2022

Permanent URI for this collectionhttps://hdl.handle.net/1807/109473

Browse

Now showing 1 - 20 of 37

A 500 ka Record of Volcanism and Paleoenvironment in the northern Garibaldi Volcanic Belt, British Columbia.
(Canadian Science Publishing, 2022-11-24) Harris, Martin A; Russell, James Kelly; Wilson, Alexander; Jicha, Brian
The Mount Meager Volcanic complex (MMVC) is one of eight major calc-alkaline volcanic centres within the Garibaldi volcanic belt, Canada. MMVC volcanism spans ~2 Ma and has been mainly intermediate to felsic in composition. However, small volume mafic centres are located around the periphery of the Mount Meager massif and have been collectively referred to as the Mosaic Assemblage or Mount Meager basalts. Here we present new 40Ar/39Ar ages and expanded chemical datasets for the MMVC mafic rocks. We show that mafic eruptive ages are both older and longer-lived than previously interpreted, spanning the last ~450 ka, and occurring in four episodes at, ~440, 200, 106, and 17 ka. We also find that chemical signatures for the MMVC mafic rocks have evolved across the four periods, fluctuating from ‘OIB’-like melt characteristics, to more typical slab-influenced, calc-alkaline, before returning to ‘OIB’-like in the youngest phase. These findings provide the first evidence of a temporal-chemical evolution of melt sourcing for the Garibaldi belt volcanism. Lastly, field mapping has identified edifices and deposits that are glaciovolcanic in origin (vs. non-glaciovolcanic) which are used in conjunction with our new 40Ar/39Ar age estimates to document the presence or absence of Coast Mountain sectors of earlier Cordilleran ice sheets in SW British Columbia over the last 500 ka.
U-Pb zircon ages from metasedimentary and plutonic rocks in the Bras d'Or terrane of Cape Breton Island, Nova Scotia, Canada: Insights into the Ediacaran-Cambrian tectonomagmatic evolution of Ganderia
(Canadian Science Publishing, 2022-11-25) van Rooyen, Deanne; Barr, Sandra M.; White, Chris E; Crowley, James L.
The Bras d’Or terrane of central Cape Breton Island, Nova Scotia, Canada, contains a well-preserved record of the Ediacaran to Early Cambrian evolution of Ganderia, a Gondwana-derived terrane in the northern Appalachian orogen. A complex assemblage of low- to high-grade metasedimentary rocks have varied detrital zircon signatures from LA-ICP-MS U-Pb zircon dating but combining 3 or more samples yielded representative age spectra which support correlation of the low- and high-grade metasedimentary rocks throughout the Bras d’Or terrane and the corresponding Ganderian Brookville terrane of southern New Brunswick. In quartzite samples from the McMillan Flowage Formation in the northwestern Bras d’Or terrane the youngest detrital zircons have ages >900 Ma, in contrast to previously studied psammitic and semi-pelitic samples from correlative units in the eastern Bras d’Or terrane in which youngest detrital ages are 620–600 Ma. Both quartzite and semi-pelitic samples from the McMillan Flowage Formation contain Neoproterozoic dates from zircon rims which reflect metamorphic overgrowths during peak metamorphism at ca. 550 Ma, providing a robust age for peak metamorphism in the Bras d’Or terrane that supports similar, albeit sparse, ages reported previously from monazite and titanite samples. This metamorphism is coeval with the emplacement of voluminous dioritic to granitic plutons that occur throughout the Bras d’Or terrane and formed in an Andean-type continental margin subduction zone. New U-Pb zircon ages presented here from plutons in the northern Bras d’Or terrane, combined with previously published ages, are consistent with subduction-related magmatism and associated metamorphism between ca. 575 Ma and 540 Ma.
The Lower Cretaceous sequence of western Alaska – demise of the Koyukuk terrane?
(Canadian Science Publishing, 2022-11-21) Hudson, Travis; Blodgett, Robert B.; Wilson, Frederic H.
