اثر رخساره ها و اهمیت محیطی اثر فسیل ها در سازند آیتامیرحوضه کپه داغ

نویسندگان

1 کارشناس ارشد، دانشگاه فردوسی مشهد

2 دانشجوی دکتری، دانشگاه فردوسی مشهد

3 دانشیار، گروه زمین شناسی دانشگاه فردوسی مشهد

4 استاد، گروه زمین شناسی دانشگاه فردوسی مشهد

چکیده

        سازند آیتامیر (آلبین- سنومانین) در حوضه رسوبی کپه داغ در شمال خاوری ایران گسترش دارد. این سازند عمدتا از ماسه سنگ، شیل، سیلتستون و چند افق کربناته تشکیل شده است. در رسوبات سیلیسی آواری سازند آیتامیر، کاهش محسوسی در میزان آشفتگی زیستی در طبقات گلی در مقایسه با طبقات ماسه سنگی مشاهده می شود. بر اساس مطالعه اثرفسیل های این سازند، تعداد نه اثر فسیلی شامل Thalassinoides suevicus ، Thalassinoides isp. (اثر رخساره گلوسی فانجیتس)، Ophiomorpha nodosa ، Palaeophycus tubularis و Skolithos isp. (اثر رخساره اسکولایتوس) و Thalassinoides isp. ، Planolites isp. ، Chondrites isp. ، Cylindrichnous concentricus ، Teichichnus isp. ، Palaeophycus tubularis و Ophiomorpha nodosa (اثر رخساره کروزیانا) در لایه های ماسه سنگ، سیلتستونی و کربناته تشخیص داده شدند. اثر رخساره اسکولایتوس در شرایط با انرژی بالاتر نسبت به اثر رخساره گلوسی فانجیتس و اثر رخساره کروزیانا تشکیل شده است. اثر رخساره اسکولایتوس با تنوع کم اثر فسیل ها و حضور اسکولایتوس و افیومورفاهای عمودی تا مایل با کف بستر ماسه ای با جورشدگی خوب همراه با طبقات مورب تراف و پشته ای نشانگر مجموعه محیط سدی با شرایط نسبتا پر انرژی است . در صورتیکه اثر رخساره کروزیانا و اثر رخساره گلوسی فانجیتس با تنوع بیشتر اثر فسیل ها عمدتا افقی تا کمی مایل و کف بستر ماسه ای با جورشدگی متوسط و ضعیف در شرایط کم انرژی تر در محدوده حاشیه ساحلی ( Shoreface ) تشکیل گردیده است. شواهد رسوبی و مطالعه اثر رخساره ها در توالی قائم حاکی از آن است که رسوبات ماسه سنگی بخش ابتدایی سازند آیتامیر در محیط سدی و رسوبات ماسه سنگی بخش های بالایی در محیط حاشیه ساحلی ته نشست پیدا کرده اند.   

کلیدواژه‌ها

عنوان مقاله [English]

Ichnofacies and environmental significance of trace fossils in Aitamir Formation, Kopet – Dagh Basin

نویسندگان [English]

  • M. Ashuri 1
  • M Sharafi 2
  • A. Mahboubi 3
  • R Moussavi- Harami 4
1 M. Sc. Ferdowsi University of Mashhad
2 Ph. D. Student, Ferdowsi University of Mashhad
3 Associate Professor, Department of Geology, Ferdowsi University of Mashhad
4 Professor, Department of Geology, Ferdowsi University of Mashhad
چکیده [English]

  Aitamir Formation (Albian-Cenomanian) crops out in the Kopet-Dagh basin in north-east Iran. It is mainly composed of sandstone, shale, siltstone, and several carbonate beds. In siliciclastic sediments of the Aitamir Formation, mud beds show a significant decrease in bioturbations with respect to sandstone beds. Based on ichnofossils studies, nine trace fossils were identified in sandstone, siltstone and carbonate beds which include of Thalassinoides suevicus and Thalassinoides isp. (Glossifungites ichnofacies), Ophiomorpha nodosa , Palaeophycus tubularis, Skolithos isp. (Skolithos ichnofacies) and Thalassinoides isp., Planolites isp., Cylindrichnous concentricus, Chondrites isp., Ophiomorpha nodosa , Palaeophycus tubularis and Teichichnus isp. (Cruziana ichnofacies). Skolithos ichnofacies formed in high energy condition with respect to Cruziana ichnofacies and Glossifungites ichnofacies. Skolithos ichnofacies with low diversity, Skolithos isp. and vertical orientation Ophiomorpha present in well sorted and trough- hummocky cross bedded sandy substrate. This ichnofacies indicates of high energy barrier complex. Whereas Cruziana ichnofacies and Glossifungites ichnofacies with higher diversity and mainly horizontal to slightly oblique, trace fossils in sandy substrate with moderate sorting are formed in low energy condition in shoreface environment. Sedimentary evidences and investigated ichnofacies in vertical succession show that sandstones in the lower portion of the Aitamir Formation formed in barrier complex and sandstones sediment in upper portion deposited in shoreface environments.

کلیدواژه‌ها [English]

  • Keywords: Aitamir
  • Ichnofacies
  • Glossifungites
  • Skolithos
  • Cruziana

مراجع

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