Paleomagnetic ages of Miocene fluvio-lacustrine sediments in the Tianshui Basin, western China Jun Zhang a , Jijun Li a,c,⇑ , Chunhui Song b , Zhijun Zhao c , Guangpu Xie d , Xiuxi Wang a , Zhengchuang Hui a , Tingjiang Peng a a Key Laboratory of Western China’s Environmental Systems (Ministry of Education) & College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China b School of Earth Sciences & Key Laboratory of Western China’s Environmental Systems (Ministry of Education), Lanzhou University, Lanzhou 730000, China c College of Geography, Nanjing Normal University, Nanjing 210097, China d Gansu Provincial Museum, Lanzhou 730050, China article info Article history: Received 15 May 2012 Received in revised form 6 September 2012 Accepted 6 October 2012 Available online 23 October 2012 Keywords: Neogene Magnetostratigraphy Geochronology Paleoenvironment Tianshui Basin China Tibet abstract Long and continuous terrestrial paleoclimate records are important in understanding forcing mecha- nisms of Cenozoic climate. However, such records are rare. Sediments in basins near the edges of the Tibetan Plateau are potential paleoclimate archives, but dating them is a challenge. Here we report a suc- cessful application of paleomagnetism to a set of fluvio-lacustrine sediments in the Tianshui Basin, NE Tibet, and found that this set of sediments spans 17.1–6.1 Ma. Preliminary biomarker studies found that this set of sediments has climatically important organic components and, thus, these sediments are per- fect paleoclimatic archives. Generating high-resolution biomarker records will be able to cast light on cli- matic history in NE Tibet during the Miocene. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Long and continuous terrestrial paleoclimate records are rare in comparison with widely available marine paleoclimate records (Miller et al., 1987; Rea et al., 1998; Pearson and Palmer, 2000; Zachos et al., 2001, 2008; Li et al., 2006b). However, such records are necessary in order to get a better understanding of the forcing mechanisms of the Cenozoic climate changes. Well-known long and continuous terrestrial paleoclimate records include the Chinese loess-red clay sequences dating back to 8 Ma (Sun et al., 1998; Ding et al., 1999; An et al., 2001; Qiang et al., 2001; Song et al., 2001; Zhu et al., 2008; Pan et al., 2011) and the Baikal lacustrine se- quences dating back to 12 Ma (Kashiwaya et al., 2001). Longer continuous sedimentary paleoclimate archives are key to advanc- ing our understanding of forcing mechanisms of Cenozoic climate. Several studies have recently shown that sedimentary basins adjacent to the Tibetan Plateau are potential continuous paleocli- mate archives (Fang et al., 1997, 2003, 2005, 2007; Li et al., 1997; Guo et al., 2002; Dettman et al., 2003; Garzione et al., 2005; Fan et al., 2006, 2007; Wang et al., 2010, 2012b; Qiang et al., 2011). These basins have sediments covering ages from early Paleocene to late Pleistocene and are important in order to improve our under- standing of paleoclimate history of the entire Cenozoic period. However, the first step of doing paleoclimate reconstruction from these sediments is to get high-resolution age model for these sedi- ments. Due to arid climate and lack of complete preservation of macrofossils, dating these sediments is a challenge and paleomag- netism seems to be the only suitable way to assign ages to these samples. However, paleomagnetism studies on long and continu- ous sediments require a large amount of work involving fieldwork, lab preparation and analysis, with the risk of failure to produce any reasonable reversal correlation patterns to Geomagnetic Polarity Time Scale (GPTS) due to potential complexities of complicated strata structure, magnetic mineral alternations, etc. In this paper, we report a successful application of paleomagne- tism to date fluvio-lacustrine sediments from the Tianshui Basin, a sub-basin of the Longzhong Basin, NE Tibetan Plateau. Recent stud- ies suggest that sediments in this basin have important implica- tions to understanding late Cenozoic paleoclimate history of East Asia (Hui et al., 2011; Peng et al., 2012). 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2012.10.014 ⇑ Corresponding author at: Key Laboratory of Western China’s Environmental Systems (Ministry of Education) & College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China. Tel./fax: +86 931 8912724. E-mail address: lijj@lzu.edu.cn (J. Li). Journal of Asian Earth Sciences 62 (2013) 341–348 Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes