In Suspect Terrain: Dating Rock Engravings

Whitley, David S.

doi:10.1002/9781118253892.ch34

Cited by 10 publications

(6 citation statements)

References 50 publications

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“…We chose the southern Owens Valley and the adjacent Rose Valley, both parts of the Mojave Desert in southern California, as an initial test site because of its prominent role in the scientific study of rock varnish [e.g., 2 , 19 ], the existence of radiometrically dated rock surfaces [e.g., 19 , 28 , 48 – 50 ], and the presence of well-documented rock art [e.g., 24 , 51 ], including a large corpus of dated petroglyphs in this and nearby regions [ 36 , and references therein, 52 ]. The rock art in this area has been the subject of vigorous–and sometimes acerbic–debate over decades, both with regards to its meaning and function [e.g., 24 , 51 , 53 – 59 ] and its time of creation [e.g., 24 , 28 , 36 , 52 , 54 , 55 , 60 , 61 – 63 ].…”

Section: Introductionmentioning

confidence: 99%

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California

Alamri

Andreae

Garfinkel³

et al. 2020

PLoS ONE

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We investigated rock varnish, a thin, manganese- and iron-rich, dark surface crust, on basaltic lava flows and petroglyphs in the Owens and Rose Valleys (California) by portable X-ray fluorescence (pXRF) and femtosecond laser-ablation inductively-coupled-plasma mass spectrometry (fs-LA-ICPMS). The major element composition of the varnish was consistent with a mixture of Mn-Fe oxyhydroxides and clay minerals. As expected, it contained elevated concentrations of elements that are typically enriched in rock varnish, e.g., Mn, Pb, Ba, Ce, and Co, but also showed unusually high enrichments in U, Cu, and Th. The rare earth and yttrium (REY) enrichment pattern revealed a very strong positive cerium (Ce) anomaly and distinct negative europium (Eu) and Y anomalies. The light rare earth elements (REE) were much more strongly enriched than the heavy REY. These enrichment patterns are consistent with a formation mechanism by leaching of Mn and trace elements from aeolian dust, reprecipitation of Mn and Fe as oxyhydroxides, and scavenging of trace elements by these oxyhydroxides. We inferred accumulation rates of Mn and Fe in the varnish from their areal densities measured by pXRF and the known ages of some of the lava flow surfaces. The areal densities of Mn and Fe, as well as their accumulation rates, were comparable to our previous results from the desert of Saudi Arabia. There was a moderate dependence of the Mn areal density on the inclination of the rock surfaces, but no relationship to its cardinal orientation. We attempted to use the degree of varnish regrowth on the rock art surfaces as an estimate of their age. While an absolute dating of the petroglyphs was not possible because of the lack of suitable calibration surfaces and a considerable amount of variability, the measured degree of varnish regrowth on the various petroglyphs was consistent with chronologies based on archeological and other archaeometric techniques. In particular, our results suggest that rock art creation in the study area continued over an extended period of time, possibly starting around the Pleistocene/Holocene transition and extending into the last few centuries.

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Section: Introductionmentioning

confidence: 99%

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California

Alamri

Andreae

Garfinkel³

et al. 2020

PLoS ONE

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“…Bard, 1979; Bednarik, 2010, 2012; Dietzel et al, 2008; Dragovich, 2000; Guagnin et al, 2018; Whitley et al, 2017). Numerous attempts have been conducted to date petroglyphs by a variety of methods, including radiometric techniques, cation ratio changes, microlaminations, varnish thickness, colorimetric analysis, and so on (Bednarik, 2009, 2010; Bednarik and Khan, 2005; Francis et al, 1993; Liu and Broecker, 2013; Sowers, 2013; Whitley, 2012). In many cases, the results have been disappointing, as discussed in several reviews (Bednarik, 2010; Dorn, 2007; Sowers, 2013).…”

Section: Introductionmentioning

confidence: 99%

Rock varnish on petroglyphs from the Hima region, southwestern Saudi Arabia: Chemical composition, growth rates, and tentative ages

