Poisson, Blanche and Avouac, Jean-Philippe (2004) Holocene Hydrological Changes Inferred from Alluvial Stream Entrenchment in North Tian Shan (Northwestern China). Journal of Geology, 112 (2). pp. 231-249. ISSN 0022-1376 http://resolver.caltech.edu/CaltechAUTHORS:20110110-154436486
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We analyze the possible contribution of climate change or tectonics on fluvial incision from the study of a case example along the northern flank of Tian Shan. The rivers that exit the high range fed large alluvial fans by the end of the last glacial period. They have since deeply entrenched the piedmont by as much as 300 m. We have surveyed several terraces that were cut and abandoned during river entrenchment, providing information on intermediate positions of the riverbed during downcutting. They suggest a gradual decline in river slope during a major phase of incision throughout the Holocene. Tectonic uplift affects only a zone about 5 km wide, corresponding to a growing anticline, and is shown to account for about 10% of total incision. Incision was therefore most probably driven by climate change. From observed fluvial incision, we estimate the water discharge in excess of that needed to carry the sediments supplied by hillslope erosion in the headwaters. We used a model based on a transport‐limited erosion law. The model predicts relaxation process with entrenchment in the upper reach, downstream progradation of the incision‐sedimentation line, and a progressive decrease of river slope during incision consistent with our observations. According to this model, river slope might be used as a proxy for specific discharge and then for volumetric discharge, provided that an assumption is made about river width variations. We conclude that river incision in the study area has resulted from dynamic adjustment of the hydrological system to the settlement of wetter conditions in the early Holocene, when water discharge might have been about three times as high as at present. Then, a rather arid climate with enhanced seasonality has likely prevailed from the mid‐Holocene (~6 ka B.P.) until now.
|Additional Information:||© 2004 The University of Chicago. Manuscript received July 16, 2002; accepted October 16, 2003. This research was funded by the Commissariat à l’Energie Atomique and by the Eclipse Centre National de la Recherche Scientifique program. We are grateful to N. Mercier for indispensable help in doing OSL analysis and for allowing data release before publication. We thank F. Métivier and S. Dominguez for fruitful discussions and help in the field. Two anonymous reviewers have provided most helpful comments and suggestions.|
|Group:||Caltech Tectonics Observatory, Caltech Tectonics Observatory. Indo-Asian Collision Zone|
|Subject Keywords:||alluvial stream, piedmont, fluvial incision, river profile, river slope, Tian Shan.|
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|Official Citation:||Holocene Hydrological Changes Inferred from Alluvial Stream Entrenchment in North Tian Shan (Northwestern China) Blanche Poisson and Jean‐Philippe Avouac The Journal of Geology Vol. 112, No. 2 (March 2004), pp. 231-249|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||31 Jan 2011 17:48|
|Last Modified:||26 Dec 2012 12:50|
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