فهرست مطالب

رخساره های رسوبی - سال یازدهم شماره 1 (بهار و تابستان 1397)
  • سال یازدهم شماره 1 (بهار و تابستان 1397)
  • تاریخ انتشار: 1397/05/17
  • تعداد عناوین: 8
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  • علی بهرامی*، مهدی یزدی، صفوره صدری، مرجان خداوردی حسن وند صفحات 1-14

    مطالعه نهشته های کربناته و مارنی دارای بقایای لوله های زیستی کرم های حلقوی پلی کیت در منطقه سه اصفهان (ناودیس سراکه) به شناسایی گونه Rotularia spirulaea از خانواده کرم های سرپولید منجر گردید. به طورکلی Rotularia در محیط هایی که به هم ریختگی لایه ها توسط موجودات زنده زیاد باشد و در محیط های با انرژی متوسط تا بالا به طور فراوان یافت می شود. بسیاری ازکرم های Rotularia قسمت یا تمامی طول عمر خود را در لوله های آهکی یا سیمانی ترشح شده گذرانیده اند. این کرم حلقوی اغلب از زمان ژوراسیک تا پالئوژن در دریاهای کم عمق (ائوسن) وجود داشته و در مرز ائوسن الیگوسن منقرض شده است. کرم های Rotularia به همراه بقایایی از قطعات خرچنگ، شکم پا و روزن داران کف زی گویای شرایط دریایی کم عمق در زمان تشکیل نهشته های مورد مطالعه بوده است.

    کلیدواژگان: ائوسن، کرم های حلقوی پلی کیت، ناودیس سراکه، سرپولید، Rotularia
  • عفت ‍‍پاسبان، سعید خدابخش*، محمدرضا غریب رضا، شیما کبیری، ناصر بحیرایی صفحات 15-34

    رودخانه ها مهم ترین منابع آب در نواحی خشک (از جمله ایران) هستند. رودخانه ‎های الموت و شاهرود جزو رودخانه های دائمی هستند که بخش مهمی از منابع آب شمال ایران را تامین می کنند. اهداف این پژوهش شامل طبقه بندی کمی الگوی کانال و نیمرخ پهنای رودخانه های الموت و شاهرود، تعیین مهم ترین عوامل موثر بر روی تکامل این رودخانه ها و تحلیل دوره های رسوب گذاری و فرسایش بستر این رودخانه ها می باشد. تکامل کانال این رودخانه ها در یک دوره 34 ساله با تاکید بر روی الگو، هندسه و تغییرات ارتفاعی بستر در اثر فرآیندهای رسوب گذاری و فرسایش  بررسی شده است. بررسی زمانی تصاویر ماهواره ای (1981-2015) با استفاده از نرم افزار GIS همراه با  نقشه برداری های توپوگرافی و زمین ریخت شناسی جهت ارزیابی روند تکاملی و تعیین شاخص های کلیدی موثر بر تغییرات کانال انجام شده است. برای بررسی نیمرخ پهنای تاریخی (1984-2014) کانال در چهار ایستگاه، نقشه برداری زمین شناسی انجام شده است و همراه با عکس های تکراری و تحلیل بسامد سیلاب، در ارزیابی تغییرات ارتفاعی بستر و فرآیندهای موثر استفاده شده است. فرآیند ترک کانال رایج ترین دلیل تغییر کانال است. نرخ تغییر پهنای کانال 2/5 متر در سال در بالادست، 20 متر در سال در میان رود و 9/3+ و 2/4 متر در سال در بخش باختری است. نرخ رسوب گذاری و حفر بستر 12/1 و 76/0 متر در سال در ایستگاه B و 55/5 و 63/5 متر در سال در ایستگاه C است. نتایج نشان می دهد که شرایط اقلیمی، عوامل آب شناختی و فعالیت های انسان مهم ترین دلایل تغییرات بستر کانال هستند.

    کلیدواژگان: الموت، شاهرود، رسوبگااری، ررسایش، GIS
  • محمد پرندآور، فاطمه هادوی* صفحات 35-48

    در پژوهش حاضر الگوی پراکندگی و زیست چینه نگاری نانوفسیل های آهکی بخش های بالایی سازند قم (عضوهای e و f) در برش سیاه کوه مطالعه و ارزیابی شده است. بدین منظور تعداد 121 نمونه از عضوهای e و f سازند قم با ضخامت 351 متر جهت شناسایی نانوفسیل های آهکی، بررسی های آماری نیمه کمی و تفکیک دقیق بایو زون های استاندارد جهانی مورد مطالعه قرارگرفته که به شناسایی 38 گونه متعلق به 15 جنس از این گروه پلانکتونی منجر شده است. با توجه به گونه های شاخص شناسایی شده، بایو زون های استاندارد نانوفسیلی NN2-NN4 و همین طور بایوزون های CNM4-CNM6 برای عضوهای مطالعه شده از سازند قم معرفی شد. ارزش زمان چینه ای بایو زون های تفکیک شده، بیانگرسنی معادل بوردیگالین تا لانگین پیشین برای بخش های e و f سازند قم در برش سیاه کوه می باشد. همچنین مطالعات آماری نیمه کمی انجام شده بر روی الگوهای پراکندگی نانوفسیل های آهکی، بیانگر تغییرات مجموعه های نانوفسیلی از ابتدای بوردیگالین به طرف آغاز لانگین (میوسن میانی) می باشد.

    کلیدواژگان: الگوی پراکندگی، زیست چینه نگاری، سازند قم، نانوفسیلهای آهکی، سیاهکوه
  • جهانبخش دانشیان*، لیلا رمضانی دانا صفحات 49-68

    برای بررسی تغییرات رفتار ژئوشیمیایی عناصر در طول برش چینه شناسی دوبرادر واقع در جنوب شرق شهر قم، 30 نمونه بر مبنای مرزهای چینه ای منطبق بر تغییرات عضوهای سازند قم برداشت شد. پس از تجزیه شیمیایی با روش ICP AES، تغییرات عناصر Ca، Mg، Fe، Na، Zn، Mn، Sr  و نسبت Mg/Ca نمونه ها مورد بررسی قرارگرفت. تغییرات رفتار ژئوشیمیایی این عناصر با تغییرات تنوع روزن داران کف زی و شناور نیز مورد مقایسه و بررسی قرار گرفت. رفتار عناصر در طول برش مورد مطالعه نشان دهنده تغییرات زیاد در ابتدای برش (در محدوده زمانی اکیتانین) و تغییرات کمتر در قسمت بالای برش (در محدوده زمانی بوردیگالین) است. همین وضعیت در میزان تنوع روزن داران نیز مشاهده شد که گویای شرایط محیط دیرینه در زمان اکیتانین تا بوردیگالین است. نوسانات مقدار عناصر به ویژه عنصر Mg و نسبت Mg/Ca به همراه تغییرات تنوع روزن داران دلیلی بر تغییرات دمای دیرینه محیط است. افزایش غلظت عنصر Mg و افزایش نسبت Mg/Ca در بیشتر نمونه ها هماهنگ با افزایش تنوع روزن داران بوده و هر دو نشان دهنده بالا رفتن دمای دیرینه در حوضه رسوبی قم می باشند. این شواهد نشان می دهد در برش دوبرادر در زمان اکیتانین، شرایط محیط گرمتر از بوردیگالین بوده است.

