The Ordovician and Silurian are an exceptionally important interval of time for understanding the effects of ancient climate change on the paleobiodiversity of echinoderms. Despite this importance, the fossil record of many echinoderm groups during this interval is sparse. The echinoids, or sea urchins, are no exception; and new fossil finds are necessary to better understand their initial diversification during the lower Paleozoic. We herein report on material from a new genus and species of echinoid, Anticostiechinus petryki gen. et sp. nov., from the Silurian of Anticosti Island, Canada. The morphology of the tubercles and spines of A. petryki are atypical for echinoids, and the surfaces for spine articulation consist of rounded, concave indentations. Additionally, the bases of the spines are subspherical. Furthermore, A. petryki belongs to the family Echinocystitidae, which increases the known diversity and distribution of this family during the Silurian and provides insight into the biogeography of echinocystitids from the Silurian to Devonian.
奥陶纪和志留纪是了解古代气候变化对棘皮动物古生物多样性影响的一个特别重要的时期。尽管如此重要，许多棘皮动物在这段时间的化石记录却很少。海胆类动物也不例外;而新的化石发现对于更好地了解它们在下古生代的初始多样化是必要的。本文报道了加拿大安提科斯蒂岛志留系棘球蚴新属(Anticostiechinus petryki gen. et sp. nov.)的材料。石竹的结节和棘的形态在棘类动物中是不典型的，棘关节的表面由圆形凹痕组成。此外，棘的基部是近球形的。此外，A. petryki属于棘囊虫科，这增加了该科在志留纪的已知多样性和分布，为志留纪至泥盆纪棘囊虫的生物地理学提供了新的认识。
{"title":"The morphologic and paleobiogeographic implications of a new early Silurian echinoid from Anticosti Island, Quebec, Canada","authors":"J. Thompson, W. Ausich, Mario E. Cournoyer","doi":"10.1139/cjes-2022-0028","DOIUrl":"https://doi.org/10.1139/cjes-2022-0028","url":null,"abstract":"The Ordovician and Silurian are an exceptionally important interval of time for understanding the effects of ancient climate change on the paleobiodiversity of echinoderms. Despite this importance, the fossil record of many echinoderm groups during this interval is sparse. The echinoids, or sea urchins, are no exception; and new fossil finds are necessary to better understand their initial diversification during the lower Paleozoic. We herein report on material from a new genus and species of echinoid, Anticostiechinus petryki gen. et sp. nov., from the Silurian of Anticosti Island, Canada. The morphology of the tubercles and spines of A. petryki are atypical for echinoids, and the surfaces for spine articulation consist of rounded, concave indentations. Additionally, the bases of the spines are subspherical. Furthermore, A. petryki belongs to the family Echinocystitidae, which increases the known diversity and distribution of this family during the Silurian and provides insight into the biogeography of echinocystitids from the Silurian to Devonian.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"12 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77444776","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Jefferson, R. Rainbird, G. M. Young, J. White, V. Tschirhart, R. Creaser
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 (<2.3 Ga quartzite) initiates as schistose basal polymict orthoconglomerate unconformably overlying paleoweathered Neoarchean rocks. It transitions upward to lower Ps2 Resort Lake formation: gossanous, recessive, graphitic, pyritic-metalliferous phyllite (Re-Os age 2126 ± 24 Ma). Ps2 conductors beneath the <1.74 Ga Thelon Formation have been drilled for unconformity-related uranium. Gradationally overlying siliceous dolomitic marble (Aluminium River formation) completes Ps2. The gradationally overlying lower Ps3 is either foliated calcareous tholeiitic basalt (Five Mile Lake formation) or grey phyllite (Three Lakes formation). These lateral equivalents host strong linear aeromagnetic markers. The Oora Lake formation foliated feldspathic calcareous sandstone gradationally overlies only the Three Lakes formation and underlies the upper Ps3 Showing Lake formation (interbedded phyllite and foliated calcareous arkose) whose two arkose members host laterally continuous disseminated uraninite + magnetite forming linear aeromagnetic markers. Pristine sequence Ps4 molasse, deposited and later deformed during DP2, comprises four formations of rhythmically interbedded, deep maroon to pink and green, feldspathic-lithic arenite, conglomerate and mudstone that unconformably overlie and include clasts of DP1-deformed Ps1 – Ps3 + Neoarchean basement. Ps4 detrital zircon (3.05 to 1.90 Ga) suggest local + distal provenance from south Rae and Slave cratons, and Taltson-Thelon magmatic zone.
