فهرست مطالب

پژوهش های چینه نگاری و رسوب شناسی - سال سی و چهارم شماره 3 (پیاپی 72، پاییز 1397)

فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و چهارم شماره 3 (پیاپی 72، پاییز 1397)

  • تاریخ انتشار: 1397/09/12
  • تعداد عناوین: 5
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  • صدیقه جداوی، ابراهیم قاسمی نژاد*، محمودرضا مجیدی فرد صفحات 1-20
    به منظور مطالعه های چینه نگاری سنگی و زیستی سازند غیررسمی فرخی، برش عزیزآباد واقع در شمال باختری شهر خور انتخاب شد. ستبرای سازند فرخی در این برش 233 متر است، به شکل پیوسته روی سنگ آهک های سازند هفتومان قرار گرفته و همبری بالایی آن با سازند چوپانان ناپیوسته از نوع موازی است و به چهار بخش غیررسمی تقسیم شده است. درمجموع، 81 نمونه سنگی شامل 25 نمونه مارنی برای مطالعه پالینولوژیکی، 17 نمونه مارنی برای مطالعه فرامینیفرهای ایزوله و 39 نمونه سنگی برای تهیه مقاطع نازک از این سازند برداشت شدند. از مجموع نمونه های آماده شده برای مطالعه های پالینولوژیکی تنها 2 نمونه دارای سیست داینوفلاژله بودند. با مطالعه اسلایدهای پالینولوژیکی، مقاطع نازک و نمونه های شسته شده درنهایت 46 جنس و 71 گونه از داینوفلاژله ها، 13 جنس و 40 گونه از روزن بران آزاد و 9 جنس و 3 گونه از روزن بران بنتیک متعلق به کامپانین میانی- ماستریشتین شناسایی شدند. همچنین با مطالعه و شمارش عناصر پالینولوژیکی مربوط به 2 نمونه مدنظر تنها یک پالینوفاسیس (IV) تشخیص داده شد که نشان دهنده محیط دریایی باز و کم عمق برای این بخش از سازند و بیان کننده یک زون انتقالی به بخش های عمیق تر حوضه است. بر پایه داینوفلاژله های شاخص محیط، محیط گرم و به نسبت کم ژرفا با انرژی متوسط برای این قسمت از بخش مارنی سازند فرخی در زمان انبایش رسوبات پیشنهاد می شود.
    کلیدواژگان: سازند فرخی، داینوفلاژله، فرامینیفر، پالئواکولوژی، ایران مرکزی
  • فیروزه هاشمی یزدی، فرشته سجادی*، حسین هاشمی صفحات 21-36
    شیل و شیل های آهکی ژوراسیک میانی در شمال ایران پراکندگی جغرافیایی وسیعی دارند. پالینوفلورای متنوعی شامل 90 گونه اسپور (متعلق به 44 جنس) و 22 گونه پولن (منتسب به 9 جنس) در نهشته های سازند دلیچای در برش های چینه شناسی پل دختر و بلو (البرز مرکزی) و لوان (البرز شرقی) وجود دارد؛ علاوه بر پالینومورف های شاخص محیط خشکی، عناصر دریایی شامل داینوسیست ها، پوسته داخلی فرامینیفرها، تاسمانیتیدها، اسکلوکودونت ها و آکریتارک ها با حفظ شدگی خوب نیز دیده می شوند. با توجه به حضور میوسپورهایی مانند Klukisporites variegatus،Concavissimisporites verrucosus، Converrucosisporites pricei، Sellaspora asperata، Contignisporites burgeri، Osmundacidites senectusوStriatella spp.که پراکندگی چینه شناسی شناخته شده ای در رسوبات ژوراسیک میانی مناطق مختلف دنیا دارند نهشته های سازند دلیچای در برش های چینه شناسی مطالعه شده به ژوراسیک میانی نسبت داده می شوند. این تعیین سن باتوجه به وجود داینوفلاژله های با گسترش چینه شناسی شناخته شده (باژوسین پسین- کالووین) مانند Cribroperidinium crispum، Meiourogonyaulax valensii، Carpatodinium predae، Ctenidodinium combazii، Compositosphaeridium polonicum و Mendicodinium groenlandicumتایید می شود. بر اساس گسترش چینه شناسی میوسپورها بایوزون تجمعی Klukisporites variegatus, Araucariacites australis, Cerebropollenites macroverrucosus Assemblage Zone در نهشته های سازند دلیچای در البرز مرکزی و البرز شرقی معرفی می شود.
