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4-4 REGIONAL VARIABILITY OF PALEOCLIMATIC AND PALEOENVIRONMENTAL SIGNALS PRESERVED ALONG ISOCHRONOUS LANDSCAPES OF THE EOCENE-OLIGOCENE TRANSITION ACROSS THE NORTHERN GREAT PLAINS

Session: Recent Advances in Soil and Paleosol Science

Presenting Author:

Dennis Terry

Authors:

Terry, Dennis O.¹, Hren, Michael T.², Fernandes, Anjali M.³, Smith, Virginia Burton⁴

(1) Earth and Environmental Science, Temple University, Philadelphia, PA, USA, (2) Department of Earth Sciences, University of Connecticut, Storrs, CT, USA, (3) Earth and Environmental Sciences, Denison University, Granville, OH, USA, (4) , Civil and Environmental Engineering, Villanova, PA, USA,

Abstract:

The terrestrial record of the Eocene-Oligocene Transition (EOT) on the Northern Great Plains is interpreted as a shift from hothouse to icehouse conditions based on changes in sedimentology, paleopedology, and vertebrate paleontology. Newly acquired radiometric dates of airfall tuff deposits across the northern Great Plains (the White River Sequence of WY, NE and SD) allows for a refinement of the timing of regional changes across this transition. Changes in sedimentology are preserved as up-section transitions from fluvial-dominated to eolian-dominated deposits. Specifically, channel facies change up-section from meandering to flashy morphologies and pedogenic modification of floodplain deposits change from well-developed profiles with distinct horizonation to progressively less-developed profiles that eventually form in eolian deposits that shift between periods of aggradation and geomorphic stability. Indicators of paleoclimatic and paleoenvironmental change from the vertebrate record include the loss of large browsers and crocodylomorphs across the EOT in deposits from NE and SD, up-section changes in stable isotope values of skeletal material in NE, and the general up-section change in vertebrate assemblages (NALMA zones) in NE and SD. While these up-section changes in sedimentology and vertebrate records are generally consistent at individual locations across the region, lateral changes along isochronous landscapes and within distinct, geochronologically controlled intervals are not. Paleosols change from thin, weakly developed profiles in WY to thicker, well-developed profiles in NE. Eolian-dominated deposits of WY are temporally equivalent with fluvial, mudstone-dominated sections in NE. Isotopic values of vertebrate materials shift toward progressively wetter and cooler conditions from WY to NE, and the Middle Chadronian NALMA is diachronous by ~100ky from WY to NE. The degree to which these patterns are responding to local, regional, or global drivers is unknown at this time.

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

REGIONAL VARIABILITY OF PALEOCLIMATIC AND PALEOENVIRONMENTAL SIGNALS PRESERVED ALONG ISOCHRONOUS LANDSCAPES OF THE EOCENE-OLIGOCENE TRANSITION ACROSS THE NORTHERN GREAT PLAINS

Description

Session Format: Oral

Presentation Date: 10/19/2025

Presentation Start Time: 08:50 AM

Presentation Room: HBGCC, 212AB

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