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Lithification/ Diagenesis

Lithification/ Diagenesis. From pile of sand to solid rock. Loose sediment, like that shown in (A) may someday become a rock like the one in (B) if compacted and cement fills the spaces between clasts. Diagenesis: How Sediment Becomes Rock.

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Lithification/ Diagenesis

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  1. Lithification/Diagenesis • From pile of sand to solid rock Loose sediment, like that shown in (A) may someday become a rock like the one in (B) if compacted and cement fills the spaces between clasts

  2. Diagenesis: How Sediment Becomes Rock • Diagenesis: collective term for all the chemical, physical, and biological changes that affect sediment as it goes from deposition through lithification Sand or other sediment, grains separate After compaction, grains crushed together and interlocked After cementation, mineral crystals cemented grains together

  3. Diagenesis: Processes Involved 1. Compaction - packingtogether of sediment grains When sediment has been deposited we start with a pile of fragments that enclose a great deal of pore space As sediment continues to accumulate the sediment undergoes compaction: the geometric arrangement of grains changes so that pore space is reduced In principle, compacted sediment can sit there forever without becoming a rock - normally this doesn't happen

  4. Diagenesis: Processes Involved 2. Desiccation – loss of water from sediment pore spaces Desiccation cracks

  5. ie. Desiccation and Compaction of Shale

  6. Diagenesis: Processes Involved 3. Cementation – ions precipitate out in the pore spaces to form a cement that binds clasts together

  7. ie. Compaction and Cementation of Sand

  8. Clastic Sedimentary Rocks Breccia Conglomerate Shale Sandstone

  9. Breccia Angular fragments

  10. Conglomerate Rounded particles & dissimilar lithologies

  11. Sandstone Sandstone Quartz Sandstone - > 90% qtz

  12. Mudstone Shale – fissile (layered) Claystone – not fissile (not layered)

  13. Non-Clastic Sedimentary Rock • Organic sediments • Sediment precipitates from solution in water originating from chemical and organic processes • These chemical precipitants settle to the bottom of a body of water. When first deposited, these sediments are loose and non-structured. In time, they are slowly hardened by compaction, cementation, and re-crystallization

  14. Non-Clastic Sedimentary Rock • Classified based on composition: • Siliceous Rocks • Carbonates • Evaporites

  15. Non-Clastic Sediments: Siliceous rocks Siliceous rocks - The siliceous rocks are those which are dominated by silica (SiO2) Chert - Palaeoindian projectile points Chert from Washademoak Lake, NB

  16. Non-Clastic Sediments: Carbonates Carbonates - The carbonate sedimentary rocks are formed through both chemical and biochemical processes Example: Limestone Chalk cliffs - Dover, England

  17. Non-Clastic Sediments: Evaporites Evaporites form from the evaporation of water (usually sea water or lake water) Example: Rock salt (halite) Rock salt forms as a result of changing physical conditions (increasing temperature), where minerals dissolved in seawater are precipitated when the water evaporates Bonneville Salt Flats of the Great Salt Lake, Utah.

  18. Non-Clastic Sedimentary Rocks Oolitic Limestone Fossiliferous Limestone Dolostone Chalk

  19. Non-Clastic Sedimentary Rocks Fossil Fuels Deposits • Found in areas of sedimentary rock formation • Basically, plant and animal remains were deposited in swamp and mud areas. • Result: Poor oxygen quality, hence they did not decay. • Overtime, they accumulated and then sands, silts and clay buried them • As lithification of the sediments took place, the organic remains beneath turned to valuable fossil fuels

  20. Fossil Fuel Deposits: Example Coal – made of organic matter which is the end product of large amounts of plant material buried for millions of years Coal bed,Trinidad

  21. Fossil Fuel Deposits: Example • Natural Gas and Oil Deposits • Drops of oil were scattered throughout source rocks • As source rock was squeezed, this oil becomes trapped in reservoirs / traps • These reservoirs make this an economic goldmine • Common characteristics for reservoir / trap • Source rock can be squeezed • Reservoir rock is porous and permeable • Cap rock is impermeable • Groundwater pushes the lighter gas and oil to the top • When a trap is tapped, an extreme amount of pressure is released • Think oil well

  22. Fossil Fuel Deposits: Common Trap Types • Structural traps hold oil and gas because the earth has been bent and deformed in some way.  The trap may be a simple dome (or big bump), just a "crease" in the rocks, or it may be a more complex. • Types: Anticline trap, Fault trap, Salt dome • Stratigraphic traps are depositional in nature.  This means they are formed in place, usually by a sandstone ending up enclosed in shale.  The shale keeps the oil and gas from escaping the trap. • Types: Stratigraphic (pinch out) trap

  23. Types of Traps

  24. Sedimentary Rock: Non- Metallic Industrial Mineral Deposits • Products of deposition, minerals in these rocks are non-metallic • Example: • Thick salt beds are the result of the movement of ocean water into basins. As the water evaporates due to desert-like conditions, the salt is left behind • These are Evaporites

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