    کلیدواژگان: پالینوستراتیگرافی، ژوراسیک میانی، سازند دلیچای، کوه های البرز
  • سمیرا رحیمی، علیرضا عاشوری*، عباس صادقی، عباس قادری صفحات 37-52
    در پژوهش حاضر زیست چینه نگاری سازند گورپی در برش گنداب در جنوب غرب ایران مطالعه شد. سازند گورپی در برش گنداب شامل 252 متر سنگ آهک رسی و سنگ آهک است و از دو عضو سیمره (لوفادار) و امام حسن تشکیل شده است. این سازند به طور پیوسته و هم شیب سازند ایلام را پوشانده و به طور پیوسته و تدریجی زیر سازند پابده قرار گرفته است. با مطالعه 192 نمونه برداشت شده از این سازند، 20 جنس، 57 گونه و 7 بایوزون از روزن داران پلانکتون در برش گنداب شناسایی شده است که این بایوزون ها شامل Globotruncana ventricosa Zone، Radotruncana calcarata Zone، Globotruncanella havanensis Zone، Globotruncana aegyptiaca Zone، Gansserina gansseri Zone، Contusotruncana contuosa Zone و Abathomphalus mayaroensis Zone در برش مطالعه شده اند. با توجه به بایوزون های تشخیص داده شده سن کامپانین میانی- مایستریشتین پسین برای سازند گورپی در این برش پیشنهاد می شود. بایوزون های تعیین شده در این برش با برشی در یال شمالی تاقدیس کبیرکوه و دیگر نواحی زاگرس و همسایه مقایسه شدند. مرز کرتاسه- پالئوژن بر راس سازند گورپی منبطق است.
    کلیدواژگان: زیست چینه نگاری، روزن داران پلانکتون، سازند گورپی، برش گنداب، ایلام
  • سید محمدعلی موسوی زاده*، فاطمه موسوی زاده صفحات 53-72
    مطالعات انجام شده روی رسوبات سازند داریان به سن آپتین- آلبین در شمال شیراز تنوعی از ساختار های زیستی از نوع قشرزایی و حفاری را در بستر های سخت (hard substrates) نشان می دهند. دیواره اربیتولین ها که شاخص ترین روزن برهای بزرگ کف زی در این بازه زمانی معرفی شده اند یکی از فراوان ترین بسترهای انتخاب شده توسط جانداران است. در این رسوبات هر دو نوع اربیتولین های مخروطی و دیسکی شکل در معرض ساختار های زیستی قرار گرفته اند. عمده این حفاری ها را جاندارانی نظیر اسفنج ها و کلسی میکروب ها انجام داده اند که بخش عمده ای از آنها به اثرجنس Entobia نسبت داده می شوند (عمدتا اسفنج ها آنها را ایجاد می کنند). سایر ساختارهای زیستی شناسایی شده عبارتند از: لوله های کرم های سرپولید، قشرزایی جلبک های Bacinellid، قشرزایی همراه با جلبک های Thaumatoporellaceans و حفاری های کانالی با جانداران سازنده نامشخص. فراوان ترین نوع حفاری ازنظر ریخت شناختی به شکل تونل های موازی با حاشیه دیواره خارجی اربیتولین ها است و ازنظر پراکندگی رخساره ای، ساختار های زیستی عمدتا در رخساره های وکستون روزن بردار و فلوتستون اربیتولین دار دیده می شوند. این الگو پراکندگی به همراه گسترش اثرجنس Thalassinoides در این رسوبات نشان دهنده کاهش میزان رسوب گذاری در زمان تشکیل ساختارهای زیستی و ایجاد فرصت کافی برای فعالیت جانداران سازنده است.
    کلیدواژگان: ساختارهای زیستی، اربیتولین، سازند داریان، آپتین، زاگرس
  • رضا صادقی*، مریم جوکار صفحات 73-94
    در این پژوهش، توالی رسوبی سازند جهرم در برش تنگ نیم باشی با برآورد اهداف زیست چینه نگاری، تعیین سن و مقایسه با برش های دیگر بررسی شده است. برش نامبرده در دامنه شمالی تاقدیس تودج (باختر استهبان)، زیرپهنه فارس داخلی، زیرحوضه فارس و پهنه چین خورده ساده زاگرس واقع گردیده و پهنای آن 5/610 یا 5/588 متر است. سازند جهرم به صورت ناگهانی، همشیب و احتمالا پیوسته روی واحدهای مارنی و آهک مارنی سازند ساچون قرار گرفته و پس از 2 بار تغییر و تبدیل تدریجی، همشیب و پیوسته واحدهای تیغه ساز خود به واحدهای تپه مانند سازند پابده، سرانجام با نهشته های آبرفتی نامتراکم کواترنری پوشیده می شود. با شناسایی 34 جنس و 29 گونه از روزن بران کف زی، تعداد 7 زیست پهنه تجمعی درون آن تشخیص داده شد که با استفاده از پهنه بندی های زیست-زمانی زیرسیستم پالئوژن در گستره زاگرس و تتیس، سن نسبی سازند جهرم از پالئوسن بالایی؟ تا ائوسن میانی پیشنهاد می گردد.
    کلیدواژگان: زاگرس چین خورده، فارس داخلی، سازند جهرم، ریززیست چینه نگاری، روزن بران کف زی
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  • Sedigheh Jedavi, Ebrahim Ghaseminejad *, Mahmoudreza Majidifard Pages 1-20
    Introduction
    Upper Cretaceous deposits of Iran do not have the same facial features everywhere. Indeed it seems that contrary to the same conditions of the lower Cretaceous the upper Cretaceous sedimentary basins were separated from each other and had a special condition on each basin accordingly, except for the Zagros and Koppeh-Dagh they have not been officially named (Aghanabati, 2006). Several sedimentary facies have been reported to be existing during the Cretaceous period. The sequences formed in these basins in different regions, although are similar in terms of fossil content but, they are very different in terms of petrography, thickness and deposition time. Also, Cretaceous rocks are diverse in Central Iran, with varying thickness and age, and have not been officially named yet and are generally investigated. Since the most complete Cretaceous sequence in Central Iran was in the Yazd block and in the Khur area, we decided that the Farrokhi formation (Aistove et al., 1984), which is the youngest Cretaceous rock unit in the Khur region, should be studied. The Farrokhi formation is one of the Upper Cretaceous rocky units, with a variable thickness of 65 to 180 meters (Aistove et al., 1984), and made up of limestone, limestone with rubble or strips which is characterized by abundance of echinoid and bivalves. The lowest part of this formation is reportedly 45 to 120 meters of marl with sandstone layers. Based on the brachiopods, bivalves and echinoid, the formation has been aged as Senonian-Danian (Aistove et al., 1984). Therefore, in order to complete the stratigraphic and paleontological data, the Farrokhi formation is selected and studied. The formation is the youngest Cretaceous rock unit in the Khur, Anarak and Jandag areas, which in most areas there is a marl body in its base. The Farrokhi formation in this section is 233 meters thick and is placed continuously on limestones of Haftuman formation while, it upper contact with the limestones of the Chupanan formation is conformable. The formation has been divided into four informal divisions.
    Materials and methods
    In order to study lithostratigraphy and biostratigraphy of the Farrokhi informal formation, an outcrop of the formation was selected and sampled at Azizabad village northwest of Khur city. A total of 81 rock samples were taken of them 25 samples for palynological studies, 17 samples were washed for their foraminiferal contents and 39 samples were used to prepare thin sections.
    Discussion of Results & Conclusions
    The Azizabad section is located 400 kilometers northeast of Isfahan and on the edge of the great desert, northwest of the city of Khur. In this section, the Farrokhi formation conformably overlay limestones of the Haftuman fm. while, it is in turn overlain by the Chupanan formation. The Farrokhi formation at this section is mostly composed of marl and limestone so that the lower part is formed from green to buffy marls containing sponges and in the upper parts from marly limestones and marly intercalation which turn into the massive limestones of the Chupanan formation.
    Study of the palynological slides showed that only two samples in the lower part of the formation were rich in dinoflagellate cysts containing 46 genera and 71 species. The assemblage is well fitted in the Odontochitina costata Interval Zone according to the previous reports of this cyst zone.
    Two foraminiferal biozones were also differentiable according to the assemblages and index forms identified. These include:Globotruncana aegyptiaca Interval Zone (Late to Latest Campanian) and Gansserina gansseri Interval Zone (Latest Campanian to Early Maastrichtian).
    According to the fossil set, the Farrokhi formation at this locality is of middle Campania to Maastrichtian age.
    The study of the three major groups of palynological elements, as well as the organic factors, the ratio of the transparent (AOM) to the marine elements and the lability factor in the two samples indicated that this part of the section was deposited in an open shallow marine environment forming a transitional zone to the deepest part of the basin in which planktonic foraminifera bloomed.
    Keywords: Farrokhi formation, Dinoflagellate cysts, Foraminifera, Paleoecology, Central Iran
  • Firoozeh Hashemi Yazdi, Fereshteh Sajjadi *, Hossein Hashemi Pages 21-36
    Introduction
    In the geological history of Iran, the Mesozoic Era is of great significance since many important geological events occurred during this time interval. The tectonic and paleogeographic evolution of Iran during the Mesozoic controlled by the geodynamic interaction of Eurasian continental margin and the Tethyan oceanic belt. In the southern Alborz the Middle Jurassic marine transgression (Dalichai Formation overlying the Shemshak strata) began in upper Bajocian. The former rock unit is represented by greenish-grey calcareous shales, marls, and fossiliferous (ammonites) limestones (Steiger, 1966) widely distributed in the northern Alborz Mountains. It disconformably overlies the dark, siliciclastic coal-bearing Shemshak Formation and underlies gradually by the light-colored, rather uniform chert-bearing Lar limestones. The Dalichai Formation signifies the first rock unit of the Jurassic marine sediments in the Alborz Mountains. It embraces such diverse fauna as ammonites, belemnites, bivalves, brachiopods, echinoderms, sponges, miospores (spores and pollen grain), dinoflagellates, bryozoans and foraminifera (Stöcklin 1972; Sussli 1976; Nabavi & Seyed-Emami 1977; Alavi-Naini et al. 1982; Schairer et al. 1991; Seyed-Emami et al. 1985, 1989, 1995, 1996; Shafeizad et al. 2002; Shafeizad and Seyed- Emami 2005; Alvani 2006; , Niknahad 2007; Shahrabi 1994; Vaziri et al. 2008, 2011; Shams 2007; Makvandi 2000; Tutunchi 2001). Due to the presence of palynologically promising lithologies therein. The Dalichai Formation 8has been the subject of many palynological studies (e.g., Wheeler & Sarjeant 1990; Ghasemi-Nejad et al. 2012; Mafi et al. 2013; Dehbozorgi et al. 2013; Hashemi-Yazdi et al. 2015; Skupien et al. 2015; Dehbozorgi 2013; Saadati Jafarabadi et al. 2013; Hashemi Yazdi 2008, 2015; Orak 2010; Sajjadi et al. 2009; Sabbaghiyan 2009; Ghasemi-Nejad et al. 2008; Boroumand et al. 2011, 2013; Farisi Kermani 2003; Ghasemi- Nejad & Khaki 2002; Navidi 2013). The main aim of this study is to establish a palynostratigraphic scheme for the Middle Jurassic strata of central and eastern Alborz Mountains.
    Material and Methods
    A total of 104 palynological samples were collected exclusively from three outcrops of the Dalichai Formation in the central Alborz Mountains (Poldokhtar and Balu stratigraphic sections) and eastern Alborz (Lavan stratigraphic section). All samples were prepared following standard palynological processing procedures (e.g. Phipps & Playford, 1984; Traverse, 2007). Rock samples treated by acids (10%—50% hydrochloric acid to dissolve carbonates and 40% hydrofluoric acid to remove silicates); followed by application of hot 50% HCl to dissolve silica-gel formed during HF treatment. The residues then further treated with saturated ZnCl2 for mineral separation. All residues subsequently sieved through a 20μm mesh prior to make strew slides. Three slides of each preparation examined by transmitted light microscope. The slides are stored in the collection of Faculty of Geology, Tehran University, Tehran, Iran.
    Discussion of Results and Conclusions
    The Middle Jurassic shales and calcareous shales are widely distributed acorss northern Iran. Diverse palynofloras comprising spores (90 species belonging to 44 genera) and 22 pollen taxa (attributed to 9 genera) occur in 104 surface rock samples collected from the Dalichai Formation at Poldokhtar, Balu, and Levan stratigraphic sections in the Alborz Ranges. In addition to terrestrial elements, such well preserved marine palynomorphs as dinoflagellates, foraminiferal test linings, tasmanites, scolecodonts, and acritarchs are also encountered in the assemblages investigated. According to the presence of such miospores species with known worldwide stratigraphic distribution as Klukisporites variegatus, Concavissimisporites verrucosus, Converrucosisporites pricei, Sellaspora asperata, Contignisporites burgeri, Osmundacidites senectus, Striatella spp. the host strata are conceivably dated as Middle Jurassic. This age determination is supported by the occurrence in the material examined of such distinct Middle Jurassic (late Bajocian-Callovian) dinoflagellates as Cribroperidinium crispum, Meiourogonyaulax valensii, Carpatodinium predae,Ctenidodinium combazii,Compositosphaeridium polonicum,and Mendicodinium groenlandicum. Based on the co-occurrence of land-derived palynomorphs a Klukisporites variegatus-Araucariacites australis-Cerebropollenites macroverrucosus Assemblage Zone is herein introduced in the Middle Jurassic strata studied.
    Keywords: Palynostratigraphy, Middle Jurassic, Dalichai Formation, Alborz Ranges
  • Samira Rahimi, Ali Reza Ashouri *, Abbas Sadeghi, Abbas Ghaderi Pages 37-52
    Introduction
    Due to the source nature and placement of the Gurpi Formation between the Asmari and Bangestan reservoirs, it has a special importance. The name of this formation has been derived from Gurpi Mountain in the northwest of Masjid-Soleyman County. At the type section, this formation includes 320 meters of marl and bluish gray shales together with subordinate thin layers of clayey (argillaceous) limestone which overlies the limestones of the Ilam Formation, along an erosional unconformity. The Gurpi Formation has an open marine and deep sea sedimentation environment, which is why it is a good talent for biostratigraphy studies using planktonic fauna. Studies conducted by some researchers on the Gurpi Formation represent a Late Santonian – Tanetian age in different parts of the Zagros area, based on different planktonic assemblages (e.g., Kameli Azan et al., 2004; Darvishzadeh et al., 2007; Abrari et al., 2010; Senemari & Sohrabi Molla Usefi, 2012; Senemari & Azizi, 2012; Beiranvand et al., 2013; Najafpour et al., 2014; Fereydoonpoor et al., 2014; Razmjooei et al., 2014.).
    Materials and methods
    This study is based on macroscopic field description of 252 meters of Upper Cretaceous sequences (Gurpi Formation) in the Gandab section located on southern flank of Kabir Kuh anticline in Lurestan Province of Zagros, southwest Iran. In total, 192 hand specimens were taken from rock samples and sediments from these sections for paleontological study. After washing, samples were dried on sieves and put in special cellules. Released fossils were studied by binocular firstly, and then by Scanning Electronic Microscope (SEM). Determination and naming genera and species was based on Robaszynski et al. (1984), Caron (1985), Loeblich and Tappan (1988), and Premoli Silva and Verga (2004).
    Discussion of Results Biostratigraphy
    In this study, 57 species related to 20 genera and 7 biozones of planktonic foraminifers are recognized in Gandab section.
    - Globotruncana ventricosa Interval Zone
    This biozone is defined between Globotruncana ventricosa appearance at the bottom and Radotruncana calcarata appearance at the top. It is correlated with Globotruncana ventricosa biozone aged Middle to Late Campanian (Premoli Silva and Verga , 2004).
    - Radotruncana calcarata Total range Zone
    This biozone which its top and bottom is consistent with the appearance and extinction of Radotruncana calcarata respectively, It is correlated with Radotruncana calcarata biozone aged Late Campanian (Premoli Silva and Verga , 2004).
    - Globotruncana aegyptiaca Interval Zone
    This zone is defined according the appearance of Globotruncana aegyptiaca at the base and the appearance of Gansserina gansseri at the top and is parallel to Globotruncana aegyptiaca biozone aged the End of Late Campanian (Premoli Silva and Verga , 2004).
    - Gansserina gansseri Interval Zone
    It places between the appearance of Gansserina gansseriat the base andContusotruncana contuosaat the top. This biozone is parallel with Gansserina gansseri biozone aged the most final part of Campanian-Maastrichtian (Premoli Silva and Verga , 2004).
    - Contusotruncana contuosa Interval Zone
    This biozone is defined between the appearance ofContusotruncana contuosa at the base and Abathomphalus mayaroensis at the top and is equivalent of Contusatruncana contusa and Racemiguembelina fructicosa biozones and aged Early to Late Maastrichtian (Premoli Silva and Verga, 2004).
    - Abathomphalus mayaroensis Interval Zone
    It is defined between the appearance of Abathomphalus mayaroensis species at the base and its extinction at the top. This biozone equals Abathomphalus mayaroensisbiozone agedLate Maastrichtian(Premoli Silva and Verga, 2004).
    Cretaceous – Paleocene (K-P) boundary
    K-P boundary is located on top of the Gurpi Formation in Gandab section. It is characterized by the end of Abathomphalus mayaroensis zone and extinction of all planktonic foraminifers. In this research, because of the missing of Guembelitria cretacea Zone P0 as a result of far sampling distance, biozone of Abathomphalus mayaroensis related to Gurpi Formation, is located below Parvularugoglobigerina eugubina Zone (Pα) of the Pabdeh Formation (i.e. Danian).
    Correlation
    Biozones of the Gurpi Formation in Gandab section are compared with biozones of this formation at the in Kuh - e Siah anticline. In the Kuh - e Siah anticline studied by Fereydoonpoor et al, 2014, 8 biozones were introduced from the Gurpi Formation. These biozones give Early Santonian – Early Maastrichtianage for the Gurpi Formation in this section.
    Conclusions
    The Gurpi Formation at the Gandab section with a thickness of 252m composing of limestone and argillaceous limestone. The lower boundary with the Ilam Formation is conformable with sharp lithology and upper boundary is gradational with the Pabdeh Formation in two sections. Through this study, 57 species related to 20 genera and 7 biozones of planktonic foraminifers in Gandab section were distinguished. According to these biozones and fossil content, the age of Gurpi was determined Middle Campanian to Late Maastrichtian.Transition from Maastrichtian to Paleocene was continuous and the K-P boundary located at the top of Gurpi Formation.
    Keywords: Biostratigraphy, Planktonic foraminifera, Gurpi Formation, Gandab section, Ilam
  • Seyed Mohammad Ali Moosavizadeh *, Fatemeh Moosavizadeh Pages 53-72
    Introduction
    Study of carbonate sediments of the Dariyan Formation (Aptian-Albian) in northwest of Shiraz releases different types of biogenic structures in forms of encrustation and drilling in hard substrates. Generally biogenic structures are referred to as changes in soft or hard sediments, which are created by certain organisms and through biological processes (Neumann, 1966). If drilling is performed on soft substrates, it is called Burrow, and if it is created in hard substrates, it is called Bore (Golubic et al., 1975). The organisms can cause macroscale destruction and cavitation on hard surfaces, known as macroboring, which including as certain bivalves, gastropods, echinoids, sponges, polychaetes, arthropods, bryozoans or benthonic foraminiferans (Bromley, 2004). Certain organisms, like certain groups of cyanobacteria, green and red algae, as well as fungi, create microscale digestion, which, due to their small size, have been called microboring (Bromley, 2004). From paleoecology perspective, studying the hard substrates can help determine the spatial distribution and how to orientate the organisms during their lifetime. For example, an accurate investigation of encrustation or drilling on brachiopod shells can provide information on the orientation of the bedding, the pattern of feeding, coexistence, as well as the sequences of occupations by the diggers, their priority for specific mechanisms in the host shells, and that how these organisms interacted throughout life (Taylor and Wilson, 2003).
