Alluvial sequence in the north piedmont of the Chinese Tian Shan over the past 550 kyr and its relationship to climate change

A new division of Middle and Late Pleistocene alluvial sequence in the north piedmont of the Chinese Tian Shan based on geomorphologic, stratigraphic, and chronologic criteria provides a framework for examining their relationship to climate change during glacial-interglacial transitions. Over the past 550 kyr at least four major alluviation episodes occurred within the piedmont. Along the major river valleys in this region, each episode of alluvial fan deposition morphologically correlates with a major river terrace. These correlations create a regionally applicable framework for subdivision of the Quaternary alluvial sequence in the study area, where seven stepped river terraces are defined. Our new chronology of this fluvial sequence suggests that, following intervals of aggradation, three highest river terraces and equivalent alluvial fans were abandoned at similar to 530 ka, similar to 300 ka and similar to 10 ka, respectively. Paleosols at the base of the loess sequences that directly overlie the older terraces and fans suggest that episodes of aggradation occurred late in the glacial cycles. The subsequent incision that caused abandonment/stabilization of these terraces and fans occurred near to glacial-interglacial transitions. A relatively high degree of synchrony in major river incision events across the piedmont, despite disruption by several discrete structure zones with asychronous tectonic activities, supports the dominant control exerted by climatic conditions on alluvial deposition and terrace creation during the Quaternary across the north piedmont of the Chinese Tian Shan. (C) 2009 Elsevier B.V. All rights reserved.Geography, PhysicalGeosciences, MultidisciplinaryPaleontologySCI(E)0ARTICLE3-4343-35328