DEEP SOIL STRATIGRAPHY OF PALEOSOLS IN LOESS ON PORTLAND'S WEST HILLS

Examination of a deep (85 ft) soil core from Portland Oregon's West Hills provides evidence for rapid loess deposition during deglaciation events in the Pleistocene in this area. Measurements of bulk density, identification of soil color and structure were used within the core sample to classify soil horizons and infer stratigraphy. This examination shows that at least three distinct layers of sediment without significant soil development. These layers without soil development were found at depths from 20.5 ft – 27.2 ft, 47.5 ft – 57.5 ft, and 71.5 ft – 74.7 ft. The sediment is examined under microscope and is found be consistent with loess. Loess has previously been mapped as a sedimentary layer in the area. The lack of soil development in these sediment layers indicates the accretion rate of new material was sufficiently great as to not allow soil development in the sedimentary layers. This in turn provides evidence for the episodic nature of loess availability. The loess is interpreted to have been likely deposited during deglaciation periods during the Pleistocene because of increase output of glacial debris in these periods.