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Sedimentary

Sedimentary. Sediments are formed from existing rocks being weathered, eroded, and deposited. Sedimentary rocks form from these sediments becoming pressed (compacted) and/or cemented together, or when sediments precipitate out of solution.

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Sedimentary

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  1. Sedimentary • Sediments are formed from existing rocks being weathered, eroded, and deposited. • Sedimentary rocks form from these sediments becoming pressed (compacted) and/or cemented together, or when sediments precipitate out of solution

  2. Sedimentary rocks are made from loose material such as rock fragments, mineral grains, and bits of plants and animal remains (fossils) that have been moved by wind, water, ice or gravity. Sedimentary Rocks

  3. Sedimentary Rock • Sedimentary Rocks are formed at or near the Earth’s surface • No heat and pressure involved • Strata – layers of rock • Stratification – the process in which sedimentary rocks are arranged in layers

  4. There are three types of Sedimentary Rock • Clastic • Chemical Sedimentary • Biochemical (organic) Sedimentary

  5. Clastic Sedimentary Rocks They are formed from fragments of existing rocks. They are also called detrital which means “to wear away”. • Gravel2mm • Sand1/16 mm • Mud - Silt1/256 mm • Mud - Clay

  6. Clastic Sedimentary Rock Clastic – made of fragments of rock cemented together with calcite or quartz Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together.

  7. How are sediments held together? • Particles are held together by compaction and/or cementation. • Compaction: process that squeezes or compacts sediments • Cementation: when dissolved minerals are deposited in tiny spaces among sediments binding them together into a solid mass • Lithification is the process of compaction and cementation. Rocks are weathered, transported, compacted and cemented.

  8. Chemical Sedimentary Rocks • From dissolved minerals in evaporating seas. • Chemical sedimentary – minerals crystallize out of solution to become rock • Examples are limestone and rock salt. Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris.

  9. Organic Sedimentary Rocks coquina • From the remains of organisms- plants and animals • Shell fragments, leaves, coral, etc. • Examples are: • Coal from plants • Coquina from whole shell fragments • Limestone from microscopic animals with CaCO3 skeletons Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment.  Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels. 

  10. Sedimentary Rock Features Ripple marks shows rock formed in water environment Mud cracks show that rock formed in dry environment http://www.drbateman.net/gcse2003/gcsesums/modsum9/bird.gif

  11. Sedimentary Rock Features Strata- each layer records period of deposition. If undisturbed- younger rocks are close to surface. Fossils are not destroyed by compaction and cementation, but preserved http://www.drbateman.net/gcse2003/gcsesums/modsum9/bird.gif

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