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Jens,
Here is another reference related to the dolomitizing fluids using stable isotope techniques:

Yang W., Spencer R.J. and Krouse H.R. (1995) Stable isotope and major element compositions of fluid inclusions in Cambrian and Devonian dolomite cements, western Canada, Geochim. Cosmoch. Acta, v.59, p.3159-3172.

Wenbo Yang

At 03:31 PM 11/27/2001 +0100, you wrote:
Dear all,
I've been asked by a student (Dirk Sachse,[log in to unmask]) to
forward this question to the list,
Jens

Dear list members,

I analysed d18O and d13C of a dolomite core (lagoonal, southern margin
of
the Zechstein basin, E-Germany). The data show quite clearly that the
isotopic
values are derived from initial water isotopic composition (controlled
by
evaporation and freshwater inflow; correlate with lithology, high d18O
in
anhydrit bearing horizons, low d18O in shales; d13C shows opposite
behaviour)
.

So I'd like to calculate the initial isotopic composition of the
lagoonal
water (assuming a temperature range). I found several equations for the
fractionation
of d18O in water vs.
dolomite (Land, 1983). They seem to give reasonable values (0 to 4
VSMOW)
  for temperatures around 30C.
But, since the sediment was deposited as calcite first (assuming the
brine
reflux model) these equations don't give me information about the
initial
water but about the dolomitizing fluids.

So, what exactly happens especially to oxygen isotopes during
dolomitization
of calcite by hypersaline brines? Are there any references?

Thank you,
Dirk.

*****************************
Wenbo Yang, PhD.
Earth & Planetary Sciences
Harvard University
20 Oxford Street
Cambridge, MA 02138

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