Oxygen isotope analyses of co-existing carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate?

The oxygen isotopic composition of phosphate (δ18Op) and structural carbonate (δ18Oc) of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries. These two variables are highly correlate (r2 = 0.98) and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations [1,2]. According to previous measurements [3–6] on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between δ18Op and δ18Oc, as is the case with modern samples. It therefore seems possible, at least in some cases, to use these measurements for monitoring fossil bone and tooth diagenetic alteration. When a set of points lie on the equilibrium line or close to it, the δ18O values could be considered close to the original values. In contrast, when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified, due to interaction with meteoric water or18O-enriched water, respectively.