فهرست مطالب

رخساره های رسوبی - سال یازدهم شماره 2 (پاییز و زمستان 1397)
  • سال یازدهم شماره 2 (پاییز و زمستان 1397)
  • تاریخ انتشار: 1399/04/09
  • تعداد عناوین: 8
|
  • زینب اصغرنیا روشن*، محمود رضا مجیدی فرد، احمد رئوفیان، نادر کهنسال قدیم وند صفحات 163-180

    برای نخستین بار مطالعات سنگ چینه نگاری و زیست چینه نگاری سازند دلیچای در البرز شمالی در دو برش کریوش و کنف جار (جنوب بابل) و برش وانا (جاده هراز) به انجام رسیده است. سنگ شناسی سازند دلیچای در بخش های شمالی البرز عمدتا شامل مارن، سنگ آهک مارنی، سنگ آهک پبلی ماسه ای و سنگ آهک می باشد. در این منطقه سازند دلیچای به صورت ناهمساز بر روی سازند سیلیسی آواری شمشک قرار گرفته و در بخش بالایی نیز به صورت پیوسته، هم شیب و تدریجی به سازند آهکی لار ختم می شود. ستبرای سازند دلیچای در برش کریوش 3/21 متر، در برش کنف جار 9/18 متر و در برش وانا 69 متر اندازه گیری شده است که نشان دهنده ستبرای بسیار کمتر این سازند نسبت به بخش های جنوبی البرز است. تغییرات ستبرای سازند دلیچای در بخش های شمالی و جنوبی پهنه ساختاری البرز می تواند به دلیل شرایط تکتونیکی حاکم  بر منطقه و وجود یک فاز کششی و نایکنواختی شرایط رسوب گذاری و کف بستر در طی زمان تشکیل آن باشد. مطالعه زیای آمونیتی موجود به شناسایی 18 جنس و 26 گونه منجر شده است. بر اساس مجموعه فسیلی موجود 8 زون زیستی آمونیتی تشخیص داده شده است که نشان دهنده سن باژوسین پسین کالووین پسین برای سازند دلیچای در البرز شمالی می باشد.

    کلیدواژگان: آمونیت، ژوراسیک میانی، سازند دلیچای، زیست چینه نگاری، سنگ چینه نگاری، البرز شمالی
  • محمدجواد حسنی*، فاطمه حسینی پور، پیمان رضائی صفحات 181-200

    سازند میشان عضو میانی گروه فارس است که در حوضه رسوبی زاگرس در بازه زمانی میوسن پیشین پلیوسن نهشته شده است. برای بررسی ریزرخساره ها و بازسازی محیط رسوبی نهشته های این سازند در جنوب خاوری حوضه زاگرس، برشی در ناحیه شهدادی انتخاب و مورد مطالعه قرار گرفت. با توجه به مطالعات سنگ چینه نگاری، دو رخساره سنگ آهکی و مارنی در برش تشخیص داده شد. رخساره سنگ آهکی شامل نه ریزرخساره (L1-L9) و رخساره سنگی مارنی دربرگیرنده نهشته های سه محیط (MA-MC) است. بر اساس ریزرخساره های شناسایی شده، ارتباط جانبی آن ها با هم، ترکیب اجزای کربناته و فونای موجود، در محیط نهشته های پلاتفرم کربناته از نوع رمپ همشیب با سه مجموعه رخساره ای رمپ داخلی، میانی و بیرونی تشکیل گردیده است. در مجموعه رخساره ای رمپ داخلی کمربندهای رخساره ای پهنه کشندی، لاگون محصور شده و پشته های ماسه ای، در مجموعه رخساره ای رمپ میانی کمربندهای رخساره ای لاگون غیرمحصور و ریف کومه ای و در مجموعه رخساره ای رمپ بیرونی، کمربند رخساره ای دریای باز تشخیص داده شده است. بیشترین نهشته های برش به ترتیب مربوط به کمربندهای رخساره ای لاگون غیرمحصور، لاگون محصور و دریای باز بوده که در سکانس هایی عمیق شونده به سمت بالا نهشته شده اند.

    کلیدواژگان: سازند میشان، ریزرخساره، محیط رسوبی، زاگرس، شهدادی
  • مرجان خداوردی حسن وند، علی بهرامی، مهدی یزدی*، امرالله صفری صفحات 201-228

    در این مطالعه سنگواره های متعلق به 15 خانواده از شکم پایان ایوسن شامل Aprrhaidae، Campanilidae، Cancellaridae، Cerithiidae، Columbellidae، Cymatidae، Hydrobiidae، Limacinidae، Naticidae، Neritidae، Rissoida، Seraphsidae، Turritellidae، Volutomitridae و Xenophoridae در دو منطقه سه (ناودیس سراکه) در شمال غرب اصفهان و زفره (ناودیس باقری) در شمال شرق اصفهان جمع آوری و شناسایی شدند. از این تعداد 14 خانواده، 14 جنس و 3 گونه متعلق به شکم پایان کف زی و یک خانواده، 3 جنس و 4 گونه متعلق به شکم پایان پلاژیک (فقط در منطقه سه) می باشند که در هر دو منطقه در لایه های کربناته ایوسن پیشین میانی مشاهده شدند. با توجه به این که پراکندگی شکم پایان با عادات تغذیه ای آن ها کنترل می شود که آن هم مستقیما به تغییرات محیطی مانند میزان آشفتگی آب، رسوب گذاری، مواد معلق و انرژی آب بستگی دارد و همچنین بررسی روزن داران کف زی بزرگ مانند Nummulites، Discocyclina، Alveolinidae و Miliolidea که همراه با این شکم پایان در رسوبات ایوسن مناطق مورد مطالعه یافت شده اند، می توان شرایط محیطی دیرینه این نهشته ها را چنین تفسیر کرد که این نهشته ها در شرایط دریایی گرم و کم عمق میان کشندی تا بخش های کمی ژرف تر یک رمپ میانی تشکیل شده اند. بسیاری از این شکم پایان در نهشته های ایوسن مناطق بسیاری از جمله اروپای شرقی و غربی، آفریقا و مناطقی از آسیا گزارش شده اند که نشان دهنده تجمع این نهشته ها در بخشی از محدوده تتیس (ایندوپاسیفیک تا آتلانیک) است.

