Diagenesis and Lithification

Diagenesis encompasses the physical, chemical, and biological changes that convert loose sediment into solid rock and continue to alter it after deposition.

Definition

The sum of physical and chemical processes that affect sediment after deposition and during burial, transforming it into sedimentary rock and modifying its mineralogy, texture, and pore structure.

Scope

This topic covers the processes of lithification, compaction, cementation, dissolution, recrystallization, replacement, and the formation of authigenic minerals, together with the evolution of porosity and permeability. It treats the burial and fluid history of sediments from deposition through deep burial and uplift.

Core questions

• What processes lithify loose sediment into rock?
• How do compaction and cementation reduce porosity?
• How do dissolution and replacement create secondary porosity and new minerals?
• How does fluid chemistry control diagenetic reactions?

Key theories

Compaction and cementation

Burial compresses and reorganizes grains while pore fluids precipitate cements; together these processes bind sediment into rock and progressively reduce primary porosity, the central pathway of lithification.

Dissolution, replacement, and authigenesis

Changing pore-water chemistry during burial dissolves unstable grains, replaces minerals such as in dolomitization, and precipitates new authigenic phases, creating secondary porosity and resetting rock composition.

Clinical relevance

Diagenetic history controls the porosity and permeability that determine reservoir quality for oil, gas, and water, governs the precipitation of some ore minerals, and must be reconstructed to interpret original depositional conditions from altered rocks.

History

The systematic study of diagenesis grew with petroleum geology in the twentieth century as the controls on reservoir porosity became economically important; geochemical work on carbonate diagenesis, such as that of Morse and Mackenzie, quantified the fluid-rock reactions involved.

Key figures

• Frederick T. Mackenzie
• John W. Morse
• Maurice E. Tucker

Seminal works

• boggs2009
• tucker2001
• morse1990

Frequently asked questions

Is diagenesis the same as metamorphism?

No; diagenesis occurs at the relatively low temperatures and pressures of the near-surface and shallow burial, grading into metamorphism only at higher temperatures, conventionally above roughly 150 to 200 degrees Celsius.

What is dolomitization?

A diagenetic process in which magnesium-bearing fluids replace calcium in limestone, converting calcite to dolomite and often altering the rock's porosity.