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

Abstract

The Upper Kellwasser (UKW) Event featured one of the "Big Five" Phanerozoic mass extinctions, during the Frasnian-Famennian (FF) transition (∼372 Ma), alongside worldwide environmental disturbances (see Carmichael et al., 2019). The event began ∼150 kyr prior to the end of the Frasnian Stage (De Vleeschouwer et al., 2017),

Lipid biomarkers recording marine microbial community structure changes through the Frasnian‐Famennian mass extinction event

“…In our samples, isorenieratane and paleorenieratane are not detected (expected when T max ≥ 438°C; Requejo et al, 1992), but the δ 13 C values of aryl isoprenoids are more positive relative to those of algae‐derived, short‐chain n ‐alkanes (Figure 6), confirming that aryl isoprenoids were produced via the reductive tricarboxylic acid (TCA) cycle used by Chlorobium (Koopmans et al, 1996; Summons & Powell, 1987). Previous studies of the F‐F strata from the Illinois Basin and neighboring Appalachian Basin detected both aryl isoprenoids and isorenieratane, supporting green sulfur bacteria as the biological source of isoprenoids (Haddad et al, 2016, 2018; Percival et al, 2022). The highly variable but overall elevated TOC‐normalized aryl isoprenoid concentrations through the extinction interval (Figure 4) indicate a more intensive photic euxinia zone (PZE) in the Illinois Basin.…”

“…Our observation is consistent with PZE biomarkers extensively detected in strata from Late Devonian epicontinental seas and basins worldwide, including Europe, North America, South America, and Africa (Lu, Lu, Ikejiri, Sun, et al, 2021), although the onset, tempo, and magnitude of PZE appear to vary spatially. For example, Percival et al (2022) reported a concentration peak of isorenieratane below the F‐F boundary in the Kowala section (Poland) and a smaller peak at the F‐F boundary in a drill core from the Illinois Basin (Iowa). Lu, Lu, Ikejiri, Sun, et al (2021) observed that the variation in PZE biomarkers from the Appalachian Basin exhibited precession‐driven cyclicity during the UKW.…”

“…Haddad et al (2016) did not observe evident increases in 2α‐methylhopane concentrations within the F‐F strata located in both the Appalachian Basin and Madre De Dios Basin. Percival et al (2022) analyzed 2α‐MHIs from the F‐F strata deposited in the Illinois Basin (Iowa) and Chęciny–Zbrza Basin (Kowala Quarry, Poland). Although they highlighted positive shifts in the index below the F‐F boundary, the shift from the Illinois Basin is small (<5%), which is consistent with our finding.…”

“…The discussion of 2α‐MHI is frequently linked to changes in sedimentary δ 15 N values because both proxies are relevant indicators of N‐cycling processes (Haddad et al, 2016; Percival et al, 2022). Bulk sedimentary δ 15 N values usually reflect δ 15 N of marine dissolved inorganic nitrogen (DIN).…”

“…These shifts often reflect N perturbations, which appears to depend on local factors and processes because shifts of variable magnitudes, directions, and durations have been documented throughout the F‐F transition (Carmichael et al, 2019). For example, negative excursions were observed in the Illinois Basin (Iowa) and Chęciny–Zbrza Basin (Poland) across the F‐F boundary, which have been attributed to either increased nitrogen fixation or reduced denitrification (Percival et al, 2022). Positive excursions were observed at the onset of the UKW event from the basins of Western Canada and South China, and they were thought to be a result of the increasing importance of denitrification in the N cycle (Whalen et al, 2015).…”