Astronomical climate forcing of ~2.5 Ga banded iron formations

Large-scale banded iron formations (BIFs) were deposited during Neoarchean to early Paleoproterozoic and have been mainly linked to hydrothermal plume activity and the rise of oxygen in the ocean and atmosphere. However, the potential influence of astronomical “Milankovitch” forcing on their deposition has been largely neglected so far and was hindered by large uncertainties in BIF depositional rates. In a recent study, we showed that outcrops of the ~2.5 Ga Kuruman Banded Iron Formation (BIF) in South Africa reveal a characteristic pattern in weathering profile that can be laterally traced over ~250 km (Lantink et al., 2019)*. Cyclostratigraphic analysis combined with high-precision U-Pb dating indicated that this pattern reflects a hierarchy of two superimposed cycles linked to the 405 kyr and a 1.2 - 1.6 Myr eccentricity cycle. This pattern is mirrored in magnetic susceptibility and high-resolution XRF core scan data of a new drill-core through the Kuruman BIF, providing insight into the chemical variations and may be used for cyclostratigraphic correlations to the broadly time-equivalent6 Australian Dales Gorge Member BIF. Furthermore, the dominance of eccentricity implies that precession-related cycles should be visible as well within the BIF stratigraphy and may be used to reconstruct the Precambrian evolution of the Earth-Moon distance. *https://doi.org/10.1038/s41561-019-0332-8 Lantink-Astronomical climate forcing of ~25 Ga banded iron formations_Info.pdf