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The early Pleistocene history of the Puget Lowland is marked by repeated advances of the Cordilleran ice sheet into the southern Puget Lowland where deposits of at least three glaciations older than 1.0 Ma are recognized: the Orting (oldest), Stuck, and Salmon Springs, separated by the interglacial Alderton (older) and Puyallup Formations. Until recently, the chronology of these stratigraphic units was unknown and correlations were based entirely on relative age considerations. Paleomagnetic analyses of sediments and petrographic, geochemical, and fission-track analyses of associated tephra were undertaken in order to provide a basis for establishing the chronology of the type sections of these stratigraphic units and to develop a standard for correlations throughout the Puget Lowland. Although paleomagnetic overprinting is common in the sediments sampled, primary components of remanent magnetism were successfully isolated during demagnetization. Previous work (Easterbrook and others, 1981; Westgate and others, 1987) identified the Salmon Springs Drift as reversely magnetized and about 1.0 m.y. old. This investigation establishes the reversed magnetization of the pre–Salmon Springs sediments at or close to their type localities and illustrates the use of the Lake Tapps tephra in regional correlations. The 1.0-Ma fission-track age of the Lake Tapps tephra and the reversed magnetic polarity of the Orting Drift, Alderton Formation, Stuck Drift, Puyallup Formation, and Salmon Springs Drift indicate that all were deposited during the Matuyama Reversed Epoch which began about 2.48 Ma and ended about 0.73 Ma.

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