Bone diagenesis in arid environments: An intra-skeletal approach

• Bone diagenesis study in archaeological sites from Mauritania and Mali
• Mineralogy, histology and geochemistry measured at the intra-individual scale
• Each skeleton recorded its own diagenetic trajectory.
• Diagenetic trajectories might be used to refine dietary reconstruction.

Bone trace element content and isotopic composition are closely related to human nutrition. The investigation of archaeological bone geochemistry can help us to better understand the relationship between past populations and their environment alongside cultural practices as inferred from dietary reconstruction. However, dietary information may be altered post-mortem by diagenetic processes in soil. In this study, bone mineralogy (Ca/P, secondary minerals, organic matter content and bone apatite crystallinity), histology, element content (Mg, Na, F, Sr, Ba, Mn, Fe, La, Ce and U) and stable isotope composition (δ13C and δ18O carbonate) were investigated at the intra-individual scale in order to understand the effects of diagenesis on skeletons buried in different saharo-sahelian environments. Between 10 to 18 bone samples were taken from 4 Neolithic skeletons excavated in the Mauritanian Dhar Oualata and Néma and in the Daounas, Mali. Additionally, the enamel of two third molar teeth was also analysed from each skeleton for comparison with bone.The results show that the four skeletons, buried in the same desert climate area, all exhibited different degrees of diagenetic modification, related to local taphonomic conditions. Highly drained and periodically flooded environments generated substantial bone bacterial damage, low to moderate apatite crystallinity and secondary minerals in bone pores. Bone trace element content and isotopic composition were more diagenetically affected than in bones from skeletons buried in a drier environment, which display little bioerosion, high apatite crystallinity and the absence or late precipitation of secondary minerals in their bone pores.Intra-skeletal variability of the geochemical composition, and the comparison of geochemical data from bones and teeth, enables the approximation of ante-mortem bone trace element and stable isotope compositions using the best preserved bones from each skeleton.