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TitleElements of surficial geology and glacial history of the Bonaparte Lake map area
AuthorBednarski, J; Plouffe, AORCID logo; Huscroft, C A; McCuaig, S J
SourceCANQUA-CGRG Biennial Meeting, programme and abstracts volume; 2009 p. 38 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20090206
MeetingCANQUA - CGRG Biennial Meeting; Burnaby; CA; May 3-8, 2009
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
AreaBonaparte Lake
Lat/Long WENS-122.0000 -120.0000 52.0000 51.0000
Subjectssurficial geology/geomorphology; glacial deposits; glacial history; glacial landforms; glaciation; tills; ice flow; ice movement directions; Fraser Glaciation
ProgramMountain Pine Beetle
AbstractEleven 1:50 000 scale surficial geology maps covering the eastern part of the Bonaparte Lake map area (NTS 92P) were recently mapped by the Geological Survey of Canada as part of the Mountain Pine Beetle Program. The surficial geology of this area is largely determined by the growth and subsequent waning of the Cordilleran Ice Sheet, which advanced from dispersal centres outside the study area in the Coast Mountains and Cariboo Mountains. Most of the study area is a rolling plateau lying about 1200 m above sea level, which gradually rises to the east and is more rugged, culminating to over 2000 m in the Sushwap Highlands. The bedrock is very diverse with Mesozoic granitic rocks intruding into sedimentary and volcanic formations of Mesozoic and Paleozoic age. In general, the eastward increase in ruggedness coincides with underlying batholiths and deformed miogeoclinal rocks. Much of the western part in the study area is covered by Tertiary lavas, which are flat lying or gently dipping and obscure the older rocks. In general concordant uplands and plateaus are thought to be a Tertiary erosional surface that has been dissected by subsequent glaciation and fluvial incision. A south-trending valley occupied by the North Thompson and Clearwater rivers provides maximum relief along the eastern edge of the mapped area. Stratigraphy in a number of the valleys shows significant deposition of glaciofluvial sand and gravel, and more limited glaciolacustrine sand, which was deposited at the onset of the last glaciation, which culminated about 18 ka BP (Fraser Glaciation). Consequently, some large valley systems were in existence prior to the last glaciation. Extensive glacial modification took place as most of the ridges in the area are rounded and bear evidence of glacial erosion. Till cover is usually thicker in the west and in valleys where it forms continuous blankets. Ice-flow features and till provenance in the Bonaparte Lake area shows that glaciers originally flowed from the east off Cariboo/Columbia Mountains. This advance was subsequently deflected to the south by ice originating from the Coast Mountains west of the study area. At the height of the Fraser Glaciation, coalescent ice over the Bonaparte Lake area flowed to the SSE from what must have been an ice divide immediately north of the study area over the Fraser Plateau. This ice divide likely bridged the main ice divides over the Coast Mountains to the west and the Columbia Mountains to the east. As the ice thinned, the local topography imparted a greater influence on ice flow, especially evident is a strong southward ice flow down the North Thompson valley. As the plateau became ice free, it was dissected by several large meltwater systems issuing from the retreating ice margins and extensive glaciofluvial sediments were deposited. Most of the large drainage systems drained westward into the Fraser River drainage, but some meltwater systems also drained eastward into the North Thompson River valley when it became ice free.

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