Rock varnishes are thin coatings, mainly composed of Fe and Mn hydroxides and clay materials, commonly found in arid and semi-arid areas worldwide. Rock varnish has always been a keen area of interest for researchers in archaeology and geology in the form of petroglyphs and the study of climatic change in geomorphic settings. However, its formation and chemical fingerprinting still have open avenues due to claims of both biotic and abiotic processes. As reported, these rock varnishes might have protected microflora residing beneath within the layers of varnish; Mn and Fe would have functioned as a UV shield by protecting against high UV irradiation, desiccation, and widely varying temperatures for years. Therefore in the present work, rock varnish samples collected from different localities of Ladakh, India, were studied by applying a multidisciplinary approach to develop a comprehensive understanding of its formation(viz. biotic/abiotic). Geochemical fingerprinting of the rock varnish done with analytical techniques such as XRD, XRF, Raman & IR spectroscopy, IR-MS, SEM-EDS suggested contrast morphology and mineralogical signature on host rock and varnish under consideration. Ancient DNA- genome analysis for the samples indicates bacterial input of the same, complimenting it, the isotopic values of δ13C, δ15N, and the TOC/TN ratio suggest the microbial intake for the formation of varnish. Further, the Raman spectroscopic analysis detected manganese dioxide (MnO2) in the form of pyrolusite (naturally occurring mineral). As MnO2 is a very promising electroactive substance, it provokes us to study its electrochemical behavior too. Conclusively, this work could pave the way to develop materials for future needs and help answer the question about the earliest possible life signatures.

Rock varnish: Potential future product

ACS Spring Meeting 2021

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