Carbon-Isotope Composition and the Origin of Calcareous Coal Balls.
The C(13):C(12) ratios of the carbonate comprising "normal," "faunal," and "mixed" coal balls are consistent with the hypothesis that calcareous coal balls contain varying proportions of two kinds of carbonate: (i) precipitated carbonate formed in the coal swamp and characteristically deficient in C(13), and (ii) extraneous detrital material, mainly fossil fragments relatively enriched in C(13).
Weber
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Keith
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