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Canadian Journal of Earth Sciences
Journal Prestige (SJR): 0.615

Citation Impact (citeScore): 1
Number of Followers: 22

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0008-4077 - ISSN (Online) 1480-3313
Published by NRC Research Press

[19 journals]

Petrogenesis and geodynamic significance of late Early Jurassic complex in
Qinsai, Hainan Island, South China Sea
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  Authors: Zhongjie Xu, Jintao Kong, Ningchen Sun, Rihui Cheng, Li Zhang
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Whole-rock geochemical and U–Pb–Hf isotopic data were used to investigate the age, petrogenesis, and tectonic setting of a suite of gabbro–diorite–monzonite–syenite rock exposed in Qinsai area, Hainan Island. Zircon U–Pb dating shows that the gabbro and monzonite, respectively, crystallized at 179.5 ± 2.7 and 179.0 ± 2.3 Ma. The suite consists of shoshonitic alkaline intrusive rocks with SiO2 content ranging from 41.7 to 63.4 wt%, with high U, K, and Pb and low Nb, Ta, and Ti. The suite is enriched in light rare earth elements relative to heavy rare earth elements. The gabbro has no obvious Eu anomaly but a positive Eu anomaly is evident in intermediate rocks. Zircon εHf(t) values are positive and have a wide variation (gabbro εHf(t) = +5.2 ± 8.2, monzonite εHf(t) = +4.7 ± 7.1). Gabbro and syenite are both likely derived from an enriched lithospheric mantle that was metasomatized by subduction fluids. Syenite evolved from the differentiation of gabbro, monzonite, and diorite. Collectively, these intrusive rocks formed in an extensional regime within an arc formed by subduction of the ancient Pacific plate beneath the Asian margin, which was accompanied by extensional thinning of the lithosphere.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-03-14T07:00:00Z
  DOI: 10.1139/cjes-2022-0097
Mount Garibaldi: hazard potential from a long-dormant volcanic system in
the Pacific Northwest
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  Authors: Conner A. G. Morison, Catherine J. Hickson
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Mount Garibaldi Volcanic System (MGVS) is the southernmost member of Garibaldi Volcanic Belt (GVB), the northern (Canadian) segment of the Cascade Volcanic Arc. Temporally episodic explosive to effusive eruptions may be associated with peak ice unloading after glacial maxima. Rapid and widespread deglaciation of the overlying ice sheet, and glacial rebound, have altered the physical characteristics of the landscape whilst the system is thought to have been in long repose for over 10 000 years. Over the last 60 years, the region has become heavily populated due to increased tourism and all-season recreation opportunities. MGVS poses the greatest volcanic threat to the human population and built infrastructure between Vancouver and the resort municipality of Whistler. We believe that this system is a priority for further scientific research, given that its already “very high” overall threat score would likely increase if there was a better understanding of its eruptive history and hazards. Using published and field evidence, we show that potential hazards, related to the volcanic environment of this system, to the settlement of Squamish include voluminous lava flows, pyroclastic density currents triggered by lava dome collapse, tephra fallout, debris flows, and lahars. As relatively few exposures in the system have been dated using modern geochronological techniques, we take this opportunity to (re)calibrate published radiocarbon ages of relatively recent eruptions in GVB.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-03-02T08:00:00Z
  DOI: 10.1139/cjes-2022-0067
Mesoproterozoic basins (Yukon, Canada) in the evolution of supercontinent
Columbia
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  Authors: K.P.R. Medig, D.J. Thorkelson, E.C. Turner, R.H. Rainbird, H.D. Gibson, D.D. Marshall
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Geochemical and geochronological data from the Pinguicula Group and unit PR1 of the lower Fifteenmile Group (Yukon, Canada) provide information on sediment provenance and timing of break-up of supercontinent Columbia and seaway development on Laurentia’s northwestern margin. The older unit PR1, in the Coal Creek inlier, has a near-unimodal detrital zircon population with an age of 1499 ± 3 Ma. The Pinguicula Group detrital zircon data, in the Wernecke and Hart River inliers, display a polymodal detrital zircon population with a maximum age of
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-02-23T08:00:00Z
  DOI: 10.1139/cjes-2022-0055
Tectonic geomorphology of the Ottawa-Bonnechere Graben, Eastern Canada:
implications for regional uplift and intraplate seismicity
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  Authors: Ugi K. Gusti, Alexander L. Peace, Jeremy Rimando
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  In intraplate areas where regional tectonic strain is accommodated by the reactivation of pre-existing structures, the level of seismic hazard associated with faults may be underestimated due to the poor surface expression of faults, scattered earthquake distribution, and long earthquake recurrence intervals. The cause(s) of seismicity in eastern Canada remains unresolved. This is partially because surface expressions of faults have been eroded during glacial and deglacial periods and in the Ottawa-Bonnechere Graben (OBG) are undetectable until a seismic event. Morphotectonic analysis has been widely applied to assess relative tectonic activity in various geological settings. To establish whether active uplift is occurring and to investigate the spatial distribution of relative uplift rates, 131 bedrock drainage basins in OBG were analysed. The aim of this was to (1) test the applicability of geomorphic indices for quantifying active deformation, (2) quantify the spatiotemporal distribution of relative uplift rates, and (3) explore