    کلیدواژگان: ائوسن، شکم پایان، ناودیس سراکه، ناودیس باقری، سُه، زفره
  • مهدی رازیانی، محمد وحیدی نیا*، عباس صادقی صفحات 229-249

    به منظور بررسی دیرینه بوم شناسی تورونین سانتونین، برش الگو سازند سورگاه در تاقدیس کبیرکوه ایلام انتخاب و مورد نمونه برداری و بررسی دقیق چینه شناسی و فسیل شناسی قرار گرفت. این توالی دارای سنگ شناسی شیل و شیل های مارنی با میان لایه های نازک سنگ آهک مارنی به ضخامت 168 متر است. مرز زیرین و فوقانی سازند سورگاه به ترتیب با سازند های آهکی و سخت سروک و ایلام به صورت همشیب همراه با مرز مشخص سنگ شناسی است. در این پژوهش با استفاده از نسبت روزن داران شناور به کف زی و رابطه تعیین عمقVan der Zwaan ، به طور کلی برای تورونین سانتونین در سازند سورگاه محیط دریای باز عمیق (باتیال بالایی) با عمق متوسط 662  متر تعیین شد. در قاعده سازند سورگاه و در طول بایوزونMarginotruncana sigali-Dicarinella primitiva Zone  با سن تورونین پسین، میزان فراوانی فرم های عمیق(H3) و درصد روزن داران شناور (%P) افزایش می یابد که نشان دهنده افزایش سطح آب است و رونق فرم های کارن دار و k-strategic مثل Dicarinella و Marginotruncana حاکی از شرایط الیگوتروفیکی و کاهش مواد مغذی است، همچنین کاهش فرم های بدون کارن مثل Muricohedbergella و Whiteinella نشان دهنده افزایش شوری در این بایوزون است. در میانه های سازند سورگاه و در بایوزون Dicarinella concavata Zone با سن انتهای تورونین پسین کنیاسین تا اوایل سانتونین کاهش درصد روزن داران شناور (%P) و افزایش فرم های کم عمق (H1) حاکی از کاهش تدریجی سطح آب می باشد و افزایش فرم های بدون کارن و r-strategic مثل Muricohedbergella و Whiteinella حاکی از وفور مواد مغذی و شرایط یوتروفیکی و کاهش نسبی شوری آب است. در راس سازند سورگاه و در بایوزون Dicarinella asymetrica Zone با سن سانتونین پیشین شاهد نوسانات شرایط محیطی هستیم به این صورت که در ابتدا کاهش درصد روزن داران شناور (%P) و افزایش فرم های کارن دار و  k-strategicحاکی از افزایش مواد مغذی و شوری و شرایط الیگوتروفیکی است، اما در آخرین افق های آن افزایش فرم های بدون کارن و r-strategic حاکی از وفور مواد مغذی و شرایط یوتروفیکی و کاهش شوری آب است.

    کلیدواژگان: سورگاه، روزن داران شناور، کف زی، تورونین، سانتونین، یوتروفیکی، الیگوتروفیکی
  • محمدرضا عطایی، عباس قادری*، علیرضا عاشوری، مهدی بادپا صفحات 250-271

    در این پژوهش، مرجان های عضو باغ ونگ سازند جمال در دو برش چینه شناسی کوه باغ ونگ و کوه شش انگشت مورد مطالعه قرار گرفته اند. عضو باغ ونگ متشکل از توالی از شیل و سنگ آهک مارنی فسیل دار است که در بخش ابتدایی خود واحد آواری از ماسه سنگ آهکی و کنگلومرا دارند و بر روی شیل های سبز رنگ سازند سردر قرار گرفته اند. این عضو در بالا نیز به واسطه یک افق کنگلومرایی، توسط سنگ آهک های چرت دار ادامه سازند جمال پوشیده می شود. مرجان های به دست آمده از عضو باغ ونگ مشتمل بر 27 جنس، 2 زیرجنس، 35 گونه و 6 زیرگونه متعلق به 20 خانواده مختلف از فرم های روگوزای منفرد و کلنی سریویید و فاسیکولیت و نیز فرم های تابولاتا هستند و مشابه با فونای پرمین پیشین (ساکمارین تا کنگورین) در نواحی مختلف سرزمین های سیمرید می باشند. این مرجان ها در قالب دو فون کلی واگینوفیلوم و سیاتاکسونیا قابل دسته بندی بوده، اگرچه فونای سیاتاکسونیا مجموعه غالب توالی از نظر تنوع و فراوانی هستند. از دیدگاه پراکنش زیست جغرافیایی دیرینه، جنس های کلنی فاسیکولیت و سریویید فون واگینوفیلوم موید آب های گرم و کم عمق نواحی گرمسیری استوایی حوضه تتیس در پرمین و جنس های روگوزای منفرد کوچک، نشانگر فون سیاتاکسونیا و یادآور آب های سرد و معتدل ایالت وراگرمسیری تا دوقطبی شمالی جنوبی می باشند. بر این اساس، فونای سیاتاکسونیای مورد مطالعه در عضو باغ ونگ قابل مقایسه با قلمروی پری گندوانا و واگینوفیلیدهای به دست آمده مشابه با فرم های معرفی شده از چین شمالی و جنوبی در ایالت گرمسیری هستند. لذا فون مرجانی پرمین پیشین ایران مرکزی، مجموعه پیچیده و مخلوطی از فونای معتدل/سرد سیاتاکسونیا با فونای حاره ای واگینوفیلوم می باشد.

    کلیدواژگان: پرمین، مرجان، طبس، سازند جمال، عضو باغ ونگ، برش شش انگشت، جغرافیای زیستی دیرینه
  • مسعود غفاری، مسیح افقه*، وحید احمدی صفحات 272-287

    در این مطالعه توالی های کربناته دریای کم عمق ایوسن در جنوب کرمان (بلوک لوت) در برش های خان گازان و خداگن به ترتیب با ضخامت های 75 و 48 متر مورد مورد بررسی قرار گرفتند. مطالعات صحرایی و میکروسکپی بر اساس توزیع محیطی روزن داران کف زی بزرگ به شناسایی 7 رخساره شامل پکستون ماسه دار، رودستون نومولیتی، پکستون گرینستون بایوکلاستی جلبک دار، رودستون بایندستون جلبک دار، وکستون باندستون مرجانی، پکستون گرینستون نومولیتیوکلاستیک و پکستون گرینستون بایوکلاستی منجر شد که درون یک مدل رمپ کربناته برای ته نشست های ایوسن پیشنهاد شدند. همچنین نتایج حاصل از مطالعات چینه نگاری سکانسی به شناسایی دو سکانس رده سوم دربرگیرنده چهار سیستم تراکت در این مجموعه منجر شد. علاوه بر این، تجمعات پوسته های Nummulites (پشته های نومولیتی) با ساختارهای برآمده کم ارتفاع، درون بخش رمپ میانی و تحت تاثیر شرایط جریانی با انرژی متوسط تا زیاد (همچون جریانات امواج) حاصل تجمعات پوسته های تک گونه ای Nummulites perforatus برای اولین بار از این ناحیه معرفی می گردد.

