3:30 PM - 3:45 PM
[BCG06-13] Sulfur isotopic constraints on paleoenvironmental perturbations after end-Cretaceous impact event
Keywords:mass extinction, meteorite impact, acid rain, sulfate aerosol
The mass extinction at the Cretaceous–Paleogene (K–Pg) boundary was caused by environmental changes associated with a meteorite impact. The following environmental perturbations have been proposed: (1) sunlight interception by dust particles, followed by a temperature decrease and photosynthesis suppression; (2) sunlight interception and acid rain induced by sulfate aerosols originating from SO2/SO3 emitted by the impact site; (3) temperature increase due to aerodynamic heating induced by the falling of the meteorite and impact debris, followed by global wildfires and sunlight interception induced by soot emitted by these wildfires; and (4) global warming due to CO2 emitted by above-mentioned global wildfires and/or the impact heating of carbonate rocks [1]. However, researchers have not determined which of these phenomena occurred and the scales in which they occurred. Some environmental changes caused by the meteorite impact may have affected the concentrations and isotopic compositions of sulfate in the oceans. Fluctuations in the sulfate inflow/outflow balance in the oceans may be recorded in the sulfur isotope compositions of the K–Pg boundary layer. Therefore, the effects of environmental perturbations after the K–Pg meteorite impact can be constrained using the sulfur isotopic compositions of K–Pg boundary samples.
In this study, the sulfur isotope ratios of carbonate-associated sulfate (CAS) (δ34Ssulfate) and pyrite (δ34Ssulfide) of K–Pg boundary samples from the Stevns Klint site, Denmark, were investigated. Negative shifts in δ34Ssulfate and δ34Ssulfide values were observed at the K–Pg boundary layer, but these shifts had different magnitudes. The δ34Ssulfide decrease was larger than that of δ34Ssulfate, indicating that isotopic fractionation between sulfate and sulfide via bacterial sulfate reduction increased in the K–Pg boundary layer. The shift in δ34Ssulfate could be explained by suppressed sulfate reduction due to a decrease in organic matter availability and/or an enhanced influx of sulfate ions through enhanced soil erosion, possibly due to acid rain. These phenomena are consistent with the global decline in organic matter production expected from the low δ13C of carbonate and considerable continental weathering indicated by high 87Sr/86Sr values, both of which have been observed at K–Pg sites around the world.
Isotopic fractionation, or the difference between the δ34Ssulfate and δ34Ssulfide values, reflects the local (not global) environmental conditions in which sulfate reduction occurs. The increase in sulfur isotope fractionation at the K–Pg boundary may reflect reduced organic matter availability and/or a temperature decrease, both of which are consistent with the decreases in δ13C values and increases in δ18O values in foraminifera, respectively, observed at the K–Pg boundary at Stevns Klint.
[1] Maruoka, T., 2019, Mass Extinction at the Cretaceous–Paleogene (K–Pg) Boundary, in Yamagishi et al. (eds.), Astrobiology: From the Origins of Life to the Search for Extraterrestrial Intelligence, 303-320.
In this study, the sulfur isotope ratios of carbonate-associated sulfate (CAS) (δ34Ssulfate) and pyrite (δ34Ssulfide) of K–Pg boundary samples from the Stevns Klint site, Denmark, were investigated. Negative shifts in δ34Ssulfate and δ34Ssulfide values were observed at the K–Pg boundary layer, but these shifts had different magnitudes. The δ34Ssulfide decrease was larger than that of δ34Ssulfate, indicating that isotopic fractionation between sulfate and sulfide via bacterial sulfate reduction increased in the K–Pg boundary layer. The shift in δ34Ssulfate could be explained by suppressed sulfate reduction due to a decrease in organic matter availability and/or an enhanced influx of sulfate ions through enhanced soil erosion, possibly due to acid rain. These phenomena are consistent with the global decline in organic matter production expected from the low δ13C of carbonate and considerable continental weathering indicated by high 87Sr/86Sr values, both of which have been observed at K–Pg sites around the world.
Isotopic fractionation, or the difference between the δ34Ssulfate and δ34Ssulfide values, reflects the local (not global) environmental conditions in which sulfate reduction occurs. The increase in sulfur isotope fractionation at the K–Pg boundary may reflect reduced organic matter availability and/or a temperature decrease, both of which are consistent with the decreases in δ13C values and increases in δ18O values in foraminifera, respectively, observed at the K–Pg boundary at Stevns Klint.
[1] Maruoka, T., 2019, Mass Extinction at the Cretaceous–Paleogene (K–Pg) Boundary, in Yamagishi et al. (eds.), Astrobiology: From the Origins of Life to the Search for Extraterrestrial Intelligence, 303-320.