    کلیدواژگان: چینه نگاری شیمیایی، درجه حرارت دیرینه، سازند ق، ناحیه الگو
  • خلیل رضایی، شهرام فروغی شادباد* صفحات 69-90

    در مناطق مختلف کشور به غیر از پهنه ایران مرکزی، مطالعات بسیار کمی بر روی رسوبات آواری میوسن انجام گرفته است. در مطالعه پیش رو با استفاده از روش های آنالیز رخساره ای، پتروگرافی، دانه شماری و ژئوشیمیایی به مطالعه این رسوبات در البرز مرکزی پرداخته شده است. این توالی به طور عمده از رسوبات مارن و ماسه سنگ تشکیل شده و به طور محلی دارای میان لایه های کنگلومرا با قطعاتی در حد پبل است. رخنمون و برش مورد مورد مطالعه از توالی رسوبات دانه ریز (مارن)، ماسه سنگ ها (فلدسپاتیک لیت آرنایت و لیت آرنایت از نوع ولکانیک آرنایت) و کنگلومرا (ارتوکنگلومرا و پاراکنگلومرای پلی میکتیک) به ضخامت 2/127 متر تشکیل شده است. لایه های سنگی این سازند از دو رخساره گراولی Gmm و Gcm و سه رخساره ماسه ای St، Sh و Sm تشکیل شده اند. خرده سنگ های آذرین بیرونی با جورشدگی ضعیف تا متوسط و گردشدگی متوسط تا خوب، اجزای اصلی تشکیل دهنده این رسوبات هستند که با سیمان غالب هماتیتی به هم جوش خورده اند. بر اساس نتایج به دست آمده، این رسوبات دارای سنگ منشا آذرین فلسیک مشابه پوسته قاره ای بالایی می باشند که در اقلیم خشک تا نیمه خشک تحت هوازدگی ضعیف قرار گرفته اند. رسوبات حاصل مسافت نسبتا کمی را طی کرده و با درجه پایین بلوغ و هوازدگی کم شیمیایی در محیط فعال تکتونیکی و در چرخه اول رسوب گذاری نهشته شده اند. این رسوب گذاری در محیط نزدیک به منشا و در کانال رودخانه های بریده بریده و دشت سیلابی مربوط به مخروط افکنه با تفکیک هیدرولیکی ضعیف و در جایگاه زمین ساختی کمان قوسی اقیانوسی اتفاق افتاده است.

    کلیدواژگان: پتروترا ی، ژئوشیمی، رسوبات وواری، میوسن، طالقان
  • حسین سعادتی، بهرام علیزاده*، الهام ترهنده، مهراب رشیدی صفحات 91-112

    سازند کشف رود به کمک روش ژئوشیمیایی دارای پتانسیل هیدروکربوری نسبتا خوب تا ضعیف ارزیابی می گردد. داده های راک ایول کروژن های نوع II و مخلوط II-III و بلوغ حرارتی انتهای مرحله پنجره نفتی تا کاندنسیت گاز تر را نشان می دهند. برای مدل سازی بلوغ حرارتی، زون های I2، I4 و I6  در چاه B (کپه داغ پیش ژرفا) و زون های I1، I3 و I5 در چاه E (کپه داغ چین خورده) به عنوان لایه های سنگ منشا سازند کشف رود معرفی شدند. زون های چاه B از 167 تا 107 میلیون سال پیش وارد پنجره نفتی، از 115 تا 72 میلیون سال پیش وارد اوج اصلی زایش نفت و از 90 تا 45 میلیون سال پیش وارد زون گاز تر شده اند. زون های I4 و I6 (عمیق ترین زون) بیشینه بلوغ حرارتی 5/2 تا 2% انعکاس ویترینایت (VRo) با °C 200<-192 و زون I2 (کم عمق ترین زون) کمینه بلوغ حرارتی 58/1% و دمای °C 171 را در الیگوسن پیشین تحمل کرده اند. جریان حرارتی بالا در طول ریفت زایی به همراه باقی مانده ضخامت سازند کشف رود باعث زایش سریع هیدروکربور در زون I6  شده است. این در حالی است که به واسطه چین خوردگی وکاهش دما (°C 175-130) هیدروکربورزایی متوقف شده است. زون های چاه E از زمان 110 تا 83 میلیون سال پیش وارد پنجره نفت زایی و از 90 تا30 میلیون سال پیش وارد اوج اصلی زایش نفت شده اند. زون های I3 و I5 بیشینه بلوغ حرارتی 4/1تا 1/1% VRo و دمای°C  155-135 را در الیگوسن پیشین تحمل کرده اند در حالی که زون I1 به اوج زایش نفت (95/0% VRo و دمای °C  128) رسیده است. در حال حاضر به واسطه بالاآمدگی، چین خوردگی و کاهش دما به °C 95-63، هیدروکربور زایی متوقف شده است. در نهایت به دلیل سپری شدن مرحله اصلی زایش هیدروکربور در کپه داغ پیش ژرفا و توقف هیدروکربورزایی به واسطه بالاآمدگی در کپه داغ چپن خورده و پیش ژرفا، تشکیل تله های ساختمانی بر اثر چین خوردگی الیگوسن پیشین تاثیری در تجمعات هیدروکربوری کپه داغ شرقی نداشته و باید زمی ن ریختارهای دیرینه به عنوان اهداف اکتشافی در منطقه کپه داغ شرقی در الویت قرار گیرند.

