Author

Min Gao

Graduation Semester and Year

2017

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Earth and Environmental Science

Department

Earth and Environmental Sciences

First Advisor

Majie Fan

Abstract

The central Rocky Mountains in western U.S.A. is a geologic province formed by the low-angle subduction of the Farallon oceanic plate under the North American continental plate during the latest Cretaceous–early Eocene Laramide orogeny. The tectonic processes and mechanism, the paleotopography and depositional environment, and the evolution of continental hydroclimate during the Laramide deformation remain controversial. This dissertation examines the tectonic processes of the Laramide orogeny throughout the entire central Rocky Mountains, and paleotopography, depositional processes, and paleoclimate in the Greater Green River Basin in southwestern Wyoming. The first project of this study uses a 2D flexural subsidence modeling method to explore the mechanism that links the surface deformation pattern to deep mantle processes during the Laramide deformation. The stiffness of Wyoming lithosphere decreased spatially from northeastern Wyoming (Te=32–46 km) to southwestern Wyoming (Te=6–9 km), while varied slightly in each basin during the ~30 Myr duration of the Laramide deformation. We attribute this southwestward weakening pattern to bending stresses, crust–mantle decoupling and end loads effect. We also suggest a two-stage Laramide deformation based on the accelerated uplift of Laramide mountains during the early Eocene. The second project combines lithofacies analysis, sandstone petrography and oxygen isotope paleoaltimetry to examine the depositional environment, sediment provenance, and paleotopography of the early Paleogene Greater Green River Basin, southwestern Wyoming. The reconstructed paleoelevation of the Uinta Mountains to the south of the Greater Green River Basin was at least 3.5 km during the earliest Eocene. Surface uplift of the Uinta Mountains during the earliest Eocene resulted in changes in drainage pattern, depositional environment and sediment sources in the Greater Green River Basin. The third project uses multiple climate proxies including bulk organic carbon isotope record (δ13Corg), paleosol morphology, atmospheric CO2 concentration (pCO2) and mean annual precipitation (MAP) to study the continental hydroclimate characteristics in the Greater Green River Basin during the late Paleocene-early Eocene. Two negative δ13Corg excursions were recognized, representing two early Paleogene hyperthermals: PETM and ETM-2. The climate in the basin was generally warm and humid during late Paleocene-early Eocene, but transient drying occurred during the extreme hot hyperthermals.

Keywords

Laramide deformation, 2D flexural subsidence, Lithospheric stiffness, Low angle subduction, Slab rollback, Lithofacies, Provenance, Paleoaltimetry, Oxygen isotope, Early Paleogene, Bulk organic carbon, Paleosol, PETM, CIA-K, Precipitation, Greater Green River Basin

Disciplines

Earth Sciences | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

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