CHEMICAL WEATHERING IN HETEROGENEOUS SCHIST BEDROCK

We assess the extent of chemical weathering on a deep weathering profile in schist bedrock by analyzing elemental changes throughout the weathering profile. Rotosonic drill cores were sampled on ridge and in gulley landscape positions within in a 9-hectare, first-order watershed in a forested nature preserve in the Christina River Basin Critical Zone Observatory, located in the Piedmont coastal plain of southeastern Pennsylvania. Geochemical assessment of drill core and outcrop samples reveal that fine-grained fractions, largely pulverized by drilling action, are geochemically distinct from coarse rock fragments. The weathering profile is well-developed within the coarse fraction in the upper three meters of drill core. The two wells have different geochemical profiles, which may be the result of geomorphic position. Vertical elemental variability within the deep weathering profiles may be a function of initial bedrock heterogeneity, while topographic position and fluid infiltration rates may be the controlling factors for elemental variations within the top three meters of the weathering profile.