Calcium-magnesium carbonate solid solutions from Holocene conglomerate cements and travertines in the Coast Range of California

I. Barnes; J. R. O’Neil

doi:10.1016/0016-7037(71)90068-8

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Calcium-magnesium carbonate solid solutions from Holocene conglomerate cements and travertines in the Coast Range of California

I. Barnes·J. R. O’Neil

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Abstract

Two calcium-magnesium carbonate solid solutions form Holocene travertines and conglomerate cements in fresh water stream channels of the Coast Range of California. Calcite does not yield the {015} diffraction maximum. The {006} diffraction maximum is lacking over most of the range of composition of calcite. Calcite has compositions from CaCO 3 to Ca 0.5 Mg 0.5 CO 3 . Dolomite yields both the {006} and {015} diffraction maxima over its entire composition range, Ca 0.6 Mg 0.4 CO 3 to Ca 0.5 Mg 0.5 CO 3 . The Ca-Mg carbonates form in isotopic equilibrium and thermodynamic disequilibrium from dispersion of Ca 2+ -rich water into CO 3 2− -rich water within the alluvium. The stable isotope data suggest that all the Mg-rich carbonates are primary precipitates and not a result of Mg-substitution in precursor CaCO 3 . There is a correlation between δC 13 and Mg content of the carbonates which predicts a 5%. fractionation of C 13 between dolomite and calcite at sedimentary temperatures. C 14 is incorporated in Ca-Mg carbonates forming from C 13 -poor meteoric waters and C 13 -rich waters from Cretaceous sediments. C 14 ages of the Ca-Mg carbonates are apparent, and cannot be corrected to absolute values. Solution rates of calcite decrease with increasing MgCO 3 content; dolomite dissolves slower than any calcite.

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Geochimica et Cosmochimica Acta Article

Source-reported bounding extent: 32.534156° to 42.009247° latitude; -124.409591° to -114.134768° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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I. Barnes, J. R. O’Neil. 1971. Calcium-magnesium carbonate solid solutions from Holocene conglomerate cements and travertines in the Coast Range of California. https://doi.org/10.1016/0016-7037(71)90068-8

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