the implications for faulting mechanisms, deformation styles, and ultimately regional seismic hazard. We measured valley floor width-to-height ratio (Vf), basin elongation ratio (Re), basin hypsometric integral, and normalized channel steepness index (ksn). The results show that high relative uplift rates exist in all the six bedrock escarpment sections investigated, suggesting that they are presumably related with regional broad wavelength uplift (epeirogeny) caused by a complex interaction between far-field tectonic stress and glacial isostatic adjustment (GIA). Our analysis showed that Vf, Re, and ksn reveals no considerable spatial differences in high relative uplift rates, consistent with the Canadian Base Network GPS uplift rates. Highlights Geomorphic indices are applied in a low relief and low-medium seismicity area. Geomorphic indices reveal a broad wavelength regional uplift and show relative tectonic activity in the OBG. Relatively high geomorphic indices values provide longer term deformation history compared to global positioning system (GPS) records. Landscape formation and river incision is driven by a complex interaction between GIA and far-field tectonic stresses. Relative uplift rate results show similar patterns to published GPS uplift rates. Possible link between relative tectonic activity and current seismicity.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-02-15T08:00:00Z
  DOI: 10.1139/cjes-2022-0137
Detrital zircon geochronology and provenance of the Mesoproterozoic Husky
Creek Formation: a fluvial sandstone recording the waning stages of one of
Earth's largest magmatic episodes
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  Authors: Robert D. Meek, Alessandro Ielpi, Robert H. Rainbird, William J. Davis
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Mesoproterozoic Husky Creek Formation is an interlayered redbed and basalt package that overlies a ca. 2.5 km thick, regionally extensive basaltic plateau linked to the 1.27 Ga Mackenzie Large Igneous Province. This succession provides an opportunity to study the interaction between contemporaneous fluvial sedimentation and flood basalt volcanism. The Husky Creek Formation is approximately 1900 m thick, consisting predominantly of fluvial channel and subordinate floodplain and eolian strata dominated by lithic detritus intercalated with basalt flows. U–Pb dating of detrital zircon grains collected from four stratigraphic levels in the Husky Creek Formation reveals two main age groupings: (1) a 1270 Ma peak attributed to the Mackenzie Large Igneous Province; and (2) Pre-1.6 Ga detrital zircon ages, which reflect sources from a broad region of northwestern Laurentia and are interpreted to be recycled from underlying sedimentary rocks of the Hornby Bay Basin. An upsection decrease in the proportion of ca. 1270 Ma zircon grains, coupled with increasing sandstone compositional maturity, reflects the expansion of the drainage basin during burial of a volcanic pile, with recycling becoming more dominant as the Husky Creek Formation accumulated. The Husky Creek Formation was deposited in the waning stages of the Mackenzie Igneous Event by west-flowing rivers into a geographically restricted basin above an extensive mafic volcanic plateau. This paper provides insight into fluvial basin development during the aftermath of one of Earth's largest igneous events.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-02-08T08:00:00Z
  DOI: 10.1139/cjes-2022-0059
Cratonal tidal deposits of the Paleoproterozoic Mesnard Quartzite, Lake
Superior region: interpretation challenges
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  Authors: David K. Larue
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Mesnard Quartzite of Paleoproterozoic age is believed to represent among the first preserved cratonal continental rocks in the Lake Superior region, was deposited above Archean basement in the Marquette structural trough and is estimated to contain more than 99% sandstone (now quartzite) beds. The Mesnard Quartzite is interpreted to have been deposited largely by tidal currents. Evidence of tidal current deposition includes lack of wave-influenced structures such as hummocky cross-beds, and presence of strongly unidirectional paleocurrents from cross-beds, mud-drapes on cross-bed foresets, evidence of current reversal including herringbone cross-bedding and sigmoidal cross-bedding. Sandstone bedding types include homogeneous or structureless beds, parallel-laminated beds, cross-beds, and symmetric ripple marks. Unidirectional paleocurrents from cross-beds are largely subparallel to the axis of the Marquette structural trough, leading to the interpretation that the trough was subsiding during deposition. Cross-bed set thickness and symmetric ripple marks both support the interpretation of shallow water marine deposition, likely only a few meters. Although the Mesnard Quartzite is on the order of 110 m thick, there is no evidence of internal sequence boundaries or flooding surfaces, and low accommodation during deposition is inferred. The climate during deposition is interpreted to be humid, and tropical to subtropical based on the quartz arenite composition. Deposition likely occurred in a failed rift basin or in an intracratonic extensional basin.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-02-06T08:00:00Z
  DOI: 10.1139/cjes-2022-0049
SHRIMP U–Pb geochronology of Mesoproterozoic basement and overlying
Ocoee Supergroup, NC–TN: dating diagenetic xenotime and monazite
overgrowths on detrital minerals to determine the age of sedimentary
deposition
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  Authors: John N. Aleinikoff, Scott Southworth, C. Mark Fanning