    کلیدواژگان: ائوسن، چینه نگاری سکانسی، کرمان، رخساره، نومولیت
  • مهسا نوری، افشین زهدی*، حسین کوهستانی، قاسم نباتیان، میرعلی اصغر مختاری صفحات 288-303

    نهشته های سازند قم در محدوده کانسار سلستین مادآباد (جنوب زنجان) با 190 متر ضخامت از نظر سنگ شناسی عمدتا شامل سنگ آهک های متوسط تا ضخیم لایه و توده ای به همراه سنگ آهک مارنی می باشد. در این منطقه، سازند قم به طور هم شیب بر روی رسوبات تخریبی متعلق به سازند قرمز زیرین قرار گرفته و به طور هم شیب توسط سازند قرمز بالایی پوشیده می شود. اجزای اصلی تشکیل دهنده سازند قم شامل روزن داران کف زی با دیواره هیالین و روشن، قطعات مرجان، جلبک قرمز و به میزان کم تر، روزن داران پلانکتون می باشد. نتایج بررسی های صحرایی و مطالعات میکروسکپی به شناسایی پنج ریزرخساره در واحدهای سنگ آهکی سازند قم در منطقه مادآباد منجر گردید. تجزیه و تحلیل ریزرخساره ها و حضور فراوان روزن داران کف زی با دیواره هیالین و نبود ریزرخساره متعلق به لاگون های محصور، بیانگر این است که سازند قم در برش مادآباد عمدتا در محیط دریای باز رسوب گذاری کرده است. پراکندگی روزن داران و دیگر اجزای اسکلتی و همچنین تغییرات عمودی ریزرخساره ها نشان می دهد که مدل رخساره ای سازند قم در برش موردنظر متعلق به بخش های انتهایی شلف داخلی تا شلف میانی می باشد.

    کلیدواژگان: چینه شناسی، ریزرخساره، محیط رسوبی، سازند قم، مادآباد، زنجان
  • فاطمه هادوی*، فرح جلیلی، سمیه سنجری صفحات 304-314

    در این مطالعه استراکدهای کرتاسه در برش شوشود (شمال بیرجند) مورد بررسی قرار گرفته اند. سنگ شناسی نهشته های مذکور شامل شیل مارنی، مارن با میان لایه های شیل، ماسه سنگ های دریایی و سنگ آهک های ماسه ای به ضخامت 480 متر است. بر اساس مطالعات فسیل شناسی در توالی مورد مطالعه، تعداد 16 جنس و 36 گونه از استراکدها شناسایی شده اند. بر مبنای استراکدهای شناسایی شده سه بایوزون Hermanites sagittal Zone، Zone Limburgina Formosa و Schuleridea sp.1 Zone در این برش تعیین شده است. مطابق با بایوزون های استراکدی شناسایی شده و انطباق با، بایوزون های نانو فسیلیCC20-CC26 از بایوزوناسیون Sissingh (1977) در این توالی، سن نهشته های مورد مطالعه انتهای کامپانین پیشین انتهای مایستریشتین پسین در نظر گرفته می شود.

    کلیدواژگان: استراکد، نانوفسیل های آهکی، کرتاسه پسین، شوشود، بیرجند
|
  • Zeynab Asgharnia Roshan*, MahmoudReza Majidifard, Ahmad Raoufian, Nader Kohansal Ghadimvand Pages 163-180
    Introduction

    The Middle and Upper Jurassic strata of the Alborz are named the Dalichai and Lar formations. The Dalichai Formation is introducing primary unites of Alborz Jurassic marine deposites and lithologically consist of a sequence of greyish limestones and marls that specially exposed in the south of Alborz Mountains. Most of the studies on the Dalichai Formation mainly focus on the ammonite fauna and their biostratigraphical importance (e.g. Seyed-Emami et al. 1985, 1989, 1995, 2013, 2015; Seyed-Emami and Schairer 2010, 2011a, 2011b; Dietze et al. 2014; Seyed-Emami and Raoufian 2017, Majidifard 2003, 2015; Schairer et al. 1991 and Raoufian et al. 2014, 2019). Ammonites are the most important fossils in the Dalichai Formation, they are of fundamental importance in determining the age and conditions of its paleoenvironment. In most area of the Alborz, the Dalichai Formation has marl, marly limestone, spary and thin bedded limestone with intercalation of marl and marly shale. In the sections studied this Formation consists of marl, marly limestone, sandy limestone and limestone. The aim of this study is to give an overview of the Oppeliidae fauna of the Dalichai Formation in Northern Alborz. The family of Oppeliidae has a high frequency as one of the Bathonian and Callovian index families in Alborz (e.g. Seyed-Emami et al. 2013). In the studied sections, this family has a frequency of 21.5%.

    Methods and Material

    Lithostratigraphy and biostratigraphy of Middle Jurassic Dalichai Formation in Northern Alborz ranges have been studied for the first time. Three stratigraghical sections of Dalichai Formation in Northern Alborz ranges include Keriush in south of Babol, Kanefejar in south of Babol and Vana in Haraz road have been chosen for the paleontological studies. After field studies due to the abundance and importance of ammonite fauna in these sections, detailed sampling of ammonite fauna within the layers was done. After cleaning and preparing the ammonite samples and taking photograph of them, these samples were identified up to the species level and based on the international standard zonation (Cariou & Hantzpergue, 1997); zones of ammonites have been identified.

    Results and Discussion

    The studied ammonites come from three localities in northern Alborz Mountains. These are: 1. Keriush: 65 km south of Babol (N 36° 2'53.61", E 52°40'22.23"). The thickness of the Dalichai Formation at this section is 21/3 meters and can be subdivided into four members. The age of the Dalichai Formation is Upper Bajocian to Upper Callovian. 2. Kanefejar: 60 km south of Babol (N 36° 3'15.59", E 52°36'26.74"). The thickness of the Dalichai Formation is measured at this section 18/9 meters and can be subdivided, from bottom to top, into four members. The age of the Dalichai Formation is Upper Bajocian to Upper Callovian. 3. Vana: 75 km south of Amol (N 35°56'31.48", E 52°15'40.36"). The thickness of the Dalichai Formation is 70 meters and can be subdivided into four members. The age of the Dalichai Formation is Upper Bajocian to Upper Callovian. In this region, Dalichai Formation follows discontinuously on the dark, siliciclastic Shemshak Formation and is overlain gradationally by the light and cliff-forming carbonates of the Lar Formation. The biostratigraphy of the Dalichai Formation is discussed with special emphasis on the ammonite fauna (Oppeliidae family).

    Conclusion

    Palaeobiogeographically the middle Jurassic ammonite fauna in this area is closely related to that of the northwest-Tethyan, with relations to Subboreal / Submediterranean provinces. The study of ammonite fauna in this region led to identification of 48 genus, 18 subgenus and 26 species. Existing ammonite fauna indicates 8 ammonite biozones and Late Bajocian-Late Callovian ages for Dalichai Formation in Northern parts of Alborz ranges. The thickness of the formation in Northern parts of Alborz represents a much lower thickness of this formation than the southern parts of Alborz. The thickness changes of the Dalichai Formation in the northern and southern parts of the Alborz Mountains can be due to the tectonic conditions of the area and the existence of an extensional phase during its formation.

