Introduction. Diagenesis encompasses all the physical and chemical processes that affect sediments and sedimentary rocks in the portion of the rock cycle that includes the period of burial between deposition and weathering, and also between deposition and the onset of metamorphism.hysical grain rearrangement in very early diagenesis of unconsolidated sediment is an important control on the subsequent path of chemical diagenesis because of the effects on permeability and grain surface characteristics.