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