Parent Materials 2

Hi, Everyone. In this post we will learn about the remaining four parent materials.

So, Let's start.

Marine Sediments: Streams deposit much of their sediment loads in oceans, estuaries and gulfs. Over long periods of time, these underwater sediments build up. In some cases it become hundreds of meter thick.

Changes in the elevations of sea and land may later raise these marine deposits above sea level and create a coastal plain.

Marine deposits are quite variable in texture. Some are sandy and some are high in clay.

Marine sediments are subjected to soil forming processes for a shorter period of time than their upland parts. As a result, the properties of the soils that form are heavily influenced by those of the marine parent material. Because sea water is high in sulfur. So, these sediments go through a period of acid forming sulfur oxidation at some stage of soil formation.

Lacustrine Deposits: Lacustrine deposits formed in the glacial lakes range from coarse delta materials and beach deposits near the shore to larger areas of fine silts and clay deposited from the deeper, more still waters at the center of the lake. Areas of inherently fertile soils developed from these materials as the lakes become dry.

Glacial Ice and Meltwaters: During the Pleistocene era, up to 20% of the world's land surface was invaded by a succession of great ice sheets. Some were more than 1 km thick. Even so, if all present day glaciers were to melt, the world sea level would rise by about 65 m.

Glaciers are powerful transportation agents that can move earth material ranging in size from clays to boulders. They act as bulldozers, scraping material underneath them, and conveyor belts, moving material that falls on them. These actions create glacial till type of parent material.

Glacial till: As glacier advances, it grinds up rock and carries it. These are then deposited as glacier melts. Much glacial till is deposited in irregular ridges called moraines. Material that deposited in relatively uniform layer during retreat is called ground moraine. Material left pushed up in ridge at southern most edge of advancing glacier is called terminal or end moraine. Recessional moraine is more advanced form of terminal moraine.

Eolian Deposit: Deposition of Wind transported materials also called eolian deposits is important for soil formation. It includes from largest to smallest particle size. Such as, Dune sand, Loess, Aerosolic dust and volcanic ash.

Sand Dune: A sand dune is a hill of loose sand built by wind.The dunes ranging up to 100 m in height, may continue to slowly shift their locations in response to the prevailing winds.Beach sand is mainly consisted of quartz which is devoid of plants nutrients and highly resistant to weathering action. Nonetheless, over time dune grasses and other pioneering vegetation may take root and soil formation may begin.


Loess: The windblown materials called loess are composed of silt with some very fine sand or coarse clay. Loess maybe blown for hundreds of kilometers. The deposits farthest from the source are thinnest and consist of the finest particles.

Palouse Loess

Aerosolic Dust: Very fine particles carried high into the air may travel for thousands of kilometers before being deposited. These finer particles are called aerosolic dust because they can remain suspended in air.

Volcanic Ash: Soil developed from volcanic ash are most prominent within a few hundred kilometers of the volcanoes. The volcanic ash tends to weather rapidly into allophane, a type of clay with unusual properties.

Besides these transported parent materials, there is another deposition called organic deposition.

Organic deposits: Organic matter accumulates in wet places where plant growth exceeds the rate of residue decomposition. These residues sink into the water, where their decomposition is limited by lack of oxygen. As a result, organic deposits often accumulate up to several meters in depth. Collectively, these organic deposits are called peat.

These were about the Parent Materials of soil. One of the most important factors that influence soil formation.

In my next post, we will learn about other four factors. Can you remember what are they?

Okay, they are Climate, Biota, Topography and Time.

Reference:

Brady, N.C. and Weil, R.R., The nature and properties of soil. 13th Edition.