Can CO2 outgassing explain Lomagundi Excursion?

The Lomagundi-Jatuli event (2.3-2.0 Ga) is one of the grandest carbon isotopic (δ¹³C_carbonate) excursion events in the Earth’s history, marked by anomalous δ¹³C_carbonate reaching up to + 30 ‰. Several hypotheses have been proposed to explain this excursion; however, they remain inadequate due to associated drawbacks. The conventional explanation is organic carbon burial due to enhanced productivity. But, the lack of organic rich stratas synchronous with the excursion demands the reconsideration of alternative biogeochemical processes to explain this isotopic anomaly. Moreover, the excursion is observed only in the evaporitic and nearshore carbonates, with no evidence from open ocean; demanding facies based biogeochemical explanation. Here, we explore the possibility of CO₂ outgassing and calcite precipitation as potential drivers responsible for this excursion as these two processes remain the least explored among the proposed hypotheses. Through sedimentological evidences from previous studies and Rayleigh fractionation calculations, we argue that dominant loss of DIC through CO₂ outgassing in the evaporitic facies and calcite precipitation in the nearshore facies along with a well-mixed DIC reservoir in the open ocean led to observed Lomagundi Excursion.