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Distribution and Characteristics of Loessial Soil Parent Material in Northwestern Oregon
Author(s) -
Theisen Arthur A.,
Knox Ellis G.
Publication year - 1959
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1959.03615995002300050026x
Subject(s) - loess , silt , geology , quartz , geomorphology , floodplain , basalt , deposition (geology) , alluvium , geochemistry , hydrology (agriculture) , mineralogy , sediment , geotechnical engineering , paleontology , geography , cartography
Field study, mechanical analysis, and X‐ray diffraction analysis (of fine silt) were used to identify as loess a silty deposit bordering the Columbia River near Portland, Oregon. The loess material is 65 to 75% silt and pale brown. It commonly overlies reddish brown clay derived from Columbia River basalt. Quartz and feldspars were found in fine silt of the loess. Only quartz was positively identified in fine silt of the underlying material from basalt. Thinning with distance from the Columbia River and also from a point north of Portland indicates that the loess source was a former Columbia River floodplain, particularly the wide area north of Portland. Vertical discontinuities in particle size distribution and mineralogy, not coinciding with genetic horizons, suggested the existence of more than one period of loess deposition.