فهرست مطالب

پژوهش های چینه نگاری و رسوب شناسی - سال سی و چهارم شماره 2 (پیاپی 71، تابستان 1397)

فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و چهارم شماره 2 (پیاپی 71، تابستان 1397)

  • تاریخ انتشار: 1397/05/20
  • تعداد عناوین: 6
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  • جابر پیله کوهی، مهدی جعفرزاده *، عزیزالله طاهری، افشین زهدی صفحات 1-21
    برش چپقلو در فاصله 90 کیلومتری جنوب شرق شهر زنجان و در کوه های سلطانیه قرار دارد. مطالعه حاضر درباره نهشته های پرکامبرین پسین شامل سازند بایندور به ضخامت 605 متر و متشکل از شیل با میان لایه های دولومیتی و بخش دولومیت زیرین سازند سلطانیه به ضخامت 100 متر انجام شده است. مطالعه های پتروگرافی و ژئوشیمیایی (XRD ICP-OES) دولومیت های این دو سازند نشان داد این برش دارای 5 نوع دولومیت به شرح زیر است: 1. دولومیت های بسیار ریزبلور؛ 2. دولومیت های ریزبلور؛ 3) دولومیت های متوسط بلور؛ 4. دولومیت های متوسط تا درشت بلور؛ 5. سیمان دولومیتی. نتایج پژوهش حاضر نشان می دهند بیشترین تنوع دولومیت ها در برش یادشده به انواع دولومیت های ریزبلور و متوسط بلور مربوط است. دولومیت های بسیار ریزبلور به دیاژنز اولیه مربوط هستند. دولومیت نوع دوم از تبلور دوباره دولومیت نوع اول تشکیل شده است. دولومیت های نوع سوم تا پنجم در مراحل آخر دیاژنز و در اثر سیالات دولومیت ساز (احتمالا آب های بین حفره ای) تشکیل شده اند. سازوکار دولومیتی شدن برای دولومیت نوع اول الگوی سبخا، دولومیت های نوع دوم از نوع تدفینی کم عمق و دولومیت های سوم تا پنجم از نوع تدفینی عمیق است. مطالعه های ژئوشیمیایی نشان می دهند مقدار کم استرانسیم در دولومیت های درشت بلور این برش نسبت به آب دریا و دولومیت های عهد حاضر و حتی نسبت به دولومیت های بسیار ریزبلور نشان از درشت بلورشدن و عمق تدفین بیشتر این دولومیت ها دارد. مقدار فوق العاده زیاد آهن و منگنز در دولومیت های برش چپقلو نسبت به دولومیت های عهد حاضر و آب دریا نشان دهنده تشکیل این دولومیت ها در شرایط احیایی و حضور باکتری های احیاکننده سولفات است.
    کلیدواژگان: ژئوشیمی، دولومیتی شدن، پرکامبرین پسین، چپقلو، زنجان
  • محبوبه فریدونپور، اعظم ماهانی پور *، محمد داستانپور صفحات 23-42
    در مطالعه حاضر، سازند گورپی در تاقدیس کوه سیاه واقع در شمال شرقی شهرستان دهدشت (منطقه کهگیلویه) ازنظر نانوفسیل های آهکی بررسی شد. مطالعه زیست چینه نگاری نانوفسیل های آهکی سازند گورپی در برش یادشده با 212 متر ضخامت به شناسایی 48 جنس و 115 گونه از نانوفسیل های آهکی منجر شد. بر اساس نانوفسیل های آهکی شاخص، بایوزون های CC15 تا CC25 از بایوزوناسیون (Sissingh 1977) تصحیح شده توسط (Perch-Nielsen 1985) و UC11a تا UC19 از بایوزوناسیون (Burnett 1998) برای این برش تعیین و سن سازند گورپی در این برش کنیاسین پسین تا انتهای مایستریشین پیشین پیشنهاد شد. در مطالعه حاضر، مرز اشکوب های موجود در مقایسه با مقاطع نمونه مرزی جهانی (Global Stratotype Section and Point) و سایر برش های دنیا تعیین شد؛ ازاین رو، مرز اشکوب های کنیاسین - سانتونین در محدوده بین نخستین حضور گونه Lucianorhabdus cayeuxii و آخرین حضور گونه Lithastrinus septenarius، مرز سانتونین - کامپانین با نخستین حضور گونه Aspidolithus parcus و مرز کامپانین - مایستریشین با آخرین حضور گونه Quadrum trifidum مشخص شد.
    کلیدواژگان: زاگرس، زیست چینه نگاری، سازند گورپی، کرتاسه فوقانی، نانوفسیل های آهکی
  • حسن محسنی *، روح الله زیبرم جوانمرد صفحات 43-67
    به منظور مطالعه محیط رسوبی سازند سروک، دو برش از رخنمون‎های آن پیرامون شهرستان ملکشاهی (استان ایلام) بررسی شدند. درمجموع، 430 نمونه با فاصله میانگین 3 متر برداشت و برش‎های نازک رنگ آمیزی شده مطالعه شدند. در نتیجه، 13 ریزرخساره شناسایی شدند که در 5 زیرمحیط رسوبی پهنه جزر و مدی، لاگون، سد، شلف ژرف و شیب‎قاره و حوضه ژرف رسوب کرده اند. شواهدی مانند توربیدیت و تغییرات ناگهانی در رخساره‎ها وجود پلت‎فرم کربناته از نوع شلف لبه‎دار را نشان می دهند که به سوی بخش بالایی رسوبات دارای ویژگی‎های شیب و حوضه عمیق است. به نظر می‎رسد نخست شرایط یک حوضه پلت‎فرمی بر منطقه حاکم بوده است اما پس از فاز کوه زایی ساب‎هرسینین رسوبات رخنمون یافته اند و کارستی شده اند؛ سپس حوضه ای پیش‎خشکی با بالاآمدن دوباره سطح نسبی آب دریا در زمان تورونین پیشین یا میانی پدید آمده که به نهشته شدن 106 متر آهک رسی نازک تا ضخیم لایه تا پایان تورونین منجر شده است.
