studied deposits is presented directly within the framework of a braided river model with an effective role played by debris flows. Sequence stratigraphy of the Kashkan Formation—as a prominent representative of high-energy fluvial depositional environments in the Zagros (Lorestan) basin—provides a powerful tool for reconstructing the basin's evolutionary history and understanding the influence of sea-level fluctuations on river dynamics. The dominant lithological composition of the Kashkan Formation includes thick conglomerates, coarse-grained sandstones, and mudstone, which directly indicates high-energy depositional conditions, such as those found in braided river systems. The significance of sequence stratigraphy for the Kashkan Formation extends beyond understanding sea-level changes; it holds the key to the tectonic history of the Zagros Basin by identifying sedimentary units related to erosion and deposition during periods of base-level fall. The formation of sedimentary sequences, particularly lowstand systems tracts (LSTs) that occur during periods of pronounced sea-level fall (i.e., reduction in river base level), is often associated with deep incision of riverbeds and the development of valleys and channels that are subsequently filled by conglomeratic and sandy sediments. These processes are closely linked to regional tectonic uplifts and changes in basin slope. Therefore, identifying and delineating LST units within the Kashkan Formation can serve as an indicator of tectonic activity and uplift events associated with the Zagros orogeny. Based on the vertical and lateral changes in facies, the depositional environment of these deposits was a proximal braided river system with a gravelly and sandy bed. Paleocurrent direction analysis for this formation shows a northeast-to-southwest trend, which is evidence of unidirectional (fluvial) flows within the Kashkan Formation. The shallow depth and low sinuosity of the channels, along with the presence of coarse-grained gravelly and sandy sediments, support the interpretation that the clastic facies of the Kashkan Formation accumulated in a proximal braided river environment. هدف از این پژوهش، بررسی رخساره‎‍های سنگی و محیط رسوبی سازند کشکان (ائوسن میانی) در حوضۀ رسوبی لرستان است. در این راستا چهار برش چینه‎‍شناسی انتخاب شد. سازند کشکان در محدودۀ‎‍ مطالعه‎‍شده با ضخامت 150 تا 200 متر، از توالی غالب کنگلومرا و ماسه‌سنگ و به میزان کمتر رخساره‌های ریزدانۀ گلسنگی، سیلت‎‍سنگی و شیلی تشکیل شده است. لایه‌های ریزدانه بیشتر به‎‍صورت میان‌لایه‌های پراکنده در بین واحدهای کنگلومرایی و ماسه‌سنگی مشاهده می‌شوند. مطالعات صحرایی بر‎‍ چهار برش، به شناسایی 12 رخسارۀ سنگی منجر شد که شامل پنج رخسارۀ سنگی کنگلومرایی (Gm, Gms, Gp, Gh, Gt)، پنج رخسارۀ سنگی ماسه‎‍سنگی (Sp, St, Sm, Sh, Sr) و دو رخسارۀ سنگی گلی (Fm, Fl) شد. بر‎‍اساس تغییرات عمودی و جانبی رخساره‎‍ها، محیط رسوب‎‍گذاری این نهشته‎‍ها سیستم رودخانه‎‍ای بریده‎‍بریده با بستر گراولی و ماسه‎‍ای در نواحی نزدیک به منشأ بوده است. توالی‎‍های آواری سازند کشکان بر‎‍ کربنات‎‍های دریایی سازند تله‎‍زنگ قرار گرفته است که نشان از پس‌روی دریا و گسترش رودخانه‎‍های بریده‎‍بریده به‎‍سمت حوضه است. کاهش فضای رسوب‎‍گذاری نسبت‎‍به تأمین رسوب سبب پیشروی رخساره‎‍های رودخانه‎‍ای نوع بریده‎‍بریده در دسته رخسارۀ LST برای سازند کشکان بوده است. آنالیز جهت جریان دیرینه در این سازند، روند شمال شرق به جنوب غرب را نشان می‎‍دهد که شاهدی بر جریان‎‍های یک‎‍طرفه (رودخانه‎‍ای) در سازند کشکان است.

https://jssr.ui.ac.ir/article_30406_cf0ef620ac5015f9ce884bcc58648903.pdf