Abstract:

The Archean 2.7Ga Abitibi volcanic belt has many locations where organic kerogenous/graphitic carbon is preserved. Carbon isotope values of -45‰ have been interpreted to result from incorporation of 13C-depleted CO2 that is derived from methane oxidation. New analyses found in the whole Abitibi complex variations from -20 to -45‰ and even in one location variations of 8‰ which are very difficult to interpret. Three models will be discussed

1) Yellowstone model: pCO2 controlled variations

2) Various degrees of methane oxidation

3) Florida seep model: Mixing of methane-derived organic matter with background carbon.

All models are unsatisfactory, each for different reasons.