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Revised age of proximal deposits in the Zagros foreland basin and implications for Cenozoic evolution of the High Zagros

Fakhari, Mohammad D. and Axen, Gary J. and Horton, Brian K. and Hassanzadeh, Jamshid and Amini, Abdolhossein (2008) Revised age of proximal deposits in the Zagros foreland basin and implications for Cenozoic evolution of the High Zagros. Tectonophysics, 451 (1-4). pp. 170-185. ISSN 0040-1951.

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The regionally extensive, coarse-grained Bakhtiyari Formation represents the youngest synorogenic fill in the Zagros foreland basin of Iran. The Bakhtiyari is present throughout the Zagros fold-thrust belt and consists of conglomerate with subordinate sandstone and marl. The formation is up to 3000 m thick and was deposited in foredeep and wedge-top depocenters flanked by fold-thrust structures. Although the Bakhtiyari concordantly overlies Miocene deposits in foreland regions, an angular unconformity above tilted Paleozoic to Miocene rocks is expressed in the hinterland (High Zagros). The Bakhtiyari Formation has been widely considered to be a regional sheet of Pliocene–Pleistocene conglomerate deposited during and after major late Miocene–Pliocene shortening. It is further believed that rapid fold growth and Bakhtiyari deposition commenced simultaneously across the fold-thrust belt, with limited migration from hinterland (NE) to foreland (SW). Thus, the Bakhtiyari is generally interpreted as an unmistakable time indicator for shortening and surface uplift across the Zagros. However, new structural and stratigraphic data show that the most-proximal Bakhtiyari exposures, in the High Zagros south of Shahr-kord, were deposited during the early Miocene and probably Oligocene. In this locality, a coarse-grained Bakhtiyari succession several hundred meters thick contains gray marl, limestone, and sandstone with diagnostic marine pelecypod, gastropod, coral, and coralline algae fossils. Foraminiferal and palynological species indicate deposition during early Miocene time. However, the lower Miocene marine interval lies in angular unconformity above ~ 150 m of Bakhtiyari conglomerate that, in turn, unconformably caps an Oligocene marine sequence. These relationships attest to syndepositional deformation and suggest that the oldest Bakhtiyari conglomerate could be Oligocene in age. The new age information constrains the timing of initial foreland-basin development and proximal Bakhtiyari deposition in the Zagros hinterland. These findings reveal that structural evolution of the High Zagros was underway by early Miocene and probably Oligocene time, earlier than commonly envisioned. The age of the Bakhtiyari Formation in the High Zagros contrasts significantly with the Pliocene–Quaternary Bakhtiyari deposits near the modern deformation front, suggesting a long-term (> 20 Myr) advance of deformation toward the foreland.

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Additional Information:© 2008 Elsevier B.V. Available online 23 December 2007. This research was supported by the U.S. National Science Foundation (grant EAR-0337775 awarded to G.J. Axen and B.K. Horton) and by the Research Council of the University of Tehran. We thank M. Ghavidel-Syooki and S. A. Hosseini for valuable insights on fossil age control, and B. Guest, Y. Gavillot, D. Stockli, and numerous geologists from the National Iranian Oil Company for beneficial discussions on the structure and stratigraphy of the Zagros. We also acknowledge the constructive reviews provided by K. Hessami, an anonymous reviewer, and editors E. Heydari and R. Sorkhabi.
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University of Tehran Research CouncilUNSPECIFIED
Subject Keywords:Arabia–Eurasia collision; Bakhtiyari Formation; Foreland basins; Iran, Zagros fold-thrust belt
Issue or Number:1-4
Record Number:CaltechAUTHORS:20130827-094451650
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Official Citation:Mohammad D. Fakhari, Gary J. Axen, Brian K. Horton, Jamshid Hassanzadeh, Abdolhossein Amini, Revised age of proximal deposits in the Zagros foreland basin and implications for Cenozoic evolution of the High Zagros, Tectonophysics, Volume 451, Issues 1–4, 28 April 2008, Pages 170-185, ISSN 0040-1951,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40950
Deposited By: Tony Diaz
Deposited On:18 Sep 2013 22:22
Last Modified:03 Oct 2019 05:44

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