Abstract

The Critical Zone Observatory (CZO) is a National Science Foundation program whose goal is to develop a model of how physical, biological, and chemical processes interact within the “living skin” of the Earth. Specifically, the Calhoun CZO examines landscape degradation as a result of agricultural processes. Calhoun, SC is an area that has historically been farmed which lead to extensive erosion and the production of legacy sediments, or sediments eroded as a result of post-European settlement farming practices. An organic-rich paleosol was identified within the Calhoun CZO at Old Rays Tributary that had been subsequently buried by legacy sediments. This paleosol defined the surface between pre-legacy sediments and the legacy sediments themselves. I hypothesized that the respective mineral assemblages in this deposit would vary across this boundary. Using X-ray powder diffraction with internal zincite and external corundum standards, descriptive mineralogies across the depth profile were produced. Results indicate that pre-legacy sediments carry a signature of amphibole and discrete micas while legacy sediments carry a signature of increased kaolin group minerals and degraded micas (i.e. clays). These findings support the hypothesis and draw into question the provenance of the two sediment groups. One possible explanation for the higher clay content of the legacy sediments is from erosion of interfluvial B-horizon material adjacent to the floodplain. The abundance of primary minerals (amphibole and mica) in the pre-legacy sediments may also reflect an allochthonous deposition due to backwater flood events.

Citation

Jordan, Bear (2018): Changes in clay mineral assemblages of legacy sediments in the Calhoun Critical Zone Observatory, SC: Evidence for anthropogenic landscape change. Center for Undergraduate Research Opportunities (CURO) Symposium, University of Georgia, Athens, 9 April 2018.

This Paper/Book acknowledges NSF CZO grant support.