21 Frontiers in Geochronology: Advances and Applications in the Geosciences

This session highlights cutting-edge geochronologic advances and applications that illuminate Earth’s dynamic history. We welcome contributions spanning new analytical techniques, integrative studies, and innovative case examples demonstrating the essential role of time in geosciences.

Tuesday, 10 March 2026
10:00 AM - 12:00 PM
RCC, 104

Expanding Upon the Early Eocene Geochronological Record of the Wind River Basin, WY, USA Using Paleosol-Based Magnetostratigraphy

Paper number: 21-4
Program: Technical Sessions
Time: 11:00 AM – 11:15 AM

Authors

Abstract

The Early Eocene was a time of globally warm climate highlighted by hyperthermal events which drove fluctuations in fluvial systems in response to elevated CO2 levels. The Wind River Formation (WRF) in the Wind River Basin of central Wyoming is characterized by fluvial sandstones and conglomerates interbedded with floodplain paleosols and mudstones. The construction of a magnetostratigraphic record and the identification of geomagnetic reversals and a deeper evaluation of the recorded mammalian biostratigraphy will provide additional age constraints for the WRF. We can constrain the bottom of the section using chemostratigraphy to identify the Paleocene Eocene Thermal Maximum (PETM), which coincides with the possible North American Land Mammal Age (NALMA) of the latest Clarkforkian, Cf3, or earliest Wasatchian,Wa0. The top of the measured section is constrained by a detrital zircon maximum depositional age of 50.87 Ma ± 0.46 or latest Wasatchian, Wa7. Combined with the magnetostratigraphy (geomagnetic polarity chrons 24r through 23r), this chronology will allow us to understand the response of terrestrial environments to hyperthermals like the PETM, Eocene Thermal Maximum 2, and the Early Eocene Climate Optimum. Here, data will be presented on magnetostratigraphy and biostratigraphy for a site in the Dubois Badlands Wilderness Study Area outside of Dubois, WY.

 

Lithostratigraphic sections measured at the Dubois site capture ~150 m of fluvial and floodplain sandstones and mudstones. Floodplain paleosols were described based on pedogenic features (e.g., color, grain size, texture, horizonation, etc.). Oriented samples of floodplain paleosols were used for construction of a magnetostratigraphic record through a combination of alternating field and thermal demagnetization protocols. Although these samples contain goethite, magnetite, and pigmentary hematite, our results show that detrital hematite is the carrier of remanence at the time of deposition. Paleomagnetic analyses cover the first ~50 m of measured section based on paleomagnetic samples that were collected every ~3 m or bracketed thick, coarse sandstones. Preliminary results are consistent with reversed polarity throughout. Ongoing paleomagnetic work will refine the chronology of the section to chron 23n.1n or 22r. The improved chronology of the WRF will allow for high resolution paleoenvironmental reconstructions using bulk geochemistry proxies for paleoprecipitation and pedogenic carbonates for clumped isotope thermometry. These proxies tied into the chronology can help determine the impact of hyperthermal events

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411892

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