Sedimentary rocks are types of rocks formed by sedimentary layers deposited and solidified at the bottom of oceans, lakes, and other bodies of water.
These rocks are composed of sedimentary materials such as minerals and biological materials.
This post will cover eight essential facts regarding sedimentary rocks that kids building amateur geology knowledge should be aware of.
Sedimentary Rocks For Kids: 8 Essential Facts
Fact 1: Sedimentary rocks go through several processes before being formed
Sedimentary rocks are formed from sediment deposits through the process of weathering, transportation, deposition, and lithification.
Weathering: This is the first step in the formation of sedimentary rocks. Solid rocks are broken into fragments and small particles by physical or mechanical processes, like the action of water and wind) and chemical factors (variation in temperature and pressure). This is called weathering.
Erosion: This is the process through which dirt and rocks on the Earth’s surface are acted upon by natural forces and transported to another area. Erosion is the transition phase between weathering and transportation.
Transportation: Carrying the broken-down matter to a different locality involves transportation. The shape of rock fragments after transportation helps in analyzing the distance traveled and the environmental conditions.
Deposition: This step follows transportation where the material or sediments get deposited after the energy of transportation drops.
Lithification: Lithification helps in the formation of sediments into a rock. As the layers of sediment get deposited over one another, the process of compaction starts. The overlying weight increases the pressure on the sediment layers below, thus eventually cementing them together, resulting in sedimentary rock.
Fact 2: Sedimentary rocks are the earth’s major surface rocks
Most of the Earth’s rocky land surface is covered by sedimentary rocks, which account for a significant portion of the total.
Sedimentary rock covers approximately 73 percent of the Earth’s surface area.
However, when compared to the other types of rocks, such as the metamorphic and igneous types, they account for a minor proportion of the Earth’s crust.
In terms of overall volume, they account for around 8% of the total volume of the Earth’s crust.
Fact 3: Sedimentary rocks are classified into four groups
Based on how they were formed, sedimentary rocks are typically divided into four groups.
- Clastic sedimentary rocks are made up of fragments that have been consolidated by silicate minerals during geologic time. They can be any type of mineral, but the majority of them are made up of quartz, feldspar, mica, and clay minerals. Sandstone, shale, and siltstone are examples of clastic sedimentary rocks.
- Biochemical sedimentary rocks, also known as biogenic sedimentary rocks, are formed when organisms use components dissolved in water or air to build the tissues of their body parts, which results in the formation of biochemical sedimentary rocks. Limestone, coal, and chert are examples of biochemical sedimentary rocks that are commonly encountered.
- Chemical sedimentary rocks are formed when the concentration of mineral elements in a solution becomes supersaturated, causing them to precipitate. In addition to oolitic limestone and barite, additional chemical sedimentary rocks that are regularly encountered include gypsum, and halite or rock salt.
- Miscellaneous: Impact events, volcanism, and other minor processes have created “other” sedimentary rocks that don’t fit into the above categories. Volcanic tuff and breccia are two examples.
Fact 4: Sedimentary rocks occur in layers
Sedimentary rocks form layers called strata, which form a structure called beds or bedding.
Strata are composed of parallel layers that are stacked upon one another after deposition by natural processes.
These layers extend across hundreds of thousands of square kilometers.
The strata differ from each other in terms of color and structure and are typically seen in cliffs, riverbanks, and quarries.
Each stratum varies in thickness.
Some are several millimeters thick, and some are more than a kilometer thick.
Beds are the strata of sedimentary rocks that are distinguishable and nonidentical from the overlying and underlying beds of sedimentary rocks.
Beds are differentiated by rock type, mineral type, and particle size, among other things.
The arrangement of strata is determined in the order that they were deposited.
The older beds are found below while the younger ones form on top.
Fact 5: Limestones are the most common sedimentary rocks
Limestones account for over ten percent of all sedimentary rocks on the face of the planet.
Calcium carbonate, also known as calcite, is secreted by marine species to construct their shells and other skeletal parts.
The calcium carbonate and skeletal remains of the organism accumulate when the creature dies, resulting in the formation of biochemical limestone.
Warm seas and abundant biological production occur on shallow continental shelves.
The formation of limestones is facilitated by such an environment.
This means that limestones are found in abundance on shallow continental ledges, but are scarce on abyssal plains.
The use of limestone in the construction of buildings and architecture has been around for thousands of years.
The pyramids in Egypt are notable examples of this type of architecture.
Fact 6: Grain size determines the kind of rock formed
The size of the grain defines the kind of sedimentary rock.
Claystone and mudstone are composed of extremely tiny grains.
Siltstone is distinguished from coarse-grained sandstone by the presence of fine granules.
Conglomerate is distinguished by the presence of large grains and boulders.
Fact 7: Sedimentary Rocks provide ideal conditions for the preservation of fossils
Fossils are the preserved remains of animals, plants, and other organisms from the distant past.
Fossils are most abundant in sedimentary rocks due to the favorable conditions for their preservation.
On the other hand, igneous and metamorphic rocks are subjected to high temperatures and pressures, effectively destroying any fossils.
Organisms immediately covered by sediment after death have a better chance of complete preservation.
Even the organism’s feathers or skin are preserved in such cases.
However, if the organism or plant matter is subjected to some degree of decay before being buried beneath the sediments, only the skeletal remains of the organism or plant matter are preserved.
If fossil hunters are aware of the age of the rock layer in which the fossils were discovered, they can determine the age of the fossils.
Fact 8: Sedimentary rocks can be used as fuel
Coal is a combustible sedimentary rock with a black or brownish-black color and forms as rock strata known as coal seams.
In its most basic form, coal is composed of carbon, with varying amounts of other elements such as hydrogen, sulfur, oxygen, and nitrogen.
Decomposing organic material decays into peat, which is turned into coal by the pressure and temperature of underground burial over millions of years.
Because coal burns easily, it is used as fuel for heating and cooking.
Sedimentary rocks are generated when eroded fragments of old rocks and dead creatures mix to form sediment (typically in seas or rivers).
Sedimentary rocks such as limestone, sandstone, and shale are common examples.
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