    کلیدواژگان: سازند کشف رود، کپه داغ شرقی، مدلسازی بلوغ حرارتی
  • سعیده سنماری* صفحات 113-126

    در مطالعه پیش رو 95 متر از رسوبات سازند گورپی در برش شمال شهر اوز واقع در جنوب شرق شیراز از دیدگاه نانوفسیل های آهکی مورد بررسی قرارگرفت. در این برش سازند گورپی از مارن، شیل و سنگ آهک رسی تشکیل شده است. بررسی نانوفسیل های آهکی در این قسمت به تشخیص22 جنس و 33 گونه منجر شد. براساس پراکندگی گونه های شاخص نانوفسیلی، بایوزون های Aspidolithus parcus zone، Calculites ovalis zone، Ceratolithoides aculeus zone، Quadrum sissinghii zone، Quadrum trifidum zone، Reinhardtites levis zone  و Tranolithus phacelosus zone از زون بندی Sissingh (1977) تشخیص داده شدند که این بایوزون ها با بخش زیرین بایوزون NC18 تا بخش زیرین بایوزون  NC21 از زون بندی Roth (1978) و بایوزون های UC14 تا UC18 از زون بندی Burnett (1998) مطابقت دارند. بر اساس بایوزون های به دست آمده بازه زمانی سازند گورپی در این برش از کامپانین پیشین تا اواخر مایستریشتین پیشین است. مطالعه در برش اوز نشان می دهد که نهشته های سازندگورپی با کاهش عمق حوضه رسوبی در اواخر مایستریشتین پیشین، به صورت همشیب و ناگهانی به سنگ آهک های سازند تاربور ختم می شوند.

    کلیدواژگان: بایوزون، گورپی، زیست چینه نگار، فارس، نانوفسیلآهکی
  • فرج الله فردوست، مهدی جعفرزاده، حامد زند مقدم*، فاطمه عابدینی مقانکی صفحات 127-144

    به منظور مقایسه سنگ شناسی و ژئوشیمیایی (مطالعات خاستگاه) ماسه سنگ های سازند پادها به سن دونین پیشین میانی در دو بلوک طبس و یزد، دو برش ازبک کوه (شمال بلوک طبس) و درونه (شمال بلوک یزد) انتخاب و نمونه برداری شده است. ضخامت سازند پادها در برش ازبک کوه 492 متر اندازه گیری شده که اغلب از سنگ های سیلیسی آواری، دولومیتی و تبخیری تشکیل شده در حالی که در برش درونه، این سازند شامل 310 متر سنگ های سیلیسی آواری و دولومیتی است. مطالعات پتروگرافی ماسه سنگ ها در برش ازبک کوه عمدتا نشان دهنده پتروفاسیس های کوارتزآرنایت و ساب لیت آرنایت (ساب چرت آرنایت) است درحالی که ماسه سنگ های برش درونه از دو پتروفاسیس کوارتزآرنایت و ساب آرکوز تشکیل شده است. داده های ژئوشیمیایی عناصر فرعی و نادر خاکی و مقایسه آن ها با پوسته بالایی همراه با نسبت های بین برخی از عناصر فرعی از قبیل La/Co، Th/Sc، La/Sc و  Th/Coنشان می دهد که سنگ مادر ماسه سنگ های سازند پادها در برش های ازبک کوه و درونه از نوع آذرین اسیدی است. همچنین استفاده از نمودار مثلثی Th-La-Sc و Th-Sc-Zr/10 نشان داده است که ماسه سنگ های برش ازبک کوه، اکثرا در محدوده غیرفعال قاره ای و ماسه سنگ های برش درونه هم در محدوده فعال قاره ای و هم غیرفعال قاره ای قرار می گیرند. این مطالعات نشان می دهند که نهشته های مورد مطالعه به سن دونین پیشین میانی به احتمال در راستای باز شدن اقیانوس پالئوتتیس و حد فاصل تبدیل حاشیه ریفتی به حاشیه غیرفعال پالئوتتیس نهشته شده اند.

    کلیدواژگان: ماسه سنگ، ژئوشیمی، خاستگاه، سازند پادها، ازبککوه، درونه
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  • Bahrami A.*, Yazdi M., Sadri S, Khodaverdi Hassanvand M Pages 1-14
    Introduction

    Generally, the rotularians have high frequency in bioturbated environment in moderate to high water energy. Rotularians were also cemented to the substrate during their earliest growth stage, but they became detached shortly after the formation of first whorls. Tube records of rotularia are known from Mesozoic (Late Jurassic) to Early Tertiary sediments, becoming very common during the Cretaceous and Eocene and also has a global distribution. The fossil species Rotularia spirulaea has become extinct close to the end of Eocene - Oligocene time (Howell, 1962; Fauchald & Jumars, 1979; Macellari, 1984; Ruppert et al., 2004; Hove & Kupriyanova, 2009; Sørensen & Surlyk, 2010). 

    Geological settings

    Outcrops in the Soh area include the widely distributed Paleozoic (Zahedi, 1973; Adhamian, 2003; Wendt et al., 2005; Ghobadipour et al., 2013; Bahrami et al., 2015) and Mesozoic deposits (Mannani & Yazdi, 2009; Yazdi et al., 2010), as well as the Paleocene to Oligo-Miocene deposits, the youngest marine sequences, which start with terrigenous red to white sequence of Paleocene conglomerate and sandstone, continued by Eocene fossiliferous carbonates and marls. The Sabkha deposits at the top of the Oligo-Miocene Qom Formation terminates the depositional cycle of the marine sequence. A thick Eocene succession is widely exposed in the studied region (Sadri, 2011; Janssen et al., 2013). The studied section is located near the village of Soh-in Sarakeh Syncline (90 km Northwest of Isfahan)  and  is accessible by a 35 km unpaved road off the Isfahan - Tehran highway. The section is situated on the right side of a seasonal river valley that is observable from a distance in the plain. Coordinates for the fossil locality are: N 33º28´36˝, E 51º27´6˝. Structurally, the locality belongs to the Central Iran microplate, which is restricted by the NW-SE Sanandaj- Sirjan metamorphic belt to the West, and by the Great Kavir fault to the East.

    Discussion

    The studied section is about 354 meters thick. Based on field observation, sedimentological features and fossil contents, 11 lithological packages are discriminated. 18 meters of Marl at the base of the Eocene (Package 1) contains rich with high diversity of marine faunas e.g. : Benthic foraminifers, Crustacean remains, bivalves, Gastropods and Polychaet tube worms (Rotularia spirulaea). Fossil rotularia with accompanying fauna: crab remains, gastropods, bivalves and benthic foraminifers are indicatives of warm shallow marine paleoenvironments during the deposition of the studied interval. Specimens are deposited in the Department of Geology, Faculty of Science, University of Isfahan, 81746, Iran, under acronym EUIC.

    Acknowledgment

    This study undertaken at the Department of Geology, Faculty of Science, University of Isfahan. The financial supports by the Vice Chancellor for Research and Technology, University of Isfahan highly appreciated.

