Magnetostratigraphy of the Kelasu section in the Baicheng depression, Southern Tian Shan, northwestern China Zhiliang Zhang a,b,⇑ , Zhongyue Shen a , Jimin Sun b,c , Xin Wang a , Zhonghua Tian b , Xiaoqing Pan a , Linquan Shi a a Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China b Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China c CAS Center for Excellence in the Tibetan Plateau Earth Sciences, China article info Article history: Received 21 January 2015 Received in revised form 31 May 2015 Accepted 16 June 2015 Available online xxxx Keywords: Magnetostratigraphy AMS Kelasu Baicheng Southern Tian Shan abstract In order to better constrain chronology of the Cenozoic sediments in the foreland basin of the Southern Tian Shan, we carried out a magnetostratigraphic study along the Kelasu River, in the Baicheng depres- sion, northwestern China. This is the basis for future studies of the tectonic shortening history and paleoclimatic changes. Stepwise thermal demagnetization was used to isolate the high-temperature characteristic component (ChRM) from 1521 oriented samples collected along two overlapped sections. The ChRM directions are interpreted to be acquired at or close to the time of rock formation. A composite magnetostratigraphic column composed of 86 (45 normal and 41 reversed) polarity chrons can correlate with GPTS (CK95) from 54 Ma to 7.6 Ma. The basal ages of the Kumugeliemu, Suweiyi, Jidike and the Kangcun formations are 54 Ma, 46 Ma, 34 Ma and 9.7 Ma, respectively. The changes of anisotropy of magnetic susceptibility (AMS) parameters (P j and T) cannot be used to reflect the Cenozoic uplift of the southern Chinese Tian Shan due to the parameters have a significant linear positive correlation with the bulk magnetic susceptibility (K m ), suggesting a sedimentary provenance control. Based on the alignments of the AMS, we concluded that the paleo-river channel flowed from north to south, being similar to the present river flowing direction, suggesting that there was still a residue relief of the Tian Shan orogen after the long-term Mesozoic denudation or the reactivation of the Tian Shan may have been initiated as early as 54 Ma. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The Tian Shan orogen is one of the longest mountain ranges in central Asia, with peaks exceeding 7000 m and stretching about 2500 km from east to west (Fig. 1). This mountain has experienced multiple episodes of tectonic reactivation in the Cenozoic, as a response to the intracontinental deformation within the India– Eurasian collision zone (Tapponnier and Molnar, 1979; Coleman, 1989; Windley et al., 1990; Allen et al., 1991, 1994; Burchfiel and Royden, 1991; Avouac and Tapponnier, 1993; Liu et al., 1994; Lu et al., 1994; Carroll et al., 1995). Thick Cenozoic terrigenous sediments denuded from the Tian Shan have been tectonically deformed and formed a series of fault-related anticlines, providing geological archives for studying the relationship between continental deformation, rock denuda- tion and sediment deposition. The chronology of the Cenozoic suc- cessions is the basis for tectonic and paleoclimatic implications of the thick sediments. Magnetostratigraphy of the Cenozoic sediments in the foreland basins of Tian Shan has been widely studied during the last two decades (e.g., Teng et al., 1997; Sun et al., 2004, 2007, 2009; Charreau et al., 2005, 2006, 2009; Huang et al., 2006, 2010; Zheng and Meng, 2006; Ji et al., 2008; Sun and Zhang, 2009; Jing et al., 2011; Li et al., 2011; Zhang et al., 2014). However, due to the scarcity of paleontological fossils and volcanic rocks appropri- ate for accurately dating, there have been many debates about the magnetostratigraphic time scales in the foreland basins of the Tian Shan Range. For example, the magnetostratigraphy of the Cenozoic http://dx.doi.org/10.1016/j.jseaes.2015.06.016 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Key Laboratory of Cenozoic Geology and Environ- ment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. E-mail address: zlzhang@mail.iggcas.ac.cn (Z. Zhang). Journal of Asian Earth Sciences xxx (2015) xxx–xxx Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Please cite this article in press as: Zhang, Z., et al. Magnetostratigraphy of the Kelasu section in the Baicheng depression, Southern Tian Shan, northwestern China. Journal of Asian Earth Sciences (2015), http://dx.doi.org/10.1016/j.jseaes.2015.06.016