Biogenic origin of coastal honeycomb weathering

Abstract

Honeycomb weathering occurs in two environments in Late Cretaceous and Eocene sandstone outcrops along the coastlines of south-west Oregon and north-west Washington, USA, and south-west British Columbia, Canada. At these sites honeycomb weathering is found on subhorizontal rock surfaces in the intertidal zone, and on steep faces in the salt spray zone above the mean high tide level. In both environments, cavity development is initiated by salt weathering. In the intertidal zone, cavity shapes and sizes are primarily controlled by wetting/drying cycles, and the rate of development greatly diminishes when cavities reach a critical size where the amount of seawater left by receding tides is so great that evaporation no longer produces saturated solutions. Encrustations of algae or barnacles may also inhibit cavity enlargement. In the supratidal spray zone, honeycomb weathering results from a dynamic balance between the corrosive action of salt and the protective effects of endolithic microbes. Subtle environmental shifts may cause honeycomb cavity patterns to continue to develop, to become stable, or to coalesce to produce a barren surface. Cavity patterns produced by complex interactions between inorganic processes and biologic activity provide a geological model of 'self-organization'. Surface hardening is not a factor in honeycomb formation at these study sites. Salt weathering in coastal environments is an intermittently active process that requires particular wind and tidal conditions to provide a supply of salt water, and temperature and humidity conditions that cause evaporation. Under these conditions, salt residues may be detectable in honeycomb-weathered rock, but absent at other times. Honeycomb weathering can form in only a few decades, but erosion rates are retarded in areas of the rock that contain cavity patterns relative to adjacent non-honeycombed surfaces.

Application of an S‐shaped curve model to the temporal development of tafoni of salt‐weathering origin

“…As cavities grow deeply, they increase lateral dimensions gradually eroding the side wall and eventually coalesce with contiguous cavities to form larger ones. Repetition of coalescence causes the disappearance of cell‐like structures (Pestrong, , figure ; Mottershead, , figure 10.4; Mustoe, , figure ), which results in occurrence of tafone‐like features. Thus, honeycombs may be reckoned as an ephemeral micro‐morphology.…”

The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

“…van der Westhuizen et al, 2006, their Figs 8 and9). A possible interpretation of the structures that obviously find similar forms in high-Mg basalts interpreted as ocelli or lithophysae of the Ventersdorp lavas could be tafoni weathering that has been described from different rocks, but also from lava flows (Mustoe, 2010 and references therein).…”

“…Most recent literature explains these cavity patterns to develop when permeable rocks are exposed to solutions containing dissolved salts in environments characterized by cyclic wetting and drying. In arid regions, salt weathering commonly involves alkaline sulfates or carbonates released from rock decomposition, in combination with wetting and drying cycles that are related to dew, capillary transport of moisture through soil, or subsurface flow of moisture within permeable bedrock (Mustoe, 1983(Mustoe, , 2010.…”

Characterization, performance and replacement stone compatibility of building stone in the 12th century tower of Dudzele (Belgium)

“…Alveolization or honeycomb weathering is commonly attributed to salt action in combination with casehardening agents or biofilms (McBride and Picard, 2004;Mustoe, 2010). The capillary uptake test clearly demonstrated the occurrence of salts inside the stones (Fig.…”