Types of Sedimentary Deposits and Soil Genesis
Types of Sedimentary Deposits
Lacustrine deposits: These occur when earth is moved or transported by rivers and streams and deposited on lake bottoms.
Proluvial deposits: These are materials occupying the bed of dry streams.
Fluvial deposits: These are formed by sediments that accumulate from the activity of rivers and the processes associated with gravity sliding.
Wind deposits: These are formed through the accumulation of transported material, forming dunes and sand dune materials.
EOI: A special material from sedimentary rocks, it is characterized by being gray to pale yellow. These porous materials have a linen texture. They are easily washed away by runoff and are therefore susceptible to erosion.
Moraines: These are materials collected by ice and are found in areas near places of temporary or permanent freezing. They present an acid reaction, i.e., the pH is below 5.
Frequently Found Primary Minerals
- Quartz (SiO2): This is silicon oxide; the compound in the hydrated form is called opal.
- Silicate: These minerals are widespread in the crust but are not very resistant to weathering; their content is very low, at 5 to 10%. Examples include nesosilicates, sorosilicates, cyclosilicates, inosilicates, phyllosilicates, and tectosilicates.
- Alumo-silicates: Among the most common are feldspars (orthoclase and plagioclase, 1% to 10%) and micas (biotite and muscovite).
Secondary Minerals
These form as a result of the synthesis of products of chemical weathering of rocks. They are divided into three groups:
- Simple salts: These are composed of minerals that accumulate in areas of arid or semi-arid summits where dissolution and percolation are limited. Examples include calcite, magnetite, gypsum, and siderite.
- Oxide hydroxides: These are the most widespread compounds and are formed as a result of chemical weathering of bedrock, leading to hydrated compounds that then crystallize. Among the most common oxides and hydroxides are Al2O3, Al(OH)3, FeO3, FeO, CaO, and Ca(OH)2.
- Clays: These are the result of the synthesis product of weathering of primary rock and make up the fine soil particles. Clay particles of all sizes are made up of plates of silica and aluminum. According to the number of plates that integrate them, these clays are divided into two groups:
Bilaminal Clays 1:1
These are made of one sheet of silica and one of aluminum. These fine, three-dimensional silicate clays represent the 1:1 clay kaolinite. Type 1:1 clays are characterized by having a low water absorption capacity and therefore a low capacity for further expansion. They have a low cation exchange capacity (CEC).
Genesis and Morphology of the Soil
Soil Genesis
Soil forms from the rocks of the crust. Rocks inside the crust become unstable when coming to the surface, and any material on the surface suffers the effect of environmental factors. It is gradually colonized by plants: initially forbs, then brush, and finally arboreal vegetation in wet areas. Parallel processes of fragmentation or decomposition of rocks occur, which is known as weathering.