Pulsed atmospheric oxygenation recorded by Mo isotopes and Ce anomalies during Lomagundi Event from Jingshan Group marble of North China Craton

Abstract

The Lomagundi Carbon Event (LE), the large, long-lived Paleoproterozoic positive carbon isotope excursion, is traditionally associated with a significant increase in atmospheric oxygen. However, the magnitude and extent of atmosphere–ocean oxygenation during this critical period of Earth’s history remain poorly constrained. Here, we present molybdenum isotope data and Ce anomaly values of Paleoproterozoic Jingshan Group marble samples deposited coincident with the peak of LE. Analyzed samples are characterized by near-modern seawater δ⁹⁸Mo_carb values (maximum = 2.13 ‰ ± 0.05), crustal Ce anomalies (average = 1.03), and δ⁹⁸Mo_carb values (average = 0.41 ‰). The great variation of Mo isotope values displayed by samples recovered from a thin stratigraphic interval likely reflect the existence of a small Mo reservoir during LE. We suggest that Mo removal from poorly oxygenated oceans under ferruginous conditions was responsible for the contraction of the Mo oceanic reservoir. Mo concentrations and isotope values of deposits coincident with this time interval appear to have been controlled by iron and manganese oxides shuttle. Placed in the context of Earth’s oxygenation history, our findings suggest that O₂ levels of the atmosphere–ocean system remained much less (1 % PAL) than the present level with occasional episodes of increased or pulsed atmospheric oxygen during the peak of LE.