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Elevation of the Shaler Group to supergroup status and the following internal revisions are proposed in order to more properly reflect rock units of the Amundsen Basin. The names Escape Rapids, Mikkelsen Islands, Nelson Head and Aok are proposed to replace the lower clastic, cherty carbonate, upper clastic, and orange-weathering stromatolite members of the Glenelg Formation in Minto and Cape Lambton inliers, informal map units 19 to 21,22,23, and 24 in the Coppermine area and informal map units PI , P2, P3, and P4a in Brock Inlier, respectively. Collectively these are to be known as the Rae Group; the name Glenelg Formation is abandoned. The former Reynolds Point Formation is raised to group status and comprises the Grassy Bay, Boot Inlet, Fort Collinson and Jago Bay formations, which replace the lower clastic, lower carbonate, upper clastic and upper carbonate members in Minto Inlier and informal map units P4b, P4c, lower P4d and upper P4d in Brock Inlier, respectively. RCsumC : On propose d'tlever le Groupe de Shaler au rang de Supergroupe, et d'apporter les modifications internes suivantes pour offrir une meilleure image des unites lithologiques du bassin d'Amundsen. Les appellations de formations d'Escape Rapids, de Mikkelsen Islands, de Nelson Head et d'Aok sont propostes afin de remplacer : le membre clastique inftrieur, le membre de carbonate cherteux, le membre clastique superieur et le membre stromatolitique A alttration orange, respectivement, de la Formation de Glenelg dans les boutonnikres de Minto et de Cape Lambton; les unitts cartographiques 19-21, 22 ,23 et 24, respectivement, dans le secteur de Coppennine; et les unites cartographiques PI, P2, P3 et P4a, respectivement,dans la boutonnibre de Brock. Ensemble, ces formations constituent le Groupe de Rae; I'appellation de Formation de Glenelg est abandonnte. L'ancienne Formation de Reynolds Point est Clevte au rang de groupe et comprend les formations de Grassy Bay, de Boot Inlet, de Fort Collinson et de Jago Bay qui remplacent : le membre clastique inftrieur, le membre carbonate inftrieur, le membre clastique superieur et le membre carbonatt superieur, respectivement, dans la boutonniere de Minto; et les unitts cartographiques P4b, P4c, la partie inftrieure de P4d et la partie suptrieure de P4d, respectivement, dans la boutonnitke de Brock. I Contribution to Canada-Northwest Territories Mineral Initiatives (1991-1996), an initiative under the CanadaNorthwest Territories Economic Development Cooperation Agreement. Mineral Resources Division Department of Earth Sciences, Carleton University (deceased) Current ResearchlRecherches en cours 1994-C INTRODUCTION The first complete geological reconnaissance of Victoria and Banks Islands was that of Washburn (1947), who recognized the similarity of Proterozoic strata of the Coppermine area and the Duke of York Inlier on the south shore of Victoria Island. Later, Thorsteinsson and Tozer (1962), proposed the name "Shaler Group" and its original formational subdivisions for the thick sequence of Proterozoic sedimentary strata that are exposed in Minto and Cape Lambton inliers (Fig. 1). Shaler Group strata were later recognized on the adjacent northern mainland coast in Brock Inlier (Cook and Aitken, 1969) and the Coppermine area where they are called Rae Group (Baragar and Donaldson, 1973). Stratigraphic correlation and sedimentological studies indicate that the inliers were part of the formerly contiguous intracratonic Amundsen Basin (Fig. I ). Jefferson (1 985) realized the need for further subdivision of the upper Shaler Group in southwest Minto Inlier and proposed the name Kuujjua Formation for a prominent quartzarenite unit, originally defied as an upper member of the Kilian Formation (Thorsteinsson and Tozer, 1962). Rainbird (1993) included the Natkusiak Formation, a basaltic succession which conformably overlies the Kuujjua Formation, with the Shaler Group. In this paper and henceforth we prefer to exclude the Natkusiak Formation from the proposed Shaler Supergroup, because of its contrasting lithological character and its partly unconformable relationship with underlying sedimentary strata (Table 1). Furthermore, the 723 Ma age of the Natkusiak Formation (Heaman et al., 1992) places it in Sequence C of Young et al. (1979), equivalent to the Windermere Supergroup in the Cordillera. It is generally accepted that sedimentary strata of the Shaler Supergroup, described herein, are equivalent to Sequence B of the Mackenzie Mountains Supergroup in the Cordillera (see Young et al., 1979). . . ~ ~ . . . a a a a a t m s , , . . ,,,.. Arctic Circle Figure 1. Location of Neoproterozoic inliers comprising Amundsen Basin of northwestern Canada. B=Brock Inlier, C=Coppermine area, M=Minto Inlier. GBL=Great Bear