Bone diagenesis in archaeological and contemporary human remains: an investigation of bone 3D microstructure and minero-chemical assessment

The major difficulty to study bone preservation is to define which diagenetic parameters need to be taken into account when any information on environmental conditions is missing. Through this research, we contribute towards understanding the complex interplay of factors that affects human bones during diagenetic process. The work focuses on how organic and mineral components influence each other and how they influence the resulting micro-structural assessment of human bone. The mineral and organic properties of 24 adult human long bones from archaeological to contemporary burials in Milan (Italy) were characterized through different analytical techniques, in relation to the preservation of their microstructure and porosity. The 3D microstructure of the bone tissue was carried out through the use of phase contrast synchrotron radiation computed micro-tomography (SR-mu CT). The results show that when diagenesis proceeds, (i) the bone tissue is progressively attacked by microbes; (ii) the diagenetic porosity increases at the expense of vascular ones; (iii) the volumes, diameters, and interconnections of vascular canals are markedly reduced; (iii) the amount of organic and carbonate fraction decreases whereas bone crystallinity and mean crystal length increase; (iv) the Ca/P mole ratio in CHA crystals increases; (v) the anisotropy along c-axis in CHA crystals is lost, resulting in an increase of their domain size. Since the conservation of organic and mineral fractions is variable in relation to bone microstructure within the same period and site, the research points out the needs to perform a multi-analytical approach to characterize the bone diagenesis at different scales of observation.