Sedimentary rocks are a type of rock formed by the accumulation or deposition of organic particles or minerals and their consolidation at the earth’s surface. The whole process of formation of these rocks is called sedimentation.
Types of Sedimentary Rocks
These rocks are of the following types:
- Argillaceous (Aqueous Rocks)
- Aeolian rocks
- Glacial rocks.
Argillaceous (Aqueous Rocks):
These are a group of rocks formed by detritus. these are detrital rocks made of mudstones, siltstones, etc.
Types of Argillaceous rocks:
- Marine: These rocks are formed due to the deposition and consolidation of sediments in the marine (ocean) and seas in the littoral zones.
- Lacustrine: These are Agrilaceous sedimentary rocks, that are formed at the bottom of ancient lakes (i.e. their formation takes place in the lake environment). Lacustrine deposits can be formed in every variety of basins found in nature. These deposits are formed by the accumulation of highly laminated beds of silts, clays, and occasionally carbonates.
- Riverine: These rocks are formed due to the deposition of sediments in the riverine environment.
The rocks are formed by wind action may be through erosion or deposition. These include:
- sand dunes: The loose sandhills which are made by aeolian processes or by the water flow.
- Loess Deposits: it is clastic, predominantly silt-sized sediment which is formed by the accumulation of dust by wind. It is found as ten percent of the land area of the earth is covered by loess or similar deposits. It is one of the most important aeolian deposits. These are bound together but not cemented, so they are permeable. The losses are not found in equatorial tropics because of heavy rainfalls which wash away the loess.
- Deflation Hollow or Blowout: It is formed by the depression in a sand dune by the removal of sediments by wind action.
- Barchan: It is a crescent-shaped dune.
- Erg (landform): It is a broad flat area of desert that is covered with wind-swept sand.
- Desert pavement: It is a surface of a desert covered with closely packed, interlocking angular or rounded rock fragments of pebble size and cobble size.
- Sandhill: It is a type of ecological community or xeric wildfire-maintained ecosystem.
- Sink: it is also called the playa, a depression within the endorheic basin. An endorheic basin normally retains water and checks the outflow of water to external water bodies
These are the sediments deposited by glaciers. The glacial sedimentary rocks are also called moraines.
Four types of moraines deposits:
- Lateral moraines: The glacial deposit found on either side of a glacier.
- Medial moraines: The glacial sedimentary materials are deposited along the joining glacier.
- Ground moraines: glacier material deposited in the bed of the glacier.
- Terminal moraines.
Types and examples of sedimentary rock are given in the table below:
Characteristics of sedimentary rocks:
- The materials of these rocks are derived from pre-existing rock which may be from any of the three rock classes- igneous, sedimentary or metamorphic. Igneous rocks are the most important source of inorganic minerals, that form sedimentary rocks.
- These rocks contained layers or strata. sedimentary rocks are called stratified rocks.
- The sedimentary rocks are deposited in seas and oceans in sequential order.
- These rocks are characterized by joints of different sizes.
- usually, these rocks are porous and permeable.
- The rocks contain fossils.
- This class of rocks may be well consolidated, poorly, or even unconsolidated.
- Polygonal-shaped rocks are developed by riverine sedimentary rocks after exposure to the sun.
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