Topsoil alterations influence the genesis and composition of unusual organic-rich speleothems in volcanic caves from the Canary Islands

摘要

This multidisciplinary study combines the use of mineralogy,chromatography,light stable isotopes and nuclear magnetic resonance spectroscopy to reveal the origin of black sludge-like speleothems found in a volcanic cave from La Palma Island(Spain).The combination of these analytical tools permitted the identification of specific biomarkers for tracing the potential sources of the organic compounds identified in these speleothems.Analytical pyrolysis revealed the presence of polysaccharides,plant lipids and specific terpenoids derived from the surface vegetation.In addition,polycyclic aromatic hydrocarbons and N-containing heterocyclic compounds were detected.They probably derived from the leaching of charred vegetation resulting from a wildfire occurred in the surface area in 2012.The δ ~(13)C data of the cave speleothems,topsoil and overlying vegetation confirmed that the organic fraction of the speleothem samples is a combination of partially charred vegetation and organic compounds from the andic soil over the cave.