Alteration of Enamel Carbonate Environments during Fossilization

Abstract

An understanding of enamel diagenesis is necessary to ensure sound isotopic palaeodietary and palaeoenvironmental reconstructions. Although carbon isotope signals of browsing and grazing herbivores remain distinct in enamel even after millions of years, subtle alteration of isotopic signatures does occur. To better understand this change we analysed modern and fossil enamel from a number of South African sites using Fourier Transform Infra-Red spectroscopy. Our results indicate that while there is little evidence of increased crystallinity in fossil enamel, there is a small but significant change in the proportion of carbonate ions occupying hydroxyl and phosphate sites. This seems to occur early in the process of fossilization, after which there is no noticeable change. It is also important to note that the degree of alteration varies significantly within and between sites. We suggest that this change results from one or some combination of three mechanisms: exogenous carbonate incorporation, endogenous carbonate loss, and endogenous carbonate reorganization. Determining which mechanism(s) contribute to this alteration is important because all three are likely to affect biogenic carbon isotope ratios differently. FTIR spectroscopy promises to increase our knowledge of diagenesis, and in so doing, should improve our palaeodietary and palaeoenvironmental reconstructions.