Prehistory of the Lomagundi–Jatuli Event in the Karelian Craton: Lithology of the Jatulian Terrigenous Rocks in the Segozero Structure

Terrigenous sedimentation conditions and provenance in the Segozero structure, Karelian Craton, which predates the Lomagundi–Jatuli Event (LJE) (2.20–2.06 Ga) are deciphered based on lithology, geochemistry, and U–Th–Pb zircon geochronology. The section of this structure is a stratotype of the Jatulian Group, which comprise three formations (from bottom to top): Jangozero, Medvezhegorsk, and Tulomozero, each consisting of two units. Their lower parts consist of terrigenous rocks, whereas the upper parts are composed of basalts of the Jangozero and Medvezhegorsk formations and carbonates of the Tulomozero Formation. The lower terrigenous unit (Jangozero Formation) is composed of quartz sandstones with shales interbeds, which are anomalously enriched in Al2O3, K2O, TiO2,Th, Nb, Zr, REE, W, and Ga, and contains zircon with the age of ~2.7 and 2.9 Ga. Granitoids of the Vodlozero domain, which were altered in situ to lateritic paleosoil, were the sources of these rocks. The homogeneity and a large volume of the lower terrigenous unit suggest a significant thickness of the pre-Jatulian paleosoil on the Karelian Craton, indicating high atmospheric oxygen content prior to the LJE. The middle terrigenous unit (Medvezhegorsk Formation) is composed of quartz and arkose sandstones with siltstone and mudstone interbeds, which formed as a result of erosion of weakly weathered granitoids with age of 2.7 Ga, probably, upon active extension and increasing the depth of the basin. The upper terrigenous unit (Tulomozero Formation) combines geochemical characteristics of the lower and middle terrigenous units with a significant contribution of mafic material and could have formed during erosion and redeposition of the underlying sedimentary rocks and basalts. The lithology of terrigenous rocks indicate the predominance of fluvial processes during sedimentation and formation of an alluvial–deltaic succession and a general transgressive trend. The lithology of terrigenous rocks and their association with basaltic volcanism indicate a rifting environments of the Jatulian basin. The reconstructed NW direction of material transport by channel flows is correlated with NW orientation of the rift. The data on oxygen-rich atmosphere and intracontinental rift evolution of the Jatulian basin, which accumulated carbonate rocks of the Tulomozero Formation with positive δ13C values, are additional arguments in favor of canonical LJE model and a leading role of regional factors responsible for this event.