فهرست مطالب

رخساره های رسوبی - سال هشتم شماره 2 (زمستان 1394)
  • سال هشتم شماره 2 (زمستان 1394)
  • تاریخ انتشار: 1394/11/30
  • تعداد عناوین: 8
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  • مقاله پژوهشی
  • الهام داوطلب، ابراهیم قاسمی نژاد، محمد وحیدی نیا، علیرضا عاشوری صفحات 158-175
    دو برش چینه شناسی گله وار و باغک (شرق حوضه رسوبی کپه داغ) از سازند تیرگان برای مطالعات زیست چینه نگاری و محیط رسوبی انتخاب گردید. مطالعات پالینولوژی در این سازند برای نخستین بار انجام شده و با نتایج حاصل از بررسی روزن داران آن انطباق داده شده است. مطالعه داینوفلاژله ها سن انتهای بارمین پسین آپتین پیشین را برای این سازند در شرق حوضه کپه داغ پیشنهاد می کنند که با بایوزون Paleorbitolina lenticularis (بارمین پسین آپتین پیشین) مطابقت نشان می دهد. با توجه به چهار نوع پالینوفاسیس شناسایی شده در این برشها، محیط رسوب گذاری سازند تیرگان با یک محیط کم عمق نزدیک ساحل شروع و در نهایت به محیط عمیق تر (در شیلهای انتهایی) منتهی می شود. با توجه به ریزرخساره های شناسایی شده، مدل رسوبی سازند تیرگان در ناحیه مورد مطالعه را می توان به صورت یک پلاتفرم کربناته کم عمق نوع رمپ تفسیر کرد که سنگ آهکهای آن در چهار کمربند رخساره ای پهنه جزرومدی، لاگون، پشته سدی و دریای باز بر جای گذاشته شده اند. نتایج حاصل از مطالعه پالینوفاسیسها و رخساره های رسوبی در این برشها همخوانی خوبی با یکدیگر نشان می دهند.
    کلیدواژگان: کپه داغ، سازند تیرگان، کرتاسه پیشین، پالینومورف، روزن داران، محیط رسوبی
  • فاطمه ذبیحی زوارم، محمد وحیدی نیا، عباس صادقی، حسن امیری بختیار، اسدالله محبوبی صفحات 176-197
    سازند شهبازان توالی کربناته پس رونده ای است که در شمال غرب زاگرس مرکزی در حوضه لرستان نهشته شده است. روزن داران کف زی بزرگ در توالی کربناته شهبازان (سنگ آهک، سنگ آهک دولومیتی و دولومیت) در تاقدیس کوه چناره در مرز جنوب شرقی حوضه لرستان مورد مطالعه قرار گرفته و بر اساس گسترش و فراوانی آنها محیط رسوبی دیرینه، بازسازی شده است. این سازند به صورت هم شیب و پیوسته روی سازند پابده و به طور هم شیب و ناپیوسته در زیر سازند آسماری قرار گرفته است. بر مبنای روزن داران کف زی شناسایی شده، محدوده سنی سازند شهبازان در برش مورد مطالعه، ائوسن میانی (SBZ13-SBZ18?) تعیین شده است. مطالعات حاصل به تشخیص 6 تجمع از روزن داران منجر شد که در محیط رمپ خارجی تا درونی میانی نهشته شده اند. این تجمعات به ترتیب از بخش ژرف به سمت بخش کم ژرفای حوضه عبارتند از: 1 تجمع روزن داران پلانکتونی که در محیط رمپ خارجی نهشته شده است و مربوط به بخش گذر تدریجی بین سازند پابده و شهبازان است؛ 2 تجمع دیسکوسیکلینید نومولیتید متعلق به بخش میانی؛ 3 تجمع نومولیتید مربوط به محیط رمپ میانی؛ 4 تجمع نومولیتید آلوئولینید متعلق به محیط رمپ میانی تا درونی؛ 5 تجمع آلوئولینید مربوط به رمپ درونی؛ 6 تجمع سوریتید میلیولید که متعلق به محیط بسیار کم عمق لاگون محصور شده در رمپ داخلی است.
    کلیدواژگان: حوضه لرستان، سازند شهبازان، روزن داران کف زی بزرگ، محیط رسوبی دیرینه، رمپ
  • رضا عزیزی، امرالله صفری، حسین وزیری مقدم صفحات 198-215
    سازند تاربور در جنوب غرب سمیرم به سن مایستریشتین پسین و با ضخامت 462 متر، به طور عمده از سنگهای کربناته و آواری تشکیل شده است. مرز زیرین سازند تاربور با واحد آواری قرمز رنگ (S2) به صورت تدریجی و هم شیب و مرز بالایی آن با سازند کشکان هم شیب و ناپیوسته است. بر اساس مطالعات صحرایی سه واحد سنگ چینه ای در ناحیه سمیرم شناسایی گردید. مطالعه و بررسی بافتهای رسوبی، پتروگرافی و محتوای فسیلی موجود، به شناسایی 6 ریزرخساره کربناته مربوط به محیط لاگون (L1-L3)، سد (B) و دریای باز (O1-O2) و 2 رخساره آواری مربوط به دریای کم عمق (Lsh) و عمیق (Osh) منجر شده است. سازند تاربور در ناحیه مورد مطالعه بخشی از یک شلف باز با شیب کم را تشکیل می داده است. با بررسی چینه نگاری سکانسی، دو چرخه رسوبی درجه سوم تشخیص داده شد و سکانسهای شناسایی شده قابل تطابق با سکانسهای جهانی می باشند.
