ارزیابی میکروفاسیس، محیط رسوبی و کانی‌شناسی اولیه سازند گرو در برش سطح‌الارضی الیگودرز، لرستان

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه حوضه‌های رسوبی و نفت، دانشکده علوم زمین، دانشگاه شهید بهشتی، تهران، ایران

چکیده

مقدمه: با توجه به اهمیت سازند گرو به ­عنوان سنگ منشأ مهم در حوضه رسوبی زاگرس، در این پژوهش سعی بر آن است که میکروفاسیس ها، مدل رسوبی، ژئوشیمی رسوبی این سازند در برش الیگودرز واقع در جنوب شرق لرستان شناسایی و معرفی گردد.
مواد و روش­ها: 235 برش الیگودرز (جنوب شرق لرستان) در زون زاگرس مرتفع و در محدوده جغرافیایی عرض شمالی ″05 ′04°33 و طول شرقی″17 ′00°49 واقع شده است. مقطع نازک با هدف شناسایی میکروفاسیس­ها و محیط رسوبی تهیه و مطالعه شدند همچنین 40 نمونه­ برای تعیین گستره­ مقادیر عناصر اصلی و فرعی (Ca, Mg, Sr, Na, Mn, and Fe) توسط دستگاه طیف­سنج جذب اتمی (AAS) تجزیه شدند.
بحث و نتایج: ضخامت سازند گرو در برش سطح­الارضی الیگودرز 483 متر است، و لیتولوژی به­طور عمده شامل شیل­آهکی و آهک­شیلی می­باشد. مرز زیرین سازند گرو با سنگ آهک­های برشی معادل سازند گوتنیا به­ صورت ناپیوستگی فرسایشی و مرز بالایی به­ دلیل قرار گرفتن سازند در هسته ناودیس نامشخص است. مطالعه مقاطع میکروسکوپی این برش منجر به­ شناسایی 7 میکروفاسیس در کمربند رخساره­ای بخش عمیق دریا گردید. سازند گرو براساس عناصر اصلی و فرعی و نسبت این عناصر در مقابل هم، ترکیب کانی­شناسی اولیه عمدتاً آراگونیتی بوده است و تحت­تأثیر دو نوع انحلال در سیستم بسته و باز قرار گرفته­اند. همچنین سازند گرو دارای شرایط احیایی و یا افزایش تأثیر دیاژنز متائوریکی بوده است.
نتیجه ­گیری:

سازند گرو دارای ضخامت 483 متر است، که غالباً از شیل­های­آهکی و سنگ آهک­های­ شیلی تشکیل شده است. مرز زیرین سازند گرو برروی سنگ آهک­های برشی معادل سازند گوتنیا قرار گرفته است و مرز بالایی آن به­ دلیل قرار گرفتن در هسته ناودیس نامشخص است.
مهم­ترین اجزاء زیستی شناسایی شده در بخش­های مختلف سازند گرو شامل رادیولر­ها، فرامینیفر­های پلانکتون (گلوبیژرنیلوئیدس، هدبرگلا، لئوپولدینا) می­باشد. از جمله مهم­ترین ترکیبات غیرکربناته شناسایی شده ترکیبات آهن­دار است.
سازند گرو در یک کمربند رخساره­ای بخش عمیق دریا متعلق به یک پلاتفرم کربناته از نوع رمپ تشکیل شده است. ترکیب کانی­شناسی اولیه عمدتاً آراگونیتی بوده است و تحت­تأثیر دو نوع انحلال در سیستم بسته و باز قرار گرفته­اند. همچنین دارای شرایط احیایی و یا افزایش تأثیر دیاژنز متائوریکی بوده است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evaluation of microfacies, sedimentary environment and original mineralogy of the Garau Formation in Aligudarz section, Lorestan

نویسندگان [English]

  • Saeed Shabrang
  • Ehsan Dehyadegari
  • Mohammad Hoseyn Adabi
Department of Sedimentary Basin and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
چکیده [English]

Introduction: Since the Garau Formation is important as a source rock in the Zagros sedimentary basin, in this research, tried to identify and introduce microfacies, sedimentary model, and sedimentary geochemistry of this formation in Aligudarz section located in the southeast of Lorestan.
Materials and Methods: Aligudarz section (southeast of Lorestan) is located in the high Zagros zone and in the geographical range of north latitude 33°04′05″ and east longitude 49°00′17″. To identifying microfacies and sedimentary environment, 235 thin sections were prepared and studied. Also, 40 samples were analyzed by atomic absorption spectrometer (AAS) to determine the range of values of major and minor elements (Ca, Mg, Sr, Na, Mn, and Fe).
Results and discussion: The Garau Formation thickness in Aligudarz section is 483 m, and lithology consists mainly of limestone, shale and shaly limestone. The lower boundary of the Garau Formation with brrecia limestones is equivalent to the Gotnia Formation in the form of unconformity and the upper boundary is not clear due to its location in the syncline core. Study of this section microscopic sections led to the identification of 7 microfacies in the deep-sea facies belt. Based on the major and minor elements and the ratio of these elements to each other, original mineralogy composition has been mainly aragonite and have been affected by two types of dissolution in closed and open systems. And also has anoxic conditions or an increase in the effect of meteoric diagenesis. The original mineralogy composition has been mainly aragonite and have been affected by two types of dissolution in closed and open systems. Due to anoxic conditions or an increase in the effect of meteoric diagenesis.
Conclusions:

Thickness of this section is 483 meters, and lithology consists mainly of limestone, shale and shaly limestone. The lower boundary of the Garau Formation with brrecia limestones is equivalent to the Gotnia Formation in the form of unconformity and the upper boundary is not clear due to its location in the syncline core.
The most important biological components identified in different parts of the Garau Formation include radiolarian, planktonic foraminifera (Globigerinelloides, Hedbergella, Leupoldina). Among the most important non-carbonate compounds are iron oxides.
The Garau Formation is formed in the deep-sea facies belt belonging to a ramp-type carbonate platform. The original mineralogy has been mainly aragonite and have been affected by two types of dissolution in closed and open diagenetic systems, possibly due to anoxic conditions or an increase in the effect of meteoric diagenesis

کلیدواژه‌ها [English]

  • Aligudarz
  • Sedimentary Geochemistry
  • Garau Formation
  • Sedimentary Environment
  • Microfacies

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