Combined Nitrogen‐Isotope and Cyclostratigraphy Evidence for Temporal and Spatial Variability in Frasnian–Famennian Environmental Change

Widespread marine anoxia triggered by the runoff and recycling of nutrients was a key phenomenon associated with Frasnian–Famennian (FF) mass extinction. However, relative importance global-scale processes versus local influences on site-specific environmental change remains poorly understood. Here, nitrogen-isotope (δ15N) trends are combined organic-biomarker, phosphorus, Rock-Eval data in FF sites from USA (H-32 core, Iowa), Poland (Kowala Quarry), Belgium (Sinsin). Up-to-date cyclostratigraphic age models for all three allow nature timing changes to be precisely compared across globe. Negative δ15N excursions interval H-32 core Kowala correlate geochemical evidence euxinic, phosphorus-rich, water columns, possible cyanobacterial activity, suggestive increased diazotrophic N fixation, potentially coupled ammonium assimilation at latter site. By contrast, previously studied Western Canada South China document enhanced water-column denitrification around onset Upper Kellwasser (UKW) Event, re-emphasizing geographical heterogeneity perturbations that time. Moreover, degradation began >100 kyr earlier Poland, coeval major increase bioavailable phosphorus supply, than Iowa, where no such influx is recorded. These regional differences both during likely resulted variable terrigenous different basins time, highlighting as terrestrial driving times climate cooling UKW Event.