Os and Nd isotope constraints on Paleoproterozoic global events as recorded in sediments from Russian Fennoscandia

Temporal constraints on the rise of atmospheric oxygen have fundamental implications for the trajectory of biological evolution, yet the rate of change of atmospheric O₂ in the aftermath of the Paleoproterozoic Great Oxidation Event is uncertain. Following this rise, the Lomagundi-Jatuli positive carbon isotope excursion (LJE) documents a massive and anomalous disruption to the global carbon cycle (sustained 𝛿¹³C >10‰) for as long as ~260 Myr. The distinctly positive carbon isotope values recorded in marine carbonates throughout the LJE have been interpreted to correspond with a surge in atmospheric O₂, however, the driving mechanisms, duration, and the global versus local extent of the LJE perturbation are poorly understood. The age models have different implications for the operation of global biogeochemical cycles in the Paleoproterozoic and thus it is important to discern between them in order to understand what impact, if any, increasing levels of atmospheric oxygen had on the development of complex life. We use the Re-Os geochronometer to provide direct radiometric age constraints for sedimentary sequences in the Fennoscandian Shield (the Zaonega and Polisarka formations). These sections currently have age uncertainties of several 100 Myr and therefore our improved age constraints critically refine the LJE 𝛿¹³C-time record and the relative temporal placement of events in the Onega Basin. Additionally, the coupling of these new age constraints with Os and Nd isotope stratigraphy enables us to assess cause-and-effect relationships with significant changes to the style of chemical and physical weathering and therefore nutrient delivery to the oceans and the evolution of complex life.