    Keywords: Eocene, Annelid worm, Sarakeh synclinal, Rotularia, Serpulid
  • Pasban E, Khodabakhsh S *, Gharibreza M, Kabiri Sh., Bahiraei N Pages 15-34
    Introduction

    Changes in the geometric shape of the river channel can be studied in horizontal and transverse views; Plan view changes in river systems based on aerial photographs or satellite imagery (using remote sensing and geographic information systems) are tracked at specific time intervals and include: channel widening and narrowing, channel simplification, braiding, meander migration, sinuosity growth, chute cut-off, neck cut-off, avulsion, simple irregularities in the bank, as well as the combination of two or more of these processes (David et al., 2016; Li et al., 2017). River channel profile changes can be mapped through the time intervals, and the most important are degradation and aggradation (Ollero, 2010; Little et al., 2013). The main objectives of this study are: 1- Investigation of geometric variations of Alamut and Shahrood rivers on the basis of field visits, geological maps and plan view mapped from satellite images (1981, Landsat 3; 1991, Landsat 5; 2002,  Landsat 7; 2009, Landsat 5 and 2015, Landsat 8) in almost certain months; 2- Estimating the rate of aggradation and degradation of the channel bed based on the survey of the profile of the channel (based on mapping) in the years mentioned at the four selected stations (Khooban Baghkalayeh, Late and Rajaee Dasht stations). The most important features used to determine the geometric variations of the channel were the extension, width, branching index and sinuosity.  
    Alamut-Shahrud catchment (49° 30' to 51° 10' E and 36° 07' to 36° 30' N; 4853.67 km2 area) is one of the two Sepidrudsub-catchments and is situated in the South Caspian Sea catchment. The main outcrops of this catchment is in the eastern (upstream) zone and are composed of the Miocene terrigenous rocks, Eocene volcaniclastic rocks and some Mesozoic carbonate rocks in mid zone and Eocene volcanic units in downstream zone (Annels et al., 1977).

    Result and Discussion

    The most significant changes from 1981 to 2015 in 130 locations have been recorded from upstream to the outlet of the basin and include the following: Channel migration (57 locations), meander cutoff (23 locations), sinuosity growth (28 locations) and branching (22 locations).
    Based on the migration of the channel, the following are observed: The maximum displacement is in the eastern (upstream) and central regions; in the central-range (Razmian), the length of channel shift occurred  about 3 km and reaches up to 575 meters. The lateral displacement of the channel in the western part is less (161 m) than other intervals and is neck cut off. The river in the eastern and central part (Khooban to Bahram Abad) is on a nearly straight path. In terms of the sinuosity, the channel has open angles and the sinuosity index is between 1.1 to 1.2. While the sinuosity angle of the channel in the western part is steep and its range is much shorter than the eastern and central parts of the river. The reason for the difference in the sinuosity pattern is the existence of two fault systems with an angle of about 120 degrees along the river course in the western part. Increasing more than three times the amount of channel shift in the central region (Rajaei Dasht-Bahram Abad, Figure 8) is also evident with the decrease of the slope of the river.This change was simultaneously happened by changing the single-channel river pattern to braided channel; the drop in water velocity as a result of slope reduction, caused the sediments to be deposited more like bars and the branching ratio has increased.

    Channel profile change

    Profile changes of rivers were measured in 4 hydraulic stations; Khooban (56° 38' 47.56″ ; 36° 23' 51.23″) and Baghkalayeh (56° 29' 40.50″ ; 36° 23' 35.25″) on the Alamut River, respectively in the period from 2005 to 2014 and 1984 to 2014; and Rajaee dasht (50° 16' 46.38″ ; 36° 27' 34.98″) and Lats (50° 03' 59.96″ ; 36° 36' 36.88″) in the Shahroud River; between the years 1984 to 2014 and 2005 to 2014. Mapping cross-sectional profile was carried out during the years mentioned by Qazvin Regional Water Company. The measurements were done from the right to the left of banks in the channel.
    The main goal of the study is to examine cross section, diagnosis of aggradation and degradation channel. Effective factors in these two processes can be indicated by the discharge, sediment load, bed slope and human activity. These factors are in dynamic equilibrium with controlling the morphology of the river channel, and whenever one of them increases or decreases, the river channel changes to become stable under the new conditions.
    By increasing flow rate or decreasing sediment load, the capacity of river transport sediment is more than that, and this led to degradation, while decreasing flow rates or increasing sediment load led to aggradation (David et al., 2016). At Baghkalayeh Station between 1988-1991, 2000-2001, 2007-2008 and 2012-2014, discharge decreasing led to aggradation process, between the years 1992-1993 and 2002-2007, with increasing flow rate; the bed degradation process has occurred. The highest rate of bed degradation between 2002 and 2007 was followed by the highest increase in bed aggradation in 2007-2008. In the Rajaee dasht station, the trend is almost identical. In the Lat station, from 2007 to 2011, changes in the flow rate and bed height of the channel were similar, and from 2011 to 2014, the bed aggradation was evident with decreasing flow rate.
    Some important results are summarized as follows:1- The most important changes in the plan view of the river channel are the channel abandont process, neck cutoff, sinuosity growth, increased branching index (ie bar migration, sedimentation and branching) and lateral migration.                                                        
    2- The reasons for these changes are: migration of channel bars, changes in sediment load and flow discharge, flood, growth of the fans/mouth bar formation, changes in branching and sinuosity index, geology of the watershed.
    3- The bed aggradation, degradation and channel width variation processes in the studied stations in a complex site and time unit under the influence of changes in flow rate and sediment load.

    Keywords: Alamut, Shahrud, Aggradation, Degradation, GIS
  • Parandavar M, Hadavi F * Pages 35-48
    Introduction

    The Qom Formation is widely distributed in the Qom back-arc, arc, and fore-arc basins (Reuter et al., 2007). The Siah-Kuh section has the best outcrop of the Qom Formation in back-arc basin and is located northeast of type section. Despite of several studies that having been carried out on the biostratigraphy of the Qom Formation, no comprehensive agreement is still present for its dating, especially upper part of the formation. Therefore, the aim of the present work is to document, through a high-resolution study, the stratigraphic occurrence of calcareous nannofossils into “e” and “f” members of the Qom Formation at the Siah-Kuh section in the north side of the Qom sedimentary basin (south of Garmsar city).

    Materials and Methods

    In the present study, the upper part of the Qom Formation (“e” to “f” members) with a thickness of 351 m consists of green to gray marlstones, green calcareous marlstones and argillaceous limestone that overlies the thick-bedded gypsum of the “d” member. A total of 121 samples obtained from the top of “d” member to marlstones and marly limestones succession of “e” and “f” members. The collected samples prepared using the simple smear slide and Gravity techniques that described by Bown & Young (1998). Slides were studied using an Olympus BX53 light microscope at 1250X magnification inside of the PPL, XPL, XPL+GP, XPL+QP areas and species images were taken using an Olympus DP73 camera. In the present study, the Martini (1971; NN zones) zonation pattern is used as the standard zonation scheme. However, the zonal marker of Okada & Bukry (1980; CN zones) and Backman et al. (2012; CNM zones) used for high-resolution biostratigraphic study.As well as, the semi-quantitative analysis was utilized to reconstructing distribution pattern of calcareous nannofossil taxa. The preservation, species abundance and slide abundance of species was determined by counting the number of specimens on the 46 smear slide following Lupi & Wise (2006), and Self-Trail (2011).

