Earth Sciences - Theses, Dissertations, and other Required Graduate Degree Essays

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Seismic and potential field constraints on the shallow crustal structure of inner Bering shelf, offshore southwestern Alaska

Author: 
Date created: 
2017-12-08
Abstract: 

South-western Alaska comprises a collection of major fault bounded tectonostratigraphic terranes that were accreted during Mesozoic and early Tertiary time. To characterize the offshore extension of these terranes and the various major faults identified onshore, I have reprocessed three intersecting multichannel deep seismic reflection profiles totalling ~750 line-km that were shot by the R/V Ewing across part of the inner Bering continental shelf in 1994. Since the uppermost seismic section is often contaminated by high amplitude water layer multiples from the hard and shallow seafloor, I have supplemented the migrated reflection images with high-resolution P wave velocity models derived by both traveltime tomography and waveform tomography of the recorded first-arrivals to depths of 2000 m. In addition, I have also incorporated other geophysical datasets such as: well logs, ship-board gravity, ship-board magnetics, satellite-altimetry gravity and air-borne magnetics to produce an integrated interpretation. The results delineate the offshore extension of the major geological elements onshore including: the Togiak-Tikchik fault, East Kulukak fault, Chilchitna fault, Lake Clarke fault, Togiak terrane, Goodnews terrane, Peninsular terrane, Northern and Southern Kahiltna flysch deposits, and the Regional Suture Zone.This thesis also focuses on mitigation of guided wave contamination in the application of 2-D acoustic waveform tomography to two small sections of a seismic line across the shelf: one section with deep igneous basement overlain by a thick pile of sediments and the other section with shallow basement and a thin sedimentary cover. I discuss the appearance of dispersive guided waves in both datasets, and show that with appropriate data preconditioning, suitable forward modelling parameters and careful choice of objective function, it is possible to invert the data using 2-D acoustic waveform tomography. I highlight use of the gradient image as a quality control tool at each iteration of the inversion process to assess the corresponding model updates. This thesis also discusses the practical limitations of waveform tomography applied to seismic data contaminated with strong dispersive guided waves, and concludes that traveltime tomography is sufficient in cases where the objective is to image relatively large low-velocity anomalies.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Andy Calvert
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Late Cretaceous to Paleocene evolution of the Blanchard River assemblage, southwest Yukon; implications for Mesozoic accretionary processes in the northwestern Cordillera

Author: 
Date created: 
2017-11-02
Abstract: 

Bedrock mapping, petrography and U-Pb in-situ monazite and detrital zircon geochronology elucidates the geological evolution of the Blanchard River assemblage, southwest Yukon. The Blanchard River assemblage belongs to a series of Middle Jurassic to early-Late Cretaceous pull-apart basinal assemblages deposited between the Insular and Intermontane terranes. Detrital zircon maximum depositional ages from 130-120 Ma suggest Early Cretaceous deposition of the Blanchard River assemblage along the western Laurentian margin, detritus was sourced primarily from inboard Intermontane terranes with minor input from outboard Insular terranes. Collapse of the Blanchard River basin is recorded by 83-76 Ma deformation and associated amphibolite-facies metamorphism, interpreted as the timing of terminal Insular terrane accretion to the western Laurentian margin. A second phase of Blanchard River assemblage metamorphism indicates ca. 70 Ma retrograde metamorphism associated with exhumation. Intrusion of the Ruby Range suite induced contact metamorphism within the Blanchard River assemblage from 63-61 Ma.

Document type: 
Thesis
Senior supervisor: 
Dan Gibson
Steve Israel
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

The role of intact rock fracture in rockfall initiation

Date created: 
2017-10-11
Abstract: 

High, near-vertical rock faces were investigated to determine the role of intact rock fracturing in rockfall initiation. Terrestrial LiDAR and photogrammetry were used to characterize historical and recent rockfall failure surfaces at two sites – one natural cliff face, and one engineered mine wall. Intact rock fracturing associated with each rockfall was estimated by comparing failure surface geometry to mapped discontinuity orientation and persistence; and by the application of two point cloud roughness analysis techniques. Estimates of intact rock bridge proportion provided the constraints for input parameters of slope-scale distinct element models. These models used a time-dependent strength degradation code, applied to a Voronoi network, to reproduce observed failure mechanisms. These analyses also provided the basis for proposed LiDAR monitoring at each site, and a system for classifying and prioritizing areas of high rockfall initiation hazard. Results of this research allow for better understanding of the interaction between intact rock bridges and discontinuities in high vertical slopes.

Document type: 
Thesis
Senior supervisor: 
Doug Stead
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Channelized deposits and regional parasequence sets of the Grouse Paleovalley: McMurray Formation, Alberta, Canada

Author: 
Date created: 
2017-09-20
Abstract: 

The Grouse Paleovalley occurs in the south-central portion of the McMurray Sub-Basin. Regionally continuous parasequence sets and associated channel belts, capped by allogenic flooding surfaces were investigated within the McMurray Formation to determine depositional settings and their stratigraphic significance. Core descriptions and wireline data were used to map surfaces and facies associations across the study area. Three stacked parasequence sets were investigated. The two oldest parasequence sets are interpreted to represent deposition of a prograding, sheltered shoreface to bay-margin, punctuated by brackish-water channels in a low accommodation setting. The youngest parasequence set is interpreted to have been deposited in a wave/storm-dominated prograding delta, also in a low accommodation setting. A new stratigraphic model for the upper McMurray is proposed, consisting of transgressive and highstand systems tracts. The progradational successions represent the highstand phases, whereas ravinement and retrogradation constitute the transgressive phases.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Shahin Dashtgard
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Volcanic architecture and unrest processes: Insights from static and time-varying potential field models

Date created: 
2017-11-27
Abstract: 

Knowledge of a volcano's architecture or internal anatomy, provides critical context for correctly interpreting signals of volcanic unrest. In this thesis, I use measurements and models of Earth's gravity and magnetic fields, applied at two contrasting volcanoes, Laguna del Maule volcanic field, Chile, and Mt Tongariro, New Zealand, to model their architecture and time-varying processes occurring within. I reveal relationships between magma bodies, hydrothermal systems, basement and fault structures, and provide a quantitative basis for improving understanding of the causes of volcanic unrest indicators. Gravity inversion, constrained by thermodynamic modelling at Laguna del Maule volcanic field, images a shallow, volatile rich, silicic magma body, above a previously modelled inflating sill, bound to the west by the regional scale Troncoso fault. Magnetic models show NE trending, remanently magnetised features, parallel to the Troncoso fault, interpreted as dykes intruding along faults. Further evidence of magma and fault interaction, from time-varying gravity changes, shows the inflating sill produces stress changes on the Troncoso fault, allowing shallow hydrothermal system fluids to migrate into it, resulting in mass addition and positive gravity changes through time. Fluid flow into the fault zone may be further modulated by shaking from nearby earthquake swarms. At Mt Tongariro, geologically-constrained gravity and magnetic models map large faults cutting the basement beneath the volcano, and delineate an extensive hydrothermal system. The hydrothermal system is bound laterally by the basement faults, while the basement itself acts as a low permeability barrier. The 2012 eruption at Upper Te Maari crater depressurised the hydrothermal system, promoting subsidence from the evacuation of pore space. Time-varying gravity models show shallow mass addition above the subsidence source, derived from a combination of pore fluid migration, condensation, cooling, and meteoric input, indicating the system is still repressurising. I show that the illumination of volcano architecture provides a rich, quantitative environment, to better interpret volcanic unrest. I combine traditional potential field geophysical methods and ground deformation data, with state of the art modelling techniques, and create a powerful and effective toolbox for the 21st century volcanologist.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Glyn Williams-Jones
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Paleoproterozoic to Mesoproterozoic evolution of Yukon Territory, Canada

Author: 
Date created: 
2017-11-20
Abstract: 

The supercontinent Columbia existed from approximately 1.8 to 1.3 Ga. During this time, complex tectonic interactions occurred between northwestern Laurentia and Australia. This thesis concerns three geologic events on northwestern Laurentia. The first event is the development of a post-collisional sedimentary overlap assemblage at 1.6 Ga herein called the Wernecke-Ogilvie unlithified succession (WOUS). The second event is the formation of the Wernecke Breccia, a set of 1.60 Ga hydrothermal breccia zones. The third is the emplacement of the 1.38 Ga Hart River sills. The WOUS was a succession of sandstone and mudstone that was deposited after collision between Laurentia and Australia at ~1.6 Ga, and prior to the formation of the Wernecke Breccias at 1.60 Ga. The WOUS is contained as clasts within the Wernecke Breccia. On the basis of detrital zircon U-Pb ages, Lu-Hf model ages and neodymium isotope geochemistry, the WOUS is correlated to sedimentary units within the hydrothermal breccias of the Olympic Dam deposit on the Gawler Craton of Australia. The Wernecke Breccia occurs as zones that are metres to kilometres in size that are scattered over an area of 300 x 150 km. The breccia zones are post-orogenic and are hosted by the deformed and metamorphosed Wernecke Supergroup. The breccias formed from voluminous hydrothermal surges with a significant gaseous component. These surges vented, and overlying rock units foundered kilometres deep into the breccia zones. The Hart River sills extend from the eastern Ogilvie Mountains to the Wernecke Mountains. Individual sills are up to 200 km long and 500 m thick. The sills are mafic to intermediate, and tholeiitic. The sills are dated herein at 1382.15 ± 0.39 Ma and 1382.14 ± 0.36 Ma. The magma that formed the sills resulted from ~10% partial melting of spinel bearing mantle similar to a MORB source. Coeval and possibly related magmatism occurred farther south on Laurentia, and to the north on Siberia. These magmatic events occurred on a possible rift axis that extended along the western margin of Laurentia and may signify breakup of the supercontinent Columbia.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Derek Thorkelson
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Multi-scale investigation of winter balance on alpine glaciers

