Parent material
Encyclopedia
In soil science
, parent material is the underlying geological material (generally bedrock
or a superficial or drift deposit) in which soil horizon
s form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are often classified based upon their contents of consolidated or unconsolidated mineral material that has undergone some degree of physical or chemical weathering and the mode by which the materials were most recently transported.
parent material.
Parent material transported by streams is called alluvium
of which there are three main types. Floodplain
s are the parts of river valleys that are covered with water during floods. Due to their seasonal nature, floods create stratified layers in which larger particles tend to settle nearer the channel and smaller particles settle nearer the edges of the flooding area. Alluvial fans are sedimentary areas formed by narrow valley streams that suddenly drop to lowlands and widen dramatically. Sedimentary in these types of deposits tend to be larger closer to the uplands and finer near the edges of the fan. Delta deposits, the third of type of alluvium, are finer sediments that are discharged from streams into lakes and eventually settle near the mouth of the river.
Lake deposited parent material is called lacustrine
parent material. Beach ridges may be present where glacial lakes once washed up sand. Lacustrine material is well sorted and fine-textured, having finer silt
s and clay
s. Soils formed from lacustrine parent material have low permeability in part because of this high clay content.
Ocean deposited parent materials, called marine sediments, are collections of material that have been carried by rives and streams to the ocean and eventually sink to the bottom. Such materials can vary in texture .
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Physical weathering is especially important during the early stages of soil development. Rock can be disintegrated by changes in temperature which produces differential expansion and contraction. Changes in temperature can also cause water to freeze. The forces produced by water freezing can be as great as 2.1 × 105 kPa, which can split rocks apart, wedge rocks upward in the soil, and heave and churn soil material.
Chemical weathering
The principal agent is percolating rainwater charged with carbon dioxide from the atmosphere. Parent material becomes hydrolyzed by the acidic solution to produce minerals and to release cations.
Soil science
Soil science is the study of soil as a natural resource on the surface of the earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.Sometimes terms which...
, parent material is the underlying geological material (generally bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
or a superficial or drift deposit) in which soil horizon
Soil horizon
A soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time...
s form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are often classified based upon their contents of consolidated or unconsolidated mineral material that has undergone some degree of physical or chemical weathering and the mode by which the materials were most recently transported.
Consolidated
Parent materials that are predominately composed of consolidated rock are termed residual parent material. The consolidated rocks consist of igneous, sedimentary, and metamorphic rock. CONSOLIDATEDItalic textResidual
Soil that develops in residual parent material is that which forms in consolidated geologic material.Unconsolidated
Parent material is classified by its last means of transport. Material that was transported to a location by glacier, then deposited elsewhere by streams, is classified as stream-transported parent material, or glacial fluvialFluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
parent material.
Ice transported
Glacial till is material dragged with a moving ice sheet. Because it is not transported with liquid water, the material is not sorted by size.Water transported
Within water transported parent material there are several important types.Parent material transported by streams is called alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
of which there are three main types. Floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
s are the parts of river valleys that are covered with water during floods. Due to their seasonal nature, floods create stratified layers in which larger particles tend to settle nearer the channel and smaller particles settle nearer the edges of the flooding area. Alluvial fans are sedimentary areas formed by narrow valley streams that suddenly drop to lowlands and widen dramatically. Sedimentary in these types of deposits tend to be larger closer to the uplands and finer near the edges of the fan. Delta deposits, the third of type of alluvium, are finer sediments that are discharged from streams into lakes and eventually settle near the mouth of the river.
Lake deposited parent material is called lacustrine
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
parent material. Beach ridges may be present where glacial lakes once washed up sand. Lacustrine material is well sorted and fine-textured, having finer silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
s and clay
Clay
Clay 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...
s. Soils formed from lacustrine parent material have low permeability in part because of this high clay content.
Ocean deposited parent materials, called marine sediments, are collections of material that have been carried by rives and streams to the ocean and eventually sink to the bottom. Such materials can vary in texture .
Gravity transported
Collections of large rock fragments that have traveled downslope by gravity are called colluvial debris or colluviumColluvium
Colluvium is the name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often...
.
Climate and weathering
Climate is generally considered the most important factor influencing physical and chemical weathering processes.Physical weathering is especially important during the early stages of soil development. Rock can be disintegrated by changes in temperature which produces differential expansion and contraction. Changes in temperature can also cause water to freeze. The forces produced by water freezing can be as great as 2.1 × 105 kPa, which can split rocks apart, wedge rocks upward in the soil, and heave and churn soil material.
Chemical weathering
The principal agent is percolating rainwater charged with carbon dioxide from the atmosphere. Parent material becomes hydrolyzed by the acidic solution to produce minerals and to release cations.