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Sedimentary rocks of the Ocoee Supergroup crop out in the Appalachian Blue Ridge of western North Carolina and eastern Tennessee. This ∼12 km thick sequence of strata was mapped as nonconformably overlying Mesoproterozoic crystalline basement (about 1.20–1.02 Ga) and beneath the lower Cambrian Chilhowee Group, leading to the traditional interpretation that the Ocoee Supergroup was deposited between about 1.02 and 0.54 Ga. This interpretation was challenged by Unrug and Unrug (1990, Geology, 18: 1041–1045) and Unrug et al. (2000, Geological Society of America Bulletin. Vol. 112, pp. 982–996), who claimed that Paleozoic fossils were recovered from rocks of the Walden Creek Group (upper Ocoee), and thereby created a new tectonic model for the origin of Laurentia. To resolve the age controversy concerning the time of deposition of the Ocoee Supergroup, diagenetic xenotime overgrowths on detrital zircon and diagenetic monazite on detrital monazite were dated by the U–Pb method. Sensitive High Resolution Ion Microprobe ages of diagenetic xenotime from three samples of sandstone (Thunderhead Sandstone, Cades Sandstone, and Shields Formation) indicate that the Ocoee Supergroup was deposited in the interval of about 580–550 Ma. A sample of Sandsuck Formation (uppermost Ocoee) yielded xenotime overgrowths of about 410 Ma, probably related to post-depositional low-grade metamorphism. Various origins of xenotime overgrowths may be distinguished by trace element distributions. Ages and trace element concentrations of monazite overgrowths support the xenotime age results, although concordia systematics are complicated by high concentrations of common Pb and inheritance of ages (∼1.2 and 0.6 Ga). These age data support the observed field relations for a late Neoproterozoic depositional age of the Ocoee Supergroup.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-02-01T08:00:00Z
  DOI: 10.1139/cjes-2022-0093
Geomorphic diversity of the Newfoundland and Labrador Shelves Bioregion
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  Authors: John Shaw, M.Z. Li, V.E. Kostylev
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Newfoundland and Labrador Shelves Bioregion, located on the glaciated continental shelf and adjacent continental slope of eastern Canada, is classified into units that reflect its great physiographic diversity. There are ten shelf units: bedrock zone, fjord systems, major inlet, shelf-crossing troughs, four types of offshore banks, basin, and disturbed (glaciotectonic) terrain. There are three units on the continental slope: channelized areas, trough-mouth areas, and large sedimentary drifts. A series of vignettes illustrates both the distinguishing characteristics of the principal geomorphic units and the morphologic diversity within them. A sediment mobility analysis reveals that wave- and current-generated disturbances are dominant and largely depth-controlled within the shelf units, while the south-flowing Labrador Current impacts sediment transport and mobility along the continental slope.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-01-23T08:00:00Z
  DOI: 10.1139/cjes-2022-0080
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
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  Authors: Deanne van Rooyen, Sandra M. Barr, Chris E. White, James L. Crowley
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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 has varied detrital zircon signatures from laser ablation inductively coupled plasma mass spectrometry U-Pb zircon dating, but combining three or more samples yielded representative age spectra that 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 semipelitic samples from correlative units in the eastern Bras d'Or terrane in which youngest detrital ages are 620–600 Ma. Both quartzite and semipelitic 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 form 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 and 540 Ma.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-01-10T08:00:00Z
  DOI: 10.1139/cjes-2022-0103
Late Paleoarchean to Neoarchean sedimentation on the Singhbhum Craton,
eastern India: a synthesis
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  Authors: Shuvabrata De, Rajat Mazumder, Trisrota Chaudhuri, Wilfried Bauer
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Subaerial rise of Earth's first continents took place 3.3–3.2 Ga years ago. This had significant influence on the ocean, atmosphere, and biosphere. Two important sedimentological consequences of continental emersion were (1) development of terrestrial (alluvial fan–fluvial–aeolian) depositional systems and (2) formation of shallow-marine sedimentary basins near the continental margin. Late Paleoarchean–Neoarchean terrestrial deposits, including development of an extensive paleosol around 3.2 Ga, and Meso–Neoarchean shallow-marine deposits have been reported from the Singhbhum Craton, eastern India from several localities. However, lateral and vertical changes in sedimentary facies associations and stratigraphic correlation between these terrestrial to shallow-marine sedimentary deposits have not yet been investigated. In this paper, we have reviewed the sedimentological characteristics of Late Paleoarchean to Neoarchean (3.2–2.8 Ga) stratigraphic successions of the Singhbhum Craton and have discussed sea level change and mode of stratigraphic sequence building. Our analysis shows that Singhbhum granitoid complex was emplaced around 3.3 Ga in an intracontinental setting, resulting in high continental freeboard conditions that triggered terrestrial (alluvial fan–braided fluvial) sedimentation (Dhosrapahar Formation). Continental sedimentation continued until ca. 3.0 Ga. In the eastern (Simlipal Group), western (Birtola Formation), and southwestern (the Mankarchua, Mahagiri, and Keonjhar formations) parts, shallow-marine sedimentation occurred after 3.0 Ga as a result of transgression. However, in the northern part (Dhanjori Formation), continental sedimentation prevailed throughout the Archean. These Late Paleoarchean to Neoarchean terrestrial and near-coastal successions of Singhbhum Craton should be the prime targets for intense geobiological research.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-01-10T08:00:00Z
