Diagenesis is sometimes divided into early and late phases. Early diagenesis covers everything that may happen after sediment is laid down (deposition) until it first becomes rock (consolidation). Processes in this stage are mechanical (reworking, compaction), chemical (dissolution/precipitation, cementation) and organic (soil formation, bioturbation, bacterial action). Lithification takes place during early diagenesis. Russian geologists and some American geologists restrict the term "diagenesis" to this early stage.
Late diagenesis, or epigenesis, covers everything that may happen to sedimentary rock between consolidation and the lowest stage of metamorphism. Emplacement of sedimentary dikes, growth of new minerals (authigenesis) and various low-temperature chemical changes (hydration, dolomitization) mark this stage.
There isn't an official boundary between diagenesis and metamorphism, but many geologists set the line at about 1 kilobar pressure, corresponding to depths of a few kilometers, or temperatures over 100°C. Processes such as petroleum generation, hydrothermal activity and vein emplacement occur in this borderline region.