clastic sedimentary rocks derived from the mechanical breakup and redeposition of older rocks
TRANSCRIPT
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Clastic Sedimentary Rocks
Derived from the Mechanical Breakup and Redeposition of Older Rocks
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Clastic Rocks
Classified by:• Grain Size • Grain Composition • Texture
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The Wentworth Scale
• Phi (φ) = -log2(Diameter in mm)
• Best way to remember:–1mm: φ = 0–φ increases as diameter decreases– Every factor of 2 change in diameter = one
step in φ
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Particle Descriptions
Name Phi Diameter mmBoulder < -8 256 +Cobble -6 to -8 64 - 256Pebble -2 to -6 4 - 64Granule -1 to -2 2 - 4Sand -2 to 4 1/16 - 2Silt 4 - 8 1/256 - 1/16Clay > 8 < 1/256
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Sediment Sizes and Clastic Rock Types
Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks.
Rock Type Sediment Grain Size
Shale Clay less than 0.001 mm
Siltstone Silt .001-0.1 mm
Sandstone Sand .01-1 mm
Conglomerate Gravel 1mm +
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Clastic Terms
Latin Greek
Gravel Rudite Psephite
Sand Arenite Psammite
Silt Lutite Pelite
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Super-Size Me
• Blair and McPherson, J. Sed. Res., v. 69, no. 1, Jan. 1999, p. 6-19.
• Block: 4-65 m (φ = -12 to -16)• Slab: 65-1000 m (1 km) (φ = -16 to -20)• Monolith: 1-33 km (φ = -20 to -25)• Megalith: 33-1000 km (φ = -25 to -30)
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Some Special Clastic Rock Types
• Arkose Feldspar-Rich • Breccia Angular Fragments • Graywacke Angular, Immature
Sandstone
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Sandstone Terminology
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Maturity
• Stability of Minerals • Rock Fragments • Rounding or Angularity • Sorting
Removal of Unstable Ingredients - Mechanical Working
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Diagenesis
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Diagenesis
CompactionCementing• Quartz • Calcite • Iron Oxide • Clay • Glauconite • Feldspar
Alteration• Limestone - Dolomite • Plagioclase – AlbiteRecrystallization• Limestone
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Tectonic Settings and Sediment
• Cratonic: Mature sandstone• Continental slope: Graywacke, turbidite• Trench: Wildflysch (contorted graywacke)• Post-orogenic basin: Molasse (red sandstone
and conglomerate)
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Tectonic Settings and Sediment
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Lithic Sand, Washington
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Lithic Sandsone, Washington
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Molasse, Switzerland
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Molasse and the High Alps
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Conglomerates
• Clast Supported vs. Matrix Supported• Polymictic (Outwash, alluvial fans, flood
plains)• Oligomictic (Lag deposits)• Diamictic (Tills, Glacio-marine, Submarine
Landslides)
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Diamictite, Ontario