Lower Cretaceous marine sedimentary rocks, deposited in shallow shelf and basin settings and unconformity-bound, are well exposed in southwest Alaska. Collections of Early Cretaceous fossils from across western Alaska show that similar and coeval Lower Cretaceous clastic rocks are widely distributed though only locally exposed. Volcanic rocks become an important part of the Lower Cretaceous sequence in the Yukon-Koyukuk basin where they have been interpreted to represent a mobile intra-oceanic island arc, the Koyukuk terrane, that collided with Arctic Alaska to form the Brooks Range orogen. The volcanic rocks are chemically unlike Aleutian arc rocks but share compositional characteristics with spatially related, mid-Cretaceous alkaline intrusive rocks. The volcanic-bearing sequence was also deposited on an angular unconformity, includes both shallow shelf and basin depositional settings, and is unconformably overlain by mid-Cretaceous clastic rocks. The volcanic rocks are therefore considered part of the Lower Cretaceous sequence now identified across western Alaska. In this interpretation, the Lower Cretaceous volcanic rocks are an initial expression of the mid-Cretaceous tectonic regime that included extensional exhumation and subsidence, crustal and upper mantle melting, and high temperature metamorphism in the hinterland of the Brooks Range orogen. The Cretaceous heating that led to hinterland crust and upper mantle change may have been caused by deep mantle disturbances in a post-subduction setting. This interpretation has implications for the timing of contractional orogenesis, the location and nature of the related continental borderland, and the tectonic setting for development of the Anguyucham and related oceanic terranes.
Glacial Microsedimentology – a new lens to investigate Glacial Sediments – a review
(Canadian Science Publishing, 2022-10-28) Menzies, John
Glacial sediment research using thin sections began post-1945. Microsedimentology examines sediments at the microscopic level deriving insights into the processes of glacial erosion, transport, and deposition. Two issues exist (1) the difficulty by some in recognizing microstructures in thin section; and (2) the absence of quantitative data making data reproduction difficult. The latter is hard to resolve but more image capture and software methodologies are now becoming available at reasonable costs. Thin sections are two-dimensional sections of three-dimensional objects, and this must be considered when measurements, fabrics and other data are assessed. Research into the micro-aspects of glacial sediments followed a typical scientific trajectory: thin sections description with little uniformity or common ‘language’ for observed microstructures: standardization allowed comparison between different sediments; with standardization, came an open-ended classification; and with cross-comparison with multiple thin sections - a quantitative means of study needs developed. It has become apparent that the basic principles of structural geology had to be applied. Thus, micromorphology has subsumed into a microsedimentological study of glacial sediments where stress parameters, structural fabrics and the mapping of deformation structures and contextual integration allows an understanding of how these sediments have been formed. Examples of the development stages of glacial micromorphology / sedimentology are presented here as well as discussion of future avenues of study. In addition, multiple thin sections are used to illustrate the many aspects of glacial micromorphology and the parameters necessary to understand glacial sedimentology and the processes of glacial sedimentation.
Introduction to Landscape Seascape Responses to Canada’s Changing Climate
(Canadian Science Publishing, 2022-08-30) James, Thomas S; Blais-Stevens, Andrée; Clague, John J.; Forbes, Donald L.; Leblanc, Anne-Marie; Smith, Sharon L.
No abstract for this introductory article.
The Paleoproterozoic Amer supergroup, Amer Fold Belt, Nunavut: stratigraphy, structure, correlations and uranium metallogeny
(Canadian Science Publishing, 2022-10-13) Jefferson, Charles W.; Rainbird, Robert H; Young, Grant M.; White, Joseph C.; Tschirhart, Victoria; Creaser, Robert A.
