diagenesis

• Porosity is determined by the porosity equation.
• Pore spaces in sediments are un-connected if water cannot travel through the rock, making it porous impermeable.
• Silts, clay and mud have high porosity but low permeability due to the poorly connected pore spaces caused by the platy grains.
• Lithification is the process of converting loose, unconsolidated material into consolidated rock.
• Diagenesis is the changes that take place in a sediment after deposition, including the processes that cause lithification.
• Diagenesis occurs at low temperatures and low pressures, below 200dc and shallow depths, less than 200-300MPa.
• Burial and compaction are processes that occur as sediments become buried, the overlying weight increases and air and water are squeezed out, reducing porosity and causing the sediments to become compacted or reduced in volume.
• Grain fusion occurs as grains continue to be compacted and the edges are forced together and they fuse.
• Cementation from porewaters is minerals precipitating from porewaters around the edges of the grains to bind the sediment.
• Calcite, quartz and haematite are minerals that can precipitate from porewaters around the edges of the grains to bind the sediment.