Bone diagenesis variability among multiple burial phases at Al Khiday (Sudan) investigated by ATR-FTIR spectroscopy

Abstract

In this study the diagenetic pathways of archaeological human bones are investigated through Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). Archaeological excavations at Al Khiday (16-D-4 site, Khartoum, Sudan) revealed a multi-stratified cemetery with distinct burial phases, chronologically attributed to different periods spanning from the Early Holocene to the beginning of the 1st millennium CE. ATR-FTIR measurements are carried out on a set of 56 bone samples, representative of each burial phase. Parameters related to collagen content and to bioapatite crystallinity and structural carbonate are calculated from infrared spectra in order to monitor the types and extent of diagenetic alteration, to assess the preservation state of bones and to define the alteration processes occurring during burial. A new method is here developed to quantify the amount of secondary calcite and to remove its contribution to the infrared spectrum, when interfering with the signal of structural carbonate from bioapatite.Considering the wide span of time covered by the archaeological record, the variability of bones alteration among burial phases is related to the climatic changes occurring in central Sudan during the Holocene. The more humid environment occurring in the Early Holocene, characterised by higher precipitation rates, seasonal swamps and palaeo-lakes, progressively changed towards drier conditions until the current arid climate of the Sub-Saharan belt. The change of palaeoenvironmental and local burial conditions over time differently influenced the types and extent of diagenetic processes affecting bones during burial.In this research are also discussed advantages and disadvantages of ATR-FTIR spectroscopy with respect to the more established FTIR spectroscopy in transmission mode.