ALIGNMENT AND DIVERGENCE OF PEDOLOGIC, GEOMORPHIC, AND GEOCHEMICAL DATA FOR HILLSLOPE SOILS IN CENTRAL PA

Hillslope form and process in tectonically stable landscapes delicately reflect the driving forces of climate, hydrology and weathering acting on the resisting forces of rock-type and structure. Critical Zone Observatories and surrounding regions offer new opportunities to explore hillslope stratigraphy, including soils and paleosols that are an integrated record of these forces over Pleistocene time scales. We are interested in reconstructing hillslope processes and documenting its steadiness or unsteadiness using the diverse, but complementary data sets of field soil geomorphology and bulk geochemical analysis. We aim to understand how these data sets align or diverge in reconstructing hillslope processes. Here, we report on three hillslopes underlain by variable rock type and exhibiting visually obvious differences in stratigraphy. Within Millheim Narrows thick colluvial wedges (>4m) have been deposited on ridge flanks underlain by Bald Eagle Sandstone. These deposits possess deep-red paleosols with visually distinct horizon boundaries. In contrast, hillslope stratigraphy in the Shale Hills CZO that is underlain by the Rose Hill Shale consists of thin (< 2 m) shale chip colluvium in the swales and very thin (<1 m) rubble shale colluvium on the interfluves.. Similarly, hillslopes in the watershed north of the CZO consist of thin (<1m) rubble shale colluviums that have accumulated in toe slope and valley floor positions. We describe colluvial and soil stratigraphy in the field, using standard NRCS criteria. Soil samples taken at 10 cm intervals were wet sieved for particle size distribution analysis and finely pulverized for bulk geochemistry analysis. The pulverized samples were fluxed with lithium metaborate, dissolved in nitric acid and analyzed by ICP-MS. Resulting tau plots show that there is good correlation among the geochemical and field stratigraphic data for the CZO hillslope stratigraphy despite the fact that these exposures lack the obvious buried soils characteristic of the Millheim Narrows site. We are broadening our geochemical analysis to include iron species with the intent of further developing independent field and geochemical criteria for the determination of diverse hillslope and weathering processes over the time represented by preserved stratigraphy.