Re-examining the chemical evaluation of diagenesis in human bone apatite

Isotopic analysis of human bone is becoming an increasingly important tool for the archaeologist in divining past life-ways. The isotopic ratios within bone are often assumed to be preserved as in life, but diagenetic change can alter the ratios, invalidating the results of isotopic analysis. Diagenesis can be evaluated in a number of ways, but most often spectroscopic techniques are utilised as the most efficient and easiest to understand methods for the archaeologist. Many isotopic studies do not report the possibility of diagenetic change, and if it is reported it has often been quantified using a single method of chemical analysis, FTIR spectroscopy. This study set out to test the value of FTIR analysis using human remains from the prehistoric site of Ban Non Wat, Northeast Thailand, and to compare the results with the non-destructive technique of FT-Raman spectroscopy. The study shows that FTIR spectroscopic analysis gives far less detail on the condition of bone than Raman spectroscopy, which does not merely indicate recrystallisation has occurred, but also shows clearly whether or not collagen is present, allows identification of ionic substitions which have occurred and identification of secondary minerals which have formed. Raman spectroscopy, combined with LA-ICP-MS analysis also revealed that soil composition and groundwater flow are the conditions which most affect diagenesis at Ban Non Wat.