30. Calcareous gradational soils/Calcareous dunefields: Hummocky dunes subdominant

These soils have developed on Quaternary unconsolidated material in the North West Dunefields, particularly with hummocky dunefields including lunettes. This is a minor soil type for this land type.

The surface soil is usually a dark brown sandy clay loam, which is apedal (massive) to weakly structured. It occasionally overlies a weakly structured subsurface transitional horizon. There is a clear change to a dark greyish brown to yellowish red, light clay subsoil horizon. This is weakly to moderately structured (with coarse parting to medium sized peds). This soil grades with depth into decreasing structure (pedality) with increasing calcium carbonate soft segregations. This grades into a heavier textured yellowish red clay which is structured, which in turn grades into lighter textured browner clayey material with slickensides (less aerated) at depth. The profile depth is about 150 cm or more, grading into unconsolidated material (regolith) with variable depths of the surface horizons, generally 5-10 cm for the surface and 15 cm for the subsurface, where it occurs.

Notable features include:

• Gradational soil, calcareous throughout with highly calcareous upper soil with some free carbonate but high sodium and salts at depth.
• Variable surface friability (generally hardsetting, weak strength).
• Weaker consistence (strength) with high free carbonate.
• Occasional manganiferous flecks at depth.
• Noticeable increase in clay at depth, slickensides (vertic), browner and mottled and more restrictive drainage.
• Generally strongly sodic at depth (and likely to be dispersive), occasionally sodic at the surface.