The rock weathering literature contains the hypothesis that case hardening exemplifies equifinality, where the same end state can be reached by many potential processes in an open system. We present analytical data from six different sites in the western USA to assess the hypothesis of equifinality. Case hardening can be produced on: (1) sandstone in Petrified Forest National Park, Arizona, from the addition of silica glaze, rock varnish and heavy-metal skins; (2) sandstone in Whoopup Canyon, Wyoming, from silica glaze that formed originally inside subsurface joints combined with externally applied iron film, silica glaze, and rock varnish; (3) welded tuff in Death Valley, California, from the accumulation of rock varnish and heavy metal skins of Mn and Fe; (4) sandstone in Sedona, Arizona, from the protective effects of rock varnish accretion and heavy metal skins of Mn and Fe; (5) basalt on the Big Island, Hawai'i, from the accumulation of silica glaze inside vesicles; and (6) sandstone at Point Reyes, California, from a lithobiont mat of fungi and lichen. Each developed the general form of a case-hardened shell, protecting the surface from erosion. In accordance with the hypothesis of equifinality, the processes that led to similar appearance differ.
The western Great Basin contains thousands of constructed rock features, including rock rings, cairns, and alignments. Unlike subtractive geoglyphs, such as the Nasca Lines of Peru, that remove desert pavement, these surface features alter the location and positioning of cobble-to bouldersized rocks. The chronology of surface rock features has remained unconstrained by numerical ages because no prior chronometric approach has been able to yield age control. We propose a new strategy for studying these features by analyzing anthropogenic modifications to rock coatings, an approach that permits the use of several dating methods, two of which are assessed here: radiocarbon dating of pedogenic carbonate and rock-varnish microlaminations. Initial results from Searles Valley, eastern California, suggest that constructed rock features may be as old as early Holocene and terminal Pleistocene. Archaeological surveys of desert areas would be greatly enhanced if they noted altered positions of rock coatings.
The Rock Art Stability Index (RASI) is a rapid, quantitative approach to rock art condition assessment. Research carried out at Petrified Forest National Park, USA, demonstrates that, following a 2-day training session, site evaluators obtained replicable results, facilitating a condition assessment of over 3500 engraved panels. Two electron microscopy case studies allowed us to identify the specific rock decay processes and major causes of destruction on panels that were RASI-scored as in
Located in northeastern Arizona (USA), Petrified Forest National Park (PEFO) presents a unique story of both geologic and human history. Though perhaps most well-known for its abundant petrified wood and being part of the Painted Desert, visitors are often surprised when they discover PEFO hosts many ancient petroglyph sites. Over the years, many attempts have been made to record the petroglyph sites, but nothing has been done to assess their geomorphic stability. To address this shortcoming, we employed the Rock Art Stability Index (RASI) to assess geologic stability and (potential) deterioration of rock art sites in PEFO. Used for more than a decade as a triage for researchers assessing which rock art panels/sites are in the most danger of eroding, RASI uses a rank-based system to assess over three-dozen rock decay parameters, resulting in an overall condition analysis of a rock art panel. The findings can then be grouped together by site location to gain a clearer understanding of overall decay processes responsible for (potential) erosion. This study highlights RASI, its use as a low-cost, non-invasive, rapid field assessment technique, and assesses the geomorphic stability of five major petroglyph sites in the Petrified Forest National Park.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.