CGRG Bibliography of Canadian Geomorphology
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Author : Anderson, F.E.
Date : 1968
Title : Seaward terminus of the Vashon continental glacier in the Strait of Juan de Fuca.
Publication : Marine Geology
Issue : 6(6):
Page(s) : 419-438.
Abstract
The Strait of Juan de Fuca is the major marine connection between the Pacific Ocean and Puget Sound. The oldest sediments collected from the strait range from 21,000 to greater than 30,000 years B.P., and the texture and foraminifera indicate that these deposits were laid down in a quiet-water, shallow estuarine environment during the Olympia Interglaciation. Overlying these deposits are glaciomarine-like sediments consisting of ice-rafted pebbles in a fine-grained matrix, and foraminifera ranging from estuarine species at the base of the unit to marine species near the top. The age of this unit (17,000 to greater than 21,500 years B.P.) corresponds with the advance of Vashon continental ice into Puget Sound. The salinity change evidenced within the unit is related either to a relative rise in sea level or to an intrusion of salt water along the bottom of the strait as a result of increased fresh water outflow from the ice. There is no sedimentary evidence that the Vashon "Juan de Fuca" ice lobe penetrated to the Pacific Ocean as previously postulated. Instead it appears likely that the Vashon ice was halted in the easternmost portion of the strait and formed a series of terminal and recessional moraines. Later, as the Vashon ice retreated from the Puget Sound region, large isostatically depressed basins in this area were invaded by marine waters coming through the strait. These broad quiet basins received great quantities of glaciomarine sediment from the retreating ice. In the Strait of Juan de Fuca, however, the tidal currents were greatly increased as the larger tidal prism associated with the depressed basin area was forced to flush through the narrow strait. Consequently, in the strait, only the coarsest fraction of the sediment was deposited during the retreat of the ice.
Bibliography of Canadian Geomorphology