Diagenesis is the set of biochemical, physicochemical and mineralogical changes affecting a sediment after its deposition, before it passes into the metamorphic
domain. It begins as soon as the sediment is deposited and has the essential effect of transforming a loose sediment into compact sedimentary
rock. This lithification is carried out in particular by compaction and dehydration, caused by the burial of the sediments. The increase in pressure favors the chemical reactions of dissolution, and the diagenesis is accompanied by discrete mineralogical transformations ; the transition with metamorphism is gradual and therefore remains rather vague.