Diagenetically

Diagenetically is an adverb describing processes that occur during diagenesis, the suite of physical, chemical, and biological changes that sediments experience after deposition and during early lithification, but before significant metamorphism. Diagenesis operates at relatively low temperatures and pressures, typically within the upper crust, and over geological timescales. It includes mechanical compaction and dewatering, cementation, dissolution, replacement, and authigenesis of minerals, as well as alteration of clay minerals and minor mineralogical transformations.

Common diagenetic processes include lithification through cementation by minerals such as calcite or silica, pore-fluid–driven dissolution, and precipitation of secondary minerals such as pyrite or dolomite. Authigenic mineral formation, neomorphic mineral changes, and clay mineral transformations (for example illitization) also occur diagenetically. These processes modify porosity and permeability, often reducing pore space through compaction and cementation while potentially increasing it locally via dissolution or the creation of secondary porosity during mineral replacements.

Diagenetically altered rocks differ from those that have undergone metamorphism, which involves higher temperatures and pressures and more extensive recrystallization. Understanding diagenetic pathways is essential for interpreting sedimentary rock properties, including reservoir quality in hydrocarbon systems, groundwater behavior, and the diagenetic history of sedimentary basins.