    Keywords: Ammonite, Middle Jurassic, Dalichai Formation, Biostratigraphy, Lithostratography, North Alborz
  • MohammadJavad Hassani*, Fatemeh Hosseinipour, Peyman Rezaei Pages 181-200
    Introduction

    The Zagros structural Zone is an important structural zone in the Middle East because of its valuable and enormous hydrocarbon reservoirs. In this zone, the Fars Group is a key stratigraphic unit; which consists of valuable reservoir and cap rocks. The Mishan Formation is the middle member of the Fars Group, was deposited in the Zagros Basin during the Early Miocene to Pliocene. The facies changes of the Mishan Formation in the Zagros basin is considerable and interesting for researchers. One of the unique lithofacies of this formation is the Guri Member, which is out cropped in the Hormozgan province in many of anticlines. In the Hormozgan province, the Mishan Formation is poorly studied because of harsh climatic condition and accessibility, therefore, there are few published literatures have been carried out about it (Heidari et al., 2014a, b; Rashidi et al., 2014a, b).To consider the microfacies and reconstructing the depositional environment of this formation in the southeast of the Zagros Basin, a stratigraphic section of this formation in the Shahdadi Area has been chosen and sampled. The studied section locates at 27° 29ˊ 1.5 ̋ N & 56° 43ˊ 30  ̋ E near the Shahdadi area, 105 km north of the Bandar Abbas. The main surrounded unites include Cenozoic strata of the Zagros basin. The studied section overlays the Razak Formation and underline by the Aghajari Formation unconformably.

    Materials and methods

    The total thickness of the studied section is 446 m, 78 loos and 236 hard samples have been collected from the Mishan Formation strata. For microfacies analyses, thin sections prepared from hard samples. The loos samples have disaggregated by sodium sulfate solution and frizzing method and Sodium Hexa Meta Phosphate solution for micropaleontological and grain size analyzes. The microfacies have named after Dunham (1962) and Carozzi (1989). The faunal content and grain size of the marly strata compared with Geel (2000), BouDagher-Fadel (2008).

    Discussion

    Based on the lithostratigraphic analyzes, tow lithofacies, include limestone lithofacies and marl lithofacies have been distinguished. The limestone lithofacies involves three rock unites and includes nine microfacies (L1-L9) base on the carbonate components and textural characteristics. These microfacies have been compared with the Wilson (1975) and Flugel (2010) standard microfacies. This comparison shows that the identified microfacies have deposited in intra tidal, restricted lagoon, sand shoal, path reef, non-restricted lagoon and open marine facies belts. The marl lithofacies, based on the faunal content and grain size analyzes, includes deposits of the restricted lagoon, non-restricted lagoon and open marine environments and involves tow rock unites. The charactristics of identified facies belts, such as lateral extend, lack of the onchoids, pizzoids, aggregates and turbidities have suggest a homoclinal carbonate ramp as the sedimentary model in the studied area for the Mishan Formation. This platform can be divided to distinct facies associations include inner ramp, middle ramp and outer ramp.The inner ramp facies association includes intra tidal, restricted lagoon and sand shoal facies belts; the middle ramp facies association includes non-restricted lagoon and patch reef facies belts and the outer ramp facies association includes open marine facies belt. Deposits of the non-restricted lagoon, restricted lagoon and open marine facies belts are the most common deposits in the studied section respectively, which are deposited in deepening upward cycles.

    Conclusion

    The field, microfacies and micropaleontological studies show that the Mishan Formation in the Shahdadi area, the north of Bandarabbas, overlays the Razak Formation’s clastic strata unfonformably. This formation underlays by the Aghajari formation unconformably and the effects of erosional activities are observed at the top of the Mishan formation. The Mishan Formation in the studied area consists of three limestone and tow marl rock unites and considerably includes the Guri Member. The microfacies analyses of the marly and limestone strata suggest a hemoclinal carbonate ramp as the sedimentary model for the Mishan Formation in this area. The suggested ramp includes inner ramp, middle ramp and outer ramp facies assemblages and intra tidal, restricted lagoon, sand shoal, non restricted lagoon, patch reef and open marine facies belts.

    Keywords: Mishan Formation, Microfacies, Depositional environment, Zagros, Shahdadi
  • Marjan Khodaverdi, Ali Bahrami, Mehdi Yazdi*, Amrollah safari Pages 201-228
    Introduction

    In the Paleocene-Eocene boundary, major climate and geological events have occurred throughout the world (PETM), which has led to an increase in deep water temperatures and has caused significant changes in the marine Organisms environment (Bown & Kochpl, 2004). The Eocene deposits in the central Iran extends very wide from the western border of the Zagros Mountains, in to the the northern border of the Alborz Mountains and its southern border extends to the Sirjan and southern Kerman areas (Hajiian, 1996). In Isfahan basin, the age of Eocene deposits are predominantly lutetian, the sedimentary unit including periodic conglomerate, marl and limestone (Zahedi, 1991). Eocene deposits at the Soh and Zefreh areas consist of the macrofossils such as bivalves, gastropods, crab, and microfossils such as foraminifera, charophyte and ostracod (Zahedi, 1991; Sadri, 2011; Khodaverdi Hassan-vand et al., 2016, 2018). This research is focused on the systematic paleontology and paleoecology of the gastropods.

    Materials and Methods

    In order to study of the gastropods from the Soh and Zefreh areas (central Iran), 300 fossils samples were collected and classified based on the shape of shells and their external and internal structural characteristics, e.g.: ratio of length to width, apertural shape and existence or absence of siphonale canal. In addition, to study the paleoecology and palaeoenvironment of these areas, 200 thin sections and also 50 marl samples were prepared and processed.

    Discussion

    Gastropods are one of the most abundant macrofossils found in the Eocene deposits in the Soh and Zefreh areas. In this research, 15 families from gastropods, consisting of 14 families (Aprrhaidae, Campanilidae,  Cancellaridae, Cerithiidae, Columbellidae, Cymatidae, Naticidae, Neritidae, Rissoida, Seraphsidae, Turritellidae, Volutomitridae and Xenophoridae), including 14 genera (Aporrhais, Bonellitia, Campanile,  Cerithium, Cymatium, Lutetiella, Mesalia, Microvoluta, Mitrella, Natica, Pseudotaphrus, Seraphs, Velates and Xenophora) and 3 species (Seraphs Sopitus, Seraphs volutatus and Velates perversus) from Benthic gastropods, also, 1 family (Limacinidae), from pelagic gastropods (pteropoda)  including 3 genera (Altaspiratella, Heliconoides and Limacina) and 4 species (Altaspiratella gracilens, Altaspiratella tavianii, Heliconoid mercinensis and Limacina aryanaensis) were identified. In addition to the gastropods, large benthic foraminifers are one of the most important microfossils that can be found in the Soh and Zefreh areas. The presence of large benthic foraminifers such as, Alveolina, Discocyclina, Nummulites and Miliolida can help to determine the palaeoenvironmental analysis of the deposits (Reiss & Hottinger, 1984; Racey, 1994; Loucks et al., 1998; Geel, 2000; Beavington-Penney & Racey, 2004; Beavington-Penney et al., 2006; Papazzoni et al., 2006).

