142 Undergraduate and Graduate Geoscience Student Lightning Talk Showcase (Posters)
This hybrid session offers undergraduate and graduate students the opportunity to present research findings in a brief, one-slide oral presentation (morning) and a poster presentation (afternoon). This session promotes science communication skills to audiences in multiple formats.
Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Reconstructing Precession Driven Climate Fluctuations in the Late Paleozoic using Conodont Oxygen Isotopes
Paper number: 142-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
-
Julie GriffinCalifornia State University Sacramento, Carmichael, CA
Abstract
The last icehouse analogous to Earthโs 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 (๐ฟ18OPO4). Higher ๐ฟ18OPO4 signals higher rates of evaporation, whereas lower ๐ฟ18OPO4 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 ๐ฟ18OPO4. 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 ๐ฟ18OPO4 between the black shale and limestone facies is 1.96โฐ. 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 0.01โฐ change in ๐ฟ18OPO4 per meter of sea level change. Temperature affects fractionation rate of ๐ฟ18OPO4, which likely reduces this estimate. Within the black shale facies, there are smaller scale fluctuations in ๐ฟ18OPO4 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 Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-414556
© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.