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Lithification – Geology Optional Notes – For W.B.C.S. Mains Examination.
Lithification, complex process whereby freshly deposited loose grains of sediment are converted into rock. Lithification may occur at the time a sediment is deposited or later. Cementation is one of the main processes involved, particularly for sandstones and conglomerates.Continue Reading Lithification – Geology Optional Notes – For W.B.C.S. Mains Examination.
In addition, reactions take place within a sediment between various minerals and between minerals and the fluids trapped in the pores; these reactions, collectively termed authigenesis, may form new minerals or add to others already present in the sediment.
Lithification (from the Ancient Greek word lithos meaning ‘rock’ and the Latin-derived suffix -ific) is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithification is a process of porosity destruction through compaction and cementation. Lithification includes all the processes which convert unconsolidated sediments into sedimentary rocks.
Petrifaction, though often used as a synonym, is more specifically used to describe the replacement of organic material by silica in the formation of fossils.
Minerals may be dissolved and redistributed into nodules and other concretions, and minerals in solution entering the sediment from another area may be deposited or may react with minerals already present. The sediment may be compacted by rearrangement of grains under pressure, reducing pore space and driving out interstitial liquid.
Fresh sediment is usually loose material that is full of open spaces, or pores, filled with air or water. Lithification acts to reduce that pore space and replace it with a solid mineral material.
The main processes involved in lithification are compaction and cementation. Compaction involves squeezing the sediment into a smaller volume by packing the sediment particles more closely, by removing water from the pore space (desiccation) or by pressure solution at the points where sediment grains contact each other. Cementation involves filling pore space with solid minerals (usually calcite or quartz) that are deposited from solution or that enable existing sediment grains to grow into the pores.
The pore space does not need to be eliminated for lithification to be complete. All of the processes of lithification can continue to modify a rock after it has first become a rigid solid.
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