    Conclusion

    Many of the identified gastropods have been reported from the Eocene deposits of other Eocene outcrops in the world, e.g.; Eastern and Western Europe, Africa and parts of Asia that shows these areas were part of the Tethys (Indopacific-Atlantic). According to, the distribution of gastropods the paleo environments is been controlled by trophic habitats that directly depend on the environmental changes such as water turbulence, sedimentation and suspension rates and water energy and also the presences of large benthic foraminifers (Alveolina, Discocyclina, Nummulites and Miliolida) interpret a shallow marine with  a higher energy.

    Keywords: Eocene, Gastropoda, Bagheri Syncline, Sarake Syncline, Soh, Zefreh
  • mehdi raziani, Mohammad Vahidinia*, Abbas Sadeghi Pages 229-249
    Introduction

    Sediments of Turonian to Santonian age are located in Surgah formation and characterized by Shale and marly Shale. Surgah formation as one of the formations of Bangestan group against other formations this group has limited expansion so that it only outcrops in Lurestan subbasin. During the Cretaceous time, two warming cycles occurred, the first cycle is observed in the Lower cretaceous (Albian) and second cycle is observed in the Upper Cretaceous (Turonian-Santonian). (Lowenstam & Epstein, 1954; Bowen, 1961). Therefore, in this study has been attempted to investigate the influencing factors on the planktonic foraminifera ecology during the seconded cycle Turonian-Santonian.

    Materials and methods

    In this study, 168 samples were systematically collected during a Surgah formation. The samples include Shales and marly Shales. About 1 kg of each sample wase processed. The samples were dried, soaked in hydrogen peroxide (%10) for 12 hours. The mixture was washed over three sieves of 70, 100 and 120µm mesh to remove the clay fraction. This procedure was repeated several times when necessary. The residue was dried at 40˚ C. then, Foraminifera were identified and counted. At least 300 foraminifera were counted in each sample. The general taxonomy followes Robaszynski and Caron (1979), Caron (1985), Premoli Silva & Sliter (1999), Robaszynski et al. (2000), Premoli Silva & Verga (2007). Paleoecological indicators were obtained using the results of the counting process.

    Discussion

    A type section of Surgah Formation in Ilam Kabir-Kuh anticiline in order to Paleoecology of Turonian -Santonian was selected, sampled and precisely studied for stratigraphy and paleontology. This sequence with a thickness of 168 m is composed of shale and marlyshales with interla of marlylimestone. Lower and upper boundaries of the Surgah Formation with Sarvak and Ilam limestone Formations are conformable with sharp lithological boundary respectively. Three biostratigraphic zones are proposed for the Turoniane - Coniacian interval in Surgah formation:1- Marginotruncana sigali - Dicarinella primitiva partial range Zone (latest middle (?) - late Turonian). Because the usual index species for this interval, Helvetoglobotruncana helvetica, has not been found at Surgah formation, therefore the base of this zone is not exposed in the this formation, then age of this zone is latest Middle (?) - late Turonian.2- Dicarinella concavata Interval Zone (latest Turonian - earliest Santonian).3- Dicarinella asymetrica Total Range Zone (Early Santonian - Campanian).Because Dicarinell asymetrica has been found all over Surgah formation, the top of this zone is not exposed in the Surgah Formation, then age of this zone is latest Early Santonian. On this basis, generally the age of the Surgah formation latest Middle Turonian - latest Early Santonian is determined. The ratio between planktonic and benthonic foraminifera (P/B) is one of the most reliable proxies to estimate palaeo-water depths.It has been known for a long time that the percentage of planktonic foraminifera in modern sediments increases with water depth (e.g., Boltovskoy & Wright, 1976; van der Zwaan et al., 1999). Van der Zwaan et al. (1990) described the regression curves with a mathematical formula, which can be used to estimate the water depth. Planktonic foraminifera are divided into five groups according to morphology and lifestyle (Hart & Bailey (1979); Coccioni & Luciani (2005); Reolid et al. (2015):1- Strongly keeled trocospiral: these forms are k- strategic and develop in conditions of reduced nutrients (oligotrophic - mesotrophic), increased oxygen and deep waters. Like geniuses: Dicarinella and Marginotruncana. 2- Weakly keeled trocospiral: these forms are k/r strategic and develop in conditions of oligotrophic - mesotrophic and increased oxygen. Like genus: Archaeoglobigerina.3- Unkeeled trocospiral: these forms are r- strategic and develop in conditions of increased nutrients (mesotrophic - euotrophic), reduced oxygen and surface waters. Like geniuses: Whiteinella and Hedbergella.4- Planispiral: these forms are r-strategic (opportunist) and develop in conditions of eutrophic, increased oxygen and surface to medium waters. Like genus: Macroglobigerinelloides.5- Biserial: these forms are r-strategic (opportunist) and develop in conditions of rincreased nutrients (eutrophic), poorly oxygenated and surface to intermediate waters. Like genus: Heterohelix.

    Conclusion

    Sediments of Turonian-Santonian age are located in Surgah formation and characterized by Shale and marly Shale with 168 m thickness. Lower and upper boundaries of the Surgah Formation with Sarvak and Ilam limestone Formations are conformable with sharp lithological boundary respectively. Generally for the Turonian to Santonian in the Surgah Formation deep open marine (upper bathyal) with an average depth of 662 m was determined. At the base of the Surgah Formation, Late Turonian, the frequency of deep forms (H3) and percentage of planktonic foraminifera (%P) increased therfore suggests sea-level rise, also killed-forms and K-strategies increasment suggests a lack of nutrients and Oligotrophic condition, whereas decrease of non-killed forms indicates increasment of water salinity in this biozone. In the middle of the Surgah Formation. late Turonian-Coniacian to earliest Santonian, the percentage decrease of planktonic foraminifera (%P) and shallow forms (H1) increasment is indicated sea level gradually falling also none-keeling forms and r-strategies increasment offers abundance of nutrients , Euotrophic conditions, and relative decrease of water salinity. On top of the Surgah Formation, Early Santonian fluctuations in environmental conditions are observed.

