64-6 Micromorphological Analysis of Weathering Patterns in Columbia River Basalt Group Paleosols

Session: Emerging Voices in Soil and Paleosol Science (Posters)

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Abstract:

Basalt paleosols and their pedogenic features are useful tools for paleoclimate reconstruction as they preserve a record of weathering conditions between eruptions. The Columbia River Basalt Group (CRBG) in the Pacific Northwest is the youngest example of continental flood basalts on Earth. Eruption of the flood basalts began in the late Early Miocene (Burdigalian) and continued for nearly 11 m.y. The young age of the CRBG makes the paleosols developed between flows notably well-preserved. In this study, we focus on micromorphological observations of weathering patterns in CRBG paleosols ranging in age from 15.6 Ma to 8.5 Ma, including less-studied sites in Eastern Washington and Oregon. Thin sections from about ten different basalt paleosol sites were analyzed using standard petrographic techniques and scanning electron microscopy. Samples within each site demonstrate a range of weathering intensities, from less weathered corestones to more altered weathering rinds. Among primary basaltic minerals, plagioclase feldspar remains resistant to weathering the longest, whereas pyroxenes are more altered, and olivine is almost completely replaced by secondary minerals such as iddingsite and chlorite. Siliceous minerals were observed in some thin sections, mainly as coatings and infillings within voids. More highly weathered samples retain remnants of basaltic structure but exhibit later stages of pedoplasmation.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7597

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