  DOI: 10.1139/cjes-2022-0050
Precise U–Pb zircon dates from silicic super-eruptions during late
Ediacaran extension in the Avalonian Caledonia terrane of southern New
Brunswick, Canada
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  Authors: Alicia P. Escribano, Sandra M. Barr, James L. Crowley
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Coldbrook Group and related plutons in the Caledonian Highlands of southern New Brunswick contain voluminous late Ediacaran silicic rocks formed in a magmatic event not recognized in other parts of Avalonia in the northern Appalachian orogen. To better constrain the age and origin of these rocks, we used U–Pb zircon dating by laser ablation inductively coupled plasma mass spectrometry to check for older inherited zircon and obtain trace element data, followed by chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS) to obtain precise dates. Four silicic samples were dated from the Coldbrook Group, one from the Bonnell Brook pluton, and, for comparison, a felsic lithic-crystal tuff sample from the older arc-related Broad River Group. Overlapping CA-TIMS dates of 551.57 ± 0.23, 551.38 ± 0.24, and 551.70 ± 0.20 Ma for samples from the lower, middle, and upper Coldbrook Group, respectively, and 551.71 ± 0.19 Ma for granite from the Bonnell Brook pluton show that these units crystallized in 760 000 years or less, consistent with a super-eruption event. Rhyolite from the uppermost unit of the Coldbrook Group yielded a younger date of 549.18 ± 0.09 Ma, but the large extent of that unit is consistent with the possibility of a second younger super-eruption. The felsic lithic-crystal tuff sample from the Broad River Group yielded a date of 615.48 ± 0.16 Ma, consistent with previously published dates from that group and associated plutons. Differences in zircon chemistry between the Broad River Group sample and the late Ediacaran samples are consistent with the contrasting subduction-related vs within-plate extensional tectonic settings as suggested by previous studies of whole-rock petrological characteristics of the two age groups.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-01-09T08:00:00Z
  DOI: 10.1139/cjes-2022-0100
An experimental baseline for ice-till strain indicators
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  Authors: L.K. Zoet, D.D. Hansen, N. Morgan-Witts, J. Menzies, P. Sobol, N. Lord
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Subglacial till can deform when overriding ice exerts shear traction at the ice–till interface. This deformation leaves a strain signature in the till, aligning grains in the direction of ice flow and producing a range of diagnostic microstructures. Constraining the conditions that produce these kinematic indicators is key to interpreting the myriad of features found in basal till deposits. Here, we used a cryogenic ring shear device with transparent sample chamber walls to slip a ring of temperate ice over a till bed from which we examined the strain signature in the till. We used cameras mounted to the side of the ring shear and bead strings inserted in the till to estimate the strain distribution within the till layer. Following the completion of the experiment, we extracted and analyzed anisotropy of magnetic susceptibility (AMS) samples and created thin sections of the till bed for microstructure analysis. We then compared the AMS and microstructures with the observed strain history to examine the relationship between kinematic indicators and strain in a setting where shear traction is supplied by ice. We found that AMS fabrics show a high degree of clustering in regions of high strain near the ice–till interface. In the uppermost zone of till, k1 eigenvector azimuths are generally aligned with ice flow, and S1 eigenvalues are high. However, S1 eigenvalues and the alignment of the k1 eigenvector with ice flow decrease nonlinearly with distance from the ice–till interface. There is a high occurrence of microshears in the zone of increased deformation.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-01-09T08:00:00Z
  DOI: 10.1139/cjes-2022-0074
Celebrating dinosaurs: their behaviour, evolution, growth, and physiology
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  Authors: Philip J. Currie
  First page: 263
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Dinosaurs have attracted varying degrees of scientific and public interest since their initial description in 1824. Interest has steadily increased, however, since the late 1960s when the Dinosaur Renaissance began, and when the Canadian Journal of Earth Sciences started to publish. Since then, there has been a feedback system (international in scope) promoting increased scientific activity and ever-increasing public attention. This has led to ever more dinosaur discoveries internationally; increased numbers of museums and parks displaying dinosaurs; more publications, blogs, and other media on dinosaurs; and (most importantly) increased numbers of people and institutions doing research on dinosaurs. About 30 new species of dinosaurs are now being described every year, adding to the more than 1000 species already known. Furthermore, it is now acknowledged by most biologists and palaeontologists that modern birds are the direct descendants of dinosaurs, and that they are classified as part of the Dinosauria. Recognizing that there are more than 11 000 species of living dinosaurs has given us a better understanding of many aspects of the biology of nonavian dinosaurs. Along with technological improvements, this has revealed new—and often surprising—facts about their anatomy (bones, soft tissues, and even colours), interrelationships, biomechanics, growth and variation, ecology, physiology, behaviour, and extinction. In spite of the intensity of research over the last six decades, there is no indication that the discovery of new species and new facts about their biology is slowing down. It is quite clear that there is still a lot to be learned!
