Origin and development of tafoni in Tunnel Spring Tuff, Crystal Peak, Utah, USA

Abstract

Bedding-parallel tafoni are well developed over much of the surface of the Tunnel Spring Tuff (Oligocene) exposed in 300-m-high Crystal Peak, an inselberg. The Tunnel Spring Tuff is a crudely stratified, non-welded rhyolite ash-flow tuff with b 30 per cent porosity. Clasts of Palaeozoic dolomite, limestone and quartzite make up 10 per cent of the tuff. The tafoni are remarkable because of their size (up to 20 m wide but rarely wider than 4 m), shape of the openings (spherical, arch-like or crescent-shaped) and abundance (up to 50 per cent of an outcrop face). They are actively forming today. Calcite is abundant (10 to 40 per cent by weight) in tafoni as an efflorescence in spalling flakes of tuff on their roofs and walls. Halite and gypsum generally make up less than 0Á01 per cent of the efflorescence. The absence of corroded quartz and feldspar grains in spall fragments indicates that chemical weathering is unimportant in development of the tafoni.Calcite, aragonite, halite and gypsum dust from modern salt pans less than 20 km from Crystal Peak are potential sources of salt in the tuff, but the prevailing winds are in the wrong direction for significant amounts of these evaporite minerals to reach the inselberg. Calcite is the only evaporite mineral present in the tafoni in more than trace amounts, and this mineral is readily available within the tuff itself as a result of rock weathering. We propose that meteoric water containing carbonic acid infiltrates the tuff, dissolves carbonate clasts, and migrates to the steep flanks (b20 ) of the peak through abundant megapores and micropores. There it evaporates and precipitates calcite. Crystallization pressure spalls off grains and sheets as the physical manifestation of salt weathering. The quasi-uniform spacing of tafoni suggests that a self-organization process is active in the water flow.

Microclimate and weathering in the central Namib Desert, Namibia

“…doi:10. 1016/j.geomorph.2004.04.006 debated (Mustoe, 1982;Young, 1987;Turkington, 1998;McBride and Picard, 2000), and uncertainty still remains as to how weathering relates to larger scale, longer term landform development. In order to make progress on answering many of these questions, two major types of research need to be done.…”

Tafoni development in a cryotic environment: an example from Northern Victoria Land, Antarctica

“…Tafoni dimensions and shape were collected by means of a detailed geomorphological survey and the results reported according to the terminology proposed by Martini (1978) and Mc Bride andPicard (2000), as shown in Figure 3 Tafoni development in a cryotic environment 1505 Figure 3. Sketch of the dimension axes of the tafoni.…”

Relação entre a geodiversidade intrínseca e a estruturação de habitat na escala do geossítio: exemplos na Serra do Segredo e nas Pedras das Guaritas (Caçapava do Sul, RS, Brasil)

“…Suertegaray & Silva, 2009). As feições de intemperismo observadas na Serra do Segredo são compatíveis com aquelas descritas por Mustoe (1982), Rodríguez-Navarro et al (1999), McBride & Picard (2000) e por Paradise (2013), nas quais os fatores preponderantes seriam a dissolução e recristalização de soluções salinas (no caso dos trabalhos citados, de calcita ou sílica) e, adicionalmente, a ação do vento na retirada (erosão) dos produtos desse intemperismo. Figura 4.…”