Mineral Transformations in Soils Formed in Glacialmarine Drift, Northwestern Washington

Abstract

AbstractThe Whatcom (Aquic Xerochrept) and Labounty (Typic Humaquept) series are soils formed in volcanic ash‐influenced, 10000‐year‐old glacialmarine drift. Surface horizons contain 5 to 10% volcanic ash; pyroxenes show pronounced cockscomb morphology, but associated hornblende is less weathered. Clay‐size minerals in unweathered drift are chlorite, smectite, mica, and in minor amounts, kaolinite and amphibole. The constant abundance of kaolinite throughout the profile and in the fresh parent drift suggests that it is not pedogenic. In the C horizon, chlorite has weathered to mixed‐layer chlorite/vermiculite (or chlorite/smectite) with 40 to 50% chlorite layers. The B horizon is dominated by chlorite, vermiculite, and chlorite/vermiculite. Smectite decreases upward and is absent from the uppermost part of the profile, where it has dissolved or possibly been converted to mixed‐layer kaolinite/smectite and chlorite/smectite.