The Amer Belt, hosting eleven informal formations of the Amer supergroup, is proposed as type area for four regional Paleoproterozoic sequences (Ps1-Ps4) in central Rae Craton, western Churchill Province. The ca. 1.9-1.865 Ga Snowbird orogeny (DP1) affected only Ps1-Ps3, whereas the ca. 1.87-1.81 Ga Hudsonian orogeny (DP2) affected all four. Sequence Ps1 Ayagaq Lake formation (
Probabilistic Assessment of Induced Seismicity at the Alberta No. 1 Geothermal Project Site
(Canadian Science Publishing, 2022-09-19) Yaghoubi, Ali; Dusseault, Maurice; Leonenko, Yuri; Hickson , Catherine
Alberta No.1 is a geothermal project targeting deep carbonate, conglomerates, and sandstone formations in a potential production and injection zone for geothermal energy exploitation within the Municipal District of Greenview south of Grande Prairie, Alberta, Canada. In geothermal systems without a steam fraction (typically systems under 170°C), rapid widespread pore pressure changes and slow temperature changes have led to increased deviatoric stresses, resulting in induced seismicity. A concern for the Alberta No.1 Geothermal Project is that anthropogenic seismicity from oil, gas, and well field fluid injection has created felt events in Alberta. Thus, at the beginning of this type of project, it is prudent to review the potential for induced seismicity. In this study, a geomechanical study of the Leduc and Granite Wash Formations, two potential geothermal fluid exploitation zones, has been undertaken based on borehole geophysics and regional injection-induced earthquake data. Determining subsurface properties such as state of stress, pore pressure, and fault properties, however, poses uncertainties in the absence of actual data from the target formations. Geomechanical analysis results (with associated uncertainties) are used to assess the potential for injection-induced earthquakes. A Monte Carlo probability analysis is employed to estimate the likelihood of slippage of the known faults close to the Alberta No.1 Geothermal Project. A cumulative distribution function of the critical pore pressure on each fault is derived from the local tectonic stress state and Mohr-Coulomb shear parameter analyses. The resultant probabilistic fault stability maps can serve as a baseline for future fluid injection projects in the region including wastewater disposal, hydraulic fracture stimulation, CO2 sequestration, as well as geothermal energy extraction.
Trans-Avalonian green–black boundary (early Middle Cambrian): transform fault-driven epeirogeny and onset of 26 m.y. of shallow marine anoxia in Avalonia (Rhode Island–Belgium) and Baltica
(Canadian Science Publishing, 2022-08-19) Landing, Ed; Westrop, Stephen R.; Geyer, Gerd
The Avalonia microcontinent has diagnostic terminal Ediacaran–Ordovician lithostratigraphy, depositional sequence architecture, and igneous activity that extends for 2000+ km and reflects epeirogeny related to the Avalonian transform fault. Avalonia records an abrupt early Middle Cambrian (late Wuliuan) change from green, purple, or light grey to overlying black, dark grey, and brown facies in platform and off-platform areas (Meguma, North Wales). This change within one trilobite zone marks onset of ca. 26 m.y. of shallow-marine anoxia/strong dysoxia lasting into the Ordovician with Hatch Hill OMZ onlap onto the shelf. A Bakken model (new, based on the middle Paleozoic Bakken Formation) is applied to shallow-shelf–shoreline organic-rich mud deposition. Erosion of greenish Avalonian depositional sequence (Ads) 7 was followed by Ads 8 tilting, volcanism, debris flows, and bentonite deposition on a cryptic unconformity in SE Newfoundland. The early Middle Cambrian age of the Ads 7–8 boundary is obscured by referring the lower Manuels River Formation and Cristallinium cambriense Zone to the younger Drumian Stage. Ads 8 has thin ashes in coterminous British and American Avalonia where erosion and subaerial exposure with caliche development preceded onlap of upper Middle or Upper Cambrian Ads 9 black muds and sands. The green–black change emphasizes Avalonian unity; it precludes multiple Avalonian “micro-terranes” or assigning parts of Avalonia to West Gondwana or “Ganderia” (the Little River, Brookville, and Bras d’Or “terranes” are part of the Avalonian marginal platform). Coeval green–black transitions and similar later Cambrian faunas show comparable paleoenvironments in Avalonia and Baltica.
