Bone diagenesis in the medieval cemetery of Vratislavs’ Palace in Prague

Diagenetic modifications in human bones from the early-medieval cemetery discovered in the garden of Vratislavs’ Palace, in the central Malá Strana district of Prague, have been investigated combining histological analysis and instrumental analysis with X-ray diffraction, infrared, and 31P NMR spectroscopy. A total of 15 ribs samples were collected for the study. One sample belonged to a child, whereas, of the other samples from adults, 7 belonged to males, 5 to females, and for 2 the sex attribution was uncertain. A diagenetic pathway common to most of the studied samples was considered the result of a burial environment characterized by a nearly static water regime, with limited temperature excursions, moderately oxic to suboxic, and with pH fluctuations around the limit of apatite recrystallization window, in agreement with the fine textured clay-rich soil, its low hydraulic conductivity, and the measured soil pH. A second pattern, related to variations in the microenvironment, interested a limited number of samples with poorer histological preservation. This was interpreted as the result of higher pH and a better oxygenated environment, which favoured mineral recrystallization. Further reactivation of deterioration processes probably occurred later in some of the graves perturbed by works conducted in the seventeenth century. This work highlights the complementarity of the information obtained from the adopted techniques in order to gain insights into the post-mortem fate of the human remains and their sedimentary environment. In this respect, the quantification of the amount of phosphorus in the amorphous hydrated layer of apatite provided a unique type of information on the mineral component of bone and its reorganization during diagenesis, revealing that a relevant fraction can survive diagenesis, at variance with what previously supposed.