Late Devonian facies variety in Iran: volcanism as a possible trigger of the environmental perturbation near the Frasnian-Famennian boundary

Authors

  • Mohammad Hosein Mahmudy Ghara Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan
  • Ryo Matsumoto Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan
  • Yoshitaka Kakuwa Graduate School of Arts and Sciences, University of Tokyo, Tokyo, Japan
  • Paul G. Milroy Badley Ashton and Associates Ltd., Horncastle, Lincolnshire, UK

Keywords:

Frasnian-Famennian boundary, Iran, black shale, ironstone, greenhouse, volcanism

Abstract

Upper Devonian successions surrounding the Frasnian-Famennian (F-F) boundary in Iran consist of mixed carbonate/silisiclastic deposits. The successions are characterized by conspicuous ferruginous limestones, clay-rich units, black shales, and mafic volcanic rocks that provide important insights into palaeoenvironmental conditions during this interval of Earth's history. An increase of kaolinite/illite ratio in clays associated with the F-F boundary suggests that increased chemical weathering was facilitated by warm and humid climatic conditions. Distinctive ferruginous-oolite deposits overlying the crucial Frasnian-Famennian boundary interval indicate a high supply rate of Fe-bearing clay originated during enhanced weathering under such climatic conditions. Black shales associated with the F-F boundary are interpreted to be the result of a high primary productivity caused by an increased influx of land-derived nutrients and regional volcanic activity. Widespread rift-related, basaltic activity along eastern Laurussia and northern Gondwana during the mid-Late Devonian is believed to have contribution to this global warming surrounding the F-F boundary.

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Published

2010-03-27

Issue

Vol. 48 No. 4 (2004)

Section

Articles

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