Sedimentary Facies and their Analysis

Sedimentary facies refer to the biological, physical and chemical aspects of a sedimentary layer and the lateral change within the sequences of such layers. All these layers of beds belong to the same geologic age. One can see the formation of sedimentary rocks only in places where the sediments are deposited for a long time. The types of sedimentary facies are based on petrological characters. They include mineralogy, lithofacies or grain size, biofacies, etc. Here we will know about sedimentary facies and sedimentary facies analysis in detail.

Meaning of sedimentation

Sedimentation refers to the process of particles settling out from the suspension of water because of the effect of gravity. These particles are called sediments, and the water treatment is called sludge. When a thick layer of sediments settles down, it is called consolidation. Whenever any mechanical means assists in consolidating sediments, it is called thickening.

Cyclic or rhythmic sedimentation

Cyclic sedimentation may occur in various ways in different parts of the world. It mostly takes place when there is a repeated change in depositional environments. That speaks for the multiple documentation made on the same to date. However, many of these successions called cyclic have been re-assessed. It concludes that this is not a common phenomenon and is not consistent, as considered earlier.

What are sedimentary facies?

The term sedimentary facies was used initially by Swiss geologist Amanaz Gressly in 1838. The sedimentation process occurs in environments where a particle constantly lies without being disturbed for years. These areas are also called sedimentary basins. Some of these are small, while others cover large areas. 

Many biological, physical and chemical factors affect these environments. Different sedimentary bodies can be seen side by side within a basin that is distinct from the adjacent sediments due to certain conditions. These different sedimentary rocks settled along the sides are thus termed sedimentary facies. 

Types of sedimentary facies

Sedimentary facies can be designated or described in various ways. Each of them has a distinct type of sediment based on its environment.

Lithofacies

One can identify this type based on the principal physical characteristics of the sedimentary facies. These physical characteristics are also termed lithological characteristics. So, lithofacies is the subdivision of a designated stratigraphic unit. The latter is differentiated from the rest of the adjacent subdivisions based on lithology.

Biofacies

One can identify this type based on the biological characteristics of the sedimentary facies. These characteristics are also termed paleontological characteristics. Moreover, one may refer to biofacies as fossils. So, biofacies are bodies of rocks with characteristic biological features.

Cyclothems

These types of sedimentary facies lie beneath clay, coal, sandstone, or shale. They may also be repeated several times and are termed cyclothems. These are stratigraphic sequences of marine and non-marine sediments. Most of the time, they are interbedded with coal seams. One may refer to them as a sequence of repeating sediments.

Significance of sedimentary facies

The result of sedimentary facies analysis is the recognition that they help control hydrocarbon accumulation. Sedimentary facies and other lithological characters play a major role in the process. This refers to reservoirs having high permeability and porosity favourable for hydrocarbon accumulation. Once the favourable facies are identified, they help identify the distribution of favourable exploration areas. These areas are the sedimentary basins.

Reservoirs emerging from different sedimentary facies are different from each other. This difference is made based on structure, composition, particle size, sorting, thickness, etc. That also makes it clear that their original conditions were different earlier. One can associate favourable sedimentary facies to high permeability and porosity-based reservoirs. They become a prime area for the accumulation of hydrocarbons.

Hydrocarbon experiences and exploration conclude that the formation and distribution of reservoirs control the paleo-sedimentary environment. The preservation and accumulation conditions are different for different sedimentary facies. That is because of the differences in the sedimentary environment.

So, the study of hydrocarbon accumulation through sedimentary facies holds importance for improving the efficiency of explorations. It also helps predict the favourable hydrocarbon accumulation areas.

Uses of sedimentary rocks

Sedimentary rocks are used to make cement, glass, plaster and build stones. Coal, uranium and some other energy resources also emerge in the form of sedimentary rocks. All of them have different uses and are considered a vital part of the planet. 

Hydrocarbon distribution in sedimentary facies

Hydrocarbons are distributed in the delta sandstone rocks in relatively strong hydrodynamic environments. This is as per different sedimentary facies analysis in basins. However, these facies are never an alluvial fan where only mudstone or coarse sand are formed. So, only a few hydrocarbon reserves and reservoirs have been discovered in facies under environments such as alluvial fans. Some of them have also been discovered under weak hydrodynamic environments. 

Conclusion

Sedimentary facies always indicate a depositional environment. Each of them has different sediments based on the area or environment. One can identify the different types of sedimentary facies based on their geological provenance. They play a significant role in the hydrocarbon accumulation and the formation of reservoirs. These facies combine with other lithological factors to ensure the accumulation occurs under strong hydrodynamic environments. This results in sedimentary rock formation also called facies.