Entisols are
soils, as defined under
USDA soil taxonomy, that do not show any profile development other than an
A-horizon (or “A” horizon). Entisols have no diagnostic horizons, and are unaltered from their parent material, which could be unconsolidated sediment, or rock. Entisols are the most common soils, occupying about 16% of the global ice-free land area.
Aquents – heavily saturated or soaked soils, mostly present at
riparian locations (such as river banks, tidal
mudflats,
estuaries, etc). Here, consistent saturation limits development.
Fluvents –
alluvial soils, where development is prevented by repeated deposition of
sediment during periodic
flooding events; present in
valleys or
river deltas, especially those with high sediment load.
Orthents – shallow or "skeletal" soils; found at sites of recent
erosion events, or very old landforms completely devoid of weatherable
minerals.
Psamments – Entisols that are sandy (through all layers), and in which development is precluded by the impossibility of weathering the sand; formed from shifting or
glacialsand dunes.
Wassents – Entisols that have a positive water potential at the soil surface for more than 21 hours of each day, in all years.
Paleopedology
Most
fossil soils, before the development of terrestrial vegetation in the
Silurian, are entisols that show no distinct soil horizons. Entisols are common in the
paleopedological record ever since the Silurian; however, unlike other soil orders (
oxisol,
ultisol,
gelisol, etc) they do not have value as indicators of climate. Orthents may, in some cases, be indicative of an extremely ancient landscape with very little soil formation (i.e., Australia today).