Morphology and Tectonic modification of the Sudbury Impact Crater - The North Range
(Canadian Science Publishing, 2022-10-24) Morris, William A.; Underhay, Sara-Lise; Ugalde, Hernan
The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include: variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20o, and differing magnetic fabrics in the norite / gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC is established using, dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show: a) the elliptical form of the North Range is a primary feature associated with a near circular impact crater, b) some of the original crater wall must have been preserved, and c) deformation of the North Range is limited to regional scale block rotation producing a SW dip modified by minor block rotation tilting and vertical displacement associated with north-northwest trending faults.
The Terreneuvian MacCodrum Brook section, Mira terrane, Cape Breton Island, Nova Scotia, Canada: age constraints from ash layers, organic-walled microfossils, and trace fossils
(Canadian Science Publishing, 2022-09-19) Barr, Sandra M.; White, Chris E; Palacios, Teodoro; Jensen, Soren; van Rooyen, Deanne; Crowley, James L.
The MacCodrum Formation is a classical "lower" Cambrian unit in southeastern Cape Breton Island stratigraphy, described since the 1800s. The age of this formation and its correlation with Cambrian units in Avalonian eastern Newfoundland and southern New Brunswick have remained uncertain through numerous revisions. Here we present U-Pb CA-TIMS ages from an ash bed in the basal part of the MacCodrum Formation in its type-section on MacCodrum Brook that fix the maximum time of deposition at 531.86 ± 0.34 Ma. Organic-walled microfossils sampled throughout the MacCodrum Formation type-section yield acritarch taxa identifying the Asteridium-Comasphaerdium Zone, whereas the first acritarchs of the Skiagia-Fimbriaglomerella Zone appear in the overlying Canoe Brook Formation in other sections. The radiometric age and acritarch zonation place the MacCodrum Formation in the upper Fortunian, Cambrian Stage 2. Among trace fossils in the MacCodrum Formation the meandering trace fossil Didymaulichnus dailyi comb. nov. is of particular note and morphologically identical to the type material from the lower part of the Ratcliffe Brook Formation in New Brunswick. The new radiometric and biostratigraphic data presented here provide the first firm constraints on the age of the MacCodrum Formation and enable more precise correlation with sections in southern New Brunswick and eastern Newfoundland.
Linking Archaean climate change with gold metallogeny
(Canadian Science Publishing, 2022-08-10) Frimmel, Hartwig Egbert
First large-scale concentration of gold to ore grade in Earth’s crust took place at around 2.9 Ga in quartz-pebble conglomerates, well before endogenous deposits, such as porphyry and epithermal systems or orogenic-type deposits, started to play a significant role from ca. 2.75 Ga onwards. The conglomerate-hosted gold placers, typified by those in the Mesoarchaeaen Witwatersrand Basin in South Africa, are thought to have been sourced from the leaching of background levels of gold in the Archaean continental crust, promoted by deep chemical weathering under a reducing acidic atmosphere. Gold dissolved in meteoric waters was trapped by possibly acidophile microbes, fossil remnants of which are preserved as kerogen layers in the 2.9 Ga lower Central Rand Group of the Witwatersrand Supergroup. Mechanical reworking of the delicate microbial mat-bound gold led to rich gold placers from 2.9 Ga onwards. Well-endowed gold placers older than 2.9 Ga are conspicuously missing, although suitable siliciclastic host rocks, even containing relics of former microbes, are known from continental sediment sequences as old as 3.22 Ga. A review of climate-sensitive rock types and geochemical data on the extent of chemical weathering reveals that the period from 2.96 – 2.91 Ga was cold, with repeated glaciations as evidenced by glaciogenic diamicite, whereas warmer and/or wetter climates reigned from 2.90 to 2.78 Ga. In concert with the temporal distribution of placer gold accumulation, the conclusion is reached that chemical weathering rate, dictated by climate, was a key determining factor in the exogenous binding of Au into sedimentary deposits.
