Sedimentary Rocks

Introduction

The sedimentary rocks are formed naturally by the deposition of the pieces of rocks or materials that already exist on earth get accumulated. If these sediments are buried deep within the earth, due to cementation and compaction they accumulate to form the sedimentary rocks.

There are several other processes by which these sedimentary rocks are formed. These are deposition of other rock materials that are carried by the wind from sedimentary rocks, precipitation of several solutions, deposition of biogenic activities, and dissolution and erosion of materials. There are several types of sedimentary rocks like organic sedimentary rocks, chemical sedimentary rocks, and clastic sedimentary rocks.

What is sedimentation?

The process through which the rocks materials and other particles style down under the gravitational effects in the water bodies is determined as the sedimentation process. The materials that settle out from this suspension is often denoted as the sediments and after water treatment, they are called sludge. Hence, the settlement of heavier rock materials in water bodies is denoted as sedimentation of rocks and formation of sedimentary rocks. Several types of sedimentary rocks are formed by this process, like clay, iron, shale, limestone, chalk, and sandstone (Abdi et al. 2018).

These rocks cover about 75% of the earth's land in total. The major particles that help in the formation of sedimentary rocks are sediments and these sediments are being transported to the place of deposition by water, glaciers, ice, and wind.

Formation of sedimentary rocks

Sedimentary rocks are formed due to the hardening of the sediments present with the layers of earth: outer core, mantle, core, and the crust. Sedimentary rocks are mainly formed by the composition of metamorphic and igneous rocks formed within earth's core .These rocks are formed by cementation and compaction means lithification and burial of sediments. The stages by which the sedimentary rocks are formed are erosion, weathering, burial and lithification stage.

Figure 1: Sedimentary Rocks formation

The weathering stage involves wind, ice, glaciers, and water activities. Through this process, the materials that are carried by wind and water get broken into small pieces or grains and accumulated to form sedimentary rocks. Then raw materials are carried away from weathering sites by the erosion process (Bristow et al. 2018). In the burial stage the raw materials get deposited to form a sediment layer and in the last stage is the lithification stage, cementation and compaction takes place where the porosity and volume of rocks get changed.

Sedimentary rocks: Types

There are several types of sedimentary rocks that are found on earth and cover about a total of 75% of earth's surface. These rocks are classified according to their clastic, chemical, and biochemical nature. Clastic sedimentary rocks are formed from already existing rocks by the weathering process that is carried to a basin. Organic sedimentary rocks are formed by biochemical processes. Calcium carbonate or snail shells that later forms limestone, are the organic sedimentary rocks (Garia et al. 2019).

Chemical sedimentary rocks are formed when the mineral gets mixed in solutions or in water, they become supersaturated and precipitated inorganically. Gypsum and halite are examples of these Chemical sedimentary rocks.

Sedimentary rocks: Characteristics

The main characteristics of sedimentary rocks are mentioned in the table below.

Rill Marks	Sedimentary rocks have riff marks that are formed by the sea waves that are returning back to the ocean after hitting the sea shore.
Porosity	It is found in sedimentary rocks that range from 1%-50%. It is found in both clastic, chemical, and organic sedimentary rocks. Sandstones have about 5% of porosity and clay has around 50% of porosity (Bourg et al. 2017).
Includes Fossils	The sedimentary rocks contain animal and plant fossils which are millions of years old. Limestone is basically formed from remains of living things fossils that died millions of years ago and are found in the ocean bed.
Have Mud cracks	Mud cracks are there in Sedimentary rocks that are determined as fissures created when water comes out from the sediments gets dried.

Table 1: Sedimentary rocks: Characteristics

Conclusion

Sedimentary rocks are formed due to erosion, precipitation, weathering, and accumulation of the heavier rock particles in a place by water, glaciers, ice, and wind. The rock types can be checked from the sediment grain variation and size. There are three main types of sedimentary rocks that are found on earth such as organic sedimentary rocks, chemical sedimentary rocks, and clastic sedimentary rocks. The texture of these sedimentary rocks is referred to their arrangement and features of grains. The sedimentary rocks cover about 75% of the earth's land in total. The total contribution of these rocks is only estimated to be about 8% of crust volume in total.

FAQs

Q1. What do you mean by Sedimentary rocks?

Ans: On earth, nearly 73% of sedimentary rocks are present. The main composition of these sedimentary rocks is igneous and metamorphic rocks which are formed in the inner core of the earth. By the process of erosion, lithification, weathering, precipitation, and dissolution these rocks are formed.

Q2. What are the properties of Sedimentary rocks?

Ans: The properties of these sedimentary rocks can be denoted by their texture and colour. These rocks are often found in the arid continental region and when they come in contact with air have an orange or red colour. Iron is a metal got ist greenish or grey colour as it is made of sedimentary rocks.

Q3. What are the uses of Sedimentary rocks?

Ans: There are various uses for these sedimentary rocks based on their nature. For construction purposes, limestone and sandstone are used. Sedimentary rocks is the primary source of natural gas, coal, and oil. Shale made from sedimentary rocks is utilized in the production of cement.

Q4. Which Sedimentary rock is much useful?

Ans: The sedimentary rock like Sandstones are determined to be important economically as building material and helps to build reservoirs of water and petroleum. Sandstones are also a valuable source of metallic ores.