چینه‌نگاری زیستی، ریزرخساره ها و محیط رسوبی سازندهای گدوان و داریان در میدان نفتی گچساران، جنوب غرب ایران

نوع مقاله : مقاله پژوهشی

نویسندگان

1 پژوهشگاه استاندارد، پژوهشکده فناوری و مهندسی، گروه پژوهشی ساختمانی و معدنی، کرج، ایران

2 گروه علوم تجربی، واحد دزفول، دانشگاه آزاد اسلامی، دزفول، ایران

چکیده

مقدمه: سیستم کرتاسه شامل رسوبات کربناته که بسیاری از قسمت­های زاگرس را پوشانده است. سازندهای گدوان و داریان در قسمت فوقانی گروه خامی واقع شده­اند. این تشکیلات توسط بسیاری از محققین در موارد زیادی بررسی شده است. هدف از این مطالعه بررسی زیست چینه­نگاری سازندهای گدوان و داریان و همچنین شناسایی رخساره­های رسوبی برای بازسازی محیط دیرینه آنها می­باشد.
مواد و روش­ها: در این تحقیق مقاطع نازکی از هسته و برش تهیه و با میکروسکوپ مورد بررسی قرار گرفت. مطالعه میکروسکوپی برای شناسایی میکروفسیل ها انجام شد (Loeblich and Tappan, 1988). همچنین عناصر اسکلتی و غیراسکلتی و خصوصیات میکروسکوپی تعیین گردید (Flugel, 2010). هر کدام براساس روش دانهام (1962) نامگذاری شدند.
نتایج: بیواسترتیگرافی در چاه  A و B: در چاه A در منطقه 1 از عمق 4740 متری (حد پایین سازند گدوان) تا 4623 متر معرفی شده است. در منطقه 2 از عمق 4623 متر تا 4552 متر معرفی شده است. در چاه B در منطقه 1 از عمق 4860 متری (قسمت پایین سازند گدوان) تا 4744 متر معرفی شده است و در منطقه 2 از عمق 4744 متر تا 4677 متر معرفی شده است.
A&B: 1) Choffatella decipiens - Pseudocyclammina littus -Trocholina elogatus assemblage Zone   2) Mesorbitolina texana - Choffatella decipiens assemblage Zone
رخساره­های سازند داریان در چاه A شامل مداستون (MF1) مرتبط با ریز رخساره­های حوضه عمیق، پلانکتونیک فورامینوفورا واکستون (MF2)  و بیوکلاستیک پلانکتونیک فورامینوفورا واکستون (MF3) که هردو نشان دهنده یک رخساره منطقه کم انرژی است. رخساره­های سازند گدوان شامل بنتیک فورامینوفورا بیوکلاست پاکستون (MF4) نشان دهنده شوری زیاد، بیوکلاستیک واکستون (MF5) نشان دهنده محیط کم انرژی رمپ میانی و مداستون (MF6) نشان دهنده ریز رخساره ها یک محیط تالاب است، این است.
رخساره­های سازند داریان و گدوان در چاه B شامل مداستون (MF1) رخساره­ها در رمپ بیرونی، پلانکتونیک فورامینوفورا واکستون (MF2)  رخساره­ها در یک رمپ خارجی با انرژی کم رسوب و بیوکلاستیک پلانکتونیک فورامینوفورا واکستون (MF3) یک رخساره در رمپ بیرونی است.  اوربیتولینا پلویید پکستون (MF4) رخساره­ها بیانگر محیطی با شوری بالا در آب­های کم عمق و در محیط تالاب، بیوکلاستیک واکستون (MF5) رسوب رخساره­ها در رمپ میانی و مداستون (MF6) که رخساره از میکریت تشکیل شده است.
محیط رسوبی: این رخساره­ها در محیط دریایی و در رمپ بیرونی و میانی و قسمت کوچکی از رمپ داخلی نهشته شده­اند.
نتیجه ­گیری: به منظور بررسی محیط رسوبی سازندهای گدوان و داریان در میدان نفتی گچساران، مقاطع نازک مورد مطالعه قرار گرفته است. براساس داده­های زیست چینه­نگاری، سن بارمین تا آپتین برای گدوان و آپتین پسین برای داریان در نظر گرفته شد. بررسی ریز رخساره سازندهای داریان و گدوان منجر به شناسایی 6 ریز رخساره در 3 کمربند رخساره، رمپ داخلی، رمپ میانی و رمپ بیرونی در محیط دریایی شد. همچنین براساس تنوع ریزرخساره ها، منطقه مورد مطالعه به صورت رمپ کربناته هموکلینیکال پیش­بینی شد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Biostratigraphy, microfacies and depositional environment of the Gadvan and Dariyan formations, in the Gachsaran oilfield, southwest Iran

