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Tectonic and climatic controls on fan systems: The Kohrud mountain belt, Central Iran

Jones, S.J.; Arzani, N.; Allen, M.B.

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Authors

N. Arzani



Abstract

Late Pleistocene to Holocene fans of the Kohrud mountain belt (Central Iran) illustrate the problems of differentiating tectonic and climatic drivers for the sedimentary signatures of alluvial fan successions. It is widely recognised that tectonic processes create the topography that causes fan development. The existence and position of fans along the Kohrud mountain belt, NE of Esfahan, are controlled by faulting along the Qom-Zefreh fault system and associated fault zones. These faults display moderate amounts of historical and instrumental seismicity, and so may be considered to be tectonically active. However, fluvial systems on the fans are currently incising in response to low Gavkhoni playa lake levels since the mid-Holocene, producing incised gullies on the fans up to 30 m deep. These gullies expose an interdigitation of lake deposits (dominated by fine-grained silts and clays with evaporites) and coarse gravels that characterise the alluvial fan sediments. The boundaries of each facies are mostly sharp, with fan sediments superimposed on lake sediments with little to no evidence of reworking. In turn, anhydrite–glauberite, mirabilite and halite crusts drape over the gravels, recording a rapid return to still water, shallow ephemeral saline lake sedimentation. Neither transition can be explained by adjustment of the hinterland drainage system after tectonic uplift. The potential influence in Central Iran of enhanced monsoons, the northward drift of the Intertopical Convergence Zone (ITCZ) and Mediterranean climates for the early Holocene (~ 6–10 ka) point to episodic rainfall (during winter months) associated with discrete high magnitude floods on the fan surfaces. The fan sediments were deposited under the general influence of a highstand playa lake whose level was fluctuating in response to climate. This study demonstrates that although tectonism can induce fan development, it is the sensitive balance between aridity and humidity resulting from changes in the climate regime of Central Iran that influences the nature of fan sequences and how they interrelate to associated facies.

Journal Article Type Article
Acceptance Date Dec 31, 2014
Online Publication Date Jan 9, 2014
Publication Date Apr 1, 2014
Deposit Date Jun 12, 2014
Publicly Available Date Feb 22, 2017
Journal Sedimentary Geology
Print ISSN 0037-0738
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 302
Pages 29-42
DOI https://doi.org/10.1016/j.sedgeo.2013.12.008
Public URL https://durham-repository.worktribe.com/output/1450120

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Copyright Statement
NOTICE: this is the author’s version of a work that was accepted for publication in Sedimentary Geology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Sedimentary Geology, 302, 1 April 2014, 10.1016/j.sedgeo.2013.12.008.






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