Depending on the origin and formation, on our planet there are different types of rocks. Today we are going to talk about sedimentary rocks. Among all the various geological formations that can be known, there are these types of rocks that make up 75% of the earth's surface. Although this percentage seems quite high, they are a very small proportion and we compare them with the igneous rocks that make up most of the earth's crust. The entire mantle of the earth is also composed of igneous rocks.
In this article we are going to tell you all the characteristics, origin and formation of sedimentary rocks.
Key features
They are called like this to those rocks that are formed as a result of the accumulation of various particles that have different sizes and that come from others with rocky formations. All the particles that make up the rock are called sedimentsThis is where the name comes from. These sediments are transported by external geological agents such as water, ice, and wind. The sediments that form sedimentary rocks are transported by various geological agents and then deposited in what are known as sedimentary basins.
During the transport of sediments, the stone particles are subjected to various physical and chemical processes that are known by the name of diagenesis. This name refers to the process of rock formation. Sedimentary rocks most commonly form on riverbanks, ocean floors, lakes, 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 time scale must be taken into account. geological time.
Formation of sedimentary rocks
In order to analyze the formation of these types of rocks, it is necessary to consider that there are different types of external geological processes. One of the processes that most affects the transport of rocks is the wind. Geological processes in their first stage are responsible for weathering and eroding pre-existing rocks. Weathering is nothing more than a process that consists of the original rocks breaking into other small pieces. On the other hand, erosion is nothing more than the wear of rocks and their subsequent fracture into smaller particles. The particles that they are eroded and weathered are known by the name of clasts or debrisLet's not forget that water is also an agent that manifests itself through precipitation, just like wind.
All the smallest rock fragments produced through weathering or erosion are transported by external agents. Once transported over a significant distance, all the particles are lodged in sedimentary basins. Throughout these basins, all the sedimentary particles gradually accumulate. The route from the clasts to the basin depends on their size. That is to say, those smaller sediments will have a much greater distance traveled until they are permanently lodged in the sedimentary basins. On the other hand, the type of dragging and transport that exists depending on the size of the sediments must also be taken into account.
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.