Earth’s oldest terrestrial red beds as direct evidence for the Great Oxidation Event ca. 2.3 Ga

Abstract

Reconstructing the trajectory of Earth’s initial rise of atmospheric oxygen (i.e., the Great Oxidation Event, GOE) remains a significant but important challenge due to the intricate connections between oxygen and life. Further refinement in our understanding of the GOE requires establishing tighter links between geochemical and mineralogical oxygenation proxies specifically in terrestrial environments where signals reflect oxygen accumulation beyond realms of localized production. The appearance of terrestrial red beds in the Paleoproterozoic rock record is oft-cited evidence for the GOE; however, there is a lack of robust evidence that establishes Fe(III)-(oxy)(hydr)oxides (now hematite) as a primary clastic sedimentary feature, and often insufficient stratigraphic and geochronological context to link red beds to other oxygenation proxies. This study revisits the transition from the youngest detrital pyrite- and uraninite-hosting terrestrial (alluvial-fluvial) strata to the oldest reddened fluvial strata in the ca. 2.45–2.22 Ga Huronian Supergroup, with the aim to directly link the mineralogy of the latter deposits to environmental oxygenation and thus the GOE. Key fluvial sandstone units preserve hematite as rims of “dust” on detrital quartz encased by epitaxial quartz overgrowth cements, providing unequivocal evidence for Fe(III)-(oxy)(hydr)oxide adhesion to detrital quartz during early meteoric diagenesis, and thus indicating terrestrial Fe oxidation pathways were more widespread than oxidized paleosols formed at this time. Geochronological constraints place the appearance of these terrestrial red beds at ∼2.31 Ga, timing that closely matches with the S-isotope evidence for the GOE in correlative strata of the Transvaal Supergroup. The S-isotope and red bed proxy records show promise for a closely coupled oxygenation threshold, with the advantage that they are typically preserved in different depositional environments.