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TitlePost-Vashon Wisconsin Glaciation, Fraser Lowland, British Columbia
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AuthorArmstrong, J E
SourceGeological Survey of Canada, Bulletin 322, 1981, 34 pages, https://doi.org/10.4095/109532 (Open Access)
Year1981
PublisherGeological Survey of Canada
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92G/01; 92G/02; 92G/03; 92G/06; 92G/07; 92G/08; 92H/03NW; 92H/03SW; 92H/04; 92H/05; 92H/06NW; 92H/06SW
AreaFraser Lowland; Marion Lake; Surprise Lake; Vancouver; Fraser Lake
Lat/Long WENS-123.5000 -121.7500 49.5000 49.0000
Subjectssurficial geology/geomorphology; stratigraphy; glaciers; glaciomarine deposits; fossils; radiometric dating; Fort Langley Formation; Gastropoda; Pelecypoda; Foraminifera; Quaternary
Illustrationsstratigraphic charts; stratigraphic sections; photomicrographs
Released1981 05 01; 2014 06 12
AbstractThe late Wisconsin Fraser Glac iation in southwestern Br itish Columbia commenced on the mainland between 23 000 and 26 000 radiocarbon years ago and terminated about 11 000 radiocarbon years ago. It reached its climax during the Vashon Stade about 15 000 to 15 500 years ago when it extended south to 47°N. The Vashon ice was more than 1800 m thick in the Fraser Lowland, and the weight of the ic e iso stat ically depressed the area at least 350 m and possibly 400 m or more. Withdrawal of Vashon ice was rapid, and from about 13 000 to 11 000 years BP most of t he F raser Low land was invaded by the sea. During this interval the eastern part of the Fraser Lowland was occupied by a piedmont glacier or glaciers that at various times retreated, were stationary, or surged forward. The glacier or glaciers terminated in the sea for much of their history, prob ab ly in a manner similar to the glaciers of the Yakutat Bay area of Alaska. Throughout the period glaciomarine sediments were formed largely from dropstones and debris deposited into seafloor muds by floating pieces of ice ( inclu ding bergs). During surges a nd standst ills drift was deposited in places above sea level a nd on the seafloor. The depos its laid down du ring the occupation of the sea comprise t he Fort Langley Formation and the Cap ilano Sediments. Isostat ic, eustatic a nd tectonic adjustments be tween the withd rawal of Vashon ice and withdrawal of the sea were not uniform for the whole area; however, at least two major submerg ences separated by unusually rapid emergences are indic ated. The final withdrawal of the sea and disappearance of floating ice in the eastern part of the Fraser Lowland coincided with a final surge of piedmont ic e. The deposits laid down during this last stade have been called Sumas. This ice apparently began to advance about 11400 years ago when sea level was at least 50 m higher than at present. The date at which Sumas ice disappeared is indefinite but was probably about 11 ODD years ago, at which t ime the sea no longer occupied the area.
GEOSCAN ID109532