    کلیدواژگان: سازند سروک، ریزرخساره، تنگ باولک، ملکشاهی، محیط رسوبی
  • زهرا حسنی، مریم مرتضوی مهریزی *، سید ناصر رئیس سادات صفحات 69-94
    بررسی پتروگرافی و ژئوشیمیایی (عناصر اصلی و فرعی) نهشته های پالئوسن شمال بیرجند به منظور تعیین برخاستگاه، سنگ منشا و شرایط هوازدگی دیرینه انجام شد. شواهد پتروگرافی ازجمله کوارتزهای مونوکریستالین نیمه گرد شده با خاموشی مستقیم، فراوانی خرده سنگ های رسوبی و به مقدار کمتر خرده سنگ های دگرگونی و ولکانیکی و همچنین رسم نتایج تجزیه وتحلیل مودال ذره های آواری روی نمودارهای QtFL و QmFlt نشان می دهد ماسه سنگ های پالئوسن مطالعه شده حاصل چرخه دوباره رسوبات پس از کوه زایی هستند. بر اساس مطالعه های ژئوشیمیایی، موقعیت تکتونیکی ماسه سنگ های مطالعه شده احتمالا حاشیه قاره ای فعال است. اندیس های هوازدگی شیمیایی CIA و PIA محاسبه شده برای ماسه سنگ های این برش نشان دهنده شرایط هوازدگی متوسط تا زیاد در ناحیه منشا هستند. داده های پتروگرافی، ژئوشیمیایی و نقشه های جغرافیایی دیرینه منطقه در زمان پالئوسن شرایط آب وهوایی نیمه خشک را در زمان نهشته شدن این ماسه سنگ ها نشان می دهند.
    کلیدواژگان: برخاستگاه، پتروگرافی، ژئوشیمی، توالی پالئوسن، شمال بیرجند
  • عباس قادری * صفحات 95-119
    مطالعه دیرینه بوم شناسی کمی روی 528 نمونه کاملا برجا از بازوپایان سازند جلفا در شمال باختر ایران به ارائه تحلیلی از شیوه انتشار این بی مهرگان دریایی در بوم سازگان لوپینگین پیشین منجر شد. بررسی شیوه استقرار این بازوپایان در کف بستر نشان دهنده غلبه فرم های خاردار شاخص محیط های کم انرژی و بسترهای استحکام یافته در بخش های ابتدایی لایه های جلفای پایینی و تسلط فرم های پدیکولیت درشت شاخص محیط های پرانرژی تر در بخش بالایی این لایه هاست. اندازه گیری شاخص تنوع گونه ای شانون- وینر برای بازوپایان و بررسی آن در طول ستون چینه شناسی وجود شرایط محیطی نه چندان مطلوب برای این جانوران در طول زمان لوپینگین را نشان می دهد؛ ضمن اینکه این شرایط به سمت انتهای پرمین رو به وخامت گذاشته است. این امر هماهنگی خوبی با افزایش شاخص مرگ ومیر بازوپایان در طول توالی مطالعه شده دارد که بر اساس تجزیه وتحلیل اندازه صدف به دست آمد. مقایسه بازوپایان موجود در سازند جلفا با ایالت های دیرینه زیست جغرافیایی معرفی شده برای زمان لوپینگین گویای قرابت بازوپایان ناحیه جلفا با ایالت کاتایسین به سمت ایالت تتیس باختری است. برخلاف باورهای پیشین که گرایش این فونا به سمت ایالت تتیس باختری را از زمان چانگزینگین درنظر می گرفتند، با توجه به حضور برخی گونه ها نظیر Tschernyschewia typica (یک گونه شاخص ایالت تتیس باختری) در لایه های جلفای پایینی، گرایش به سمت این ایالت از زمان ووچیاپینگین پیشین آغاز شده است.
    کلیدواژگان: بازوپایان، پرمین، جلفا، ووچیاپینگین، زیست جغرافیای دیرینه
  • زهرا ماروسی، مسعود علی پوراصل *، رضا قوامی، ریابی صفحات 121-139
    کوه زر از مناطق مستعد برای اکتشاف مس - طلا در شمال شرق ایران است. زمین شناسی این منطقه شامل سنگ های گدازه ای با ترکیب حدواسط تا مافیک به سن ائوسن میانی - بالایی است. گرانودیوریت، مونزونیت، دیوریت به سن اولیگوسن در سری آتشفشانی ائوسن تزریق شده است. سنگ های نفوذی سبب دگرسانی سنگ ها و کانه زایی مس و طلا شده است. برای مطالعه توزیع اندازه ذرات و ارتباط آن با تمرکز فلزها تعداد 6 ایستگاه نمونه برداری انتخاب شد. نمونه های رسوب به 6 بخش (2 تا 425/0، 425/0 تا 18/0، 18/0 تا 125/0، 125/0 تا 063/0، کوچک تر از 063/0 و کوچکتر از 150/0 میلی متر) سرند شدند. مطالعه توزیع اندازه ذرات نشان می دهد ذرات با اندازه های 425/0 تا 2 و 125/0 تا 180/0 میلی متر به ترتیب بیشترین و کمترین درصد وزنی رسوبات آبراهه ای را تشکیل می دهند. بررسی داده های ژئوشیمیایی نشان می دهد عناصر طلا، نقره، آرسنیک، مس، سرب، آنتیموان، مولیبدن، و گوگرد در ایستگاه های نمونه برداری 4، 5، و 6 غنی شدگی درخور ملاحظه ای دارند. مقادیر این عناصر در جزء مش های 063/0 تا 125/0، 125/0 تا 180/0 و 180/0 تا 425/0 میلی متر بیشتر از سایر جزء مش هاست و جزء مش کوچک تر از 150/0 میلی متر معرف دامنه های مختلف غلظت عناصر در رسوبات آبراهه ای این منطقه نیست. در رسوبات آبراهه ای محدوده کوه زر عنصر طلا در فاصله حدود 700 متر از کان سنگ های منشا دارای بیشترین تمرکز است؛ درحالی که این فاصله برای تمرکز بهینه مس، سرب، نقره، آرسنیک، آنتیموان و مولیبدن حدود 1200 متر است. روش کانی سنگین نیز همانند کاوش های ژئوشیمیایی جزء مش 425/0 تا 063/0 میلی متر را برای اکتشاف طلا و عناصر همراه در محدوده کوه زر پیشنهاد می کند.
    کلیدواژگان: رسوب آبراهه ای، ژئوشیمی، اندازه ذرات، کانسار مس - طلا، کوه زر
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  • Jaber Pilekouhi, Mahdi Jafarzadeh *, Azizollah Taheri, Afshin Zohdi Pages 1-21
    Introduction: Dolomite is mainly composed of internal structures and geochemical properties that usually indicate the conditions of formation environments and can be formed through the different mechanisms. For all these mechanisms, fluid flow and suitable amount of the magnesium in the fluid are required. During recent years, studies of dolomites have been one of the most important issues in the international sediment researches. Most of the Precambrian carbonate sequences are affected by dolomitization. Due to the spread amount of dolomites in the late Precambrian rocks of the Alborz Basin, carbonate systems of Chopoghlu section which are located in the southeast of Zanjan into the Soltanieh Mountains have been discussed in this research. Despite the significant presence of dolomite in the late Precambrian carbonate platforms of the Chopoghlu section, no work has been done up to now related to the texture, geochemical properties and also the origin of the late Precambrian dolomitization in this section. Therefore, this study was carried out to determinate the textural, mineralogical and geochemical characteristics of the late Precambrian dolomites in Chopoghlu section to determinate its dolomitization mechanism and the nature of dolomite fluids. Material & Methods: Different fieldwork and laboratory methods were used in this research. During the fieldwork studies, 50 rock samples from carbonate deposits (limestone and dolomite) have been taken for petrography and geochemical studies of these dolomites to determinate dolomitization mechanisms. The thickness of the layers is measured and the stratigraphic column of this section drowns. For the petrography study, 18 thin sections of these dolomites have been prepared. After petrography studies, 14 samples of these dolomites were selected for geochemical analysis to determinate the mechanisms of dolomitization by ICP-OES method. Also, 4 samples were analyzed for mineralogy studies and the determination of major and minor minerals by XRD method. Discussion of Results & Conclusions: The study of dolomite in the Chopoghlu section identified five types of dolomite including: very fine-crystalline, fine-crystalline, medium-crystalline, medium to coarse-crystalline and also dolomitic cement. It should be noted that the fine-crystalline dolomites is the most abundant type of dolomite in the region. In this section, dolomite cements which filled the vugs and fractures have been distinguished into the some of the studied samples. XRD results from dolomite samples in the region indicate that the most abundant mineral is dolomite, and calcite, quartz and muscovite minerals are present as minor and trace minerals in the studied rocks.
    The results of this study clearly show that the very fine-crystalline dolomite is related to primary diagenesis and is formed under a sabkha dolomitization model in a shallow and saline environment (average of sodium is around 478 ppm). The low amount of the strontium content into the coarse-crystalline dolomite in this section (average of 43 ppm) relative to sea water and the present-day dolomites, and even related to the very fine-crystalline dolomites, clearly shows that the coarse crystalline dolomites are formed during greater burial depths. Second type of dolomite or fine-crystalline dolomite is formed under shallow burial depth. These dolomites are formed via marine fluids with normal salinity and are interpreted from the progressive recrystallization of previous dolomite. The presence of stylolite is the main characteristic of this type of dolomite into the studied section. Third to fifth type dolomites formed during the last stages of diagenesis and are related to deep burial and impact of hypersaline interstitial fluids. The higher amount of iron and manganese into the chopoghlu late Precambrian dolomites in comparison with modern dolomites and seawater probably indicate that the formation of these kinds of dolomites may be associated with reduction conditions and the presence of sulfate-reducing bacteria. In general, the dolomitization mechanism for the first-type of dolomite is related to Sabkha model, for the second-type of dolomite is related to shallow burial dolomitization and finally for the third to fifth-types of studied dolomites are related to deep burial dolomitization.
    Keywords: Late Precambrian, Chapoghlu, geochemistry, Dolomitization, Sulfate-reducing bacteria
  • Mahboobeh Fereydoonpour, Azam Mahanipour *, Mohammad Dastanpour Pages 23-42
    Introduction
    The Zagros mountain belt extends over 1800 km from Kurdistan in N Iraq to the Strait of Hormuz in Iran (Lacombe and Mouthereau 2006). Zagros Mountain belt is one of the richest oil provinces in the world (Emmami 2008) and is important to paleontological, sedimentological, structural and geological studies. The Cretaceous sediments in the Zagros Mountain Belt (SW Iran), is characterized by a large diversity of rocks and facies. The Gurpi Formation is one of the source rock for petroleum in Zagros basin and outcrops extensively to southwest Iran (James and Wynd 1965). The type section of this Formation (49° 13´ 47″ E, 32° 26´ 50″ N) is measured at Tang-e Pabdeh, north of the Lali oilfield in Khuzestan (James and Wynd 1965). This section is composed of 320 meters of dark bluish gray, thin-bedded marl and shale beds and occasionally thin beds of marly limestone (Motiei, 1995). The following publications have appeared for this formation (e. g. Kalantari, 1976; Vaziri Moghaddam, 2002; Ghasemi-Nejad et al. 2006; Darvishzad et al. 2007; Bahrami 2009; Rabbani et al. 2009; Bahrami and Parvaneh-Nejad Shirazi 2010; Bieranvand and Ghasemi-Nejad 2013; Parvaneh-Nejad Shirazi et al. 2013; Beiranvand et al. 2013, 2014 and Fereydoonpour et al. 2014). Late Cretaceous calcareous nannofossils study is still scarce in Zagros basin and is a strong motivation for investigating calcareous nannofossils in southwest Iran. Late Cretaceous calcareous nannofossils in Gurpi Formation were studied by (Senemari and Azizi 2012; Badri and Kani 2014; Razmjooei et al. 2014; Najafpour et al. 2015; Senemari 2015 and Hadavi et al. 2016).
    The aim of the present study was to establish the biostratigraphic zonation for the Gurpi Formation and determine age range of this formation in Izeh sub- zone by means of calcareous nannofossils. A 215-m-thick, well-exposed section was chosen for this purpose. The Kuh-e Siah section is located about 15 Km to the north of Deh-Dasht area. This section was measured in detail at 30°54'31. 86 N and 50°36 38. 80 E. Lithologically, it consists of shale, shaly limestone, and shales with thin bedded limestone. It conformably overlies the Ilam Formation and is overlain unconformably by the pabdeh Formation. Material and Methods: In this study a 215-m thick of Cretaceous sediments including the upper part of Illam Formation, Gurpi Formation and the lower part of Pbdeh Formation were recognized. A total of 122 samples with ~ 1 ‒ 2 m sampling interval were collected. Calcareous nannofossils were processed by smear slides technique described by Bown and Young (1998). The slides were studied with a polarized microscope Olympous (BH2) with 1000×magnification. The zonal scheme proposed in this study is based on the ranges of the most important stratigraphically nannofossil taxa. Calcareous nannofossil taxonomy follows Perch-Neilsen (1985) and Bown, (1998). In this study the stratigraphic zonation developed by Sissingh, (1977) modified by Perch-Nielsen (1985) was applied and is compared with, Burnett, (1998) biozones. Discussion of Result and Conclusion: According to the first and last occurrences of the index species of calcareous nannofossils, Late Coniacian to Early Maastrichtian age were recognized for the sediments of Gurpi formation in this area. The standard zones identified are listed below from the oldest to the youngest:Reinhardtites anthophorus biozone (CC15) (Equivalent of Subzone UC11a and UC11b), late Coniacian.
    Lucianorhabdus cayeuxii biozone (CC16) (Equivalent of Subzone UC11c and UC12), late Coniacian- middle Santonian.
    Calculites obscurus biozone (CC17) (Equivalent of Subzone UC12 and UC13), middle Santonian- Santonian Campanian boundary.
    Aspidolithus parcus biozone (CC18) (Equivalent of Subzone UC14 a, b, cTP), early Campanian.
    Calculites ovalis biozone (CC19) (Equivalent of Subzone UC14dTP and UC15aTP), late early Campanian.
    Ceratolithoides aculeus biozone (CC20) (Equivalent of Subzone UC15bTP), late early Campanian.
    Quadrum sissinghii biozone (CC21) (Equivalent of Subzone UC15cTP), early late Campanian.
    Quadrum trifidum biozone (CC22) (Equivalent of Subzone UC15dTP andUC15eTP), middle late Campanian.
    Tranolithus phacelosus biozone (CC23) (Equivalent of Subzone UC16 and UC17), middle late Campanian- early Maastrichtian.
    Reinhardtites levis biozone (CC24) (Equivalent of Subzone UC18), middle early Maastrichtian.
    Arkhangelskiella cymbiformis biozone (CC25) (Equivalent of Subzone UC19), late early Maastrichtian.
    Using of these results and their comparison to other global nanno events, which were reported on upper Cretaceous stage boundaries, can be used to better identify of these boundaries in this section. In this study the Coniacin- Santonian, Sntonian- Campanian and Campanian- Maastrichtian boundaries were identified as follows:Coniacin/ Santonian boundary: This boundary has been reported as the interval from the FO of M. staurophora to the FO of R. anthophorus by Perch-Nielsen (1985). Bralower et al. (1995) have been shown this boundary between the FO of the M. staurophora to the FO of L. cayeuxii. Burentt (1998), Melinte and Lamolda (2002) and Melinte and Lamolda (2007) have been considered the FOs of R. anthophorus, L. grillii, Micula concav, Lucianorhabdus inflatus and L. cayeuxii in the late Coniacin and the LO of L. septenarius in the Early Santonian. The Coniacin- Santonian boundary (CSB) has been placed between the FO of L. cayeuxii and the LO of L. septenarius, within the CC16 Zone of Sissingh (1977), and in the UC11c sub-zone of Burnett (1998). Also the presence of C. obscures after the FO of L. cayeuxii and higher abundance of M. concava, has been reported the CSB (Lamolda et al. 2014). The first sample of the Kuh-e Siah section contains R. anthophorus, L. grillii, Q. gartneri and M. staurophora. The FO of L. cayeuxii and the LO of L. septenarius has been recorded at 5m and 15 m, respectively. Based on these data, the lowermost part of the Kuh-e Siah section is late Coniacian and the CSB was considered in the Kuh-e Siah section in the UC11c/ CC16/ NC17 zones, between the FO of L. cayeuxii and the LO of L. septenarius.
