Lithodiversity and cultural use of desert varnish in the Northern Desert of Mexico

Litodiversidad y uso cultural del barniz de desierto en el Desierto del Norte de México

Pável U. Martínez-Pabello^1,*, Beatriz Menéndez Iglesias^2,3, Rafael López Martínez¹, Teresa Pi-Puig⁴, Jesús Solé⁴, Aldo Izaguirre Pompa⁵, Sergey Sedov¹

¹ Institute of Geology, Universidad Nacional Autónoma de México, 04510, CDMX, Mexico.

² Institute of Anthropological Research, Universidad Nacional Autónoma de México, 04510, CDMX, Mexico.

³ Gerda Henkel Foundation. Patrimonies Funding Initiative, 40211, Düsseldorf,, Germany.

⁴ National Laboratory of Geochemistry and Minerology, Institute of Geology, Universidad Nacional Autónoma de México, 04510, CDMX, Mexico.

⁵ Institute of Engineering and Technology, Universidad Autónoma de Ciudad Juárez, 32310, Chihuahua, Mexico.

* Corresponding author: (P. U. Martínez- Pabello) This email address is being protected from spambots. You need JavaScript enabled to view it.

How to cite this article:

Martínez-Pabello, P.U., Menéndez Iglesias, B., López Martínez, R., Pi-Puig, T., Solé, J., Izaguirre Pompa, A., Sedov, S., 2022, Lithodiversity and cultural use of desert varnish in the Northern Desert of Mexico: Boletín de la Sociedad Geológica Mexicana, 74 (3), A100622. http://dx.doi.org/10.18268/BSGM2022v74n3a100622

Manuscript received: December 15, 2021; Corrected manuscript received: May 5, 2022; Manuscript accepted: June 8, 2022.

ABSTRACT

Rock varnish is a thin layer (1-40 microns every 1000 years), dark-reddish in color (30% Mn and Fe oxides, 70% clay minerals), that coats a rock surfaces in the northern Mexican deserts. This accretion has been used as a canvas by ancestral human groups to record different types of motifs (zoomorphic, geometric and anthropomorphic) in the northern Mexican desert (Sonora and Chihuahua). These petroglyphs reflect the cultural and artistic nature of past inhabitants and the varnish preserves them through the millennia. Rock varnish coats a variety of rock types, and this paper explores differences in the chemical composition and interaction of varnish and the underlying rock. We studied varnish from three different sites: Samalayuca (Chihuahua); El Álamo (Sonora); and La Proveedora (Sonora). The analytical techniques of microscopy, X-Ray Diffraction (XRD) and Laser Breakdown Spectra (LIBS), reveals a similar chemical composition (Mn, Fe, Ca and Al mainly) that it does not depend on the lithodiversity or location (Samalayuca -sandstone-, El Álamo -sandstone- and La Proveedora -granite-). We observed differences in the contact between the varnish and the underlying rock. Varnish penetrate into decayed minerals such as plagioclase; thick accumulations can occur on hard minerals such as quartz. Like prior research, we find little important contribution of material from the underlying to its varnish coating and conclude its main component derives mostly from aeolian deposition.

Keywords: desert varnish, petroglyphs, Sonoran Desert, Chihuahuan Desert, lithodiversity.