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Strata

Strata. Sedimentary Rocks. Sedimentary rocks are formed from the breaking apart of other rocks (igneous, metamorphic, or sedimentary rocks) and the cementation, compaction and recrystallization of these broken pieces of rock. They can also be rocks formed from sediments or solutions.

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Strata

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  1. Strata

  2. Sedimentary Rocks • Sedimentary rocks are formed from the breaking apart of other rocks (igneous, metamorphic, or sedimentary rocks) and the cementation, compaction and recrystallization of these broken pieces of rock. • They can also be rocks formed from sediments or solutions

  3. Where does sediment come from ? Geological processes that make and destroy rock: • Weathering breaks rock down into fragments called sediment • Water • Wind • Ice • Heat • Erosion is the carrying of that broken up rock or sediment by: • Water • Wind • Ice • Gravity • Deposition is the process by which sediment is dropped and comes to rest

  4. Two actions turn sediment into rock: • Compaction: sediment is squeezed together by the weight above • Cementation: the sediment is “glued” together by mineral material crystallizing between the grains • Two common cement minerals are quartz and calcite

  5. Classification of Sedimentary Rocks Sedimentary rocks are classified by the way in which they form: • Clastic Rocks- Made of the fragments of previously existing rocks • Organic Rocks- Come from organisms • Chemical Rocks- Formed by inorganic processes such as evaporation

  6. Clastic (Detrital) Rocks • Clastic sedimentary rocks are formed from pieces of sediment cemented together. Examples of clastic rocks: • Sandstone is a clastic rock made of sand-sized grains. • Shale is made of fine, mud-sized grains of sediment. • The grain is so fine that is shows the fine details of fossils. • Shale forms in very still water, as in a lake, swamp or • calm sea. Only in still water can very fine sediment deposit. • Conglomerate is made of pebbles and is coarse • textured.

  7. Clastic Rocks Conglomerate Breccia

  8. Clastic Rocks • Mudstone • Conglomerate • Sandstone

  9. Chemical Sedimentary Rock • Rocks formed when minerals dissolved in water come out of solution • Examples: • Gypsum • Limestone • Halite

  10. Chemical Rocks Gypsum Halite Limestone

  11. Organic Sedimentary Rocks • Some examples: • Coal – formed from partially decomposed plant material • Chalk • Limestone - • Rocks made from the remains of once-living organisms • Limestone is formed when pieces of shells from sea • creatures build up, get compacted and cemented to • form stone. • Shells or parts of them may be visible as fossils.

  12. Organic Rocks • Limestone Fossiliferous Limestone Coquina

  13. Sedimentary Features • Fossils: any traces or remains of once living organisms • Strata: layers in sedimentary rock • oldest layers are generally lower • They can tell us what organisms lived • And what kind of environment was there • Mud cracks: which indicate that the mud was sometimes dried out • Ripple marks: which tell that water or wind was moving over the sediment

  14. Features Fossils Ripple Marks Mud Cracks

  15. Grand Canyon • http://www.nature.nps.gov/views/layouts/Main.html#/GRCA/geology/ • http://www.nps.gov/grca/photosmultimedia/fly-through.htm

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