Recrystallization of dolomite: evidence from the Monterey Formation (Miocene), California

摘要: Dolomites from the upper calcareous-siliceous member of Miocene Monterey Formation exposed west Santa Barbara, California, were analysed for geochemical, isotopic and crystallographic variation. The data clearly document progressive recrystallization dolomite during burial diagenesis in marine pore fluids. Recrystallization is recognized by following compositional variations. have decreasing δ18O δ13C compositions, Sr contents increasing Mg with depths temperatures east to study area. values vary 5·3‰ − 5·5‰ PDB are interpreted reflect greater extent higher temperature west. correlate decrease 13·6‰ 8·7‰ concentrations positively a mean 750 ppm 250 Mol% MgCO3 inversely increase minimum 41·0 maximum 51·4 west. Rietveld refinements powder X-ray diffraction indicate that more recrystallized dolomites contracted unit cells increased cation ordering. fraction Ca sites occupied atoms increases slightly approach stoichiometry. strongly correlates mol% MgCO3. Even early diagenetic, non-stoichiometric dolomites, there little substitution sites. During recrystallization, amount substituting decreases even further. Most disorder least recrystallized, related excess on