Document generated on 09/29/2021 10:50 p.m. Géographie physique et Quaternaire Glacial and Sea Level History of Lowther and Griffith Islands, Northwest Territories: A Hint of Tectonics Histoire glaciaire et évolution des niveaux marins aux îles Lowther et Griffith, Territoires du Nord-Ouest : quelques indices de tectonique Glazialgeschichte und Entwicklung des Meeresspiegels auf den Insein Lowther und Griffith, Northwest Territories: Ein Hinweis auf die Tektonik Arthur S. Dyke Volume 47, Number 2, 1993 Article abstract Lowther and Griffith islands, in the centre of Parry Channel, were overrun by URI: https://id.erudit.org/iderudit/032944ar the Laurentide Ice Sheet early in the last glaciation. Northeastward Laurentide DOI: https://doi.org/10.7202/032944ar ice flow persisted across at least Lowther Island until early Holocene déglaciation. Well constrained postglacial emergence curves for the islands See table of contents confirm a southward dip of raised shorelines, contrary to the dip expected from the ice load configuration. This and previously reported incongruities may indicate regionally extensive tectonic complications of postglacial Publisher(s) rebound aligned with major structural elements in the central Canadian Arctic Islands. Les Presses de l'Université de Montréal ISSN 0705-7199 (print) 1492-143X (digital) Explore this journal Cite this article Dyke, A. S. (1993). Glacial and Sea Level History of Lowther and Griffith Islands, Northwest Territories: A Hint of Tectonics. Géographie physique et Quaternaire, 47(2), 133–145. https://doi.org/10.7202/032944ar Tous droits réservés © Les Presses de l'Université de Montréal, 1993 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ Géographie physique et Quaternaire, 1993, vol. 47, n°2, p. 133-145, 8 fig., 1 tab!. GLACIAL AND SEA LEVEL HISTORY OF LOWTHER AND GRIFFITH ISLANDS, NORTHWEST TERRITORIES: A HINT OF TECTONICS Arthur S. DYKE, Terrain Sciences Division, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE8. ABSTRACT Lowther and Griffith islands, in RÉSUMÉ Histoire glaciaire et évolution ZUSAMMENFASSUNG Glazialgeschichte the centre of Parry Channel, were overrun by des niveaux marins aux îles Lowther et und Entwicklung des Meeresspiegels auf the Laurentide Ice Sheet early in the last gla­ Griffith, Territoires du Nord-Ouest: quelques den Insein Lowther und Griffith, Northwest ciation. Northeastward Laurentide ice flow indices de tectonique. Les îles Lowther et Territories: Ein Hinweis auf die Tektonik. Die persisted across at least Lowther Island until Griffith, situées au centre du chenal de im Zentrum des Parry-Kanals gelegenen early Holocene déglaciation. Well con­ Parry, ont été recouvertes par l'Inlandsis lau- Insein Lowther und Griffith wurden zu Beginn strained postglacial emergence curves for rentidien tôt au cours de la dernière glacia­ der letzten Vereisung durch die laurentidis- the islands confirm a southward dip of raised tion. Un écoulement glaciaire vers le nord- che Eisdecke bedeckt. Der laurentidische shorelines, contrary to the dip expected from ouest a persisté à l'île Lowther, tout au EisfluB in Richtung Nordosten hat zumindest the ice load configuration. This and previ­ moins, jusqu'à la déglaciation au début de ùber die Insel Lowther hinweg bis zur frùhen l'Holocène. Les courbes d'émersion bien ously reported incongruities may indicate Holozan-Enteisung gedauert. Die deutlich regionally extensive tectonic complications identifiées de l'île confirment une inclinaison erkennbaren postglazialen Auftauchkurven of postglacial rebound aligned with major des plages soulevées vers le sud, contraire­ der Insein bestâtigen eine Neigung der structural elements in the central Canadian ment à l'inclinaison prévue à partir de la con­ angehobenen Kùstenlinien nach Sùden, Arctic Islands. figuration de la charge glaciaire. Ce fait ainsi entgegen der Neigung, die man entspre- que d'autres anomalies déjà signalées pour­ chend der Eismassenkonfiguration erwartet raient indiquer des complications d'ordre hàtte. Dies und zuvor schon aufgezeigte tectonique à l'échelle régionale au moment Anomalien kônnten auf regional extensive du relèvement isostatique postglaciaire cor­ respondant aux principaux éléments structu­ tektonische Komplikationen beim postglazia­ raux des îles du centre de l'Arctique len isostatischen Rùckprall hinweisen, ents- canadien. prechend den wichtigsten strukturellen Elementen der Insein im Zentrum der kana- dischen Arktis. Manuscrit reçu le 13 octobre 1992; manuscrit révisé accepté le 10 février 1993 134 