2021

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Regional geology and tectonic framework of the Southern Indian domain, Trans-Hudson Orogen, Manitoba
(Canadian Science Publishing, 2021-12-09) Martins, Tania; Rayner, Nicole; Corrigan, David; Kremer, Paul
The collaborative federal-provincial Southern Indian Lake project in north-central Manitoba covered an area of more than 3500 km2 of the Trans-Hudson orogen. Regional-scale geological mapping, sampling, and lithogeochemical, isotopic and geochronological studies resulted in the identification of distinct assemblages of supracrustal rocks and varied episodes of plutonism. A granodiorite gneiss dated at ca. 2520 Ma is interpreted to represent the basement of the Southern Indian domain and is considered a separate crustal domain, named the Partridge Breast block. The Churchill River assemblage is composed of juvenile pillow basalt with intervening clastic sedimentary rocks, possibly a reflection of plume magmatism related to initial rifting of the Hearne craton margin. The Pukatawakan Bay assemblage consists mainly of massive to pillowed, juvenile metabasaltic rocks and associated basinal metasedimentary rocks. The Partridge Breast Lake assemblage is dominated by continental-arc volcanic and volcaniclastic rocks associated with basinal metasedimentary rocks. The Strawberry Island assemblage, consisting of arenite and polymictic conglomerate, is interpreted to have been deposited in a foreland-basin basin or intra-orogen pull-apart basin environment. The Whyme Bay assemblage is characterized by fluvial-alluvial orogenic sediments and is temporally linked to the Sickle Group rocks in the Lynn Lake greenstone belt. Granitoid rocks, dominantly monzogranite and granodiorite, range in age from ca. 1890 to 1830 Ma and occur throughout the Southern Indian domain, and intermediate and mafic intrusions of similar ages are also present. In this paper we integrate these new data into a tectonic framework for the Southern Indian domain of the Trans-Hudson orogen in Manitoba.
Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada
(Canadian Science Publishing, 2021-11-01) Westgate, John Arthur; Naeser, Nancy D; Barendregt, Rene W.; Pearce, N. J.G.
Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes – necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe-Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.
A new plastomenid trionychid (Testudines: Pan-Trionychidae) from Milk River Formation of southern Alberta (Cretaceous: Santonian)
(Canadian Science Publishing, 2021-12-13) Edgar, Shauna C.; Brinkman, Donald B.; Ryan, Michael J.; Evans, David C.
The pre-Campanian trionychid fossil record in North America is composed of highly fragmentary specimens, which are often not identifiable beyond Pan-Trionychidae. Here, we describe a new species of plastomenid soft-shelled turtle based on a partial shell (ROM 56647) from the Santonian Milk River Formation of southern Alberta, estimated at approximately 84 MY. This represents the oldest relatively complete shell of a trionychid from North America. Plastomenidae, a pan-trionychid clade known only from the fossil record, is classically characterized by the complete suturing of its posterior plastral bones along the midline, a crescent-shaped entoplastron, and enlarged costals VIII. ROM 56647 has a unique combination of plastomenid characters (i.e., mid-line contact of hypoplastra and xiphiplastra, anteroposteriorly long eighth costal) and apomorphies (an emarginate nuchal, enlarged tubercles on the carapace, a wide pygal notch with a straight anterior edge, and a fused hyo-hypoplastron) that allows us to identify it as a new taxon, Jimemys glaebosus gen. et. sp. nov. Phylogenetic analysis places Jimemys glaebosus within Plastomenidae as the sister taxon to a clade containing Plastomenus, Helopanoplia and Hutchemys. This phylogenetic position implies that Aspideretoides foveatus, Atoposemys, and Gilmoremys, all of which are more basal within Plastomenidae, had ghost lineages extending at least to the Santonian. As the oldest pan-trionychid that is diagnostic to the species level in North America, J. glaebosus provides new insights into both the early evolution of trionychids in North America and the biodiversity of southern Alberta during a poorly sampled time in the Late Cretaceous of North America.
Multi criteria assessing approach of the slow-moving urban landslide hazard, the case of Moulay Yacoub town (Morocco)
(Canadian Science Publishing, 2021-10-20) Obda, Ilias; El Kharim, Younes; Bounab, Ali; Lahrach, Abderrahim; Ahniche, Mohammed; Mansouri, Hamou
Since many decades, the town of Moulay Yacoub (MY) has undergone an intensification of its urbanization to meet the demands of rental housing for the visitors of the hydrothermal springs, which is considered as the only attraction of the town. Unfortunately, the majority of the buildings, both private and public, suffer from varying levels of damages where the lithological and geomorphic field features are to blame, without omitting the anthropogenic effects. In fact, the town is built on a marly hill conducive to slope movements, ranging from shallow solifluctions to large landslides, besides the swelling/shrinkage behaviour of these marls. The paper presents a multi-source approach to investigate the activity and the interactions of slow urbanized landslides and expansive soils within the urban perimeter of Moulay Yacoub. Indeed, the desiccation cracks of marly soils reveal their expansive behaviour, also attested by the swelling values. The other geotechnical parameters obtained from laboratory tests show that the shallow marls samples are severely weathered compared to those of the compacted deep ones. The Borehole data and seismic noise survey allows the detection of several impedance contrasts corresponding to the shallow weathered-deep marls interfaces which in some cases represent the rupture surfaces of gravitational processes. The very slow but perennial activities of the later are attested by the inclinometers, the PS-InSAR monitoring and building damages. The case study provides a good opportunity to highlight the complementarity of the multi-source tasks which stand as a further contribution to fostering this kind of integrated approaches at the slope scale.
Biostratigraphic evidence for incremental tectonic development of early Cambrian deep-water environments in the Misty Creek embayment (Selwyn basin, Northwest Territories, Canada)
(Canadian Science Publishing, 2021-10-25) Scott, R. William; Turner, Elizabeth C.; MacNaughton, Robert B; Fallas, Karen M
The early evolution of the Misty Creek embayment (MCE), a prominent, northwest-trending sub-basin of the economically important Selwyn basin, is poorly understood. The abrupt contact between Cambrian Stage 4 (traditional lower Cambrian) carbonate ramp strata of the Sekwi Formation and overlying Miaolingian (traditional middle Cambrian) deep-water, calciturbiditic strata of the Hess River Formation has been regarded as diachronous. This important transition, which marks the onset of long-lived, deep-water conditions in the MCE, remains unexplained. This study uses biostratigraphic data from a previously undescribed location in the MCE, existing biostratigraphic and lithostratigraphic data from the 1970s, and regional thickness patterns to characterise the sharp yet diachronous transition from lithofacies typical of the Sekwi Formation to those typical of the Hess River Formation. The dramatic change in depositional environments was diachronous yet non-gradational, precluding a eustatic cause. The change was geologically abrupt, probably through two extension-related subsidence events, with different geographic extents, which heralded the MCE’s long life as a deep-water basin. The onset of deep-water conditions in the MCE occurred semi-contemporaneously with other extension-related events that are recorded in the northern Canadian Cordillera, demonstrating that Cambrian Series 2 - Miaolingian was a time of widespread extension and subsidence along the western margin of Laurentia.
