Laser-induced breakdown spectroscopy (LIBS) is a form of optical emission spectroscopy that can be used for the rapid analysis of geological materials in the field under ambient environmental conditions. We describe here the innovative use of handheld LIBS for the in situ analysis of rock varnish. This thinly laminated and compositionally complex veneer forms slowly over time on rock surfaces in dryland regions and is particularly abundant across the Mojave Desert climatic region of east-central California (USA). Following the depth profiling examination of a varnished clast from colluvial gravel in Death Valley in the laboratory, our in situ analysis of rock varnish and visually similar coatings on rock surfaces was undertaken in the Owens and Deep Spring valleys in two contexts, element detection/identification and microchemical mapping. Emission peaks were recognized in the LIBS spectra for the nine elements most abundant in rock varnish—Mn, Fe, Si, Al, Na, Mg, K, Ca and Ba, as well as for H, Li, C, O, Ti, V, Sr and Rb. Focused follow-up laboratory and field studies will help understand rock varnish formation and its utility for weathering and chronological studies.
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Funding for the purchase of the Z-300 LIBS analyzer was provided by North Carolina State University. Support for fieldwork and salary was provided to L.A.O. under the university startup funding. J.R.K. was supported by National Science Foundation grant EAR-1516593.
The LIBS spectra for all of the samples described in this paper are archived in the LIBS Rock Varnish Analysis folder in the NCSU’s Data Management Plan Center (https://www.lib.ncsu.edu/do/data-management) (accessed on 23 August 2021).
Harmon, Russell S.; Khashchevskaya, Daria; Morency, Michelle; Owen, Lewis A.; Jennings, Morgan; Knott, Jeffrey R.; and Dortch, Jason M., "Analysis of Rock Varnish from the Mojave Desert by Handheld Laser-Induced Breakdown Spectroscopy" (2021). Kentucky Geological Survey Faculty and Staff Publications. 7.