Late Pliocene–Quaternary evolution of redox conditions in the western Qaidam paleolake (NE Tibetan Plateau) deduced from Mn geochemistry in the drilling core SG-1 Yibo Yang a , Xiaomin Fang a,b, ⁎, Erwin Appel c , Albert Galy d , Minghui Li a , Weilin Zhang a a Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China b Key Laboratory of Western China's Environmental Systems, Ministry of Education of China and College of Resources and Environment, Lanzhou University, Lanzhou 730000, China c Department of Geosciences, Center for Applied Geoscience, University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany d Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK abstract article info Article history: Received 29 January 2013 Available online 22 August 2013 Keywords: Late Pliocene–Quaternary Qaidam Basin Manganese geochemistry Lake redox conditions Asian inland drying Manganese (Mn) in lake sediments reacts strongly to changes of redox conditions. This study analyzed Mn concentrations in oxides, carbonates, and bulk phases of the calcareous lacustrine sediments of a 938.5-m-long core (SG-1) taken from the western Qaidam Basin, well dated from 2.77 Ma to 0.1 Ma. Comparisons of extrac- tions from diluted hydrochloric acid, acetic acid and citrate–bicarbonate–dithionite demonstrate that variations of Mn concentrations from acetic acid leaching (Mn HOAc ) are mostly responsible for Mn (II) fluctuations in the carbonate phase. Taking into account the relevant processes during weathering, transportation, deposition and post-deposition of Mn-bearing rocks, we conclude that Mn input from catchment weathering and paleolake redox condition provide the primary controls on variations in the Mn records of carbonate and oxide phases. We propose Mn HOAc as a new sensitive indicator of paleolake redox evolution and catchment-scale climate change. The Mn HOAc variations show a long-term upward decreasing trend, indicating a long-term decrease of Mn input from catchment weathering associated with increasing oxygen content in the paleolake bottom water. The great similarities of the Mn HOAc record with other regional and global records suggest that paleolake redox changes and climatic drying in the Qaidam Basin may be largely related to global cooling. © 2013 University of Washington. Published by Elsevier Inc. All rights reserved. Introduction Manganese (Mn) in lake sediments reacts sensitively to changes in oxidation–reduction (redox) conditions. The redox behavior of Mn in lakes has been well studied and comprehensively reviewed by a num- ber of previous researchers (e.g., Dean et al., 1981; Davison, 1993; De Vitre and Davison, 1993; Hamilton-Taylor and Davison, 1995; Wetzel, 2001). In brief, Mn is soluble in reduced phases and insoluble in oxi- dized ones, and readily converted in the vicinity of a redox boundary (Davison, 1993; Wetzel, 2001). Furthermore, Mn (IV) is easily reduced whereas Mn (II) does not oxidize as readily. Mn sulfides are very soluble under reducing conditions (Algeo and Maynard, 2004), and dissolved Mn is not readily taken up significantly by any organic or mineral phase (Huerta-Diaz and Morse, 1992). These two properties of Mn result in a diffuse and homogeneous distribution of Mn (II) throughout the lake water body (Hamilton-Taylor and Davison, 1995). The Mn (II) can be sequestered by carbonate formation in low Eh and slightly oxic conditions (Calvert and Pedersen, 1993; Hild and Brumsack, 1998; Caplan and Bustin, 1999; Stevens et al., 2000; Maynard, 2004; Tribovillard et al., 2006). Hence, Mn in carbonate can serve as a valuable proxy, sensitive to lake-water redox conditions. Various analyses of the geochemical dynamics of Mn and short-term Mn-bearing carbonate records have indi- cated that the Mn-bearing carbonates link directly to the oxygen content of the bottom water and water depth (e.g., Barnaby and Rimstidt, 1989; Huckriede and Meischner, 1996; Neumann et al., 1997; Schaller and Wehrli, 1997; Stevens et al., 2000). However, the reliability of this proxy has not yet been examined in long-term lake sediment records. A maximum thickness of ~15,000 m of Cenozoic sediments fills the closed inland Qaidam Basin, which has an area of 12,000 km 2 and a catchment of 25,000 km 2 and is located on the northeastern Tibetan Plateau (Huang et al., 1996; Xia et al., 2001). The Cenozoic sediments consist of mudstones, calcareous mudstones and marls, intercalated silt- stones, gypsum, and rock salt beds, many of which are carbonate-rich (Tuo and Philp, 2003). This site provides an excellent opportunity for studying Mn-bearing carbonates in its long-term sedimentary record. In 2008, our team carried out a deep drilling program in the central western Qaidam Basin under the Sino-German TiP-TORP projects. Quaternary Research xxx (2013) 586–595 ⁎ Corresponding author at: Key Laboratory of Continental Collision and Plateau uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China. Fax: +86 10 8409 7079. E-mail address: fangxm@itpcas.ac.cn (X. Fang). 0033-5894/$ – see front matter © 2013 University of Washington. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.yqres.2013.07.007 Contents lists available at ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres