A geochemical approach to fossilization processes in Miocene vertebrate bones from Sahabi, NE Libya

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In the present paper a multi-technique approach was followed in order to study the diagenetic alterations of fifteen fossil bones derived from the Miocene site of Sahabi in NE Libya. Specifically, X-ray Diffraction (XRD) supplemented by the Rietveld method, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDS), Electron Probe Microanalysis (EPMA) and Fourier Transform Infrared Spectroscopy in the Mid-IR (FTIR, Mid-IR), were performed on fossilized bone fragments belonging mainly to artiodactyl mammals. From the qualitative observation of bone histology by means of SEM, a moderate preservation of the internal bone morphology and limited microbial attack were inferred. The high percentage (wt.%) of F concentration that the EPMA analyses yielded, combined: (a) with the absorbance bands of carbonate anions in the FTIR spectra and (b) the structural parameters calculated by the Rietveld method, revealed the partial substitution of F− for OH− and CO32− for PO43− in the apatite structure. As a result, one of the basic diagenetic trends was the preservation of the inorganic part of the studied samples as carbonate fluorapatite. Additionally, according to our infrared spectra, CO32− substituted for OH− and a carbonate species known to be labile was also present. Apart from F, EPMA also detected S and Fe. Sulfur speciation was studied by micro-XANES, that confirmed the presence of S6+ (sulfates). Iron speciation was investigated with Mössbauer spectroscopy, which indicated the possible presence of goethite-type (FeOOH) submicroscopic inclusions. In nearly all specimens, quartz and gypsum were identified as the main secondary phases.