| The catena concept, as originally articulated, encompasses both the pattern and process dimensions of soil geography. Recent developments in spatial analysis—including spatial statistics, Geographic Information Systems (GIS), Global Positioning Systems (GPS) and Digital Elevation Models (DEM{rcub}—make it possible to study soil landscapes quantitatively with precision and analytical rigor. Spatial analysis techniques have been successfully used to describe and predict soil-landscape patterns. But researchers have had limited success in using these tools to explain processes of soil-landscape formation.; In this dissertation, I employ spatial analysis tools and geochemical analyses to study the geographic problem of catena formation in central Uganda—the landscape that inspired Geoffrey Milne to formulate the catena concept. Three specific problems are addressed: (1) the role of fluvial erosion and deposition in soil formation; (2) the process of iron accumulation in soils and ferricrete duripans; and (3) stone line formation.; By posing specific questions and hypotheses in a rigorously analytical framework, a number of clear answers are obtained regarding catena formation on this landscape. Strong statistical relationships between terrain indices, soil color and texture, indicate that fluvial processes control soil hydrology and particle deposition on the lower portion of the landscape. For well-drained “red” soils, parent material variability and termite activity control surface texture. Thin-plate spline terrain modeling detects subtle, clay-enriched convexities thought to be indicative of collapsed termite mounds.; A number of weathering and redox geochemical indicators are developed for landscape application. A clear K-feldspar signal is found in K, Na and Ba concentrations as determined by neutron activation analysis, supporting the use of K/Hf ratios as indicative of weathering. Scandium is proposed as a robust index element for determining absolute vs. relative Fe enrichment. Extremely high Ce anomalies (5000μg g−1) are associated with Mn-Ce-Ba concretions and nodules.; A statistical analysis of gravel distributions and geochemical characterization of materials above and below stone lines confirm that these are depositional features, not formed by bioturbation. Overall, the results of this study accent the dynamic nature of earth surface processes in East Africa, with important implications for understanding interactions between climate change and landscape evolution. |
