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The Neogene Xiyu Formation, a diachronous prograding gravel wedge at front of the Tianshan: Climatic and tectonic implications

Charreau, Julien and Gumiaux, Charles and Avouac, Jean-Philippe and Augier, Romain and Chen, Yan and Barrier, Laurie and Gilder, Stuart and Dominguez, Stéphane and Charles, Nicolas and Wang, Qingchen (2009) The Neogene Xiyu Formation, a diachronous prograding gravel wedge at front of the Tianshan: Climatic and tectonic implications. Earth and Planetary Science Letters, 287 (3-4). pp. 298-310. ISSN 0012-821X. doi:10.1016/j.epsl.2009.07.035.

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The Tarim and Junggar basins in central Asia are capped by a thick pile of conglomerates, called the Xiyu Formation, that are commonly linked to a change in climate and/or accelerated uplift near the Plio- Pleistocene boundary. In order to better understand their origin and significance, we carried out a combined structural and magnetostratigraphic study in the Quilitage syncline (southern Tianshan), where the base of the Xiyu conglomerates is observed at both sides of the syncline. A balanced cross-section shows that, even at a local-scale, the base of the Xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer. On the southern flank of the Quilitage syncline, we collected 172 samples collected for magnetostratigraphic dating identify 17 polarity chrons that date the new section from 5.2 to ~1.7 Ma and constrain the base of the Xiyu conglomerate here at ~1.7 Ma. This is 4.2 Ma younger than the age of the Xiyu previously found on the northern limb of the same syncline. Together with other magnetostratigraphic studies carried out around the Tianshan, our study unambiguously demonstrates that the onset of deposition of the Xiyu conglomerates is diachronous, and that the conglomerates are systematically younger toward the basin. Consequently, the Xiyu Formation should not be considered as a chronostratigraphic marker related to any particular tectonic or climatic event, but is instead a prograding gravel wedge that has prograded over the underthrusting forelands. A synthesis of chronologic and structural results yields progradation rates over the last 10 Ma on the order of ~2.0 mm/yr and ~3.9 mm/yr south and north of the Tianshan Mountains respectively. These rates are comparable to the shortening rate across the Tianshan range, suggesting that underthrusting is the main factor governing the progradation rate of the Xiyu Formation.

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Avouac, Jean-Philippe0000-0002-3060-8442
Additional Information:© 2009 Elsevier B.V. Received 25 February 2009; revised 24 July 2009; accepted 28 July 2009. Editor: T.M. Harrison. Available online 28 August 2009. This study was financed by the French ECLIPSE program, the Chinese project kzcx3-sw-147 and 973 No 2005CB422101, PRA (T05- 02/T06-04), the French ANR (ANR-05-BLAN-0143-01) and the Gordon Betty Moore Foundation. We present our thanks to Dr. S. Peng and K. Chen for their supports to magnetostratigraphic sampling and to M. Laumonier and E. de Oliveira for their help in the laboratory. This is Caltech Tectonics Observatory contribution 123.
Group:Caltech Tectonics Observatory, Caltech Tectonics Observatory. Indo-Asian Collision Zone, Seismological Laboratory
Funding AgencyGrant Number
Chinese projectkzcx3-sw-147
Chinese project973 No 2005CB422101
French L'Agence nationale de la recherche (ANR)ANR-05-BLAN-0143-01
Gordon Betty Moore FoundationUNSPECIFIED
Subject Keywords:Xiyu Formation; magnetostratigraphy; Tianshan; gravel wedge progradation; shortening rates
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Caltech Tectonics Observatory123
Issue or Number:3-4
Record Number:CaltechAUTHORS:20091209-095229076
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Official Citation:Julien Charreau, Charles Gumiaux, Jean-Philippe Avouac, Romain Augier, Yan Chen, Laurie Barrier, Stuart Gilder, Stephane Dominguez, Nicolas Charles, Qingchen Wang, The Neogene Xiyu Formation, a diachronous prograding gravel wedge at front of the Tianshan: Climatic and tectonic implications, Earth and Planetary Science Letters, Volume 287, Issues 3-4, 15 October 2009, Pages 298-310, ISSN 0012-821X, DOI: 10.1016/j.epsl.2009.07.035. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16921
Deposited By: Tony Diaz
Deposited On:05 Jan 2010 17:17
Last Modified:08 Nov 2021 23:31

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