Abstract
High δ 13 C values of up to 12‰ (PDB) occur in two-billion-year-old high-grade marbles from Lofoten-Vesterȧlen, Norway. Correlations of high δ 13 C with high δ 18 O of up to 25‰ (SMOW) suggest that premetamorphic δ 13 C values were above 10‰ (PDB) over a broad area. These marbles are associated with graphite rich schists, often containing in excess of 25 wt% carbon and having δ 13C ∼ −25‰ (PDB). A compilation of data in the literature suggests that the deposition of limestones with isotopically heavy carbon was common at around 2.0 Ga. The data are consistent with worldwide or localised positive excursions in the δ 13 C of marine bicarbonate. Positive excursions in δ 13 C of seawater at this time may have coincided with a transition to a more oxidising atmosphere and ocean.
Published Version
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