Sedimentary Petrology - Diagenesis of Carbonate Sediments

oolite thin section

Oobiosparite grainstone, Jurassic, N Yorkshire, UK. Image: Anton Kearsley.

Please note


Diagenesis refers to the physical and chemical changes which take place after the deposition of a sediment; it may include:

during diagenesis:

Carbonates are much more susceptible to diagenesis than terrigenous clastic sediments, and original structures and textures are often completely destroyed.

Diagenesis of carbonates is of great economic importance. Many important oilfields are produced from carbonate reservoirs - e.g. the giant onshore oilfields of the Middle East. Diagenesis controls the porosity and permeability of carbonate reservoirs.



Tucker, 1991, pp. 133-154


Note: all references to Boggs, 1995 and Tucker, 1991 in these pages refer to:

BOGGS, S. 1995. Principles of Sedimentology and Stratigraphy (2nd edition). Prentice Hall.

TUCKER, M.E. 1991. Sedimentary Petrology (2nd edition). Blackwell.


 Diagenetic processes in carbonates

Can be summarised as:

 1. solution of more unstable minerals (especially aragonite), creating secondary porosity

 2. pore-filling by cements

 3. alteration of original minerals to new ones, especially replacement by neomorphic calcite:


Calcium carbonate cement and its recognition

chemically precipitated material, whether a new mineral, or an addition to an existing mineral, may form a cement, which binds the grains of the sediment together to form a rock.

It is important to distinguish between sparite cement (pore fill) and neomorphic spar, an in situ replacement of calcium carbonate in the solid state.

Cement is deposited in pores: these may be primary - voids between or within grains, or they may be secondary, formed during diagenesis by solution, or other chemical or physical changes.

 Some of the features which characterize cements include:

 The composition and crystal habit of calcium carbonate cements are highly dependent on variations in physical and chemical conditions.

Carbonate cement types

The type of cement which forms depends particularly on Mg/Ca ratio and salinity of the solution.

Carbonate cements can be divided into several important types

Early submarine and beach cementation

is common in modern warm water carbonates:

Freshwater (Meteoric Water) Cements


As the stress is usually vertical, due to overburden pressure, there is preferential solution of the upper & lower surfaces of grains, across a solution film. This results in irregular, sutured contacts between the grains.

Grain-to-grain pressure solution must occur before the filling of all the pore spaces by cement - a pore-filling cement protects the grains against compaction and pressure solution.


in more cemented rocks, pressure solution takes place along much more extensive surfaces - these are stylolites. Dissolution often starts along a bedding surface, due to overburden pressure. A burial depth of at least several tens of metres is required for stylolite formation.


This page was written by Roger Suthren

Last Modified: 24 April, 2015 21:10