What is litigation?

Lithification is the geological process by which dispersed substances or materials are compacted to form rocks. In fact, the word lithification literally means the process of transformation into rock. From another point of view, lithification can be seen as the process of formation of sedimentary rocks through the compaction of different types of sediments.

Lithification represents one of the early stages of diagenesis, the process that describes the physical, chemical, and biochemical changes that occur in sediments as a consequence of the chemical interaction between rocks and water after sedimentation. What characterizes lithification and what distinguishes it from the other stages of diagenesis is that it only involves the compaction and cementation of sediments, but without any change in chemical composition. This means that the same minerals that are present in the sediments are still present in the sedimentary rock after lithification.

The litigation process

Broadly speaking, the lithification process begins with the erosion of different minerals by the effect of air and water. This erosion transforms solid minerals into small particles or sediments that are transported by gravity and driven by the wind to sedimentation basins where they are progressively deposited to form layers of sediments that accumulate one on top of the other to form sedimentary blankets.

Over time, these layers build up one on top of the other, increasing the pressure on the lower layers. This pressure slowly compacts the sedimentary layers and, over time, ends up triggering the metamorphosis of the sediments into sedimentary rock, that is, it culminates in the lithification of the sediments.

Lithification vs. petrification

Because both concepts involve rock formation, lithification is sometimes confused with petrification, or taken synonymously. The difference between both concepts is that, in lithification, sedimentary rocks are formed from inorganic sediments, while petrification refers to the formation of fossils by replacing organic matter with minerals.

Lithification phases

Lithification occurs through the occurrence of the following successive phases:

• compaction
• Cementation
• recrystallization

compaction

The compaction process involves the loss or elimination of water from sediments deposited in the lower layers in a basin due to the pressure exerted by successive layers that accumulate one on top of the other (the overlying layers). This increase in pressure tends to reduce the space between the solid particles of the sediment, which forces the water out and moves up due to its lower density.

Cementation

The cementation process is the stage during which the hardening of the sediments itself occurs. It consists of filling the pores found between the sedimentary particles, effectively associating or uniting them with each other. In many cases, cementation is the consequence of chemical reactions involving materials such as silica (SO ₂ ), calcite and aragonite (CaCO ₃ ), siderite (FeCO ₃ ), different iron oxides and other minerals.

Cementation may occur concurrently with sedimentation processes or they may occur afterward.

recrystallization

Recrystallization consists of the dissolution and subsequent crystallization of minerals within the sediments. This process slowly creates larger crystals or particles that have the same original chemical composition.

Examples of lithification

• Lithification of clay turns it into shale.
• The silt is transformed into siltstone.

• The sand when lithified becomes a sandstone.
• The gravels are transformed into conglomerates or breccias.

References

• Britannica, T. Editors of Encyclopaedia (2006, December 8). Cementation. Encyclopedia Britannica . Retrieved from https://www.britannica.com/science/cementation-sedimentary-rock
• Britannica, T. Editors of Encyclopaedia (2014, March 25). Lithification. Encyclopedia Britannica . Retrieved from https://www.britannica.com/science/lithification
• Chapter VII Diagenesis-Metamorphism. (1990). Clays, Muds, and Shales, 417–524.  Retrieved from https://www.sciencedirect.com/science/article/pii/S007045710870671X
• Diagenesis and its phases (2017). Retrieved from https://espaciociencia.com/la-diagenesis-fases/