Graduation Semester and Year
Spring 2026
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Earth and Environmental Science
Department
Earth and Environmental Sciences
First Advisor
Majie Fan
Second Advisor
Nathan D. Brown
Third Advisor
Steven L. Forman
Fourth Advisor
Dennis O. Terry Jr.
Fifth Advisor
Arne M. Winguth
Abstract
This project examines the timing of loess emergence, the nature of the fluvial–eolian transition, orbital forcing on dust accumulation, and sediment recycling in the late Paleogene White River Formation (Group) of Wyoming and Nebraska, western United States. By integrating traditional sedimentology with machine learning–enhanced grain-size analysis, this research shows that loess accumulation at Flagstaff Rim in central Wyoming began during active fluvial deposition at approximately 35.8 Ma, indicating a gradual transition from fluvial to eolian conditions. Machine learning complements field sedimentology and granulometric interpretation while enabling the development of new, testable hypotheses. Extending this framework eastward to Toadstool Geologic Park in northwestern Nebraska, astronomical tuning of medium grain-size records indicates that pure loess deposition began later, at approximately 33 Ma. Spectral analyses of local dust mass accumulation rates and medium grain size further demonstrate that late Paleogene dust dynamics were persistently paced by ~100-kyr short-eccentricity cycles across the Eocene–Oligocene Transition, with peak dustiness occurring near eccentricity maxima, likely driven by amplified seasonality. Large-n, grain-size–resolved detrital zircon U–Pb geochronology and zircon morphology, combined with mineralogical, geochemical, and heavy-mineral data, further show that the White River loess is tuffaceous rather than purely reworked volcanic ash. Similar provenance signals between fluvial deposits and loess indicate that the White River loess formed primarily through eolian reworking of contemporaneous fluvial sediments sourced from nearby Laramide uplifts and sedimentary covers, containing both first-cycle and recycled zircon grains. Grain-size–resolved detrital zircon data also show that hydraulic sorting and eolian entrainment filter provenance signals by preferentially reducing large, locally derived first-cycle zircons while enhancing smaller, recycled or distal components in mixed fluvial–eolian environments. Together, these results provide new insights into late Paleogene dust systems and improve interpretation of paleoclimate signals preserved in deep-time loess deposits.
Keywords
White River Formation, loess, fluvial-eolian transition, depositional environments, machine learning, grain-size analysis, end-member modeling, astronomical tuning and analysis, sediment recycling, detrital zircon U-Pb geochronology
Disciplines
Geochemistry | Geology | Sedimentology | Stratigraphy
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Guo, Xiangwei, "Timing, Orbital Pacing, and Provenance of Late Paleogene Loess in the Western United States" (2026). Earth & Environmental Sciences Dissertations-Archive. 96.
https://mavmatrix.uta.edu/ees_dissertations/96
Comments
I am deeply grateful to The University of Texas at Arlington for the opportunity to pursue my doctoral studies, and to the Department of Earth and Environmental Sciences for its generous financial support. I sincerely thank my advisor, Dr. Majie Fan, for her dedicated mentorship, timely and detailed feedback, and unwavering support throughout my Ph.D. journey. I am also grateful to my committee members, Dr. Nathan D. Brown, Dr. Steven L. Forman, Dr. Dennis O. Terry Jr., and Dr. Arne M. Winguth, for their time, insight, and service on my dissertation committee. I further thank my co-authors, Dr. Ran Feng, Dr. Feng Gao, Dr. Yiquan Ma, Dr. Yike Shen, and Dr. Victor A. Valencia, for their collaboration and contributions to this work.
I am also grateful to Shankhadeep Baul, Mary Ann M. Moody, and Aaron X. Parada for their assistance with granulometry analysis, and to Aaron X. Parada for his additional help with detrital zircon U--Pb analyses. I would like to express my sincere appreciation to Dr. Ogochukwu Azike for instruction in XRD analysis, and to Rijumon Nandy for guidance in detrital zircon and heavy mineral separation. My thanks also go to Ms. Liliana Marin, Alix Fournier, and Ashley Gonzalez for their assistance with operation of the Malvern Mastersizer. I further appreciate Dr. Gábor Újvári and Dr. János Kovács for their helpful instruction on quartz separation. Finally, this research was supported by the National Science Foundation under grants EAR-2114166 to Dr. Majie Fan and EAR-2114204 to Dr. Ran Feng, with additional financial support provided by the Arizona LaserChron Center.