DiagenieVerhalten

Diagenese is the sum of all physical and chemical changes that occur in sediments after their deposition and before metamorphism. These changes take place at relatively low temperatures and pressures, typically below 200 degrees Celsius and a few kilobars. Diagenesis is a crucial process in the formation of sedimentary rocks and plays a significant role in the preservation of fossils and the generation and migration of hydrocarbons.

The processes involved in diagenesis can be broadly categorized into physical and chemical alterations. Physical processes include compaction, which is the reduction in pore space due to the weight of overlying sediments, and cementation, where minerals precipitate from pore fluids to bind sediment grains together. Other physical changes can involve the rearrangement of sediment particles and the expulsion of pore water.

Chemical diagenesis involves a variety of reactions. Dissolution of unstable minerals can create secondary porosity, while the precipitation of new minerals, such as clays, carbonates, or silica, can fill existing pore spaces or cement grains. Redox reactions, changes in pH, and the activity of microorganisms also contribute to the chemical transformation of sediments. The specific diagenetic pathway is highly dependent on the original sediment composition, the chemistry of the pore fluids, and the burial history.

Diagenetic changes can significantly alter the porosity and permeability of rocks, impacting their potential as reservoirs for oil, gas, and groundwater. Understanding diagenesis is therefore essential in fields such as petroleum geology, hydrogeology, and paleontology. The transition from diagenesis to metamorphism is generally considered to occur when temperatures exceed approximately 200 degrees Celsius, at which point recrystallization and new mineral growth become more extensive and characteristic of metamorphic rocks.