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The Middle Wisconsinan History of the Laurentide Ice Sheet

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The Middle Wisconsinan History of the Laurentide Ice Sheet Document généré le 29 sept. 2021 13:50 Géographie physique et Quaternaire The Middle Wisconsinan History of the Laurentide Ice Sheet Évolution de la calotte glaciaire laurentidienne au Wisconsinien moyen Geschichte der laurentischen Eisdecke im mittleren glazialen Wisconsin Lynda A. Dredge et L. Harvey Thorleifson La calotte glaciaire laurentidienne Résumé de l'article The Laurentide Ice Sheet Les indices sur les limites glaciaires et les climats du Wisconsinien moyen Volume 41, numéro 2, 1987 proviennent d'endroits situés en bordure de la calotte glaciaire laurentidienne et des basses terres de la baie d'Hudson. Les interprétations se fondent sur la URI : https://id.erudit.org/iderudit/032680ar datation du bois, de la tourbe, des coquilles et des sédiments, sur les DOI : https://doi.org/10.7202/032680ar indicateurs biologiques de climat et sur les séquences stratigraphiques des unités glaciaires et non glaciaires. Les meilleurs indices proviennent des Prairies et des Grands Lacs; ils révèlent un recul marqué de la glace à partir Aller au sommaire du numéro des limites méridionales antérieures et des climats frais de type boréal ou de toundra. L'ouest de l'Arctique a peut-être initialement connu une période chaude, mais cette région, les plaines du nord-ouest et les Maritimes seraient Éditeur(s) par la suite devenues des zones d'accumulation de glace. Trois cartes montrent les diverses limites glaciaires proposées. Dans la première, la couverture Les Presses de l'Université de Montréal glaciaire est très étendue dans l'Arctique et moins étendue dans les Prairies et les Grands Lacs; on y voit de grandes calottes glaciaires maritimes dans le ISSN sud-est et dans l'île de Baffin. Cette répartition de la glace pourrait résulter du 0705-7199 (imprimé) déplacement des masses d'air et des courants océaniques au cours du 1492-143X (numérique) Wisconsinien moyen. Un autre modèle, légèrement différent, résout certains problèmes associés aux basses terres de la baie d'Hudson; la baie de vêlage, qui s'avance jusqu'au centre de l'inlandsis, est le produit de l'instabilité dynamique Découvrir la revue de la masse glaciaire marine dans la baie d'Hudson. Un troisième modèle fait voir une déglaciation étendue provoquée par des changements climatiques; la glace laurentidienne persiste uniquement à certains endroits dans le Citer cet article nord-ouest, dans la région du Labrador et de l'Ungava et dans la zone appalachienne atlantique. Dredge, L. A. & Thorleifson, L. H. (1987). The Middle Wisconsinan History of the Laurentide Ice Sheet. Géographie physique et Quaternaire, 41(2), 215–235. https://doi.org/10.7202/032680ar 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. 215-235, 4 fig. THE MIDDLE WISCONSINAN HISTORY OF THE LAURENTIDE ICE SHEET* Lynda A. DREDGE and L. Harvey THORLEIFSON, Geological Survey of Canada, Terrain Sciences Division, 601 Booth Street, Ottawa, Ontario K1A 0E8. ABSTRACT Evidence for Middle Wiscon- RÉSUMÉ Évolution de la calotte glaciaire ZUSAMMENFASSUNG Geschichte der sinan ice limits and climates comes from sites laurentidienne au Wisconsinien moyen. Les laurentischen Eisdecke im mittleren glazialen scattered around the periphery of the Lau- indices sur les limites glaciaires et les climats Wisconsin. Anhaltspunkte fur Eisgrenzen und rentide Ice domain and from the Hudson Bay du Wisconsinien moyen proviennent d'en­ Klima im mittleren glazialen Wisconsin er- Lowlands. Interpretations are based on dated droits situés en bordure de la calotte glaciaire geben sich aus Plàtzen, die um die Peripherie wood, peat, shell and sediment; biological laurentidienne et des basses terres de la baie des von der laurentischen Eisdecke bedeckten climate indicators (chiefly cool-climate indi­ d'Hudson. Les interprétations se fondent sur Gebiets verstreut sind, sowie aus dem Tiefland cators); and stratigraphie sequences of both la datation du bois, de la tourbe, des coquilles der Hudson Bay. Die lnterpretationen grunden glacial and nonglacial units. The best evidence et des sédiments, sur les indicateurs biolo­ sich auf datiertes HoIz, Torf, Muscheln und comes from the prairie provinces and the giques de climat et sur les séquences stra- Sedimente, biologische Klima-lndikatoren und Great Lakes areas, both of which indicate tigraphiques des unités glaciaires et non die stratigraphischen Abfolgen sowohl gla- substantial ice retreat from earlier southern glaciaires. Les meilleurs indices proviennent zialer als auch nichtglazialer Einheiten. Die glacial limits, and cool, boreal-tundra climates. des Prairies et des Grands Lacs; ils révèlent besten Zeugnisse stammen aus den Pràrie- The western arctic may have experienced an un recul marqué de la glace à partir des limites