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Clastic Sedimentary Rocks Derived from the Mechanical Breakup and Redeposition of Older Rocks.

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Presentation on theme: "Clastic Sedimentary Rocks Derived from the Mechanical Breakup and Redeposition of Older Rocks."— Presentation transcript:

1 Clastic Sedimentary Rocks Derived from the Mechanical Breakup and Redeposition of Older Rocks

2 Clastic Rocks Classified by: Grain Size Grain Composition Texture

3 The Wentworth Scale Phi (φ) = -log 2 (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

4 Particle Descriptions NamePhiDiameter mm Boulder< Cobble-6 to Pebble-2 to Granule-1 to Sand-2 to 41/ Silt4 - 81/ /16 Clay> 8< 1/256

5 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 TypeSedimentGrain Size ShaleClayless than mm SiltstoneSilt mm SandstoneSand.01-1 mm ConglomerateGravel1mm +

6 Clastic Terms LatinGreek GravelRuditePsephite SandArenitePsammite SiltLutitePelite

7 Super-Size Me Blair and McPherson, J. Sed. Res., v. 69, no. 1, Jan. 1999, p Block: 4-65 m (φ = -12 to -16) Slab: m (1 km) (φ = -16 to -20) Monolith: 1-33 km (φ = -20 to -25) Megalith: km (φ = -25 to -30)

8 Some Special Clastic Rock Types Arkose Feldspar-Rich Breccia Angular Fragments Graywacke Angular, Immature Sandstone

9 Sandstone Terminology

10 Maturity Stability of Minerals Rock Fragments Rounding or Angularity Sorting Removal of Unstable Ingredients - Mechanical Working

11 Diagenesis

12 Compaction Cementing Quartz Calcite Iron Oxide Clay Glauconite Feldspar Alteration Limestone - Dolomite Plagioclase – Albite Recrystallization Limestone

13 Tectonic Settings and Sediment Cratonic: Mature sandstone Continental slope: Graywacke, turbidite Trench: Wildflysch (contorted graywacke) Post-orogenic basin: Molasse (red sandstone and conglomerate)

14 Tectonic Settings and Sediment

15 Lithic Sand, Washington

16 Lithic Sandsone, Washington

17 Molasse, Switzerland

18 Molasse and the High Alps

19 Conglomerates Clast Supported vs. Matrix Supported Polymictic (Outwash, alluvial fans, flood plains) Oligomictic (Lag deposits) Diamictic (Tills, Glacio-marine, Submarine Landslides)

20 Diamictite, Ontario


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