Diagenesis
Résumé
Reefs have caused a tremendous interest in diagenetic studies in the past decades, with a particular exponential development during the 70’ and 80’, just after the major discovery of the early submarine cements in modern coral reef complexes in the late 60's (Ginsburg et al. 1967; Macintyre et al. 1968; Land and Goreau 1970; ...). In the general topic of carbonate diagenesis, reefs represent highly favourable systems for the study of diagenetic processes because they are especially susceptible to diagenesis occurring either in marine, mixed or non-marine waters, and as sedimentary systems, they have relatively clearly defined geometries. Another reason explaining their scientific interest is their reservoir potential, and, from this point of view also, the precise analysis of reef-limestones diagenesis is of critical importance for the assessment of their economic significance. Independently from their age and setting, reefs presents several fundamental specificities as regarding carbonate diagenesis: 1- They are formed with a very high primary porosity, 2- They are lithified at their time of growth, this limiting the effects of compaction and hence permitting the preservation of initial porosity; 3- Reef facies are usually composed of chemical unstable minerals, such as aragonite and high-Mg calcite, which can easily undergo various chemical and mineralogical changes through interaction with circulating pore fluids. The aim of this Encyclopaedia is to focus on Modern reefs. For this reason, the diagenetic features and processes described here are related to the early diagenesis in the sense of syndepositional diagenetic processes and do not include those depending on burial diagenesis.