    کلیدواژگان: ریزرخساره، سازند تاربور، سمیرم، مایستریشتین، محیط رسوبی
  • محمدرضا غریب رضا صفحات 216-235
    خور ریگ در سواحل غربی استان بوشهر، از محیطهای رسوبی ساحلی مهم شمال خلیج فارس به شمار می رود. این خور مشخصا از خورهای به وجود آمده در پناه سدهای ماسه ای است که از رخساره های رسوبی سد ماسه ای، رودخانه ای، مرداب و دریایی تشکیل شده است. خور ریگ در واقع بخشی از یک توالی رسوبی پس رونده است که با فروکش شدن نسبی تراز دریا در کواترنر پسین به وجود آمده است. در این پژوهش فرض شد که خور ریگ جایگاه رسوب گذاری رسوبات گل کربناته در مرداب و ماسه کربناته اوولیتی در بخش دریایی به ویژه در طول سد ماسه ای است. هدف این مطالعه، شناخت دقیق ابعاد رخساره های رسوبی خور ریگ و تعیین منشا نهشته های رسوبی به ویژه رسوبات آهکی اوولیتی وگل کربناته در این خور بوده است. به منظور آزمون مفروضات تحقیق در مطالعات میدانی نمونه برداری فراگیری از مناطق منشا و رخساره های رسوبی خور ریگ و در مطالعات آزمایشگاهی توزیع اندازه رسوبات و شاخصهای آماری و مقاطع نازک از 20 نمونه از رسوبات درشت دانه مناطق منشا و خور ریگ تهیه شد. نتایج نشان داد که درصد آهک در رسوبات ریز دانه بخش مرداب خور ریگ به بیش از 50 درصد می رسد. میانگین فراوانی ذرات درشت دانه خور ریگ به ترتیب 11±77 درصد خرده سنگ ، 8±14 درصد فلدسپات و 6±9 درصد کوارتز به دست آمد که خرده سنگ های آهکی، دارای بیشترین فراوانی هستند. ماسه های آهکی اوولیتی با جور شدگی عالی تا 90 درصد رسوبات رخساره های دریایی خور ریگ را تشکیل داده اند. ترکیب غالب رسوبات درشت دانه مناطق برخاستگاه و رخساره های خور ریگ، کالک لیتایت به دست آمد. سازندهای بختیاری و آغاجاری و افقهای درشت دانه پادگانه های آبرفتی و رسوبات بادرفتی مهم ترین منابع رسوبات درشت دانه ماسه های نهشته شده در سدهای جزرومدی و زبانه های ماسه ای هستند. این تحقیق بار دیگر قابلیت محیطهای رسوبی ساحلی شمال خلیج فارس برای رسوب گذاری نهشته های کربناته را اثبات کرده است.
    کلیدواژگان: خور ریگ، رخساره های رسوبی، گل کربناته، ماسه اوولیتی، خرده سنگ آهکی، کالک لیتایت
  • حسن محسنی، موسی اسفندیاری، محمدعلی کاووسی صفحات 236-255
    سازند فهلیان با سن نئوکومین بارمین بخشی از گروه خامی و از مخازن مهم هیدروکربنی در جنوب باختر ایران می باشد. بر پایه مطالعه پتروگرافی 670 نمونه مقاطع نازک فراهم شده از تراشه های حفاری چاههای کوشک-1 و حسینیه-3 در میدان یادآوران و تفسیر نگاره گامای سازند فهلیان، بیست و دو ریزرخساره کربناته و دو لیتوفاسیس آواری در قالب چهار کمربند رخساره ای دریای باز، حاشیه شلف/ سد، لاگون و پهنه کشندی، در این سازند شناسایی و تفکیک شده است. سیمانی شدن، انحلال، دولومیتی شدن، نوریختی، میکرایتی شدن، زیست آشفتگی، انحلال فشاری و تراکم رایج ترین فرآیندهای دیاژنزی موثر بر سازند فهلیان در میدان یادآوران می باشند. بررسیهای چینه نگاری سکانسی در ناحیه مورد مطالعه نشان می دهد نهشته های سازند فهلیان از سه سکانس رسوبی رده سوم تشکیل شده است که در یک پلاتفرم کربناته از نوع شلف نهشته شده اند. بررسی سکانسهای رسوبی و فرآیندهای دیاژنزی سازند فهلیان، بیانگر ارتباط مستقیم میان این فرآیندها و دسته های رخساره ای است. در دسته های رخساره ای متفاوت، فرآیندهای دیاژنزی ویژه ای چیره بوده که توسط محیط رسوبی و نوسانهای سطح نسبی آب دریا کنترل شده به طوری که در سیستم تراکتهای تراز بالای آب، فرآیندهای دیاژنزی اولیه دریایی و در سیستم تراکتهای تراز پایین آب فرآیندهای دیاژنزی متئوریک بر رسوبات تاثیر گذار بوده است.
    کلیدواژگان: فروافتادگی دزفول، سازند فهلیان، میدان نفتی یادآوران، دیاژنز، چینه نگاری سکانسی
  • حامد محمدیان، محمدحسین محمودی قرایی، اسدالله محبوبی، سید رضا موسوی حرمی، ئارام بایت گل صفحات 256-277
    دریای کم عمق کرتاسه سازند آیتامیر (آلبین سنومانین) از حوضه رسوبی کپه داغ در شمال شرق ایران غنی از افقهای پرفسیل است که عمدتا از دوکفه ایها (غالبا اویستر) همراه با مقادیر کمی گاستروپود، براکیوپود و آمونیت تشکیل شده است. مطالعات رسوب شناسی و چینه نگاری توالیهای مورد بررسی حاکی از تشکیل رخساره های رسوبی در یک الگوی منظم کم عمق شونده عمیق شونده رده سوم می باشد که سیستم تراکت پس-رونده سریع و سیستم تراکت تراز پایین در آن حضور ندارند. بر پایه مشاهدات تافونومیکی و رسوب شناسی، شش نوع افق پرفسیل در طیفی از محیطهای رسوبی مختلف شناسایی شده است که عمدتا متعلق به محیطهای کم عمق هستند. این افقهای پرفسیل در موقعیتهای مشخصی میان سکانسهای رسوبی، به عنوان لاگهای قاعده ای در قاعده سیستم تراکت پیش رونده، در پهنه حداکثر غرقابی و نزدیک به بالای سیستم تراکت تراز بالا یافت می شوند. وجود سطوح فرکند، جورشدگی ضعیف، آرایش محدب بالارونده، آرایش پراکنده، پوسته های شکسته و ساییده شده با الگوی مفصل نشده حاکی از تشکیل افقهای پرفسیل در قاعده سیستم تراکت پیش رونده در محیط حاشیه ساحلی می باشد که انتقال و جابه جایی محلی، فرآیندهای غالب در تشکیل آنها هستند. افقهای پرفسیل نزدیک به راس سیستم تراکت تراز بالا خصوصیات مشابهی را نشان می دهند، با این تفاوت که سطح فروکند را نشان نمی دهند و به صورت سنگ فرشی یا لنزی هستند. ساختارهای رسوبی همراه با افقهای پرفسیل سیستم تراکت تراز بالا، محیط پرانرژی بالای موجسار هوای آرام را نشان می دهند. در مقابل افق های پرفسیل پهنه حداکثر غرقابی، برجازا هستند و در زمان نرخ رسوب گذاری کم، زیر موجسار هوای طوفانی نهشته شده اند. بنابراین افق های پر فسیل وسیله ای مفید برای تعیین کردن سکانسهای رسوبی هستند.
