Tropical Temperatures during the Late Paleozoic Ice Age: Proxy Fidelity in Pennsylvanian to Permian Carbonates of the US Midcontinent Sea, Eastern Kansas
Restricted (Penn State Only)
- Author:
- Shepherd, Garrett
- Graduate Program:
- Geosciences (MS)
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 22, 2022
- Committee Members:
- Mark Patzkowsky, Program Head/Chair
Brian Kelley, Thesis Advisor/Co-Advisor
Miquela Ingalls, Committee Member
Mark E Patzkowsky, Committee Member - Keywords:
- Late Paleozoic Ice Age
Oxygen Isotope Paleothermometry
Clumped Isotope Paleothermometry
US Midcontinent
Midcontinent Sea
Eastern Kansas - Abstract:
- The Late Paleozoic Ice Age (LPIA) provides an opportunity to better understand how climate variations influence large-scale changes to the Earth’s physical and chemical systems. Trends of LPIA climate have been compiled for decades using oxygen isotope (δ18O) thermometry and calcitic brachiopods from the US Midcontinent. These trends, however, may have been subject to more than 300 million years of post-depositional alteration and geochemical overprint. To evaluate the fidelity of these records and establish better constraints for LPIA temperature, this study utilizes petrographic microscopy and dual proxy paleothermometers—δ18O and carbonate clumped isotopes (Δ47). Brachiopods and bulk-rock carbonates from three stratigraphic successions in the US Midcontinent of eastern Kansas—spanning uppermost Pennsylvanian to Lower Permian strata—reported δ18O temperatures ranging from 10–29 °C. Clumped isotope measurements from the same interval produced values of 35–79 °C, indicating that all sites in Kansas were influenced by some degree of diagenetic alteration. This alteration resulted in compromised Δ47 values and distinct δ18O and Δ47 populations between northeastern and southeastern Kansas. These isotopic differences, paired with petrographic evidence, are interpreted to reflect regionally divergent alteration styles. Isotopic evidence and good textural preservation from northeastern Kansas indicate its deposits were primarily impacted by burial diagenesis with little water-rock interaction. Southeastern samples, however, display poor preservation and isotopic signatures suggestive of alteration through both burial and hydrothermal activity, likely related to Ouachitan tectonism. Because fluid interaction overprints original geochemical signatures, carbonate deposits from southern Kansas, Oklahoma, and Texas should be used with caution for LPIA climate interpretation due to their proximity to Late Paleozoic tectonism. Previous LPIA trends from the Midcontinent also exhibit isotopic heterogeneity between northern and southern locations and generally agree with the results of this study. This evidence suggests diagenesis has played a significant role in the geochemistry of Midcontinent carbonates. It also indicates that perhaps samples from northern regions of the US Midcontinent represent the most accurate records of LPIA climate.