2019

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We investigated rock varnish formed on sandstone and petroglyphs in the Hima area, southwestern Saudi Arabia. To characterize the rock varnish, we made in-situ measurements by portable x-ray fluorescence (pXRF) and analyzed samples by femtosecond laser-ablation inductively coupled–plasma mass spectrometry (fs LA-ICP-MS). Detailed chemical analysis of the rock varnish samples and adjacent soil or aeolian dust yielded information about the varnish’s geochemical context and formation mechanism. Untypically low positive Ce anomalies in the rock varnish samples correlated with negative Ce anomalies in the dust, supporting the hypothesis that the dust is the source of the varnish material. To study the varnish development, we made use of the fact that engraving the petroglyphs exposes a fresh bare sandstone surface without varnish, on which varnish regrows subsequently. We determined by pXRF the areal density of manganese (Mn) and iron (Fe) that had been deposited as rock varnish since the creation of the rock art. The rates of Mn deposition in the newly formed varnish were then estimated by correlating the areal density of Mn in Ancient Arabian and Old Arabic inscriptions with their known age ranges. The observed deposition rates showed substantial variability resulting from differences in exposure conditions of the rock surface, but were in a range comparable with that of our previous measurements in northwestern Arabia. This variability could be reduced significantly by referencing the measurements to the intact varnish adjacent to the individual petroglyphs. This normalization provided a much clearer relationship between varnish deposition and age, and enabled tentative ages to be assigned to rock art motifs without previously known ages. These tentative ages spanned most of the Holocene period and were consistent with the culturally or ecologically derived ages of the animal and human figures depicted in the rock art and the styles of scripts used in different periods.

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“…Several attempts have been made, such as carbon isotope dating, U-series dating of precipitated carbonates, OSL-dating of quartz grains covered by mineral encrustations, the degree of exfoliation, colorimetry of repatination, microerosion, superimposition sequences, and development of macro-wanes (Bednarik, 2017; Bednarik and Khan, 2005). However, many of these techniques were unsuccessful and much of the work is highly controversial (Whitley, 2012). Indirect dating by microerosion measurements, conducted by Bednarik and Khan (2005), appears to have been successful, but it exhibits several other difficulties, such as the need of a valid calibration curve, the frequent lack of feldspar within the sandstones, and the need to assume a constant climate (Bednarik, 2017; Bednarik and Khan, 2005).…”

Section: Introductionmentioning

confidence: 99%

Growth of desert varnish on petroglyphs from Jubbah and Shuwaymis, Ha’il region, Saudi Arabia

et al. 2018

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Petroglyphs, engraved throughout the Holocene into rock varnish coatings on sandstone, were investigated in the Ha’il region of northwestern Saudi Arabia, at Jabal Yatib, Jubbah, and Shuwaymis. The rock art has been created by removing the black varnish coating and thereby exposing the light sandstone underneath. With time, the varnish, a natural manganese (Mn)-rich coating, grows back. To study the rate of regrowth, we made 234 measurements by portable X-ray fluorescence (pXRF) on intact varnish and engraved petroglyphs. Since many petroglyphs can be assigned to a specific time period, a relationship between their ages and the Mn surface densities (DMn) of the regrown material could be derived. This relationship was improved by normalizing the DMn in the petroglyphs with the DMn of adjacent intact varnish. In turn, we used this relationship to assign a chronologic context to petroglyphs of unknown ages. Following the removal of the varnish by the artist and prior to the beginning of Mn oxyhydroxide regrowth, a thin Fe-rich film forms on the underlying rock. This initial Fe oxyhydroxide deposit may act as catalyst for subsequent fast Mn oxidation. After a few decades of relatively rapid growth, the regrowth of the Mn-rich varnish slows down to about 0.017 µg cm–2 a–1 Mn, corresponding to about 0.012% a–1 Mn of the intact varnish density, or about 1.2 nm a–1, presumably due to a change of the catalytic process. Our results suggest that petroglyphs were engraved almost continuously since the pre-Neolithic period, and that rock varnish growth seems to proceed roughly linear, without detectable influences of the regional Holocene climatic changes.

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In Suspect Terrain: Dating Rock Engravings

Cited by 10 publications

References 50 publications

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California

Rock varnish on petroglyphs from the Hima region, southwestern Saudi Arabia: Chemical composition, growth rates, and tentative ages

Growth of desert varnish on petroglyphs from Jubbah and Shuwaymis, Ha’il region, Saudi Arabia

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