Table 1

Carbon data from the Isua supracrustal belt. Samples 810212, 810213, and 810214 are from sedimentary rocks; samples 930049 and 930055B are from a sedimentologically unconstrained outcrop; and samples 810227 and 810228 are from a discordant graphite vein that crosscuts talc schist. Samples were finely ground in agate and decarbonated in hot HCl. Carbon was converted to CO2 in an oxygen furnace at 1000°C and analyzed by standard procedures at the Danish Center for Isotope Geology (26). Values of δ13C are referenced to the Pee Dee belemnite standard.

SampleTypeReduced C (weight %)δ13C (per mil)
810212Turbidite graywacke0.1−19.07
810214Mica schist0.3−18.77
930049Garnet-biotite schist0.9−14.10
930055BMicaceous quartzite0.2−20.21
810227Graphite vein0.4−12.58
810228Graphite vein1.0−11.40