Analysis of chemical weathering trends across three compositional dimensions: applications to modern and ancient mafic-rock weathering profiles
(Canadian Science Publishing, 2022-10-24) Babechuk, Michael G.; Fedo, Christopher M.
Chemical weathering indices (one-dimensional/1D index values) and accompanying ternary plots (two-dimensional/2D compositional space) facilitate quantitative comparison of whole-rock and mineral major-element data, and empirical chemical trends with predicted weathering vectors. However, data analysis in ternary plots is restricted by poles grouping elements that are hosted in different minerals or that are influenced selectively by later alteration (e.g., diagenesis/metasomatism). Tetrahedral plots (three-dimensional/3D compositional space) offer enhanced analytical utility of major-element data by shifting elements across four poles and/or incorporating additional proxy elements. Tetrahedral space can better reveal combined effects on major-element compositions from independent mineralogical controls and post-depositional alteration via curvilinear trends that are otherwise simplified and linear in ternary space. This study focuses on mafic rock weathering and first reviews applications and limitations of the 1D mafic index of alteration (MIA) and index of lateritization/bauxitization (IOL/IOB) that integrate into molar Al2O3–CaO*–Na2O–K2O–(FeO(T)/Fe2O3(T))–MgO and SiO2–Al2O3–Fe2O3(T) ternary compositional space, respectively. Analysis in tetrahedral space is then demonstrated with Phanerozoic weathering profile and Precambrian paleosol data in two plots of the molar Al2O3–CaO*–Na2O–K2O–(FeO(T)/Fe2O3(T))–MgO system (A–CN–K–FM and AF–CN–K–M plots) and one plot of the molar Al2O3–CaO*–Na2O–K2O–(FeO(T)/Fe2O3(T))–MgO–SiO2 system (A–L–F–S plot). Common chemical weathering indices are integrated into these 3D tetrahedral spaces or onto some of their 2D ternary faces. However, the tetrahedral compositional space is a key to: (1) assessing integrative effects from labile element loss while accounting for the variable, redox-dependent behaviour of Fe, (2) better exposing, and correcting for, overprinting effects of diagenesis/metasomatism, and (3) tracking Si loss across all stages of chemical weathering.
Petrogenesis of siliciclastic sediments and sedimentary rocks explored in three-dimensional Al2O3 – CaO*+Na2O – K2O – FeO+MgO (A-CN-K-FM) compositional space
(Canadian Science Publishing, 2022-09-02) Fedo, Christopher M.; Babechuk, Michael G.
Quantitatively determining the amount of chemical weathering within sedimentary rocks (and weathering profiles) took a major step forward with the creation of the chemical index of alteration (CIA) forty years ago. The CIA relates the proportion of immobile aluminum to the mobile cations calcium, sodium, and potassium and is grounded in empirical and modeled geochemical data for mineral reactions that occur during hydrolysis. However, the CIA should be applied cautiously because it is a one-dimensional value that in the most complex situations, as with clastic sedimentary rocks, homogenizes the compositional inputs of source, weathering, sorting, and diagenesis. Subsequently developed two-dimensional ternary diagrams (Al2O3–CaO*+Na2O–K2O; Al2O3–CaO*+Na2O+K2O–FeO+MgO) permitted the capacity to explore mineralogical-geochemical pathways in data sets that may separate those inputs, but interpreting the ternary diagrams may be complicated because they differentiate and group certain elements. Here we develop a three-dimensional tetrahedral diagram (Al2O3–CaO*+Na2O–K2O–FeO+MgO, A-CN-K-FM) that incorporates the same critical elements and permits the simultaneous assessment of felsic and mafic rocks and minerals on the same diagram, while retaining the ability to separate plagioclase from alkali feldspar and monitor post-depositional potassium changes. Using the tetrahedral plot, we show that both the CIA value and positions on the 2D ternary diagrams can generate potentially misleading interpretations without properly budgeting the ferromagnesian components in parallel. We first show how the tetrahedron works, then use it with numerous previously published examples to identify how the competing mafic and felsic inputs shape the composition of source rocks, weathering profiles, actively transporting sediment, paleosols, and sedimentary rocks in sedimentary petrogenesis.
