Diagenesis of Strontium in Fossil Bone: A Reconsideration of Nelson et al.(1986)

Abstract

In experiments on marine animal fossils that had been buried in terrestrial sediments, Nelson et al.(1986, Geochimica et Cosmochimica Acta 50:1941-1949) reported that the strontium (Sr) of prehistoric bone had nearly completely exchanged with that of the burial environment, and therefore cannot be used for paleodietary reconstruction. However, Sealy et al.(1991, Journal of Archaeological Science 18:399-416), using a solubility profile procedure, reported that it was possible to remove diagenetic Sr and obtain biologically meaningful Sr. Nevertheless, the Nelson et al.study is often cited as evidence that a biological signal is irretrievable. Here infra-red spectrometry, XRD spectrometry and elemental analyses were used to compare the effects of the Nelson et al.protocol with the solubility profile protocol on the crystal structure and crystallinity of the bone and fossil specimens. The results show that the procedures used by Nelson et al., which include a preliminary ashing step, result in severe recrystallization of apatite both before and during the leaching step, which deleteriously affects any attempt to recover biological Sr. By contrast no observable recrystallization takes place in the solubility profile procedure. The results imply that the conclusions reached by Nelson et al.are primarily artefacts of the specific methods used in their study, rather than due to any inherent mechanism of diagenesis.