A pulse of seafloor oxygenation at the Late Devonian Frasnian-Famennian boundary in South China

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

“…Additionally, positive δ 15 N excursions recorded at Section C and Fuhe suggest increased importance of water‐column denitrification versus N fixation, rather than the other way around, in the Western Canada and Yangshuo basins during the onset of the UKW Event (Whalen et al., 2015; see also Figure S6 in Supporting Information ). Increased seawater oxygenation during the FF transition has also been proposed for the Yangshuo region (Cui et al., 2021). Furthermore, no major nitrogen‐cycle perturbation is documented by sedimentary δ 15 N records in FF boundary strata of the Madre de Dios Basin (Bolivia, Pando X‐1 core; Haddad et al., 2016), although this archive is stratigraphically incomplete due to the preservation of thick sandstone units within the studied interval.…”

Geochemical and Hydrographic Evolution of the Late Devonian Appalachian Seaway: Linking Sedimentation, Redox, and Salinity Across Time and Space

“…The observed trend is consistent with a shift from MSR and pyrite formation mostly in pore waters in the lower Cleveland Shale (i.e., a more closed system where less isotopic fractionation is expressed) to MSR and pyrite formation in a more persistently euxinic water column for the upper Cleveland Shale, expressed by larger degrees of isotopic fractionation between sulfate and sulfide (Lyons, 1997; Gomes & Hurtgen, 2015). Sulfur isotope studies of carbonate‐associated sulfate and sulfate evaporites suggest δ 34 S values of seawater sulfate between +20 and +30‰ during the Famennian, slightly heavier than modern seawater (Claypool et al., 1980; Cui et al., 2021; John et al., 2010; Kampschulte & Strauss, 2004; Strauss, 1997). In the upper Cleveland Shale, δ 34 S py values are consistently lower than −30‰ across all six cores with values as low as −43‰, indicating fractionation up to 60‰ or higher from seawater sulfate, which is approaching the limit of MSR observed in culture experiments (Sim et al., 2011).…”