There's more Wrangellia - Magnetic characterization of southern Alaska crust
(Canadian Science Publishing, 2021-07-21) Saltus, Richard W.; Hudson, Travis
In southern Alaska, Wrangellia-type magnetic crustal character extends from the Talkeetna Mountains southwest through the Alaska Range to the Bristol Bay region. Magnetic data analyses in the Talkeetna Mountains showed that there are mid-crustal differences in the magnetic properties of Wrangellia and the Peninsular terrane. After converting total field magnetic anomaly data to magnetic potential, we applied Fourier filtering techniques to remove magnetic responses from deep and shallow sources. The resulting mid-crustal magnetic characterization delineates the regional magnetic potential domains that correspond to the Wrangellia and Peninsular terranes throughout southern Alaska. These magnetic potential domains show that Wrangellia-type crust extends southwest to the Illiamna Lake region and that it overlaps the mapped Peninsular terrane. Upon reconsidering geologic ties between Wrangellia, Peninsular, and Alexander terranes we conclude that Peninsular terrane is part of what we here call Western Wrangellia. Western Wrangellia contains the Lower Jurassic Talkeetna volcanic arc and is similar to Wrangellia of the Vancouver Island area, Canada (Southern Wrangellia) which contains the Lower Jurassic Bonanza volcanic arc. Others have previously made this correlation and proposed that the Talkeetna arc-bearing part of southern Alaska was displaced from the Bonanza arc-bearing part of Canada. We generally agree and propose that about 1000 km of dextral displacement along ancestral Border Ranges fault segments and other faults of south-central Alaska separated Western Wrangellia from Southern Wrangellia. We think this displacement was mostly in the Late Jurassic and earliest Cretaceous, perhaps between about 160 and 130 Ma.
Boulder-strewn flats in a high-latitude macrotidal embayment, Baffin Island: geomorphology, formation, and future stability
(Canadian Science Publishing, 2021-07-02) Hatcher, Scott Vincent; Forbes, Donald L.; Manson, Gavin K.
Tidal flats are widely distributed on high-latitude coasts, where sea ice processes have been invoked to explain the abundance and distribution of boulders. This study documents the surface morphology and sediment dynamics of a low-Arctic macrotidal system, the boulder-rich tidal flats of Koojesse Inlet, fronting the Nunavut capital, Iqaluit, on Baffin Island. This is a region of postglacial isostatic uplift and forced regression, with raised littoral, deltaic, and glaciomarine deposits. The spring-tidal range is 11.1 m and sea ice cover lasts roughly 9 months of the year. The extensive intertidal flats are up to 1 km wide, with a veneer of sand and gravel (including large boulders) resting on an erosional unconformity truncating the underlying glaciomarine mud, forming a terrace within the present tidal range. Over a three-year study, no consistent pattern of erosion or deposition was evident. Over a longer time scale, the concave hypsometry, low sediment supply, slight ebb-dominance of weak tidal currents, abrasion by wave-entrained sand, ebb-oriented ripples formed under subaerial drainage, and slumps on the terrace flanks are consistent with seaward hydraulic and gravitational sediment transport. These processes may be of greater importance than shoreward ice transport. This study underlines the importance of relict glaciomarine deposits, postglacial uplift, and falling relative sea level in the erosional development of these high-latitude tidal flats. Relative sea-level projections for Iqaluit are ambiguous, but a switch to rising sea level, if it occurs, combined with more open water and wave energy, could alter the foreshore dynamics of the system.
Landfast ice properties over the Beaufort Sea region in 2000-2019 from MODIS and Canadian Ice Service data
(Canadian Science Publishing, 2021-09-13) Trishchenko, Alexander P.; Kostylev, Vladimir; Luo, Yi; Ungureanu, Calin; Whalen, Dustin; Li, Junhua
Two decades (2000-2019) of the landfast ice properties in the Beaufort Sea region in the Canadian Arctic were analyzed at 250-m spatial resolution from two sources: 1) monthly maps derived at the Canada Centre for Remote Sensing from the Moderate Resolution Imaging Spectroradiometer clear-sky satellite image composites; 2) Canadian Ice Service charts. Detailed comparisons have been conducted for the landfast ice spatial extent, the water depth at and the distance to the outer seaward edge from the coast in four sub-regions: 1) Alaska coast; 2) Barter Island to Herschel Island; 3) Mackenzie Bay; 4) Richards Island to Cape Bathurst. The results from both sources demonstrate good agreement. The average spatial extent for the entire region over the April-June period is 48.5 (5.0)10
Reconstruction of isostatically-adjusted paleo-strandlines along the southern margin of the Laurentide Ice Sheet in the Great Lakes, Lake Agassiz and Champlain Sea basins
(Canadian Science Publishing, 2021-10-14) Lewis, Michael; Breckenridge, Andy; Teller, James