{"title":"The Paleoproterozoic Amer supergroup, Amer Fold Belt, Nunavut: stratigraphy, structure, correlations and uranium metallogeny","authors":"C. Jefferson, R. Rainbird, G. M. Young, J. White, V. Tschirhart, R. Creaser","doi":"10.1139/cjes-2022-0077","DOIUrl":"https://doi.org/10.1139/cjes-2022-0077","url":null,"abstract":"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 (<2.3 Ga quartzite) initiates as schistose basal polymict orthoconglomerate unconformably overlying paleoweathered Neoarchean rocks. It transitions upward to lower Ps2 Resort Lake formation: gossanous, recessive, graphitic, pyritic-metalliferous phyllite (Re-Os age 2126 ± 24 Ma). Ps2 conductors beneath the <1.74 Ga Thelon Formation have been drilled for unconformity-related uranium. Gradationally overlying siliceous dolomitic marble (Aluminium River formation) completes Ps2. The gradationally overlying lower Ps3 is either foliated calcareous tholeiitic basalt (Five Mile Lake formation) or grey phyllite (Three Lakes formation). These lateral equivalents host strong linear aeromagnetic markers. The Oora Lake formation foliated feldspathic calcareous sandstone gradationally overlies only the Three Lakes formation and underlies the upper Ps3 Showing Lake formation (interbedded phyllite and foliated calcareous arkose) whose two arkose members host laterally continuous disseminated uraninite + magnetite forming linear aeromagnetic markers. Pristine sequence Ps4 molasse, deposited and later deformed during DP2, comprises four formations of rhythmically interbedded, deep maroon to pink and green, feldspathic-lithic arenite, conglomerate and mudstone that unconformably overlie and include clasts of DP1-deformed Ps1 – Ps3 + Neoarchean basement. Ps4 detrital zircon (3.05 to 1.90 Ga) suggest local + distal provenance from south Rae and Slave cratons, and Taltson-Thelon magmatic zone.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"94 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74656731","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Analysis of chemical weathering trends across three compositional dimensions: applications to modern and ancient mafic-rock weathering profiles","authors":"M. Babechuk, C. Fedo","doi":"10.1139/cjes-2022-0053","DOIUrl":"https://doi.org/10.1139/cjes-2022-0053","url":null,"abstract":"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.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"6 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90923589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
By examining the minor and trace element contents of chromites from three intrusions; the Bushveld Complex (South Africa), the Stillwater Complex (USA) and the Great Dyke (Zimbabwe), and comparing these chromite compositions to those of magmas from which they could have formed (komatiites and picrites) we conclude that: a) the variations in Ti, V, Sc and Ga contents across stratigraphy and across individual layers do not support the model of magma mixing leading to chromite-only crystallization; b) the chromites from the lowest levels of the intrusions could have crystallized from komatiite liquids that were contaminated with continental crust; c) the Great Dyke chromites have the highest Cr# and lowest incompatible element contents and formed from a liquid closest to komatiite; d) all of the chromites, except those of the Dunite Succession of the Great Dyke have equilibrated with a liquid that had also crystallized pyroxene; e) the Great Dyke and Stillwater chromites show a narrower range in composition than the Bushveld chromites; f) Chromites from the western limb of the Bushveld Complex contain much higher V contents than all the other chromites. This requires either, that the fO2 was lower in the western Bushveld or that the chromites equilibrated with a V-rich magma. We favor a model where chromite and silicate minerals crystallized in cotectic proportions (~2:98). The chromite, silicates and transporting liquid are emplaced into the magma chamber. During emplacement the chromite and silicate separated due to viscous particle flow to form a massive chromite layer overlain by silicates.
通过对三种侵入体铬铁矿微量元素和微量元素含量的测定;南非Bushveld杂岩、美国Stillwater杂岩和津巴布韦Great Dyke杂岩的铬铁矿组成，并与可能形成它们的岩浆(komatiites和苦荞岩)的铬铁矿组成进行比较，得出以下结论:a)不同地层和不同层间的Ti、V、Sc和Ga含量的变化不支持岩浆混合导致铬铁矿纯结晶的模式;B)侵入层底部的铬铁矿可能是由受大陆地壳污染的科马铁矿液体结晶而成;c)大堤铬铁矿的Cr#含量最高，不相容元素含量最低，形成于最接近科马铁矿的液体;d)所有铬铁矿，除了大堤泥质演替中的铬铁矿外，都与一种同样结晶辉石的液体平衡;e) Great Dyke和Stillwater铬铁矿的组成范围比Bushveld铬铁矿窄;f) Bushveld杂岩西翼铬铁矿的钒含量远高于其他铬铁矿。这要么说明布什维尔德西部的fO2较低，要么说明铬铁矿与富v岩浆平衡。我们倾向于铬铁矿和硅酸盐矿物以共晶比例结晶的模式(~2:98)。铬铁矿、硅酸盐和输送液被注入岩浆房。在放置过程中，由于粘性颗粒流，铬铁矿和硅酸盐分离，形成由硅酸盐覆盖的块状铬铁矿层。
{"title":"A comparison of trace element concentrations in chromite from komatiites, picrites and layered intrusions: Implications for the formation of massive chromite layers.","authors":"S. Barnes, E. Mansur, W. Maier, S. Prevec","doi":"10.1139/cjes-2022-0064","DOIUrl":"https://doi.org/10.1139/cjes-2022-0064","url":null,"abstract":"By examining the minor and trace element contents of chromites from three intrusions; the Bushveld Complex (South Africa), the Stillwater Complex (USA) and the Great Dyke (Zimbabwe), and comparing these chromite compositions to those of magmas from which they could have formed (komatiites and picrites) we conclude that: a) the variations in Ti, V, Sc and Ga contents across stratigraphy and across individual layers do not support the model of magma mixing leading to chromite-only crystallization; b) the chromites from the lowest levels of the intrusions could have crystallized from komatiite liquids that were contaminated with continental crust; c) the Great Dyke chromites have the highest Cr# and lowest incompatible element contents and formed from a liquid closest to komatiite; d) all of the chromites, except those of the Dunite Succession of the Great Dyke have equilibrated with a liquid that had also crystallized pyroxene; e) the Great Dyke and Stillwater chromites show a narrower range in composition than the Bushveld chromites; f) Chromites from the western limb of the Bushveld Complex contain much higher V contents than all the other chromites. This requires either, that the fO2 was lower in the western Bushveld or that the chromites equilibrated with a V-rich magma. We favor a model where chromite and silicate minerals crystallized in cotectic proportions (~2:98). The chromite, silicates and transporting liquid are emplaced into the magma chamber. During emplacement the chromite and silicate separated due to viscous particle flow to form a massive chromite layer overlain by silicates.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"21 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79680664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include: variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20o, and differing magnetic fabrics in the norite / gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC is established using, dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show: a) the elliptical form of the North Range is a primary feature associated with a near circular impact crater, b) some of the original crater wall must have been preserved, and c) deformation of the North Range is limited to regional scale block rotation producing a SW dip modified by minor block rotation tilting and vertical displacement associated with north-northwest trending faults.
{"title":"Morphology and Tectonic modification of the Sudbury Impact Crater - The North Range","authors":"W. Morris, S. Underhay, H. Ugalde","doi":"10.1139/cjes-2022-0066","DOIUrl":"https://doi.org/10.1139/cjes-2022-0066","url":null,"abstract":"The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include: variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20o, and differing magnetic fabrics in the norite / gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC is established using, dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show: a) the elliptical form of the North Range is a primary feature associated with a near circular impact crater, b) some of the original crater wall must have been preserved, and c) deformation of the North Range is limited to regional scale block rotation producing a SW dip modified by minor block rotation tilting and vertical displacement associated with north-northwest trending faults.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"4 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80502726","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Purcell anticlinorium (PA) and the Kootenay arc (KA) are two adjacent Mesozoic tectonic domains in the southeastern Omineca belt of the Canadian Cordillera. Mesoproterozoic rocks of the Belt-Purcell Supergroup (BPSG) core the PA and have open, upward-facing structures. Deeper levels of the BPSG (Aldridge Formation) preserve a Mesoproterozoic phyllitic cleavage (S1) and biotite zone mineral assemblages. The KA, on the west flank of the PA, has a younger Neoproterozoic through Paleozoic stratigraphy. The central part of the KA, the focus of this study, experienced Jurassic recumbent folding and greenschist facies metamorphism that was overprinted by Early Cretaceous ductile deformation (S2 schistosity) and Barrovian metamorphism. The interface between the PA and KA is taken as the easternmost occurrence of the S2 schistosity. K–Ar and 40Ar/39Ar mica dates in the PA range from 1318 to 240 Ma and show no consistent spatial distribution. They are interpreted to reflect partial resetting of Ar following initial cooling in the Mesoproterozoic, indicating that the PA was never sufficiently buried or heated during younger tectonism to uniformly reset the mica cooling ages. In the KA, 40Ar/39Ar dates range from 139 to 55 Ma and reflect previously documented periods of Mesozoic and Cenozoic metamorphism, magmatism, and exhumation. The PA–KA interface occurs above a west-dipping ramp in the Laurentian basement. The thick Mesoproterozoic sequence of turbidites and sills in the PA may have acted as a rigid buttress against which the more ductile rocks of the central KA “piled up” during Early Cretaceous compressional orogenesis.
{"title":"Structure, metamorphism, and mica 40Ar/39Ar thermochronology of the southern Purcell anticlinorium and its transition into the central Kootenay arc, Omineca belt, southeastern British Columbia","authors":"N. A. Rioseco, D. Pattison, A. Camacho","doi":"10.1139/cjes-2021-0056","DOIUrl":"https://doi.org/10.1139/cjes-2021-0056","url":null,"abstract":"The Purcell anticlinorium (PA) and the Kootenay arc (KA) are two adjacent Mesozoic tectonic domains in the southeastern Omineca belt of the Canadian Cordillera. Mesoproterozoic rocks of the Belt-Purcell Supergroup (BPSG) core the PA and have open, upward-facing structures. Deeper levels of the BPSG (Aldridge Formation) preserve a Mesoproterozoic phyllitic cleavage (S1) and biotite zone mineral assemblages. The KA, on the west flank of the PA, has a younger Neoproterozoic through Paleozoic stratigraphy. The central part of the KA, the focus of this study, experienced Jurassic recumbent folding and greenschist facies metamorphism that was overprinted by Early Cretaceous ductile deformation (S2 schistosity) and Barrovian metamorphism. The interface between the PA and KA is taken as the easternmost occurrence of the S2 schistosity. K–Ar and 40Ar/39Ar mica dates in the PA range from 1318 to 240 Ma and show no consistent spatial distribution. They are interpreted to reflect partial resetting of Ar following initial cooling in the Mesoproterozoic, indicating that the PA was never sufficiently buried or heated during younger tectonism to uniformly reset the mica cooling ages. In the KA, 40Ar/39Ar dates range from 139 to 55 Ma and reflect previously documented periods of Mesozoic and Cenozoic metamorphism, magmatism, and exhumation. The PA–KA interface occurs above a west-dipping ramp in the Laurentian basement. The thick Mesoproterozoic sequence of turbidites and sills in the PA may have acted as a rigid buttress against which the more ductile rocks of the central KA “piled up” during Early Cretaceous compressional orogenesis.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"35 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81853492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Mosher, M. Dickson, J. Shimeld, H. Jackson, G. Oakey, K. Boggild, C. Campbell, P. Travaglini, Walta-Anne Rainey, A. Murphy, S. Dehler, J. Ells
Canada ratified the United Nations Convention on the Law of the Sea in 2003. With that ratification came an obligation to submit data and information to the United Nations pertaining to the limits of the country’s extended continental shelf; the portion of the juridical continental shelf that extends beyond 200 nautical miles. A team of scientists spent 13 years compiling and acquiring data to provide the scientific evidence to support delineation of Canada’s outermost maritime limits. The submission has the potential to provide Canada with 2.4 million km2 of additional submarine landmass in the Atlantic and the Arctic oceans over which Canada exercises sovereign rights for the purpose of exploring and exploiting its natural resources. Specific information such as the tectonic framework of the continental margin, the geomorphology of the margin, sedimentation on the continental slope, the geologic nature of adjoined ridges, rises, and plateaux, and sediment thickness within adjacent basins are examples of fundamental pieces of geoscientific information needed. This paper highlights a number of segments of Canada’s continental margins to showcase this scientific evidence and how it is applied in the UNCLOS context. In so doing, the paper demonstrates the immensity of new knowledge gained of Canada’s offshore lands.
{"title":"Canada’s maritime frontier: the science legacy of Canada’s extended continental shelf mapping for UNCLOS","authors":"D. Mosher, M. Dickson, J. Shimeld, H. Jackson, G. Oakey, K. Boggild, C. Campbell, P. Travaglini, Walta-Anne Rainey, A. Murphy, S. Dehler, J. Ells","doi":"10.1139/cjes-2022-0069","DOIUrl":"https://doi.org/10.1139/cjes-2022-0069","url":null,"abstract":"Canada ratified the United Nations Convention on the Law of the Sea in 2003. With that ratification came an obligation to submit data and information to the United Nations pertaining to the limits of the country’s extended continental shelf; the portion of the juridical continental shelf that extends beyond 200 nautical miles. A team of scientists spent 13 years compiling and acquiring data to provide the scientific evidence to support delineation of Canada’s outermost maritime limits. The submission has the potential to provide Canada with 2.4 million km2 of additional submarine landmass in the Atlantic and the Arctic oceans over which Canada exercises sovereign rights for the purpose of exploring and exploiting its natural resources. Specific information such as the tectonic framework of the continental margin, the geomorphology of the margin, sedimentation on the continental slope, the geologic nature of adjoined ridges, rises, and plateaux, and sediment thickness within adjacent basins are examples of fundamental pieces of geoscientific information needed. This paper highlights a number of segments of Canada’s continental margins to showcase this scientific evidence and how it is applied in the UNCLOS context. In so doing, the paper demonstrates the immensity of new knowledge gained of Canada’s offshore lands.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"35 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80118771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Oliver Conway-White, C. Steelman, E. Arnaud, H. Ugalde, J. Munn, B. Parker
Buried bedrock valleys are common erosional features in northern mid-latitude environments forming through glaciofluvial or paleoalluvial processes and are typically infilled by Quaternary-aged sediments. The erosional extent and geometry of the valley including a weathered interface, along with sediment infill that can contain complex sequences of unconsolidated aquifer and aquitard sediments, mean these features may act as preferential pathways to deeper bedrock aquifers. Non-invasive geophysical tools can provide rapid, high-resolution subsurface characterization of these features. This study evaluates the application of electrical resistivity and seismic refraction tomography along two transects centred over a buried bedrock valley in Elora, Ontario, Canada. Geophysical measurements were combined with existing continuous core records and an electrofacies model based on downhole geophysical logs to constrain the morphology and infilled lithostratigraphic architecture of the valley. Bedrock competency associated with lithology may act as a control on depth and width of valley incision during erosion, with resistivity measurements of the bedrock revealing a potential association between interpreted mechanical properties and variations in the resolved valley morphology. Seismic velocity corroborated these contrasting valley widths but could not assess bedrock competency variability below the bedrock interface. This study reveals the sequence of events depositing sediments in the valley, yielding a revised architectural mapping that improves on previous regional-scale lithostratigraphic interpretations. Results will be of use to groundwater practitioners requiring detailed conceptualization of this buried bedrock valley and its role on preferential zones of groundwater flow. Similar approaches can be used for delineation of these common and hydrogeologically significant features.
{"title":"Constraining the lithostratigraphic architecture of a buried bedrock valley using surface electrical resistivity and seismic refraction tomography","authors":"Oliver Conway-White, C. Steelman, E. Arnaud, H. Ugalde, J. Munn, B. Parker","doi":"10.1139/cjes-2021-0062","DOIUrl":"https://doi.org/10.1139/cjes-2021-0062","url":null,"abstract":"Buried bedrock valleys are common erosional features in northern mid-latitude environments forming through glaciofluvial or paleoalluvial processes and are typically infilled by Quaternary-aged sediments. The erosional extent and geometry of the valley including a weathered interface, along with sediment infill that can contain complex sequences of unconsolidated aquifer and aquitard sediments, mean these features may act as preferential pathways to deeper bedrock aquifers. Non-invasive geophysical tools can provide rapid, high-resolution subsurface characterization of these features. This study evaluates the application of electrical resistivity and seismic refraction tomography along two transects centred over a buried bedrock valley in Elora, Ontario, Canada. Geophysical measurements were combined with existing continuous core records and an electrofacies model based on downhole geophysical logs to constrain the morphology and infilled lithostratigraphic architecture of the valley. Bedrock competency associated with lithology may act as a control on depth and width of valley incision during erosion, with resistivity measurements of the bedrock revealing a potential association between interpreted mechanical properties and variations in the resolved valley morphology. Seismic velocity corroborated these contrasting valley widths but could not assess bedrock competency variability below the bedrock interface. This study reveals the sequence of events depositing sediments in the valley, yielding a revised architectural mapping that improves on previous regional-scale lithostratigraphic interpretations. Results will be of use to groundwater practitioners requiring detailed conceptualization of this buried bedrock valley and its role on preferential zones of groundwater flow. Similar approaches can be used for delineation of these common and hydrogeologically significant features.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"39 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88391729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Barr, C. White, T. Palacios, S. Jensen, De Wet van Rooyen, J. Crowley
The MacCodrum Formation is a classical "lower" Cambrian unit in southeastern Cape Breton Island stratigraphy, described since the 1800s. The age of this formation and its correlation with Cambrian units in Avalonian eastern Newfoundland and southern New Brunswick have remained uncertain through numerous revisions. Here we present U-Pb CA-TIMS ages from an ash bed in the basal part of the MacCodrum Formation in its type-section on MacCodrum Brook that fix the maximum time of deposition at 531.86 ± 0.34 Ma. Organic-walled microfossils sampled throughout the MacCodrum Formation type-section yield acritarch taxa identifying the Asteridium-Comasphaerdium Zone, whereas the first acritarchs of the Skiagia-Fimbriaglomerella Zone appear in the overlying Canoe Brook Formation in other sections. The radiometric age and acritarch zonation place the MacCodrum Formation in the upper Fortunian, Cambrian Stage 2. Among trace fossils in the MacCodrum Formation the meandering trace fossil Didymaulichnus dailyi comb. nov. is of particular note and morphologically identical to the type material from the lower part of the Ratcliffe Brook Formation in New Brunswick. The new radiometric and biostratigraphic data presented here provide the first firm constraints on the age of the MacCodrum Formation and enable more precise correlation with sections in southern New Brunswick and eastern Newfoundland.
{"title":"The Terreneuvian MacCodrum Brook section, Mira terrane, Cape Breton Island, Nova Scotia, Canada: age constraints from ash layers, organic-walled microfossils, and trace fossils","authors":"S. Barr, C. White, T. Palacios, S. Jensen, De Wet van Rooyen, J. Crowley","doi":"10.1139/cjes-2022-0044","DOIUrl":"https://doi.org/10.1139/cjes-2022-0044","url":null,"abstract":"The MacCodrum Formation is a classical \"lower\" Cambrian unit in southeastern Cape Breton Island stratigraphy, described since the 1800s. The age of this formation and its correlation with Cambrian units in Avalonian eastern Newfoundland and southern New Brunswick have remained uncertain through numerous revisions. Here we present U-Pb CA-TIMS ages from an ash bed in the basal part of the MacCodrum Formation in its type-section on MacCodrum Brook that fix the maximum time of deposition at 531.86 ± 0.34 Ma. Organic-walled microfossils sampled throughout the MacCodrum Formation type-section yield acritarch taxa identifying the Asteridium-Comasphaerdium Zone, whereas the first acritarchs of the Skiagia-Fimbriaglomerella Zone appear in the overlying Canoe Brook Formation in other sections. The radiometric age and acritarch zonation place the MacCodrum Formation in the upper Fortunian, Cambrian Stage 2. Among trace fossils in the MacCodrum Formation the meandering trace fossil Didymaulichnus dailyi comb. nov. is of particular note and morphologically identical to the type material from the lower part of the Ratcliffe Brook Formation in New Brunswick. The new radiometric and biostratigraphic data presented here provide the first firm constraints on the age of the MacCodrum Formation and enable more precise correlation with sections in southern New Brunswick and eastern Newfoundland.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"32 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85212368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Yaghoubi, M. Dusseault, Y. Leonenko, C. Hickson
Alberta No.1 is a geothermal project targeting deep carbonate, conglomerates, and sandstone formations in a potential production and injection zone for geothermal energy exploitation within the Municipal District of Greenview south of Grande Prairie, Alberta, Canada. In geothermal systems without a steam fraction (typically systems under 170°C), rapid widespread pore pressure changes and slow temperature changes have led to increased deviatoric stresses, resulting in induced seismicity. A concern for the Alberta No.1 Geothermal Project is that anthropogenic seismicity from oil, gas, and well field fluid injection has created felt events in Alberta. Thus, at the beginning of this type of project, it is prudent to review the potential for induced seismicity. In this study, a geomechanical study of the Leduc and Granite Wash Formations, two potential geothermal fluid exploitation zones, has been undertaken based on borehole geophysics and regional injection-induced earthquake data. Determining subsurface properties such as state of stress, pore pressure, and fault properties, however, poses uncertainties in the absence of actual data from the target formations. Geomechanical analysis results (with associated uncertainties) are used to assess the potential for injection-induced earthquakes. A Monte Carlo probability analysis is employed to estimate the likelihood of slippage of the known faults close to the Alberta No.1 Geothermal Project. A cumulative distribution function of the critical pore pressure on each fault is derived from the local tectonic stress state and Mohr-Coulomb shear parameter analyses. The resultant probabilistic fault stability maps can serve as a baseline for future fluid injection projects in the region including wastewater disposal, hydraulic fracture stimulation, CO2 sequestration, as well as geothermal energy extraction.
{"title":"Probabilistic Assessment of Induced Seismicity at the Alberta No. 1 Geothermal Project Site","authors":"A. Yaghoubi, M. Dusseault, Y. Leonenko, C. Hickson","doi":"10.1139/cjes-2022-0070","DOIUrl":"https://doi.org/10.1139/cjes-2022-0070","url":null,"abstract":"Alberta No.1 is a geothermal project targeting deep carbonate, conglomerates, and sandstone formations in a potential production and injection zone for geothermal energy exploitation within the Municipal District of Greenview south of Grande Prairie, Alberta, Canada. In geothermal systems without a steam fraction (typically systems under 170°C), rapid widespread pore pressure changes and slow temperature changes have led to increased deviatoric stresses, resulting in induced seismicity. A concern for the Alberta No.1 Geothermal Project is that anthropogenic seismicity from oil, gas, and well field fluid injection has created felt events in Alberta. Thus, at the beginning of this type of project, it is prudent to review the potential for induced seismicity. In this study, a geomechanical study of the Leduc and Granite Wash Formations, two potential geothermal fluid exploitation zones, has been undertaken based on borehole geophysics and regional injection-induced earthquake data. Determining subsurface properties such as state of stress, pore pressure, and fault properties, however, poses uncertainties in the absence of actual data from the target formations. Geomechanical analysis results (with associated uncertainties) are used to assess the potential for injection-induced earthquakes. A Monte Carlo probability analysis is employed to estimate the likelihood of slippage of the known faults close to the Alberta No.1 Geothermal Project. A cumulative distribution function of the critical pore pressure on each fault is derived from the local tectonic stress state and Mohr-Coulomb shear parameter analyses. The resultant probabilistic fault stability maps can serve as a baseline for future fluid injection projects in the region including wastewater disposal, hydraulic fracture stimulation, CO2 sequestration, as well as geothermal energy extraction.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"25 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83219237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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