This study conducted the geological fieldworks in Gabon, and investigated the detailed litho-, bio-, and chemo-stratigraphy of the Paleoproterozoic sedimentary basins that yields the putative oldest eukaryotic fossils. The depositional environment of the fossil horizons in the Franceville Basin was clarified to be relatively anaerobic. The local high-radiation setting by the uranium-concentrated bed possibly accelerated the evolution of eukaryotes. In the Lastoursville Basin, the continuous δ13Ccarb stratigraphy was newly established, and a negativeδ13Ccarb shift was identified across the fossil appearance. This negative shift may correspond to the terminal Lomagundi Excursion and suggests that the appearance of eukaryotes dramatically changed the global oceanic carbon cycle.
