Sedimentary Rocks/EPCC/LM5 B

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Sedimentary Rocks/EPCC/LM5 B

  1. 1. Chapter 7: Sediments andChapter 7: Sediments and Sedimentary RocksSedimentary Rocks
  2. 2. Sedimentary RocksSedimentary Rocks Two Categories:Two Categories: Clastic(Detrital) and ChemicalClastic(Detrital) and Chemical
  3. 3. Sedimentary RocksSedimentary Rocks • Clastic ( or detrital) sedimentary rocks reflect several processes. – Weathering – Generation of detritus via rock disintegration. – Erosion – Removal of sediment grains from rock. – Transportation – Dispersal by wind, water and ice. – Deposition – Accumulation after cessation of transport. – Lithification – Transformation into solid rock. • Burial – Continued deposition buries sediments. • Compaction – Squeezing by the weight overlying material. • Cementation – Grains “glued” by pore-filling minerals.
  4. 4. Sediments In The Rock CycleSediments In The Rock Cycle • Sediments are transported by: – Water. – Ice. – Wind. – Gravity. • The transport and deposition of sediments are initial phases of the rock cycle. • The ultimate fate of most sediment is burial and conversion to sedimentary rock.
  5. 5. Sediments Types AndSediments Types And CharacteristicsCharacteristics • Three broad classes: – Clastic sediment is loose fragments of rock debris produced by physical weathering. – Chemical sediment precipitates from solution in water. – Biochemical/Biogenic/Bioclastic sediment is composed of the fossilized remains of plants or animals.
  6. 6. Characteristics of ClasticCharacteristics of Clastic Sediment (1)Sediment (1) • Clastic sediment is divided into four main size classes: – Gravel and larger ( 2mm and larger) – Sand (0.0625 to 2 mm) – Silt (0.0625 to 0.0039 mm) – Clay (less than 0.0039 mm)
  7. 7. Characteristics of ClasticCharacteristics of Clastic Sediment (2)Sediment (2) • Gravel is subdivided into: – Boulder gravel. – Cobble gravel. – Pebble gravel.
  8. 8. SortingSorting • Sorting identifies sediment in terms of the variability in the size of its particles. – Poorly sorted (wide range of particle size), – Well sorted (range is small). • Changes of grain size typically result from fluctuations in the velocity of the transporting agent, such as water or wind.
  9. 9. Figure 7.2 Sorting in Sediments
  10. 10. Figure 7.4 Sorting, rounding and sphericity
  11. 11. SortingSorting • The greater the speed and energy involved, the larger or heavier are the particles that can be transported.
  12. 12. SortingSorting • Nonsorted sediment is a mixture of different sizes arranged chaotically. – Till is a nonsorted sediment of glacial origin. • Smooth and rounded particles are transported by water or air.
  13. 13. TransportTransport • Sediments move by air, wind, rain, water, organisms - With increasing transport, average grain size decreases.
  14. 14. Sedimentary RocksSedimentary Rocks Chemical/BiochemicalChemical/Biochemical
  15. 15. Characteristics of ChemicalCharacteristics of Chemical SedimentsSediments • Chemical sediments are formed by precipitation of minerals from solution in water. • They form in two principal ways: – Through biochemical reactions resulting from the activity of plants and animals in the water. – Inorganic reactions in the water. • When water from a hot spring cools, it may precipitate opal (a hydrated silicate) or calcite (calcium carbonate).
  16. 16. Some Chemical SedimentarySome Chemical Sedimentary RocksRocks
  17. 17. SaltsSalts • Evaporation of sea water or lake water forms salts. • Lake waters precipitate sodium carbonate (Na2CO3), sodium sulfate Na2SO4), borax (Na2B4O7.10H2O),and trona (Na2CO3.NaHCO3.2H2O).
  18. 18. Biochemical/BiogenicBiochemical/Biogenic SedimentsSediments • Biogenic sediments contain fossils. • If the remains are broken and scattered it is bioclastic sediment.
  19. 19. Depositional EnvironmentsDepositional Environments
  20. 20. Sedimentary or DepostionalSedimentary or Depostional EnvironmentsEnvironments • Each environment will have distinctive physical, chemical, and biological characteristics.
  21. 21. Figure 7.14
  22. 22. Sediments to RocksSediments to Rocks How do we do this?How do we do this?
  23. 23. How Sediment Becomes RockHow Sediment Becomes Rock • Lithification is the overall process of creating sedimentary rock.
  24. 24. How Sediment Becomes RockHow Sediment Becomes Rock • Processes involved include: – Compaction. • As the weight of an accumulating sediment forces the grains together. The pore space is reduced. – Cementation. • Substances dissolved in water precipitate to form a cement that binds the sediment grains together.
  25. 25. What do we call theseWhat do we call these rocks?rocks?
  26. 26. Clastic Sedimentary RocksClastic Sedimentary Rocks • The four basic classes of clastic sedimentary rocks are: – Conglomerate/Breccia, a lithified gravel. – Sandstone, consisting mainly of sand grains. – Siltstone, composed mainly of silt-size mineral fragments, commonly quartz and feldspar. – Mudstone, still-finer grain size.
  27. 27. Figure 7.24A
  28. 28. Figure 7.24B
  29. 29. Figure 7.24C
  30. 30. Chemical Sedimentary RocksChemical Sedimentary Rocks • Chemical sedimentary rocks result from Lithification of organic or inorganic chemical precipitates.
  31. 31. Figure 7.27B
  32. 32. Figure 7.27C
  33. 33. Rock Salt Rock Gypsum
  34. 34. Figure 7.27D Chert
  35. 35. Sedimentary StructuresSedimentary Structures Clues to the EarthClues to the Earth
  36. 36. Environmental clues inEnvironmental clues in sedimentary rockssedimentary rocks • Sedimentary rocks reflect the environment in which they were formed. • Clues from bedding planes. – Ripples marks preserved in sandstones and siltstones. – Footprints, trails, and raindrop impressions.
  37. 37. Clues in the RocksClues in the Rocks • Clues from fossils. – Some animals and plants are restricted to warm, moist climates, whereas others are associated only with cold, dry climates.
  38. 38. Figure 7.30 Ripples
  39. 39. Figure 7.31 Mud cracks
  40. 40. Crossbedding
  41. 41. Layering and fining upward
  42. 42. Tilted Bedding or strata
  43. 43. Trace Fossil Trace Fossil from Mt Cristo Rey
  44. 44. Where do we go next?Where do we go next? • Metamorphic Rocks

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