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

Geochimica et Cosmochimica Acta
By:  and 
https://doi.org/10.1016/0016-7037(71)90068-8

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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 CaCO3 to Ca0.5Mg0.5CO3. Dolomite yields both the {006} and {015} diffraction maxima over its entire composition range, Ca0.6Mg0.4CO3 to Ca0.5Mg0.5CO3. The Ca-Mg carbonates form in isotopic equilibrium and thermodynamic disequilibrium from dispersion of Ca2+-rich water into CO32−-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 CaCO3. There is a correlation between δC13 and Mg content of the carbonates which predicts a 5%. fractionation of C13 between dolomite and calcite at sedimentary temperatures. C14 is incorporated in Ca-Mg carbonates forming from C13-poor meteoric waters and C13-rich waters from Cretaceous sediments. C14 ages of the Ca-Mg carbonates are apparent, and cannot be corrected to absolute values. Solution rates of calcite decrease with increasing MgCO3 content; dolomite dissolves slower than any calcite.

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    Publication type Article
    Publication Subtype Journal Article
    Title Calcium-magnesium carbonate solid solutions from Holocene conglomerate cements and travertines in the Coast Range of California
    Series title Geochimica et Cosmochimica Acta
    DOI 10.1016/0016-7037(71)90068-8
    Volume 35
    Issue 7
    Year Published 1971
    Language English
    Publisher English
    Description 20 p.
    First page 699
    Last page 718
    Country United States
    State California
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