    کلیدواژگان: افق های پرفسیل، چینه نگاری سکانسی، سازند آیتامیر، آلبین-سنومانین
  • مرضیه نطقی مقدم، فاطمه هادوی، لیدا خدادادی صفحات 278-289
    در این پژوهش نهشته های کرتاسه پیشین در برش رمشتیک جهت مطالعات زیست چینه نگاری برمبنای نانوفسیل های آهکی، نمونه برداری گردید. برش نمونه برداری شده در جنوب شرق سرایان است و براساس تقسیمات ساختاری ایران در حاشیه ی شرقی بلوک لوت قرار دارد. براساس مطالعات فسیل شناسی، 33 گونه نانوفسیلی با تنوع نسبتا بالا و حفظ شدگی خوب تا متوسط در برش رمشتیک شناسایی و معرفی شد. برمبنای نانوفسیلهای آهکی موجود و بایوزون های CC3 تا CC5 از زون بندی Sissingh (1977)، سن توالی مورد بررسی والانژینین پسین هوتروین پسین تعیین شده است.
    کلیدواژگان: نانوفسیل های آهکی، رمشتیک، سرایان، خراسان جنوبی
  • بهاره ولی پوری گودرزی، احمدرضا خزاعی، شاهین زمان، غلامرضا میراب شبستری صفحات 290-302
    سازند پروده در برشهای مزینو و کمرمهدی (جنوب غرب طبس) ستبرایی از یک توالی سنگ آهک می باشد. از این توالیها به ضخامت 58 متر در برش مزینو و 111 متر در برش کمرمهدی، تعداد 22 گونه متعلق به 15 جنس مرجان اسکلرکتینا مطالعه و مورد شناسایی قرار گرفت. مرجانهای اسکلرکتینای موجود در برشهای مزینو و کمرمهدی نقش مهمی در بازسازی شرایط حاکم بر محیط دیرینه ژوراسیک میانی سازندپروده دارند. این اجتماعات آبهای گرم، کم عمق، پهنه یوفوتیک، شوری نرمال، شرایط الیگوتروفیک و سنگ بسترکربناته را برای رشد انتخاب می کنند. براساس شواهد ریختاری، آرایش کورالیتها و ضخامت دیس اپیمنتها می توان محیط رسوبی دیرینه توالی مورد مطالعه را به قسمتی از پشت سد، بخش راس تا ابتدای بخش جلوی ریف (قسمت کم عمق) یک پلاتفرم کربناته به ترتیب در برشهای مزینو و کمرمهدی در نظر گرفت.
    کلیدواژگان: سازند پروده، برش مزینو، برش کمرمهدی، مرجان اسکلرکتینا، محیط دیرینه
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  • Elham Davtalab, Ebrahim Ghasemi Nejad, Mohammad Vahidinia, Alireza Ashori Pages 158-175
    Introdaction The Kopet-Dagh sedimentary basin was formed in northeast Iran, southwestern Turkmenistan and north Afghanistan after closure of the Paleotethys Ocean following the Middle Triassic orogeny (Ruttner, 1993). Tirgan Formation, in Kopeh-Dagh basin consists of thick-bedded orbitolinid limestones, limy shale – marl with thin intercalation of limestone.
    Materials and Methods 20 rock samples were selected for palynology and 60 for foraminiferal studies. Palynological preparation procedures followed those of Traverse (1988). Removal of carbonates and silicates were done with HCL and HF, then remaining samples sieved with 200µm and 20µm mesh (nylon sieve), using zinc chloride (ZnCl 2) (separation of organic material). The prepared slides were scanned and their palynological contents were identified and counted. The identified specimens were grouped in dinoflagellate cysts and sporomorphs. Moreover, 60 thin sections of Chalky limestone and limy marl have been prepared and studied. Thin sections were stained using Alizarin red and studied using standard petrographic microscopic techniques. Carbonate rocks were classified according to Dunham’s carbonate classification (1962).
    Discussion This study led to identification of 16 species of dinocysts and six benthic foraminifera (Orbitolinids). Of the 20 rock samples prepared for palynology eight sample were from Baghak and 10 sample from Gallehvar sections. Some samples have good preservation and diversity of dinocysts. Based on the obtained biostratigraphy data, a late Barremian-early Aptian age is suggested for these deposits.
    According to Palynological studies of Oosting et al. (2006), Skupien & Vašíček (2002) and Torricelli (2000), Barremian- Aptian boundary have been identified by presence of Pseudoceratium pelliferum, Cribroperidinium tenuiceras. Palynological contents of the slides were used for environmental interpretations. These include of three main organic groups: Marine Palynomorphs (MP), Amorphous Organic Matter (AOM) and palynomacerals or Phytoclasts (PH). Palynofacies are related to the composition and state of preservation of organic content of a rock unit or loose sediments (Batten, 1996). Based on Tyson diagram (1993), four palynofacies have identified for both sections: II: Marginal dysoxic-anoxic basin. IV: Shelf to basin transition. VI: Proximal suboxic-anoxic shelf. IX: Distal suboxic-anoxic basin. According to the quantitative palynological studies of the Tirgan Formation, depositional environment of the formation starts with a shallow, near shore environment and eventually leds to deeper environments (in the terminal shales).
