diagenesis

Diagenesis is the set of physical, chemical, and biological processes that mobilize and transform sediments after deposition and before metamorphism, at relatively low temperatures and pressures. It encompasses changes such as compaction and dewatering, cementation by minerals precipitated from pore fluids, recrystallization, dissolution, replacement, and the authigenesis of new minerals within the sediment.

Key diagenetic processes include compaction as overburden squeezes pore spaces, cementation by minerals such as calcite or quartz that precipitate from circulating pore waters, and the growth of clays and other authigenic minerals. Dissolution can enlarge pore spaces, while recrystallization and mineral replacement alter texture and mineralogy. Diagenesis is strongly influenced by pore-water chemistry, temperature, pressure, fluid flow, redox conditions, and microbial activity, leading to a variety of mineralogical pathways such as quartz overgrowths in sandstone, calcite or dolomite cementation, dolomitization, micritization, and pyritization.

The diagenetic realm is typically divided into early diagenesis (near-surface, governed by sediment pore waters and biological activity) and burial or late diagenesis (progressing with depth, temperature, and pressure). The overall effect on sedimentary rocks is to modify porosity and permeability, usually reducing them through cementation, though dissolution can enhance pore spaces and create complex pore networks.

Examples include sandstone diagenesis, characterized by quartz cement and feldspar dissolution, and limestone diagenesis, featuring calcite or dolomite cement, micritization, and dissolution. Diagenesis differs from metamorphism by its lower temperature/pressure regime and often operates over extended timescales.