Record of large, Late Pleistocene outburst floods preserved in Saanich Inlet sediments, Vancouver Island, Canada

Abstract Two anomalous, gray, silty clay beds are present in ODP cores collected from Saanich Inlet, Vancouver Island, British Columbia, Canada. The beds, which date to about 10,500 14C yr BP (11,000 calendar years BP), contain Tertiary pollen derived from sedimentary rocks found only in the Fraser Lowland, on the mainland of British Columbia and Washington just east of the Strait of Georgia. Abundant illite-muscovite in the sediments supports a Fraser Lowland provenance. The clay beds are probably distal deposits of huge floods that swept through the Fraser Lowland at the end of the Pleistocene. Muddy overflow plumes from these floods crossed the Strait of Georgia and entered Saanich Inlet, where the sediment settled from suspension and blanketed diatom-rich mud on the fiord floor. The likely source of the floods is Late Pleistocene, ice-dammed lakes in the Fraser and Thompson valleys, which are known to have drained at about the time the floods occurred.

[1]  D. Huntley,et al.  The Late Wisconsinan deglacial history of the east-central Taseko Lakes area, British Columbia , 1997 .

[2]  J. Clague.  Late Quaternary Geology and Geochronology of British Columbia Part 2 : Summary and Discussion of Radiocarbon-Dated Quaternary History , 1981 .

[3]  J. Clague,et al.  Late Quaternary sea levels and crustal movements, coastal British Columbia , 1982 .

[4]  J. Clague,et al.  Paleoseismic signature in late Holocene sediment cores from Saanich Inlet, British Columbia , 2001 .

[5]  J. Clague,et al.  Ocean Drilling Program Leg 169S: surficial geology, stratigraphy and geomorphology of the Saanich Inlet area, southeastern Vancouver Island, British Columbia , 2001 .

[6]  J. Clague,et al.  Sedimentary environments and postglacial history of the Fraser Delta and lower Fraser Valley, British Columbia , 1983 .

[7]  A. Blais-Stevens.  bte Holocene sedimentation in Saanich Inlet, British Columbia, and its paleoseismic implications1 , 1997 .

[8]  E. E. Mackintosh,et al.  A MINERALOGICAL AND CHEMICAL STUDY OF LOWER FRASER RIVER ALLUVIAL SEDIMENTS , 1966 .

[9]  C. Bacon.  Eruptive history of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A. , 1983 .

[10]  W. A. Dawson,et al.  Varved Marine Sediments in a Stagnant Fjord , 1963, Science.

[11]  P. Friele,et al.  Younger Dryas readvance in Squamish river valley, southern Coast mountains, British Columbia. , 2002 .

[12]  Klas Lackschewitz,et al.  Proceedings of the Ocean Drilling Program , 2002 .

[13]  W. Hopkins.  Palynology of the Eocene Kitsilano Formation, southwest British Columbia , 1969 .

[14]  D. J. Kovanen,et al.  Late Pleistocene, post-Vashon, alpine glaciation of the Nooksack drainage, North Cascades, Washington , 2001 .

[15]  M. Pellatt,et al.  High-resolution Holocene vegetation history and climate from Hole 1034B, ODP leg 169S, Saanich Inlet, Canada , 2001 .

[16]  D. J. Kovanen,et al.  Timing and Extent of Allerød and Younger Dryas Age (ca. 12,500–10,000 14C yr B.P.) Oscillations of the Cordilleran Ice Sheet in the Fraser Lowland, Western North America , 2002, Quaternary Research.

[17]  A. Blais-Stevens,et al.  Overview of Late Quaternary stratigraphy in Saanich Inlet, British Columbia: results of Ocean Drilling Program Leg 169S , 2001 .

[18]  M. C. Roberts,et al.  Deglaciation of Chilliwack River valley, British Columbia , 1987 .

[19]  D. J. Kovanen.  Morphologic and stratigraphic evidence for Allerød and Younger Dryas age glacier fluctuations of the Cordilleran Ice Sheet, British Columbia, Canada and Northwest Washington, U.S.A. , 2002 .

[20]  M. Stuiver,et al.  High-Precision Bidecadal Calibration of the Radiocarbon Time Scale, AD 1950–500 BC and 2500–6000 BC , 1993, Radiocarbon.

[21]  J. Ryder.  Terrain inventory and quaternary geology, Lytton, British Columbia , 1981 .

[22]  J. Barrie,et al.  Evidence for a Late Quaternary outburst flood event in the Georgia Basin, British Columbia , 2001 .

[23]  R. Fulton.  Radiocarbon geochronology of southern British Columbia , 1971 .

[24]  M. R. McQuoid,et al.  A Holocene record of diatom and silicoflagellate microfossils in sediments of Saanich Inlet, ODP Leg 169S , 2001 .

[25]  R. Fulton.  Glacial Lake history, southern interior plateau, British Columbia , 1969 .

[26]  P. Friele,et al.  Readvance of glaciers in the British Columbia Coast Mountains at the end of the last glaciation , 2002 .

[27]  R. Herlinveaux.  Oceanography of Saanich Inlet in Vancouver Island, British Columbia , 1962 .

[28]  M. Stuiver,et al.  Modeling Atmospheric 14C Influences and 14C Ages of Marine Samples to 10,000 BC , 1993, Radiocarbon: An International Journal of Cosmogenic Isotope Research.

[29]  J. Clague.  Quaternary stratigraphy and history, Williams Lake, British Columbia , 1987 .

[30]  P. Mustard,et al.  Stratigraphy and evolution of Tertiary Georgia Basin and subjacent Upper Cretaceous sedimentary rocks, southwestern British Columbia and northwestern Washington State , 1994 .