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TitleLake Winnipeg: geological setting and sediment seismostratigraphy
AuthorTodd, B J; Lewis, C F M; Nielsen, E; Thorleifson, L H; Bezys, R K; Weber, W
SourcePaleolimnology of Lake Winnipeg, Canada; by Last, W M; Journal of Paleolimnology vol. 19, no. 3, 1997 p. 215-244, https://doi.org/10.1023/A:1007997024412
Year1997
Alt SeriesGeological Survey of Canada, Contribution Series 1997129
MeetingGeological Association of Canada Special Session on the Physical Environment and History of the Lake Winnipeg Basin; Winnipeg, Manitoba; CA; May 27-229, 1996
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®)
ProvinceManitoba
NTS62I; 62J; 62K; 62N; 62O; 62P; 63A; 63B; 63C; 63F; 63G; 63H
AreaWinnipeg
Lat/Long WENS-101.5000 -96.0000 54.2500 50.0000
Subjectssedimentology; seismic profiles; bedrock geology; lakes; moraines; carbonates; tills; erosion; deformation; glacial lakes; glacial lake deposits
Illustrationslocation maps; geological sketch maps; cross-sections, stratigraphic; schematic diagrams; graphs; stratigraphic columns; seismic profiles
ProgramManitoba Conservation, Manitoba Sustainable Development Innovations Fund
AbstractLake Winnipeg, the seventh largest lake in North America, is located at the boundary between the Interior Plains and the Canadian Shield in Manitoba, Canada. Seismic profiles were obtained in Lake Winnipeg on two geoscientific cruises in 1994 and 1996. These data indicate the morphology of the bedrock surface. In most cases, a clear distinction between low relief Paleozoic carbonate rock and high relief Precambrian rock can be made. In northern Lake Winnipeg, the eastern limit of Paleozoic rock is clearly demarcated 30 km west of the previous estimate of its position. In southern Lake Winnipeg, all or most of the Paleozoic sequence terminates at a prominent buried escarpment in the centre of the lake. This indicates that Paleozoic rock on the eastern shore, known from drilling and outcrops, is an outlier. Major moraines are apparent as abrupt, large ridges having a chaotic internal reflection pattern. These include the Pearson Reef Moraine, the George Island Moraine and the offshore extension of The Pas Moraine. Little evidence for extensive or thick till was observed. Instead, fine-grained sediments deposited in glacial Lake Agassiz rest directly on bedrock over most of the lake basin. Hence an episode of erosion to bedrock was associated with glaciation and/or deglaciation. The Agassiz Sequence sediments are well-stratified, drape underlying relief and in some areas are over 100 m thick. In places, stratification in these sediments is disrupted, perhaps by dewatering. Evidence of erosion of Agassiz Sequence sediments by recent currents was observed. The contact between the Agassiz Sequence and the overlying Winnipeg Sequence sediments is a marked angular unconformity. The Agassiz Unconformity indicates up to 10 m of erosion in places. The low-relief character of this unconformity precludes subaerial erosion and the lack of till, moraines, or extensive deformation precludes glacial erosion. Waves appear to be the most likely erosional agent, either in waning Lake Agassiz or early Lake Winnipeg time. Winnipeg Sequence sediments, in places very thin, mantle most of the lakefloor. These sediments were deposited in the present Lake Winnipeg and are faintly stratified to massive and reach about 10 m in thickness in deep water. On the surface of the Winnipeg Sequence, vigorous, episodic currents are thought to contribute to the construction of flow-transverse sand waves as much as 6 m high in a deep, narrow constriction in the lake.
GEOSCAN ID208827