https://www.govtech.com/public-safety/German-Robot-Space-Technology-Testing-to-Take-Place-in-Utah-Desert.html
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Rock Varnish Dating
Rock Varnish Dating
(Hint: it doesn't really work)
Rock varnish dating was a numerical dating technique to identify the that desert varnish was established. It is now used mainly as a relative dating method as the numerical methods are unreliable. Rock varnish is primarily oxidized iron and manganese that is embedded in clay particles near the surface of rocks in desert environments. These elements oxidize over time in arid climates and create a smooth dark-reddish surface distinctly different from more freshly eroded rock around it.
Cation ratio dating was one method used for numerical dating of varnishes. It relied on the assumptions of stable rates of cation leaching and change to determine the age that the varnish. This method had interesting potential but could not show consistent results on a wide scale.
Radio carbon dating is a technique that utilizes small particles of embedded organic material to determine the age of the varnish. This relies on the known carbon 14 ratio of organic material as well as the half life decay of this carbon. This method is well established and reliable for dating organic material but inconsistencies in rock varnish make it problematic in this context.
https://commons.wikimedia.org/wiki/File:Desert_Varnish_-_Horseshoe_Canyon.jpg
Ultimately, both numerical methods are not able to be used reliably by geomorphologists. The cation ratio comparison cannot be used due to several complex variables that were not taken into account originally. The cation ratios vary more based on local variability than universally consistent leaching rates. Carbon dating is not reliable because of problems definitively separating organic from inorganic material and in linking organic material to a certain layer of the varnish.
However, varnish dating can still be a useful tool in terms of relative dating of comparing surface ages of nearby samples. More thoroughly developed varnish samples show an older relative age compared to lighter color nearby samples. This can show differential erosion rates in alluvial fans as well as aeolian erosion and other relative disturbances.
https://commons.wikimedia.org/wiki/File:Desert_Varnish_-_Horseshoe_Canyon.jpg
Watchman, A., 2000. A Review Of The History Of Dating Rock Varnishes. [online] Science Direct. Available at: <https://www.sciencedirect.com/science/article/abs/pii/S0012825299000598> [Accessed 2 October 2020].
This paper outlines the history of rock varnish dating, mainly from its formation as a numerical science in the 1980s and its subsequent problems following further research in the 1990s. This paper highlights the formation and structure of rock varnish, cation ratio dating (and its problems) and radiocarbon dating (and its problems). It does note several possibilities for other avenues of rock varnish dating.
Schneider J.S., Bierman P.R. (1997) Surface Dating Using Rock Varnish. In: Taylor R.E., Aitken M.J. (eds) Chronometric Dating in Archaeology. Advances in Archaeological and Museum Science, vol 2. Springer, Boston, MA. https://doi.org/10.1007/978-1-4757-9694-0_12
This paper introduces rock varnish highlighting its structure and relevance to science. The authors then diver deeper into the two main methods of varnish dating and then discusses the severe limitations of these methods. This paper ends by hitting home the point that there is no reliable method for numerical dating of rock varnish.
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