138-6 Fishing through the fallout: Oxygen isotope analyses of fish remains to test for post-impact warming at the K–Pg boundary, Stevns Klint, Denmark

Session: The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms

Presenting Author:

Authors:

Abstract:

The asteroid impact at the Cretaceous–Paleogene (K–Pg) boundary triggered mass extinctions and abrupt climatic perturbations. Model simulations suggest a severe impact winter forced by soot, dust and/or stratospheric aerosols with cooling effects but short atmosphere residence times that may have been followed by a centuries to multi-millennia long interval of greenhouse warming. The timing, duration, and reality of these post-impact events, though, remain poorly constrained due to the difficulty of resolving very short intervals in the geologic record and because taxonomic turnover and diagenetic concerns that challenge assumptions made in reconstructing temperature history from calcareous microfossils are considerable in many early Danian deposits. Measurement of the 𝛿¹⁸O values of fish microfossils from classic K-Pg sections from Denmark have two advantages for testing the existence of a post-impact warming pulse. Fish microfossils are composed of bioapatite, a mineral whose 𝛿¹⁸O values are relatively resistant to diagenetic alteration and the basal Danian deposits are laminated increasing the potential for fine temporal resolution in a critical part of the record.

We will present high-resolution 𝛿¹⁸O data from fish microfossils collected across the K–Pg boundary at Stevns Klint, Denmark. Samples were obtained from 84 samples collected from a composite 22-m thick stratigraphic section spanning the late Maastrichtian upper Sigerslev Member of the Mons Klint Formation through early Danian lower Korsnaeb Member of the Stevns Klint Formation including a ~30 cm thick exposure of the basal Danian Fiskeler Clay from the Kulstirende locality. Pilot results suggest a 1‰ negative excursion beginning within ~2 cm of the K-Pg boundary and extending through the lower third of Fiskeler Member. If the Fiskeler was deposited over ~10,000 years and the isotopic shift was due entirely to temperature change, the excursion would represent ~4.5 °C of warming beginning only decades to centuries after the impact and lasting for several thousand years. However, both sample density and stratigraphic control is low in the pilot data. If ongoing analyses are successful, we will have generated a well-resolved, high latitude 𝛿¹⁸O record that should provide an important test of the extent and magnitude of proposed post-impact warming currently supported best by results from only a few mid- to low-latitude sites. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10504

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.