Soils on hillslopes in acid gray and black shales
Sobecki, T.M. | Karathanasis, A.D.
The effect of hillslope geomorphology on properties of sods formed over horizontally bedded acid gray and black shale was evaluated in the Knobs region of eastern Kentucky. The geology and geographic extent of the Knobs made it possible to apply state factor analysis by systematizing local variation in parent material, while regional climate and vegetation were held constant. Nose-, head-, and sideslopes truncating black shale are steeper (36-62%) than respective hillslopes truncating gray shale (20-32%). Hapludults on these hillslopes are polygenetic: colluvium overlies buried Bt horizons formed in shale residuum. This discontinuity is characterized by a zone of soil creep, differences in soil fabric, and changes in particle size and TiO2/ZRO2 depth functions. Soil chemical properties vary with hillslope geomorphic component and parent material. Although black shale strata have 20 to 30 times more organic C and up to 10 times more S than gray shale, soil material formed from the two types of strata have similar organic C and S contents. Soil material that formed from black-shale-derived colluvium or residuum in noseslopes, however, has lower pH (< 4) and higher Al saturation (> 90%) than soil material derived from black or gray shale in other hillslope geomorphic components.
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