Abstract: Strandlines document the former presence of lakes and a sea in east-central North America along the southern margin of the retreating Laurentide Ice Sheet (LIS). The strandlines of these formerly level water bodies are uplifted to the north and provide evidence of glacial isostatic adjustment (GIA) of the Earth’s crust to the former ice load. We compile published ages and measurements of the present elevation and location of shore features in the strandlines of 8 major paleo-waterbodies from the St. Lawrence Valley to the northern Great Plains in digital format as an aid for the numerical modelling of GIA. Data for eastern water bodies were extracted and digitized from publications during the past 120 years. Digital position co-ordinates were scaled from published maps of survey sites or were determined using Google Earth Pro software. Published data for paleo-lakes Duluth and Agassiz were mainly obtained from field measurements and digital elevation models (DEMs). Two-sigma or 95% probability values are provided for the strandline ages and for isobase (contour) positions representing the deformed water surfaces. Peak strandline gradients reported here were largest at about ca. 13,000 years ago. Lower strandline gradients for older shores may reveal areas closer to the peripheral bulge and areas of thinner ice (lighter crustal loads). Concave upward strandline profiles characterize most paleo-basins whereas a linear uplift profile characterizes the Champlain Sea strandline. Directions of strandline maximum uplift within the former water body basins point towards the thickest part of the LIS near the Qubec-Labrador ice dome.
A revised Coastal Sensitivity Index for Canada’s marine coasts calculated using nonparametric statistics
(Canadian Science Publishing, 2021-05-18) Hatcher, Scott Vincent; Manson, Gavin K.
A Coastal Sensitivity Index (CSI) quantifies a coastline's sensitivity to its physical environment in a useful way for coastal management. Traditionally a CSI is calculated as the mathematical aggregation of coastal sensitivity indicators, which may include factors such as coastal material, relief, and wave energy. The indicators differ depending on study area, but generally are assigned a score ranging from one to five in order of increasing sensitivity. These scores are then aggregated using either the square root of the product mean (the “classic” method), or the geometric mean. Both of these methods are limited by mathematical assumptions, lack of comparability, and the need for empirical validation. In this study, we applied an alternative nonparametric method of calculation, known as μ-statistics, to Canada's marine coasts to investigate a novel approach. μ-statistics, which offer a mathematically sound method of aggregating ordinal indicators, have a number of theoretical advantages over the classic and geometric mean methods. In practice, when applied to Canada’s marine coast, we find that the μ-statistics method (1) compresses the mid-range variability in the resulting sensitivity index, (2) accentuates positive and negative distribution tails, and (3) minimizes propagated errors by 190% and 50% respectively, compared to the classic and geometric mean methods. Additionally, the μ-statistics method has a theoretical foundation that relieves the necessity to empirically validate the aggregating assumptions and relies only on the assumptions inherent in the scoring method. μ-statistics thus provide a new, rigorous method for the calculation of coastal sensitivity indices.
POSTGLACIAL SEA-LEVEL LOWSTAND ON CUMBERLAND PENINSULA, BAFFIN ISLAND, EASTERN ARCTIC CANADA
(Canadian Science Publishing, 2021-09-03) Cowan, Beth; Carter, Johnathan; Forbes, Donald L.; Bell, Trevor
This study investigates the postglacial sea-level history of eastern Cumberland Peninsula, a region of Baffin Island, Nunavut where submerged terraces were documented in the 1970s. The gradient in elevation of emerged postglacial marine-limit deltas and fiord-head moraines led Dyke (1979) to propose a conceptual model for continuous postglacial submergence of the eastern peninsula. Multibeam mapping over the past decade has revealed eight unequivocal submerged deltas at 19-45 m below [present] sea level (bsl) and other relict shore-zone landforms (boulder barricade, spits, and sill platform) at 16-51 m bsl. Over a distance of 115 km from Qikiqtarjuaq to Cape Dyer, the submerged coastal features increase in depth toward the east, with a slope (0.36 m/km), somewhat less than that of the marine-limit shoreline previously documented (0.58-0.62 m/km). The submerged ice-proximal deltas, deglacial ice limits, and radiocarbon ages constrain the postglacial lowstand between 9.9 and 1.4 ka cal BP. The glacial-isostatic model ICE-7G_NA (VM7) (Peltier 2020) computes a lowstand relative sea level at 8.0 ka, the depth of which increases eastward at 0.28 m/km. The difference between observed and model-derived lowstand depths ranges from 1 m in the west to 10 m in the east and the predicted tilt is significantly less than observed (p=0.0008). The model results, emerging data on Holocene glacial re-advances on eastern Baffin Island, and evidence for proglacial delta formation point to a Cockburn (9.5-8.2 ka) age for the lowstand, most likely later in this range. This study confirms the 1970s conceptual model of postglacial submergence in outer Cumberland Peninsula and provides field evidence for further refinement of glacial-isostatic adjustment models.
U–Pb zircon geochronology and implications of Cambrian plutonism in the Ellsworth belt, Maine
(Canadian Science Publishing, 2021-06-25) Pollock, Jeffrey C; Reusch, Douglas N.; Dunning, Greg R.
The Ellsworth belt is one of several fault-bounded blocks exposed along the southeastern coast of Maine that formed within Ganderia. New ID-TIMS U–Pb geochronological data integrated with field relationships provide additional insights into the timing of magmatism and deformation in the Ellsworth belt. The deformed Lamoine Granite was selected for U–Pb zircon analysis in order to: i) establish the protolith age; ii) provide direct temporal constraints on regional low-grade metamorphism and deformation; and iii) elucidate relationships between the Ellsworth belt and coeval rocks elsewhere in the Appalachian orogen. The Lamoine Granite was emplaced within the Ellsworth Schist at 492 1.7 Ma; this is the first unequivocal evidence for a Furongian magmatic event in the Ellsworth belt. The schistosity in the Lamoine Granite is parallel to the main fabric of the host Ellsworth Schist and provides a maximum estimate for timing of the regional metamorphic overprint. Widespread deformation in the Ellsworth belt where kinematic indicators indicate a top-to-northwest sense of shear is attributed to thrusting during which progressive horizontal shortening, caused crustal thickening and peak greenschist facies metamorphism. The Cambrian U–Pb age permits correlation of the Lamoine Granite with the Cameron Road Granite in the Annidale belt of New Brunswick where subduction-related magmas intruded the Penobscot arc–back-arc and were subsequently deformed during the Penobscot Orogeny.
Petrogenesis and mode of emplacement of a Neoarchean tonalite-trondhjemite-diorite (TTD) suite: the Eau Jaune Complex, Abitibi greenstone belt
(Canadian Science Publishing, 2021-08-06) Kieffer, Marie A.; Mathieu, Lucie; Bedeaux, Pierre; Gaboury, Damien; Hamilton, Michael A.
Magmatism during the maturation phase of Archean greenstone belts produced voluminous tonalite-trondhjemite-granodiorite (TTG) suites, as well as a lesser amount of tonalite-trondhjemite-diorite (TTD) suites. Such TTD suites have recently been recognized in the Archean Abitibi greenstone belt, on the southern flank of the Superior Craton, Canada, but their source(s), differentiation processes and depths of emplacement remain poorly constrained. The Neoarchean Eau Jaune Complex (EJC) lies in the northeastern corner of the Abitibi greenstone belt and represents one of the most voluminous tonalite-dominated and diorite-bearing intrusive suites of the Chibougamau region. This TTD suite comprises six intrusive phases with distinct petrology and chemistry. All units were emplaced as laccolith-like intrusions injected along discontinuities within the volcanic succession at ca. 2724 Ma (U-Pb zircon dating), during the synvolcanic interval (i.e., construction and maturation phase), at a depth of approximately 7–8 km. The most HREE-depleted phases (granodiorite, tonalite and trondhjemite) correspond to magmas that fractionated amphibole and were likely produced by partial melting of a garnet- and titanate-bearing amphibolite, akin to TTG magmas. The least HREE-depleted phases are dioritic in composition and correspond to mantle-derived magmas that may have interacted with TTG melts. This indicates interaction between coeval mantle-derived and crustal melts during the maturation phase of the Abitibi greenstone belt. Models formulated to address the geodynamic evolution of greenstone belts must account for the coeval production of basalt-derived (TTG suites) and mantle-derived (tholeiitic magmatism) melts occasionally interacting to form TTD suites.
