142-2 Reconstructing Precession Driven Climate Fluctuations in the Late Paleozoic using Conodont Oxygen Isotopes

Session: Undergraduate and Graduate Geoscience Student Lightning Talk Showcase (Posters)

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The last icehouse analogous to Earth’s current climate state was the Late Paleozoic Ice Age (LPIA). Reconstructing the climate of the LPIA can improve our models to better understand and predict modern climate change. Conodonts are early chordates that lived from the Cambrian to Triassic, and their fossilized teeth are made of bioapatite. Oxygen isotopes record orbitally-driven glacioeustatic and regional hydrologic change. This study reconstructs local evaporation and precipitation patterns within the Late Pennsylvanian Midcontinent Sea using oxygen isotopes of conodonts (𝛿¹⁸O_PO4). Higher 𝛿¹⁸O_PO4 signals higher rates of evaporation, whereas lower 𝛿¹⁸O_PO4 signals higher rates of rainfall. If the regional hydroclimate is driven by eccentricity-modulated precession, these fluctuations will occur on a smaller spatial and temporal scale than glacioeustatic fluctuations in 𝛿¹⁸O_PO4. Conodonts were extracted from the Dennis cyclothem in Kansas City, MO at centimeter-scale stratigraphic heights. Sampled lithologies range from the deep-water black shale facies to the shallower-water limestone facies. Digital microscope photos enabled genus identification. Conodonts were converted to silver phosphate for oxygen isotopic analysis via thermal conversion/elemental analyzer-isotope ratio mass spectrometry. Idiognathodus is the most abundant genus, present in every sample with identifiable genera. The lower black shale contains exclusively Idiognathodus, while Streptognathodus and Swadelina appear in the upper black shale and limestone. This indicates that Streptognathodus and Swadelina may have been more specialized, preferring shallower seas, while Idiognathodus may have been more generalized, thriving in a wide range of sea levels. The minimum average difference of 𝛿¹⁸O_PO4 between the black shale and limestone facies is 1.96‰. This indicates an increase in ice volume between the black shale and limestone facies, and an associated fall in sea level of about 196m, assuming a 0.01‰ change in 𝛿¹⁸O_PO4 per meter of sea level change. Temperature affects fractionation rate of 𝛿¹⁸O_PO4, which likely reduces this estimate. Within the black shale facies, there are smaller scale fluctuations in 𝛿¹⁸O_PO4 likely signaling variations in local evaporation and precipitation rates driven by cycles in orbital precession. As the LPIA icehouse is analogous to modern icehouse conditions, the influence of precession on tropical hydroclimate may be a consistent forcing mechanism of climate through geologic time.

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

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