diagenéza

Diagenesis refers to all physical, chemical, and biological changes that happen to sediment after it is deposited and buried, but before it metamorphoses into a rock. These processes occur at relatively low temperatures and pressures, typically near the Earth's surface. Diagenesis is a crucial stage in the transformation of loose sediment into solid sedimentary rock.

Physically, diagenesis includes compaction, where the weight of overlying sediment squeezes out pore water and reduces the volume of the sediment. Cementation is another key physical process, where minerals precipitate from pore water and bind the sediment grains together. Biological activity, such as the burrowing of organisms or the decomposition of organic matter, can also influence diagenetic changes, particularly in the early stages.

Chemically, diagenesis involves reactions between the sediment grains and the pore water. Dissolution of unstable minerals and precipitation of more stable ones are common. Redox reactions can alter the mineralogy and color of the sediment. The chemistry of the pore water itself changes significantly during burial and diagenesis, driven by the dissolution and precipitation of minerals and the decay of organic matter. These changes are fundamental to processes like the formation of petroleum and the preservation of fossils.