New insights about the presence of celestite into fossil bones from Molí del Baró 1 site (Isona i Conca Dellá, Lleida, Spain)

We have addressed an X-ray fluorescence (XRF) and X-ray diffraction (XRD) on a collection of thirteen fossil bone belonging to the Molí del Baró 1 paleontological site located near Sant Romà d'Abella (Isona i Conca Dellà Municipality, Lleida Province, Spain, dated to about 66.5 Ma, to investigate the fossilization occurred in this site in terms of physico-chemical properties. As a general behaviour, the XRD patterns showed the bioapatite mineral at a varying level of percentage, and accordingly, the correspondent XRF spectra turned out to be mainly dominated by the presence of Ca, obviously accompanied by phosphorus. Simultaneously, other elements such as Sr, Fe, Ba and Zn were found at non-negligible concentration levels and helped to assign the phase components in the XRD spectra. In three specimens, it was observed by XRD the rather unusual case where the original bioapatite bone mineral was completely substituted for by other mineralogical phases. In addition to this, celestite was also found as an important phase in ten specimens out of the thirteen examined. The occurrence of celestite in the bone structure appears a rather unusual observation within the literature of bones diagenesis. Its provenance is generally ascribed to marine vertebrate organisms, but the presence in the fossil bones of this site, where no evidence of marine environment exists, can be reconciled with occurrence of refluxing processes involving diagenetically altered fluids which were discharged into beds containing strontium sulphate-rich waters.