EXAMINING THE MARINE ISOTOPIC GRADIENT THROUGH THE LATE DEVONIAN USING MICROFOSSILS FROM THE KELLWASSER HORIZONS
The δ13C values of individual kerogen grains were isotopically similar between grains, as well as similar to bulk δ13Corg within each section. The δ13C values of individual microfossils were variable between fossils and significantly different from coeval kerogens. The difference between the microfossil and kerogen values, Δacritarch or Δa, varies between sections, with the largest Δa values occurring in the bed below the Lower Kellwasser horizon and the bed containing the Upper Kellwasser Horizon. While the paleoecology and taxonomic affinity of these fossils is uncertain, the δ13C values suggest that they are consistent with an algal origin. We speculate that the isotopic difference between bulk organic matter and the organic-walled microfossils may be the result of a surface water ecology where DIC is 13C-enriched because of a strong biological pump. This work sets the stage for more nuanced analyses of carbon cycle dynamics across the end-Devonian extinction event and for a better understanding of Paleozoic organic-walled microfossil paleoecology.