    Material & Methods
    In order to study the biological structures, 267 thin sections were studied the facies were named by Dunham (1962) and Embry and Klovan (1973) methods. For distinguished calcite and dolomite, thin sections were stained with Alizarin Red-S and Dickson (1966). In order to identify the types of existing biotechnology, their factors and classification of these effects have been used from references such as Bromley (1970), Taylor and Wilson (2003), Schlagintweit and Bover-Arnal (2013) and Schlagintweit et al (2015). Finally, the conditions of formation and characteristics of these biological structures are discussed.
    Discussion and conclusions
    One of the most selected substrates by borer organisms is orbitolina test, as an index large benthic foraminifer in this episode. Both conical and discoidal orbitolina have been subjected to these type of biogenic structure. The most likely options for producer organisms of these bioerosive structures are “colinid sponges” and “calcimicrobes” and much of them can be attributed to Entobia Ichnogenus (mostly produced by sponges). In the studied samples, Entobia has been created in parallel with the outer surface of the orbitolina wall, which is also vertically viewed in the longitudinal section and horizontally in the transverse section while others have no orientation. In these cases they also extend from the wall to the central part. Some of these types of drills are a single central cavity with radial channels leaving it. Other identified biogenic structures include tubes of serpulid worms, bacinellid encrustation, thaumatoporellaceans encrustation and channel shape borings by unknown producers. Tubes of serpulid worms are seen both in the form attached to shells and colonies within the limed mud matrix. Bacinellid encrustation has created a dark wall around the cellar and in some rare cases, the two adjacent orbitolinids form a tangential state and connect both of them, so that the encrustation extended to the limestone between two orbitolins. Thaumatoporellaceans encrustations were observed on the tests of the orbitalins (upper and lower levels) or even attached to the shells of brachiopods. The size of the chamber wall occupied by this algae is about 8 microns and in appearance is similar to Entobia. Borings by unknown producers is characterized by a straight-to-slightly irradiated channel pattern, which shows continuous increase in the diameter of the channel from the beginning to the end of the path. Often, these drills are single channels, but in some cases they are seen as branching channels. In morphological aspects, the most boring structure is parallel tunnels to external side of orbitolina test and in terms of facies distribution, they mostly found in the foraminiferal wackestone and orbitolinid floatstone facies contain orbitolina and green algae. This dispersal pattern accompanied by Thalassinoides ichnogenus somehow reflects low sedimentation rate and providing the opportunity for organism’s activities.
    Keywords: Biogenic structure, Orbitolina, Dariyan Formation, Aptian, Zagros
  • Reza Sadeghi *, Maryam Jokar Pages 73-94
    Introduction
      Zagros sedimentary basin in the south and southwest of Iran holds oil and gas huge reservoirs. This basin which bordered the closure of the Paleotethys ocean (Berberian and King 1981), with high thickness of sedimentary sequences laid down in the Mesozoic and Cenozoic. The Jahrum Formation is carbonate sequence that has deposited during the Paleocene–Eocene series (Motiei 1993) and is the carbonate reservoirs rock of the same age in the Zagros sedimentary basin. This research investigates the sedimentary sequence of the Jahrum Formation in TangNimbashi section, to reach the purposes of biostratigraphy, determination of relative age and compare with other sections. This stratigraphic section was measured in detail at 29° 07' 49" N and 53° 55' 30" E and is located in northern flank of Tudej (Toudaj) anticline (west Estahban, Fars province), in the Interior Fars subzone, Fars sub-basin and Zagros simply folded belt.  