Neodymium isotope mapping a polygenetic TTG batholith: Failed back-arc rifting in the Central Metasedimentary Belt, SW Grenville Province
(Canadian Science Publishing, 2021-08-03) Strong, Jacob; Dickin, Alan
Fifty-five new Nd isotope analyses are presented for plutonic orthogneisses from the Grimsthorpe domain in the marble-rich segment of the Grenvillian Central Metasedimentary Belt (CMB) to test the back-arc aulacogen model for its origin. Nd isotope analyses from the Weslemkoon batholith, Elzevir batholith, Lingham Lake complex and Canniff tonalite are used to probe the crustal formation age of their source rocks. Despite its concentric foliation, the Weslemkoon batholith displays a complex geochemical pattern consisting of several NE trending domains with older TDM ages, surrounded by juvenile crustal material. The new Nd isotope results, coupled with geochemistry for the Weslemkoon and Elzevir batholiths depict the fragmentation of a block of old crust that formed a screen between en echelon segments of a mid-Mesoproterozoic back-arc rift zone. The isotope boundaries identified within the Weslemkoon batholith delineate magma pulses sampling two distinct sources, interpreted as Laurentian basement and juvenile basaltic underplate. Underplating could be attributed to slab rollback under the pre-Grenvillian continental margin arc. The intensification of rift-related magmatism in the CMB is demonstrated by its bimodal petrological character. A modern analogue for the tectonic context of the CMB is the Gulf of California, where subduction-related magmatism has transitioned to rift-related magmatism. However, the Gulf of California exhibits more transcurrent motion than is evidenced by the geometry of the CMB rift. A geometrical analogue for the break-up of the Elzevir block between two rift segments is provided by the Danakil block of the Red Sea, which is currently undergoing similar tectonic fragmentation.
Evidence for microbially mediated silver enrichment in a middle Cambrian Burgess Shale-type deposit, Mackenzie Mountains, northwestern Canada
(Canadian Science Publishing, 2021-08-10) Kimmig, Julien; Pratt, Brian R.
The Selwyn basin and Mackenzie platform of northwestern Canada house an array of mineral deposits and prospects that are rich in silver, including Neoproterozoic red-bed or Kupferschiefer-type Cu and lower Paleozoic sedimentary exhalative (SEDEX) and Zn-Pb deposits. Within this overall metallogenic setting, the middle Cambrian (Drumian) Rockslide Formation was deposited under a largely oxic water column on the platform-to-basin slope along the eastern side of the Selwyn basin. The formation includes an interval termed the Ravens Throat River Lagersttte which is a localized Burgess Shale-type calcareous mudstone about 2 m thick that preserves soft-bodied fossils. The mudstone contains comparatively large amounts of organic carbon preserved as thin carbonaceous laminae and discontinuous seams, representing benthic microbial mats, the remains of cyanobacteria and algae that were living in the water column, fecal pellets, large coprolites, and degraded animal tissues. The upper part of the Rockslide Formation, including the fossiliferous interval, contains elevated concentrations of Ag, up to 0.47 ppm. Some of the Ag in the mudstone occurs as aggregates of elemental particles ~10 m in size preferentially on the carbonaceous material comprising the coprolites. This localized enrichment suggests bioaccumulation of Ag nanoparticles or Ag+ from the water column by microorganisms on the coprolites or degrading organic matter in them. The source of the Ag may have been from penecontemporaneous SEDEX metallogeny or from broadly related subsurface fluids in the Selwyn Basin that enriched the overlying seawater.