Late Quaternary changes in sediment sources in the Labrador Sea
(Canadian Science Publishing, 2022-09-02) Andrews, John T.; Piper, David J. W.
Quaternary sediment in the Labrador Sea was derived from many proglacial sources in Greenland and eastern Canada. Understanding the spatial and temporal changes in sediment provenance provides information on ice extent and sediment dispersal patterns. Variations in mineral composition of sediment from late Quaternary cores has been determined by a whole pattern quantitative X-ray diffraction procedure. Mineral facies were extracted statistically by a supervised analysis of 90 samples from bedrock and ice-rafted clasts, which were then used to predict the most probable mineral facies in 1443 marine sediment samples. We used a non-parametric Classification Decision Tree (CDT) to validate that decision. Only 26% of the samples were misclassified in the CDT. The six facies identified consisted of four facies reflecting differences in the composition of Canadian and Greenland Precambrian igneous and metamorphic bedrock, a set of samples dominated by high wt%s of calcite and dolomite (detrital carbonate (DC) and Hudson Strait Heinrich (HS-H) events), and a “shale” facies. We isolated 284 sediments from the HS-H detrital carbonate facies and determined that they could be divided into four categories based on differences in their mineral proportions. These categories vary geographically, based on non-carbonate sediment supply during these events from Greenland, the Canadian Shield, the Appalachians and the outer continental shelf. In the Holocene of the Labrador Sea, dolomite is derived from Baffin Bay and abundance of calcite is influenced by both biogenic productivity and dissolution.
Geology, geochemistry, and apatite/titanite U-Pb geochronology of ca. 1.88 Ga alkaline ultrabasic dykes in the Southern Province near Sudbury, Ontario
(Canadian Science Publishing, 2022-07-13) Kawohl, Alexander; Frimmel, Hartwig Egbert; Whymark, Wesley E.; Millonig, Leo J.; Gerdes, Axel
The area northeast of Sudbury, Ontario, is well-known for hosting one of the largest unexplained geophysical anomalies in the Canadian Shield, the Temagami Anomaly. In search of a geological explanation for this anomaly, low-grade metamorphic ultrabasic dykes have been discovered in the overlying Huronian Supergroup sedimentary rocks, both in outcrop and in a deep drill core. Here we report on the first geochemical and geochronological data obtained on these dykes and compare these data with known magmatic units in and around the 1850 Ma impact-generated Sudbury Igneous Complex (SIC). The NW-striking dykes, which cut across sedimentary rocks of the ~2.3 Ga Cobalt Group, and which are, in turn, crosscut by pseudotachylitic breccia, are characterised by distinctively high concentrations of Ti, P, Nb and Zr, highly fractionated REE patterns (La/YbN 7.6–15.5), and a lack of crustal contamination (Nb/Th >10). Such features are typical of modern ocean island basalt (OIB) but very different from Palaeoproterozoic rocks previously documented in the wider region. Multigrain U-Pb LA-ICP-MS analyses performed on magmatic titanite and apatite with high Th/U ratios yielded 1876.0 ± 8.7 Ma and 1880.9 ± 8.3 Ma, respectively, which we interpret as the intrusion age of the dykes. This interpretation is supported by similar whole-rock Sm-Nd model ages of 1890–2000 Ma (initial εNd +2.5). This magmatic event in the footwall of the SIC shortly before the impact was coeval with, and likely genetically related to, the 1.88–1.87 Ga Circum-Superior Large Igneous Province.
