Letter | Published:

Stable Carbon Isotope Ratios within Carbonate Concretions: a Clue to Place and Time of Formation


NATURALLY occurring carbon shows considerable variability with respect to its stable isotope composition. The 13C/12C ratio in plant material (and in ancient residues) is generally roughly 2.5% lower than in the carbonate of marine limestones as a result of fractionation during photosynthesis. A summary of carbon isotope distribution and fractionation is given by Degens1.

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    Degens, E. T., Geochemistry of Sediments, a Brief Survey (Prentice-Hall, New Jersey, 1965).

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