Abstract
In Alborz Mountains, the thickness of sediments in Member 2 of the Mila Formation (Middle Cambrian) underwent dramatic and abrupt deformations, which were accompanied by normal and reverse faults and asymmetrical folds. These deformed sediments are covered by parallel beds both in the upper and lower sides. The existence of such extension and compression structures adjacent to each other indicates the influence of non-tectonic factors in their evolution. These deformations induced by downslope gliding of sediment packages are fully compatible with the dislocation model of Farrell (J Struct Geol 6:727–736, 1984) and Farrell and Eaton (1987). Moreover, the occurrence of synsedimentary deformations in a vast area in Alborz Mountains reinforces the probability of the impact of seismic shocks in their formation. In fact, incessant seismic events in the Middle Cambrian led to numerous submarine slumpings in the sediments of Member 2 of the Mila Formation.
الملخص العربى:-
إذا تتبعنا في سلسلة جبال ألبرز شمالي إيران لوجدنا أن سماكة الترسبات العائدة إلى العضو2 للميلافورميشن ( العصر الكمبري الأوسط ) قد مرت بتغييرات شديدة و مفاجئة و قد صحبت هذه التغيرات تصدعات طبيعية و عكسية و تجاعيد غير متوازنة . و تغيرت أشكال هذه الرواسب و تلبست بطبقات متوازية في الأعلى و الأسفل . إن تواجد مثل هذه الهيكليات و التركيبات الامتصاصية و المتراكمة [ بفعل الضغط ] إلى جانب بعضها يدل على تأثير عوامل غيرتكتونية في مسار تطورها . مثل هذا النوع من التغيير في الأشكال و الذي يحدث إثر انزلاق [هبوط] مجموعات مترسبة [مجموعات الرواسب ] نحو الأسفل ، يطابق تماماً نموذج الانتقال Farrel and Eaton(1987) and Farrel(1984) . و إضافة إلى ذلك ، ان حدوث تغييرات في الشكل تزامناً مع الترسب في قسم واسع من سلسلة جبال البرز يعزز احتمال تأثير الصدمات الارتجاجية(الزلزالية) في تكوينها ، على ان تكون قد تسببت الارتجاجات(الزلازل) المتتالية في العهد الكمبري الأوسط في انزلاقات عديدة في أعماق البحار بالنسبة للترسبات (الجزء2) العائدة إلى الميلافورميشن . المفردات الأساسية : الميلافورميشن ، جبال البرز ، تغيرات الشكل المتزامنة للترسب ، الهبوط (slumping)
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I owe an immense debt of gratitude to Mr. Ali Rastgou who cooperated closely in the completion of this article.
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Kangi, A., Aryaei, A.A. & Maasoomi, A. Synsedimentary deformations in member 2 of the Mila Formation in the Central Alborz Mountains, Northern Iran. Arab J Geosci 3, 33–39 (2010). https://doi.org/10.1007/s12517-009-0044-2
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DOI: https://doi.org/10.1007/s12517-009-0044-2