Understanding topographic evolution of continents with landscape evolution simulations: the case of North America

Chang, Ching

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Description

Title

Understanding topographic evolution of continents with landscape evolution simulations: the case of North America

Author(s)

Chang, Ching

Issue Date

2021-04-14

Director of Research (if dissertation) or Advisor (if thesis)

Liu, Lijun

Doctoral Committee Chair(s)

Liu, Lijun

Committee Member(s)

• Anders, Alison
• Marshak, Stephen
• Guenthner, William

Department of Study

Geology

Discipline

Geology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Landscape Evolution Simulation
• Geomorphology
• Geodynamics
• Continent
• North America
• Dynamic Topography
• Flexural Isostasy
• Mantle
• Subduction

Abstract

Earth’s topography is constantly evolving due to tectonics, surface processes, and climatic forcing. Since Mid-Cretaceous, the North American continent has experienced dramatic topographic fluctuations, from the Cretaceous Western Interior Seaway (WIS) to the present high elevations within the middle-western continent. The WIS produced widespread marine sediments in the continental interior, far (>500 km) from tectonically active regions. This region also largely corresponds to the highest elevations of western North American today, i.e., Wyoming, Colorado Plateau and the Rockies. Formation mechanisms of both the WIS and the subsequent uplift remain debated. In general, proposed mechanisms of continental-scale vertical motions can be categorized into: 1) isostatic topographic variation due to changes in lithospheric buoyancy, and 2) dynamic topography driven by flow within the sub-lithospheric mantle. Here I use landscape evolution simulations to investigate the mechanisms of continental topographic histories. First, I designed synthetic landscape evolution experiments to study the responses of surface processes to end-member geodynamic mechanisms that cause different patterns of subsidence within the continental interior. The results suggest that only a subsidence signal that is geographically migratory can explain the tilted strata observed in WIS stratigraphy, and such subsidence is consistent with dynamic topography caused by the sinking Farallon slab beneath the moving North American plate. Then, I constructed more realistic landscape evolution simulations mimicking the Late Cretaceous surface conditions to quantify the effect of flexural vs. dynamic subsidence in forming the WIS and its sedimentation record. Comparisons between modeled and observed sedimentation patterns show that 1) flexural subsidence was the dominant driver of sedimentation before 90 Ma within the Sevier foreland basin, 2) the main driving force of sedimentation transitioned to dynamic subsidence during 90 – 84 Ma, and 3) dynamic subsidence dominated sedimentation after 84 Ma when the most intense sedimentation migrated east far beyond the foreland basin. The timing of this transition coincides with the emplacement and passage of the Shatsky conjugate oceanic plateau underneath North America. Therefore, I concluded that the flattening of the Farallon slab due to subduction of the oceanic plateau is the ultimate origin of the WIS formation, during which a migratory dynamic subsidence signal with ~1 km in amplitude and ~1000 km in wavelength traversed western North America. Lastly, I developed a novel inversion approach to constrain the uplift history of the western U.S. since the retreat of Cretaceous WIS. This approach is based on landscape evolution simulations that include Gulf of Mexico (GOM) sedimentation history as a key constraint. By testing a wide range of uplift scenarios, I found that the GOM sedimentation increases after the onset of Cenozoic uplift of the western U.S. The inversion results reveal that the western U.S. experienced long-wavelength (>500 km) uplift with an average elevation gain of ~1.5 km during 40–20 Ma, a result largely independent of surface process intensities. This time is coeval with the ignimbrite flare-up in the western U.S. and the drainage reversal within the Colorado Plateau. I conclude that this mid-Cenozoic regional uplift is due to increased lithospheric buoyancy and dynamic uplift, both of which are associated with the removal and passage of the Farallon flat slab.

Graduation Semester

2021-05

Type of Resource

Thesis

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Copyright 2021 Ching Chang

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