    Santonian/ Campanian boundary:At informal sections of GSSP (Hancock and Gale, 1996; Hampton et al. 2007). , this boundary is marked by the FO of A. parcus parcus. Two main suggested markers, i. e. the FO of A. parcus parcus and the LO of Dicarinella asymetrica occur closely to the base of Chron 33r which may be suggested as the main events for the base of the Campanian (Wagreich et al. 2015). The Santonian- Campanian boundary is described within the intetrval from the FO of A. cymbiformis (UC13a) to the FO of A. parcus parcus (UC14) (Gale et al. , 2008), while Melinte and Bojar, (2010) placed this boundary within the CC17/ UC13 and the LO of A. cymbiformis is located before the boundary. The Santonian- Campanian boundary is located at the base of CC18/UC14 zone, marked by the FO of Broinsonia parca parca, (Wagreich et al. , 2010; Cetean et al. , 2011; Russo, 2013; Dubicka et al. , 2017). In the Kuh-e Siah section, the Santonian- campanin boundary was marked by the FO of A. parcus parcus at the base of the CC18/ UC14/ NC18 at 45 m.
    Campanian‒ Maastrichtian bondary: The Campanian ‒ Maastrichtian boundary (CMB) at GSSP is defined below the LO of Q. trifidum and Q. gothicus. The LO of B. parcus constricta is also recorded about 1. 8 Ma above the CMB (Gardin et al. 2001) and considered as an indicator of the CMB which is observed above the LO of Q. trifidum and Q. gothicus (Odin and Lamaurelle, 2001). At Gubbio area (Gardin et al. 2012), similar to Tercis-Les-Bains (Gardin et al. 2001), the LOs of Q. gothicus and Q. trifidum are followed by the LOs of A. parcus constrictus and Q. trifidum and differs with the proposed CC and UC zonations. It must be mentioned that the LOs of T. orionatus (Gardin et al. 2012) and A. parcus constrictus (Gardin et al. 2012; do Monte Guerra et al. 2016) are diachronous between different latitudes. Thibault also used the LO of Quadrum trifidum as marker for the CMB at low latitude site. In the Kuh-e Siah section, the Campanian- Maastrichtian boundary is identified by the LO of the Quadrum trifidum.
    1- The presented data suggest that the age of sediments of Gurpi Formation in Kuh-e Siah section are late Coniacian to late early Maastrichtian. In kuhe Siah section
    2- According to the continuous presence of L. grillii، M. concava و M. staurophora in samples of Illam and Gurpi Formations and the presence of Q. gartneri and R. anthophorus in the first sample of the Gurpi Formation, the Illam and Gurpi formations boundary is conformably.
    3- The LO of B. hayi bio- evente has a reverse order in this study relative to biozones was described by Sissingh (1977). Although the LO of B. hayi was recorded in zone CC19 (Sissingh 1977), the LO of this species has been recorded up to the middle part of the CC20. In this section, the LO of Bukryaster hayi was recorded in the CC20. Razmjooei et al. , (2014) in the northeast of Kazeroon in Iran (Fars area) and Melinte and Bojar (2010) in southern Romania have also recorded the LO of B. hayi in zone CC20. Based on Melinte and Bojar, (2010), the LO of B. hayi in CC20 is attributed to diachronism or reworking.
    4- Due to the presence of Biantholithus sparseus, Fasciculithus tympaniformis and Markalius inversus in the first sample of the Pabdeh Formation and the non-identification of the end zone of the CC25/ UC19 zones in this section, the Gurpi and Pabdeh Formations boundary is unconformably.
    Keywords: Biostratigraphy, Calcareous nannofossils, Gurpi Formation, Late Cretaceous, stage boundaries, Zagros Basin
  • Hassan Mohseni*, Rohollah Zeybaram Javanmard Pages 43-67
    Introduction
    The study area is located in the Zagros fold-thrust belt in which numerous amounts of hydrocarbon reserves are trapped in the Sarvak Formation (Cretaceous) and the Asmari Formation (Oligo-Miocene) (Mc Clay et al. 2011). The Sarvak Fm. is an important part of the Bangestan Group and laterally passes into the Garau Formation shales toward the Lorestan zone. Furthermore its lateral facies equivalents are well appreciated in the surrounding countries (i.e. the Madud and Mishrif formations in Kuwait, the Vasia Group in UAE, the Natih Formation in Oman, the Ahmadi, Madud and Rumayleh formations in Iraq and KSA (Alsharhan and Kendall 1991; Hajikazemi et al. 2010; Razin et al. 2010; Sadooni et al. 2005). Hence understanding any possible lateral changes of the Sarvak reservoir is crucial. The present study attempts to figure out such changes via examining microfacies characteristics and depositional environment of the Sarvak Fm.