    Material & Methods
    Includes five stages: a) survey and recording geographic coordinates with global positioning system (GPS) and recognition of the lower and upper boundaries. b) Measuring of the degree and direction of dip (32˚SW) and strike (N85˚W) of layers with compass and determining the direction of the travelling angle (N5˚E). c) Measuring the true thickness of the strata perpendicular to their strike by Jacob Staff and numbering of beds. d) Field description (lithology, stratification, color, fossils) and photography of outcrops. e) Systematic sampling at intervals of two meters and sometimes one meter. Finally the stratigraphic section was measured 628 meters and 338 rock samples were collected and also 153 photos were taken. Then thin sections were evaluated and photographed with binocular microscope in plane polarized light (PPL). Also, different references were used to identify the genus and species of microfossils: (Rahaghi 1980; Loeblich and Tappan 1988; Vecchio et al. 2007; Hottinger 2007 & 2014; Boudagher-Fadel 2008 & 2018; Ozgen-Erdem 2008; Sirel 2009; Di Carlo et al. 2010; Alan 2011; Salih 2012; Molina et al. 2013; Zhang et al. 2013; Deveciler 2014; Bukhari et al. 2016).  
    Discussion of Results & Conclusions
    The Jahrum Formation with dolostone, dolomitic limestone and limestone units and medium to very thick stratification, has been deposited on the low-rise, foothills, limestone and marly limestone units of Sachun Formation with very thin to medium stratification. Due to the lack of a detritus unit and paleosol this boundary is sharp, homocline and probably conformable. Its upper boundary after two steps of gradual change and conversion, homocline and conformable its own longer and bladed units to low-rise and foothills units in 505-553.5, 553.5?-575.5? and 575.5-593 meters of the Pabdeh Formation, finally this formation (Jahrum Formation) is covered by Quaternary poorly consolidated alluvial deposits. So, it is impossible to get exact and certain conclusions about this boundary, now. In fact, based on field studies, petrography, microfacies, and microbiostratigraphy, it seems that inthe thicknesses mentioned above, the Jahrom and Pabdeh formations have become interfingering or intertonguing (Pinch-out) each other. With detailed field and laboratory examinations on outcrops and thin sections from the bottom to the top of the Jahrom Formation has been includes 7 lithostratigraphic units (J.1-J.7) and the Pabdeh Formation has been includes 2 lithostratigraphic units (P.1&P.2). Based on identification of 34 genus and 29 species of benthic foraminifera, and 7 genus and 1 species of planktonic foraminifera and according to their pattern of dispersal 13 zonations were recognized. In order 9 assemblage biozones, 2 barren intrazones, 1 barren interzone and 1 indeterminate zone (not well determined). Separated assemblage biozones with biozonation of the benthic foraminifera of the Paleogene sub-system in Zagros basin was suggested by Wynd (1965) and Adams and Bourgeois (1967), also with biozonation of the shallow larger benthic foraminifera (SLBF) of the Tethys basin was proposed by Serra-Kiel et al., 1998, were compared and then their age was determined. The relative age of the Jahrum Formation in this section from 0–20 meters not well determined because of processes of dolomitizatoin, recrystallization, diagenesis and finally absence of index microfossils (foraminifers). But the relative age is estimated from 20 to 143 meters: Late Paleocene? to Early Eocene series (Late Thanetian? –Ilerdian) and from 143–628 meters: Middle Eocene series (Lutetian–Bartonian). This age is suggested with 7 assemblage biozones, including: Alveolina ellipsoidalis-Orbitolites spp. assemblage biozone, Dictyoconus-Coskinolina-Haymanella assemblage biozones (this assemblage has three assemblage sub-biozones: Alveolina-Haymanella-Medocia, Dictyoconus-Coskinolina-Alveolina and Dictyoconus-Coskinolina-Haymanella), Somalina-Medocia assemblage biozone, Nummulites-Alveolina assemblage biozone, Linderina assemblage biozone, that is comparable with assemblage zone 43 and assemblage subzones 44, 48, 49, 50 and 51 (Wynd 1965), Coskinolina sp.-Rhapydionina sp. assemblage zone (Adams and Bourgeois 1967) and also shallow benthic zones (SBZ.) 6, 13, 14 and 17 (Serra-Kiel et al. 1988).
    Keywords: Folded Zagros, Interior Fars, Jahrum Formation, Microbiostratigraphy, Benthic Foraminifera