    Microfacies characteristics allow interpretations of lateral and vertical shifts in facies zones that reflect major and minor variations in environmental patterns, such as climate, water circulation, and siliciclastic input or sea-level fluctuations (Bachmann et al., 2006). Based on petrographic and washed samples, four lithofacies (A, B, C and D) have been identified in the Tirgan Formation. Petrographic studies were carried out to describe the microfacies and interpret the depositional environments. Therefore, 4 facies associations were identified.
    Facies association A: This association is composed of 3 microfacies A1, A2, A3 (Mudstone and Sandy Mudstone). Abundant carbonate mud with quartz grains in this association represent shallowing parts of the basin and indications of the supratidal conditions (Shine, 1983). This facies association has been observed in both sections (Baghak and Gallehvar) and most abundant in the lower parts of the sections.
    Facies association B: This facies association includes 3 microfacies B1, B2 and B3 (Peloidal Wackstone, Bioclastic Wackstone and Bioclastic Oolithic Wackstone). Abundant of Peloids in this association show deposition in low energy condition such as lagoon (Adachi et al., 2004). The evidences represent formation of this facies association in a lagoon environment. This association has been observed in both sections but its frequency is in Gallehvar section.
    Facies association C: This facies association contains 3 microfacies C1, C2 and C3 (Oolitic grainstone, Biocalstic Oolitic garinstone and Orbitolina Oolitic grainstone). Presence of abundant tangential ooids in this association represent formation in the shallow, warm, agitated and calcium carbonate supersaturated conditions. Generally, ooids are index for sedimentation in shallow turbulent waters (Milliman, 1974). Presence of cross-stratification represents high-energy conditions during the formation of this facies (Bachmann & Hirsch, 2006). Aboundant discoidal and elongated orbitolina in the oolitic grainstone show formation of this facies in the seaward margin of the shoal. Given this evidence, it can be said that high-energy conditions of shoal prevailed in both studied sections.
    Facies association D: This facies association is mainly composed of Orbitolina Oolithic Packstone. Due to existance of stenohaline organisms such as Echinoderms, Brachiopods, Briozoers and discoidal Orbitolina, this association have been deposited in an open marine environment. Presence of aboundant mud lime in this association represents low energy conditions (Adachi et al., 2004) and deposition under the normal waves.
    The facies model of Tirgan Formation in the studied area can be interpreted as a shallow carbonate platform of ramp type where carbonate rocks have been deposited in four facies belt: tidal flat, lagoon, shoal and open marine. One the reasons that prevented the reef formation is, supply of siliciclastic particles from the land that are seen in some of the facies in both studied sections. The results of the palynofacies study can also support the interpretation of sedimentary facies in these sections.
    Keywords: Kopeh Dagh, Tirgan Formation, Lower Cretaceous, Palynomorphs, Foraminifera, sedimentary environments
  • Fatemeh Zabihi Zoeram, Mohammad Vahidinia, Abbas Sadeghi, Hasan Amiri Bakhtiar, Asadallah Mahboobi Pages 176-197
    Introduction Zagros foreland basin in Iran on the basis of sedimentary history is divided into five provinces including Lurestan, Fars, Zagros, Dezful embayment and Izeh Zone (Farzipour-Saein et al. 2009). In northeast Lurestan, the exposure of Mesozoic-Cenozoic stratigraphic column consists of about 4-5 km of pre-orogenic strata and about 6 km of synorogenic deposits. The Mesozoic pre-orogenic succession is mainly composed of passive margin carbonate units. The overlying synorogenic deposits include, from bottom to top, the Amiran- Kashkan detrital sequence, the Shahbazan-Asmari shallow-marine platforms, the Gachsaran evaporitic Formation, and the Agha Jari and Bakhtyari detrital formations.
    Materials and Methods In order to determine the age and paleoenvironment of the Shahbazan Formation, one surface section measured and sampled at the Kuh e Chenareh anticline. Chenareh stratigraphic section is located near the last tunnel of the Khorramabad – Andimeshk road about 5 km east of Zal city, at 32°47′N, 48°18′E.
    Results We have identified 20 genera and 26 species of larger foraminifera in the studied sediments of the Shahbazan Formation. In the study area, four foraminiferal assemblages identified ascribed to the Shahbazan Formation span time with the Lutetian–Bartonian (SBZ13-SBZ18?) age according to Serra-Kiel et al. (1998).
    The following six foraminiferal assemblages are arranged on a palaeobathymetric profile, ranging from the shallow-marine inner ramp to the deep-marine basin including: (1) soritid-miliolid assemblage, (2) alveolinid assemblage, (3) nummulitid-alveolinid assemblage, (4) nummulitid assemblage, (5) nummulitid-discocyclinid assemblage and (6) planktic foraminifera assemblage. The transitions between the individual foraminiferal assemblages are gradual and occasionally interfere with each other.
    Discussion The modal analyses of the bioclastic components and composition of foraminifera assemblages allowed six facies (assemblages) to be recognised. These facies can be interpreted as having accumulated in open marine, fore-bank, bank and lagoonal environments (back bank setting). The nummulitic packestone/flotestone with abundant B-forms and minor A-forms and the nummulitic packestone with abundant A-forms and minor B-forms dominates in the lower and upper part of the bank, respectively. The Discocyclinid-Nummulitid facies is observed at the basal parts of the section. The presence of elongate Discocyclina in this facies may reflect an increases in water depth, although they may also be allochthonous (Beavington-Penney and Racey, 2005). The nummulites facies overlain by nummulitid-alveolinid packestone facies and this facies also overlain by alveolinid facies. Anketell and Mriheel (2000) in their study of the Jdeir Formation infer that the orbitolites-alveolina facies accumulated in a back-bank lagoonal setting. Wackeston-packestone facies with soritids and miliolids accumulated in the uppermost parts of this formation. The gradual variations in facies from shallow to deep photic zone deposits in this succession is more compatible with a suggested ramp model by Anketell and Mriheel (2000) and Höntzsch (2011). This model (in the northern areas of the Lurestan basin), in comparison with their counterparts in the most southern parts of the Arabic platform (Seeb Formation in the north of Oman and Dammam Formation in Saudi) (Boukhary et al., 2006), shows that there is a broad correlation between these sedimentary environments.
