The upper Bajocian (Middle Jurassic) vegetation and paleoenvironment dynamics in the eastern Binalud mountains (NE Iran)

Document Type : Research Paper

Author

Palaeobotany Department, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

10.22092/ijb.2025.368996.1515

Abstract

The lower part of the Dalichai Formation was analyzed to reconstruct the vegetation, paleoenvironment, and paleoclimate dynamics of these deposits in the Binalud Mountains. The shale and marlstone deposits of the studied section contain abundant and diverse terrestrial and marine palynomorphs. The consistent presence of the dinoflagellate cyst genus Cribroperidinium crispum throughout the section and the absence of early Bajocian index taxa support an upper Bajocian age for this interval. Palynofacies indicates a highly proximal to marginal marine depositional setting. The vegetation reconstruction reveals an expanded lowland environment dominated by ferns and Cycadales in the lower part of the section. The overlying interval is characterized by a sea-level rise, which correlates with an increased abundance and diversity of upland SEG conifers and seed ferns. The coastal environment expanded during this phase, leading to the proliferation of coastal SEG such as Cheirolepidiaceae and Araucariaceae, which persisted until the end of the section. The sporomorph assemblages suggest a generally warm and dry climate throughout the studied interval. However, the increase in cool-dependent Araucariaceae toward the uppermost Bajocian is interpreted as evidence of a cooling phase, which aligns with global records of similar climatic shifts during this period.

Keywords

Article Title [Persian]

تغییرات پوشش گیاهی و محیط دیرینه در نهشته های باژوسین بالایی (ژوراسیک میانی) شرق کوه‌های بینالود (شمال شرق ایران)

Author [Persian]

  • بهناز کلنات
گروه دیرینه شناسی گیاهی، مؤسسه تحقیقات جنگل ها و مراتع کشور، سازمان تحقیات، آموزش و ترویج کشاورزی، تهران، ایران
Abstract [Persian]

بخش پایینی سازند دلیچای در کوه‌های بینالود به‌منظور بازسازی پوشش گیاهی، محیط و اقلیم دیرینه مورد بررسی قرار گرفت. نهشته‌های شیلی و مارنی برش مورد مطالعه حاوی تعداد فراوان و متنوعی از پالینومورف‌های دریایی و خشکی است. حضور دینوفلاژله‌ جنس Cribroperidinium crispum در سرتاسر برش مورد مطالعه، همراه با عدم حضور تاکسون‌های شاخص باژوسین پایینی، سن باژوسین بالایی را برای این نهشته‌ها مشخص می‌کند. تحلیل پالینوفاسیس نشان‌دهنده یک محیط رسوبی بسیار نزدیک به ساحل تا حاشیه‌ای دریایی است. بررسی گروه‌های اکولوژیکی اسپورومورف‌ها(SEGs)  نشان‌دهنده گسترش یک محیط lowland در بخش پایینی برش مورد مطالعه است که سرخس‌ها و سیکادها پوشش گیاهی غالب را در آن تشکیل می‌دهند. در ادامه، با افزایش سطح دریا، گروه اکولوژیک upland شامل مخروطیان و سرخس‌های دانه‌دار افزایش پیدا می‌کنند. افزایش سطح دریا و گسترش محیط ساحلی منجر به افزایش گروه‌های اکولوژیک ساحلی مانند Cheirolepidiaceae و Araucariaceae شده که تا انتهای برش مورد مطالعه ادامه پیدا می‌کنند. اجتماع اسپورومورف‌ها حاکی از غلبه اقلیم گرم و خشک در برش مورد مطالعه است. هرچند افزایش گرده‌های مربوط به Araucariaceae که وابسته به آب‌و‌هوای سردتر هستند، در بخش انتهایی باژوسین به‌عنوان شاهدی از یک فاز خنک‌شدگی تفسیر می‌شود که با داده‌های جهانی از تغییرات اقلیمی مشابه در این دوره مطابقت دارد.

Keywords [Persian]

  • پالینوفاسیس
  • پالینواستراتیگرافی
  • سازند دلیچای
  • گروههای اسپورومورفی
  • شمال شرق ایران

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The Iranian Journal of Botany
Volume 31, Issue 1
June 2025
Pages 110-127

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History

  • Receive Date: 29 March 2025
  • Revise Date: 07 May 2025
  • Accept Date: 22 May 2025

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