Modelling diagenesis in archaeological bone

Abstract

This thesis presents a series of papers intended to further our knowledge and understanding of bone taphonomy, with special attention given to the survival of organic molecules (collagen and DNA). An integrated modelling and measuring approach has been taken. Initially, the rate of chemical degradation of bone collagen was estimated from data derived from high temperature laboratory experiments. These rates were then extrapolated to realistic archaeological burial temperatures using palaeoclimatic reconstructions. The model was tested using radiocarbon databases using data on location and collagen yield. Despite the simplicity of the approach and the large errors involved, it does appear that the model may be useful for predicting the limits of collagen survival, although most bones have less collagen than the model predicts. A similar model was produced for the depurination of DNA. The models which are based on rates of chemical deterioration, highlight the role that temperature may play in biomolecular preservation, however they fail to address the complexity of bone taphonomy. A study of bones from a site in southern Italy (Apigliano) identified bone with no evidence of microbial attack, but otherwise severe diagenesis (including little or no collagen) - so called `pre-fossilised' bone. In a wider study of 200+ archaeological bones excavated form 40 sites across Europe this `pre-fossilisation' was identified as one of four possible diagenetic states, the others being, `microbial attack', `complete dissolution' and `good preservation'. These states of preservation are defined by characteristic sets of diagenetic parameters, although the environmental and taphonomic conditions that control these states of preservation are less well defined. In addition to the standard diagenetic parameters measured, the preservation of osteocalcin (a potential proxy for DNA) was investigated using immunological techniques.