Accurate paleoecological interences from the elemental composition of human and faunal bone recovered from archaeological and paleontological sites will depend on controls for postmortem diagenesis. In vivo chemical signatures in bone can be obscured by postmortem changes in the soil environment. Models addressing the fossilization process in bone must consider both ionic substitution and mineralization mechanisms of diagenesis. Current solubility profile techniques for the differentiation of biogenic and diagenetic chemical phases in fossil bone neglect ionic substitution. Ionic soil solution data from an arid-land South Australian archaeological site are represented to demonstrate the importance of such information to the development and testing of these predictive models. Elemental rations in the soil solution are compared with those in rib bone from archaeological human skeletons and modern terrestrial mammal controls. The archaeological bone is enriched with Si, Al, Mn, Ba, Fe, S, Sr, K and Ti and depleted in Mg relative to the modern controls. A variety of processes including contamination with quartz and secondary carbonates and ionic substitution from the soil solution are responsible for these postmortem chemical alterations.