Eccentricity forcing of late Paleogene dust accumulation in the western USA across the Eocene-Oligocene Transition

Xiangwei Guo¹†, Majie Fan¹, Yiquan Ma² ³, Steven L. Forman⁴, Dennis O. Terry Jr.⁵, and Ran Feng⁶

¹ Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, Texas, USA ² State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation & Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, China ³ Key Laboratory of Deep-Time Geography and Environment Reconstruction and Applications, Ministry of Natural Resources, Chengdu University of Technology, Chengdu, China ⁴ Department of Geosciences, Baylor University, Waco, Texas, USA ⁵ Department of Earth and Environmental Science, Temple University, Philadelphia, Pennsylvania, USA ⁶ Department of Geosciences, College of Liberal Arts and Sciences, University of Connecticut, Storrs, Connecticut, USA

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Figure 1

Maps illustrate modeled late Paleogene wind and moisture pathways across the western United States (Fan et al., 2020) and show key White River Formation (Group) sections with depositional ages of loess onset, revealing the eastward younging of loess accumulation.

Figure 2

Lithostratigraphic and grain-size analyses constrained loess–fluvial transitions at Toadstool Geologic Park and refined the regional framework of loess initiation in the western United States by updating the onset of loess accumulation at the Toadstool section using an astronomically tuned timescale developed in this study.

Figure 3

Grain-size distributions show that loess samples exhibit characteristic well-sorted bimodal distributions, and statistical analyses demonstrate that they are distinct from fluvial samples, supporting differentiation of depositional processes.

Figure 4

End-member modeling of bulk and quartz grain-size data from loess identifies distal suspension and local suspension–saltation components, enabling extraction of local suspension–saltation end members for calculating mass accumulation rates and conducting spectral analyses while excluding pedogenically affected distal components.

Figure 5

Temporal variations in end-member abundances recorded shifts among fluvial, transitional, and eolian environments at the Flagstaff Rim and Toadstool sections, while stratigraphic relationships and dated ash layers constrained the timing of these changes.

Figure 6

Cyclostratigraphic and spectral analyses demonstrated persistent cyclicity in mean grain size at both sites, with dominant periodicities consistent with short eccentricity forcing, enabling astronomical tuning to build the age framework of the sections.

Figure 7

Spectral analyses of astronomically tuned high-resolution grain-size records demonstrated tracking of ~100 kyr eccentricity cycles with small phase leads, with the tuning anchored by well-dated ash layers, providing a robust chronological framework for interpreting orbital control on dust flux in the White River Formation (Group).

Figure 8

Spectral analysis of dust mass accumulation rates within the astronomically tuned timeframe revealed pronounced ~100 kyr eccentricity cyclicity, with dust mass accumulation in phase with eccentricity, suggesting coupling between orbitally driven climate variability and dust activity.