Soil Chemistry and Clay Mineralogy of an Alluvial Chronosequence from the North Carolina Sandhills of the Upper Coastal Plain, USA

Abstract

Temporal changes in soil development were assessed on fluvial terraces of the Little River in the upper Coastal Plain of North Carolina. We examined five profiles from each of six surfaces spanning about 100,000 years. Soil-age relationships were evaluated with inter-surface clay mineral comparisons and regression of chemical properties versus previously reported optically-stimulated luminescence ages using the most developed subsoil horizon per profile. Bases to alumina (Bases/Al2O3) ratios have negative correlations with age, whereas dithionite-Fe (FeD) concentrations are positively correlated with time and differentiate floodplain (<200 yr BP) from terrace (≥10 ± 2 ka) soils and T4 pedons (75 ± 10 ka) from younger (T1-T3b, 10 ± 2–55 ± 15 ka) and older (T5b, 94 ± 16 ka) profiles. Entisols develop into Ultisols with exponentially decreasing Bases/Al2O3 ratios, reflecting rapid weatherable mineral depletion and alumina enrichment during argillic horizon development in the first 13–21 kyr of pedogenesis. Increasing FeD represents transformation and illuviation of free Fe inherited from parent sediments. Within ~80–110 kyr, a mixed clay mineral assemblage becomes dominated by kaolinite and gibbsite. Argillic horizons form by illuviation, secondary mineral transformations, and potentially, a bioturbation-translocation mechanism, in which clays distributed within generally sandy deposits are transported to surface horizons by ants and termites and later illuviated to subsoils. T5b profiles have FeD concentrations similar to, and gibbsite abundances greater than, those of pedons on 0.6–1.6 Ma terraces along Coastal Plain rivers that also drain the Appalachian Piedmont. This is likely because the greater permeability and lower weatherable mineral contents of sandy, Coastal Plain-sourced Little River alluvium favor more rapid weathering, gibbsite formation, and Fe translocation than the finer-grained, mineralogically mixed sediments of Piedmont-draining rivers. Therefore, recognizing provenance-related textural and mineralogical distinctions is crucial for evaluating regional chronosequences.

The Vital Roles of Parent Material in Driving Soil Substrates and Heavy Metals Availability in Arid Alkaline Regions: A Case Study from Egypt

“…The variability of the mineralogical and physicochemical characteristics of soils reflects the parent material origin [2]. In agricultural, environmental, and geological investigations, parent material is used as a significant factor in soil classification and explaining soil units [3]. Under identical conditions of vegetation and topography, Water 2023, 15, 2481 2 of 20 various parent materials impact the chemistry and morphology of soils, particularly in arid and semiarid areas [4].…”

“…Alluvial soils are among the most important and productive soil resources. The silt deposited by fluvial systems, such as streams and rivers, is alluvium, the parent material of alluvial soils [3]. Depending on the depositional environment and geologic materials source, alluvium can have a wide range of textures and compositions.…”

“…Our study hypothesized that parent material would be the most important factor affecting soil substrates and heavy metal availability in arid alkaline regions. alluvium, the parent material of alluvial soils [3]. Depending on the depositional environment and geologic materials source, alluvium can have a wide range of textures and compositions.…”

“…Depending on the depositional environment and geologic materials source, alluvium can have a wide range of textures and compositions. Alluvium can be found in all temperate zones and sits beneath geomorphic surfaces with ages ranging from zero to millions of years; it is therefore widely diverse [3]. Lacustrine deposits are sedimentary rock formations that developed at the bottom of ancient lakes [25].…”