PRISM :: Browsing by Author "Grasby, Stephen E."

Browsing by Author "Grasby, Stephen E."

Now showing 1 - 9 of 9

Open Access
Controls on the chemistry of the Bow River, southern Alberta, Canada
(1997) Grasby, Stephen E.; Hutcheon, Ian E.
Open Access
Devonian to Carboniferous Earth Systems Change in Western Laurentia
(2019-05-22) Hedhli, Makram; Beauchamp, Benoît; Grasby, Stephen E.; Meyer, Rudi; Henderson, Charles M.; Dutchak, Alexander
The Devonian to Carboniferous (DC) transition is marked globally by carbonate factories turnover, anoxia, profound unconformities and mass extinctions. Various authors have proposed global mechanisms such as meteorite impact, global climate cooling, anoxia, intensification of upwelling, etc. The DC boundary in western Canada and western United States has recorded this major Earth Systems change. Yet, a holistic study of this subject is non-existent. Sixteen sections across the DC boundary from Famennian to Viséan strata, in Alberta, Montana and Nevada were measured, sampled and analyzed. The DC sequence stratigraphy of western Laurentia was revisited based on microfacies analysis and field observations performed in these sections. The DC anoxia was also studied from five outcrop sections, providing the first coherent understanding of environmental changes along the continental margin of western Laurentia. Sediment provenance was examined based on detrital zircon analysis. Carbonate factories turnover and a depositional change from a Devonian warm-water carbonate ramp to a Carboniferous cool-water carbonate distally-steepened ramp were documented. Microfacies distribution in time was compared with geochemical proxies to emphasize the interaction between the biosphere, oceanography and palaeoclimate at the onset of the Permian-Carboniferous ice-house climatic mode. Two low-order T-R sequences were correlated from Alberta to Nevada. Results from this work provide clarification of the spatial-temporal extent of environmental changes and anoxia across Laurentia. This work demonstrates that these events are unrelated to the Hangenberg event recorded in Europe, as commonly suggested by various authors. Carbonate factories shut down and turnover, influx of westerly-derived sediments that are sourced from the Antler terranes, with northern affinities suggest that the Antler Orogeny, and associated plate tectonic reorganization, were the main contributors to the DC Earth Systems change in western Laurentia, rather than being part of a global event. This study demonstrates that the simple global-event paradigm across the D-C boundary does not adequately explain regional changes in the rock record.
Open Access
Groundwater contribution to Sylvan Lake, Alberta, Canada
(2009) Baker, Jennette L.; Grasby, Stephen E.; Ryan, M. Cathryn
Open Access
Influence of saline groundwater discharge on river water chemistry in the Athabasca oil sands region – A chloride stable isotope and mass balance approach
(Elsevier, 2017-12-01) Gue, Anita; Grasby, Stephen E.; Mayer, Bernhard
A chloride mass and stable isotope (δ37Cl) balance approach was employed to calculate the effect of saline groundwater discharge into the Athabasca and Clearwater rivers in the Athabasca Oil Sands Region (AOSR) in north-eastern Alberta, Canada. Saline groundwater affected by halite, carbonate, and anhydrite dissolution discharges Na-Cl type water with total dissolved solids (TDS) up to 51,700 mg/L from exposed Devonian and Cretaceous units in the river valleys in this area. In this study, nine springs discharging groundwater with a median Cl concentration of 9800 mg/L were sampled and chloride stable isotope ratios were determined, with δ37Cl values ranging from 0.2 to 1.0‰. In contrast, river waters had historical monthly median Cl concentrations between 5.9 and 49.5 mg/L and δ37Cl values between −2.2 and −1.4‰. The discharge rate of saline groundwater was calculated to be 100 ± 20 L/s into the Clearwater River and 134 ± 68 L/s into the Athabasca River. The chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions, metals, and PAHs in the Athabasca and Clearwater rivers. Overall, saline groundwater contributed less than 0.2% of river discharge, but 0.04–39% of major ion concentrations in the rivers, with highest contributions under winter low-flow conditions. In the Clearwater River, saline groundwater contributed 23–39% of average monthly Cl flux and 18–32% of average monthly Na flux. For the same major ion fluxes in the Athabasca River, saline groundwater contributed 12–18% and 6–12%, respectively. The influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible, contributing less than 1% of river fluxes of Cu, Ni, Pb, and Zn. Similarly, the influence on mass flux of PAHs in the rivers was found to be negligible (<0.03%) but quantifiable. These results provide important insights on the natural contributions of saline groundwater discharge to river chemistry in the AOSR, a necessary factor to consider when monitoring for anthropogenic effects of oil sands development on river water quality.
