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Glacial Isostatic Adjustment of the Laurentian Great Lakes Basin

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Glacial Isostatic Adjustment of the Laurentian Great Lakes Basin Document généré le 27 sept. 2021 22:16 Géographie physique et Quaternaire Glacial Isostatic Adjustment of the Laurentian Great Lakes Basin: Using the Empirical Record of Strandline Deformation for Reconstruction of Early Holocene Paleo-Lakes and Discovery of a Hydrologically Closed Phase Réajustement glacio-isostatique du bassin des Grands Lacs : reconstitution des anciens lacs au début de l’Holocène et mise en évidence d’une phase de fermeture hydrologique par des témoins empiriques de la déformation des lignes de rivage C.F. Michael Lewis, Steve M. Blasco et Pierre L. Gareau Volume 59, numéro 2-3, 2005 Résumé de l'article Dans la région des Grands Lacs, le soulèvement isostatique lié à la dernière URI : https://id.erudit.org/iderudit/014754ar glaciation a ralenti selon une courbe de décroissance exponentielle établie à DOI : https://doi.org/10.7202/014754ar partir du gauchissement observé dans les anciennes lignes de rivage lacustres. Une surface de référence composite de la réponse isostatique datant de Aller au sommaire du numéro 10,6 ka BP (12,6 cal ka BP) a été préparée pour l’ensemble du bassin-versant des Grands Lacs, par rapport à une région au sud-ouest du lac Michigan située au-delà de la limite du dernier maximum glaciaire. Le calcul du soulèvement Éditeur(s) des sites en fonction des altitudes de la surface de référence a facilité la conversion d’un modèle altimétrique de terrain du bassin actuel des Grands Les Presses de l'Université de Montréal Lacs en des cartes paléo-géographiques pour différents âges choisis. De plus, afin de définir l’évolution des niveaux lacustres, les altitudes initiales des ISSN indicateurs géomorphologiques et stratigraphiques des paléo-niveaux lacustres, datés au 14C, ont été reconstituées puis reportées en fonction de l’âge. 0705-7199 (imprimé) La comparaison de cette courbe à celles des paléo-altitudes des exutoires 1492-143X (numérique) lacustres, calculée indépendamment, révèle, entre 7,9 et 7 ka BP (8,7 et 7,8 cal ka BP), une phase d’abaissement majeur des niveaux lacustres au-dessous de Découvrir la revue ceux des exutoires et la fermeture hydrologique des lacs dans le bassin des lacs Huron-Michigan. La forte évaporation nécessaire à l’abaissement du niveau d’eau est attribuée à un climat sec peu après le début de l’Holocène, dans un Citer cet article contexte de détournement progressif hors des Grands Lacs des eaux de fonte du lac Agassiz. Michael Lewis, C., Blasco, S. M. & Gareau, P. L. (2005). Glacial Isostatic Adjustment of the Laurentian Great Lakes Basin: Using the Empirical Record of Strandline Deformation for Reconstruction of Early Holocene Paleo-Lakes and Discovery of a Hydrologically Closed Phase. Géographie physique et Quaternaire, 59(2-3), 187–210. https://doi.org/10.7202/014754ar Tous droits réservés © Les Presses de l'Université de Montréal, 2007 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/ GPQ_59-2-3.qxd 12/01/07 10:39 Page 187 Géographie physique et Quaternaire, 2005, vol. 59, nos 2-3, p. 187-210, 13 fig., 3 tabl. GLACIAL ISOSTATIC ADJUSTMENT OF THE LAURENTIAN GREAT LAKES BASIN: USING THE EMPIRICAL RECORD OF STRANDLINE DEFORMATION FOR RECONSTRUCTION OF EARLY HOLOCENE PALEO-LAKES AND DISCOVERY OF A HYDROLOGICALLY CLOSED PHASE* C.F.Michael LEWIS**, Steve M. BLASCO and Pierre L. GAREAU: first authors: Geological Survey of Canada (Atlantic), Natural Resources Canada, Bedford Institute of Oceanography, Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada and School of Oceanography, University of Rhode Island, Narrangansett, Rhode Island 02882, United States ; second author: Geological Survey of Canada (Atlantic), Natural Resources Canada, Bedford Institute of Oceanography, Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada; third author: XY GeoInformatics Services, 28 Crichton Park Road, Dartmouth, Nova Scotia B3A 2N8, Canada. ABSTRACT In the Great Lakes region, the vertical motion of crustal RÉSUMÉ Réajustement glacio-isostatique du bassin des Grands rebound since the last glaciation has decelerated with time, and is Lacs : reconstitution des anciens lacs au début de l’Holocène et mise described by exponential decay constrained by observed warping of en évidence d’une phase de fermeture hydrologique par des témoins strandlines of former lakes. A composite isostatic response surface rel- empiriques de la déformation des lignes de rivage. Dans la région ative to an area southwest of Lake Michigan beyond the limit of the last des Grands Lacs, le soulèvement isostatique lié à la dernière glacia- glacial maximum was prepared for the complete Great Lakes water- tion a ralenti selon une courbe de décroissance exponentielle établie