Caratterizzazione mineralogica della matrice che ingloba resti ossei dl Elephas mnaidriensis rinvenuti nella Sicilia nord-occidentale: considerazioni riguardanti il microambiente dI formazione dei depositi

Abstract

Three bone deposits, two of them hypogeous and the third superficial, in north-western Sicily are considered. All deposits are characterized by a great quantity of bones of Elephas mnaidriensis, the last elephantine species to live in Sicily (about 180,000 years ago). Evident signs of abrasion in most of the larger bone remains have been ground of discussion since the time of discovery of these sediments, and contrasting opinions on their enviroment of formation have been expressed, paleontologists being divided between a marine origin and a continental origin. In this paper, nature and origin of the sediments are defined on the basis of mineralogical, petrographic and geochemical analyses. The sediments are usually clastic and their provenance from sedimentary formations cropping out in the vicinity is explained as occurring either through karstic canals, or as an alluvial deposition or through eolian transport, as suggested by the similarity among residual element (Al, Si and Fe) ratios and the presence of the same accessory minerals (ilmenite, magnetite, zircon, tourmaline, rutile, garnet and sphene). No microfossils and mineralogical phases of marine origin have been found. Strengite (FePO₄ • 2H₂O) is present among authigenic minerals. δ¹⁸O values of the carbonatic fraction of hyena coprolites, which are present in the same layer containing elephantine bones, indicate a contribution of meteoric water in the mineralization process; δ¹³C values emphasize the contribution of biogenic CO₂. Such elements therefore suggest that sedimentation occurred in a continental environment. Field surveys, carried out to define the geomorphological and spelaeological characters of studied sites, strenghten laboratory data in hypothesizing the succession of events which brought to the accumulation of fossil bones.