Sedimentary & Metamorphic Rocks
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Sedimentary & Metamorphic Rocks

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Sedimentary & Metamorphic Rocks Sedimentary & Metamorphic Rocks Presentation Transcript

  • Sedimentary Rocks
  • Sedimentary Rocks
    • Sediments = pieces of solid material deposited on the Earth’s surface.
  • Sedimentary Rock
    • Rocks that are composed of the weathered remains of preexisting rock, or plant and animal remains.
    • Sedimentary rocks commonly originate from sediments laid down in horizontal strata by water or wind.
  • Horizontal Beds of Sedimentary Rock Beds Bedding planes
  • Sedimentary Rocks
    • How is a sedimentary rock formed?
      • Sediments get compacted and cemented together.
  • Deposition Compaction Cementation
  • Sedimentary Rocks
    • Clastic – made from fragments of other rocks, that have been transported, deposited, then compacted and cemented together.
      • Shale, sand, conglomerate, siltstone, breccia
      • Classified by the size of the fragments in the rocks
  • Cemented Rocks
    • Clastic sedimentary rock – rocks composed of weathered sediments:
      • Pebbles or gravel – usually quartz
      • Sand – usually quartz
      • Clay and silt – weathered feldspars and mica :
    • held together by a natural cement
      • or by compaction of clay and silt.
  • 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.
  • 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
  • Sandstone in the Pinnacle Desert, Australia Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  • Sedimentary Rocks
    • Chemical – formed when minerals fall out of solution. From evaporation of salt water or from chemical reactions.
      • Rock salt, rock gypsum, some limestones
  • Chemical Sedimentary Rock
    • Rocks formed either as precipitates or as evaporites of dissolved chemical sediments.
    • Mineral salts that accumulate in water become concentrated by evaporation until they precipitate from solution, or
  • Rock salt , the mineral halite (NaCl), left as an evaporite as a shallow sea evaporated. Alabaster , the mineral gypsum (CaSO 4 ), also an evaporite.
  • 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.
  • Sedimentary Rocks
    • Organic Rocks – formed from the remains of plants and animals.
      • Shells of marine animals pile up, compact and cement to create fossiliferous limestone (coquina).
      • Sedimentary rocks are the only rocks that contain fossils
  • 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.
  • 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.
  • 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.
  • Sedimentary Rock Features
    • Features in sedimentary rock that reflect the sedimentary environment.
    • Not found in other rock types.
    • Features:
      • Stratification
      • Fossils
      • Ripple marks & crossbeds
      • Mud cracks
      • Nodules, concretions & geodes
  • Rock Stratification (layering) Bryce Canyon, UT Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  • 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.
  • Mud cracks in drying mud Mud cracks preserved on the bedding surface of a shale.
  • 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
  • Cross-bedding at Checkerboard Mesa Zion National Park, UT Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  • Dinosaur skeleton preserved in sedimentary rock - China Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL
  • Metamorphic rocks
    • Metamorphic rocks are formed a few kilometers below the earth’s surface and extend into the upper mantle
    • 2 types of metamorphism
      • Contact - when magma forces its way into the rock
      • Regional -results in large scale deformation of rock, usually takes place during mountain building
    • Agents of metamorphism
      • Heat - the most important agent because it drives the energy needed for a chemical reaction
      • Pressure - results in a more compact rock
      • 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)
    • Metamorphic rocks are classified by texture
      • 2 types
        • 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
          • Example- Gneiss and Schist
        • Nonfoliated-rocks that does not have banded texture
          • Examples- marble, quartzite, and anthracite
    • Foliated Metamorphic Rock
    • Example- gneiss
    • Nonfoliated Metamorphic rock
    • Example- marble