A Paleomagnetic Age Investigation of Pre-Salmon Springs Drift Pleistocene Deposits in the Southern Puget Lowland, Washington

• Main Author: Roland, John L.
• Format: Text
• Language: unknown
• Published: Western Washington University 1983
• Subjects: Ice Sheet
• Online Access: https://dx.doi.org/10.25710/pab9-0c23; https://cedar.wwu.edu/wwuet/739

The Pleistocene history of the southern Puget Lowland is marked by repeated invasions by the Puget Lobe of the Cordilleran ice sheet. The present stratigraphic sequence is represented by four glaciations (Orting, Stuck, Salmon Springs, and Fraser) of northern provenance, separated by unconformities and two nonglacial formations (Alderton and Puyallup) of central Cascade and Mount Rainier provenances. Paleomagnetic work conducted on pre-Salmon Springs sediments at their type localities and correlative exposures in the Puyallup Valley provide evidence for the ages of the Orting Drift, Alderton Formation, Stuck Drift, and Puyallup Formation. The silts sampled demonstrate an array of soft (unconsolidated) sediment magnetic behavior. Overprinting is common and is largely attributed to VRM or CRM, yet the sediments do preserve remanent components identified as DRM or PDRM. These primary components are the result of grain alignment during a period of reversed polarity. The successful isolation of reversed remanent directions in the pre-Salmon Springs units leads to a magnetostratigraphic interpretation which restricts the deposition of these sediments to the Matuyama Reverse Epoch.