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Strongly Contrasting Redoximorphic Patterns in Virginia Valley and Ridge Paleosols

Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061-0404

*Corresponding author.

ABSTRACT

Soils with bisequel morphology and classified as Typic or Plinthic Paleudults are common in the Virginia Valley and Ridge Province. Horizons in the older materials have redoximorphic features that are strongly contrasting with respect to color and distinctness of boundary. Research documenting these horizons is nonexistent. We examined the physical and chemical properties of these horizons to describe the strongly contrasting redoximorphic patterns (SCRP) and investigate their genesis. Two types of SCRP occur. In both types, redox concentrations have Munsell colors of 2.5 YR 3/6, 4/6, or 3/2. In one case, depletion features (10YR 5/6 or 6/2) are randomly distributed throughout the horizon. These horizons are dense (bulk density of 1.75 g cm^–3), which restricts water movement and promotes Fe segregation. In the other type of SCRP, most Fe concentrations, depletions, and planar voids are oriented parallel to the soil surface. These soils have a fluctuating water table. Dithionite-extractable Fe ranges from 70 g kg^–1 in redox concentrations to 4 g kg^–1 in adjacent depletion features. Goethite occurs in both redox concentration and depletion clay fractions. Hematite only occurs in the redox concentration clay fractions. Depletion features have lower coarse/fine ratios (separated at 20 µm), more oriented clay, and 10 to 20% more clay than associated redox concentrations. Horizons with SCRP are dominated by nodules and masses in ped interiors, and Fe depletion features along voids. Thus, Fe is primarily reduced along voids and moves into the matrix. Horizons with a fluctuating water table also contain Fe-rich pore linings. Iron is concentrated on these surfaces because these pores are the first to drain as the water table recedes.

Received for publication January 22, 1993.