PETROLOGY AND AGE OF THE LEPREAU RIVER DYKE, SOUTHERN NEW BRUNSWICK, CANADA: SOURCE OF THE END-TRIASSIC FUNDY GROUP BASALTS
(Canadian Science Publishing, 2021-07-21) McHone, James Gregory; Barr, Sandra M.; Jourdan, Fred
A large dyke of quartz-tholeiitic gabbronorite has been mapped for 59 km in southern New Brunswick, Canada, between Lepreau River in the northeast and Indian Island in the southwest. Scattered outcrops occur along a positive aeromagnetic lineament, providing a dyke strike of N42E overall (segments N30E to N72E), dips of 80 to 90NNW, and widths of 4 to 30 m. A new 40Ar/39Ar plagioclase age of 201.67 0.35 Ma for the Lepreau River Dyke is similar to dates for the massive North Mountain Basalt in the Fundy Basin to the east. The dyke is associated with the Ministers Island and Christmas Cove dykes, which are indistinguishable in chemistry, petrology, and probable age, and we regard them as segments of the same co-magmatic dyke system. In addition, their petrology is similar to that of the basalts of the adjacent Early Mesozoic Fundy and Grand Manan basins. We propose that the Lepreau River and associated dykes were sources for the regional basin basalts, which in turn are part of the Central Atlantic Magmatic Province (CAMP) that overlaps the Triassic-Jurassic boundary and associated mass extinction event.
Geophysical reassessment of the role of ancient lineaments on the development of the western Laurentian margin and its sediment-hosted Zn-Pb deposits, Yukon and NWT, Canada
(Canadian Science Publishing, 2021-07-14) Hayward, Nathan; Paradis, Suzanne
A new 3-D inversion strategy is applied to new compilations of gravity and magnetic data, to reassess the role of crustal lineaments in the development of the western Laurentian margin, Selwyn basin and associated sediment-hosted Zn-Pb deposits. The region’s history is obscured by multiple tectonic overprints including terrane accretion, plutonism, and thrust faulting. Regionally continuous, broadly NE-trending crustal lineaments including the Liard line, Fort Norman structure, and Leith Ridge fault, were interpreted as having had long-standing influence on craton, margin, and sedimentary basin development. An ENE-trending lineament, Mackenzie River, traced from the Misty Creek Embayment to Great Bear Lake, is interpreted as the southern edge of a cratonic promontory. The location of the Liard line, associated with a transfer fault that bounds the Macdonald Platform promontory, is refined. New geophysical results support the continuity of the Fort Norman structure below the Selwyn basin, but limited evidence exists for the Leith Ridge fault in this area. A NW-trending lineament that bounds the craton is interpreted as a crustal manifestation of lithospheric thinning of the Laurentian margin, as echoed by a change in the depth of the lithosphere-asthenosphere boundary. The structure delimits the eastern extent of mid-Late Cretaceous granitic intrusions and is straddled by Mississippi Valley-type Zn-Pb occurrences, following their palinspastic restoration. Clastic-dominated Zn-Pb occurrences are aligned along another NW-trending lineament interpreted to be associated with a shallowing of lower crustal rocks.
Chemostratigraphy as a tool for sequence stratigraphy in the Devonian Hare Indian Formation in the Mackenzie Mountains and Central Mackenzie Valley, Northwest Territories, Canada
(Canadian Science Publishing, 2021-07-08) Harris, Brette; LaGrange, Maya T.; Biddle, Sara K.; Playter, Tiffany L.; Fiess, Kathryn Mildred; Gingras, Murray
The Hare Indian Formation (HIF) is a Late Eifelian to Givetian organic-rich mudstone constituting the lower portion of the Horn River Group (HRG) that has been minimally scrutinized in the literature. This paper proposes depositional environments and a sequence stratigraphic framework for the HIF. Using composition data collected via energy-dispersive X-ray fluorescence, geochemical proxies inform detrital input, silica source, and paleoredox conditions. Cross-plots and chemostratigraphic profiles of detritally sourced Al, Ti, and K and redox-sensitive Mo and V inform depositional and stratigraphic constraints. Silica proportions vary, indicating that sediment was derived from detrital and biogenic sources. Al, Ti and K distributions increase upwards, showing increased continentally-sourced minerals. Redox-sensitive metals are highest in the Bluefish Member (BM), suggesting intermittent euxinia. Based on the presence of continental- and pelagic-sediments, the sedimentary environment is interpreted as proximal- to mid-shelf. These proxies guide systems tract interpretations. Si and redox-sensitive metal concentrations peak higher in the BM, accompanied by lowered concentrations of Al, Ti and K, suggesting a maximum flooding surface. At the top of the Prohibition and Bell Creek members redox-sensitive enrichments are lower with higher concentrations of Al, Ti and K, suggesting a maximum regressive surface. Transgression occurred during the initial deposition of the BM, followed by regression for the remainder of the HIF. The sedimentology of the HIF can be difficult to decipher; the use of chemostratigraphy supports its geological history (including sedimentation trends and a local record of relative sea level) using methods that may be applied to other fine-grained successions.
