A new magnetostratigraphic framework for late Neogene Hipparion Red Clay in the eastern Loess Plateau of China Yanming Zhu a , Liping Zhou a, ⁎, Duowen Mo a , Anu Kaakinen b , Zhaoqun Zhang c , Mikael Fortelius b,d a Laboratory for Earth Surface Processes, Department of Geography, Peking University, Beijing 100871, China b Department of Geology, P.O. Box 64 (Gustaf Hällströmin katu 2a) FIN-00014 University of Helsinki, Finland c Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China d Institute of Biotechnology, P.O. Box 56, FIN-00014 University of Helsinki, Finland abstract article info Article history: Received 1 May 2008 Received in revised form 2 August 2008 Accepted 5 August 2008 Keywords: China Magnetostratigraphy Late Neogene Red Clay Mammalian fossils, especially the Hipparion fauna, found in the Red Clay of the Loess Plateau, are of immense value for reconstructing late Neogene paleoecology and paleoclimatology in northern China. The lack of a precise chronological framework for these fossil sites has impeded our understanding of the evolution of the Chinese mammalian fauna, their correlation with European mammalian units, and the retrieval of paleoclimatic information. In this study, a field survey of regional stratigraphy in the Baode area of Shanxi was carried out and three profiles (Tanyugou, Yangjiagou-I and Yangjiagou-II) of Late Neogene deposits were selected for detailed investigation. A new chronological framework of the Late Neogene sequences in the Baode area is established by means of paleomagnetism. Our results show that the Red Clay accumulation in the Baode area began at least 7.23 Ma ago. Deposition continued to the superposed Jingle Formation. The most continuous and complete exposure of the Jingle Formation known to date was identified and dated to 2.72~5.34 Ma. A lithological distinction between the Jingle Formation and the underlying Baode Formation forms a clear boundary in the Red Clay that is not coincident with the Miocene/Pliocene boundary documented elsewhere. Three rich fossil layers are found in the Yangjiagou-II profile and dated to 6.43–6.54 Ma, 6.83–6.86 Ma and 7.15–7.18 Ma, respectively. With the application of three different demagnetization techniques, the Matuyama–Gauss geomagnetic reversal boundary was identified in a transitional unit between loess and typical Red Clay deposits. A lock-in depth of as large as 6.8 m (corresponding to ca. 65 ka) was inferred but remains unexplained. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Continuous late Cenozoic aeolian deposits are widely distributed in the Loess Plateau of China (Liu, 1985). Spatially, the Loess Plateau can be divided into northern, southern, western, eastern and central parts, each with characteristic thicknesses of aeolian sequences depending on local geomorphological and climatic conditions. Lithostratigraphically, the aeolian sequences can be broadly divided into two major units: the upper Quaternary loess–paleosol sequence and the lower Miocene–Pliocene red earth. With the recent discovery of aeolian sequences back to 22 Ma, the Miocene–Pliocene red earth can be further divided into Late Miocene–Pliocene Red Clay and the Miocene loess (Guo et al., 2002). The upper loess–paleosol sequences have been intensively studied for reconstructing the Quaternary paleoclimate history in northern China (Heller and Liu, 1982, 1986; Liu, 1985; Liu and Ding, 1990; Zhou et al., 1990; An et al., 1990, 1991; Rutter et al., 1991; Hus and Han, 1992; Liu and Ding, 1998). The underlying Red Clay sequence was first described as Hipparion red earth due to the wide occurrence of hipparionine horses in the deposits (Anderson, 1923; Zdansky, 1923; Jokela et al., 2005). It started to attract international attention immediately after the report of the extremely rich mammalian faunas in the 1920's (e.g., Anderson, 1923; Zdansky, 1923; Sefve, 1927), and was the subject of intensive taxonomic research in the following decades. The results of this early work were synthesised by Kurtén (1952). For a long time, the chronology of the Red Clay sequence was based on isolated local fossil faunas according to their evolutionary stages. With the introduction of magnetostratigraphy to the late Neogene sequences in northern China since the 1980s, new chronological framework for a series of Red Clay sequences has been established mainly in the central and southern part of Loess Plateau (Liu et al., 1988; Evans et al., 1991; Zheng et al., 1992; Sun et al., 1998; Ding et al., 1998a, 1998b; Qiang et al., 2001). Magnetic susceptibility, grain size, geochemical and lithologic properties, and micromorphology of the Red Clay sequences have been extensively examined under the new chronological framework, and have yielded valuable information on the paleoclimatic variability of northern China and the Asian monsoon evolution. This has also allowed investigation of the link between aeolian deposition in Asia and the growth of the Tibetan Plateau and Palaeogeography, Palaeoclimatology, Palaeoecology 268 (2008) 47–57 ⁎ Corresponding author. Tel.: +86 10 62756052; fax: +86 10 62754411. E-mail address: lpzhou@pku.edu.cn (L. Zhou). 0031-0182/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2008.08.001 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo