Polygenesis and cementation pathways for plinthic and non-plinthic soils on the Upper Coastal Plain, South Carolina

• Published in: Geoderma Vol. 427; p. 116130
• Main Authors: Ogg, Charles M., Kelley, John A., Wilson, Michael A., Tuttle, J. Wes, Gulley, Caleb D., Reed, Jackie M., Sullivan, George E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2022
• Subjects: Brick material; Cementation; Coastal Plain; Fragipan; Ground-penetrating Radar; Plinthite; Coastal Plain; Ground-penetrating Radar; Fragipan; Plinthite; Brick material; Cementation
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2022.116130

•Plinthic and non-plinthic U.S. Upper Coastal Plain soils have fragic soil properties.•Ubiquitous, older, underlying resistant material affects cementing conditions.•Secondary iron and silica products appear to be cementing agents.•The underlying, older material has pedogenic features.•A new theory for origin of plinthic soils incorporates nearby soils and landscapes. Plinthic soils on the Upper Coastal Plain (UCP) of South Carolina are directly underlain by hard but unconsolidated older Coastal Plain sediment, as are non-plinthic soils on adjacent dissected landforms. The older deposit, called brick material, is integral to plinthite formation via perched soil water hence intensified redox conditions. Currently, few causes are known for horizon matrix cementation of these soils. Six pedons from three hillslope positions were investigated for soil uniformity, selectively dissolved Fe and Si distributions, and micromorphology. Particle-size indices and ground-penetrating radar (GPR) confirmed uniform soils and thick plinthic horizons on summit positions and a discontinuity at shoulder and backslope positions. Contrasts in GPR radar reflections corresponded to the brick material and were thought to be associated with changes in moisture contents, iron mineralogy, pore size, and clay content. Illuvial clay infillings and minute channels confirmed pedogenesis in brick material. In plinthic horizons above the brick material, excess citrate dithionite Fe (Fed) was indicated by over-bulging distributions relative to Fed/clay ratios. Water-soluble silica (Siw) may be recycled in upper sola by capillarity and leaching, move through the discontinuity, and interact with Fe throughout the solum compatible with coarse material encapsulated with Fe-enriched fine material in the brick matrix. Absolute molar contents of oxalate extractable Si (Sio) and Fe (Feo) were low throughout all pedons, however, Sio/(Feo + Sio) ratios ranged from 0.30 to 0.60 in Btvx, Btx, and 2Btx horizons to account for fragic soil properties. Nascent UCP parent material or soils evidently provided adequate constituents for plinthic soil formation. A new theory proposes UCP plinthic soils evolved simultaneously with uniform soils that do not have a water table and have Bt horizons that begin as yellowish or brownish then redden with depth. Ferricrete sourced from nearby extant landscapes may have provided detrital ironstone to the parent material mix.