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-02-21T08:00:00Z
  DOI: 10.1139/cjes-2022-0131
Ontogeny of Euphanerops longaevus from the Upper Devonian Miguasha
Fossil–Fish–Lagerstätte and comparison with the skeletogenesis of the
sea lamprey Petromyzon marinus
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  Authors: Marion Chevrinais, Catherine Morel, Claude B. Renaud, Richard Cloutier
  First page: 350
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Ontogeny is of paramount importance to understand evolutionary relationships of organisms. However, in the fossil record, early developmental stages are rarely preserved because of their unmineralized skeleton. Here, we describe the ontogeny of the Devonian jawless fish, Euphanerops longaevus, based on observations from more than 3500 specimens. The ontogeny of Euphanerops is compared with the development of the median fins of the extant jawless fish, the sea lamprey (Petromyzon marinus). From a subsample of 216 specimens of Euphanerops, we define three ontogenetic stages: larvae (2–38 mm total length (TL), mostly composed of “Scaumenella mesacanthi”), juveniles (28–98 mm TL), and adults (≥90 mm TL) based on the degree of skeletal development, chemical and microscopic compositions. Larvae display three cranial plates, a simple branchial apparatus, notochordal elements, and caudal fin supports. In juveniles, we document the development of paired anteroventral, anal, and median dorsal fins. Given how little information is generally available on ostracoderm ontogeny, the growth series of Euphanerops provides an unparalleled opportunity to understand the development of early vertebrate characters.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2023-01-16T08:00:00Z
  DOI: 10.1139/cjes-2022-0062
The Ediacaran–Cambrian Chapel Island Formation of Newfoundland, Canada:
evaluating the impact of outcrop quality on trace-fossil data sets at the
Cambrian GSSP and less-explored sections
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  Authors: Romain Gougeon, M. Gabriela Mángano, Luis A. Buatois, Guy M. Narbonne, Brittany A. Laing, Maximiliano Paz
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  In 1992, the Chapel Island Formation at Fortune Head was selected as the Cambrian GSSP, which was placed at the first appearance of the ichnotaxon Treptichnus pedum. Although the transition from the Ediacaran to the Cambrian was well studied in Fortune Head and Grand Bank Head, it is also exposed at Lewin’s Cove and Point May. Here, we report new ichnologic and sedimentologic data sets from the four localities. Ichnologic data sets consist of bioturbation intensities, burrow width and depth, ichnotaxonomic composition, and stratigraphic appearances. Sedimentologic data sets include sediment grain size, bed thickness and architecture, sandstone/mudstone ratio, and physical sedimentary structures. In addition, the quality of each outcrop is evaluated (i.e., accessibility, lateral and vertical continuity, stratigraphic completeness, and type of exposure). At the four localities, the base of the Cambrian can be placed at the first appearance of Treptichnus pedum or of vertical trace fossils of the T. pedum Ichno-Assemblage Zone. In addition, Fortune Head, Grand Bank Head, and Lewin’s Cove display increases in ichnodiversity and bioturbation intensities that are concomitant with the first appearance of penetrative trace fossils. Point May stands out as a section with low ichnodiversity and an inconsistent data set on bioturbation intensities. Its limited data set is a consequence of poor bed surface exposures, which impact negatively on the preservation and visibility of horizontal trace fossils. This study demonstrates that evaluation of outcrop quality should be an essential procedure to any research addressing evolutionary trends that took place at this critical time of the history of life.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-12-23T08:00:00Z
  DOI: 10.1139/cjes-2022-0060
A 500 ka record of volcanism and paleoenvironment in the northern
Garibaldi Volcanic Belt, British Columbia
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  Authors: Martin A. Harris, James K. Russell, Alexander Wilson, Brian Jicha
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Mount Meager volcanic complex (MMVC) is one of the 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 found 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. nonglaciovolcanic), which were 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 southwest British Columbia over the last 500 ka.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-12-20T08:00:00Z
  DOI: 10.1139/cjes-2022-0101
The Lower Cretaceous sequence of western Alaska—demise of the
Koyukuk terrane'
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  Authors: Travis L. Hudson, Robert B. Blodgett, Frederic H. Wilson
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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 postsubduction 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-12-14T08:00:00Z
  DOI: 10.1139/cjes-2022-0041
Glacial microsedimentology—a new lens to investigate glacial
sediments—a review
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  Authors: John Menzies
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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 microaspects 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-12-09T08:00:00Z
  DOI: 10.1139/cjes-2022-0048
The Paleoproterozoic Amer supergroup, Amer Fold Belt, Nunavut:
stratigraphy, structure, correlations, and uranium metallogeny
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  Authors: C.W. Jefferson, R.H. Rainbird, Grant M. Young, J.C. White, V. Tschirhart, R.A. Creaser
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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 (
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-11-21T08:00:00Z
  DOI: 10.1139/cjes-2022-0077
Analysis of chemical weathering trends across three compositional
dimensions: applications to modern and ancient mafic-rock weathering
profiles
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  Authors: Michael G. Babechuk, Christopher M. Fedo
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-11-03T07:00:00Z
  DOI: 10.1139/cjes-2022-0053
Morphology and tectonic modification of the Sudbury impact crater: the
North Range
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  Authors: William A. Morris, Sara-Lise Underhay, Hernan Ugalde
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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 20°, 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 are 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 southwest dip modified by minor block rotation tilting and vertical displacement associated with north–northwest-trending faults.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-10-28T07:00:00Z
  DOI: 10.1139/cjes-2022-0066
Structural evolution and U-Pb geochronology of the metasedimentary
Nemiscau subprovince, Canada: implications for Archean tectonics in the
Superior Province
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  Authors: Rocío Pedreira Pérez, Alain Tremblay, Yannick Daoudene, Jean David, Daniel Bandyayera
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Nemiscau subprovince is a metasedimentary rocks-dominated sequence of the Archean eastern Superior Province. It is bounded by the gneissic and tonalite-trondhjemite-granodiorite (TTG) rocks-dominated La Grande and Opatica subprovinces. The Nemiscau consists of variably migmatized metasedimentary rocks and felsic to intermediate gneisses and plutonic suites. Mafic-to-ultramafic metavolcanic rocks occur along its northern and southern boundaries. Previous structural and metamorphic studies suggested that it was the result of subduction-related, accretionary and collisional tectonics with adjacent plutonic terranes during the Kenorean orogeny. This study integrates various sets of structural, metamorphic, and U-Pb geochronological data suggesting a long-lasting tectonometamorphic evolution between ca. 2843 and 2598 Ma. Four tectonometamorphic events have been recognized. The first event (D1) is only locally preserved and occurred shortly after the deposition of the oldest volcanic sequences of the Nemiscau (ca. 2756–2736 Ma) under amphibolite facies metamorphic conditions (M1). The kinematic analysis of shear zones bounding the supracrustal sequences of both the Nemiscau and La Grande subprovinces suggests their relative crustal sinking as compared to TTG of the La Grande and Opatica subprovinces, shortly after deposition (at ≤2724 and ≤2706 Ma, respectively). Sedimentation was followed by regional dip-slip-dominated (D2) deformation between ca. 2704 and 2671 Ma, coeval with extensive high-grade granulite facies metamorphism (M2) and anatexis in the Nemiscau subprovince from ca. 2697 to 2685 Ma, followed by exhumation between ca. 2677 and 2671 Ma. This D2 event was followed by regional-scale dextral strike-slip shearing (D3) from ca. 2658 until 2621 Ma at amphibolite facies metamorphism (M3). The youngest deformation event, D4, was accompanied by strain localization along brittle-to-ductile conjugated shear zones and waning crustal cooling from amphibolite to greenschist facies conditions at ca. 2598 Ma and younger. It is suggested that the Nemiscau, La Grande, and Opatica subprovinces represent a single composite terrane, and that their mutual boundaries do not correspond to “collisional sutures” between different crustal blocks or microcontinents. The Nemiscau subprovince is interpreted as a sedimentary sequence unconformably overlying a ca. 2760–2756 Ma (and older) basement made up of volcanic and crosscutting TTG. In terms of tectonic evolution, the overall structural architecture and isotopic ages of the Nemiscau, La Grande, and Opatica subprovinces support a tectonic model in which the vertical transfer of crustal material occurred during the early stages (D2) of regional deformation, which evolved into a predominant lateral crustal flow of the ductile crust during later stages (D3–D4). A non-uniformitarian tectonic model for the Archean more adequately accounts for synchronous vertical and horizontal tectonism as preserved in the Nemiscau basin.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-09-27T07:00:00Z
  DOI: 10.1139/cjes-2022-0054
Petrogenesis of siliciclastic sediments and sedimentary rocks explored in
three-dimensional Al2O3–CaO*+Na2O–K2O–FeO+MgO (A–CN–K–FM)
compositional space
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  Authors: Christopher M. Fedo, Michael G. Babechuk
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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) 40 years ago. The CIA relates the proportion of immobile aluminum to the mobile cations of 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 (2D) 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-09-22T07:00:00Z
  DOI: 10.1139/cjes-2022-0051
Linking Archaean climate change with gold metallogeny
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  Authors: Hartwig E. Frimmel
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-08-18T07:00:00Z
  DOI: 10.1139/cjes-2022-0058
A micromorphological perspective on the Neoproterozoic Smalfjord and
Mortensnes Formation diamictites—Varangerfjord, Norway
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  Authors: John Menzies
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Many Neoproterozoic diamictites are glacial in origin (Young, G.M. 2018. Precambrian glacial deposits: their origin, tectonic setting, and key role in Earth evolution. In Past glacial environments. 2nd ed. Edited by J. Menzies, and J.J.M. van der Meer. Elsevier. Chapter 2, pp. 17–45. doi:10.1016/B978-0-08-100524-8.00001-4). However, many are thought to be nonglacial mass movement deposits. Discussion on the nature of Neoproterozoic climate change focuses on the controversial origin of diamictite-bearing strata and the criteria to determine the extent and nature, or not, of glacial influence on their deposition. At the macroscale, sediments (diamictites) deposited beneath palaeo-ice masses or debris flows are massive, lack few visible signs of stratification, or deformation signatures. Microscopic investigations have resulted in specific sedimentary structures being identified, indicative of stress during glacial deposition, or developed in transit within mass movements. Case examples derived from the Neoproterozoic in Varanger, Norway have been investigated that provide strain signatures of “unique sequences” of microstructures. Micromorphology, relatively new to Precambrian research, can deliver far greater detail on the depositional and deformation histories recorded by these diamictites than obtained from macroscale studies alone. The technique provides evidence of composite deformation histories of potential glacigenic and nonglacigenic sequences. Many microstructures can be observed in most diamictites. It can be demonstrated that diamictites, both glacigenic and non-glacigenic, contain most of these microstructures in varying levels of abundancy and can be separated on specific “sets” of summative structures present. At Varanger, 12 samples were analyzed for thin sectioning. As illustrative of the thin sections as a whole, 6 are presented here that offer a microscale perspective on the diamictites from this area and establish that both the Smalfjord and Mortensnes Formation diamictites are of glacial terrestrial or subaqueous origin.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-07-25T07:00:00Z
  DOI: 10.1139/cjes-2022-0019
Microbial, tidal, and storm activity in a macrotidal to shallow marine
shelf environment during the Paleoproterozoic era
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  Authors: Carolyn M. Hill-Svehla, Patricia L. Corcoran
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  The Gordon Lake Formation (GLF) of the Paleoproterozoic Huronian Supergroup is a siliciclastic-dominated succession ranging from 300 to 1100 m in thickness. Lithostratigraphic and sedimentological analyses of the formation in the Bruce Mines and Flack Lake areas, and Killarney and Lady Evelyn-Smoothwater provincial parks, Ontario, Canada, revealed seven lithofacies, which comprise three distinct lithofacies associations. The lithofacies associations are subtidal nearshore, subtidal to shallow shelf, and mixed intertidal flat. A variety of structures interpreted to be biogenic in nature, including microbially induced sedimentary structures (MISSs) and stromatolites, are preserved, which support local microbial colonization in a tidally influenced marine environment. Wave, current, and tide-generated sedimentary structures, including symmetrical ripples, trough cross-beds, flaser and lenticular bedding, and mudstone drapes, are abundant in all study areas. Storm influence is suggested by normally graded deposits, mudstone rip-up clasts, and soft-sediment deformation structures (SSDSs), including load casts, ball-and-pillow structures, convolute bedding, and pseudonodules. Interbedding and interlamination of sandstone and mudstone units are present throughout the GLF and represent fluctuations in water level and energy, related to tidal and storm processes. A lowermost carbonate-rich unit may represent a period of low clastic influx. The contacts with the underlying Lorrain and overlying Bar River formations appear gradational. The depositional environment can be visualized as an open coast, shallow marine shelf that was influenced by microbial mats, tides, and storms.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-07-25T07:00:00Z
  DOI: 10.1139/cjes-2022-0042
Trapped in a graben: deposition of Huronian gold-bearing conglomerates in
a fault-influenced, valley-confined, fluvial system in the southern Cobalt
Basin, Ontario, Canada
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  Authors: D.G.F. Long, Robert H. Rainbird
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Isopachs of Huronian strata of the Elliot and Hough Lake groups in the southern part of the Cobalt Basin can be used to define the geometry of a 4 km wide valley system that directly influenced the location of gravel-bed rivers bearing detrital gold and auriferous pyrite in the Mississagi Formation. Distribution and thickness of these and underlying formations can be directly linked to initial valley formation parallel to existing north-south-oriented faults in the Archean basement. Thickness distributions were directly influenced by active subsidence associated with transverse, east-south-east (ESE)-oriented, normal faults, related to extension along the Huronian transform-rift margin further south. Strata underlying the Mississagi Formation were largely removed by erosion in the northern part of the paleovalley system, but thickened and then thinned south of the ESE faults. Pyrite and detrital gold in the Mississagi Formation may have been concentrated from reworking of coarse clastic rocks of the Matinenda and Ramsay Lake formations, along with significant contributions from erosion of proximal Archean basement within 3–5 km of the preserved basin margins. There is strong evidence to suggest that stream flow was initially concentrated in three main structurally influenced valley systems in the north, with one lateral tributary in the south-eastern part of the basin. The fluvial systems merged, and thickened, south of the Tee Lake fault, possibly reflecting trans-tensional influences on the basin margin faults.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-07-22T07:00:00Z
  DOI: 10.1139/cjes-2022-0025
Glacial erosion on a snowball Earth: testing for bias in flux balance,
geographic setting, and tectonic regime
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  Authors: Paul F. Hoffman
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  On the southwest cape of the Congo craton, a subtropical carbonate bank the size of Greenland was heavily glaciated during two Cryogenian panglacial episodes spaced 10–20 Myr apart. In NW Namibia, the bank underwent crustal stretching with resultant Aegean Sea-type topography during the older and longer Sturtian glaciation (717–661 Ma). This is indicated by angular discordance between glacial and preglacial strata and diamictites sourced from all older units, including crystalline basement. In contrast, the bank was flat-topped and underwent broad thermal subsidence during Marinoan glaciation (646 ± 5–635 Ma), attested by stratal parallellism and diamictites sourced from ≤100 m stratigraphic depth. However, ≥2.0 km of relief existed on the Marinoan continental slope, where most glacial erosion and accumulation occurred. The average rates of Marinoan erosion (2.55–6.80 m/Myr, n = 190) and accumulation (2.65–7.07 m/Myr, n = 211) are indistinguishable, implying that the location in a continental promontory did not bias erosion over accumulation. The average accumulation rates for the Sturtian and Marinoan, scaled for different averaging times, including Marinoan uncertainty, are 3.95–4.93 m/Myr (n = 183) and 2.65–7.07 m/Myr (n = 190), respectively, suggesting that a Marinoan glacioeustatic coastal escarpment substituted for rift-related Sturtian basin-and-range topography. These slow rates, comparable to long-term pre-Quaternary accumulation rates on existing abyssal plains, reconcile glacial sedimentology with the feeble hydrologic cycle of snowball Earth.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-06-15T07:00:00Z
  DOI: 10.1139/cjes-2022-0004
Revisiting Huronian paleoslopes
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  Authors: Darrel G.F. Long
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  It is commonly assumed that the gradients of pre-vegetation fluvial systems were greater than those of modern rivers. If the measured thickness of crossbeds is first corrected for post-depositional compaction, using thin-section-based observations, the corrected thickness data can be applied to a new suite of formulae, based on observations of >4000 modern rivers, to provide more realistic paleohydrological reconstructions of ancient river systems. Using this approach, after correction for 36% compaction, the average slope of the rivers that deposited the Mississagi Formation was calculated as 0.0013 m/m (0.0005–0.0026), with an average bankfull channel depth of 2.67 m. The slope of Serpent Formation rivers, after correction for 33.5% compaction, averaged 0.0007 m/m (0.0003–0.0016), with an average bankfull channel depth of 5.85 m. The calculation of slopes using this approach on these Paleoproterozoic and other Precambrian systems indicates that primary river gradients were similar to modern rivers, falling well below the “depositional gap”, of 0.007–0.026 m/m, between modern rivers and arid-region fans, negating the long-held idea that pre-vegetation rivers had higher slopes than their modern counterparts.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-05-24T07:00:00Z
  DOI: 10.1139/cjes-2022-0001
“Sudbury Breccia” and “Huronian Breccia”: spatial,
sedimentological, and structural evidence for separate distinct
breccia-forming events
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  Authors: W.A. Morris, G. Ferris, H.A. Slavinski
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Rounded argillite clasts within the lower Gowganda Formation of the Huronian Supergroup near Whitefish Falls, Ontario, have been historically mapped as Sudbury Breccia, implying that 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 that the formation of the breccia at Whitefish Falls was generated by faulting of the Huronian sedimentary basin during the 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 that the term Sudbury Breccia has been applied to two types of breccias. 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. The 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-04-11T07:00:00Z
  DOI: 10.1139/cjes-2022-0003
Probabilistic assessment of induced seismicity at the Alberta No. 1
geothermal project site
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  Authors: Ali Yaghoubi, Catherine J. Hickson, Yuri Leonenko, Maurice B. Dusseault
  First page: 294
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Alberta No. 1 (ABNo1) 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 ABNo1 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 ABNo1 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-12-16T08:00:00Z
  DOI: 10.1139/cjes-2022-0070
The Terreneuvian MacCodrum Brook section, Mira terrane, Cape Breton
Island, Nova Scotia, Canada: age constraints from ash layers,
organic-walled microfossils, and trace fossils
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  Authors: Sandra M. Barr, Chris E. White, Teodoro Palacios, Sören Jensen, Deanne van Rooyen, James L. Crowley
  First page: 307
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  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 other Avalonian Cambrian units in 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-10-12T07:00:00Z
  DOI: 10.1139/cjes-2022-0044
Constraining the lithostratigraphic architecture of a buried bedrock
valley using surface electrical resistivity and seismic refraction
tomography
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  Authors: Oliver Conway-White, Colby M. Steelman, Emmanuelle Arnaud, Hernan Ugalde, Jonathan D. Munn, Beth L. Parker
  First page: 333
  Abstract: Canadian Journal of Earth Sciences, Ahead of Print.
  Buried bedrock valleys are common erosional features in northern mid-latitude environments that form 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. Noninvasive 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.
  Citation: Canadian Journal of Earth Sciences
  PubDate: 2022-10-17T07:00:00Z
  DOI: 10.1139/cjes-2021-0062