The Bras d’Or terrane of central Cape Breton Island, Nova Scotia, Canada, contains a well-preserved record of the Ediacaran to Early Cambrian evolution of Ganderia, a Gondwana-derived terrane in the northern Appalachian orogen. A complex assemblage of low- to high-grade metasedimentary rocks have varied detrital zircon signatures from LA-ICP-MS U-Pb zircon dating but combining 3 or more samples yielded representative age spectra which support correlation of the low- and high-grade metasedimentary rocks throughout the Bras d’Or terrane and the corresponding Ganderian Brookville terrane of southern New Brunswick. In quartzite samples from the McMillan Flowage Formation in the northwestern Bras d’Or terrane the youngest detrital zircons have ages >900 Ma, in contrast to previously studied psammitic and semi-pelitic samples from correlative units in the eastern Bras d’Or terrane in which youngest detrital ages are 620–600 Ma. Both quartzite and semi-pelitic samples from the McMillan Flowage Formation contain Neoproterozoic dates from zircon rims which reflect metamorphic overgrowths during peak metamorphism at ca. 550 Ma, providing a robust age for peak metamorphism in the Bras d’Or terrane that supports similar, albeit sparse, ages reported previously from monazite and titanite samples. This metamorphism is coeval with the emplacement of voluminous dioritic to granitic plutons that occur throughout the Bras d’Or terrane and formed in an Andean-type continental margin subduction zone. New U-Pb zircon ages presented here from plutons in the northern Bras d’Or terrane, combined with previously published ages, are consistent with subduction-related magmatism and associated metamorphism between ca. 575 Ma and 540 Ma.
{"title":"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","authors":"De Wet van Rooyen, S. Barr, C. White, J. Crowley","doi":"10.1139/cjes-2022-0103","DOIUrl":"https://doi.org/10.1139/cjes-2022-0103","url":null,"abstract":"The Bras d’Or terrane of central Cape Breton Island, Nova Scotia, Canada, contains a well-preserved record of the Ediacaran to Early Cambrian evolution of Ganderia, a Gondwana-derived terrane in the northern Appalachian orogen. A complex assemblage of low- to high-grade metasedimentary rocks have varied detrital zircon signatures from LA-ICP-MS U-Pb zircon dating but combining 3 or more samples yielded representative age spectra which support correlation of the low- and high-grade metasedimentary rocks throughout the Bras d’Or terrane and the corresponding Ganderian Brookville terrane of southern New Brunswick. In quartzite samples from the McMillan Flowage Formation in the northwestern Bras d’Or terrane the youngest detrital zircons have ages >900 Ma, in contrast to previously studied psammitic and semi-pelitic samples from correlative units in the eastern Bras d’Or terrane in which youngest detrital ages are 620–600 Ma. Both quartzite and semi-pelitic samples from the McMillan Flowage Formation contain Neoproterozoic dates from zircon rims which reflect metamorphic overgrowths during peak metamorphism at ca. 550 Ma, providing a robust age for peak metamorphism in the Bras d’Or terrane that supports similar, albeit sparse, ages reported previously from monazite and titanite samples. This metamorphism is coeval with the emplacement of voluminous dioritic to granitic plutons that occur throughout the Bras d’Or terrane and formed in an Andean-type continental margin subduction zone. New U-Pb zircon ages presented here from plutons in the northern Bras d’Or terrane, combined with previously published ages, are consistent with subduction-related magmatism and associated metamorphism between ca. 575 Ma and 540 Ma.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"99 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85898381","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}
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), and western ( Birtola Formation), and southwestern (e Mankarchua, Mahagiri and Keonjhar formations) 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.
{"title":"Late Paleoarchean to Neoarchean sedimentation on Singhbhum craton, eastern India: a synthesis","authors":"S. De, Rajat Mazumder, T. Chaudhuri, W. Bauer","doi":"10.1139/cjes-2022-0050","DOIUrl":"https://doi.org/10.1139/cjes-2022-0050","url":null,"abstract":"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), and western ( Birtola Formation), and southwestern (e Mankarchua, Mahagiri and Keonjhar formations) 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.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"7 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84221041","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 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 (LA-ICP-MS) followed by chemical abrasion thermal ionization mass spectrometry (CA-TIMS). 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 Ma, 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 suggests the possibility of a second younger super-eruption. The Broad River Group sample 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.
{"title":"Precise U-Pb zircon dates from silicic super-eruptions during late Ediacaran extension in the Avalonian Caledonia terrane of southern New Brunswick, Canada","authors":"A. Escribano, S. Barr, J. Crowley","doi":"10.1139/cjes-2022-0100","DOIUrl":"https://doi.org/10.1139/cjes-2022-0100","url":null,"abstract":"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 (LA-ICP-MS) followed by chemical abrasion thermal ionization mass spectrometry (CA-TIMS). 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 Ma, 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 suggests the possibility of a second younger super-eruption. The Broad River Group sample 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.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"118 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79037810","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}
L. Zoet, D. Hansen, Natasha Morgan-Witts, J. Menzies, Peter Sobol, N. Lord
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 use a cryogenic ring shear device with transparent sample chamber walls to slip a ring of temperate ice over a till bed from which we examine the strain signature in the till. We use 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 completion of the experiment, we extract and analyze AMS samples and create thin sections of the till bed for microstructure analysis. We then compare 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 find that AMS fabrics show a high degree of clustering in regions of high strain near the ice-till interface. In the upper most 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.
{"title":"An experimental baseline for ice-till strain indicators","authors":"L. Zoet, D. Hansen, Natasha Morgan-Witts, J. Menzies, Peter Sobol, N. Lord","doi":"10.1139/cjes-2022-0074","DOIUrl":"https://doi.org/10.1139/cjes-2022-0074","url":null,"abstract":"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 use a cryogenic ring shear device with transparent sample chamber walls to slip a ring of temperate ice over a till bed from which we examine the strain signature in the till. We use 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 completion of the experiment, we extract and analyze AMS samples and create thin sections of the till bed for microstructure analysis. We then compare 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 find that AMS fabrics show a high degree of clustering in regions of high strain near the ice-till interface. In the upper most 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.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"43 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77057623","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}
I. Therriault, K. Larson, H. M. Steenkamp, F. Apen, R. Graziani, M. Soret, C. Guilmette, J. Cottle
The Wager shear zone is an ∼450-km long zone of high strain hosted within Proterozoic and Archean rocks of the Rae domain in northwestern Hudson Bay, Nunavut. New field mapping and microstructural analyzes, combined with titanite and apatite geochronology, define the style, kinematics, and timing of Proterozoic ductile deformation. The results indicate that the Wager shear zone accommodated high-temperature deformation between ca. 1.75 and 1.74 Ga with post-kinematic cooling through apatite U–Pb closure (425–530 °C) at ca. 1705 Ma. These new data show that the Wager shear zone was last active later than inferred in previous work, at a time when the western Churchill Province was undergoing lithospheric delamination and exhumation following the terminal collisional events in the western portion of the Trans-Hudson Orogen.
{"title":"Characterization of the Wager shear zone, Nunavut, Canada: Insights from microstructures and geochronology","authors":"I. Therriault, K. Larson, H. M. Steenkamp, F. Apen, R. Graziani, M. Soret, C. Guilmette, J. Cottle","doi":"10.1139/cjes-2022-0031","DOIUrl":"https://doi.org/10.1139/cjes-2022-0031","url":null,"abstract":"The Wager shear zone is an ∼450-km long zone of high strain hosted within Proterozoic and Archean rocks of the Rae domain in northwestern Hudson Bay, Nunavut. New field mapping and microstructural analyzes, combined with titanite and apatite geochronology, define the style, kinematics, and timing of Proterozoic ductile deformation. The results indicate that the Wager shear zone accommodated high-temperature deformation between ca. 1.75 and 1.74 Ga with post-kinematic cooling through apatite U–Pb closure (425–530 °C) at ca. 1705 Ma. These new data show that the Wager shear zone was last active later than inferred in previous work, at a time when the western Churchill Province was undergoing lithospheric delamination and exhumation following the terminal collisional events in the western portion of the Trans-Hudson Orogen.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"106 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78473040","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}
Romain Gougeon, M. Mángano, L. Buatois, G. Narbonne, Brittany Laing, M. Paz
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.
1992年，Fortune Head的Chapel Island Formation被选为寒武纪GSSP，它被放置在鱼分类单元Treptichnus pedum的第一次出现的地方。虽然在Fortune Head和Grand Bank Head对埃迪卡拉纪到寒武纪的过渡进行了很好的研究，但在Lewin 's Cove和Point May也发现了这种过渡。在这里，我们报告了来自四个地方的新技术和沉积学数据集。技术数据集包括生物扰动强度、洞穴宽度和深度、技术分类组成和地层外观。沉积学数据集包括沉积物粒度、床层厚度和结构、砂岩/泥岩比和物理沉积结构。此外，还评估了每个露头的质量(即可达性、横向和纵向连续性、地层完整性和暴露类型)。在这4个地点，寒武系基底可以定位为长柄甲龙(treptichus pedum)或长柄甲龙(T. pedum) icho -组合带垂直痕迹化石的首次出现。此外，Fortune Head、Grand Bank Head和Lewin 's Cove的生物多样性和生物扰动强度都有所增加，这是首次出现穿透痕迹化石的结果。梅点的突出特点是技术多样性低，生物扰动强度数据集不一致。其有限的数据集是由于床面暴露不良，这对水平痕迹化石的保存和可见性产生了负面影响。这项研究表明，对于任何研究在生命历史的关键时期发生的进化趋势，露头质量的评估都应该是一个必不可少的程序。
{"title":"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","authors":"Romain Gougeon, M. Mángano, L. Buatois, G. Narbonne, Brittany Laing, M. Paz","doi":"10.1139/cjes-2022-0060","DOIUrl":"https://doi.org/10.1139/cjes-2022-0060","url":null,"abstract":"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.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"35 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83395346","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}
M. Harris, J. Russell, Alexander M. Wilson, B. Jicha
The Mount Meager Volcanic complex (MMVC) is one of eight major calc-alkaline volcanic centres within the Garibaldi volcanic belt, Canada. MMVC volcanism spans ~2 Ma and has been mainly intermediate to felsic in composition. However, small volume mafic centres are located around the periphery of the Mount Meager massif and have been collectively referred to as the Mosaic Assemblage or Mount Meager basalts. Here we present new 40Ar/39Ar ages and expanded chemical datasets for the MMVC mafic rocks. We show that mafic eruptive ages are both older and longer-lived than previously interpreted, spanning the last ~450 ka, and occurring in four episodes at, ~440, 200, 106, and 17 ka. We also find that chemical signatures for the MMVC mafic rocks have evolved across the four periods, fluctuating from ‘OIB’-like melt characteristics, to more typical slab-influenced, calc-alkaline, before returning to ‘OIB’-like in the youngest phase. These findings provide the first evidence of a temporal-chemical evolution of melt sourcing for the Garibaldi belt volcanism. Lastly, field mapping has identified edifices and deposits that are glaciovolcanic in origin (vs. non-glaciovolcanic) which are used in conjunction with our new 40Ar/39Ar age estimates to document the presence or absence of Coast Mountain sectors of earlier Cordilleran ice sheets in SW British Columbia over the last 500 ka.
{"title":"A 500 ka Record of Volcanism and Paleoenvironment in the northern Garibaldi Volcanic Belt, British Columbia.","authors":"M. Harris, J. Russell, Alexander M. Wilson, B. Jicha","doi":"10.1139/cjes-2022-0101","DOIUrl":"https://doi.org/10.1139/cjes-2022-0101","url":null,"abstract":"The Mount Meager Volcanic complex (MMVC) is one of eight major calc-alkaline volcanic centres within the Garibaldi volcanic belt, Canada. MMVC volcanism spans ~2 Ma and has been mainly intermediate to felsic in composition. However, small volume mafic centres are located around the periphery of the Mount Meager massif and have been collectively referred to as the Mosaic Assemblage or Mount Meager basalts. Here we present new 40Ar/39Ar ages and expanded chemical datasets for the MMVC mafic rocks. We show that mafic eruptive ages are both older and longer-lived than previously interpreted, spanning the last ~450 ka, and occurring in four episodes at, ~440, 200, 106, and 17 ka. We also find that chemical signatures for the MMVC mafic rocks have evolved across the four periods, fluctuating from ‘OIB’-like melt characteristics, to more typical slab-influenced, calc-alkaline, before returning to ‘OIB’-like in the youngest phase. These findings provide the first evidence of a temporal-chemical evolution of melt sourcing for the Garibaldi belt volcanism. Lastly, field mapping has identified edifices and deposits that are glaciovolcanic in origin (vs. non-glaciovolcanic) which are used in conjunction with our new 40Ar/39Ar age estimates to document the presence or absence of Coast Mountain sectors of earlier Cordilleran ice sheets in SW British Columbia over the last 500 ka.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"35 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80808676","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}
Lower Cretaceous marine sedimentary rocks, deposited in shallow shelf and basin settings and unconformity-bound, are well exposed in southwest Alaska. Collections of Early Cretaceous fossils from across western Alaska show that similar and coeval Lower Cretaceous clastic rocks are widely distributed though only locally exposed. Volcanic rocks become an important part of the Lower Cretaceous sequence in the Yukon-Koyukuk basin where they have been interpreted to represent a mobile intra-oceanic island arc, the Koyukuk terrane, that collided with Arctic Alaska to form the Brooks Range orogen. The volcanic rocks are chemically unlike Aleutian arc rocks but share compositional characteristics with spatially related, mid-Cretaceous alkaline intrusive rocks. The volcanic-bearing sequence was also deposited on an angular unconformity, includes both shallow shelf and basin depositional settings, and is unconformably overlain by mid-Cretaceous clastic rocks. The volcanic rocks are therefore considered part of the Lower Cretaceous sequence now identified across western Alaska. In this interpretation, the Lower Cretaceous volcanic rocks are an initial expression of the mid-Cretaceous tectonic regime that included extensional exhumation and subsidence, crustal and upper mantle melting, and high temperature metamorphism in the hinterland of the Brooks Range orogen. The Cretaceous heating that led to hinterland crust and upper mantle change may have been caused by deep mantle disturbances in a post-subduction setting. This interpretation has implications for the timing of contractional orogenesis, the location and nature of the related continental borderland, and the tectonic setting for development of the Anguyucham and related oceanic terranes.
{"title":"The Lower Cretaceous sequence of western Alaska – demise of the Koyukuk terrane?","authors":"T. Hudson, R. Blodgett, F. Wilson","doi":"10.1139/cjes-2022-0041","DOIUrl":"https://doi.org/10.1139/cjes-2022-0041","url":null,"abstract":"Lower Cretaceous marine sedimentary rocks, deposited in shallow shelf and basin settings and unconformity-bound, are well exposed in southwest Alaska. Collections of Early Cretaceous fossils from across western Alaska show that similar and coeval Lower Cretaceous clastic rocks are widely distributed though only locally exposed. Volcanic rocks become an important part of the Lower Cretaceous sequence in the Yukon-Koyukuk basin where they have been interpreted to represent a mobile intra-oceanic island arc, the Koyukuk terrane, that collided with Arctic Alaska to form the Brooks Range orogen. The volcanic rocks are chemically unlike Aleutian arc rocks but share compositional characteristics with spatially related, mid-Cretaceous alkaline intrusive rocks. The volcanic-bearing sequence was also deposited on an angular unconformity, includes both shallow shelf and basin depositional settings, and is unconformably overlain by mid-Cretaceous clastic rocks. The volcanic rocks are therefore considered part of the Lower Cretaceous sequence now identified across western Alaska. In this interpretation, the Lower Cretaceous volcanic rocks are an initial expression of the mid-Cretaceous tectonic regime that included extensional exhumation and subsidence, crustal and upper mantle melting, and high temperature metamorphism in the hinterland of the Brooks Range orogen. The Cretaceous heating that led to hinterland crust and upper mantle change may have been caused by deep mantle disturbances in a post-subduction setting. This interpretation has implications for the timing of contractional orogenesis, the location and nature of the related continental borderland, and the tectonic setting for development of the Anguyucham and related oceanic terranes.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"32 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83173520","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}
Marion Chevrinais, C. Morel, C. B. Renaud, R. Cloutier
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 3,500 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 sub-sample of 216 specimens of Euphanerops, we define three ontogenetic stages: larvae (2-38 mm total length; mostly composed of “Scaumenella mesacanthi”); juveniles (28-98 mm total length); and adults (≥ 90 mm total length) 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.
{"title":"Ontogeny of Euphanerops longaevus from the Upper Devonian Miguasha Fossil-Fish-Lagerstätte and comparison with the skeletogenesis of the Sea Lamprey Petromyzon marinus","authors":"Marion Chevrinais, C. Morel, C. B. Renaud, R. Cloutier","doi":"10.1139/cjes-2022-0062","DOIUrl":"https://doi.org/10.1139/cjes-2022-0062","url":null,"abstract":"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 3,500 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 sub-sample of 216 specimens of Euphanerops, we define three ontogenetic stages: larvae (2-38 mm total length; mostly composed of “Scaumenella mesacanthi”); juveniles (28-98 mm total length); and adults (≥ 90 mm total length) 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.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"28 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84457971","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}
Glacial sediment research using thin sections began post-1945. Microsedimentology examines sediments at the microscopic level deriving insights into the processes of glacial erosion, transport, and deposition. Two issues exist (1) the difficulty by some in recognizing microstructures in thin section; and (2) the absence of quantitative data making data reproduction difficult. The latter is hard to resolve but more image capture and software methodologies are now becoming available at reasonable costs. Thin sections are two-dimensional sections of three-dimensional objects, and this must be considered when measurements, fabrics and other data are assessed. Research into the micro-aspects of glacial sediments followed a typical scientific trajectory: thin sections description with little uniformity or common ‘language’ for observed microstructures: standardization allowed comparison between different sediments; with standardization, came an open-ended classification; and with cross-comparison with multiple thin sections - a quantitative means of study needs developed. It has become apparent that the basic principles of structural geology had to be applied. Thus, micromorphology has subsumed into a microsedimentological study of glacial sediments where stress parameters, structural fabrics and the mapping of deformation structures and contextual integration allows an understanding of how these sediments have been formed. Examples of the development stages of glacial micromorphology / sedimentology are presented here as well as discussion of future avenues of study. In addition, multiple thin sections are used to illustrate the many aspects of glacial micromorphology and the parameters necessary to understand glacial sedimentology and the processes of glacial sedimentation.
{"title":"Glacial Microsedimentology – a new lens to investigate Glacial Sediments – a review","authors":"J. Menzies","doi":"10.1139/cjes-2022-0048","DOIUrl":"https://doi.org/10.1139/cjes-2022-0048","url":null,"abstract":"Glacial sediment research using thin sections began post-1945. Microsedimentology examines sediments at the microscopic level deriving insights into the processes of glacial erosion, transport, and deposition. Two issues exist (1) the difficulty by some in recognizing microstructures in thin section; and (2) the absence of quantitative data making data reproduction difficult. The latter is hard to resolve but more image capture and software methodologies are now becoming available at reasonable costs. Thin sections are two-dimensional sections of three-dimensional objects, and this must be considered when measurements, fabrics and other data are assessed. Research into the micro-aspects of glacial sediments followed a typical scientific trajectory: thin sections description with little uniformity or common ‘language’ for observed microstructures: standardization allowed comparison between different sediments; with standardization, came an open-ended classification; and with cross-comparison with multiple thin sections - a quantitative means of study needs developed. It has become apparent that the basic principles of structural geology had to be applied. Thus, micromorphology has subsumed into a microsedimentological study of glacial sediments where stress parameters, structural fabrics and the mapping of deformation structures and contextual integration allows an understanding of how these sediments have been formed. Examples of the development stages of glacial micromorphology / sedimentology are presented here as well as discussion of future avenues of study. In addition, multiple thin sections are used to illustrate the many aspects of glacial micromorphology and the parameters necessary to understand glacial sedimentology and the processes of glacial sedimentation.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"39 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79067734","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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