دانشگاه اصفهان پژوهش های چینه نگاری و رسوب شناسی 2008-7888 41 1 2025 03 21 Investigation of the Baba Habib and Sultan anticlines in the Lurestan sub-basin using biostratigraphy and lithostratigraphy to determine the nature of the Pyrenees Orogeny in the Zagros Basin بررسی شواهد زیست چینه‌نگاری و سنگ‌نگاری فاز کوهزایی پیرنه در حوضۀ رسوبی زاگرس مطالعۀ موردی: تاقدیس‌های باباحبیب و سلطان، زیرحوضۀ رسوبی لرستان 1 20 28809 10.22108/jssr.2024.141801.1290 FA محمدرضا نورایی نژاد دانشجوی دکتری رسوب‌شناسی و سنگ‌شناسی دانشکدۀ علوم زمین دانشگاه شهید بهشتی تهران، ایران محمد حسین آدابی استاد گروه حوضههای رسوبی و نفت، دانشکدۀ علوم زمین، دانشگاه شهید بهشتی، تهران، ایران عباس صادقی استاد گروه حوضه‌های رسوبی و نفت، دانشکدۀ علوم زمین، دانشگاه شهید بهشتی، تهران، ایران 0000-0002-5515-0781 Journal Article 2024 06 26 Abstract This investigation aims to examine the available unconformity of the Late Alpine orogenic phases in the Lurestan sub-basin, with particular emphasis on the Baba Habib and Sultan anticlines. The disconformity occurs at the boundary between the Shahbazan and Asmari formations. Biostratigraphic examinations indicate that the Shahbazan Formation belonged to the middle to late Eocene, while the Asmari Formation is dated to the early Miocene. The investigated sections indicate prevalent marine deposits from the Late Eocene. According to research, the Late Alpine Orogenic phases had an exposure on this area of the Arabian Plate during the Late Eocene, as evidenced by the development of microkarst. Based on the amount of precipitation, the study area was located in a hot and humid climate zone. Keywords: Tethys, Pyrenees, Shahbazan, Asmari, Palaeomicrokarst, Lurestan, Zagros Introduction During the Mesozoic and Cenozoic periods, the Eurasian and Gondwanan continents collided to form the Alpine-Himalaya Mountain range, which includes Iran in its central region. An important ocean called Tethys, which James and Wynd (1965) initially discovered in the Cenozoic strata of the Zagros was present at the location of the main Zagros thrust line (Piryaei and Davies 2024). The discontinuous boundary between the Asmari and Shahbazan formations can be established using karst events as indicators. This research attempts to identify and characterize the preserved discontinuity within the microkarsts development by using classified microkarren shapes. Material & Methods Based on previous research by Adams and Bourgeois (1967), Laursen et al. (2009), Van Buchem et al. (2010) and Boudagher-Fadel (2013), this study aims to identify the genera and fossil species of the Asmari Formation by sampling two sections. Two studies, one by Hottinger (2015) and the other by Sirel (2007), used the Shahbazan Formation to determine the taxa and species of fossils; the other, by Van Buchem et al. (2010) and Laursen et al. (2009), determined the biozones of the Asmari Formation and represent biological zonation. Bourgeois and Adams's (1967) study has led to the biozonation of the Shahbazan Formation. Hottinger (2015) and Sirel (2007) studied fossils from the Shahbazan Formation, while Van Buchem et al. (2010) and Laursen et al. (2009) examined the biozones within the Asmari Formation. Additionally, Bourgeois and Adams (1967) contributed to the biozonation of the Shahbazan Formation. In order to find evidence of a discontinuity in the end-Alpine Orogenic phases at the boundary of the Shahbazan-Asmari formations, the Babahabib and Sultan anticlines in the Lorestan area were examined. Discussion of Results and & Conclusions Based on variations in the thickness, color, lithology, and sedimentary geometry of the strata, the carbonate succession in these areas found in the Asmari and Shahbazan formations can be divided into eight lithostratigraphic units in the Sultan section and seven units in the Baba Habib section. According to lithostratigraphy, these formations are classified as marine carbonate strata in this study. The presence of benthic foraminifera