Lithifikations

Lithifikations, or lithification, is the set of processes by which loose sediment is transformed into solid rock. It encompasses physical and chemical changes that occur after deposition, during diagenesis, including compaction, cementation, and mineral precipitation or recrystallization that bind grains together and harden the sediment.

Compaction is driven by the weight of overlying material, which reduces pore space, squeezes out fluids, and increases grain contact. This process lowers porosity and strengthens the sediment, especially in fine-grained deposits such as mudstones.

Cementation involves mineral-rich groundwater precipitating cementing minerals in the pore spaces between grains. Common cements include silica (quartz), calcite, dolomite, and iron oxides. Cementation strengthens the rock and can significantly reduce porosity depending on cement distribution and grain size.

Recrystallization and other chemical changes can alter mineralogy during diagenesis. For example, aragonite in carbonate sediments may recrystallize to calcite, and dissolution and replacement of grains can occur, changing texture and composition without substantial recrystallization of the original grains.

Different rock types arise from lithification: sandstone and siltstone typically become cemented by silica or calcite; shale undergoes compaction with limited cementation; limestone and dolostone form by cementation of carbonate muds and grains; and chert can form from silica precipitation.

Lithification occurs at relatively shallow burial under low temperatures and pressures associated with diagenesis, and is distinct from metamorphism, which involves higher temperatures, pressures, and deformation. The process largely determines porosity and permeability, influencing groundwater flow and hydrocarbon reservoirs.