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Sedimentary Rocks "Settling"
- A.Sedimentary rocks form fromt he products of chemical and mechanical weathering
- B.Detrital Sediment
- 1.Particles derived primarily fromthe products of mechanical weathering
- C. Chemical Sediment
- 1. Ions and compounds in solution that derived from chemical weathering of rocks.
- 2. These ions and compounds eventually crystallize from solution to become solid particles
- D. Erosion
- 1. Removal and transportation of sediment by running water, wind, glaciers, or currents
- E. When the transporting agent loses energy, sediment is deposited
- F. Importance of sedimentary rocks
- 1. Oil and gas are trapped in sedimentary rocks
- 2. Two types of coal are classifed as sedimentary rocks
- 3.Sedimentary rocks preserve clues about ancient enviroments of deposition
- 4. Fossils are commonly preserved in sedimentary rocks
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Lithification
- A. The process of turning sediment into sedimentary rock
- B. Lithification may include
- 1. Compaction
- a. Weight of overlying sediment causes grains to compact more closely together
- 2. Cementation
- a. Minerals precipitate from solution in the pores spaces(openings) between grains
- b. Types of cements
- i. Quartz
- ii. Calcite
- iii. Iron oxide
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Detrital Sedimentary Rocks
- A. Form from the lithification of detital sediments
- B. Classified primarily by grain size
- C. Sorting
- 1. Well sorted-
- a. Grains that compose the rock are all about the same size
- b. Running water and wind
- 2. Poorly-sorted
- a. Grains that compose the rock are different sizes
- b. Glaciers
- D. Degree of rounding
- 1. Angular grains
- a. Indicate a short distance of trasnport
- 2. Well-rounded particles
- a. Indicate a long distance of transport
- E.Common minerals that compose detrital sedimentary rocks
- 1. Quartz
- 2. Feldspar
- 3. Clay minearls (derived from chemical weathering of feldspar minerals)
- F.Classification of Detrital Sedimentary
- 1. Conglomerate
- a. Composed of rounded, gravel sized grains
- b. May be found where energy is high -river beds
- 2. Breccia-composed of angular , gravel sized grains
- 3. Quartz Sandstone
- a. Composed of> 90 % quartz grains
- b. May form from beach or sand dune deposits
- 4. Arkose
- a. Sandstone composed of > 25% feldspar grains
- b.May form near granites that are weathering
- 5. Shale
- a. Composed of grains that are too small to see without magnification
- b. Fissile-splits along flat planes that reflect arrangement of platy clay-sized minerals
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Chemical Sedimentary Rocks
- A. Rocks formed as a result of lithification of chemical sediments
- B. Classified according to composition and grain size
- C. Classification of Chemical Sedimentary Rocks
- 1. Limestones- composed of calcium carbonate
- a. Travertine-limestone that is deposited in caves
- b. Coquina- limestone composed of visible shells and shell fragments that have been cemented together
- c. Chalk- limestone composed of microscopic calcareous (CaCO3) hard parts of marine plants and animals.
- 2. Chert-composed of the microscopic siliceous (SiO2) hard parts of marine and plants
- 3. Evaporites
- a. Composed of minearls that precipitate when bodies of water evaporate
- b. Rock salt-composed of halite
- c. Rock gypsum- composed of gypsum
- 4.Coal
- a. composed of altered plant material
- b. Coal forms in swampy enviroments where there is little / no oxygen in the water.
- c. Plant material only partially decays and goe through stages of alteration
- d. Peat
- i. partially altered plant material
- ii. Essentially the sediment stage of coal
- e. Lignite Coal
- i. When peat undergoes burial and compaction, it may alter to lignite coal
- ii. Soft brown coal
- f. Bituminous Coal
- i. If lignite coal undergoes further burial and compaction it may form bituminous coal
- ii. Soft black coal
- g. Anthracite Coal
- i. If bituminous coal undergoes metamorphism, it will alter to antracite coal
- ii. Hard black coal
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Sedimentary Structures
- A. Feature preserved in sedimentary rocks
- B. Sedimentary rocks are deposited in layers or beds
- C. Beds are separated by bedding planes
- 1. Flat planes that indicate the end of one episode of deposition and the beginning of another period of deposition
- D. Ripple Marks
- 1. Ridges on the surface of sedimentary rocks
- 2. Wave -formed ripples
- a. Formed by back and forth movement of waves
- b. Ripples are symmetrical in shape
- 3. Current ripples
- a. Formed by currents in rivers or oceans or by wind moving in one direction
- b. Ripples are asymmetrical in shape
- E. Cross-beds
- 1. Inclined layers of sand within a larger bed of rock
- 2. Sand dunes often exhibit cross-beds formed by changing wind directions
- F. Mud cracks- Form when clay- rich sediment dries and shrinks
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