29. Cracking clay soils/Calcareous dunefields: Hummocky dunes subdominant, Linear dunes subdominant

These soils have developed on Quaternary unconsolidated material, generally of aeolian and lacustrine origin in the North West Dunefields and Plains, in the north of the WCMA region. These soils occupy the plains and swales, and may occur in association with vertic sodic texture contrast soils (i.e. sodosols). This distribution of soils can relate to Gilgai microrelief e.g. gilgai.

The surface soil is often a dark pedal (often self-mulching) fine sandy clay loam to light clay. It occasionally overlies a bleached subsurface horizon. There is a clear change to a dark grey (occasionally dark greyish brown) light to medium clay subsoil horizon. This is vertic (cracking and usually slickensides) and strongly structured (coarse parting to fine sized peds). This grades into a heavier horizon, becoming heavier with depth and less obvious fine structure, but slickensides may be present. Calcareous material (carbonate) may be visibly present only in the deeper soil but the profile may still be calcareous throughout. Colour may or may not lighten within a metre depth (indicating restricted drainage). The profile depth is about 150 cm or more grading into sediments, with variable depths of the surface horizons, generally 15 cm for the surface.

Notable features include:

• Cracking clay soil, variable surface friability/surface condition (pedal or self-mulching).
• Strong consistence (strength) when dry.
• Occasional bleached subsurface horizon.
• Mottled or yellower subsoil has more restricted soil drainage.
• The soils are often sodic at the surface and strongly sodic at depth with manganiferous material (usually flecks or small concretions).