Lake. R.H. Rainbird et al. Numerous sills and dykes, equivalents of the Natkusiak Formation basalts, intrude the Shaler Supergroup throughout Amundsen Basin. These were dated by U-Pb method on baddeleyite providing a minimum age for the Shaler Supergroup of 723 Ma (Heaman et al., 1992). A maximum age of 1077 Ma was determined from U-Pb analysis of detrital zircon from the Nelson Head Formation in Minto Inlier (Rainbird and McNicoll, unpub. data, 1993). Field studies by ourselves and other workers over the past 25 years have established that formations and members of the Shaler Group are similar throughout the Amundsen Gulf region. Presently, the nomenclature used to describe packages of rocks within the region does not properly reflect these similarities, largely because the original mapping was done by different geologists who concentrated their studies in single areas and therefore did not recognize the regional consistancy of rock units. The intent of this paper is to revise stratigraphic nomenclature in Amundsen Basin. throughout Amundsen Basin (Thorsteinsson and Tozer, 1962; Rainbird et al.. 1992; Morin and Rainbird, 1993; see Table 1). Therefore, we propose elevating the Glenelg Formation and Reynolds Point Formation to group status and Shaler Group to supergroup status. Field studies in 1993 confirmed that the Rae Group in the Coppermine area contains the same rock units as does the Glenelg Formation in Minto Inlier and map units PI, P2, P3, and P4a in Brock Inlier (Table 1). Therefore, we propose retention of the name Rae Group for these strata throughout Amundsen Basin and abandonment of the name Glenelg. Retention of more than one name for the same rocks would be confusing, particularly since we propose the same formation names in all areas. Although we acknowledge that use of the word Glenelg is well established in previous publications, so is the Rae Group, and rather than abandon Rae Group and raise the Glenelg to group status, we prefer to discard the term Glenelg. THE SHALER SUPERGROUP: PROPOSED Rae Group GROUP AND FORMATIONAL SUBDIVISIONS The Rae Group (Baragar and Donaldson, 1973) as herein defined, includes strata of Proterozoic age above rocks of the Formational status is proposed for informal members of the Coppermine River Group in the Coppermine area (Fig. 2) and former Glenelg and Reynolds Point formations on the basis rocks of Goulburn Supergroup in Mint0 Inlier (Fig. 3). Elsethat they are mappable at 150 000 scale and was traced where the base is not exposed. The group is conformably Table 1. Proposed revisions to stratigraphic nomenclature in Amundsen Basin. These revisions apply also to Cape Lambton and Duke of York inliers (Fig. 1). 1 . Thorsteinsson and Tozer 1962, Young and Long 1977b, Rainbird et al. 1992 2. Cook and Aitken 1969, Jones et al. 1992 3. Baragar and Donaldson 1973 Current ResearchlRecherches en cours 1994-C overlain by rocks of the Reynolds Point Group in Minto and Brock inliers (Fig. 4); unconformably overlain by rocks of Tertiary age in Cape Lambton Inlier (Fig. 5); and unconformably overlain by strata of Cambrian age in the Coppermine area. There has been some controversy as to the stratigraphic position of the basal Paleozoic unconformity within the Coppermine area (Baragar and Donaldson, 1973; Dixon, 1979; Campbell, 1983; 1985). However, fieldwork in 1991 and 1993 indicates that strata above a conspicuous brown-weathering stromatolitic unit within map unit 24 (Baragar and Donaldson, 1973) contain vermiform trace fossils, arthropod tracks, and scratch marks: they are Cambrian rather than Proterozoic. The confusion arose because there are more than ten metres of paleotopography on the Proterozoic-Phanerozoic unconformity (Baragar and Donaldson, 1973; Dixon, 1979; Campbell, 1983; Jefferson and Young, 1989). As a result, it is easy to get the impression that Cambrian sedimentary rocks, deposited in paleovalleys, are stratigraphically below paleohills of the brownweathering stromatolitic unit. Our 1993 field studies indicate that the same relationships exist in the western part of the Duke of York Inlier (Fig. I), where paleohills of Proterozoic Figure 2. Generalized geology and geographic features in the Coppermine area (Fig. I ) . C=Coppermine, BF=Bloody Fall, ER=Escape Rapids, H=Hihotok Lake. CK=Cape Kendall. formar~ons (unsubdivided) M~kkelsen Islands Fm. 0 Escape Rapids Fm. Shaler 6D Mlnto Inlet Fm. Nelson Head Fm. SuperO Reynolds Polnt Gp. Mlkkelson Islands Fm. arour, 0 Aok Formation O Escape Raplds Fm. Figure 3. Geology, location of stratotypes and geographic Figure 4. Geology and geographic features in Brock Inlier features in northeast Minto Inlier, Victoria Island (Fig. I ) . (Fig. I ). R.H. Rainbird et al.

The Shaler Supergroup and revision of Neoproterozoic stratigraphy in Amundsen Basin, Northwest Territories