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The Early Wisconsinan History of the Laurentide Ice Sheet

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Document généré le 30 sept. 2021 19:59 Géographie physique et Quaternaire The Early Wisconsinan History of the Laurentide Ice Sheet L’évolution de la calotte glaciaire laurentidienne au Wisconsinien inférieur Geschichte der laurentischen Eisdecke im frühen glazialen Wisconsin Jean-Serge Vincent et Victor K. Prest La calotte glaciaire laurentidienne Résumé de l'article The Laurentide Ice Sheet L'identification, surtout en périphérie de l'inlandsis, de dépôts glaciaires que Volume 41, numéro 2, 1987 l'on croit postérieurs à la mise en place de sédiments non glaciaires ou de paléosols datant de l'interglaciaire sangamonien (phase 5) et antérieurs aux URI : https://id.erudit.org/iderudit/032679ar sédiments non glaciaires ou des sols mis en place au Wisconsinien moyen DOI : https://doi.org/10.7202/032679ar (phase 3) a amené de nombreux chercheurs à supposer que la calotte laurentidienne s'est d'abord développée au Sangamonien ou au Wisconsinien inférieur (phase 4). On passe en revue les différentes preuves associées au Aller au sommaire du numéro début de la formation de la calotte glaciaire wisconsinienne recueillies au Canada et au nord des États-Unis. En l'absence quasi généralisée de données géochronométriques sûres pour déterminer l'âge des dépôts glaciaires datant Éditeur(s) probablement du Sangamonien ou du Wisconsinien inférieur, on peut aussi bien supposer, pour une période donnée, que les glaces ont entièrement envahi Les Presses de l'Université de Montréal une région ou en étaient tout à fait absentes. En tenant pour acquis (?) que la calotte laurentidienne était en fait très étendue au Wisconsinien inférieur, on ISSN présente une carte montrant son étendue maximale et un tableau de 0705-7199 (imprimé) corrélation entre les unités glaciaires. Les glaciers postérieurs au Sangamonien 1492-143X (numérique) sensu stricto (sous-phase 5e) et antérieurs au Wisconsinien moyen sont généralement plus étendues qu'au Wisconsinien supérieur (phase 2). La géométrie de la marge glaciaire et les quelques données sur la direction de Découvrir la revue l'écoulement montrent que les inlandsis du Wisconsinien inférieur et du Wisconsinien supérieur se sont développés de façon similaire. On présente enfin un modèle hypothétique de croissance de la calotte laurentidienne après Citer cet article le dernier interglaciaire. Vincent, J.-S. & Prest, V. K. (1987). The Early Wisconsinan History of the Laurentide Ice Sheet. Géographie physique et Quaternaire, 41(2), 199–213. https://doi.org/10.7202/032679ar Tous droits réservés © Les Presses de l'Université de Montréal, 1987 Ce document est protégé par la loi sur le droit d’auteur. L’utilisation des services d’Érudit (y compris la reproduction) est assujettie à sa politique d’utilisation que vous pouvez consulter en ligne. https://apropos.erudit.org/fr/usagers/politique-dutilisation/ Cet article est diffusé et préservé par Érudit. Érudit est un consortium interuniversitaire sans but lucratif composé de l’Université de Montréal, l’Université Laval et l’Université du Québec à Montréal. Il a pour mission la promotion et la valorisation de la recherche. https://www.erudit.org/fr/ Géographie physique et Quaternaire, 1987, vol. XLI, n° 2, p. 199-213, 4 fig. THE EARLY WISCONSINAN HISTORY OF THE LAURENTIDE ICE SHEET* Jean-Serge VINCENT and Victor K. PREST, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8. ABSTRACT The identification, particularly RÉSUMÉ L'évolution de la calotte glaciaire ZUSAMMENFASSUNG Geschichte der at the periphery of the ice sheet, of glacigenic laurentidienne au Wisconsinien inférieur. laurentischen Eisdecke im frùhen glazialen sediments thought to postdate nonglacial L'identification, surtout en périphérie de l'in­ Wisconsin. Zahlreiche Autoren sind zu der sediments or paleosols regarded as having landsis, de dépôts glaciaires que l'on croit Annahme gekommen, dap die laurentische been laid down sometime during the San­ postérieurs à la mise en place de sédiments Eisdecke wàhrend des Sangamoniums und/ gamonian Interglaciation (stage 5) and non glaciaires ou de paléosols datant de I1In- oder des frùhen glazialen Wisconsin (Phase thought to predate nonglacial sediments or terglaciaire sangamonien (phase 5) et an­ 4) zu wachsen anting. Dièse Annahme stùtzt soils reckoned to be of Middle Wisconsinan térieurs aux sédiments non glaciaires ou des sich auf die Identifizierung glacialer Sedi- age (stage 3), has led numerous authors to sols mis en place au Wisconsinien moyen mente, die man fur alter als nichtglaziale propose that the Laurentide Ice Sheet initially (phase 3) a amené de nombreux chercheurs Sedimente oder Paleobôden halt, die ihrer- grew during the Sangamonian and/or the Early à supposer que la calotte