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Resolving the Architecture and Early Evolution of a Forearc Basin (Georgia Basin, Canada) Using Detrital Zircon

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-10-25
Abstract: 

Convergent-margin basins (CMBs) are commonly associated with active arcs, and hence are rich in detrital zircon (DZ) whose ages closely reflect the timing of deposition. Consequently, maximum depositional ages (MDA) from DZ geochronology can be employed to resolve the stratigraphy and evolution of CMBs. Herein, we use DZ to revise the internal architecture of the lower Nanaimo Group, which partially comprises the fill of the (forearc) Georgia (or Nanaimo) Basin. Maximum depositional ages and multi-dimensional scaling of DZ age distributions are employed to determine chronologic equivalency of strata and assess sediment provenance variability within the pre-existing lithostratigraphic framework. The results are compared to a recently developed sequence stratigraphic framework for the lower Nanaimo Group. The basal lithostratigraphic unit of the Nanaimo Group, the Comox Formation (Fm), comprises strata that are neither time correlative nor genetically related. The three lithostratigraphic units directly overlying the Comox Fm (Haslam, Extension, and Protection formations) comprise strata with similar genetic affinities and MDAs that indicate deposition of these units was not always sequential and locally was contemporaneous. Through this work, we provide an example of how MDAs from DZ geochronology in CMBs can resolve basin-scale stratigraphic relations, and identify chronological changes in sediment provenance.

Document type: 
Article
File(s): 

Pursuit of Optimal Design for Winter-Balance Surveys of Valley-Glacier Ablation Areas

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-08-06
Abstract: 

Efficient collection of snow depth and density data is important in field surveys used to estimate the winter surface mass balance of glaciers. Simultaneously extensive, high resolution, and accurate snow-depth measurements can be difficult to obtain, so optimisation of measurement configuration and spacing is valuable in any survey design. Using in-situ data from the ablation areas of three glaciers in the St. Elias Mountains of Yukon, Canada, we consider six possible survey designs for snow-depth sampling and N = 6–200+ sampling locations per glacier. For each design and number of sampling locations, we use a linear regression on topographic parameters to estimate winter balance at unsampled locations and compare these estimates with known values. Average errors decrease sharply with increasing sample size up to N ≈ 10–15, but reliable error reduction for any given sampling scheme requires significantly higher N. Lower errors are often, but not always, associated with sampling schemes that employ quasi-regular spacing. With both real- and synthetic data, the common centreline survey produces the poorest results overall. The optimal design often requires sampling near the glacier margin, even at low N. The unconventional “hourglass” design performed best of all designs tested when evaluated against known values of winter balance.

Document type: 
Article
File(s): 

Pursuit of Optimal Design for Winter-Balance Surveys of Valley-Glacier Ablation Areas

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-08-06
Abstract: 

Efficient collection of snow depth and density data is important in field surveys used to estimate the winter surface mass balance of glaciers. Simultaneously extensive, high resolution, and accurate snow-depth measurements can be difficult to obtain, so optimisation of measurement configuration and spacing is valuable in any survey design. Using in-situ data from the ablation areas of three glaciers in the St. Elias Mountains of Yukon, Canada, we consider six possible survey designs for snow-depth sampling and N = 6–200+ sampling locations per glacier. For each design and number of sampling locations, we use a linear regression on topographic parameters to estimate winter balance at unsampled locations and compare these estimates with known values. Average errors decrease sharply with increasing sample size up to N ≈ 10–15, but reliable error reduction for any given sampling scheme requires significantly higher N. Lower errors are often, but not always, associated with sampling schemes that employ quasi-regular spacing. With both real- and synthetic data, the common centreline survey produces the poorest results overall. The optimal design often requires sampling near the glacier margin, even at low N. The unconventional “hourglass” design performed best of all designs tested when evaluated against known values of winter balance.

Document type: 
Article
File(s): 

Changes in Ground Deformation Prior To and Following A Large Urbanlandslide in La Paz, Bolivia Revealed By Advanced InSAR

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-03-29
Abstract: 

We characterize and compare creep preceding and following the complex 2011 Pampahasi landslide (∼40 Mm3±50 %) in the city of La Paz, Bolivia, using spaceborne radar interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilized deposits of an ancient complex landslide in weakly cemented, predominantly fine-grained sediments and affected ∼1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm a−1 and localized parts of the scarp area showed displacements of up to 14 cm a−1. Changes in deformation in the 10 months following the landslide demonstrate an increase in slope activity and indicate that stress redistribution resulting from the discrete failure decreased stability of parts of the slope. During that period, most of the landslide toe and areas near the head scarp accelerated, respectively, to 4–14 and 14 cm a−1. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns, supplemented by field observations and optical satellite images, reveal complex slope activity; kinematically complex, steady-state creep along pre-existing sliding surfaces accelerated in response to heavy rainfall, after which slightly faster and expanded steady creeping was re-established. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities; such details are especially useful where knowledge of landslide extent and activity is limited. Characterizing slope activity before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar large paleolandslides.

