Introduction

All those processes taking place after initial deposition, leading to the stabilisation and lithification of the sediment.

Carbonate sediment is in geochemical equilibrium with the environment in which it forms (e.g., seawater). When it later comes into contact with other fluids – shallow marine burial fluids, meteoric, deep burial fluids, it is subjected to mineralogical and fabric transformation, stabilisation and lithification.

1. Original mineralogical composition (aragonite and HMC unstable, LMC more stable)
2. Diagenetic fluids (marine, meteoric, burial)
3. Burial history (burial brines, T, P)

Diagenetic products

Micrite envelopes, micritized grains (peloids)

• Aragonite and HMC with acicular, botryoidal, fibrous and bladed cements;
• isopachous rims in marine phreatic setting;
• syntaxial cement.
• Micrite peloidal cement

Beachrock

Hardgrounds

Dolomite crusts, penecontemporaneous replacive mimetic dolomite

Karst, caves, vug porosity

Meniscus, pendant cement, LMC

Isopachous rims to mosaics of granular, blocky, equant LMC; syntaxial cement.

• Aragonite dissolution-replacement by LMC;
• biomouldic and oomouldic porosity;
• moulds infilled by equant LMC cement

Caliche, rhizocretion

• Dolocrete (groundwater calcrete);
• mixing zone dolomite

Transformation into calcite of previously formed dolomite.

Diagenetic products

Vug porosity

• Isopachous rims and mosaics of equant granular and blocky calcite spar (LMC); drusy, poikilotopic and syntaxial fabric.
• Fe-calcite (blue when stained with K ferricyanide) in reducing conditions of burial.

Replacement by LMC

Replacement of carbonate minerals by SiO₂ as amorphous silica or chalcedony.

• Fe-dolomite (mauve to green when stained with K ferricyanide) in reducing conditions of burial.
• Baroque (saddle) dolomite due to hydrothermal fluids, T = 80-120°C.