Sea-level change and paleogeographic reconstructions, southern Vancouver Island, British Columbia, Canada
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| Authors: | James, T; Gowan, EJ; Hutchinson, I; Clague, JJ; Barrie, JV; Conway, KW |
| Year: | 2009 |
| Journal: | Quat. Sci. Rev. 28: 1200-1216 Article Link (DOI) |
| Title: | Sea-level change and paleogeographic reconstructions, southern Vancouver Island, British Columbia, Canada |
| Abstract: | Forty-eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern Vancouver Island, British Columbia. Sea level fell rapidly from its high stand of about +75 m elevation just before 14000 cal BP (12000 radiocarbon yrs BP) to below the present shoreline by 13 200 cal BP (11400 radiocarbon years BP). The sea fell below its present level 1000 years later in the central Strait of Georgia and 2000 years later in the northern Strait of Georgia, reflecting regional differences in ice sheet retreat and downwasting. Direct observations only constrain the low stand to be below -11 m and above -40 m. Analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the Cascadia subduction zone, however, places the low stand at -30 +/- 5 m at about 11200 cal BP (9800 BP). The inferred low stand for southern Vancouver Island, when compared to the sea-level curve previously derived for the central Strait of Georgia to the northwest, generates differential isostatic depression that is consistent with the expected crustal response between the two regions. Morphologic and sub-bottom features previously interpreted to indicate a low stand of -50 to -65 m are re-evaluated and found to be consistent with a low stand of -30 +/- 5 m. Submarine banks in eastern Juan de Fuca Strait were emergent at the time of the low stand, but marine passages persisted between southern Vancouver island and the mainland. The crustal uplift presently occurring in response to the Late Pleistocene collapse of the southwestern sector of the Cordilleran Ice Sheet amounts to about 0.1 mm/yr. The small glacial isorstatic adjustment rate is a consequence of low-viscosity mantle in this tectonically active region. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved. |
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