    Keywords: Lurestan Basin, Shahbazan Formation, larger benthic foraminifera, paleoenvironment, ramp
  • Reza Azizi, Amrollah Safari, Hossein Vaziri-Moghaddam Pages 198-215
    IntroductionThe study area is located in Semirom sub zone (between Zagros and Sanandaj-Sirjan zones). Considering the main Zagros zonation, Navai and Mehdi Zadeh Tehrani (1986) used satellite data and tectonic studies, other than the two main structural zone of Zagros and Sanandaj-Sirjan, and introduced another subzone for Semirom. This sub zone, based on stratigraphy and folding, is different than Zagros zone. Therefore, different facies can be formed based on different movements of the independent blocks in the basement. These blocks with differential vertical movements have changed physical and chemical conditions of the sedimentary basins. In the current paper, a detailed microfacies, paleoenvironmental analyses, depositional models and sequence stratigraphic approaches are used to understand the relationship between paleoenvironmental parameters and change of sedimentary facies.
    Material and methodsThe studied area, with geographical coordinate of 31° 22' 48" N and 51° 32' 01" E, is located about 5 km southwest of semirom. The thickness of the Tarbur Formation with Maaestrichtian age in the study area is about 462 meters. This formation consists mainly of carbonate and terrigenous rocks and has a gradual and conformable contact with underlying red shale unit (S2) while its upper contact with Kashkan Formation is marked by an erosional surface. The microscopic studies were performed on carbonate samples and shale samples were studied. Quantative and qualitative microscopic studies were conducted by polarizan microscope. A textural classification was obtained according to Dunham (1962) and Embery and Klovan (1975). Lateral and vertical changes of microfacies were studied and were compared with modern sedimentary environments. Finally, based on lithostratigraphy, sequence stratigraphy and vertical variations of microfaceis, environmental model are presented.
    DiscussionAccording to the field observation, three litholigical units are recognized in the Tarbur Formation at the study area. The study of depositional textures, petrography and fossil content of 110 thin section led to recognition of six carbonate microfacies. The depositional setting includes orbitoidae bioclastic wackestone-packstone and rudist packstone (rudstone) of open marine, rudist boundestone of bar, miliolids loftusia orbitoidae rudist packstone and dicyclina/ dasycladacea/ loftusia miliolids bioclastic wackestone-pacstone of lagoon enviroments. Other than the above carbonate facies, two terrigenous facies (shallow (Lsh) and deep marine (Osh) are distinguished in the study area. The Tarbur Formation in the study area is deposited on a low-angle open shelf environment. Based on the sequence stratigraphy data, two sedimentary cycles with 3rd order sequences are recognized. These sequences are comparable to the global sequences.
    Keywords: Microfacies, Tarbur Formation, Semirom, Maastrichtian, depositional environment
  • Mohammadreza Gharibreza Pages 216-235
    IntroductionThe Reeg estuary is an important coastal sedimentary environment in the north of the Persian Gulf that is located at the west of the Boushehr Province (Gharibreza, 2005). This basin shows morphology of the bar built estuary and includes three main sections of riverine, lagoon, and marine which is separated from land by the fossil beach. The Reeg estuary is an example of a retrogressive coast that is emerged by sea level fall since Late Quaternary (Gharibreza et al., 2002; Lak et al., 2010). This estuary might be a suitable coastal environment to collect carbonate mud and calcareous oolitic sands assuming similarities between south and north of the Persian Gulf. Determining of Reeg Estuary sediment sources especially carbonate mud and oolitic sands and identification its sedimentary facies were the aims of present research.
    Materials and MethodsA comprehensive sediment sampling plan and laboratory analysis were implemented to test the research assumption. Forty-eight sediment samples were taken from different sedimentary facies of the sink and source areas. Thin section of 24 sandy texture samples of the sink and source areas were studied by binocular microscope to identify source of coarse-grained sediments. Composition of sediment was studied using Folk and Ward (1957) method. Distribution of sedimentary facies was studied using geographical information system tools which is widely used around the world (Heap, 2004).
    Results and DiscussionCalcimetry tests showed that carbonate content of fine-grained sediments in lagoon section is more than 50%, which was emphasized to suitable chemical conditions for accumulation of carbonate mud. The mean content of the rock fragments, feldspar, and quartz particles were obtained 77±11%, 14±8%, and 9±6%, respectively. Resultant data showed significant profusion of calcareous rock fragments in sediments in both sink and source areas, which represents the Calclithite class of composition. Results also revealed that oolitic sands are the main constituents of marine facies (≈ 90%) particularly along the recent barrier island. In addition, Bakhtiary and Aghajari formations and coarse-grained strata of old and young terraces are the origin of coarse sediments which have been deposited in the Reeg Estuary. Once again, capability of the northern Persian Gulf's coastal sedimentary environments for deposition of carbonate sediments like as what has reported from the southern coasts was proved by present research.
    AcknowledgementThe research was supported by Soil Conservation and Watershed Management Research Institute (SCWMRI), Tehran, Iran. The author gratefully acknowledges all academic staffs of coastal protection department for their helps on the implementation of this research.
    Keywords: Reeg Estuary, sedimentary facies, carbonate mud, oolitic sand, calcareous rock fragment, Calclithite
  • Hassan Mohseni, Mossa Esfandyari, Mohammad Ali Kavousi Pages 236-255
    IntroductionInvestigation on mutual relation between depositional facies and diagenesis in a sequence stratigraphic framework is essential for systematic recognition of a reservoir (Lucia, 2004; Ahr, 2008). Spatial distribution of porosities of carbonate rocks may drastically change due to diagenetic processes (Mehrabi and Rahimpour- bonab, 2013). Facies analysis and diagenetic studies in sequence stratigraphic framework could facilitate for reservoir simulation (Masse and Masse, 2011). Hence, combination between diagenesis and sequence stratigraphy is useful for better understanding of diagenetic processes (Morad et al., 2000). This research will discuss distribution and variations of diagenetic processes of the Fahliyan Formation in a sequence stratigraphic framework in the northern part of the Dezful Embayment.