Document type: 
Article

Late Mesozoic Reactivation of Precambrian Basement Structures and their Resulting Effects on the Sequence Stratigraphic Architecture of the Viking Formation of East-Central Alberta, Canada

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-02-06
Abstract: 

The Lower Cretaceous Viking Formation is a siliciclastic unit that occurs in the subsurface of Alberta in the Western Canadian sedimentary basin. This study focuses on a lowstand paleoshoreline trend extending along strike between two hydrocarbon-producing fields, Joarcam and Judy Creek (250 km NW). The Viking Formation in these fields records depositional thicknesses ranging from 20 to 30 m. Between these two fields, however, the formation is anomalously thick (45–60 m), complicating the recognition and correlation of key stratigraphic surfaces. Marine flooding surfaces above and below the Viking Formation are routinely employed as stratigraphic datums in order to remove postdepositional deformation and facilitate the development of a sequence stratigraphic framework. However, as each successive surface is employed as the datum, the other flooding surfaces within the formation become distorted, resulting in unrealistic depositional geometries. These geometries are best explained to be the result of structural readjustments during Viking deposition.

The Precambrian lithosphere of the Canadian Shield forms the Western Canadian sedimentary basin basement, with major structures previously mapped using gravity and magnetic anomaly studies. Locally, the increased accommodation observed within the Viking Formation of central Alberta is attributed to differential reactivation of the Paleoproterozoic Snowbird tectonic zone basement structures, which flank the areas of anomalously thick deposits and trend approximately normal to the regional strike of the Western Canadian sedimentary basin. The Snowbird tectonic zone faults are interpreted to have been reactivated during renewed tectonic loading in the southern Canadian Cordillera during Aptian–Albian time, causing subtle readjustments along basement faults that caused variable syndepositional subsidence. By selecting successive datums, the gross Viking interval can be recognized to have accumulated prior to, during, and following structural reactivation.

Document type: 
Article
File(s): 

An Assessment of the Methodologies Used for Analyzing Hydraulic Test Data from Bedrock Wells in British Columbia

Author: 
Peer reviewed: 
No, item is not peer reviewed.
Date created: 
1999-04
Abstract: 

Hydraulic test data are typically analyzed using one of several common analytical methods (e.g. Theis, Cooper-Jacob). However, each analytical method has its specific limitations, and should be used only when the assumptions inherent to the model are valid for the aquifer being characterized. The aim of this research was to identify what types of flow conditions are typically present in bedrock aquifers around the province of BC to determine how these are manifest as subtle departures from ideal flow conditions as exhibited in the hydraulic test data.

Document type: 
Technical Report

Vulnerability Assessment for Groundwater Dependent Streams

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-04
Abstract: 

This guidance document “Vulnerability Assessment for Groundwater Dependent Streams”, describes a multi-step, risk-based approach for evaluating the vulnerability of groundwater dependent streams to changes in the aquifer system. There is a particular emphasis on the summer low flow period, because it is during this time that streams can be sensitive to changes in the aquifer system; however, in principle the methodology can be used to assess stream vulnerability year round.

Document type: 
Technical Report
File(s): 

Groundwater—Surface Water Interactions in a Mountain-to-Coast Watershed: Effects of Climate Change and Human Stressors

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015
Abstract: 

Watersheds located within a mountain to coast physiographic setting have been described as having a highly interconnected surface water and groundwater environment. The quantification of groundwater—surface water interactions at the watershed scale requires upscaling. This study uses MIKE SHE, a coupled numerical model, to explore the seasonally and spatially dynamic nature of these interactions in the Cowichan Watershed on Vancouver Island, British Columbia, Canada. The calibrated model simulates a transition of the Cowichan River from mostly gaining within the valley, to losing stream near the coast where groundwater extraction is focused. Losing and gaining sections correlate with geological substrate. Recharge across the watershed accounts for 17% of precipitation. Climate change is projected to lessen snowpack accumulation in the high alpine and alter timing of snowmelt, resulting in higher spring and winter river discharge and lower summer flows.

Document type: 
Article
File(s): 

Structural Interpretation of the Mamfe Sedimentary Basin of Southwestern Cameroon along the Manyu River Using Audiomagnetotellurics Survey

Author: 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2012
Abstract: 

Five audiofrequency magnetotelluric AMT soundings were collected northwest-southeast along the Manyu river in the Mamfe sedimentary basin of southwestern Cameroon. The soundings were performed with frequencies in the range 3 to 2500 Hz and covered a distance of approximately 28 km. Sounding curves and geoelectric and geological sections were processed, and the results were compared with rocks' resistivity to characterize the lithostratigraphy of the eastern part of the basin. The results show above 1000 m depth, sedimentary layers with resistivities in the range of 1 to 100 Ohm-m, which decrease with depth. We identified three types of sedimentary rocks: laterite-clay mixture, shale, and sandstones. Various faults were also identified, illustrating the structural complexity of the Mamfe basin, along the Manyu River.

Document type: 
Article
File(s): 

A Novel Approach to Modelling Water Transport and Drug Diffusion Through the Stratum Corneum

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2010
Abstract: 

Background: The potential of using skin as an alternative path for systemicallyadministering active drugs has attracted considerable interest, since the creation ofnovel drugs capable of diffusing through the skin would provide a great steptowards easily applicable -and more humane- therapeutic solutions. However, fordrugs to be able to diffuse, they necessarily have to cross a permeability barrier: thestratum corneum (SC), the uppermost set of skin layers. The precise mechanism bywhich drugs penetrate the skin is generally thought to be diffusion of moleculesthrough this set of layers following a “tortuous pathway” around corneocytes, i.e.impermeable dead cells.Results: In this work, we simulate water transport and drug diffusion using a threedimensionalporous media model. Our numerical simulations show that diffusiontakes place through the SC regardless of the direction and magnitude of the fluidpressure gradient, while the magnitude of the concentrations calculated areconsistent with experimental studies.Conclusions: Our results support the possibility for designing arbitrary drugs capableof diffusing through the skin, the time-delivery of which is solely restricted by theirdiffusion and solubility properties.

Document type: 
Article