نویسندگان [English]

  • Behzad Saeedi Razavi 1
  • narges monjezi 2
1 Construction and minerals Group, Technology and Engineering Research Center, Standard Research Institute (SRI), Karaj, Iran
2 Department of Experimental Sciences, Dezful Branch, Islamic Azad University, Dezful, Iran
چکیده [English]

Introduction: The Cretaceous system includes carbonate sediments and covers a large part of Zagros. Gadwan and Darian formations are located in the upper part of Khami group. These formations have been investigated by many researchers in several terms. The purpose of this study is to investigate the biostratigraphy of Gadwan and Darian formations, as well as to identify sedimentary facies to reconstruct their paleo-environment.
Materials and methods: In this study, thin sections were prepared from cores and cutting and examined with a microscope. A microscopic study was done to identify microfossils (Loeblich and Tappan 1988). Also, skeletal and non-skeletal elements and microscopic characteristics were determined (Flügel, 2010). These were named according to Dunham's method (1962).
Results and discussion: Biostratigraphy in Well A: 1) Choffatella decipiens - Pseudocyclammina littus -Trocholina elogatus assemblage Zone. It is introduced from the depth of 4740 m (the lower limit of Gadvan Formation) to 4623 m.
2) Mesorbitolina texana - Choffatella decipiens assemblage Zone. This zone is introduced from the depth of 4623 m to 4552 m.
Biostratigraphy in Well B: 1) Choffatella decipiens - Pseudocyclammina littus -Trocholina elogatus assemblage Zone. Zone No. 1 is introduced from the depth of 4860 m (the lower part of Gadvan Formation) to 4744 m.
2) Mesorbitolina texana - Choffatella decipiens assemblage Zone. This zone is introduced from the depth of 4744 m to 4677 m.
Facies of Darian Formation (Well A): MF1) Mudstone. This facies is associated with deep basin microfacies.
MF2) Planktonic Foraminifora Wackestone. This microfacies represents the low-energy environment.
MF3) Bioclastic Planktone Foraminifora Packstone. The presence of micrite indicates a low energy zone.
Facies of Gadvan Formation: MF4) Bentic Foraminifera Bioclast Packestone. It indicates a high salinity and indicates a lagoon.
MF5) Bioclastic Wackestone. It indicates low-energy environment of the middle ramp.
MF6) Mudstone. This microfacies represent a lagoon environment.
Facies of Darian and Gadvan formations (Well B)
Facies of Darian Formation: MF1) Mudstone. The facies formed in the outer ramp.
MF2) Planktonic Foraminifora Wackestone. The facies deposited in a low-energy in the external ramp.
MF3) Bioclastic Plankton Foraminifora Wackestone. The facies deposited in the outer ramp.
MF4) Orbitolina Peloid Packstone. The facies indicate an environment with high salinity in shallow waters and in the lagoon environment.
MF5) Bioclastic Wackestone. The facies deposited in the middle ramp.
MF6) Mudstone. The facies composed of micrite and has less than 10% bivalves and bryozoans.
Sedimentary environment: These facies were deposited in the marine environment and in the outer and middle ramp and a small part of the inner ramp.
Conclusion: In order to study the depositional environment of Gadvan and Dariyan formations in Gachsaran oil field, thin sections have been studied. Based on the biostratigraphy data, the age of Barremian to Aptian for Gadvan and late Aptian for Dariyan was considered. Microfacies study of Dariyan and Gadvan formations led to recognition of 6 microfacies in 3 facies belt, Inner ramp, Mid-ramp, Outer ramp in marine environment. Also, based on variation of microfacies, the studied area predicted as hemoclinical carbonate ramp.

کلیدواژه‌ها [English]

  • Biostratigraphy
  • Microfacies
  • Dariyan and Gadvan formations
  • Gachsaran oilfield
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