Sedimentary & Metamorphic Rocks


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Sedimentary & Metamorphic Rocks

  1. 1. Sedimentary Rocks
  2. 2. Sedimentary Rocks <ul><li>Sediments = pieces of solid material deposited on the Earth’s surface. </li></ul>
  3. 3. Sedimentary Rock <ul><li>Rocks that are composed of the weathered remains of preexisting rock, or plant and animal remains. </li></ul><ul><li>Sedimentary rocks commonly originate from sediments laid down in horizontal strata by water or wind. </li></ul>
  4. 4. Horizontal Beds of Sedimentary Rock Beds Bedding planes
  5. 5. Sedimentary Rocks <ul><li>How is a sedimentary rock formed? </li></ul><ul><ul><li>Sediments get compacted and cemented together. </li></ul></ul>
  6. 6. Deposition Compaction Cementation
  7. 7. Sedimentary Rocks <ul><li>Clastic – made from fragments of other rocks, that have been transported, deposited, then compacted and cemented together. </li></ul><ul><ul><li>Shale, sand, conglomerate, siltstone, breccia </li></ul></ul><ul><ul><li>Classified by the size of the fragments in the rocks </li></ul></ul>
  8. 8. Cemented Rocks <ul><li>Clastic sedimentary rock – rocks composed of weathered sediments: </li></ul><ul><ul><li>Pebbles or gravel – usually quartz </li></ul></ul><ul><ul><li>Sand – usually quartz </li></ul></ul><ul><ul><li>Clay and silt – weathered feldspars and mica : </li></ul></ul><ul><li>held together by a natural cement </li></ul><ul><ul><li>or by compaction of clay and silt. </li></ul></ul>
  9. 9. Conglomerate – cemented sand, silt, and pebble sediments. If large fragments are angular this rock is called a breccia. Sandstone – cemented quartz sand grains. Feels gritty. Unfilled spaces between grains make most sandstones porous and permeable to water.
  10. 10. Shale – clay and silt sized particles lithified by dehydration and compaction. Note the cleavage at bedding planes. Thumps when you tap it with a nail and, moistened, it smells like damp earth. Bedding planes
  11. 11. Sandstone in the Pinnacle Desert, Australia Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  12. 12. Sedimentary Rocks <ul><li>Chemical – formed when minerals fall out of solution. From evaporation of salt water or from chemical reactions. </li></ul><ul><ul><li>Rock salt, rock gypsum, some limestones </li></ul></ul>
  13. 13. Chemical Sedimentary Rock <ul><li>Rocks formed either as precipitates or as evaporites of dissolved chemical sediments. </li></ul><ul><li>Mineral salts that accumulate in water become concentrated by evaporation until they precipitate from solution, or </li></ul>
  14. 14. Rock salt , the mineral halite (NaCl), left as an evaporite as a shallow sea evaporated. Alabaster , the mineral gypsum (CaSO 4 ), also an evaporite.
  15. 15. Compact (or precipitate) limestone , the mineral calcite (CaCO 3 ), precipitated from sea water as evaporation increased concentration. Many cavern systems are formed in this type of limestone.
  16. 16. Sedimentary Rocks <ul><li>Organic Rocks – formed from the remains of plants and animals. </li></ul><ul><ul><li>Shells of marine animals pile up, compact and cement to create fossiliferous limestone (coquina). </li></ul></ul><ul><ul><li>Sedimentary rocks are the only rocks that contain fossils </li></ul></ul>
  17. 17. Coquina – cemented aggregate of geologically modern shell fragments. Fossiliferous limestone – a cemented aggregate of original shell fragments, molds, and casts of ancient marine organisms. Note fossil mold of a shell in this specimen.
  18. 18. Peat , a mass of matted together plant material covered by H 2 O, which impedes decay. H 2 and O 2 are lost, concentrating carbon. Lignite , so called “brown coal”, a soft coal that forms when peat is compressed and aged, about 40% carbon.
  19. 19. Bituminous coal – soft coal formed when lignite is compacted and altered for millions of years, about 85% carbon, this coal is the most commonly mined and used for a fuel.
  20. 20. Sedimentary Rock Features <ul><li>Features in sedimentary rock that reflect the sedimentary environment. </li></ul><ul><li>Not found in other rock types. </li></ul><ul><li>Features: </li></ul><ul><ul><li>Stratification </li></ul></ul><ul><ul><li>Fossils </li></ul></ul><ul><ul><li>Ripple marks & crossbeds </li></ul></ul><ul><ul><li>Mud cracks </li></ul></ul><ul><ul><li>Nodules, concretions & geodes </li></ul></ul>
  21. 21. Rock Stratification (layering) Bryce Canyon, UT Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  22. 22. Ripple marks caused by wave action on the sandy bottom of a shallow bay Almost identical ripple marks on the surface of a sandstone millions of years old.
  23. 23. Mud cracks in drying mud Mud cracks preserved on the bedding surface of a shale.
  24. 24. Groundwater dissolves hollow spaces in sedimentary rock, typically limestone, and mineral material is deposited inside the hollow with crystal points growing toward the center. Geode Thunder Egg
  25. 25. Cross-bedding at Checkerboard Mesa Zion National Park, UT Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  26. 26. Dinosaur skeleton preserved in sedimentary rock - China Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  27. 27. Metamorphic rocks
  28. 28. <ul><li>Metamorphic rocks are formed a few kilometers below the earth’s surface and extend into the upper mantle </li></ul><ul><li>2 types of metamorphism </li></ul><ul><ul><li>Contact - when magma forces its way into the rock </li></ul></ul><ul><ul><li>Regional -results in large scale deformation of rock, usually takes place during mountain building </li></ul></ul>
  29. 29. <ul><li>Agents of metamorphism </li></ul><ul><ul><li>Heat - the most important agent because it drives the energy needed for a chemical reaction </li></ul></ul><ul><ul><li>Pressure - results in a more compact rock </li></ul></ul><ul><ul><li>Hydrothermal solution- very hot water based solution. When solution comes in contact with rock it will dissolve crystals and deposit new ones (only agent that changes the overall chemical composition of rock) </li></ul></ul>
  30. 30. <ul><li>Metamorphic rocks are classified by texture </li></ul><ul><ul><li>2 types </li></ul></ul><ul><ul><ul><li>Foliated-minerals recrystallize at right angles to the direction of the force, rocks are said to be folded or have bands that go around rocks </li></ul></ul></ul><ul><ul><ul><ul><li>Example- Gneiss and Schist </li></ul></ul></ul></ul><ul><ul><ul><li>Nonfoliated-rocks that does not have banded texture </li></ul></ul></ul><ul><ul><ul><ul><li>Examples- marble, quartzite, and anthracite </li></ul></ul></ul></ul>
  31. 31. <ul><li>Foliated Metamorphic Rock </li></ul><ul><li>Example- gneiss </li></ul><ul><li>Nonfoliated Metamorphic rock </li></ul><ul><li>Example- marble </li></ul>