    Discussion

    The investigation of calcareous nannofossil assemblages led to the identification of 38 species belonging to 15 genera. Based on the index taxa, the Discoaster druggii Zone (NN2) to Helicosphaera ampliaperta Zone (NN4) of Martini (1971) are distinguished from the studied interval of the Qom Formation. The established biozones can be correlated with CN1c-CN2-CN3 zones of Okada & Bukry (1980) and CNM4-CNM5-CNM6 zones of Backman et al., (2012), that is confirmed the Burdigalian-early Langhian age for the studied interval from the “e” and “f” members of the Qom Formation in Siah-Kuh section.The semi-quantitative analysis shows that the preservation of nannofossil specimens is poor to good and richness of nannofossil assemblages (Slide abundance) is frequent (F) to Abundant (A). The significant decreases in abundance of some species such as Helicosphaera ampliaperta, Helicosphaera euphratis, and Cyclicargolithus floridanus etc. has been observed towards the Burdigalian-Langhian boundary. Although, the calcareous nannofossil species have a good to moderate abundance from the base of the "e" member to the below of the boundary.

    Conclusion

    The studied interval of “e” and “f” members, spanning from NN2 to NN4 zones of Martini (1971) and CNM4 to CNM6 zones of Backman et al., (2012). The recognition of these biozones confirms the Burdigalian-early Langhian age of sediments in the Siah-Kuh section.The Burdigalian-Langhian boundary at the studied interval is marked by an important decreases in the abundance of Helicosphaera ampliaperta, Helicosphaera euphratis and Cyclicargolithus floridanus which is followed by continuously recording of Sphenolithus heteromorphus. Above the boundary, Helicosphaera carteri species have been observed dominantly.Acknowledgment The authors thanks to Professor Marie Pierre Aubry (University of Rutgers, USA) and Professor Jeremy Young (University College of London, UK) for their advices and who checked determinations of calcareous nannofossils. We would like to acknowledge the Exploration Directorate of NIOC (National Iranian Oil Company) for laboratorial facilities provided. This paper is extracted from the research project No. 3/39428 of Ferdowsi University of Mashhad that is necessary to the gratitude.

    Keywords: Distribution pattern, Biostratigraphy, Qom Formation, Calcareous nannofossils, Siah-Kuh
  • Daneshian J*, Ramezani Dana L Pages 49-68
    Introduction

    Chemostratigraphy is a part of stratigraphy which study chemical changes of sedimentary units in a sequence. Nowadays, the changes of elements in carbonate sediments use as a criteria for the detection of their old sediments equivalents (Adabi, 2004). Marine carbonate rocks often contain low and high magnesium calcite and aragonite which their frequency are not constant in the environment, and their changes depend on environmental factors such as temperature, salinity, carbon dioxide, pressure and the ratio of magnesium to calcium (Rao, 1996).  Kasaei Najafi (1993) investigated the elements of Sr, Na, Mn, Fe, Ca from the Qom deposits in south to southeast of Qom city and determined a concentration of elements in carbonate rocks depend on the microfacies features.  Okhravi (1999) considered a concentration of rare elements and their relation to the facies by studying of  "f " Member in the same areas. The study area and the stratigraphic section are available through the Tehran-Qom and the cross road of Qom-Jamkaran. This area belong to Central Iran Zone which is formed by collision of Arabian-African plate to Iranian plate. Central Iran connected eastern and western Tethys (Schuster & Wielandt, 1999; Reuter et al., 2009; Mohammadi et al., 2011) and the Qom Formation was deposited during the final marine transgression in Central Iran Basin during the Oligo-Miocene (Daneshian & Ramezani Dana, 2007; Reuter et al., 2009; Seddighi et al., 2012; Mohammadi et al., 2011, 2013, 2015; Daneshian et al., 2017). Dozy (1944) was the first  geologist that  used the term of  Qom Formation for marl and limestone of shallow water with high variations in facies and was not permitted  to introduce a type section for this formation in southern Qom plain by having good outcrops and considerable thickness (Bozorgnia, 1966; Stocklin & Setudehnia, 1971; Hadavi et al., 2010).

    Methods and Materials

    The sedimentary sequence of the studied section consists of a, b, c-1, c-2, c-3, c-4, d, e, f and g members with 1328 meters thickness. 676 samples, systematically, collected with approximate intervals of 0.5 to 3 meters. Among them, 30 samples were selected based on lithological characteristics and stratigraphic boundaries of the members for the purpose of investigation of elements and their changes. The specimens were powdered up to 60 microns and these specimens were analyzed by the ICP AES method for understanding the variations of Ca, Mg, Fe, Na, Zn, Mn, Sr elements, and Mg / Ca ratio.  Then, the variations of the examined elements compared to the benthic and planktic foraminifera diversity. Among the diversity of benthic species, the type of test (agglutinated, hyaline and porcelaneous) were determined separately for recognition of the paleotemperature changes.

    Results and Discussion

    The chemical analysis of elements including Ca, Mg, Fe, Mn, Na, Zn, Sr, and changes in species diversity of benthic foraminifera indicate sharp variations of the elements in the lower part of the succession between  "a" to "e" members, while in the upper parts of the section, "f" and "g" members, the variations are not very sharp. Also, the highest rate of variation for elements is observed in the base of the studied sequence, in the boundary between "b" and "c-1" members especially for Manganese, and in the boundary between "d" and "e" members for Strontium. All elements other than Manganese significantly reduced on the boundary between "b" to "c-1" members, but between "d" and "e" members, all the elements show increasing trend, except Sodium, Manganese and Strontium which indicate deduction and the greatest decreasing  is belong to the Strontium. Besides, species diversity changes of the foraminifera, particularly benthic forms show a definite increase between the boundary of "d" and "e" members.In general, the high variation of the species diversity of benthic foraminifera suggests a relative increase in temperature of the paleoenvironment. Reducing the species diversity at the boundary of "d' Member depends on changes in the depth of sedimentary environment and existing the evaporate environment. In the "e" Member, the diversity of the benthic and planktonic foraminifera show an increasing trend that indicates a high temperature in the environment. In "g" Member, the diversity of foraminifera is low at the base, and is almost constant.  It seems the temperature with a slight increase has reached to a relative stability in this part. But due to the gradual decrease in the depth of the environment at the end of the stratigraphic section and the sea level fall, appear faunal changes to be affected by changes in environment depth.

    Conclusion

    Study of the elements and their variations along the examined section show the high variety at the bottom (Aquitanian), and a low variety at top with Burdigalian age. This state of variations is observed in foraminiferal diversity changes and corresponds to palaeoenvironmental conditions. Fluctuations of the elements, especially Magnesium and Mg/Ca ratio with foraminifer’s diversity changes are environmental indicators and show paleotemperature changes. Increasing concentration of Mg and the proportion of Mg / Ca ratio in the most samples coordinate with increment of foraminifer’s diversity. Both are indicators of increasing of paleotemperature in the Qom basin. These evidences show that the Qom sedimentary basin during Burdigalian were warmer than Aquitanian in Dobaradar section. In fact, the temperature fluctuations at the Aquitanian and Burdigalian are relatively high, and in the middle part of the Burdigalian, and maximum at the beginning of the Late Burdigalian, there is a relative stabile in temperature. 

    Keywords: Chemostratigraphy, Paleotemperature, Qom Formation, Type area
  • Rezaei Kh, Foroughi, Shadbad Sh* Pages 69-90
    Introduction

    Three main goals have driven studies of sandstone in the past ten years: Firstly, the academics motive to understand the tectonic setting, climatic situation, paleo-geographic position. Secondly, the economic motive to predict reservoir ability and porosity and permeability in hydrocarbon fields. Thirdly, the motion or stasis of pore fluids and the scale of mass-transport to form cements. This research involved the first one. Sedimentary rocks are principal sources of information concerning past conditions on the Earth’s surface. Clastic rocks may preserve detritus from long-eroded source rocks and may provide the only available clues to the composition and timing of exposure of source rocks. Geochemistry of sedimentary rocks may complement the petrographic data, especially when the latter are ambiguous. The geochemical composition of sedimentary rocks is a complex function of various variables such as source material, weathering, transportation, physical sorting, and diagenesis. Very few studies on Miocene clastic sediments have been conducted in the country, in zones other than the Central Iran. Hence there are many questions without response in this area. This research is trying to get some solution for these questions

    Methods and Results

    In this research, clastic sediments in the central Alborz have studied using facies analysis, petrography, grains counting and geochemical methods. For this propose, from two sections in the Taleqan area fresh rock samples were collected from outcrops exposed in stream and road cuts and were washed thoroughly in distilled water to remove dust contamination. 52 samples were selected for detailed petrographic study. Also 24 thin sections selected for grain counting and modal analyses according to Dickinson method. Coarse grains classified based on Miall method.  In geochemical studies, we used XRF Philips 1480 for determination of major and minor elements oxides. After preparation, 15 samples were selected for analysis. Measurement accuracy ranges were 0.1 to 0.001. This sequence is mainly composed of marl, sandstone and locally intercalation of conglomerate with Pebble size particles. Studied outcrop is formed of fine grained sedimentary sequence (Marl), sandstones (Feldespatic litharenite and volcanic arenite) and conglomerate (poly-mictic ortho and Para-conglomerate) with 127.2 m thickness. The strata in this formation are composed of two gravelly (Gmm and Gcm) and three sandy (St, Sh and Sm) facies. The main components of these deposits are igneous rock fragments with poorly to moderate sorting and moderate to good roundness that are welded together with hematite dominant cement.

    Discussion

    Roser & Korsch (1986) established a discrimination diagram using log (K2O/Na2O) versus SiO2 to determine the tectonic setting of terrigenous sedimentary rocks. These authors used CaO and LOI-free 100% adjusted data to determine their field boundaries. Both parameters (SiO2 and log (K2O/Na2O) values) increase from volcanic-arc to active-continental-margin to passive-margin settings.  Discrimination of tectonic settings on the basis of major-element data also was proposed by Bhatia (1983); it includes oceanic island arc, continental island arc, active continental margin, and passive margin. Most of our sandstone samples fall in the general area of passive margin and active-continental-margin fields of the TiO2 versus Fe2O3* 1 MgO plot, but mostly in the passive-margin field of the Al2O3/SiO2 versus Fe2O3* 1 MgO diagram. Petrographic data show that K-feldspar dominates over plagioclase, which may result from intense weathering in the source area or from diagenetic alteration. The latter can be ruled out by the presence of abundant carbonate cement that developed probably during early diagenesis. The intensity and duration of weathering in sedimentary rocks can be evaluated by examining the relationships among alkali and alkaline earth elements (Nesbitt & Young, 1982, 1984). Feldspars are by far the most abundant of the reactive minerals. Consequently, the dominant process during chemical weathering of the upper crust is the alteration of feldspars and the neo-formation of clay minerals. During weathering, calcium, sodium, and potassium are largely removed from feldspars (Nesbitt et al., 1997). The amount of these elements surviving in the soil profiles and in the associated sediments is a quantitative index of the intensity of weathering (Fedo et al., 1995; Nesbitt et al., 1997). A good measure of the degree of chemical weathering can be obtained by calculation of the chemical index of alteration (CIA; Nesbitt & Young, 1982) using the formula (molecular proportions). According to results, these sediments have felsic igneous source rock similar to upper continental crust, which has been deposited in the semi-arid dry climate with weak weathering. Final deposits were traveled relatively small distance and were deposited in the first sedimentation cycle with low degree of maturity, low chemical weathering, in active tectonic environment. Thus, the low CIA values of the Taleqan sandstones do not reflect the general chemical weathering conditions in the source region, which can be inferred from the petrographic observations. This is probably due to the sedimentary sorting effect. Physical sorting of sediment during transport and deposition led to concentration of quartz and feldspar with some heavy minerals in the coarse fraction and of secondary lighter and more weathered minerals in the suspended-load sediments.

    Conclusion

    This sedimentation happened in the alluvial braided river’s channel and floodplain near the origin with weak hydraulic separation and oceanic arc tectonic Setting.

    Keywords: Petrography, Geochemistry, Clastic sediments, Miocene, Taleqan
  • Saadati H, Alizadeh B *, Tarhandeh E, Rashidi M Pages 91-112
    Introduction

    Hydrocarbon (HC) exploration in the Eastern Kopeh-Dagh basin (southwest of Amo-Darya Basin) have faced challenges due to the structural complexity and limited geochemical study. Kopeh-Dagh fold and thrust belt and Kopeh-Dagh foredeep were moved from each other by the Main Kopeh-Dagh Fault (Fig. 1). All drilled anticlines in Kopeh-Dagh fold and thrust belt are dry which are in contrast with the Kopeh-Dagh foredeep. Generation, migration, and accumulation of petroleum occured in the region during the Late Miocene and migration of gas started not earlier than 10 Ma years ago (Moussavi-Harami & Brenner, 1992, 1993). It is suggeseted that the hydrocarbon potential of Kashafrud Formation is by the dark shale and abundant vascular-plant fragments (Poursoltani et al., 2007; Taheri et al., 2009) with sufficient thermal maturity to generate hydrocarbons (Poursoltani & Gibling, 2011). Chaman Bid Formation with total organic carbon 0.8% introduced as gas prone (Ghasemi-Nejad et al., 2005). The main objectives of this study are to geochemically investigate the Kashafrud Formation as well as constructing burial history and one dimension (1D) thermal maturity models in the eastern Kopeh-dagh (wells B and E; Fig. 1).