    Keywords: Surgah, Planktonic foraminifera, Benthonic, Turonian, Santonian, Oligotrophic, Eutrophic
  • MohammadReza Ataei, Abbas Ghaderi*, AliReza Ashouri, Mahdi Badpa Pages 250-271
    Introduction

    Coral fossils of Jamal Formation Bagh-e-Vang member in Bagh-e-Vang and Shesh-Angosht stratigraphic sections (Tabas area of East-Central Iran) have been investigated in this research. Except the studies by Flügel (e.g.; 1964, 1968, 1972, 1995) and Ezaki (1991) Permian corals are poorly known from Iran. The Jamal Formation was firstly introduced by Stöcklin et al. (1965) for the Permian rocks of east central Iran consisting mainly of limestone and dolomite in Shotori and Shirgesht Mountain ranges of the Tabas Block. With 293 to 473 m thickness (Stöcklin et al., 1965; Ruttner et al., 1968; Leven and Vaziri Mohaddam, 2004), its succession confined unconformably upon eroded surface of siliciclastic rocks  belonging to the Carboniferous Sardar Formation and is conformably overlain by the Lower Triassic Sorkh Shale Formation (Partoazar et al., 2014). Jamal Formation in the studied sections is divided into 2 members, Bagh-e-Vang and Cherty Limestone member. The first one which is the main subject of the current research consists of shale and fossiliferous limestone with a siliciclastic rock unit of conglomerate and sandstone at the base, which is overlaid on the green shales of the Sardar Formation. The member is overlaid by cherty limestone of the Jamal Formation through a conglomeratic horizon. This study discuss paleontologically and paleobiogeographically the new material collected from the Jamal Formation in the mentioned localities, Bagh-e-Vang (coordinates of N33°58′27″ and E56°47′33″) on the southwestern flank of the Bagh-e-Vang Mountain and Shesh-Angosht (coordinates of N33°59′15″ and E56°46′50″) on the western flank of the Shesh-Angosht Mountain, at the north of Tabas.

    Materials and methods

    Beside the lithostratigraphical studies in the field, we looked the whole succession of the Bagh-e-Vang member to investigate the coral contents. Totally more than 350 specimens of in situ and float solitary and colonial corals have been collected bed by bed. The specimens were immersed in cold water for one week for study to remove the soft sediment particles attached to them with a special brush. Subsequently, the descriptive characteristics of the specimens included external features such as overall shape, length, diameter, diameter, base and calyx diameter, presence or absence of transverse and longitudinal bands, preservation and wall thickness, rejuvenation, columella and its diameter and depth of calyx were recorded in the respective tables and photographed from various positions with a Canon XD60 camera. In addition, coral fossils serially sectioned in the transverse and longitudinal directions according to the size and conditions of the study. They were studied under normal light (PPl) binocular microscope with a magnification of 5. In the thin section studies, coral diameter, dissepimentarium thickness, number of dissepiment rows, their size and slope, types of dissepiments, central structure, number, shape and thickness of septa as well as their types (Alar septa, cardinal septa, etc.), granule, fossula, tabularium and their number in cm, tabular diameter, type of wall, its thickness and ornamentation, central area diameter and septotheca were investigated. The final determination is carried out based on the proper literatures such as Flügel (1964, 1972, 1990), Ezaki (1991), Flügel & Hubmann (1993), Fedorowski (2010), Berkowski (2012), Kossavaya et al. (2012), Somerville et al. (2012).

    Discussion and conclusion

    The stratigraphic interval in which all examined tabulate corals occur represents the lowest ca. 60 m part (= Bagh-e Vang Member in Partoazar, 1995), where carbonate facies are sandy to marly and contain interlayers of sandstone, shale, and olistolith. The Bagh-e-Vang member was dated by various taxa. These results are as follows: Bolorian (=Kungurian; fusulinids; Leven and Vaziri Mohaddam, 2004), Yakhtashian (=Artinskian) to Bolorian (fusulinids; Arefifad, 2006), Artinskian to Kungurian (bryozoans; Ernst et al., 2006), Bolorian to early Kubergandinian (=early Roadian; fusulinids; Leven and Gorgij, 2011), and Sakmarian to Kungurian (conodonts; Voulo, 2014). Taking these information into consideration, the age of corals examined herein is best constrained as late early Permian. The Tabas Block forms the Central-East Iranian Microcontinent with the Yazd and Lut blocks, whose paleogeographic position is interpreted to have been part of northern margin of Gondwana during early Permian time (e.g. Berberian and King, 1981; Ruban et al., 2007). It is concluded that, therefore, habitat of the Jamal coral assemblage was on the southern shelves of the Paleotethys.The coral assemblage of the Bagh-e-Vang member comprises 27 genera, 2 subgenera, 35 species, and 6 subspecies belong to 20 families of solitary and cerioid-fasiculate colonial Rugosa and Tabulata corals. This fauna is similar to Early Permain (Sakmarian – Kungurian) assemblages of the Cimmerian blocks. They are categorized into two distinct Waagenophyllum and Cyathaxonia fauna; although the Cyathaxonian forms with more diversity and abundance are dominant in the studied sequences. The Fasciculat and cerioid colonial genera of the Waagenophyllum fauna approve the shallow warm water tropical realms of the Tethys Ocean, however the small solitary Cyathaxonia fauna mostly tends to cool - temperate antitropical, antiequatorial or bipolar realms of the northern and southern hemispheres in the Permian (Wang et al., 2013). It means the Cyathaxonia fauna of the Bagh-e-Vang member are comparable with the Pri-Gonwanan realm and the Waagenophyllum fauna are similar to those from North and South China in the tropical realm. Consequently, the Early Permian coral fauna in the Bagh-e-Vang member suggests a complex paleobiogeographic pattern consist of tropical Waagenophyllum and cool-temperate Cyathaxonia fauna.

    Keywords: Permian, Coral, Tabas, Jamal Formation, Bagh-e-Vang Member, Shesh-Angosht section, Paleobiogeopraghy
  • masoud Ghafari, massih afghah*, vahid ahmadi Pages 272-287
    Introduction

    Up to now, the few studies have been investigated on the shallow benthic Eocene successions from the eastern Lut Block. Here, the larger benthic foraminifera were practically one of the most important components for reconstructing of the paleoenvironmental conditions. In fact, they were abundant during the Paleogene, and are as a useful tool for sedimentary and paleoecology interpretations. The highest diversity and abundance of the Large Benthic Foraminifera (LBF) was during Eocene, where they were known as the Foraminiferal limestones within (neritic) carbonate succession. The LBF are generally recognized with calcareous algae (red algae) which can be used as paleoenvironment indicator.  However, the investigation of the facies data which is combined with paleontologic characteristics confirm paleoecologic condition during deposition of Eocene strata in the studied area. Eventually, vertical distribution of identified microfacies and sequence stratigraphy of the mentioned succession supports the depositional system and paleoenvironmental condition.