Open Access
Microbial Taxonomic and Functional Diversity in Canadian Saline and Thermal Springs
(2019-07-15) Ruhl, Ilona Albertovna; Dunfield, Peter F.; Strous, Marc; Grasby, Stephen E.; Fox, Jeremy W.
By demonstrating a strong effect of salinity on microbial species diversity, this work expanded the known environmental parameters that influence microbial taxonomic diversity. Additionally, this work showed that environmental stress reduces both taxonomic and functional diversity of microbial communities. pH and temperature are strong drivers of microbial taxonomic diversity, with extreme environments supporting reduced diversity. To examine the effect of another environmental parameter, salinity, on diversity, 16S rRNA and 18S rRNA gene amplicon libraries constructed from 55 sediment samples ranging in conductivity from near-fresh to halite-saturated were sequenced on the Illumina platform. Increasing conductivity, as a proxy for salinity, was found to be correlated with a reduction in bacterial taxonomic diversity in a linear manner, with peak diversity occurring at the lowest salinities examined. Conductivity also influenced the diversity of Archaea and microbial Eukarya, and these trends were explained in terms of energetic costs of salinity tolerance and mechanisms of energy production in these organisms. A small number of studies suggest that functional diversity (all of the different metabolic functions within a community) declines with decreasing taxonomic diversity of microbial communities. This relationship was tested using a dataset of 12 geothermal springs ranging in temperature from 24 to 86 °C. Functional diversity was calculated by quantifying the Pfam (protein family) diversity contained within metagenomic libraries constructed from these samples. Functional diversity was found to decrease with temperature in a similar manner to taxonomic diversity. Lastly, a study of an uncultivated clade of Bacteria, GAL08, dominating microbial communities in a geothermal spring at Dewar Creek, British Columbia, was undertaken. Material from Dewar Creek was subjected to single-cell sorting and sequencing, resulting in the identification of 13 partial single-cell genomes belonging to GAL08. Analysis of the genomes revealed the presence of three species of GAL08 at Dewar Creek. Surveys of sediment from Dewar Creek showed that GAL08 is a persistent and stable member of the microbial community, and is thermophilic, with a temperature preference of 55 to 70 °C. Laboratory enrichment experiments determined that GAL08 is likely microaerophilic. By demonstrating that the effect of salinity on microbial species diversity can be explained in terms of energy constraints, this work expanded our understanding of how environmental parameters may drive microbial diversity. Furthermore, this work represented one of the few thorough investigations into the relationship between functional diversity and environmental stress in microbial communities. Elucidating how microbial taxonomic and functional diversity responds to changes in environmental parameters, such as temperature, is timely considering the ongoing changes in global climate.
Open Access
Origin and geochemistry of saline spring waters in the Athabasca oil sands region, Alberta, Canada
(Elsevier, 2015-10-01) Gue, Anita E.; Mayer, Bernhard; Grasby, Stephen E.
The geochemistry of saline spring waters in the Athabasca oil sands region (AOSR) in Alberta (Canada) discharging from Devonian carbonate rocks into the Athabasca and Clearwater rivers was characterized for major ions, trace elements, dissolved gases, and polycyclic aromatic hydrocarbons (PAHs). In addition, stable isotope analyses of H2O, SO4, dissolved inorganic carbon (DIC), Sr, and CH4 were used to trace the sources of spring waters and their dissolved solutes, and to identify subsurface processes affecting water chemistry. The spring waters had δ18O values as low as −23.5‰, suggesting they are composed of up to 75% Laurentide glacial meltwater. Tritium and radiocarbon age-dating results, analyzed for three spring waters, supported a glacial origin. The high salinity of the spring waters (TDS 