A.S. DYKE INTRODUCTION additional 14 emergence curves from the adjacent central Arctic region and numerous isolated radiocarbon samples, This paper presents new radiocarbon-dated emergence mainly of early Holocene (deglacial) age, completed the data curves for Lowther and Griffith islands in an attempt to better base for a series of isobase maps. define the apparently incongruous crustal deformation pat­ tern in that area (Dyke et al., 1991). Additional observations Dyke et al. concluded that all emergence curves for Prince of the glacial geology of the islands extend earlier of Wales Island follow a smooth exponential decay form with conclusions. a half-response time of 2000 years, and thus resemble most other curves published for Arctic Canada (e.g. Blake, 1975). REGIONAL CONTEXT But the spatial pattern of postglacial crustal deformation in the central Arctic deviates from a normal glacioisostatic pattern Islands south of Barrow Strait, the central segment of due to tectonic complications (Fig. 2). These tectonic anom­ Parry Channel (Fig. 1), were strongly affected by the Late alies most strongly affect early postglacial shorelines in the Wisconsinan Laurentide Ice Sheet, but the islands north of area of best dating control. They comprise: (1) a ridge-like the strait are thought to show evidence of glaciation by either deformation over the structural Boothia Arch on Somerset the (still hypothetical) lnnuitian Ice Sheet or by local ice caps Island and Boothia Peninsula with an amplitude of 60-120 m, during the Late Wisconsinan (Blake, 1970; Dyke and Prest, and (2) a lack of delevelling on Prince of Wales Island that 1987; Dyke and Dredge, 1989; Hodgson, 1989). Laurentide resulted in a large "isobase plateau". The isobase ridge dis­ erratics occur on the northern islands (Barnett et al., 1976) sipated quickly but the plateau persisted throughout the but have been considered to date from an earlier advance Holocene. Further explanation of the data, as well as of possibly because no Laurentide ice frontal deposits of Late assumptions and sources of error in both radiocarbon dates Wisconsinan age are recognized in the region. Lowther and and elevation measurements, are in the original paper. But Griffith islands rise from Barrow Strait. Lowther Island is near the features of importance here are far too large in extent and the middle of the strait whereas Griffith Island is near the amplitude to result from any fortuitous convergence of errors northern side. in either dating or elevation in such a large data base. Although they have received only cursory attention, the In contrast to the well controlled emergence pattern on Late Wisconsinan Laurentide Ice Sheet limit has been placed and east of Prince of Wales Island, isobase patterns north of between Lowther and Griffith islands. Prest era/. (1968) arbi­ Prince of Wales Island were poorly constrained. But the gen­ trarily drew the Laurentide "Classical Wisconsin" limit eral pattern (Fig. 2) pointed to a further element that was between the islands, but both islands might well have been incongruous with the known or inferred pattern of glacial load­ placed either within or beyond the limit as no observations ing and that, therefore, may suggest further tectonic compli­ were available on the glaciation of either at that time (V.K. cation. Dyke et al. pointed out that the northern uplift cell, Prest, personal communication, 1992). The intention was which either is centred on or has the southern end of its axis merely to indicate that the limit lay north of Prince of Wales on northern Bathurst Island, is problematic and bears consid­ and Somerset islands and south of Bathurst and Cornwallis eration in this regard. islands. However, the speculation that the limit lay between There are two contrasting current models of the last glaci­ Lowther and Griffith islands was bolstered when Barnett ef a/. ation of the Bathurst Island area. One model proposes that (1976) reported evidence of "fresh" Laurentide glaciation on Bathurst Island lay beneath the south-central part of an Lowther Island in the form of generally northward trending lnnuitian Ice Sheet, which is thought to have covered all or striae and of till rich in shield erratics; similar evidence was most of the islands north of Parry Channel (Blake, 1970; not reported from Griffith Island (Barnett et al., 1976). Prest, 1969; McLaren and Barnett, 1978; Mayewski et al., Consequently, a Late Wisconsinan limit between the islands 1981); the other model proposes that Bathurst Island, along fitted comfortably