    Methods and Results 

    In this study, the Eocene carbonate marine successions were investigated in south of Kerman from the Khan Gazan and Khadagan sections with thickness of 75 m and 48 m, respectively. The identification of the microscopic data are provide by Embry and Kelovan (1971) and Dunham (1962). Field work and laboratory studies based on LBF stratigraphic distribution of the Eocene deposits led to the identification of seven facies includes: (FT1) Terrigenous bioclast packstone, (FT2) Nummulites rudstone, (FT3) Bioclast–coralline algal packstone/grainstone, (FT4) Coralline algal rudstone/bindstone, (FT5) Coral wackstone/boundstone, (FT6) Nummulithoclastic packstone/grainstone, (FT7) Bioclast packstone/ grainstone into a carbonate ramp model, which can be divided into four depositional environments: tidal flat, lagoon, shoal and open marine. The regional discrimination most likely reflects their position on separate tectonic blocks on which different facies conditions developed due to different tectonic movements. Based on Catuneanu (2006), the results of sequence stratigraphy studies were identified two third-order depositional sequences containing of four systems tracts.  The gradual vertical changes of the facies and the process of rising of sea-level from the shallow area to seaward direction are well illustrated with lateral facies changes such as the nummulitic accumulations or banks that represents of a high-energy conditions and tests transport to the deepest parts of the basin.

    Discussion

    According to studies, the frequency of microspheric forms increases with increasing water depth, while megalospheric forms are frequently in shallower or relatively deep areas (Beavington- Penny and Racey, 2004). Quartz grains are characterized by well sorting, sub-rounded, and maturity, which represents a large transport distance to the deepest parts of the basin. The proximity of coralline red algae facies trough FT5 can be referred to the margins of coral reefs. Also, Field observation suggests the development of small reefal build-ups (Patch Reef) with limited lateral extensions resulting from coral and coralline red algae assemblages in the Khan Gazan section. The evidence of our study on the FT5 in the Kagan section is indicating a gradual deepening trend of the basin. Likewise, developing of the Nummulites banks show a decrease in seawater levels as major sea-level fluctuation, thereby, the Khan Gazan section is deposited in an environment with high energy conditions and near to the origin of sediments.In addition, the nummulite accumulations (nummulite banks) or low-relief buildups into the middle ramp area under influence of a moderate-high energy condition (e.g. currents and waves) were represented with predominance of Nummulites perforatus monospecific tests for the first time in this region. According to field work, the mentioned nummulites Bank is assigned to B form (reaching to 10 cm in diameter).  The Nummulites banks were not referred to original biocoenosis which were formed by wave activity as parautochtonous or residual assemblage (Papazzoni, 2008). Combination of LBF and coralline algal facies was previously recorded from northeastern Italy (Bassi, 2005) which is close to FT5 of studied sections. The predominant facies associations are shown an overall transgression-regression cycle of the Eocene successions in the east Lut Block.

    Conclusion

    In order to reconstruction of the paleoenvironment and geologic history of the Eocene succession of the Lut Block, the litho and biostratigraphic studies of other exposures are required. Actually, vertical distribution of facies of several stratigraphic sections and their correlation supports paleo-tectonic behavior of various location during deposition of Lut Block Eocene sediments.

    Keywords: Eocene, Sequence Stratigraphy, Kerman, Facies, Nummulites
  • Mahsa Noori, Afshin Zohdi*, Hossein kouhestani, Ghasem Nabatian, MirAliAsghar Mokhtari Pages 288-303
    Introduction

    The Qom Formation was deposited at the north-eastern coast of the Tethyan Seaway, in the Oligocene - Miocene, during the final sea transgression, in Central Iran (Reuter et al., 2009). Although the Mohammadi et al. (2013) believe that above 35˚N (including the study area in this research) deposition of the Qom Formation started during the Miocene. It is essential and important to study different properties of the oil-bearing Qom Formation because of economic importance and communicative role between Eastern Tethys (the proto-Indian Ocean) and the Western Tethys region (the proto-Mediterranean Sea) in the Iranian Plate at the same time (Mohammadi et al., 2013). Furrer & Soder (1955) subdivided the Oligocene-Miocene marine strata of the Qom Formation in the type locality of the formation near the town of Qom, into six members (a-f members: a-member basal limestone, b-member sandy marls, c-member alternating marls and limestones, d-member evaporites, e-member green marls and f-member top limestone). In the Zanjan area, only f-member of the Qom Formation has been deposited (Aghanabati, 2004). In general, the f-member consists of light colored, porous, in part chalky and in part cemented limestone. Although many studies have carried out for nearly four decades on the f-member of the Qom Formation outcrops in Central Iran back-arc basin (which they are listed in Mohammadi et al., 2013), stratigraphical, microfacies analysis and sedimentary environments studies of the f-member of the Qom Formation deposits of the Zanjan area has been the subject of only a few studies. So, here for the first time, we document and discuss the results of detailed fieldwork and microfacies analysis from the early Miocene carbonate platform succession in the south of Zanjan (f-member of the Qom Formation).

    Materials and Methods

    This study involves one stratigraphic section that was measured bed by bed and investigated sedimentologically.During the fieldwork study, detailed stratigraphic sections were measured, sampled and described with respect to carbonate facies and biota. The petrographic description is based on approximately 73 thin sections. Thin sections were stained using the method of Dickson (1965) to distinguish ferron and non-ferron calcite from dolomite. The petrographic classification for carbonates is based on Dunham limestone classification (Dunham, 1962). Flügel (2010) facies belts and sedimentary models were also used. The composition of associated fauna (presence of red-algae, coral, benthic foraminifer and echinoderm) and non-skeletal grains (e.g. intraclasts and peloids) was considered. Sedimentologic texture and structure (e.g. crossbedding, dolomitization, presence of silt-size quartz grains, boring and burrowing) have been considered qualitatively.

