Depending on their origin and formation, different types of rocks exist on our planet . Today we're going to talk about sedimentary rocks . Among all the diverse geological formations, these types of rocks make up 75% of the Earth's surface. Although this percentage may seem quite high, it's a very small proportion compared to igneous rocks, which form most of the Earth's crust. The entire Earth's mantle is also composed of igneous rocks.
In this article we will tell you all about the characteristics, origin and formation of sedimentary rocks.
Key features
These rocks are formed from the accumulation of various particles of different sizes, originating from other rock formations. All the particles that make up the rock are called sediments , hence the name. These sediments are transported by external geological agents such as water, ice, and wind. The sediments that form sedimentary rocks are transported by these various geological agents and then deposited in what are known as sedimentary basins.
During sediment transport, rock particles undergo various physical and chemical processes known as diagenesis. This term refers to the process of rock formation. Sedimentary rocks typically form along riverbanks, on the seabed, in lakes, at river and stream mouths, and in ravines. As expected, the formation of sedimentary rocks takes place over billions of years. Therefore, to analyze the origin and formation of sedimentary rocks, the geological timescale must be considered.
Formation of sedimentary rocks
To analyze the formation of these types of rocks, it's necessary to consider the various external geological processes involved. One of the processes that most significantly affects rock transport is wind. In their initial stages, geological processes weather and erode pre-existing rocks. Weathering is simply the process of breaking down the original rocks into smaller fragments. Erosion, on the other hand, is the wearing away of rocks and their subsequent fracturing into smaller particles. The particles that are eroded and weathered are known as clasts or detritus . We must also remember that water, like wind, is an agent that manifests itself through precipitation.
All the smallest fragments of rock produced through weathering or erosion are transported by external agents. Once they have been transported a significant distance, all the particles become deposited in sedimentary basins. Throughout these basins, all the sedimentary particles gradually accumulate. The distance the clasts travel to the basin depends on their size. That is, smaller sediments will travel a much greater distance before finally settling in the sedimentary basins. Furthermore, the type of transport and movement that occurs, depending on the size of the sediments, must also be considered.
Once they have settled in the sedimentary basins, they begin a process known as sedimentation. This process is driven by the environment and the participation of other organisms. Many living organisms, both animals and plants, can contribute to the formation of sedimentary rocks. In this case, we are referring to the presence of fossils. The rest of the sedimentary rocks are formed from the pressure that sediments exert on each other. This pressure, over billions of years, causes a cementing process that ultimately forms sedimentary rocks.
Sedimentary environment of continental type
Let's look at the different sedimentary environments that exist on the continental level and give rise to the formation of sedimentary rocks. One of the most important aspects in the formation of these rocks is linked to the environment in which they are produced. The sedimentation of clasts and detritus depends on the environment in which they are found and their physical and chemical characteristics. This is a fairly broad classification since there are numerous sedimentary environments, both continental and marine.
Let's see what the different continental sedimentary environments are:
- Glacier: It is an environment where sedimentation occurs from deposits left by glaciers. Here, the debris comes from the mechanical weathering of rocks due to temperature changes and the process of freezing and thawing. The clasts have angular features and little organic matter. The sediments are usually unstratified.
- Deserts: These sedimentary environments cause clasts formed by mechanical weathering to select particles and create formations such as dunes from sands that are approximately 4 mm thick. Related to this, you can find more information about the largest desert from North America.
Sedimentary rocks of continental sedimentary environment
We are going to see what are the continental environments that can be classified according to the degree of stratification that the rocks formed here present:
- Fluvial fan: These are river currents and torrents where there are sudden changes in slope. They are usually found at the foot of mountains and create debris deposits in the form of fans.
- River: Rivers transport all the clasts that originate from mechanical weathering. Here, with the action of the water current, clay forms sedimentary rocks:
- Lacustrine and marshlands: It occurs at the bottom of lakes and swamps. Here, detritus accumulates and forms abundant organic matter, a detail that is related to the formation of sedimentary rocks.
- Albufera: It is a place where sand and mud that arrive through channels from the sea are deposited.
- Deltaics: These are those that are generated in a combination of fluvial and swamp environments. The rock is generated from both coarse and fine clasts.
I hope that with this information you can learn more about the types of sedimentary rocks that exist depending on their origin.