On Mon, 29 Sep 1997, Mark Leney <[log in to unmask]> wrote:

> I was interested in the comments about Sr/Ca ratios in fossils and
> stable isotope work in general. Andrew Millard suggested that there are
> difficulties in interpreting the signals.
.......
> Can Dr Millard, (or anyone else) fill us in or cite some of the up to
> date references so we (I) can read some of the criticism of this provoking
> work.

OK my major criticism is contained in the project proposal for my new PhD
student, whose work will include:

  a critical analysis of Sillen's solubility profile technique for
  obtaining palaeodietary information from Sr/Ca and 87Sr/86Sr
  ratios of bone through selectively leaching of mineral phases of
  differing solubility. The actual phases dissolved have never been
  identified, which casts some doubt over the validity of the technique,
  even though it has produced some convincing results.

My own studies of bone crystallinity suggest that in many cases the
solubility behaviour ought not be as simple as it appears to be in
Sillen's system.  I have also heard a paper presented by one of his
co-workers, but as far as I know not published yet, where they examined a
worst case scenario of a terrestrial animal buried in marine sediments,
and showed that its Sr isotope ratio was altered to that of the sediments
in bone, dentine and tusk, but not in enamel, but the enamel showed
variation in isotope ratio through the solubility profile.

There is very strong evidence from stable isotope and radiocarbon studies
that the carbonate in bone mineral is fairly readily exchanged with the
environment and the increases in U and F content of bone with time have
been well known for a century or more.  Whilst U uptake does not
necessarily involve the interior of bone mineral crystals, F uptake does
and so does the increase in crystallinity of bones which is widely
observed.  Processes invlolving the interior of crystals can only be
happening on archaeological timescales if they involve dissolution and
reprecipitation of the crystals, and this process will open them up to
exhange of all trace elements with percolating groundwaters.

I think that there is no reason why one of the solubility compartments in
Sillen's work should contain only biogenic material as the dissolved
material in a single wash will contain some newly dissolving crystals,
surface etching of other crystals and the interior parts of crystals
previously etched.

In short I cannot see why the Sillen Solubility Profile method should
work, but as you say it appears to give good results separating carnivores
and herbivores.

I hope this has not been too technical for the list.  I was asked to
provide a criticism, which I don't believe is in print anywhere, though
parts of the above are.  9 years in bone diagenesis studies has made me
sceptical of any technique which claims to overcome diagenesis in general,
as it is such a multifaceted thing.

Andrew

 =========================================================================
 Dr. Andrew Millard                              [log in to unmask]
 Department of Archaeology, University of Durham,   Tel: +44 191 374 4757
 South Road, Durham. DH1 3LE. United Kingdom.       Fax: +44 191 374 3619
                      http://www.dur.ac.uk/~drk0arm/
 =========================================================================