I. S. Buick, R. Uken, R. L. Gibson, T. Wallmach; High-δ13C Paleoproterozoic carbonates from the Transvaal Supergroup, South Africa. Geology ; 26 (10): 875–878. doi: https://doi.org/10.1130/0091-7613(1998)026<0875:HCPCFT>2.3.CO;2
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Marbles from the Transvaal Supergroup (Kaapvaal craton, South Africa) record two positive carbon isotope excursions to average δ13Ccarbonate values of ∼+6‰ to +8‰ (relative to V-PDB), separated by carbonates with normal-marine δ13C values (∼0‰ ± 2‰). These elevated values have been preserved through metamorphic devolatilization. Together with an already documented high-13C excursion in overlying rocks, three separate positive carbon isotope excursions occurred on the Kaapvaal craton in the interval 2.43 to 1.93 Ga. It is not yet clear how many of these excursions reflect global rather than local processes.