BAKER LAKE. Strlalton direction known,unknown, locollon ot centre of sfoff ml

Size: px

Start display at page:

Download "BAKER LAKE. Strlalton direction known,unknown, locollon ot centre of sfoff ml"

Christopher Hodges
5 years ago
Views:

W. Shilts Terrain Sciences Division Introduction In 1976 Quaternary mapping in southern Keewatin was continued in the Baker Lake area (NTS 56 D, 66 A, 65 P) and portions of adjoining map-areas.

1 SURFICIAL GEOLOGY OF THE BAKER LAKE AREA, DISTRICT OF KEEWATlN Project C.M. cunningham' and W.W. Shilts Terrain Sciences Division Introduction In 1976 Quaternary mapping in southern Keewatin was continued in the Baker Lake area (NTS 56 D, 66 A, 65 P) and portions of adjoining map-areas. The objectives of this mapping are: (I) to provide a map of surficial deposits suitable for input into environmental studies associated with the proposed eastern arctic gas pipeline; (2) to document and describe the complex ice flow directions associated with the migration of the Keewatin Ice Divide (Lee et al., 1957); (3) to describe the lateglacial relationship of the Tyrrell Sea to possible freshwater bodies dammed west of the ice divide in the Thelon-Dubawnt system; and (4) to describe the earlier Quaternary history as revealed by borehole data and the study of stratigraphic sections along Kazan, Thelon, Dubawnt, and other rivers. Surficial Deposits In the vicinity of the ice divide (Fig. 59.1), till is the main deposit. A zone of marine reworking extends up to altitudes ranging from 135 m to over 150 m a.s.1. - Area of gently rolling silty till plains with relatively few lakes; well developed marine beaches (below 150 m a.s.1.); active mudboils; relatively few outcrops; postglacial streams deeply incised into bedrock; and no strongly oriented topographic grain. - Area of bouldery, grey-brown sandy till, many outcrops with felsenmeer, many lakes, sparse vegetation, with topographic grain strongly controlled by bedrock structure. - Area of red till cover on crystalline bedrock; outcrop frequency, number of lakes, and boulder frequency intermediate between areas A and 0; topographic grain strongly lineated northwest-southeast by glacial erosion/- deposition. 'Department of Geology, University of Massachusetts, Amherst, Massachusetts From: Report of Activities, Part B; Geol. Surv. Can., Paper 77-1B (1977)

2 BAKER LAKE Strlalton direction known,unknown, locollon ot centre of sfoff / D r u m ~ n or F l u t n ~ ml I - Figure Ice flow directions generalized from striations and drumlins or fluting. Presence of quartzite erratics at Pitz Lake indicates southerly flow from at least as far north as Schultz Lake at some time. Many streams, particularly those in the Pitz Lake Pitz Lake and Baker Lake, but fine grained marine basin, are flanked below 135 m a.s.1. by deltaic sand and sediments are rare elsewhere. Beaches are particularly fine gravel (informally called 'strip deltas') deposited by well developed on glacial sediments in areas underlain by delta progradation as sea level fell at a relatively Dubawnt Group rocks. Major areas of sandy deltaic constant rate. Marine silty clays covered by thin sand deposits and spectacular flights of gravelly, sandy beaches form a persistent cover south of Thelon River between are found at the northwest and northeast sides of Pitz Lake, respectively.

3 Within the area studied in 1976, no conclusions could be drawn regarding the relationship of the Tyrrell Sea to lakes in upper Thelon Valley. All shoreline features found in the map-area can be reasonably related to marine inundation. The northern limit of marine submergence is difficult to map because the bouldery terrain north of Baker-Schultz lakes was not suitable for beach formation. Terrain underlain by late Precambrian (Helikian) rocks of the Dubawnt Group (Donaldson, 1965) (area A, Fig. 59.1) comprises a gently rolling surface of red till which is relatively rich in silt and clay derived largely from red beds of the Dubawnt Group. The till plain has few linear features related to ice flow, such as drumlins or fluting. Till surfaces generally are covered with active mudboils. The gently rolling terrain is broken in places by outcrops of resistant rocks such as the east-west trending ridges of intrusive and volcanic rocks north and south of Pitz Lake, by a major, northwest-trending diabase dyke that can be traced from Thirty Mile Lake to Schultz Lake along a line passing just west of Pitz Lake, and by hills of Aphebian age quartzites east and south of Schultz Lake. North of Baker Lake, Thelon River, and Schultz Lake (area B, Fig. 59.1), the nature of the terrain changes dramatically. Vegetation is sparse in comparison to area A. The till plain is underlain by crystalline Archean bedrock that protrudes in numerous felsenmeer-covered outcrops with sharp local relief. A major ridge of Aphebian quartzite extends east-northeast from Whitehills Lake across Quoich River. Till is the major unconsolidated sediment, but in contrast to the red tills of areas A and C, it is generally grey-brown, sandy, and very bouldery. Most mudboils are relatively inactive and are surrounded by stone rings in the form of sorted circles. The number of lakes and control of topographic detail by bedrock structure is noticeably greater in this region than in the southern parts of the map-area. Terrain underlain by crystalline Archean bedrock south of Thirty Mile Lake and between Schultz and Pitz- Princess Mary lakes (area C, Fig. 59.1) has local relief, density of lakes, and stoniness intermediate between areas underlain by Dubawnt Group rocks (area A) and areas underlain by the highly deformed and metamorphosed Archean-Aphebian rocks to the north (area 8). Red till derived from red beds of the Dubawnt Group completely covers this area, forming dispersal trains that extend northward an undetermined distance past Schultz Lake and southeastward as a 75 km-wide, more than 200 kmlong ribbon from the Pitz-Thirty Mile-Forde lakes area to Hudson Bay. Whereas the topographic grain is inherited largely from bedrock structures in the northern area (B), the orientation of topographic features of all scales and types in area C is closely related to erosion and deposition by southeastward or northeastward glacial flow. Ice Divide - Ice Flow History Figure 59.2 shows generalized ice flow directions measured in The directions of striations were determined by noting the trends of tails of uneroded rock protected in the lee of hard inclusions, such as pyrite grains, quartz grains or veins, etc. ('rat tail' striations). From Figure 59.2 it is evident that it is difficult to delimit the ice divide more precisely than it was defined by Lee (1 959). Erratics of quartzite of presumed Aphebian age are found at Pitz Lake and are interpreted to indicate a major period of southward transport from outcrops of these rocks at Schultz Lake. Despite the overwhelming evidence that late-glacial flow in this area was northwestward, this observation indicates that ice formerly flowed southward from a centre of outflow an unknown distance north of Schultz Lake. That the major flow event to affect the map area was related to a centre of outflow to the north is suggested further by southeastward trending geochemical dispersal trains in the southern part of the map area (R.A. Klassen, pers. comm., 1977) and old southward striations measured north of the ice divide in the Quoich River area. A preliminary interpretation of these observations could be that the Wisconsinan (or Late Wisconsinan) ice sheet grew with its centre of outflow in northern Keewatin and that the centre migrated to the south and east to the vicinity of Baker Lake in the final phases of glaciation. Such migration would have been controlled in a presently undefinable way by significant drawdowns caused by calving into lakes abutting the ice in the south and west and into the sea abutting the ice in the east and north. The last recorded directions of glacier flow were generally westward or northwestward and southeastward from an arcuate zone extending through Forde, Pitz, and Whitehills lakes and thence northeastward across Quoich River about 15 to 25 km south of its junction with Tehert River. In a zone from Schultz Lake to Forde Lake, west of Pitz Lake, the direction of the last ice flow seems to have been due west. The westward flow apparently postdated flow that was north to northwest in the same zone. Southeastward migration of the ice divide is confirmed by the association of southeastward oriented striations with younger westward or northwestward striations in close proximity or on the same outcrops. Meltwater channels and the distribution of icecontact deposits indicate that the Pitz Lake basin was filled with a discrete ice mass to an altitude below the hills defining the basin shortly before flooding by marine waters. Thus, this would be the site of one of the last remnants of the continental glacier west of Hudson Bay. Remnant ice masses are also thought to have occupied other major lake basins near the divide. Stratigraphy At two sections along lower Kazan River and one section on a Thelon River tributary near Schultz Lake, boulder pavements separate two texturally and compositionally contrasting till units. At present it is thought that the lower of these units represents early ice flow from northern Keewatin and that the upper unit, although not necessarily correlative among all sections, may represent the period of significant shift in ice flow associated with the migration of the ice divide into Baker Lake region. The upper till, where observed, is 2 to 4 m thick and overlies more than 10 m of lower till. Except for wave reworked zones or thin marine sands or silts at the surface, no water laid sediments were found in the sections. Preliminary examination of samples made available by Polar Gas at the time of writing this report indicates that these two tills may be underlain by fluvial sands (interglacial?) which overlie an older till along Thelon River between Schultz and Baker lakes.

4 Acknowledgments B.C. McDonald provided considerable unpublished data on eskers and marine limit in the Baker Lake region. R.A. Klassen provided logistical support and published and unpublished data, including detailed terrain observations gathered during extensive drift prospecting studies carried out in the centre of the area. Samples and stratigraphic records from overburden drilling have been graciously provided by EBA Engineering Consultants Ltd. by permission of Polar Gas. The report was critically read by R.N.W. DiLabio and R.J. Fulton. References Donaldson, 3.A. 1965: The Dubawnt Group, Districts of Keewatin and Mackenzie; Geol. Surv. Can., Paper 64-20, 11 p. Lee, H.A. 1959: Surficial geology of southern District of Keewatin and the Keewatin Ice Divide, Northwest Territories; Geol. Surv. Can., Bull. 51, 42 p. Lee, H.A., Craig, B.G'., and Fyles, J.G. 1957: Keewatin Ice Divide (abstr.); Geol. Soc. Am., Bull., V. 68, p

5 GEOLOGICAL SURVEY PAPER 77-1 B REPORT OF ACTIVITIES PART B 1 GEOLOGtCAL INFORMATION 1 DIVISION DE L'INFORMATION ( GEOLOGIQUE I

6 Minister 01 Supply and Services Canada 1977 Printing and Publishing Supply and Services Canada, Ottawa, Canada KIA 0S9, from the Geological Survey of Canada 601 Booth St., Ottawa, K1A 0E8 or through your bookseller. Catalogue No. M44-77-IB Price: Canada: $6.00 ISBN Other Countries: $7.20 Price subject to change without notice

Projects and

Projects and DRIFT PROSPECTING IN THE DISTRICT OF KEEWATIN - URANIUM AND BASE METALS Projects 700014 and 750074 W. W. Shilts and R. A. Klassen Studies of trace metal distribution in till were continued in the Yandle-Henninga