Integrated approach for the geochemical characterization of vermiculations from Pertosa-Auletta Cave (Southern Italy)

Abstract

Vermiculations are among the less known structures occurring in underground environments. They are thin, irregular and discontinuous deposits of incoherent particles, with diverse morphology (i.e. dots, dendritic, hieroglyphic), colour (red, brownish, grey, white) and size (Parenzan, 1961), typically found on the walls and roofs of natural or artificial caves all over the world (Hill and Forti, 1997). The origin of vermiculations is widely debated due to the development of data-driven theories still hindered by the scarcity of quantitative analyses on their chemistry and biology (Bini et al., 1978). The aim of this study was to investigate the geochemical characteristics of vermiculations from one of the most important karst systems of southern Italy, the Pertosa-Auletta Cave, using an integrated approach involving elemental, mineralogical and microscopic analyses. The research provides the first quantitative record of all these features in vermiculations, giving a comprehensive overview on their geochemical nature and contributing to the understanding of their genesis. The vermiculations of Pertosa-Auletta Cave exhibit an extraordinary diversity in their morphology and colour, the widest recorded from a single karst system to date. Elemental analyses also highlighted wide variations in C, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, Ni, P, S, Ti, V and Zn concentrations among vermiculations. Field emission scanning electron microscopy with Energy Dispersive X-ray Spectrometry, as well as X-ray Diffractometry, showed that vermiculations are mainly composed of calcite, associated to clays, quartz and various biologically-mediated CaCO3 crystallization features (rods and vaterite spheres). The constant association of clay minerals, occurring along cavities and niches of calcite, with microbial-like filaments, and the presence of microboring and etching patterns, indicate that microbial activity may play an important role in the development of vermiculations.