    Results and discussionThe Fahliyan Formation is composed of 24 microfacies that formed four facies associations and were deposited in tidal flat, lagoon, bar and open marine (Esfandyari, 2013). The tidal flat facies association includes quartzarenite, shale, intraclast grainstone, mudstone and dolomudstone. Absence of bioclasts, frequent detrital quartz grains and intraclast, evidently suggests a tidal flat setting (Flugel, 2010). Lagoonal facies association includes peloids wackestone/ packstone, algal boundstone and bioclastic mudstone. Abundant algal fragments (e. g. Salpingoporella, Dasycladacea, Actinoporella, Clypeina, Acicularia) are distributed in this facies association. Frequent lime mud, peloid and milliolid foraminifera suggest a lagoon environment located on mid- shelf (Flugel, 2010). Peloid- intraclast grainstone, ooid- intraclast grainstone and lithocodium boundstone are representatives of a bar/ barrier. Lack of lime mud and present of skeletal grains are evidence of dynamic high- energy setting. These are similar to bar microfacies of Flugel (2010) and facies belt 5 and 6 of Willson (1975). The open marine facies association is composed of resedimented/brecciated carbonate beds. Extraclast, bioclasts and quartz grains present in lime mud matrix. Mixed open marine and lagoonal biota may represent talus deposit formed in front of carbonate platform slope. Mudstone with sponge spicules and radiolarian are being interpreted as open shelf (Flugel, 2010) and facies belt 1 and 2 of Wilson (1975). Here, these facies association are interpreted as being deposited on a shelf type carbonate platform. Various diagenetic processes affected the Fahliyan Formation in the Yadavaran oil field such as micritization and neomorphism that are more abundant in the lagoonal facies. Bladed isopachus HMC cement was precipitated in grain- supported facies (e.g. grainstone of bar/ barrier). Moldic, vuggy and intraparticle porosities are developed within mud- supported and brecciated facies. Evidences of burial diagenesis were also observed as stylolite, along late stage dolomitization and poikilotopic cement as well.
    Sequence stratigraphyThe Fahliyan Formation is composed of three 3rd order sequences that can be correlated with Lower Zuni I and Upper Zuni II megasequences (Klonga and Kesling, (2002) in a global scene. They can also be correlated to the Mehrdad supersequence of the Early Cretaceous of the Zagros basin (Heydari, 2008). These sequence are composed of TST and HST facies which are separated by MFS. The first MFS is equal to MFS K20 of the Arabian plate (Sharland, et al. 2001), which was reported from the lower Fahliyan Formation (Shakib, 1994). The second FMS was also recognized in the mid Fahliyan Formation, correlatable to MFS K30 of the Arabian plate (Sharland, et al. 2001). Dolomitized lime mudstones on top of the second sequence, suggest a type I sequence boundary. MFS of the last sequence was recognized within the upper Fahliyan Formation that can also be correlated to K40 of the Arabian plate (Sharland, et al. 2001; Shakib, 1994). A global fall of sea- level (Haq et al., 1988) caused influx of siliciclastic sediments into the basin during final stage of HST of the last sequence designating type I sequence boundary. These sequences are correlated to those previously reported from the Zagros basin and Arabian plate as well (e.g.: Shakib, 1994; Sharland, et al. 2001; 2013; Haq and Al-Qahtani, 2005). Moldic porosity in shallowing- upward, grain- supported sediments are abundant just below and above the sequence boundaries in both wells. They were probably developed after influx of meteoric water as a consequence of sea- level fall. Sea- level rise might have restricted influx of coarse siliciclastics. Dolomitization of mud- supported facies is evident as dispersed dolomite crystals. Although these fine crystalline dolomites may reduce the porosity of carbonate rocks, but they could effectively increase the permeability of such rocks (Lucia, 2004). HST sediments of the sequences 2 and 3 are grain- supported and are expected to be more porous and permeable. These sediments were deposited on shelf margin facies with considerable intergranular porosity which was occluded by cements.
    ConclusionThe Fahliyan Formation is composed of shallow marine to deep shelf sediments. Shallow platform facies experienced various diagenetic processes which improved their porosity. The Fahliyan Formation consists of 22 carbonate microfacies and 2 siliciclastic lithofacies which were deposited in tidal flat, lagoon, bar and open marine environments on a carbonate shelf. These sediments comprise three 3rd depositional sequences. Diagenetic processes are effectively related to sequence stratigraphy. Early marine cements are closely confined to shelf- edge sediments of TST. Maximum dolomitization was also observed in TSTs, and tidal flat facies of HSTs. Evidence of meteoric diagenesis after decline in sea- level rise are evident in sediments of late HSTs in both wells, particularly in two upper sequences.
    Keywords: Dezful Embayment, Fahliyan Formation, Yadavaran oil field, diagenesis, sequence stratigraphy
  • Hamed Mohammadian, Mohammad Hossein Mahmoudi Gharaie, Asadallah Mahboobi, Seed Reza Moussavi-Harami, Aram Baytgol Pages 256-277
    IntoductionDescriptive analysis of shell beds is a useful tool within the context of the sequence stratigraphic model (Holland, 2000, 2001; Parras and Casadío, 2005; Cantalamessa et al., 2005; Di Celma et al., 2005). The formation and distribution of shell concentrations in the stratigraphic section are directly controlled by biogenic production and rate of background sedimentation (Kidwell, 1991a,b). Mid-Cretaceous shallow marine of the Albian-Cenomanian Aitamir Formation from the Kopet-Dagh basin of northeast Iran are rich in shell concentration dominated by bivalves especially Oyster, with minor admixture of gastropod, brachiopod and ammonite. The present paper focuses on Mid-Cretaceous shallow marine Aitamir Formation from the Kopet-Dagh basin with a twofold
    Purpose
    firstly, to reconstruct the sequence stratigraphic framework of this formation; secondly, to discuss the results in terms of the interpretation of the paleoecology and taphonomy of the shell beds occurring within this formation. The Aitamir Formation was studied bed-by-bed, both sedimentologically and taphonomically. Physical sedimentological studies attributes (thickness, lateral extent, geometry, stratigraphic contacts, association with significant surface, and position within depositional sequence) as well as vertical trends and stacking patterns, were all integrated to define and interpret facies and facies associations. Taphonomical attributes involves taxonomic composition, life habits, orientation, fragmentation, abrasion, disarticulation, encrustation, bioerosion, and microarchitecture (Kidwell, 1991a,b; Fürsich, 1995; Fürsich and Oschmann, 1993).
