Sedimentary dynamics and sources at the “Tsunami conglomerate locality” (Fig Tree Group, 3.28–3.23 Ga, Barberton Greenstone Belt, South Africa)

• 3.28 Ga Mapepe Formation records deep-water hemipelagic sedimentation. • Dominantly mafic–ultramafic sources with subordinate felsic contributions. • Chert-plate conglomerate generated by gravity-driven flows in deep-water basin. • Ce anomalies in Mapepe BIF reflect late goethite-related alteration. To illustrate the peculiarity of early Earth sedimentary dynamics and terrigenous pathways to the first oceans, a detailed sedimentological, petrographical, and geochemical study was conducted on a 40 m succession of the 3.28–3.23 Ga Mapepe Formation in the Barberton greenstone belt (South Africa). The “Tsunami conglomerate locality” includes terrigenous sediments (sandstones, conglomerates) and chemical sediments consisting of banded ferruginous chert (BFC) and banded iron formation (BIF). These deposits reflect a deep-water hemipelagic depositional system dominated by chemical sedimentation, punctuated by discrete terrigenous lobes and slope aprons. The 4.5-m-thick chert-plate conglomerate, known as the “Tsunami conglomerate”, represents high-density flow deposits, indicating gravity-driven instabilities near an abyssal plain. Although it lacks petrographically identifiable terrigenous material, these gravity-reworked BFC deposits exhibit a trace element signature indicating 10 % terrigenous inputs. Trace element signatures of terrigenous rocks indicate a source of 70 ± 10 % (ultra)mafic (75 % basalt, 25 % komatiite) and 30 ± 10 % felsic volcanic material, likely from erosion of the (ultra)mafic Onverwacht Group and related felsic volcanic deposits. These findings fill a gap in sample representativeness at the base of the Mapepe Formation in the Lower Manzimnyama Jaspillite Syncline and challenge previous interpretations of a gradual provenance shift from felsic to mafic sources. Instead, they suggest a predominantly mafic–ultramafic source for most of the Mapepe Formation, except for the lowermost Loenen Member, which consists almost entirely of felsic volcaniclastic material. Finally, most BFC, BIF, and terrigenous-rich units at the studied locality display highly variable Ce anomalies, suggesting that these rocks experienced syn- or post-depositional oxygenated conditions. In-situ analyses indicate that positive Ce anomalies are generally associated with goethite-rich cements, whereas negative anomalies are linked to sericite-(+/- rutile)-rich cements. The preferential distribution of Ce anomalies in secondary minerals demonstrates that these redox features were likely not acquired during sediment deposition, but rather during post-depositional history.