Soil-Geomorphic Relationships in the Western Margin of the Willamette Valley, Oregon1
- J. R. Glasmann,
- R. B. Brown and
- G. F. Kling2
Geomorphology and soils were studied in a 285-ha agricultural watershed lying between the 63-and 135-m elevations in the western Willamette Valley. Previously named geomorphic surfaces, strata, and soils are recognized, and the Brateng surface is introduced and defined.
The Irish Bend Member of the silty Willamette Formation is found only below the 80-m elevation. The Greenback Member mantles the Irish Bend silts and higher portions of the landscape, thinning out at 122 m. A paleosol, developed from soft sedimentary rock of the Spencer Formation, lies beneath the Irish Bend and Greenback silts. Above the 80-m elevation, the paleosol is part of the solum.
The concept of the late Pleistocene Bethel geomorphic surface, with which the Irish Bend silts are associated, is expanded to include low-relief ridge spurs merging upslope with the Brateng surface. The Brateng surface, between 80 and 122 m, is mantled by late-Pleistocene Greenback silts and thus is late Pleistocene in age. The mid-Pleistocene Dolph surface is found above the 122-m elevation.
Soils beneath the newly defined Brateng surface are mainly in the fine and fine-silty Ultic Haploxeralfs and fine Aquic Xerochrepts. Soil mapping in the Brateng landscape is complicated by marked soil variability, a function of variations in thickness of surface silts, in degree of expression of the buried paleosol, and in texture of the underlying bedrock.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © .