diagenestä

Diagenesis is the set of physical, chemical, and biological changes that sediments undergo after deposition and before they are lithified into rock. It operates under relatively low temperatures and pressures, in the near-surface to shallow subsurface environment, and spans a range of timescales from rapid burial to millions of years. The term covers a variety of processes that modify porosity, mineralogy, and texture.

The major processes of diagenesis include physical compaction, chemical cementation, dissolution, replacement, and the growth of authigenic minerals within pore spaces. Physical compaction reduces pore volume as grains are squeezed by overlying sediment. Cementation occurs when minerals precipitate from pore fluids and bind grains together, commonly as calcite, silica, or iron oxides. Dissolution and recrystallization can create or alter porosity and grain contacts, while authigenic minerals form in place and may significantly change rock properties. Microbial activity and organic matter decomposition can also influence diagenetic chemistry.

Conditions such as burial depth, fluid chemistry, temperature, and pressure govern diagenetic pathways. Temperature generally increases with depth, and diagenesis is typically limited to low-grade conditions; higher temperatures and pressures lead into metamorphism. Diagenetic alterations can occur relatively quickly after deposition or gradually over long timescales and may continue long after initial lithification.

Diagenesis strongly affects the properties of sedimentary rocks, including porosity and permeability, texture, and fossil preservation. It is a key concept in sedimentology and petroleum geology, where diagenetic textures and cementation patterns help interpret depositional environments and reservoir quality.