یافته‌های نوین زمین‌شناسی کاربردی

یافته‌های نوین زمین‌شناسی کاربردی

مطالعات بافتی، تجزیه عنصری و مدل دولومیتی شدن سازند شهبازان (ائوسن) در یک برش از یال شمالی تاقدیس کبیرکوه، جنوب باختر دره­ شهر

نویسندگان
استادیار گروه زمین‌شناسی، دانشکده علوم، مجتمع آموزش عالی گناباد، گناباد، ایران
چکیده
به‌منظور بررسی و درک مدل دولومیتی شدن سازند شهبازان در جنوب‌‍باختر دره­شهر یک برش چینه‌شناسی به ضخامت 65 متر، واقع در یال شمالی تاقدیس کبیرکوه انتخاب و مورد مطالعه و نمونه‌برداری قرار گرفت. سنگ­شناسی این سازند دولومیت و سنگ­آهک دولومیتی است. مطالعات سنگ­شناسی بر روی بافت دولومیت­ها منجر به شناسایی چهار گروه از دولومیت­ها (دولومیت­های خیلی ریزبلور، دولومیت­های متوسط بلور، دولومیت­های درشت­بلور و دولومیت­های بسیار درشت­بلور پر کننده شکستگی­ها و حفرات سنگ) گردید. حفظ بافت­های اولیه رسوبی، نظیر اینتراکلست­ها، لامینه­های جلبکی و فابریک فنسترال، عدم فسیل و کانی­های تبخیری و همچنین نبود فرآیندهای دیاژنتیکی تأخیری، بیانگر مدل جزرومدی برای دولومیت­های خیلی ریزبلور اولیه است. تمرکز عناصر فرعی آهن و منگنز در دولومیت‌های اولیه کمترین مقدار را دارد، در حالی‌که تمرکز این عناصر در دولومیت­های ثانویه بیشترین مقدار را دارد. همچنین تمرکز عناصر فرعی دیگر نظیر استرانسیم و سدیم در دولومیت­های اولیه بیشترین مقدار می­باشد در صورتی که تمرکز این عناصر در دولومیت­های ثانویه کم­ترین مقدار است که این موضوع دلالت بر محیط دیاژنزی تدفینی کم عمق تا متوسط و عمیق برای دلومیت­های ثانویه دارد. بر پایه مطالعات زمین­شیمی عنصری بر روی عناصر اصلی کلسیم و منیزیم و عناصر فرعی آهن، منگنز، سدیم و استرانسیم برای دولومیت­های مورد مطالعه و همچنین مطالعات بافتی بر روی دولومیت­های شناسایی شده، می­توان مدل دولومیتی شدن سازند را به مدل جزرومدی، تراوش و سپس دفن کم عمق تا متوسط و عمیق نسبت داد.
کلیدواژه‌ها

عنوان مقاله English

Textural study, elemental analysis and model of dolomitization in the Shahbazan Formation (Eocene) in a section of the northern ridge of the Kabirkoh anticline, southwest of Dareh Shahr

نویسندگان English

Yaghub Nasiri
Samira Taghdisi Nikbakht
Assist. Prof., Dept. of Geology, Faculty of Sciences, University of Gonabad, Gonabad, Iran
چکیده English

In order to investigate and understand the dolomitization model of Shahbazan Formation in the south-west Dareh Shahr, a 65-meter-thick stratigraphic section located in the Kabir Kuh anticline has been selected and studied and sampled. The lithology of this formation is mostly dolomite and dolomitic limestone. Petrological studies on the texture of dolomites led to the identification of four groups of dolomites: (very fine crystal dolomites, medium crystal dolomites, coarse crystal dolomites, and very coarse crystal dolomites in fracture and pores filling). Preservation of primary sedimentary textures, such as intraclasts, algal laminae and fenestral fabric, absence of fossils and evaporite minerals, and absence of delayed diagenetic processes, indicate the tidal model for primary very microcrystalline dolomites. The concentration of minor elements (Fe and Mn) in primary dolomites is the lowest, while the concentration of these elements is the highest in secondary dolomites. Also, the concentration of other secondary elements such as (Sr and Na) is the highest in primary dolomites, while the concentration of these elements in secondary dolomites is the lowest, which indicates a shallow to medium and deep burial diagenesis environment. Based on elemental geochemical studies on the main elements Ca and Mg and secondary elements Na, Sr, Fe, Mn for the studied dolomites as well as textural studies on the identified dolomites, it is possible to model the dolomitization of the formation attributed to seepage and then shallow to medium and deep burial to the dolomitization model.

کلیدواژه‌ها English

Shahbazan Formation
Elemental analysis
Dolomite
Tidal flat model
Zagros
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  • تاریخ دریافت 16 دی 1403
  • تاریخ بازنگری 10 بهمن 1403
  • تاریخ پذیرش 14 اردیبهشت 1404