7210–51,800mg/L) was due to dissolution of Devonian evaporite and carbonate deposits in the subsurface. Spring waters were affected by bacterial (dissimilatory) sulfate reduction, methanogenesis, and methane oxidation. Trace elements were present in spring waters at varying concentrations, with only one spring containing several predominant oil sands metals (As, Fe, Mo, Ni, Se, Zn) suggesting bitumen as a source. Five springs contained elements (Al, As, B, Fe, Se) at concentrations exceeding water quality guidelines for the protection of aquatic life. Seven PAHs were detected in spring waters (total PAH concentrations ranged from 7.3 to 273.6ng/L), but most springs contained a maximum of two PAHs (phenanthrene and naphthalene), with more PAHs being detected in springs along the Athabasca River. This geochemical characterization of the saline groundwater discharging from the Devonian carbonates underlying oil sands deposits contributes to the knowledge of baseline groundwater chemistry in the AOSR, which is of importance in the delineation of natural versus anthropogenic effects on regional surface water and groundwater quality.
Open Access
Spring geochemistry: a tool for mineral exploration in the South Nahanni River Basin, NWT
(2007) Caron, Marie-Eve; Ryan, M. Cathryn; Grasby, Stephen E.
Geochemical data from over 200 springs within the remote 37,000 kms South Nahanni River Basin of the Mackenzie Mountains, Northwest Territories, were used to evaluate the economic mineral potential of the region which is proposed for a national park designation. Trace element analyses were evaluated using three different approaches (the sum of trace element concentrations as a percentage of total dissolved solids, identifying individual elevated trace elements, and the inverse use of the Ficklin Diagram). Two out of the three approaches detected the two known deposits of the area, Prairie Creek and Tungsten, but not with the same method in each case, indicating that a multi-pronged approach is best. The springs are elevated in trace elements in comparison to mineral deposit related waters around the world. Silica geothermometry determined the average depth of circulation of the springs to be 2.1 km in the warm or hot springs and ranging from 4. 7 km to less than 200 m for the entire dataset, indicative of the accessibility of the predicted mineralized zones. These simple statistical and graphing methods can identify mineralized zones quickly and efficiently in a largely under-explored area.
Open Access
Spring geochemistry: a tool for mineral exploriation in the South Nahanni River Basin, NWT
(2007) Caron, Marie-Eve.; Ryan, M. Cathryn; Grasby, Stephen E.
Open Access
Upper Triassic Mid-Latitude Cool-Water Carbonate Deposit: Sedimentology and Stratigraphy of the Gore Point Member, Roche Point Formation, Arctic Islands, Canada
(2021-02-04) Hay, Chelsey; Beauchamp, Benoît; Grasby, Stephen E.; Meyer, Rudi; Dutchak, Alex
The Gore Point Member is a mixed carbonate-siliciclastic unit deposited in the Sverdup Basin (Canadian Arctic Islands) during the Carnian (Late Triassic). While mixed carbonate-siliciclastic deposits are not rare within the global rock record, the Gore Point Member is unique in that it is the only unit with meaningful amounts of carbonate material within the Mesozoic succession of the Sverdrup Basin. However, as detailed sedimentological or sequence stratigraphic studies of the Gore Point Member have been yet to be undertaken, the existence of this anomalous unit remains unexplained. This study applies thin section microscopy and microfacies analysis of 285 samples from 12 sites across western Ellesmere Island, and lithofacies analysis of one core on Mackenzie King Island, to interpret the depositional setting of the Gore Point Member. These observations reveal fine-grained quartz-dominated siliciclastics and heterozoan carbonate material deposited in a ramp setting in an arid, cool-temperate environment. Integration of sedimentological trends with subsurface wireline well logs throughout the Sverdrup Basin reveals deposition across three fourth-order transgressive-regressive sequences. It is postulated that the arid climate along with tectonic quiescence reduced siliciclastic input, providing a window of opportunity for heterozoan biota to propagate. The Gore Point Member is significant as it is one of very few examples globally of a ramp-type carbonate deposit from the Triassic, and the highest latitude and most cool-water example recognized thus far.

Browsing by Author "Grasby, Stephen E."

Results Per Page

Sort Options

Libraries & Cultural Resources