Tafoni and honeycomb structures as indicators of ascending fluid flow and hypogene karstification

Abstract

Abstract Tafoni and honeycombs remain some of the most enigmatic and puzzling geomorphological phenomena. Their globally widespread occurrence across a wide range of lithologies and environmental conditions suggests that their formation is determined by a factor that overarches variations in these conditions and weathering processes. Based on a study of tafoni and honeycombs in the Crimean Piedmont, this paper demonstrates that the primary factor in their formation is the pre-exposure alteration of rocks along fractures and karst conduits as a result of fluid–rock interactions. Such alteration is commonly induced by ascending flow and is related to hypogene karstification. The morphological expression of cavernous features through removal of the alterite can occur under subsurface conditions, but is more frequent on exposure to atmospheric weathering. The local or regional characteristics of a weathering system are irrelevant or of only secondary importance in determining the localization and morphology of cavernous features. New features do not form on rock surfaces where the alteration zone was totally denuded or never present. The proposed model resolves major issues inherent to previous interpretations of cavernous features. It has general applicability and important implications for geodynamic and palaeohydrogeological reconstructions. Typical tafoni and honeycombs may indicate past events of ascending flow and the potential presence of hypogene karst systems.