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Sedimentary Rocks

Sedimentary Rocks. Lithification of Sediments. Lithification – processes that turn sediments into sedimentary rocks. involves compaction and cementation. reduces volume of pores (void spaces between grains). "glues" sediment grains together. Lithification of Sediments. Fig. 5.8.

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Sedimentary Rocks

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  1. Sedimentary Rocks

  2. Lithification of Sediments • Lithification – processes that turn sediments into sedimentary rocks. • involves compaction and cementation. • reduces volume of pores (void spaces between grains). • "glues" sediment grains together.

  3. Lithification of Sediments Fig. 5.8 • Compaction: • rearrangement of grains • fragile grains crushed • due to weight of overlying sediments

  4. Lithification of Sediments • Cementation – precipitation of minerals in pore spaces. • Where do cementing minerals come from? cemented sandstone loose sand

  5. Classification of Sedimentary Rocks • Clastic sedimentary rocks classified based on grain size, sorting, and rounding. • Chemical sedimentary rocks classified based on mineral composition. Fig. 5.11 Fig. 5.12

  6. Clastic Rock Classification Fig. 5.10 • Grain size is related to energy of transport. • mountain stream, high energy, gravel • lake, low energy, clay Silt Clay Gravel Sand

  7. Clastic Rock Classification Fig. 5.10 • Sorting is related to variability of energy of transport. • high variability, poorly sorted • low variability, well sorted well poorly moderately

  8. Clastic Rock Classification Fig. 5.10 • Rounding is related to transport distance. • poorly rounded, short distance • well rounded, longer distance well poorly moderately

  9. Transport and Texture • Water (streams/rivers): • poorly to moderately sorted • well rounded • Water (lakes/oceans): • well sorted, silt and clay • well rounded Fig. 5.11

  10. Transport and Texture • Ice (glaciers): • very poorly sorted • poorly to well rounded • Wind: • well sorted, sand and silt • well rounded Fig. 5.9

  11. Chemical Rock Classification • Chemical sedimentary are usually monomineralic. Limestone – CaCO3 (calcite) Rock salt – NaCl (halite) Fig. 5.12 Fig. 5.12

  12. Depositional Environments • Texture (size, sorting, rounding), mineralogy, and sedimentary structures give clues to deposition.

  13. Depositional Environments • Mud cracks – indicate alternating wet and dry climate. Modern mud cracks Lithified mud cracks Fig. 5.15 Fig. 5.15

  14. Limestone indicates N.M. was once covered by shallow seas. Fig. 5.13 Depositional Environments • Limestone depositing in warm shallow seas today. Fig. 5.13

  15. Describe this rock in terms of grain size, sorting and rounding. What environment was this rock deposited in?

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