Parent Material

The two hardest things to remember for me was the different types of parent materials. Soil parent material is the material that soil develops from, and may be rock that has decomposed in place, or material that has been deposited by wind, water, or ice. The character and chemical composition of the parent material plays an important role in determining soil properties, especially during the early stages of development. Soils developed on parent material that is coarse grained and composed of minerals resistant to weathering are likely to exhibit coarse grain texture. Fine grain soil develop where the parent material is composed of unstable minerals that readily weather. These rocks and minerals can be divided into two main categories: parent material that has been transported and residual parent material that came directly from the rock cycle. non-transported material. Soils formed in residuum have weathered in place out of the baserock or bedrock, which may be igneous, metamorphic, or sedimentary. All other types of parent material have been transported by one or more processes. From the transported material it then can branch off into four different categories: Water, Gravity, Ice, and Wind.

Water can then branch off again into three different categories: Lacustrine which is the “ancient lake beds”

Alluvial which is parent material that is transported and deposited in streams, this streams are usually high in sand and silt.

 (Alluvial)

The last one is marine. Here parent material is deposited in the ocean. Waves are the cause of this and they are high in soluble salts. Gravity is also another way parent material can be transported. This is called colluvial. Ice is the next category that can be divided into two, Glacial Till and Glacial Outwash the differences between these two are that Till is poorly sorted and highly mixed, but Outwash is the poorly mixed and well sorted. The last transported rock and minerals is from wind this is called aeolian. Loess is also another term that is describes to be wind blown silt sand ( this eventually forms dunes).

 (Colluvial)

Parent Material Stratification Particle Size Sorting Coarse Fragment Content Typical Texture
Residuum If parent rock was stratified If parent rock was sorted Often present Dependent on source rock
Colluvium Potentially If source was sorted Generally present Dependent on source material
Loess Not generally observable except near source Highly sorted No Silt to silt loam
Eolian Sands Yes, inclined strata Highly sorted No Fine to coarse sand
Lacustrine Yes Highly sorted No Clay to silt
Alluvium Highly stratified Individual strata show sorting Common in some strata Variable
Beach Deposits Yes, inclined and cross-cutting strata Generally sorted, particularly in individual strata Common in some strata Sandy to gravelly
Fan Deposits Often highly stratified Often sorted with distance from slope break Common Variable, finer with distance from slope break
Glacial Outwash Often stratified Highly sorted Gravels often present Sandy to gravelly
Glacial Till No unless reworked by water Unsorted Generally present Variable
Volcanic Ash Yes, usually highly stratified Sorted with distance from source May occur Variable
Anthropic Materials Variable Variable Variable Variable

 

I found this chart on http://www.bcgrasslands.org/SiteCM/i/upload/8E278433BC37785973D17C8E00394E02F9148344.jpg, I feel like it fit in with my discussion on parent material.

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