Systematic Mn fluctuations in laminated rock varnish developed on coeval early Holocene flint artifacts along a climatic transect, Negev desert, Israel Yonaton Goldsmith a, b, ⁎, Yehouda Enzel a , Mordechai Stein a, b a The Fredy and Nadine Herrmann Institute of Earth Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel b Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem 95501, Israel abstract article info Article history: Received 21 January 2012 Available online 24 August 2012 Keywords: Rock varnish Holocene PPNB Negev desert Mn fluctuations Dust Paleoclimate This study presents an assessment of the potential application of Mn content in rock varnish laminae as a paleoclimate indicator. To investigate the environmental controls on varnish formation, we determined Mn composition in rock varnish formed on flint artifacts produced during the earliest Holocene from eight coeval prehistoric sites in the Negev desert, Israel. These sites lie along a north–south annual rainfall transect ranging between 120 and 30 mm yr -1 . The varnish is ~100 times enriched in Mn relative to the content in the desert dust source material. Chemical profiles across the varnish display 4–6 distinct Mn peaks in all sampled sites, pointing to systematic fluctuations within the varnish along a wide range of environmental settings. The mean Mn contents in the various sites range between 10.7 and 15.6 at.%, yet within this range, the Mn content in the Negev varnish does not show a correlation with mean annual rainfall. As moisture is needed for Mn mobility, wetting cycles by dew or light rain, which are not adequately represented by the mean annual rainfall amounts but control the number of wetting–drying cycles may explain the variance within the results from the arid and hyperarid Negev varnish. © 2012 University of Washington. Published by Elsevier Inc. All rights reserved. Introduction Rock (or desert) varnish comprises a thin (1–100s μm) coating formed primarily in micro-basins on exposed rock surfaces and is very common in arid and semi-arid regions (e.g. Liu and Dorn, 1996; Reneau et al., 1992). Former studies have shown that the varnish is composed of clay minerals and amorphous silica (70%) and Mn and Fe oxides (30%) (Dorn, 2007a; Garvie et al., 2008; Perry, 2004; Potter and Rossman, 1977, 1979). It typically displays a μm-scale alternating or- ange and black laminated structure which vary in Mn, Si, Al and Fe content. Mn is largely enriched to values of 10–30 wt% of oxides (Broecker and Liu, 2001; Garvie et al., 2008; Liu, 1994; Liu and Broecker, 2007, 2008a; Liu and Broecker, 2008b; Liu and Dorn, 1996; Perry and Adams, 1978; Reneau et al., 1992). At present, it is accepted that dust is the main source of varnish material (Bao et al., 2001; Fleisher et al., 1999; Garvie et al., 2008; Hodge et al., 2005; Potter and Rossman, 1977). The formation mechanism of rock varnish remains undetermined. Proposed mechanisms include abiotic chemical precipitation (Engel and Sharp, 1958; Hooke et al., 1969; Moore and Elvidge, 1982; Perry, 2004; Perry et al., 2005, 2006), biologically mediated precipitation (Dorn and Oberlander, 1981; Dorn and Oberlander, 1982) or a combination of these two mechanisms (Dorn, 1998, 2007b, and see references there). Varnish has been proposed as a paleoclimate archive, where its laminae record past millennial-scale climatic fluctuations (Broecker and Liu, 2001; Liu, 1994; Liu and Broecker, 2008a; Liu and Dorn, 1996; Liu et al., 2000). The most recent, surface lamina of the varnish is typi- cally Mn-poor and yellow, attributed by the above researchers to forma- tion during the recent drier stage of the Holocene in deserts. The dark, Mn-rich laminae were consequently associated with wetter climates (Liu, 1994; Liu and Dorn, 1996; Zerboni, 2008). In this way, Broecker and Liu (2001) hypothesized a general correlation between the Mn con- tent and regional annual rainfall. In addition, compiled color layering sequences within the varnish were wiggle-matched to the sub-polar North Atlantic deep sea sediment record (Liu, 1994; Liu and Broecker, 2007). The use of rock varnish as a paleoclimate indicator has been criticized based on uncertainties of the degree of variance in the varnish properties (Garvie et al., 2008; Reneau et al., 1992). In addition, no well-defined sampling method has been established and an investigation of the way modern analogs of varnish form across a large range of known modern climates under well-defined chronological contexts. In this paper, we present a systematic field-based study of the charac- teristics of varnish formed on flint artifacts from eight coeval prehistoric sites located along a north–south climatic transect in the Negev desert, Israel. By using Holocene varnish formed under known climatic settings, Quaternary Research 78 (2012) 474–485 ⁎ Corresponding author at: The Fredy and Nadine Herrmann Institute of Earth Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel. E-mail address: Yonatan.goldsmith@mail.huji.ac.il (Y. Goldsmith). 0033-5894/$ – see front matter © 2012 University of Washington. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.yqres.2012.07.009 Contents lists available at SciVerse ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres