Geoscience Canada最新文献

{"title":"Great Canadian Lagerstätten 6. Mistaken Point Ecological Reserve, Southeast Newfoundland","authors":"A. Liu, J. Matthews","doi":"10.12789/GEOCANJ.2017.44.117","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2017.44.117","url":null,"abstract":"Mistaken Point Ecological Reserve (MPER) World Heritage Site, on the southeastern coast of Newfoundland, Canada, is one of the foremost global Ediacaran fossil localities. MPER contains some of the oldest known assemblages of the soft-bodied Ediacaran macrobiota, and its fossils have contributed significantly to Ediacaran paleobiological research since their initial discovery in 1967. Preservation of multiple in situ benthic paleocommunities, some comprising thousands of specimens, has enabled research into Ediacaran paleoecology, ontogeny, taphonomy, taxonomy and morphology, offering insights into the possible phylogenetic positions of Ediacaran taxa within the tree of life. Meanwhile, a thick and continuous geological record enables the fossils to be placed within a well-resolved temporal and paleoenvironmental context spanning an interval of at least 10 million years. This article reviews the history of paleontological research at MPER, and highlights key discoveries that have shaped global thinking on the Ediacaran macrobiota.RESUMELe site du Patrimoine mondial de la Reserve ecologique de Mistaken Point (MPER), sur la cote sud-est de Terre-Neuve, au Canada, est l'une des principales localites fossiliferes ediacariennes de la planete. Le MPER renferme quelques-uns des plus anciens assemblages connus de macrobiote edicarien a parties molles, et ses fossiles ont contribue de maniere significative a la recherche paleobiologique ediacarienne depuis leur decouverte en 1967. La preservation de multiples paleocommunautes benthiques in situ, dont certaines comptant des milliers de specimens, a permis de faire des recherches en paleoecologie, ontogenese, taphonomie, taxonomie et morphologie de biotes ediacariens, ce qui a permis d’avoir un apercu de differentes positions phylogenetiques possibles des taxons ediacariens dans l'arborescence biologique. Aussi, grâce a une colonne geologique epaisse et continue, on a pu placer ces fossiles dans un contexte temporel et paleoenvironnemental bien circonscrit qui s’etend sur un intervalle d'au moins 10 millions d'annees. Cet article passe en revue l'histoire de la recherche paleontologique au MPER et souligne les decouvertes majeures qui ont faconne la reflexion sur le macrobiote ediacarien.","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44506971","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}

{"title":"The 'Rock ‘n’ Fossil Road Show:' An Enduring Earth Science Educational Outreach Initiative in Calgary, Alberta","authors":"R. MacNaughton, G. Nowlan, A. Mccracken, K. Fallas","doi":"10.12789/GEOCANJ.2017.44.119","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2017.44.119","url":null,"abstract":"Since 2004, the Calgary office of the Geological Survey of Canada has been holding ‘Rock ‘n’ Fossil Road Shows’ at Calgary Public Library branches, in partnership with the Alberta Science Network and the Alberta Palaeontological Society. These now-annual earth science education outreach events have given more than 3700 people of all ages the opportunity to view, examine, and learn about GSC-Calgary’s collection of rocks, minerals, and fossils (including many museum quality pieces), have their own samples and collections identified by experts, and gain a better understanding of local and regional geology. This article describes what goes into organizing these events, reviews their evolution, and discusses reasons for their enduring success. The ‘Road Show’ approach can be viable in a range of settings and may be a good educational outreach option for research institutes with collections of interesting geological specimens and a critical mass of interested staff. RESUME Depuis 2004, le bureau de Calgary de la Commission geologique du Canada tient des representations de son spectacle itinerant « Roche et fossiles » dans les succursales de la bibliotheque publique de Calgary, en partenariat avec l’ Alberta Science Network et l’ Alberta Palaeontological Society . Ces activites de rayonnement en sciences de la Terre, maintenant annuels, ont deja offert a plus de 3700 personnes de tous âges la possibilite de voir, d'examiner et d'apprendre a partir de la collection de roches, de mineraux et de fossiles de la CGC-Calgary (certaines pieces de qualite museale), et de voir leurs propres echantillons et collections identifies par des experts, et ainsi obtenir une meilleure comprehension de la geologie locale et regionale. Le present article decrit les details de l'organisation de ces evenements, retrace leur evolution et revoit les raisons de leur succes durable. L'approche du « spectacle itinerant » peut etre viable dans differents contextes et peut etre une bonne option de sensibilisation educative pour les instituts de recherche disposant de collections de specimens geologiques interessants et d’une masse critique d’employes interesses.","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66817965","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}

{"title":"PoLAR-FIT: Pliocene Landscapes and Arctic Remains—Frozen in Time","authors":"J. Gosse, A. Ballantyne, Joel Barker, A. Csank, T. Fletcher, G. W. Grant, D. Greenwood, R. Macphee, N. Rybczynski","doi":"10.12789/GEOCANJ.2017.44.116","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2017.44.116","url":null,"abstract":"This short summary presents selected results of an ongoing investigation into the feedbacks that contribute to amplified Arctic warming. The consequences of warming for Arctic biodiversity and landscape response to global warmth are currently being interpreted. Arctic North American records of large-scale landscape and paleoenvironmental change during the Pliocene are exquisitely preserved and locked in permafrost, providing an opportunity for paleoenvironmental and faunal reconstruction with unprecedented quality and resolution. During a period of mean global temperatures only ~2.5°C above modern, the Pliocene molecular, isotopic, tree-ring, paleofaunal, and paleofloral records indicate that the high Arctic mean annual temperature was 11°C–19°C above modern values, pointing to a much shallower latitudinal temperature gradient than exists today. It appears that the intense Neogene warming caused thawing and weathering to liberate sediment and create a continuous and thick (>2.5 km in places) clastic wedge from at least Banks Island to Meighen Island to form a coastal plain that provided a highway for camels and other mammals to migrate and evolve in the high Arctic. In this summary we highlight the opportunities that exist for research on these and related topics with the PoLAR-FIT community. RESUME Ce bref resume presente les resultats choisis d'une enquete en cours sur les declencheurs qui contribuent a l’amplification du rechauffement de l'Arctique. Les consequences du rechauffement sur la biodiversite arctique et de la reponse du paysage au rechauffement climatique sont en cours d’etre interprete. Des dossiers nord-americains de paysage a grande echelle et le changement paleoenvironnementales durant le Pliocene sont exceptionnellement preserves et scellees dans un etat de congelation qui fournissant une occasion pour la reconstruction paleoenvironnementale et faunistique avec une qualite et une resolution sans precedent. Pendent une periode de rechauffement global seulement ~2,5°C au-dessus de moderne les dossiers, moleculaire, isotopique, annaux de croissance, paleofaunistique et paleovegetation indiquent que l'Arctique a connu une augmentation de la temperature annuelle moyenne de 11°C–19°C au-dessus de moderne, en montrant un inferieur gradient de temperature latitudinal qu'aujourd'hui. Il semble que le rechauffement intense pendent le Neogene a provoque la decongelation et erosion pour liberer les sediments et creer une plaine cotiere continuel et epaisse (> 2,5 km dans lieux) qui a fourni une route pour les chameaux et autres mammiferes pour migrer et evoluer dans l’Haut-Arctique. Dans ce resume, nous soulignons les opportunites qui existent pour la recherche sur ces sujets et les sujets connexes avec la communaute PoLAR-FIT.","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45158908","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}

{"title":"Applying Phase Equilibria Modelling to Metamorphic and Geological Processes: Recent Developments and Future Potential","authors":"C. Yakymchuk","doi":"10.12789/GEOCANJ.2017.44.114","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2017.44.114","url":null,"abstract":"Phase equilibria modelling has played a key role in enhancing our understanding of metamorphic processes. An important breakthrough in the last three decades has been the ability to construct phase diagrams by integrating internally consistent datasets of the thermodynamic properties of minerals, fluids and melts with activity–composition models for mixed phases that calculate end-member activities from end-member proportions. A major advance in applying phase equilibria modelling to natural rocks is using isochemical phase diagrams to explore the phase assemblages and reaction sequences applicable for a particular sample. The chemical systems used for modelling phase equilibria are continually evolving to provide closer approximations to the natural compositions of rocks and allow wider varieties of compositions to be modelled. Phase diagrams are now routinely applied to metasedimentary rocks, metabasites and intermediate to felsic intrusive rocks and more recently to ultramafic rocks and meteorites.  While the principal application of these phase diagrams is quantifying the pressure and temperature evolution of metamorphic rocks, workers are now applying them to other fields across the geosciences. For example, phase equilibria modelling of hydrothermal alteration and the metamorphism of hydrothermally altered rocks can be used to determine ‘alteration vectors’ to hydrothermal mineral deposits. Combining the results of phase equilibria of rock-forming minerals with solubility equations of accessory minerals has provided new insights into the geological significance of U–Pb ages of accessory minerals commonly used in geochronology (e.g. zircon and monazite). Rheological models based on the results of phase equilibria modelling can be used to evaluate how the strength of the crust and mantle can change through metamorphic and metasomatic processes, which has implications for a range of orogenic processes, including the localization of earthquakes. Finally, phase equilibria modelling of fluid generation and consumption during metamorphism can be used to explore links between metamorphism and global geochemical cycles of carbon and sulphur, which may provide new insights into the secular change of the lithosphere, hydrosphere and atmosphere.RESUMELa modelisation des equilibres de phases a joue un role cle dans l’amelioration de notre comprehension des processus metamorphiques. Une percee importante au cours des trois dernieres decennies a ete la capacite de construire des diagrammes de phase en y integrant des ensembles de donnees coherentes des proprietes thermodynamiques des mineraux, des fluides et des bains magmatiques avec des modeles d'activite-composition pour des phases mixtes qui deduisent l’activite des membres extremes a partir des proportions des membres extremes. Une avancee majeure dans l'application de la modelisation d'equilibre de phase aux roches naturelles consiste a utiliser des diagrammes de phases isochimiques pour etudier les","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48835444","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}

{"title":"Who Was the First Person Known to Have Discovered Fossils of the Precambrian (Ediacaran) Organism Aspidella terranovica","authors":"Jeffrey M. Minicucci","doi":"10.12789/GEOCANJ.2017.44.115","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2017.44.115","url":null,"abstract":"This article briefly examines the possible confusion pertaining to the discoveries of Precambrian (Ediacaran) fossils made in the self-governing British colony of Newfoundland in 1868 by the amateur naturalist, the Reverend Moses Harvey, and the subsequent description and naming of the fossil organism Aspidella terranovica in 1872 by Elkanah Billings, the father of Canadian paleontology. Both events could be misinterpreted as one transaction that began with the former event and ended with the latter event. Accounts published by Alexander Murray, the director of the Geological Survey of Newfoundland at the time, arguably may have inadvertently exacerbated the possibility for confusion. The determination of who first discovered fossils of A. terranovica and whose fossil material Billings primarily relied upon when he first described and named the taxon could be placed into doubt as a consequence. Although the confusion does not affect the undisputed priority that Billings holds in having described and named A. terranovica, the opportunity to remedy the confusion serves to benefit the historical record. The incomplete or ambiguous ascertaining and documenting of contextual information whenever an historically significant fossil discovery is made arguably may precipitate subsequent misinterpretations, distortions or omissions in the resulting historical narrative as it develops and becomes entrenched or mythologized in its retelling.RESUMECet article examine brievement la confusion possible concernant les decouvertes de fossiles Precambriens (Ediacaran) fabriques dans la colonie Britannique autonome de Terre-Neuve en 1868 par le naturaliste amateur, le Reverend Moses Harvey, et la description et l'appellation suivantes de l'organisme fossile Aspidella terranovica en 1872 par Elkanah Billings, le pere de la paleontologie Canadienne. Les deux evenements pourraient etre mal interpretes comme une transaction qui a commence avec l'evenement precedent et s'est terminee avec le dernier evenement. Les comptes publies par Alexander Murray, le directeur de la Commission Geologique de Terre-Neuve a l'epoque, ont sans doute peut-etre exacerbe par megarde la possibilite de confusion. La determination de qui a decouvert les fossiles d'abord de A. terranovica et dont Billings s'appuyait principalement sur le materiel fossile dont il a d'abord decrit et nomme le taxon pourrait etre mis en doute en consequence. Bien que la confusion ne porte pas atteinte a la priorite incontestee que Billings detient en ayant decrit et nomme A. terranovica, la possibilite de remedier a la confusion sert a beneficier du dossier historique. La constatation et la documentation incompletes ou ambigues de l'information contextuelle chaque fois qu'une decouverte fossilifere historiquement significative peut etre faite peut precipiter des interpretations, des distorsions ou des omissions subsequentes dans le recit historique resultant au fur et a mesure qu'il se developpe et devient ancre o","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45537569","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}

{"title":"Logan Medallist 4. Large-Scale Impact and Earth History","authors":"R. Grieve","doi":"10.12789/GEOCANJ.2017.44.113","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2017.44.113","url":null,"abstract":"The current record of large-scale impact on Earth consists of close to 200 impact structures and some 30 impact events recorded in the stratigraphic record, only some of which are related to known structures. It is a preservation sample of a much larger production population, with the impact rate on Earth being higher than that of the moon. This is due to the Earth’s larger physical and gravitational cross-sections, with respect to asteroidal and cometary bodies entering the inner solar system. While terrestrial impact structures have been studied as the only source of ground-truth data on impact as a planetary process, it is becoming increasingly acknowledged that large-scale impact has had its effects on the geologic history of the Earth, itself. As extremely high energy events, impacts redistribute, disrupt and reprocess target lithologies, resulting in topographic, structural and thermal anomalies in the upper crust. This has resulted in many impact structures being the source of natural resources, including some world-class examples, such as gold and uranium at Vredefort, South Africa, Ni–Cu–PGE sulphides at Sudbury, Canada and hydrocarbons from the Campeche Bank, Mexico. Large-scale impact also has the potential to disrupt the terrestrial biosphere. The most devastating known example is the evidence for the role of impact in the Cretaceous–Paleocene (K–Pg) mass extinction event and the formation of the Chicxulub structure, Mexico. It also likely had a role in other, less dramatic, climatic excursions, such as the Paleocene–Eocene–Thermal Maximum (PETM) event. The impact rate was much higher in early Earth history and, while based on reasoned speculation, it is argued that the early surface of the Hadean Earth was replete with massive impact melt pools, in place of the large multiring basins that formed on the lower gravity moon in the same time-period. These melt pools would differentiate to form more felsic upper lithologies and, thus, are a potential source for Hadean-aged zircons, without invoking more modern geodynamic scenarios. The Earth-moon system is unique in the inner solar system and currently the best working hypothesis for its origin is a planetary-scale impact with the proto-Earth, after core formation at ca. 4.43 Ga. Future large-scale impact is a low probability event but with high consequences and has the potential to create a natural disaster of proportions unequalled by other geologic processes and threaten the extended future of human civilization, itself.RESUMELe bilan actuel de traces de grands impacts sur la Terre se compose de pres de 200 astroblemes et d'une trentaine d’impacts enregistres dans la stratigraphie, dont seulement certains sont lies a des astroblemes connus. Il s'agit d'echantillons preserves sur une population d’evenements beaucoup plus importante, le taux d'impact sur Terre etant superieur a celui de la lune. Cela tient aux plus grandes sections transversales physiques et gravitationnelles de la Terre","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46822766","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}

{"title":"Geology and Wine 14. Terroir of Historic Wollersheim Winery, Lake Wisconsin American Viticultural Area","authors":"S. Karakis, B. Cameron, W. Kean","doi":"10.12789/geocanj.2016.43.107","DOIUrl":"https://doi.org/10.12789/geocanj.2016.43.107","url":null,"abstract":"The viticultural history of Wisconsin started in the 1840s, with the very first vine plantings by Hungarian Agoston Haraszthy on the Wollersheim Winery property located in the Lake Wisconsin American Viticultural Area (AVA). This study examines the terroir of historic Wollersheim Winery, the only winery within the confines of the Lake Wisconsin AVA, to understand the interplay of environmental factors influencing the character and quality as well as the variability of Wollersheim wines. Soil texture, chemistry, and mineralogy in conjunction with precision viticulture tools such as electromagnetic induction and electrical resistivity tomography surveys, are utilized in the Wollersheim Winery terroir characterization and observation of spatially variable terroir at the vineyard scale. Establishing and comparing areas of variability at the plot level for two specific vineyard plots (Domaine Reserve and Lot 19) at Wollersheim Winery provides insight into the effects of soil properties and land characteristics on grape and wine production using precision viticulture tools.     The viticultural future of Wisconsin looks quite favorable, as the number of wineries keeps rising to meet the demand for Wisconsin wine and local consumption. As climate change continues to affect the grape varieties cultivated across the world’s wine regions, more opportunities arise for Wisconsin to cultivate cool-climate European varieties, in addition to the American and French–American hybrid varieties currently dominating grape production in this glacially influenced wine region.RESUMEL'histoire viticole du Wisconsin a commence dans les annees 1840, avec les premieres plantations de vigne par le Hongrois Agoston Haraszthy sur la propriete du vignoble Wollersheim situe dans la region de l’American Viticultural Area (AVA) du lac Wisconsin. Cette etude porte sur le terroir historique du vignoble Wollersheim, le seul a l'interieur de l’AVA du lac Wisconsin, qui soit soumis a l'interaction des facteurs environnementaux qui influencent le caractere, la qualite et la variabilite des vins Wollersheim. La caracterisation et l’observation des variations spatiales du terroir a l’echelle du vignoble Wollersheim se font par l’etude de la texture du sol, sa chimie et sa mineralogie en conjonction avec des outils de viticulture de precision comme l'induction electromagnetique et la tomographie par resistivite electrique. En definissant des zones de variabilite au niveau de la parcelle et en les comparant pour deux parcelles de vignobles specifiques (domaine Reserve et lot 19) du vignoble Wollersheim on peut mieux comprendre les effets des proprietes du sol et des caracteristiques du paysage sur la production de raisin et de vin.   Le nombre de vignoble augmentant pour repondre a la demande de vin du Wisconsin et a la demande locale, l'avenir viticole du Wisconsin semble assez prometteur. Comme le changement climatique continue d'influer sur la varietes des cepages cultives dans les regi","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66817673","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}

{"title":"Commitment, Collaboration and Communication: The Backbones of Geoscience","authors":"Victoria Yehl","doi":"10.12789/GEOCANJ.2016.43.106","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2016.43.106","url":null,"abstract":"","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66817605","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}

{"title":"Did the Atlantic close and then reopen?: A commentary","authors":"H. Williams","doi":"10.12789/GEOCANJ.2016.43.109","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2016.43.109","url":null,"abstract":"Tuzo Wilson’s 1966 Nature paper entitled “Did the Atlantic close and then re-open?” is truly the major turning point in the history of ideas on the evolution of the Appalachian Orogen. For a hundred years, the Appalachian Orogen was the type geosyncline, and Appalachian evolution was viewed in fixist models of geosynclinal development. Contrasting faunal realms were always enigmatic and never properly explained by notions of land barriers. Equally enigmatic was the symmetry and two-sided nature of the Newfoundland cross-section that refuted the fixist idea that continents grew like trees by the outward addition of asymmetric peripheral rings. The Wilson Cycle of closing a proto-Atlantic Ocean, then re-opening the Atlantic Ocean provided an elegant and simple solution to these enigmas. Wilson realized that island arcs existed on the North American side of the proto-Atlantic, such as the present Notre Dame Subzone in Newfoundland, and that the major faunal boundary lay to the east of these volcanic rocks. He also realized that the early Paleozoic continents may have touched in the middle Ordovician, “...for thereafter the distinction between the Atlantic and Pacific faunal realms ceases to be marked.” One continent encroaching upon another in the middle and late Ordovician explained the former borderland concept of Charles Schuchert and Marshall Kay. Likewise, Kay’s island arcs were most in evidence during the early Ordovician, the time of major proto-Atlantic closing. Wilson also recognized irregularities in ocean closing, which occurs first at promontories, then at re-entrants, with resulting clastic wedges, and an overall change from early Paleozoic marine conditions to middle and late Paleozoic terrestrial conditions. The Taconic allochthons were also part of his ocean closing scenario. The proto-Atlantic was completely closed by the end of the Paleozoic, and major spreading of the Atlantic began in the Cretaceous. Wilson then went on to trace the former course of the proto-Atlantic along the length of the Appalachian–Caledonian chain from Spitsbergen to Florida. This is no small task. It is encouraging to see that the contemporary Newfoundland analysis supported his views, and that even Tuzo had trouble finding a suture along the New England segment of the system. Northwest Africa was accommodated with ease as a Hercynian orogenic belt, in some respects symmetrical to the southern Appalachians. An important corollary of the Wilson Cycle is that the assembly and eventual breakup of Pangaea must have been an event of major significance in world geology. This is certainly true in North America, where major orogenesis and accretion in the Cordilleran Orogen on the Pacific Margin corresponds to Atlantic opening. Since the 1966 Wilson paper, we have emerged from fixist geosynclinal models that were entrenched in the literature for 100 years. Still, the Appalachian Orogen is full of surprises and there are many secrets yet to be revealed. As so aptly","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66817692","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}

{"title":"The Role of the Ancestral Yellowstone Plume in the Tectonic Evolution of the Western United States","authors":"J. Murphy","doi":"10.12789/GEOCANJ.2016.43.105","DOIUrl":"https://doi.org/10.12789/GEOCANJ.2016.43.105","url":null,"abstract":"Plate reconstructions indicate that if the Yellowstone plume existed prior to 50 Ma, then it would have been overlain by oceanic lithosphere located to the west of the North American plate (NAP). In the context of models supporting long-lived easterly directed subduction of oceanic lithosphere beneath the NAP, the Yellowstone plume would have been progressively overridden by the NAP continental margin since that time, the effects of which should be apparent in the geological record. The role of this ‘ancestral’ Yellowstone plume and its related buoyant swell in influencing the Late Mesozoic–Cenozoic tectonic evolution of the southwestern United States is reviewed in the light of recent field, analytical and geophysical data, constraints provided by more refined paleogeographic constructions, and by insights derived from recent geodynamic modeling of the interaction of a plume and a subduction zone.   Geodynamic models suggesting that the ascent of plumes is either stalled or destroyed at subduction zones have focused attention on the role of gaps or tears in the subducted slab that permit the flow of plume material from the lower to the upper plate during subduction. These models imply that the ascent of plumes may be significantly deflected as plume material migrates from the lower to the upper plate, so that the connection between the hot spot track calculated from plate reconstructions and the manifestations of plume activity in the upper plate may be far more diffuse compared to the more precise relationships in the oceanic domain. Other geodynamic models support the hypothesis that subduction of oceanic plateau material beneath the NAP correlates with the generation of a flat slab, which has long been held to have been a defining characteristic of the Laramide orogeny in the western United States, the dominant Late Mesozoic–Early Cenozoic orogenic episode affecting the NAP.   Over the last 20 years, a growing body of evidence from a variety of approaches suggests that a plume existed between 70 and 50 Ma within the oceanic realm close to the NAP margin in a similar location and with similar vigour to the modern Yellowstone hot spot. If so, interaction of this plume with the margin would have been preceded by that of its buoyant swell and related oceanic plateau, a scenario which could have generated the flat slab subduction that characterizes the Laramide orogeny.   Unless this plume was destroyed by subduction, it would have gone into an incubation period when it was overridden by the North American margin. During this incubation period, plume material could have migrated into the upper plate via slab windows or tears or around the lateral margins of the slab, in a manner consistent with recent laboratory models. The resulting magmatic activity may be located at considerable distance from the calculated hot spot track.   The current distribution of plumes and their buoyant swells suggests that their interaction with subduction zones should ","PeriodicalId":55106,"journal":{"name":"Geoscience Canada","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66817600","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}