Post-depositional alteration

Despite the inherent problems associated with in speleothems, recent work by Beck et al. (2001) has focused attention on this topic because they demonstrated that in certain circumstances the dcp correction may be sufficiently well constrained that calibration of the radiocarbon timescale might be possible. Speleothems have an advantage over marine corals (e g., Bard et al. 1990, 1998 Edwards et al. 1993), which have been used to extend the calibration curve, because they provide continuous records and are less likely to be affected by post-depositional alteration. Beck et al. (2001)... 

Even Ca, the element we used to normalize all our other measures, may be subject to post-depositional alteration. Moreover, such alteration may vaiy depending on local environmental conditions. Such a factor may account for some of the overlap or blurring we see between regional elemental signatures in our prehistoric samples. Without knowing exactly how much change may have taken place in Ca concentrations in different burial conditions, it is difficult in such sourcing studies to account for this possibility. 

In sum, the ICP-MS analyses suggest that Olivella shells are subject to fairly significant post-depositional alteration as shells are exposed to midden soils over hundreds to thousands of years. While discouraging, it does not preclude the application of elemental compositional studies for shell-bead sourcing. Some elements, such as Sc, Zr, and Al, among others not discussed in detail here, remain fairly constant when taken as ratios against Ca. It is these elements that should be the subject of provenance analyses and that we will target in future research with Olivella shell. 

The elemental contour maps serve to demonstrate that measurable differences between the painted and the slipped areas exist on pottery from the Mesa Verde region. Enrichment of certain metals (Mn, Cu, Ag, Pb) in the organic-painted sherds clearly does not result from diagenesis (post depositional alteration) but instead reflects differences in paint that are related to one or more... 

Fig. 16. Post depositional alteration of Isuaspheres included in the Isua quartzite, i. Before recrystallization of the chert matrix 2, 3. After recrystallization, 4. Higher magnification of one single Isuasphere that remained as a cavity in the quartz grain after leaching of the carbonaceous matter through the fissure fp = imprint of the sheathal structure in the wall of the cavity, c = carbonate. Bar for Figs. 1-3 see left of Fig. 1, for Fig. 4 see above the Fig. (Pflug, 1985)18>...

McArthur J. M. (1980) Post-depositional alteration of the carbonate-fluorapatite phase of Morocccan Phosphates. In Marine Phosphorites. Spec. Publ. 29 (ed. Y. K. Bentor). SEPM, pp. 53-60. 

The 813Ccarbonate record has remained fairly constant, and 513Ccarbomte values do not appear to be affected by post-depositional alteration (Veizer et al. 1992). So if it is assumed that 813C has likewise remained reason-... 

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