laurentidienne s'est seits irgendwann wàhrend der Intergtazialzeit Wisconsinan (stage 4). The evidence for the d'abord développée au Sangamonien ou au des Sangamoniums (Phase 5) abgelagert beginning of the Wisconsinan ice sheet in Wisconsinien inférieur (phase 4). On passe worden sind und vermutlich nichtglazialen various areas of Canada and the northern en revue les différentes preuves associées Sedimenten oder Bôden, die der mittleren United States is briefly reviewed. The general au début de la formation de la calotte glaciaire glazialen Wisconsin-Zeit (Phase 3) zugeord- absence of sound geochronometric frame­ wisconsinienne recueillies au Canada et au net werden, vorausgehen. Die Belege fur den works for potential Sangamonian or Early nord des États-Unis. En l'absence quasi gé­ Beginn der Wisconsin-Eisdecke in verschie- Wisconsinan glacial deposits has led to a néralisée de données géochronométriques denen Gebieten Kanadas und der nôrdlichen situation where in most areas it can be argued, sûres pour déterminer l'âge des dépôts gla­ Vereinigten Staaten wird kurz zusammen- depending on one's interpretation, that ice ciaires datant probablement du Sangamonien gefapt. Das volkommene Fehlen eines ges- completely inundated or was completely ab­ ou du Wisconsinien inférieur, on peut aussi icherten geo-chronometrischen Gerùsts fur sent at that time. On the premise (perhaps bien supposer, pour une période donnée, que môgliche glaziale Ablagerungen im Sanga- false) that Laurentide Ice was in fact extensive les glaces ont entièrement envahi une région monium oder frùhen glazialen Wisconsin during the Early Wisconsinan, a map showing ou en étaient tout à fait absentes. En tenant fùhrte dazu, dap in den meisten Gebieten je maximum possible ice extent, as put forward pour acquis (?) que la calotte laurentidienne nach Interpretationsweise das Eis in jener by some authors is presented and the gla­ était en fait très étendue au Wisconsinien Zeit entweder vollstândig ùberflutete oder gar cigenic units possibly recording the ice inférieur, on présente une carte montrant son nicht vorhanden war. Ausgehend von der advance are shown in a correlation chart. étendue maximale et un tableau de corrélation (vielleicht falschen) Prâmisse, dap sich das This post Sangamonian sensu stricto entre les unités glaciaires. Les glaciers pos­ laurentische Eis tatsâchlich wàhrend des frù­ (substage 5e) -pre Middle Wisconsinan limit térieurs au Sangamonien sensu stricto (sous- hen glazialen Wisconsin ausdehnte, wird eine of ice extent is generally more extensive than phase 5e) et antérieurs au Wisconsinien Karte mit der môglichen maximalen Eisaus- the Late Wisconsinan (stage 2) limit. The ge­ moyen sont généralement plus étendues dehnung gezeigt, entsprechend der Annahme ometry of the ice sheet margin and scanty qu'au Wisconsinien supérieur (phase 2). La einiger Autoren; und in einer dazu in Verbin- available information on direction of ice géométrie de la marge glaciaire et les dung stehenden Ùbersicht werden die gla­ movements indicate that this assumed Early quelques données sur la direction de l'écou­ zialen Einheiten gezeigt, die den vermutlichen Wisconsinan ice likely developed in a very lement montrent que les inlandsis du Wis­ Eisvorstop dokumentieren. Dièse Grenze der similar manner to that of the Late Wisconsinan consinien inférieur et du Wisconsinien Eisausdehnung im Postsangamonium sensu ice complex. A hypothetical growth model of supérieur se sont développés de façon si­ stricto (Unterphase 5e) vor dem mittleren the Laurentide Ice Sheet, following the last milaire. On présente enfin un modèle hy­ glazialen Wisconsin ist im Allgemeinen aus- interglaciation is also proposed. pothétique de croissance de la calotte gedehnter als die Grenze im spâten glazialen laurentidienne après le dernier interglaciaire. Wisconsin (Phase 2). Die Géométrie des Eisdeckenrands und ungenùgende zugân- gliche Informationen ùber die Richtung der Eisbewegungen zeigen, dap dieses vermu­ tlich aus dem frùhen glazialen Wisconsin stammende Eis môglicherweise sich àhnlich entwickelte wie die Eisdecke des spâten gla­ zialen Wisconsin. Auperdem wird ein hy- pothetisches Wachstumsmodell der laurentischen Eisdecke nach der letzten In- terglazialzeit vorgestellt. * Geological Survey of Canada Contribution 33186 200 J.-S. VINCENT and V. K. PREST INTRODUCTION for one view point at the expense of another. The documents only serve to illustrate a view point. The location of sites The continental evidence for the beginning of the Laurentide mentioned in the text is shown on Figure 1 and numbers in Ice Sheet1 sometime during the Sangamonian (marine oxygen brackets throughout the paper refer to this figure. isotope stage 5) or Early Wisconsinan (stage 4) and before the Middle Wisconsinan (stage 3) is the subject of this
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