    DiscussionA stratigraphic and sedimentologic study of the entire sedimentary succession indicated that sedimentary facies recur in consistent deepening–shallowing third-order transgressive–regressive patterns that represent a depositional sequence in which forced regressive (FRST) and lowstand system tract (LST) deposits are not present. Based on taphonomic and sedimentological observations, these shell concentrations belong to six assemblages, including; (1) fair weather wave concentration; (2) storm wave concentration; (3) distal tempestite or distal storm flow concentration; (4( primary biogenic or polyspecific concentrations; (5) winnowed concentration; (6) transgressive lag concentration. They represent a range of environments but are mainly shallow water settings. Together with sedimentologic characteristics, these fossiliferous levels are important indicators of facies architecture and, therefore, are useful tools for interpreting sequence stratigraphy. These shell concentrations are found in distinct positions within the depositional sequence: as a transgressive lags at the base of the transgressive systems tract (TST), in the maximum flooding zone (MFZ), and at or close to the top of the highstand systems tract (HST). Characteristic features of concentrations at the base of the TSTs are distinct basal erosional surface (ravinement surface), moderate time-averaging, sorting, a preferred convex-up orientation, fragmented and abraded with a chaotic orientation, and nearly total disarticulation of shells. They are suggestive of an environment (shoreface) in which reworking and local transports were frequent events. These concentrations, which form just seaward of the area of active wave ravinement, are condensed deposits resulting from general conditions of low terrigenous sediment input within high-energy settings and record stratal convergence at the costal onlap (Parras and Casadío, 2005; Cantalamessa et al., 2005; Di Celma et al., 2005). Similar features are shown by concentrations near the tops of the HSTs, except that they do not show ravinement surface and their shells were largely concentrated in lenses and in pavements rather than in beds as in the transgressive lags. Associated sedimentary structures indicate deposition above fair weather wave base in a high-energy environment. Concentrations occurring in the MFZ, in contrast, are autochthonous and highly time-averaged, having accumulated during times of low rates of sedimentation below storm wave base. Therefore, they are useful tools for defining depositional sequences.
    ResultsThe present study documents shell concentrations from the Albian-Cenomanian Aitamir Formation (from the Kopet-Dagh basin of northeast Iran) in the background of overall sediment deposition and highlights taphonomic attributes of the shell concentrations and examines their mode of occurrence in sequence stratigraphic framework of the succession. Based on the results of this study, the complexities of shell concentrations can be resolved with the help of sedimentologic and taphonomic attributes of individual skeletal elements and their mode of occurrence in sequence stratigraphic framework. Based on taphonomic and sedimentological observations, shell concentrations are classified as lag, event, composite/multi-event and hiatal types. Overall, the shell concentrations occupy the basal part of the sequence i.e. upper part of the transgressive systems tract (TST), the middle part of the sequence or the maximum flooding zone (MFZ), and close to the top of the highstand systems tract (HST). Lag concentrations are found in the lower part of the sequence as a transgressive lags at the base of the transgressive systems tract (type 6) while winnowed concentrations (type 5), the major contributors in the sequence, occur in upper part of the highstand systems tract and in the middle part of the transgressive systems tract. The hiatal concentrations (type 4; primary biogenic concentrations) are associated with maximum flooding surface while the position of event concentrations (type 1, 2 and 3) is independent of sequence stratigraphic framework.
    Keywords: shell concentration, sequence stratigraphy, Aitamir Formation, Albian-Cenomanian
  • Marziyeh Notghi-Moghaddam, Fatemeh Hadavi, Lida Khodadadi Pages 278-289
    IntroductionThe Lut Block is alsom called the "Median Mass of East Iran". This basin is a region characterized by Jurassic-Cretaceous-Tertiary sequence (Stocklin and Nabavi, 1973). In this research, to determine the age of these sequence in the Sarayan region (Rumeshtik section), a detailed study of calcareous nannofossils under optical microscope was performed. This section, based on the structural classification of Iran, is located in the east margin of Lut block. Previous nannofossils studies of Cretaceous deposits in Lut Block were done by Hadavi et al. (2012) in Gazak section (East Birjand). In the present study, for the first time the nannofloras of the Rumeshtik section were discussed and biostratigraphy of these deposits were presented. The thickness of the studied sequence is 690 meters, and consists of limestone and shale. Ninety eight samples at intervals from 4-10 meter were collected. For the nannofossils, smear-slides were prepared using the technique of Bown and Young (1998) and examined under a light microscope at 1000 magnification by both cross-polarized and phase-contrast methods.
    DiscussionIn the present study, 33 species belong to 18 genera of calcareous nannofossils in Rumeshtik section were identified. These nannofossils are well to moderately preserved. Some species are abundant in the lowermost part of the studied sections, such as Nannoconus dolomiticus, Nannoc¬onus quadrates and Nannoconus bonetii, while other species are abundant in the uppermost part of the studied sequence such as Nannoconus abundans, Nannoconus circularis, Nannoconus borealis, Lithraphidites bollii and Assipetra terebrodentariu. According to the First occurrence (FO) of marker species, in Rumeshtik section, three calcareous nannofossil biozones (CC3-CC5) were recognized.
    Calcicalathina oblongata zone (CC3): This zone explained as the interval from the FO of C. oblongata to FO C. loriei by Sissingh (1977). The age of this zone is Late Valanginian. This is the oldest identified zone in the studied section. Thickness of this biozone is about 370 meter.
    Cretarhabdus loriei zone (CC4): This zone explained as the interval from the FO of C. loriei to last occurrence (LO) Speetonia colligata by Sissingh (1977). The age of this zone is Hauterivian. Thickness of this biozone is about 220 meter.
