Geochemistry of crusts in palaeontological deposits: taphonomic settings in an Upper Pleistocene cave site (San Teodoro, Sicily)

Abstract

The mineralogical and geochemical composition of cave sediments provides crucial insights into past climatic and biological dynamics. This study investigates the authigenic crusts of San Teodoro Cave (Sicily), a key Upper Pleistocene paleontological site, through a multianalytical approach. The cave hosts two superimposed phosphatic crusts, separated by sterile sediment, reflecting shifts in depositional and post-depositional conditions. Our analyses reveal a complex mineral assemblage consisting of calcite, aragonite, and various phosphate phases. Calcite is the dominant phase in the older crust, whereas the presence of aragonite in the younger brown crust likely indicates periods of increased aridity, potentially corresponding to conditions during the Last Glacial Maximum. Aragonite precipitation was favored by elevated Mg/Ca ratios, limited water infiltration, and kinetically controlled processes. Phosphate minerals, derived from bat guano, record localized pH variations and biologically mediated geochemical activity. The development of stable crusts without evidence of bioturbation further suggests the cessation of hyena activity within the cave. These findings demonstrate that the aragonite-phosphate association is a probable indicator of extreme dryness and specific taphonomic pathways in Mediterranean Pleistocene cave environments, offering a high-resolution proxy for paleoenvironmental reconstruction during the driest phases of the Late Pleistocene.