    Discussion

    The Qom Formation in the Madabad celestite deposit (south of Zanjan), lithologically composed of 190 m of medium to thick-bedded and massive limestone and marly limestone. In this area, the Qom Formation is conformably overlies the clastic rocks of the Lower Red Formation and is in turn conformably overlain by the Upper Red Formation. In detail, the Qom Formation in the study area consist of 7 lithostratigraphic units as follow from base to top of the formation: 1) thin to medium-bedded limestone with interbedded of thin-bedded argillaceous limestone, 2) thick-bedded coral-bearing limestone, 3) thick-bedded limestone with interlayers of marly limestone, 4) thin-bedded marly limestone, 5)  thick-bedded echinoderm-bearing limestone with interlayers of marly limestone, 6) thin-bedded marly limestone and finally  and 7) thick-bedded to massive limestone with interlayers of marly limestone.The main components of the Qom Formation contain benthic foraminifera with hyaline test, coral, red algae with less frequency of planktonic foraminifera. Due to the abundance of red-algae, larger benthic foraminifera and micrite, the Qom Formation platform facies is referred to as “red algae foraminifera dominated packstone”. Field and microscopic studies led to identification of five microfacies in the limestone units of the Qom Formation in the Madabad area. These microfacies, ordered from shallower to deeper environments, include: A) red algae coral packstone, B) red algae bioclast packstone to wackestone, C) perforate benthic foraminifera packstone to wackestone, D) red algae echinoderm wackestone and E) planktonic foraminifera red algae bioclast wackestone.In general, microanalysis and paleoenviornmental interpretation of the Qom Formation show that this formation was deposited in a variable depositional system. The Qom Formation facies are dividable to four facies as follow: alluvial-deltaic facies carbonate platform-evaporatic facies, slope facies and basin facies (deep sea facies) (Rahimzadeh, 1994). Microfacies analysis including abundant hyaline-test benthic foraminifera as well as the lack of restricted lagoon microfacies show that in the Madabad section, the Qom Formation was deposited in open marine environment. According to recognized microfacies and absences of gravity deposits (turbidites), real and continuous reef, barrier and storm structures, carbonate platform of the Qom Formation developed on an open shelf without effective barriers separating it from the sea. In detail, the distribution of foraminifera and other components, in addition to the vertical microfacies relationships indicate that facies model of the Qom Formation in this section was distal-inner to middle shelf. The distal inner shelf including only the (A) microfacies and the other recognized microfacies (B-E) deposited through the proximal to distal parts of the middle shelf. Proximal middle shelf is characterized by larger benthic foraminifera with hyaline wall in addition to red algae and distal middle shelf is dominated by planktonic foraminifera and red algae.

    Conclusion

    The Qom Formation in the Madabad celestite deposit (south of Zanjan), lithologically composed of 190 m limestone and marly limestone. Field and microscopic studies led to identification of five microfacies. Distribution of foraminifera and other components, in addition to the vertical microfacies relationships indicate that facies model of the Qom Formation in this section was distal-inner to middle shelf platform.

    Keywords: Lithostratigraphy, Microfacies, Sedimentary environment, Qom Formation, Madabad, Zanjan
  • fatemeh Hadavi*, Farah Jalili, Somayeh Sanjary Pages 304-314
    Introduction

    The flysch basin of eastern Iran is in the interval between two faults, Harirud fault in the east and Nehbandan fault in the west, consisting of thick deposits of flysch- like sediments (Aghanabaty, 2004). The study area locates in the flysch Basin of eastern Iran, on the southwest of Shushud village and in the north of  Birjand (South Khorasan Province). This research carried out with the aim of identifying and introducing of ostracods and comparing the proposed biozones based on them with the provided biozones based on calcareous nannoplanktons in this region (Jalili et al., 2011). The studied section that called “Shushud section” due to its place in the southwest of Shoshud village, locates 35 kilometers far from the north of Birjand. The thick of the studied sequence is 480 m and has a lower fault boundary with a gray limestone unit. The upper boundary is covered by limestone deposits conformably.

    Methods and Materials

    The sampling of this section was carried out with a focus on shale and marl beds. The samples size is about 500 gr. Samples are prepared in the following way: At first, they were placed in water for 24 hours that has 10 ccs of 15 percent hydrogen peroxide for every liter of water. Subsequently, they were washed with 30 and 60 mesh sieves and then the remaining deposits were discharged into separate containers and were dried. In the next step, the ostracods in each sediment sample were transferred to a slide by a 00 size brush and were studied by a reflected microscope.

    Discussion

    Ostracods are one of the most useful calcareous crustaceans that contain shells composed of calcareous and chitinous valves (Hadavi, 1998). Ostracods are able to live in all ecosystems and marine ostracods can live from low to high depths (about 2800 m). This microfossil group is found abundantly in marl, shale, calcareous marl, sand, silt and clay (Cohen, 2007). The Grosdidier (1973) report is one of the relatively comprehensive reports about ostracods of Iran that describes the ostracods in the Persian coastal region of Iran. The study of Shushud deposits has led to introduce 36 species belonging to 16 genera of ostracods. In this study, based on the occurrence of the identified species, three interval biozones have been recognized which are as follows: Limburgina Formosa Zone: This biozone, which covers the first 140 meters of Shushud section is defined with the first appearance of the species Limburgina Formosa to the first appearance of the species Hermanites sagittal.  Hermanites sagittal Zone: The range of this biozone is characterized by the first appearance of the species Hermanites sagittal to the first appearance of the species Schuleridea sp.1 and including the thickness of 110 m of the studied section. Schuleridea sp.1 Zone: The first appearance of the Schuleridea sp.1 species indicates the beginning of this biozone and it is the last identified biozone in the Shushud section which continues up to the end of the section and its thickness is 230 m. In the current research, the ostracods of the formation compared with the calcareous nannofossils in the Shushud section in similar horizons in terms of age (Jalili et al., 2014). After studying the nanofossils of the section, five CC20-CC26 nanofossil biozones of the Sissingh (1977) zoning were identified and the results of the study of ostracods were compared with the nannofossils. The Limburgina formosa biozone is almost equivalent to the Cratolithoides aculeus Zone (CC20) and has an age equivalent to the end of early Campanian. The Hermanites sagittal biozone is almost equivalent to the Quadrum sissinghii Zone (CC21) and is a part of the Quadrum trifidum Zone (CC22) and is equivalent to the end of late Campanian. It is worth noting that the Tranolithus phacelosus Zone (CC23) and the Reinhardtites levis Zone (CC24) are defined in the age range of the Late Maastrichtian, but due to the studied sandstone beds did not have any nannofossil, the separation of these biozones was not possible. Therefore, Hermanites sagittal biozone is about equivalent to a part of the Quadrum trifidum Zone (CC22), the Arkhangelskiella cymbiformis Zone (CC25) and Nephrolithus frequens Zone (CC26) and the age range of this biozone is the end of  Late Maastrichtian.

    Conclusion

    The introduction of 16 genera and 36 species of ostracods was identified. The identified ostracods in this section have low diversity and variety because of the unfavorable environmental conditions of the basin, as well as the effect of diagenesis in the studied section which is evident due to the hardness of most of shale and Marl deposits. Based on the detected ostracods, 3 biozones have been identified for the studied section which are as follows: Hermanites sagittal Zone, Limburgina Formosa Zone and Schuleridea sp.1 Zone.According to the introduced biozones and their correlation with the results of the study of calcareous nannofossils, the age range of the Shushud section in the north of Birjand is suggested from the end of Campanian to Late Maastrichtian.

    Keywords: Ostracod, Calcareous nannofossil, Upper Cretaceous, Shushud, Birjand