Unravelling the presence of organic compounds in moonmilk from a lava cave by analytical pyrolysis (Py-GC/MS)
Moonmilk has been reported in subterranean environments worldwide. This term refers to carbonate deposits with pasty cheese like texture (Fig. 1), but with different origins and mineralogical composition. Generally, moonmilk deposits are found in carbonate caves, and are composed of calcite, hydromagnesite, aragonite, vaterite or huntite. The calcite that forms moonmilk is frequently observed as needle-shaped and its origin is a controversial issue. It is questionable whether the precipitation of calcite is induced by microorganisms, by abiotic physicochemical processes, or even a combination of both. The application of chromatographic techniques to study cave speleothems is scarce due to their low content of organic compounds and low volatility. Analytical pyrolysis (Py-GC/MS) is particularly useful to study materials that are not soluble and therefore not amenable by conventional GC/MS techniques. In this study, Py-GC/MS was applied for assesing the origin of organic compounds associated with moonmilk deposits from a lava cave in La Palma Island (Canary Islands, Spain; Pyrolysis of the moonmilk deposits were carried out at 500ºC. The chromatograms showed the presence of different organic compounds: fatty acids (mainly C16, C18; C18:1 and C28), pyrolysis products derived from polysaccharides (levoglucosan), phytosterols and steroids (stigmasterol, β-sitosterol, cholest-5-en-3-ol, stigmastan-3,5-diene, stigmasta-3,5-diene-7-one), triterpenoids of the oleanane (28-norolean-17-en-3-one, β amyrin), as well as ursane series. These compounds, including specific triterpanes and steranes, have been previously found in sedimentary records. They are believed to be derived from oxygenated triterpenoids in angiosperms, comprising the most common steroids in the epicuticular waxes of higher plants and are widely distributed among the plant kingdom. These data suggest that the organic compounds associated with moonmilk from La Palma Island lava cave are partially driven by the topsoil and overlying vegetation, thus demonstrating the potential use of moonmilk in palaeoenvironmental research.
| Main Authors: | , , , , , |
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| Format: | póster de congreso biblioteca |
| Published: |
Università di Messina
2016-05-29
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| Online Access: | http://hdl.handle.net/10261/160445 |
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