Provinzen und dem Gebiet der Gro(3en Seen. early warm period but both the western arctic méridionales antérieures et des climats frais Aus beiden Regionen zeigt sich ein bedeu- — northwestern plains and eastern maritime de type boréal ou de toundra. L'ouest de tender Eis-Rùckgang von den frùheren sud- areas may later have become ice accumu­ l'Arctique a peut-être initialement connu une lichen Eisgrenzen und kùhles nôrdliches lation areas. Three maps portray various période chaude, mais cette région, les plaines Tundra-Klima. In der westlichen Arktik mag possible ice limits. The first shows substantial du nord-ouest et les Maritimes seraient par wohl eine frùhe warme Période aufgetreten ice cover in the arctic, but reduced ice cover la suite devenues des zones d'accumulation sein, aber sowohl die westarktischen Ebenen in the prairies and Great Lakes, and expanded de glace. Trois cartes montrent les diverses als auch die ôstlichen Meeres-Gebiete sind maritime ice caps (rather than Laurentide Ice) limites glaciaires proposées. Dans la première, wohl spâter Gebiete starker Vereisung ge- in the southeast and on Baffin Island. This la couverture glaciaire est très étendue dans worden. Drei Karten illustrieren verschiedene ice mass distribution may reflect Middle Wis- l'Arctique et moins étendue dans les Prairies môgliche Eisdecken. Die erste zeigt eine be- consinan shifts in air masses and ocean cur­ et les Grands Lacs; on y voit de grandes tràchtliche Eisdecke in der Arktis, jedoch in rents. Ice volumes generated by this model calottes glaciaires maritimes dans le sud-est den Pràrien und dem Groften Seen-Gebiet are in accord with the marine oxygen isotope et dans l'île de Baffin. Cette répartition de la eine geringere Eisdecke und im Sùdosten record and perceived global sea level glace pourrait résulter du déplacement des und auf der Baffin-lnsel ausgedehnte Meeres- changes. A modification to this model, which masses d'air et des courants océaniques au Eiskappen. Dièse Verteilung der Eismasse resolves some of the controversy in the Hud­ cours du Wisconsinien moyen. Un autre mo­ mag die Folge von Verschiebungen von Luft- son Bay Lowlands, shows a calving bay pen­ dèle, légèrement différent, résout certains bewegungen und ozeanischen Strômungen etrating into the heart of the ice sheet, induced problèmes associés aux basses terres de la sein. Eine Abweichung von diesem Modell, by dynamic instability of the marine-based baie d'Hudson; la baie de vêlage, qui s'avance welche einige der Kontroversen im Hudson- ice mass in Hudson Bay during relatively high jusqu'au centre de l'inlandsis, est le produit Bay Tiefland klàrt, zeigt eine Kalbungs-Bucht, glacial isostatic and eustatic seas. A third de l'instabilité dynamique de la masse glaciaire welche in den Kern der Eisdecke vordringt. reconstruction portrays extensive climatically marine dans la baie d'Hudson. Un troisième Dièse Bucht wurde durch die dynamische induced déglaciation and retains Laurentide modèle fait voir une déglaciation étendue Instabilitât der marinen Eismasse in der ice only in parts of the northwest and Labrador- provoquée par des changements climatiques; Hudson-Bay wâhrend relativ hoher glazial- Ungava, with local ice in the Appalachian- la glace laurentidienne persiste uniquement isostatischer und eustatischer Gezeiten her- Atlantic region. This model is based on al­ à certains endroits dans le nord-ouest, dans vorgerufen. Ein drittes Modell beschreibt ternative genetic interpretations of lithologie la région du Labrador et de l'Ungava et dans ausgedehnte klimatisch bedingte Enteisung units and reassessment of age assignments. la zone appalachienne atlantique. und zeigt laurentisches Eis nur in Teilen des Nordwestens und von Labrador-Ungava mit ôrtlich begrenztem Eis im Gebiet der Atlantik- Appalachen. * Geological Survey of Canada Contribution 48986 216 L A. DREDGE and L. F. THORLEIFSON INTRODUCTION first major "warm climate' terrestrial or marine deposits rep­ resent an interglaciation, specifically the Sangamon ; whereas The Middle Wisconsinan Substage has long been regarded any nonglacial deposits above these units, are of mid-Wisconsin as a period of glacial recession between the two periods of age, particularly if biotic remains indicate climates cooler than Laurentide ice expansion which encompass the last glaciation. present. These assumptions presuppose that sub-till deposits However, the extent of ice recession and ice volume reduction, indicating a climate as warm as present must predate the the timing of onset of ice recession and of later glacier reex­ Wisconsinan and that deposits indicating a cooler climate pansion, the degree of synchrony of events along the Laurentide must be interstadial. The possibilities for incorrect age as­ ice margin, and the climatic character of the mid-Wisconsin signments using these criteria are obviously enormous.
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