INFLUENCE OF DISCONTINUITIES IN PARTICLE SIZE ON THE GENESIS OF TWO SOILS OF THE HONEYWOOD CATENA
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Abstract:
Particle-size discontinuities were located in two soil profiles of the Honeywood catena. Discontinuities in the distribution of clay, Na-dithionite and NH 4 -oxalate extractable Fe, Al, and Mn indicated varying degrees of translocation of these elements across the established particle-size discontinuities. The particle-size discontinuities appeared to have influenced the movement and accumulation of clay and extractable Fe, Al, and Mn through their effects on the vertical movement of water within the profiles. The degree of pedogenesis within the profiles was assessed by matching soil horizon boundaries and pedogenesis breaks with the established discontinuities. It was concluded that soil development had progressed more in the Embro profile than in the Honeywood profile. Dithionite-Fe breaks appeared to be useful in identifying the lower boundaries of Ae and Bt horizons, whereas oxalate-Fe breaks appeared to be associated with the illuvial B horizons.Keywords:
Classification of discontinuities
Soil horizon
Dithionite
Particle (ecology)
Paleosol
Podzol
Soil horizon
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Analysis of soil pattern, especially the pattern of depletion and accumulation zones, is a powerful tool to decipher pedogenic processes at the landscape scale. To clarify the pedogenesis of a distinct pattern of podzolized soils in the cool, perhumid Black Forest (Germany) we performed a study in the forested upper part of a granitic catchment (B a ¨ rhalde). From detailed soil mapping we selected a typical catena of four pedons, which were analyzed for physical (bulk densities and particle‐size distribution), chemical (pH, organic C, pyrophosphate, oxalate, dithionite, and total Al, Mn, Fe), and mineralogical (clay minerals) properties. Standard mass balance calculations were modified to include a two‐component system with regard to parent material. Results showed a shift from two‐mica granite to granite–porphyry downslope. Soil pattern revealed podzolized soils with thick E horizons and thin spodic horizons developed in the upslope areas, whereas in downslope soils the reverse was found (thick spodic B and thin E horizons). Soil chemical and mineralogical properties were linked to soil morphology in that contents of organic C, pedogenic oxides, hydroxy‐interlayered vermiculites (HIV), and pH increased from eluvial to illuvial horizons as well as from up‐ to downslope soils. Mass balances of Fe and Al showed negative fluxes in upslope soils and positive fluxes in downslope soils during pedogenesis. We concluded from these results that a catenary eluvial–illuvial sequence (lateral podzolization) develops as a result of upslope mobilization followed by a (partially) lateral transport and subsequent immobilization in downslope zones, probably because the base‐richer parent material built up a geochemical barrier.
Eluvium
Podzol
Soil horizon
Soil morphology
Pedology
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Soil horizon
USDA soil taxonomy
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Soil horizon
Topsoil
Humus
Soil morphology
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A study of tepetates found in the Glacis de Buenavista, Morelos is hereby presented. The section of study (Ahuatenco) includes a sequence of seven indurate horizons (tepetate layers), underlying a polygenetic and welldeveloped Luvisol. In this work tepetates are considered as producis of erosion-sedimentation and pedogenetic processes. Therefore they are interpreted as paleosols with different degrees of development. Macro and micromorphologic evidences indicate that the tepetate profile is constituted by a mixture of fresh coarse volcanic material, redeposited fragments of soil and pedogenetic features, which include: clay cutans, Fe-Mn nodules, weathered primary minerals and phytoliths accumulated wlthin the layer matrix. These properties show that tepetates were exposed at the surface for a sufficient time to allow pedogenesis. The tepetates' parent material are volcanic ashes derived from volcanic events, and eroded Bt-horizon remains from the upper portions that were redeposited along with volcanic materials. Because of the presence of these Bt-horizon fragments the clay content in indurate materials is high (47%), but they display a contrasting distribution, showing lithological and textural discontinuities, so each layer is likely to represent a different stage of landscape evolution. The degree of alteration observed for the different layers vary, as well as the stability periods under which pedogenesis occurs.
Volcanic ash
Paleosol
Soil horizon
Sedimentation
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Subsoil
Soil horizon
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