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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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