Spatial, sedimentological, and structural evidence for separate distinct breccia forming events
(Canadian Science Publishing, 2022-03-31) Morris, William A.; Ferris, Gregg; Slavinski, Heather
Rounded argillite clasts within the lower Gowganda Formation of the Huronian Supergroup near Whitefish Falls, Ontario, have been historically mapped as Sudbury Breccia, implying their formation was initiated by the Sudbury meteorite impact event. Alternative genetic models proposed to explain the breccia at Whitefish Falls include formation through intrusion of diabase into wet sediment accompanied by soft sediment deformation events. Outcrops in the Whitefish Falls area contain clear evidence for early post depositional fracturing: flow of argillites into brittle fractured sandstones. Linking these geological processes suggests formation of the breccia at Whitefish Falls was generated by faulting of the Huronian sedimentary basin during sedimentation of the Gowganda argillites. Using a GIS approach to compare the distribution of known breccia bodies with mapped lithology and structure it is apparent the term Sudbury Breccia has been applied to two types of breccia. First, true Sudbury Breccia, which is characterised by rounded heterogeneous clasts in an aphanitic matrix, is only found in proximity to the Sudbury Impact crater. Distribution of the second, primarily sediment derived, type of breccia, as seen at Whitefish Falls, is strongly associated with mapped faults and regional scale basement discontinuities, as defined by gravity and magnetic data. Since this type of breccia is present throughout the entire Huronian sedimentary sequence the term “Huronian Breccia” is more appropriate. This breccia is not the result of a single geological event but rather episodes of fault activity, as the geometry of the Huronian basin evolved over time.
Paleomagnetism of the Grum Zn-Pb-Ag deposit, Selwyn Basin, Yukon, Canada
(Canadian Science Publishing, 2022-06-09) Kawasaki, Kazuo; Symons, Dave T.A.
The Grum deposit is one of five large clastic-dominated Zn-Pb-Ag deposits in the Anvil district of the Selwyn Basin, Yukon. Grum’s mineralization occurs at the contact between the Late Proterozoic to Cambrian Mount Mye Formation and the Cambrian to Early Ordovician Vangorda Formation. Paleomagnetic analyses of 113 specimens from 15 mineralized sites in the Grum open pit were undertaken to date Grum’s mineralization. The analyses isolated a stable characteristic remanent magnetization (ChRM), mostly by thermal and then alternating field demagnetization. The main ChRM carrier is single- or pseudosingle-domain pyrrhotite with minor magnetite that give a paleopole at 67.8°N latitude and 317.4°E longitude (radius of the cone of 95% confidence, A95 = 7.2°). The paleopole yields an age of 176±12 Ma for the Grum deposit after a clockwise rotation and northward translation of the basin to best fit the North American apparent polar wander path. Thus, the Zn-Pb-Ag Grum mineralization significantly predates intrusion of the nearby mid-Cretaceous Anvil Batholith, but is coeval with widespread Early Jurassic metamorphism in the Selwyn Basin that correlates with the Early Jurassic collision of the Intermontane Belt terranes with the North America craton.
Constraining the lithostratigraphic architecture of a buried bedrock valley using surface electrical resistivity and seismic refraction tomography
(Canadian Science Publishing, 2022-09-19) Conway-White, Oliver; Steelman, Colby M; Arnaud, Emmanuelle; Ugalde, Hernan; Munn, Jonathan D; Parker, Beth L
Buried bedrock valleys are common erosional features in northern mid-latitude environments forming through glaciofluvial or paleoalluvial processes and are typically infilled by Quaternary-aged sediments. The erosional extent and geometry of the valley including a weathered interface, along with sediment infill that can contain complex sequences of unconsolidated aquifer and aquitard sediments, mean these features may act as preferential pathways to deeper bedrock aquifers. Non-invasive geophysical tools can provide rapid, high-resolution subsurface characterization of these features. This study evaluates the application of electrical resistivity and seismic refraction tomography along two transects centred over a buried bedrock valley in Elora, Ontario, Canada. Geophysical measurements were combined with existing continuous core records and an electrofacies model based on downhole geophysical logs to constrain the morphology and infilled lithostratigraphic architecture of the valley. Bedrock competency associated with lithology may act as a control on depth and width of valley incision during erosion, with resistivity measurements of the bedrock revealing a potential association between interpreted mechanical properties and variations in the resolved valley morphology. Seismic velocity corroborated these contrasting valley widths but could not assess bedrock competency variability below the bedrock interface. This study reveals the sequence of events depositing sediments in the valley, yielding a revised architectural mapping that improves on previous regional-scale lithostratigraphic interpretations. Results will be of use to groundwater practitioners requiring detailed conceptualization of this buried bedrock valley and its role on preferential zones of groundwater flow. Similar approaches can be used for delineation of these common and hydrogeologically significant features.
