Origin of tafoni in the Late Cretaceous aeolian sandstones, Danxiashan UNESCO Global Geopark, South China

Tafoni occur generally in granular rocks around the world, but their origin remains controversial. In this study, the roles of lithology, micro-climate, and organism in tafoni development are investigated in the Danxiashan UNESCO Global Geopark of South China. The Jinshiyan Temple and Luyitang sites along the Jinjiang River are chosen to conduct tafoni morphometry, bedrock petrography, and micro-climate analyses. The research methods used in this study include field observations and measurements, Voronoi diagrams, polarizing microscopic and scanning electron microscopic (SEM) image analysis, and meteorological detection. The tafoni are mostly 2-10 cm in length and elliptical in shape. The Late Cretaceous Jinshiyan sandstones are characterized by a grain-to-grain contact fabric and moderate sorting with a high proportion of soluble grains and cements. The Voronoi diagrams developed through the ArcGIS software are largely consistent with the tafoni openings. Moreover, owing to exposure to solar insolation, the external temperature values are higher than the internal ones, while the external relative humidity values are lower than the internal ones. Therefore, the permeable Jinshiyan sandstones are fundamental for tafoni development, while the abundant moisture from the Jinjiang River and frequent rains is favorable for salt weathering in tandem with biological activities. At last, a five-stage development model is proposed for the tafoni progression in the study area.