Erosion and Diagenesis

• Grain Shape


  Roundness:

  Very Angular

  Angular

  Sub-Angular

  Sub-Rounded

  Rounded

  Well-Rounded
• Influence on Grain Shape / Size

  Length of Transport

  Physical Properties

  Chemical Properties
• Deposition


  occurs when current looses energy , larger particles are deposited first
• Clay is only deposited in still water
• Wind Blown dune sand In high energy environment

  Fine / Medium sand

  All Quartz, sometimes red due to iron oxide

  Well-rounded

  Very well sorted
• Ice deposited as glacial till in low energy environment

  Varies from Very coarse to very fine

  Varied; any rock fragments and clay

  Angular to sub angular

  Very poorly sorted
• River deposits of sand in channel, high energy

  Coarse to fine sand

  Quartz and mica with rock fragment

  Angular heat to source, sub-angular to sub-rounded downstream

  Poorly sorted near source, moderately sorted down-stream
• Beach - high energy

  Medium sand, sometimes coarse close to shore and on beaches

  Nearly all quartz, sometimes coarse shell or rock fragments

  Sub-rounded - rounded

  Moderately sorted
• Gravity

  Varies from very coarse to very fine

  Any rock fragments

  Angular - very angular

  Very poorly sorted
• Pores


  Small gaps (voids) between the grains and clasps in a sedimentary rock
• Permeability


  The capability of a rock or sediment to permit the flow of fluid through its pore spaces
• Lithification


  The physical change from loose sediment to solid rock
• Diagenesis


  the physical, chemical and biological changes that take place in a sediment after deposition
• Occurs at low temps and pressure
• Burial and Compaction


  Sandstone typically reduce in volume by 10% during compaction, whilst mudstone may reduce by as much as 50%
• Grain Fusion


  As burial and compaction continues grain edges are forced together and they fuse
• Cementation from Porewaters


  Minerals precipitate from porewaters around the edges of grains to bind sedimeent together

  Results in reduction of porosity