    Lithraphidites bollii zone (CC5): This zone explained as the interval from the LO S. colligata to LO C. oblongata by Sissingh (1977). The age of this zone is Late Hauterivian to Barremian. Nannoconus abundans is an index species for Late Hauterivian (Taylor, 1979). Because of the continued presence of C. oblongata, and present of N. abundans, we located lower part of Lithraphidites bollii zone at the end of the studied section. Therefore age of the uppermost part of the studied section is Late Hauterivian. Thickness of this biozone is about 100 meter.
    According the calcareous nannofossil biostratigraphy, age of the sequence in the studied region is suggested to be Late Valanginian- Late Hauterivian.
    In the current study, in addition to biostratigraphy, investigation of temperature changes was done too. During the Early Cretaceous time, some nannofossils such as Lithraphidites bollii, Nannoconus spp., and Watznaueria barnesae indicate the warm surface water and more related to lower paleolatitudes (Thibault & Gardin, 2007º Street & Bown, 2000). The common occurrence of species belong to the genus Watznaueria, Lithraphidites, and Nannoconus are indicative not only of a warm climate, but also of low latitude setting.
    ResultsIn this study, 33 species with relatively well to moderately preservation were identified in the Rumeshtik section. The studied sediments belong to the zones CC3-CC5 of Sissingh (1977). These biozones attribution allow us to access an age of Late Valanginian- Late Hauterivian for the studied section. Index calcareous nannofossil species at the studied sediments indicate that the basin for deposition of these sediments located in low latitude with warm temperature.
    Keywords: Calcareous nannofossils, Early Cretaceous, Rumeshtik, Sarayan
  • Bahare Valipoori Goodarzi, Ahmad Reza Khazaei, Shaahin Zaman, Gholam Reza Mirab Shabestari Pages 290-302
    IntroductionIn northwest of Tabas (NE Iran), the type section of Parvadeh Formation with 46 meters in thickness was measured which its lower part consists of 7 meters of conglomerate and the upper parts include a succession of dense and rarely pisolitic dark gray limestones which has fixed key position between sandstones of Hojedk Formation and marls of Baghamshah Formation. Previous studies on Jurassic corals of Central Iran were done systematically by Flügel (1966) on Scleractinian corals of Shotori Mountains (east of Iran) within Shemshak, Badamu, Baghamshah, Esfandiar and Ghaleh-dokhtar Formations. In these studies, Chomatoseris iranensis were introduced for the first time from Ghaleh-dokhtar Formation (Bathonian-Callovian). Moreover, Pandey and Fürsich (2003) studied 50 genera and 92 species of Scleractinian corals of Toarcian-Kimmeridgian ages in east of Iran. Also, Khaksar (2010) introduced some of the Jurassic corals in Ghaleh-dokhtar Formation in Tabas region.
    In this research, coral specimens of carbonate units of Parvadeh Formation at Mazinou and Kamar-Mahdi sections in southwest of Tabas city were studied. In the aim of paleoecological and paleoenvironmental studies of Parvadeh Formation in these two sections, analysis of paleoenvironment with the aid of fossil records evidences have been carried out.
    Materials and methodsIn order to study paleoenvironment and paleoecology of corals in studied sections, more than 263 coral specimens and some rock samples of the studied sections were collected. Among these samples, totally more than 100 thin sections were made of diverse coral specimens. Before preparation of thin sections, samples were immersed in cold water for 10 days. Then, after labeling and preparing descriptive specifications of each sample, general characters of each specimen such as external morphology including general coral shape, length, maximum diameter, existence or lacking transversal or longitudinal linear bands, theca preservation, rejuvenation and columella were noted. Then transversal and longitudinal thin sections were made from coral specimens. The size of thin sections depend on coral size which varies from 70x25 to 90x70 mm. Internal structures and microstructures of coral specimens were studied by Nikon stereomicroscope SMZ 1000 in Department of Researches and Studies of Paleontology and Geochemistry of Exploration Directorate of National Iranian Oil Company.
    DiscussionCorals of Parvadeh Formation could be found in carbonate units of both sections, especially in the middle parts. Different factors could affect the coral's life such as sea level changes, substrate morphology, sediment supply, salinity and temperature. According to the morphological evidences, e.g. corallite arrangement, type of colony and thickness of dissepiments, paleo-environment of the studied successions could be reconstructed (Badpa et al., 2011). Systematic study of corals in Mazinou and Kamar-Mahdi sections led to identification of 15 genera and 22 species as follows:Solenocoenia sexradiata, Heliocoenia gracilis, Stylina micrommata, Pseudocoenia cf. slovenica, Montlivaltia caryophyllata, Montlivaltia cornutiformis, Coenothecazolleriana, Thecosmilia langi, Epistreptophyllum cornutiforme, Epistreptophyllum commune, Epistreptophyllum sp1, Epistreptophyllum sp2, aff. Calamophylliopsis flabellum, Thamnasteria concinna, Thamnasteria mattensis, Dimorphastraearenevieri, Actinastreapentagonalis, Isastrea aff. browni, Microsolena amorpha, Microsolena ornata, Microsolena verdati, Chomatoseris iranensis.
    Abundance of identified genera and species varies from Mazinou to Kamar-Mahdi area. Differences between species in these two sections could be resulted due to distinction of some environmental factors especially ineffective factors such as water energy which causes changes in the amount of food and insoluble sediments that controls water clarity. Consequently, species with higher potential of adaptation will survive and be found.
    Scleractinian corals have an important role in reconstruction of paleo-environment of Middle Jurassic in southwest of Tabas. These communities prefer shallow warm water, euphotic zones, normal salinity and oligotrophic conditions of carbonate platforms. Based on the mentioned morphological evidences, the suggested paleo-environment of the studied sequences could be considered as a part of back-reef, reef crest and reef front (shallow area) of a carbonate platform in Mazinou and Kamar-Mahdi sections.
    Keywords: Parvadeh Formation, Mazino Section, Kamar-Mahdi Section, scleractinian corals, paleoenvironment