Sediment and Sedimentary Rocks

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Sediment and Sedimentary Rocks

• Physical Geology 3101

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Weathering and Erosion

• Weathering physical breakdown or chemical
  alteration of rocks at the surface
• Erosion Removal of material from the Earths
  surface

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Sediment

• Material transported across the earths surface

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Sediment sizes

• Size - Table 5.2
• gravel gt2mm
• sand 1/16 - 2 mm
• mud lt1/16
• silt 1/256-1/16
• clay lt1/256

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Processes

• Erosion
• Transportation - results in abrasion, rounding
  and sorting
• sediments become smoother, rounder, and better
  sorted
• Deposition

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Concept - Maturity

• Sediments that have a long history of weathering
  and transportation are mature

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Lithification

• Sediment is transformed into rock
• Compaction
• Cementation

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Sedimentary Rocks

• Rocks made from lithified sediments
• Particles or ions transported across the earths
  surface

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Classification

• Sedimentary rocks are classified by the particles
  that make them up
• Detrital sedimentary rocks
• Chemical sedimentary rocks

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Detrital Sedimentary Rocks - Table 5.3
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Group Exercise

• If you had a rock composed of well-sorted and
  well rounded quartz grains would that be mature?
• How would you classify the following sedimentary
  rocks?

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Processes

• Erosion
• Transportation - results in abrasion, rounding
  and sorting
• sediments become smoother, rounder, and better
  sorted
• Deposition

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Sediment sizes

• Size - Table 5.2
• gravel gt2mm
• sand 1/16 - 2 mm
• mud lt1/16
• silt 1/256-1/16
• clay lt1/256

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Rock Cycle
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Detrital Sedimentary Rocks - Table 5.3
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Chemical Sediments

• Carbonates - limestone
• biochemical
• fossiliferous limestone
• coquina
• chalk
• oolitic limestone
• evaporites
• rock salt
• gypsum

• other
• chert
• amber
• coal

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Question

• If I find a chunk of limestone (chemical
  sediment) in a gravel, is it a sedimentary rock?
• Is it a chemical or detrital sediment?

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Depositional Environment

• Depositional Environments
• layers, strata, beds
• sedimentary structures
• Bedforms
• ripples
• dunes
• Cross-bedding
• Fossils
• Trace Fossils

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Concept

• Sedimentary rocks reflect the environment of
  deposition
• Sequences and geometric relationships of rocks
  gives us insight into its origin and the
  environment in which they was formed

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Identifying a sequence
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Bedforms

• Regularly repeating features on the surface of
  sediment that is being moved.
• Ripples
• Dunes
• Identifies a sequence

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Detrital Sedimentary Rocks - Table 5.3
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Group Exercise

• A gravel is overlain by
• a sandstone containing dinosaur fossils, then
• a coal full of swamp plants, then
• a shale full of marine sediments
• What geologic events have happened here?
• What following processes are occurring on the
  next slide?

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Sedimentation