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

Clastic Rocks Classified by: Grain Size Grain Composition Texture

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

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

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 +

Clastic Terms LatinGreek GravelRuditePsephite SandArenitePsammite SiltLutitePelite

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)

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

Sandstone Terminology

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

Diagenesis

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

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

Tectonic Settings and Sediment

Lithic Sand, Washington

Lithic Sandsone, Washington

Molasse, Switzerland

Molasse and the High Alps

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

Diamictite, Ontario