shed at 10.6 ka BP (12.6 cal ka BP). Uplift of sites computed using val- à partir du gauchissement observé dans les anciennes lignes de ues from the response surface facilitated the transformation of a dig- rivage lacustres. Une surface de référence composite de la réponse ital elevation model of the present Great Lakes basins to represent the isostatique datant de 10,6 ka BP (12,6 cal ka BP) a été préparée pour paleogeography of the watershed at selected times. Similarly, the orig- l’ensemble du bassin-versant des Grands Lacs, par rapport à une inal elevations of radiocarbon-dated geomorphic and stratigraphic région au sud-ouest du lac Michigan située au-delà de la limite du indicators of former lake levels were reconstructed and plotted against dernier maximum glaciaire. Le calcul du soulèvement des sites en age to define lake level history. A comparison with the independently fonction des altitudes de la surface de référence a facilité la conver- computed basin outlet paleo-elevations reveals a phase of severely sion d’un modèle altimétrique de terrain du bassin actuel des Grands reduced water levels and hydrologically-closed lakes below overflow Lacs en des cartes paléo-géographiques pour différents âges choisis. outlets between 7.9 and 7.0 ka BP (8.7 and 7.8 cal ka BP) in the De plus, afin de définir l’évolution des niveaux lacustres, les altitudes Huron-Michigan basin. Severe evaporative draw-down is postulated to initiales des indicateurs géomorphologiques et stratigraphiques des result from the early Holocene dry climate when inflows of meltwater paléo-niveaux lacustres, datés au 14C, ont été reconstituées puis from the upstream Agassiz basin began to bypass the upper Great reportées en fonction de l’âge. La comparaison de cette courbe à Lakes basin. celles des paléo-altitudes des exutoires lacustres, calculée indépen- damment, révèle, entre 7,9 et 7 ka BP (8,7 et 7,8 cal ka BP), une phase d’abaissement majeur des niveaux lacustres au-dessous de ceux des exutoires et la fermeture hydrologique des lacs dans le bas- sin des lacs Huron-Michigan. La forte évaporation nécessaire à l’abaissement du niveau d’eau est attribuée à un climat sec peu après le début de l’Holocène, dans un contexte de détournement progres- sif hors des Grands Lacs des eaux de fonte du lac Agassiz. Manuscrit reçu le 12 juillet 2005 ; manuscrit révisé accepté le 9 juillet 2006 (publié le 1er trimestre 2007) * Geological Survey of Canada contribution number 2005546 ** E-mail address: [email protected] GPQ_59-2-3.qxd 12/01/07 10:39 Page 188 188 C.F. M. LEWIS, S. M. BLASCO and P.L. GAREAU INTRODUCTION 9.5 ka BP (10.7 cal ka BP) (Table I; Dyke et al., 2003; Dyke, The Great Lakes of North America consist of five major 2004). During this retreat, a series of proglacial lakes formed basins whose water surfaces comprise 32% of a total water- shorelines of different ages that are upwarped today towards shed area of 766 000 km2 (The Great Lakes Environmental the north-northeast in the direction of thicker and longer-last- Atlas, 1995) (Fig. 1). The watershed forms the headwaters of ing ice (Fig. 2). This deformation is the cumulative isostatic the St. Lawrence River that drains to the Gulf of St. Lawrence adjustment of Earth’s crust since formation of the shorelines as and Atlantic Ocean. At the last glacial maximum, the water- a result of removal of the former ice sheet load. This differen- shed was completely covered by the southern flank of the tial rebound proceeded throughout the period of ice retreat and Laurentide Ice Sheet about 18-21 ka BP (21.3-25.4 cal ka BP). postglacial time at decelerating rates of uplift. It is continuing Deglaciation of the basins occurred as the ice margin retreated today, as evidenced by tilting of the Great Lakes basins meas- generally in a northerly direction in a series of oscillations, first ured in long-term records of lake level gauges between south- exposing the Erie basin about 15.5 ka BP (18.8 cal ka BP), ern and northern shores of the Great Lakes (CCGLBHHD, and finally receding to the northern Superior basin about 1977; Tushingham, 1992; Mainville and Craymer, 2005). HU DSO N BAY LOWLAND 50° N Lake Nipigon Thunder Bay Lake 48° N Superior (183 m asl) LLaClocheaCloche 224,4, 2 25,5, LLowlandowland ( (W,W, L LC)C) RRutherglenutherglen 112,2, 1 133 4646 - 4848 Sault Ste. Marie 4411 North MMoraineoraine 2299 3333 Lake Bay 2266 SStraitstraits o off M Mackinacackinac 4433 5500 Nipissing 553b3b RRankinankin 46° N 2288 8 444,4, 4 455 4499 MMichiganichigan S Sillill Manitoulin G CConstrictiononstriction Legend 7777 Island 9 2233 e DDallesalles 3344 org River 500 m+ Major 5544 awa 1100 4422 ian DDeane-Tovelleane-Tovell SaddleSaddle Ott r Inflows ive 331,32,1,32, 4400 ((FI,FI, L LU,U, E EC)C) e R and 5522 Ba nc 500 m re w Outflows sl) 66-7166-71 7755 y a Elevations a 7 7722 L 6644 Lake t.
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