    Materials and methods

    A total of 56 samples (15 cuttings and 25 outcrops) were collected from Kashafrud Formation in the Eastern Kopeh-Dagh (Fig.1). Bulk geochemical parameters (such as TOC, S1, S2 …) of all samples were obtained by using Standard Rock-Eval 6 pyrolazer (Table 1) in Basic Method (Behar et al., 2001). Temis suite software (1D) developed by French Institute of Petroleum (IFP) along with procedure presented by Hantschel & Kauerauf (2009), were employed for reconstructing the thermal maturity and burial history of the studied wells. The heat flow is a critical input parameter in basin modelling. In the Eastern Kopeh-Dagh, the paleo-heat flow has been affected by the tectonic evolution and rifting phase. The basement of Eastern Kopeh-Dagh basin consists of Carboniferous basic volcanoes (Ulmishek, 2004) which corroborated with the heat flow values of 60 mW/m2 (Allen & Allen, 2013). With the occurrence of rifting from 166 to 173 Ma, the heat-flow values reached to the maximum of 80 and 105 mW/m2 for B and E wells, respectively (Fig. 3). The rift affected the heat flow model, a higher heat flow occurrence during rifting phase and an exponential reduction after the post-rift phase (McKenzie, 1978). For well B which is located in Kopeh-Dagh foredeep a cooling history with decreasing heat-flow values was modelled from 72 to 166 Ma and then remained constant about 30 Ma years. Finally due to strike-slip movement in the Eastern Kopeh-Dagh, an increase of 9 mW/m2 values of heat flow is suggested (Fig. 3). But for well E from Kopeh-Dagh fold and thrust belt, heat the flow values are higher than Kopeh-Dagh foredeep. On the other hand the same scenario is played by tectonic activity (Fig. 3). It can therefore be observed that there is a good consistency between the temperature gradient and the heat flow.

    Discussion

    Geochemically, Kashafrud Formation (Aalenian-Bathonian) showed poor/fair hydrocarbon generative potential (McCarthy et al., 2011) (S2 versus TOC; Fig. 4), Type II, mixed II-III and IV kerogens (Dembicki Jr, 2009) (HI versus OI; Fig. 5) and thermal maturity from late oil window to condensate-wet gas (Hackley, 2012) (PI against Tmax; Fig. 6). For thermal maturity modelling, zones I2, I4 and I6 in Well B (Kopeh-Dagh foredeep) and I1, I3, and I5 in Well E (Kopeh-Dagh folded) were introduced as the source rock intervals of Kashafrud Formation (Fig. 7). The model indicates the onset of oil-generation in the Well B zones begining during late Middle Jurassic-Lower Cretaceous time (107-167 Ma). Peak oil generation occurred during Cretaceous time (72-115 Ma) and condensate-wet gas generation started during Late Cretaceous-Early Eocene time (45-90 Ma). I4 and I6 (deepest interval) zones experienced maximum 2-2.5% calculated vitrinite reflectance (VRo) and 192-205 °C (Fig.9) and I2 interval endured minimum 1.58% VRo and 171°C during Early Oligocene (30 Ma). High heat flow during rifting as well as the remained thickness of Kashafrud Formation caused early hydrocarbon generation in zone I6 (Figs. 7 and 9). But, due to uplift and temperature reduction as low as 130-175 °C (Fig. 9), the hydrocarbon generation has been stopped. The onset of oil-generation in the Well E zones began during late Early Cretaceous-Late Cretaceous time (83-110 Ma; Fig. 7). Peak oil generation occurred during Late Cretaceous-Early Oligocene time (30-90 Ma). I3 and I5 (deepest zone) intervals experienced maximum 1.1-1.4% VRo and 135-155 °C (Figs. 7 and 9) and I1 interval endured 0.95% VRo and 128°C during Early Oligocene. Here, due to temperature reduction (as low as 63-95 °C; Fig. 9) caused by upliftment hydrocarbon generation has been stopped.

    Conclusion

    Based on quantity and quality of geochemical parameters such as TOC, S2 and HI, Kashafrud Formation has potential to generate mostly gas with some condensate. However presence of bitumes in all cutting samples points to low permeability of Kashafrud Formation which refered to cracking of generated HC. Furthermore the effects of some low potential shale gas on gaseous HC of carbonate and clastic reservoirs in the Eastern Kopeh-Dagh (Saadati et al., 2016) which is in accordance with lower than 2% of TOC content of Kashafrud Formation. Finally, due to over pass of the main phase of hydrocarbon generation in Kopeh-Dagh foredeep and ceased hydrocarbon generation because of uplifting in Kopeh-Dagh folded and foredeep, the formation of anticlinal traps in the Lower Oligocene folding does not have any effect on HC accumulation in Eastern Kopeh Dagh Basin and paleo-geomorphological traps must be considered as the future exploration targets.

    Acknowledgments

    The authors would like to extend their thanks to the Exploration Directorate of the National Iranian Oil Company (NIOC) for providing the samples and the financial support of the project. Also support of Petroleum Geology and Geochemistry Research Centre (PGGRC) is highly appreciated. No doubt this manuscript could not come to this final stage without the valuable view points and suggestions of Professor Moussavi-Harammi for which the authors are very much grateful.  

    Keywords: Kashafrud Formation, Eastern Kopeh-Dagh, Reconstructing the Thermal Maturity
  • Senemari S* Pages 113-126
    Introduction

    One of the most extensive Cretaceous deposits in Zagros is the marine sediments of Gurpi Formation in southeast Shiraz, which was studied based on stratigraphic and paleontology. Type section of the Gurpi Formation is located in Tang-e Pabdeh (Jams & Wynd, 1965). One of the most important achievement obtained from the Gurpi Formation can be related to study of calcareous nannofossils which is used for determination of precise age and biostratigraphy. In the southeast of Shiraz, Gurpi Formation consists of 95 m thickness which consists mainly of marl, marly limestone and shale, which is gradually overlain by Tarbur Formation.
    Materials &

    Methods

    In this study, 42 samples from Gurpi Formation have been studied. Samples were prepared following standard smear slide method (Bown & Young 1998). The nomenclature of calcareous nannofossil follows the taxonomic schemes of Perch-Nielsen (1985), Bown (1998) and Burnett (1998).

