How are Sedimentary Rocks Formed

Studying different types of rocks and the natural phenomena behind their formation is an interesting aspect in geology. Say for example, molten magma after cooling down forms lightweight, porous igneous rocks, which are abundantly found in the earth's crust. In contrary to this, sedimentary rocks are formed in normal environmental conditions on the earth's surface and under water bodies. More information on 'how are sedimentary rocks formed in nature', coming in the next paragraphs.

Sedimentary Rocks Formation

Considering the sedimentary rock fact that it often possesses layers or strata, they are also known by the name, stratified rocks. Some of the common examples of sedimentary rocks are shale, sandstone, limestone, etc. In the process of sedimentary rock formation, there are some basic steps, like weathering, erosion, transportation and deposition. Discussed below are geological processes that contribute in the formation of sedimentary rocks.

Weathering
Weathering is the first step responsible for formation of sedimentary rocks. It involves mechanical and chemical breakdown of rocks, minerals and soil under the influence of atmospheric conditions. Elements like water, ice, heat and pressure altogether affect the rates of weathering. The weathered rock, soil and mineral particles are then carried away to other places by means of erosion.

Erosion
Erosion is defined as the process of breaking down larger objects into smaller ones and transporting them. Take the example of a newly formed mountain, which appears tall and steep. After being exposed to the effects of wind, water, glacier and rain for several years, its height is reduced and the shape becomes rounded. This is brought about by erosion. In the meantime, the eroded rock and mineral particles are carried away by natural agents to several places.

Sediment Transportation
While studying 'how are sedimentary rocks formed', you will find that weathering and erosion go hand-in-hand. The smaller particles generated by these processes are collectively known as sediments. Ultimately, most of the broken rocks, minerals and soil particles are transported by water and wind to other places. Besides these, dead plants and organisms are also carried in the flow of wind, water and ice. They are also used in the formation of sediment rocks.

Deposition of Sediments
Another step in sedimentary rock formation is deposition of the sediments by water and other transporting agents. Particles that flow downstream in water bodies like river, streams and lakes settle down at the bottom, because of the influence of gravity. In due course of time, layers of sediments are piled up one after the other, either in the earth's surface or under water bodies. This settling down of particles at the bottom of a water body is called sedimentation.

During the process of sedimentation, the bottom layers are pressurized by the above layers, resulting in compaction and formation of sedimentary rocks. The layers of sediments are called strata or beds. During this process, dead plants and animals can also be buried in between the beds, which become fossils afterward. If a specific strata is noticeable, it can be concluded that there was a time gap between deposition of the particular layer and the overlying strata.

Sedimentary Rocks Classification

Based on the material makeup and formation of sedimentary rocks, they are classified into three types - clastic sedimentary rock (e.g. sandstone), chemical sedimentary rock (e.g. halite) and organic sedimentary rock (e.g. coal). The first one is formed after compaction of granular sand, gravel, mud and other sediments. On the other hand, chemical sedimentary rocks are formed due to precipitation or saturation of dissolved minerals in solution. The last type is organic sedimentary rock, which is formed from materials produced by living entities, such as corals and mollusks.

So, this was an overview on how are sedimentary rocks formed and their classification. All types of rocks are cycled in nature, just like biogeochemical cycles. In the process, rocks are formed continuously, degraded and then, formed again. Nevertheless, this step-by-step phenomenon occurs in a slow and gradual manner, which is why rock cycle takes a longer period than other geochemical cycles.