18 D5. Sedimentology, Stratigraphy, and Paleontology

Monday, 15 March 2021
1:30 PM - 5:50 PM
Portland

PRELIMINARY ANALYSES OF Δ15N IN THE SHALLOW APPALACHIAN BASIN ASSOCIATED WITH THE LATE DEVONIAN MASS EXTINCTION EVENT

Paper number: 18-18
Program: Technical Sessions
Time: 5:10 PM – 5:20 PM

Authors

Abstract

The Frasnian-Famennian (F-F) mass extinction occurred in the middle of the Late Devonian (~372.36 ± 0.053 Ma) and consisted of two pulses, the Lower and Upper Kellwasser events (LKW and UKW). During this time, over two-thirds of marine species and up to 21% of marine families were extirpated. Moreover, the decline in species diversity was exacerbated by overall low origination rates.

Previous studies suggest relatively low oceanic oxygen throughout the Kellwasser events in association with negative shifts in 𝛿15N. Work in deeper portions of the Appalachian Basin suggest that intermittent low oxygen conditions occurred during the Kellwasser events, as well as extended shifts in marine nitrogen cycling throughout the extinction intervals. Nitrogen cycle perturbations have been used as indicators of oceanic anoxic events in deep time, with antithetic positive shifts in C/N ratios and negative shifts in 𝛿 15N . Preliminary data from more onshore stratigraphic sections suggest a negative shift in 𝛿15N values with corresponding positive shift in C/N ratios potentially associated with reduced oxygen conditions and a shift in sources of marine nitrogen. Understanding nitrogen cycling is critical for discerning sources of dysoxia within the onshore portions of the basin during the F-F extinction. This can lend itself to interpreting a history of eutrophication, anoxia and terrestrial input from actively uplifting adjacent highlands.

Geological Society of America Abstracts with Programs. Vol. 53, No. 1

doi: 10.1130/abs/2021NE-361740

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