The smectites were formed under ambient conditions. The dD is about -115/ -120 and d18O about 24/21 per mil. Those values are consistent with very cold waters. Does anyone have found something similar?
What is the water source? Temperature alone may not be the explanation for those values. There could also be a precipitation "amount effect" playing a role here, Rayleigh fractionation, kinetic isotope effects, disequilibrium, etc. You first need to independently establish that equilibrium effects were probably at work when the smectites formed, in order to draw any conclusions about the temperature at which they formed. Also... post-depositional alteration can complicate things.
Dear Brian, thanks for your answer, I have tried all the explanations you mentioned and still I can´t find a clue. Moreover, the smectites are patches included in a halloysite mass which isotopes values are about 19 and -70 (dO and dD respectively)...
I have a lot of work ahead.
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