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4-3 Establishing a Paleosol-based Magnetostratigraphic Framework for the Early Eocene in the Wind River Basin, WY, USA

Session: Recent Advances in Soil and Paleosol Science

Presenting Author:

Mr. Jarred Asselta

Authors:

Asselta, Jarred¹, Beverly, Emily Jane², Flynn, Andrew G.³, Feinberg, Joshua M.⁴, Blount, James⁵

(1) Earth and Environmental Science, University of Minnesota - Twin Cities, Minneapolis, Minnesota, USA, (2) University of Minnesota - Twin Cities, Minneapolis, MN, USA, (3) New Mexico State University, Las Cruces, NM, USA, (4) University of Minnesota - Twin Cities, Minneapolis, MN, USA, (5) University of Minnesota - Twin Cities, Minneapolis, Minnesota, USA,

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 (WRB) of central Wyoming is characterized by fluvial sandstones and conglomerates interbedded with floodplain paleosols and mudstones. These deposits are broadly constrained to the early Eocene based on mammalian biostratigraphy and detrital zircon U/Pb dates, but a detailed chronology is required for correlations across coeval extensional basins recording Eocene hyperthermal events. The construction of a magnetostratigraphic record and the identification of geomagnetic reversals will provide additional age constraints of the WRF. Here we present preliminary data on magnetic mineralogy and magnetostratigraphy for two sites from the Dubois Badlands Wilderness Study Area outside of Dubois, WY, and Hell's Half Acre, outside of Casper, WY in the western and eastern portions of the WRB respectively.

Lithostratigraphic sections measured at the Dubois and Casper sites capture ~170m and ~80m, respectively, of fluvial and floodplain sandstones and mudstones. Floodplain paleosols were described based on pedogenic features such as color, grain size, texture, and horizonation. Bulk geochemistry samples and pedogenic carbonates were collected for paleoenvironmental proxy and isotopic measurements. Dubois Badlands yielded ~50 bulk geochemistry samples and ~40 pedogenic carbonates, while Hell’s Half Acre yielded ~40 bulk geochemistry samples and ~5 pedogenic carbonates. Oriented paleomagnetic samples were collected every ~3 to 5m or bracketed thick, coarse sandstones.

The composition and abundance of magnetic minerals varies between sites. Diagnostic behaviors of magnetite, hematite, and goethite were observed in low-field susceptibility measurements during heating in air from room temperature to 700℃ on a Geofyzika KLY-2 KappaBridge AC Susceptibility Bridge. These data inform the optimal demagnetization approach prior to the start of alternating field (AF) demagnetization. First, a 120℃ thermal demagnetization step will remove goethite remanence, then stepwise AF demagnetization will remove magnetite remanence, and finally, thermal demagnetization steps will remove hematite remanence. In this way, it will be possible to determine if specific minerals hold similar or different magnetizations and magnetostratigraphy can be constructed. Future work will focus on reconstructing Eocene hyperthermal events with more robust age constraints for comparison between basins with contemporary records to serve as an analog for modern anthropogenic climate change.

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

Establishing a Paleosol-based Magnetostratigraphic Framework for the Early Eocene in the Wind River Basin, WY, USA

Description

Session Format: Oral

Presentation Date: 10/19/2025

Presentation Start Time: 08:35 AM

Presentation Room: 212AB

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