Entisol
Encyclopedia
In USA soil taxonomy, Entisols are defined as soils that do not show any profile development other than an A horizon. An Entisol has no diagnostic horizons, and most are basically unaltered from their parent material, which can be unconsolidated sediment or rock
. Entisols are the second most abundant soil order (after Inceptisols
), occupying about 16% of the global ice-free land area.
In Australia
, most Entisols are known as Rudosols or Tenosols, whilst Arents are known as Anthroposols. In the FAO soil classification
, because of the diversity of their properties, suborders of Entisols form individual soil orders (eg. Fluvisols
, Lithosols).
soils before the development of terrestrial vegetation in the Silurian
are Entisols, showing no distinct soil horizons. Entisols have been abundant in the paleopedological record
ever since then, though, unlike other soil orders (Oxisols, Ultisols
, Gelisols
for instance) they do not have value as indicators of climate - though Orthents might in some cases be indicated of an extremely old landscape with very little soil formation (as in Australia today).
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
. Entisols are the second most abundant soil order (after Inceptisols
Inceptisols
Inceptisols are a soil order in USDA soil taxonomy. They form quickly through alteration of parent material. They are older than entisols. They have no accumulation of clays, Iron, Aluminum or organic matter. They have an Ochric or Umbric horizon and a cambic subsurface horizon....
), occupying about 16% of the global ice-free land area.
In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, most Entisols are known as Rudosols or Tenosols, whilst Arents are known as Anthroposols. In the FAO soil classification
FAO soil classification
The Food and Agriculture Organization of the United Nations developed a supra-national classification, also called World Soil Classification, which offers useful generalizations about soils pedogenesis in relation to the interactions with the main soil-forming factors. It was first published in...
, because of the diversity of their properties, suborders of Entisols form individual soil orders (eg. Fluvisols
Fluvisols
A Fluvisol in the FAO World Reference Base for Soil Resources is a genetically young soil in alluvial deposits . Apart from river sediments, they also occur in lacustrine and marine deposits....
, Lithosols).
Causes of delayed or absent development
- Unweatherable parent materials - sandSandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, ironIronIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
oxideOxideAn oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
, aluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
oxide, kaolinite clayClayClay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
. - Erosion - common on shoulder slopes; other kinds also important.
- Deposition - continuous, repeated deposition of new parent materials by waterWaterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, windWindWind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
, colluvium, mudflows, other means. - Flooding or saturation.
- Cold climate - must not be sufficiently cold in winter for permafrostPermafrostIn geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
. - Dry climate.
- Shallow to bedrock - may be rock resistant to weatheringWeatheringWeathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
, such as quartziteQuartziteQuartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
or ironstoneIronstoneIronstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical repacement, that contains a substantial proportion of an iron compound from which iron either can be or once was smelted commercially. This term is customarily restricted to hard coarsely...
. - Toxic parent materials - serpentine soilSerpentiniteSerpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
, mine spoils, sulfidicSulfideA sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
clays.
Suborders
- Aquents - permanently or usually wet soils formed on river banks, tidal mudflats etc. Here, general wetness limits development.
- Arents - anthropogenic soils: diagnostic horizons cannot develop because of deep mixing through plowing, spading, or other methods of moving by humans.
- Fluvents - alluvial soils where development is prevented by repeated deposition of sedimentSedimentSediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
in periodic floods. Found in valleys and deltasRiver deltaA delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
of rivers, especially those with high sediment load.
- Orthents - shallow or "skeletal soils". Found on recent erosional surfaces or very old landforms completely devoid of weatherable minerals.
- Psamments - Entisols that are sandy in all layers where development is precluded by the impossibility of weathering the sand. Formed from shifting or glacial sand dunes.
Paleopedology
Most fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
soils before the development of terrestrial vegetation in the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
are Entisols, showing no distinct soil horizons. Entisols have been abundant in the paleopedological record
Paleopedological record
The paleopedological record is, essentially, the fossil record of soils. The paleopedological record consists chiefly of paleosols buried by flood sediments, or preserved at geological unconformities, especially plateau escarpments or sides of river valleys...
ever since then, though, unlike other soil orders (Oxisols, Ultisols
Ultisols
Ultisols, commonly known as red clay soils, are one of twelve soil orders in the United States Department of Agriculture soil taxonomy. They are defined as mineral soils which contain no calcareous material anywhere within the soil, have less than 10% weatherable minerals in the extreme top layer...
, Gelisols
Gelisols
Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two meters of the soil surface...
for instance) they do not have value as indicators of climate - though Orthents might in some cases be indicated of an extremely old landscape with very little soil formation (as in Australia today).