    Materials and Methods
    Two exposed sections of the Sarvak Formation (Cretaceous) were studied in the Kabirkuh around the Malekshahi city in Ilam province named the Tange- Bawlak and Shahnakhjir sections. A total of 430 samples were collected. Detailed petrographic examinations on the stained thin sections were examined under routine petrographic microscope equipped by digital camera. All field evidences were also carefully recorded which will be briefly introduced in the following section. Discussion of Results and Conclusion: Examinations of thin sections revealed 17 microfacies in the Sarvak Fm. which were deposited in 5 distinct depositional settings including tidal flat, lagoon, bar, deep shelf and slope as well. These microfacies are:A-Tidal flat facies association composed of two microfacies barren lime mudstone and dolomitic fenestral packstones to bindstones.
    B-Lagoon facies association including peloid bioclast grainstone to packstone containes Nezzazata, Textularia, Murgina apula, Pseudolituonella reicheli, Gavelinella and mudstone to wackestone partially dolomitized with Miliolids and Nezzazata, Spiroplectinata annectene.
    C-Shallow water bank, reefs and bars consist of 5 microfacies as allochthonous bioclastic rudstone, peloid bioclast rudstone, grainstone to packstone with large scale cross bedding, bioclastic rudstones with brachiopods shell concentration, glauconitic intraformational conglomerate, bioturbated bioclastic packstone to wackestones with Quinqueloculina, Vidalina, Dorothia, Muricohedbergella andmiliolid.
    D-Intrshelf basin (shallow to deep subtidal) that caontain several microfacies such as spiculite wackestone - packstone with a calcisiltite matrix and/or fecal pellets, extensively burrowed bioclastic wackestone- floatstone, glauconitic wackestones and floatstones with infauna and epifauna whole fossils, Oligostegina wackestone with calcisiltite matrix.
    E-slope and deep basin facies association that comprises thin-shelled planktonic bivalve (filaments) with intraclastwackestone, globotruncanid and calcisphere wackestone, microbreccia, bioclastic-lithoclastic packstone or rudstone.
    Interpretations of these facies associations along with field evidences suggests that the depositional environment of the Sarvak Fm. were twofold including platform and deep foreland basin sediments. The platform margin was characterized by high-energy bar/barrier designated by large-scale cross bedding in grainstone and biogenic carbonate buildups. Sporadic turbidity currents probably were responsible to transport the shallow water carbonates into surrounding intrashelf basins. The intrashelf sediments are rich in planktonic biota interbedded with shale and marls rich in open marine fossils including brachiopods, echinoderms and ammonites. Seemingly, the platform setting uplifted as the consequence of Subhersinian orogeny. The unconformity was recognized by evidences such as brecciation, karstification and conglomeratic horizon.
    Subsequent global sea level rise during Early Turonian brought a foreland basin in which about 106 m argillaceous thin to thick bedded limestones capped the interval of the Sarvak Fm. during Late Turonian. These deposits contain Helvetoglobotuncana helvetica, Clavihedbergella, Murginotruncana coronata, Whiteinella, Hedbergella, Rotalipora, Heterohelix, Margnotruncana renzi, Dorotha, Dicarinella.
    The Sarvak Fm. is 845m and 412m thick in the Tange-e Bawlak and Shahnakhjir sections respectively. In the both sections it consists of two facies types including platform facies and foreland basin deposits. The platform deposits inturn composed of neritic (shallow water) sediments and platform margin high energy facies. The foreland basin are argillaceous and fine grained displaying evidences of pressure solution and are abouut 106 thick.
    Keywords: The Sarvak Formation, Microfacies, Tange-Bawlak, Malekshahi, Depositional Environment
  • Zahra Hasani, Maryam Mortazavi Mehrizi *, Seyed Nasser Raeisosadat Pages 69-94
    Introduction
    The relation between the tectonic setting, provenance and composition of siliciclastic deposits has been investigated by many researchers. The geochemistry of major and trace elements of siliciclastic deposits provides information about provenance, the paleoweathering conditions and tectonic setting of sedimentary basins. In terms of structural division, the study area is located in the Sistan Suture Zone (SSZ). The Paleocene- Eocene siliciclastic strata in the east of Iran have significant development, diversity and thickness lithologically. The studied section is located in the 17 kilometers of north of Birjand and 3 kilometers of east of Fariznuk village the most important way to reach the study area is the main road of Birjand- Mashhad. The Fariznuk section with Paleocene age is 113 meters in thickness and forms from three lithostratigraphic units consisting lower conglomerate, middle sandstone and upper carbonate units. The purpose of this study is to investigate the petrographic and geochemical properties of Fariznuk section in the north of Birjand in order to determine the provenance, tectonic setting and paleoweathering conditions.
    Materials and Methods
    In this study, 90 rock samples were collected from the studied sequence. The study of 35 sandstone samples components composition (modal analysis) is performed by using the point counting method of Gazi- Dickinson. Folk (1980) compositional classification of sandstones is used for studied samples. Geochemical analyses (major and some trace elements) are carried out by XRF method for 15 fine grain sandstone samples. Discussion of Results and Conclusions: In the provenance studies, that are performed by petrographic methods, by using the compositional and textural evidences, the characteristics of provenance of sediments can be investigated. Fine to coarse grain sandstones of the studied sequence have angular to sub rounded grains with poorly to well sorting. Based on mineralogical composition these samples are litharenite (Q52.9, F7.3, RF39.8). The plutonic monocrystalline quartz in the studied sandstone samples confirms the presence of intrusive igneous rocks in the source area. While the existence of straight to weakly undolatory extinction in monocrystalline quartz together with metamorphic rock fragments are indicative the presence of metamorphic rocks with above igneous rocks in the source area. Also, the presence of volcanic rock fragments such as peridotite rock fragments from the underlying ophiolite set and andesite rock fragments, plagioclase and zircon heavy minerals can be suggested an igneous (intrusive and volcanic) provenance for these sandstones. The high abundance of sedimentary rock fragments such as sandstone, siltstone, chert and carbonate in these samples indicate a sedimentary source rock with above igneous and metamorphic rocks. Regarding to the litharenite composition of studied sandstones and high abundance of sedimentary rock fragments, in particular chert rock fragments, it seems that the erosion of older sedimentary deposits has the most role in the formation of sandstones in this region. Drawing the point counting results of the Fariznuk Sandstones on the QmFLt and QtFL (Dickinson et al. 1983) diagrams indicate that the most of samples plot in the recycled orogen area. The quartzolithic composition of studied sandstones low amounts of feldspars and high abundance of sedimentary rock fragments relative to volcanic rock fragments, probably suggest the collisional tectonic areas that are documented by drawing the QpLvLs diagram (Dickinson et al. 1983) for these samples.