    Discussion

    In order to study the biostratigraphy of Gurpi Formation in southeast of Shiraz, the Evaz section was selected. In this section, the Gurpi Formation is mainly composed of marl, shale, and argillaceous limestone. Calcareous nannofossils recorded in the Mesozoic strata are an appropriate tool for biostratigraphic studies. The nannofossil zonation used in the present study is based on the Nannofossils Cretaceous zonation of Sissingh (1977), Roth (1978) and Burnett (1998). According to the first and last occurrence of index species the following bio zones are identified:Aspidolithus parcus parcus zone (CC18/ UC14/NC18)
    This bio zone is recorded from the FO Aspidolithus parcus to the LO of Marthasterites furcatus. The age of this zone is Early Campanian.
    Calculites ovalis Zone (CC19/ UC15/NC18)
    This bio zone is recorded from the LO Marthasterites furcatus to the FO of Ceratolithoides aculeus. The age of this zone is late Early Campanian.
    Ceratolithoides aculeus Zone (CC20/UC15/ NC19)
    This zone spans the interval from the FO of Ceratolithoides aculeus to the FO of Uniplanarius sissinghii. The age of this zone is late Early Campanian.
    Quadrum sissinghii Zone (CC21/ UC15/NC19)
    The next nannofossil unit recorded in this study is the CC21. This zone spans the interval from the FO of Uniplanarius sissinghii to the FO of Quadrum trifidum. The age of this zone is late Early Campanian-early Late Campanian.
    Quadrum trifidum Zone (CC22/UC15/ NC20)
    This zone spans the interval from the FO of Quadrum trifidum to the LO of Reinhardtites anthophorus. The age of this zone is late Late Campanian.
    Tranolithus phacelosus Zone (CC23/UC15-UC18/ NC20-NC21)
    This zone spans the interval from the LO of Reinhardtites anthophorus to the LO of Tranolithus orionatus. The age of this zone is late Late Campanian-Early Maastrichtian.
    Reinhardtites levis Zone (CC24/ UC18/NC21)
    This zone spans the interval from the LO of Tranolithus phacelosus to the LO of Reinhardtites levis. The age of this zone is late Early Maastrichtian.

    Conclusion

    As a result of this study, 22 genera and 33 species of calcareous nannofossils have been recognized. Based on distribution of index species of calcareous nannofossils, biozones of the zonation of Sissingh (1977) have been recognized, including Aspidolithu sparcus zone, Calculites ovalis zone, Ceratolithoides aculeus zone, Quadrum sissinghii zone, Quadrum trifidum zone, Tranolithus phacelosus zone and Reinhardtites levis zone, that corresponding to lower part of NC18 to lower part of NC21of the zonation of Roth (1978) and UC14-UC18 Nannofossil Zone of the zonation of Burnett (1998). According to the identified biozones, the age of the Gurpi Formation is Early Campanian to late Early Maastrichtian. The study of the Evaz section shows that sediments of Gurpi Formation deposited in the shalloer depth of sedimentary basin during the late Early Maastrichtian, as conformable and suddenly led to the limestone formation of Tarbur Formation.

    Keywords: Biozones, Gurpi, Biostratigraphy, Fars, Calcareous nannofossils
  • Fardoost F, Jafarzadeh M, Zand, Moghadam H*, Abedini MoghanakiF Pages 127-144
    Introduction

    This research is a part of the studies of sedimentology and stratigraphy of deposits associated with the Devonian located in Central Iran, which is known as the Padeha Formation (Lower-Middle Devonian age). In this research, the Padeha Formation in north of Tabas (Ozbak-Kuh) and Yazd (Doruneh) blocks were selected and studied. These succession is measured in Ozbak-Kuh, 492 meters, which is often composed of siliciclastic, dolomitic and evaporite rocks, while in the Doruneh section, this formation consists of 310 meters of siliciclastic, calcareous and dolomitic rocks. The aim of this study is to focus on the petrography and geochemistry aspects for provenance studies.

    Materials & Methods

    Twenty one sandstone samples from Ozbak-Kuh and fifteen sandstone samples from Doruneh section were selectedand studied with Polarized microscope. In each thin section, about 300 points were counted using the Gazzi-Dickinson method. According to the point counting, the major and accessory components of this sandstones are identified and quartz, feldspar and rock fragments modes are utilized for naming the sandstones according to the Folk classification (Folk, 1980). 16 samples of medium grain sandstones with the lowest amount of carbonate cement were selected for geochemical analysis (ICP-MS method).

    Petrography & Geochemistry

    Petrographic studies of sandstone in Ozbak-Kuh section are mainly indicative of quartzarenite and sublitharenite (subchertarenite) petrofacies, however, quartzarenite and subarkose petrofacies have been identified in the Doruneh section. Compared to the Upper Continental Crust (UCC) (Taylor & McLennan, 1985), sandstones of the Padeha Formation in the Ozbak-Kuh section are somewhat enriched in some elements, such as zirconium and hafnium, but in the Doruneh section, zirconium and hafnium are slightly depleted compared to the Upper Continental Crust. All sandstone samples in both sections are strongly depleted compared to UCC. In both the Ozbak-Kuh and Doruneh sections, vanadium, cobalt, nickel and scandium exhibit much depletion compared to the UCC.

    Discussion of Results & Conclusions

    Geochemical diagram of Zr/Sc against Th/Sc (McLennan et al., 1993), along with plotting the data of Padeha Formation on this diagram shows that the samples of Doruneh section are plotted near the UCC. This shows that Padeha Formation sandstones in the Doruneh section are derived from intermediate to acidic igneous rocks, and recycling have not been affected. But the Ozbak-Kuh samples often reflect the granitic parent rock, which is located in the range of recycling. Additionally, the La/Sc versus Co/Th (Gu et al., 2002) is also a confirmation of the felsic to granitic parent rocks for Padeha Formation in both sections. For determination of tectonic setting, in this reseach, triangular diagrams based on trace elements (Bhatia, 1985) have been used. According to these diagrams, Ozbak-Kuh samples, mostly plotted in the passive continental margin field and Doruneh section sandstones are plotted in passive and active continental margin fields. The present study, using the results of petrography and geochemistry and the paleogeographic investigations, shows that the deposits of the Lower-Middle Devonian Padeha Formation can be formed in the transition between the transformations of rifted margin to passive continental margin of Paleo-tethys.

    Keywords: Sandstone, Geochemistry, Provenance, Padeha Formation, Ozbak-Kuh, Daroneh