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MINERALS THAT REMEMBER: PETROGRAPHIC AND STABLE ISOTOPIC STUDY OF PALEOSOLS FROM LATE MISSISSIPPIAN PENNINGTON FORMATION

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Mysti Stotts

Authors:

Stotts, Mysti D¹, Belt, Katherine Ann², Bolix, M. Jace³, Da, Jiawei⁴, McIntosh, Julia⁵, Michel, Lauren A.⁶

(1) Department of Earth Sciences, Tennessee Technological University, Cookeville, TN, USA, (2) Department of Arts and Sciences, Tennessee Technological University, Cookeville, TN, USA; Department of Chemistry, Virginia Tech, Blacksburg, Virginia, USA, (3) Department of Arts and Sciences, Tennessee Tech University, Cookeville, TN, USA, (4) The University of Texas at Austin, Austin, TX, USA, (5) U.S. Geological Survey, Denver, CO, USA, (6) Tennessee Tech University, Cookeville, TN, USA,

Abstract:

Evidence of global glacial advance and retreat on a vegetative world, makes the Late Paleozoic an important analogue for understanding and predicting trends in modern climate dynamics. One important archive to reconstruct paleoclimate is using fossilized soils, or paleosols, which preserve organic matter and minerals that have been used to quantitively estimate atmospheric CO₂ levels and paleotemperature. The Pennington Formation, exposed in Kentucky and Tennessee, USA contains carbonate-bearing paleosols that provide an opportunity to validate Late Mississippian CO₂ estimates (250-1000ppm) that have similar values to modern measurements (>420ppm). The formation contains interbedded paleosols and limestones which suggest deposition influenced by transgressive-regressive sea level cycles. Paleosol field observations include pedogenic carbonate nodules and vertic features including slickensides, mukkara structures, and wedge-shaped peds, that classify the Pennington paleosols as calcic Vertisols and suggest evidence of seasonality. Petrographic analysis suggests the preservation of both pristine pedogenic carbonates and those that experienced diagenetic alteration, evidenced by non-luminescent micrite and luminescence sparry calcite and dolomite, respectively. Drilling of micrite nodules produced d13C_VPDB values between-3.9‰ to -5.7‰ (n=20) whereas d13C_VPDB values of disseminated micrite range from -5.7‰ to -2.4‰ (n=9). These values overlap with those of sparry calcites (-6.2‰ and -5.6‰) (n=2) and dolomites (-5.7‰ to -3.9‰) (n=16). d18O_VPDB values of the nodules are between -4.2‰ to -0.3‰, the d18O_VPDB values for disseminated micrite are between -1.4‰ to -2.2‰, sparry calcite values are -3.5‰ and -3.0‰ and dolomite ranges from -3.5‰ to -1.7‰. Diagenetic alteration extends beyond carbonate nodules, with X-ray Diffraction analysis suggesting the illitization of primary smectites. O-H stable isotope analysis of the illite will add to the understanding of diagenetic processes of the Pennington. Together, these methods allow for a more accurate interpretation of the Pennington paleosols as paleoclimate proxies.

This work will further refine paleosol-based reconstructions and help us better understand the preservation potential of foreland and intermontane basins during periods of climate change.