Date created: 
2017-11-17
Abstract: 

Accurately estimating winter balance on glaciers is central to assessing glacier health and predicting glacier runoff. However, measuring and modelling snow distribution is inherently difficult. Here I explore rigorous statistical methods of estimating winter balance and its uncertainty from multiscale measurements of snow depth and density. In May 2016 we collected over 9000 manual measurements of snow depth across three glaciers in the St. Elias Mountains, Yukon, Canada. Linear regression, combined with cross correlation and Bayesian model averaging, as well as simple kriging and regression kriging are used to interpolate point-scale values. Elevation and a wind-redistribution parameter exhibit the highest correlations with winter balance, but the relationship varies considerably between glaciers. A Monte Carlo analysis reveals that the interpolation itself introduces more uncertainty than the assignment of snow density or the representation of gridcell-scale variability. Despite challenges associated with estimating winter balance, glacier-wide values are consistent with a regional-scale winter-balance gradient.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Gwenn Flowers
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Optical dating of stabilized parabolic dunes, Savary Island, British Columbia

Date created: 
2017-06-13
Abstract: 

Research has shown that the south coast of British Columbia (BC) has experienced changes in relative sea level and climate since deglaciation (~15 ka ago); however, there has been little study of the landscape’s response to these changes. On Savary Island, in the Strait of Georgia, there exist large parabolic dunes that are unique to the region. These dunes are stabilized, supporting mature forest growing in well-developed soil, and they contain eroded palaeosols indicating that their formation was punctuated by periods of episodic stabilization and soil formation. Optical ages from K-feldspar indicate that dune formation began prior to 7.69 ± 0.71 ka and stabilized by about 5.47 ± 0.36 ka ago when relative sea level lowering was slowing and climate was becoming cooler and moister. Periods of landscape stability during dune formation were brief, probably lasting only a few hundred years.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Brent Ward
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Characterizing Recharge to Fractured Bedrock in a Temperate Climate

Date created: 
2017-05-16
Abstract: 

Fractured bedrock aquifers can have large seasonal water table fluctuations due to their low storage capacity. This study uses a land surface – subsurface model, MIKE SHE, to investigate the spatial and seasonal rainfall-runoff-recharge dynamics on Gabriola Island, in a temperate region of British Columbia, Canada. The model results suggest that recharge averages 20% of the annual precipitation, occurring dominantly over 70% of the island, typically at higher elevation. Perennial seepage areas are simulated over 4% of the island, and are generally confined to breaks in slope in low topography areas. The high water table in late fall to early spring causes both seepage and saturated overland flow to contribute to more runoff. Increases in precipitation due to climate change leads to increased runoff (+36% to +40%) and recharge (+8% to +10%) relative to today. Recharge changes are most significant in winter (+13% to +16%), compared to summer (-3% to -4%).

Document type: 
Thesis
File(s): 
Senior supervisor: 
Diana Allen
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Channel scour on temperate alluvial fans in British Columbia

Date created: 
2017-06-01
Abstract: 

This thesis examined the morphometric controls on channel scour depth on temperate fans in British Columbia, Canada. Scour measurements and morphometric variables were catalogued for 116 fans and used to develop a predictive multivariate equation. Stepwise regression and multimodel inference were used to rank the importance of each morphometric variable and to develop the final predictive models. Watershed area, fan gradient, and fan relief were identified as the most important variables that contributed to channel scour. The predicted scour values explained approximately half of the variance in the observed scour measurements, with the largest deviations observed at higher values. A case study of a debris flow event at Neff Creek demonstrated that intense fan scour can amplify the final deposit volume and cause significant damage on the distal fan. The results of this study can be used to prioritize scour hazard assessments for infrastructure development on fans.

Document type: 
Thesis
Senior supervisor: 
Brent Ward
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.