    In addition to petrographic data and modal analysis, the major element geochemistry can be effective in the classification of sedimentary rocks as well as separation between mature and immature sediments. Based on major oxides geochemical analysis, Fariznuk sandstone samples are located in the litharenite area in the Pettijohn et al. (1987) diagram that is correlated with petrographic data. By using the geochemical data of the siliciclastic rocks also can be obtained many information about the source rock types. The plot of geochemical results of studied samples on the presence diagrams indicates that the provenance of studied siliciclastic rocks probably were quartzose sedimentary, felsic and intermediate igneous rocks that are matched with petrographic results. The results of the major oxides analysis of Fariznuk sandstone samples are drawn in different diagrams to determine the tectonic setting of these sediments. The studied sandstone samples are plotted in the active continental margin and island arc tectonic settings. The Sistan Suture Zone (SSZ) during Cretaceous to Early Paleocene, prior to sedimentation of the studied siliciclastic deposits, was tectonically active and some researchers documented the existence of magmatic arcs associated with subduction at this time. Therefore, the results of geochemical and petrographical data of the studied sandstone samples (active continental margin and island arcs) can be correlated with the Sistan Suture Zone tectono magmatic conditions at this time. According to geological map of this region, the probable source rocks of the studied siliciclastic deposits were ophiolite units, felsic and intermediate igneous rocks (granite, andesite and tuff) and cretaceous flysch rocks (shale, sandstone, limestone and conglomerate) with cretaceous age in the western and southwestern parts of the Fariznuk section.
    The calculated chemical weathering index of Fariznuk sandstone samples (CIA, PIA) indicates medium to high paleoweathering conditions in the source area. According to petrographical and geochemical studies and its integration with world paleogeographic map during the Paleocene time, the climatic conditions
    Keywords: Provenance, Petrography, geochemistry, Paleocene sequence, north of Birjand
  • Abbas Ghaderi * Pages 95-119
    Introduction
    Lopingian succession in the vicinity of Julfa (East Azerbaijan Province, NW Iran) have been known for a long time among the most fossiliferous sections in the south of Paleotethys, especially those of the Ali Bashi Mountains (Stepanov et al 1969). They play a key role in the subdivision of the Late Permian sedimentary successions of the Tethyan Realm. The Wuchiapingian Julfa Formation was accumulated on a shelf environment with a gradual deepening upward trend into the Changhsingian Ali-Bashi Formation. Brachiopods are the most important macrofaunal content of the Julfa Formation while the Ali-Bashi Formation (Sensu Teichert et al 1973) comprises a considerably rich pelagic fauna consisting of conodonts and cephalopods, allowing for the separation of a number of biozones within this time unit. The Julfa Formation contains well diversification of Wuchiapingian brachiopods, grade into 4 biozone in both Main Valley section of the Ali Bashi Mountains and the Zal section (Ghaderi et al., 2014 a, b). The aim of this research is the study of species diversity and settling preferences of these marine invertebrate and their relations with the sedimentary environment. For these purpose, 528 in situ brachiopod specimens have been collected from the Main Valley section of the Ali-Bashi Mountains and the Zal section. Material & Methods: The brachiopods specimens have been collected in situ from the shale, marl and limestone beds of the Julfa and Ali Bashi formations. Also, the upper parts of the Khachik Formation in the Zal section have been yielded few brachiopods (only 2 species). The total number of brachiopods obtained from both the Main Valley and Zal sections are 528 specimens, of which 275 of them belong to the Main Valley and 253 of them belong to the Zal section. The Shannon Wiener index has been used to study the biodiversity and the relative richness of the brachiopod communities. The trend of their diversity changes has also been analysed during the stratigraphic column of the Julfa and Ali-Bashi formations. Interpretation of the brachiopods settling preferences have been done based on Angiolini and Carabelli (2010), analysis of biodiversity and shell size changes according to the method by Angiolini (2007) and recognition of paleobiogeographic position is mainly based on Shen and Shi (2000) and Shen et al (2000). Discussion of Results & Conclusion: Paleoecological studies on 528 in situ specimens of Lopingian brachiopods from the Julfa area in the northwest of Iran provided an analysis of their distribution pattern on the Late Permian ecosystems. The present brachiopod fauna are mainly articulate specimens indicating that they are in life assemblages, with no or minor transport. Brachiopods have been grouped into five categories according to their settling preferences:1- Concavo-convex with stout halteroid spines (i.e. Araxilevis);
    2- Concavo-convex spiny semi-infaunal (i.e. Cathaysia, Spinomarginifera, Haydenella, Tschernyschewia, and Sarytchevinella);
    3- Pediculate taxa (i.e. Transcaucasathyris, Araxathyris, Permophrycodothyris);
    4- Pediculate stabilized by penetration of the elongate umbonal region (i.e. Meekella,
    Orthothetina, Perigeyerella);
    5- Cemented taxa (Lyttoniidina).
    Evaluation of the brachiopod’s settling preferences demonstrate the dominance of spinoid taxa which authenticate the firmground substrates of low energy environments in the lower parts of the Lower Julfa beds. In contrast, the upper part of these Beds is the place of development of pediculate taxa, belong to higher energy conditions. The abundance and diversity of the brachiopods decrease in accordance with the facies changes from bioclastic rudstone/packston of the upper part of the Lower Julfa Beds into the lime mudstone/wackstone of Upper Julfa Beds and Ali-Bashi Formation (Leda et al 2014), where dominance of pelagic ammonoids and conodonts confirm the outer shelf environment. This suggests a deepening upward trend from rich nutrient settings below fair weather wave base into the deep water meagre nutrient substrates below the storm weather wave base in agreement with lithological and sedimentological data.
    Measurement of the Shannon-Wiener biodiversity index for the brachiopod contents and its inspection alongside the stratigraphic log indicates unfavorable environmental conditions for these animals during late Lopingian, while these conditions have deteriorated toward end Permian. This is in accordance with an increase in the mortality rate of brachiopods during the succession which is obtained from the analysis of the shell size.
    Comparison of the Julfa Formation brachiopods with the paleobiogeographic provinces of the Lopingian epoch (for example: Shi and Grunt 2000; Shen and Shi 2000) reveals the faunal affinity with the Cathaysian to Western Tethyan provinces. Contrary to previous beliefs that consider the tendency of the fauna from Cathaysian to Western Tethyan Province since the Changhsingian age, abundant presence of some species such as Tschernyschewia typica in the lower part of the Lower Wuchiapingian Julfa Beds suggest this inclination begins from the Wuchiapingian age.
    Keywords: Brachiopods, Permian, Julfa, Wuchiapingian, Paleobiogeography
  • Zahra Marousi, Masood Alipour, Asll *, Reza Ghavami, Riabi Pages 121-139
    Introduction
    The Kuh-Zar copper-gold mineralization is located in 110 km south of Damghan at Torud-Chah Shirin volcanic-plotonic belt. Stream sediments are used as useful technique in the regional geochemical exploration. Mineralogy, geochemistry and particle size of stream sediments reflecting the composition of source rocks, mechanical and chemical weathering, morphological and hydrological features of the basin, sorting, and climate, as well as several other factors. It is important to consider the influence of geochemical and mineralogical controls on particle size distribution of stream sediments. Studies of distribution of trace elements in relation to the size fraction of stream sediments generally show that several elements, including Mo, Cu, Zn, Mn, and Fe are concentrated in the finest fractions of the sediments. Therefore the majority of stream sediment surveys have been based on the collection of < 200 µm materials. The Forum of European Geological Survey standard sieve mesh is < 150 µm. However, in present study geochemical distribution of elements investigate in various size fractions of stream sediments to obtain optimum mesh size.
    Material and
    methods
    In order to achieve the scope of this study were collected samples from stream sediments, igneous rocks, and silicic veins. The number of 11 thin, thin-polished, and polished samples was studied by optical microscope. To study the effect of particle size distribution on stream sediment geochemistry, 6 stations was selected on the base of lithological, alteration, mineralization, tectonic, and watershed criteria. Each silt sample in every site consisted of 25 sub-samples that were collected along some 30–50 m from active part of stream channel. Silt samples at the field have been screened by a sieve of 2 mm to remove coarse sand. Each sample has been screened with a series sieve from 0.063 to 2 mm (ASTM codes). The ratio of size fractions was determined by weighing of each fraction. All of size fractions were digested in HNO3+HCl (aqua regia) and then analyzed for multi-elements by Varian 735-ES ICP-OES at Zarazma laboratory in Tehran. For measuring the concentrations of Au, fire assay preparation method was employed and the final aliquote was analyzed by Perkin-Elmer 5300 AAS at Zarazma laboratory. Along with silt geochemical samples, 6 heavy mineral and 3 lithogeochemical samples are also studied. Finally, based on the results interpretations have been made.
    Discussion of Results &
    Conclusions
    The Kuh- Zar is one of the most important prospecting areas for copper-gold in the northeast of Iran. Geology of the area consists of intermediate to mafic lava with middle-upper Eocene age. The Oligocene granodiorite and diorite were injected into Eocene volcanic series. Intrusive rocks lead to alteration and mineralization of copper and gold. The study of particle size distribution shows that 2-0.425 mm and 0.180-0.125 mm size fractions are forming the maximum and minimum weight percent of stream sediments, respectively. Geochemical data surveying demonstrate that the Au, Ag, As, Cu, Pb, Sb, Mo, and S are considerably enriched at the 4, 5, and 6 sampling stations. Concentration of these elements in 0.425-0.180 mm, 0.180-0.125 mm, and 0.125-0.063 mm mesh size is more than any other fraction. The < 0.150 mm is not representative size fraction of sediments in this area. Gold concentrate in a distance about 700 meters from mineralized source rocks in the Kuh-Zar stream sediments, whilst optimum distance for concentration of Cu, Pb, Ag, As, Sb, and Mo is about 1200 meters. The heavy mineral technique same geochemical surveys suggest that the 0.425 to 0.063 mm size fractions are useful for prospecting of gold and associated elements in the Kuh-Zar area.
    Keywords: Stream sediment, Geochemistry, Particle size, Copper-gold mineralization, Kuh-Zar