Evolution of a Stratigraphic Model in a Fluvial Deltaic Wedge: Implications for Groundwater Resource Protection in an Oil and Gas-Bearing Region in the Upper Cretaceous Dunvegan Formation, Northwest Territories, Canada
(Canadian Science Publishing, 2022-06-27) Glas, Nathan H; J., Bhattacharya; Steelman, Colby M; Munn, Jonathan D; Pierce, Amanda A; Parker, Beth L
The Liard Basin, in northwest Canada, contains one of Canada’s largest natural gas reserves. There are concerns about degradation of Dunvegan Formation groundwater quality, which is the basins main shallow freshwater aquifer, as a consequence of oil and gas development. Previous lithostratigraphic studies interpreted the Dunvegan as conglomeratic alluvial fans. In this study, newly collected cores and surface resistivity surveys are integrated with legacy hydrocarbon well data and measured sections for improved sedimentary bedrock characterization. Rather than alluvial fans, we interpret the upper Dunvegan as a coarse-sand to gravel bed fluvial system that was likely tributive to incised valleys associated with linked Alberta Basin base-level falls. Correlation of well logs and measured sections suggest the lower Dunvegan comprises a prograding delta complex with off-lapping clinoforms fed by smaller sand-bed rivers that grade into the upper Dunvegan conglomeratic system, which built southeast towards the Cretaceous Western Interior Seaway. This sequence stratigraphic and facies architectural approach is employed to inform the aquifer-aquitard flow system and aid in understanding the 3D groundwater flow system, once hydrogeologic characterisation confirms position and thickness of important hydrogeologic units. Resistivity surveys suggest upper Dunvegan channel-belt facies may be well-connected and laterally extensive, potentially acting as interconnected aquifer units; whereas lower Dunvegan channel belts may be discontinuous, indicating smaller-scale flow units separated by floodplain and marine shale. This revised geologic understanding provides opportunities for determining impacts or resilience from shallow and deep sources of contamination associated with human activities, including oil and gas development, land-use and/or climate change.
Seven hydrogeological terrains characteristic of southern Ontario
(Canadian Science Publishing, 2022-07-19) Sharpe, David Robert
Groundwater is an important component of the hydrological cycle of southern Ontario, significant to water supply and discharge to surface water. To improve overall understanding of key hydrological mechanisms, a proof of concept framework is presented that consists of seven typical terrains or hydrogeological settings. Geologic and topographic controls influence each setting as recorded by climate, streamflow, and groundwater level data, which trace how water moves through various parts of the southern Ontario landscape. This hydrogeological framework considers the geology of surface sediment and bedrock, permeability and porosity (inferred), physiography, and topographic gradients to define seven distinctive hydrogeological terrains. The data and watershed selection process allows for concentration on patterns of hydrologic response across the landscape, not so much on hydrologic accounting of the terrain. The analysis identifies events in climate, stream, and well-monitoring data indicative of influxes and temporal patterns of hydrological and hydrogeological response to local geology and topography, thus differentiating styles of groundwater movement in sediment/ bedrock landscapes of the Paleozoic basin and Shield margin. A case study is provided for each setting: five in sediment (clay, sand, gravel, till upland, and thick till); and two in bedrock (crystalline and carbonate). The selected hydrogeological terrains characterize ~90% of the landscape based on a simplified geological map of southern Ontario. The main hydrogeological characteristics and behaviour of these terrains are proposed as a set of conceptual models representative of near-surface groundwater regimes. Such models can inform water and land resource management as future climates change.

Browse

Recent Submissions