A Lower Devonian age for the Corvock Granite and its significance for the structural history of South Mayo and the Laurentian margin of western Ireland
(Canadian Science Publishing, 2021-05-06) Graham, John; Riggs, Nancy
The Silurian Croagh Patrick succession, which crops out just south of a fundamental Caledonian structural zone near Clew Bay, western Ireland, is a series of psammites and pelites with a strong penetrative cleavage. These rocks are intruded by the Corvock granite. A suite of minor intrusions associated with the granite contains the regional cleavage whereas the Corvock granite is undeformed. New U-Pb dates are 413 + 7 / -4 Ma for a strongly cleaved sill and 410 4 Ma for the main granite and closely constrain the age of crystallization of the granite and coeval cleavage formation as Lower Devonian (Lochkovian or Pragian), implying syn- to late-kinematic granite emplacement. These data are consistent with evidence for strong sinistral shear shown by the Ox Mountains granodiorite just to the north-east dated at 412.3 0.8 Ma. This Devonian cleavage is superimposed on Ordovician rocks of the South Mayo Trough. The localisation of the strong deformation is interpreted as being due to its position at a restraining bend during regional sinistral motion on a segment of the Fair Head-Clew Bay Line to the north. Contemporaneous deformation in the syn-kinematic Donegal batholith suggests a transfer of sinistral motion to this intra-Grampian structure rather than simple along-strike linkage to the Highland Boundary Fault in Scotland. Our new data indicate diachronous deformation during the late Silurian and early Devonian history of the Irish and Scottish Caledonides and also support previous interpretations of diachronous deformation between these areas and the Appalachian orogens.
Multi-decadal coastal evolution of a North Atlantic shelf-edge vegetated sand island – Sable Island, Canada
(Canadian Science Publishing, 2021-05-09) Eamer, Jordan B.R.; Didier, David; Kehler, Dan; Manning, Ian; Colville, David; Manson, Gavin K.; Jagot, Alexandre; Kostylev, Vladimir
Impacts from a changing climate, in particular sea-level rise, will be most acutely felt on small oceanic islands. A common configuration of mid-latitude islands is the sandy barrier island. Sable Island, Nova Scotia, Canada is a vegetated sand island near the shelf edge, 160 km from the nearest point of land, that is morphologically similar to a barrier island. This study uses 60 years of airphoto records to analyse changes in coastline position through digitized shore and vegetation (foredune proxy) lines. Rates of coastal movement are analysed to model the future (2039) coastal configuration. The analyses suggest that the majority of the coastline on Sable Island is in retreat, with net retreat on the south side of the island only partially offset by modest net advance on the north side. The different morphologies of the beach-dune systems of South and North Beach, driven by incident wind and waves, yield these different coastline responses. Projected loss of 10 ha by 2039 of the climax heath vegetative community to shoreline retreat suggests a trend toward island instability due to coastline migration. Island-wide dataset trends show support for two different but complementary hypotheses about whole-island evolution: either the island is mobile via bank migration driving southern coastline changes and experiencing sediment transport toward the east, or the island is generally immobile and losing subaerial sediments (and thus shrinking) likely due to ongoing (and accelerating) sea-level rise.

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