Supplementary Online Material
Water-rock modeling of Neoproterozoic carbonates
We adapt the approach of Banner and Hansen (1990) to explore how isotopic
compositions (both rock and fluid) and temperatures would evolution during closed-system
diagenesis. The interpretation of closed-system behavior arises from the positively correlated
array in Figures 4-7 of the main text. A similar approach has been applied by Huntington et al.
(2011) and Bergmann et al. (2011). The model utilizes the following equations:
o = [(f,o)(Cf,o)F + (s,o)(Cs,o)(1–F)]/Co
s = [(o)(Co)(s–f) – (1000(Cf)F(1–s–f)]/[(Cs)(1–F)(s–f) + Cf(F)]
f = [(s + 1000)/s–f] – 1000
where, o, s, f, f,o and s,o correspond to the oxygen isotopic composition of the total system,
solid phase (here, either calcite or dolomite), fluid phase, initial fluid and initial solid phase. Cf,o,
Cs,o, Co, Cf, and Cs are the concentration of oxygen in the original fluid, original solid, total
system (all oxygen in all phases), fluid and solid. Here, we assume that Cf,o = Cf and Cs,o = Cs
because the oxygen concentrations of the different phases is not expected to change, only their
isotopic compositions. F represents that fraction of fluid in the total system (in weight fraction).
s–f correspond to the equilibrium fractionation factor between solid and fluid in the system.
Here, the phases correspond to solid carbonate and H2O between which, the fractionation is
temperature dependent (Kim and O’Neil, 1997; Vasconcelos et al., 2005). The specific input
parameters that yield the contours (Figures 5-7 main text) are provided below. The results are
shown in Figures 5-7 in the main text.
Input Parameter
Cs (calcite) (mol)
Cs (dolomite) (mol)
Cf (mol)
o,s (‰, VPDB)
o,f (‰, VSMOW)
W/R Range (g/g)
Co Range (mol)*
F Range (g/g)*
Temperature Range (°C)
Range
Value
0.48
0.55
0.89
0
0, -10, -15
0.01 to 1
0.484 to 0.720
0.01 to 0.5
0 to 400
0.994 to 1.037
Model input parameters. Note that Co and F are dictated by the W/R ratio.
References
Banner, J.L., Hanson, G.N. (1990) Calculation of simultaneous isotopic and trace element
variations during water-rock interaction with applications to carbonate diagenesis. Geochim
Cosmochim Acta 54, 3123–3137.
Bergmann, K.D., Eiler, J.M., Fischer, W.W., Osburn, M.R., Grotzinger, J.P. (2011) The clumped
isotopic record of Neoproterozoic carbonates, Sultanate of Oman. AGU Annual Meeting
Abstract #B41F-0255, San Francisco, CA.
Huntington, K.W., Budd, D.A., Wernicke, B.P., Eiler, J.M. (2011) Use of clumped-isotope
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Kim, S.-T., O’Neil, J.R. (1997) Equilibrium and non-equilibrium oxygen isotope effects in
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