has allowed researchers to determine the age of sediments. In the biostratigraphic study, two biozones for the Shahbazan Formation were identified. An area with barren index fossils is determined. It is concluded that the Shahbazan Formation is between the Lucene and Priabonine periods of the Middle to Late Eocene based on the fossil accumulations that have been found. Biostratigraphic studies of benthic foraminifera in the Miocene (Aquitanian–Burdigalian) period indicate that the Asmari Formation was deposited in this region. Two different biozones were identified within the Asmari Formation in the study area which does not contain any elements of the Rupelian–Chattian or the Eocene age. A paraconformity between the Shahbazan and the Asmari deposits are located within these sections. Evidence of discontinuity, such as limestone conglomerate fragments between the Asmari-Shahbazan contact, and the extinction and subsequent appearance of particular foraminifera microfossil species are observed in this study along the boundary between the two formations. Additionally, palaeomicrokarst phenomena as result of sea level fall in the upper part of the Shahbazan Formation are also observed. The upper section of the Shahbazan Formation is marked by discontinuities observed in the fifth unit of the Babahabib transect and the seventh unit of the Sultan anticline. During the Eocene period, as the seas began to form, these discontinuities were revealed due to erosion and the creation of subaerial outcrops. The karst phenomena seen in this research originate from the interaction of tectonic activity and the dissolving of limestone deposits by meteoric fluids with particular acidity. The temperature significantly influences the evolution of karst formations. Tectonic forces during the late Alpine Orogeny caused the compressive force necessary for the uplift and displacement of strata, eventually leading to the closure of the Neotethys. The investigation of the Eocene deposits demonstrates that tectonics and climatic cycles significantly influence the transgressions and regressions of the sea level within the sedimentary basins. Structural and field evidence, particularly the occurrence of ancient red soils like bauxite and laterite, indicate that Eocene deposits formed under oxidizing conditions characteristic of continental and humid environments. This implies the disconformity surface between the Shahbazan and Asmari formations. It contains remnants of several microkarsts evidence for the hot and humid climatic conditions prevalent throughout the Eocene–Oligocene epoch. این مطالعه با هدف بررسی شواهد ناپیوستگی فازهای کوهزایی آلپی پایانی در مرز بین سازندهای شهبازان - آسماری در دو برش تاقدیس باباحبیب و سلطان در ناحیۀ لرستان انجام شده است. بر‌اساس مطالعات زیست ‌چینه‌نگاری در دو برش مذکور، سازند شهبازان با سن ائوسن میانی پسین و سن سازند آسماری میوسن پیشین است. در برش‌های مذکور، رسوب‌گذاری دریایی نرمال برای یک فاصلۀ زمانی معین در انتهای ائوسن قطع‌ می‌شــود و پیشروی مجدد دریا در میوسن رخ داده است. عملکرد و تأثیرات فازهای کوهزایی آلپی پایانی، به‌ویژه فاز کوهزایی پیرنه در حوضۀ رسوبی زاگرس، به شکل‌های مختلف باعث عدم رسوب‌گذاری و یا حذف رسوبات می‌شود، به‌طوری‌که در این مطالعه، قاعدۀ سازند آسماری با یک ناپیوستگی فرسایشی بر‌ سازند شهبازان قرار دارد. فعالیت‌های کوهزایی پس‌روی دریای اوخر ائوسن و رخنمون‌یافتن (ناشی از تأثیرات فاز کوهزایی پیرنه) موجب فرسایش و رخنمون تحت جوى بخش فوقانی سازند شهبازان شده است. در این مطالعه برای اولین بار، ناپیوستگی بین سازند‌های آسماری و شهبازان براساس شواهد پالئومیکروکارست در زاگرس شناسایی شده است. وجود آهک‌های قلوه‌ای، گسترش کارست و خاک‌‌های قرمز در این توالی، شاهدی بر وجود شرایط بارش شدید در زمان ائوسن پسین است. براساس مطالعات و شرایط تشکیل میکروکارست‌، این بخش از پلتفرم عربی در زمان ائوسن پسین متأثر از فازهای کوهزایی و خشکی‌زایی آلپی پایانی بوده و با توجه به میزان بارش، از‌نظر جغرافیایی در شرایط آب و هوای گرم مرطوب قرار داشته است.

https://jssr.ui.ac.ir/article_28809_b2d9c1f40281c71402a84fd2e2cabd7b.pdf