Factors that Control Texture of Sedimentary Rocks

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Factors that Control Texture of Sedimentary Rocks

• Energy of Transporting agent
• Higher energy results in larger particle size and
  greater rounding of grains
• Distance of transport
• Greater distance sorts particles so that the
  coarser particles are deposited closer to the
  source and the finer particles are deposited
  farther from the source
• Rapidity of Deposition
• Rapid deposition results in less well-sorted
  sediment, while more even deposition, especially
  with reworking (as on a beach or in sand dunes),
  results in more well-sorted sediment
• Viscosity of Transporting Agent
• More viscous medium results in more poorly sorted
  angular sediment
• More fluid medium results in more well sorted,
  better rounded sediment

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Platteville Ls and Decorah Shale, Spring Grove, MN
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Sedimentary Environments
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Siliciclastic Sedimentary Rocks

• Rocks made of grains of quartz, feldspar and rock
  fragments
• Particles derived by weathering of pre-existing
  rocks
• Transported from source to basin of deposition,
  either on continents or in oceans
• Classified by grain size
• Composition of grains reveals source area (rock
  type, climate, and relief)
• Texture and nature of bedding (sedimentary
  structures) reveal transport and depositional
  history
• gt2mm Conglomerate (rounded grains) and Breccia
  (angular grains) - mostly rock fragments
• 2mm - 1/16mm Sandstone - mostly quartz and
  feldspar
• lt1/16mm Shale - mostly clay

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Conglomerate Swift Formation
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Conglomerate - Cretaceous, Blacks Beach
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Ripples on Bedding Surface - Sundance Fm
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Ripple marks - Sundance Fm
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Ripple Bedding - Franconia Fm
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Formation of Cross Bedding
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Cross Bedding in Jordan Formation, Homer, MN
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Bipolar cros bedding - Franconia
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Cross Bedding in Swift Fm.
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Bipolar ripple bedding, Swift Fm
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Bi-polar cross bedding - San Diego
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Pebbly Cross-bedded Sandstone, Mt. Davis, PA
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Intraclasts - Franconia Fm
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Sedimentary rocks - Blacks Beach
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Submarine Fan Channel Fill - Blacks Beach
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Turbidites - Point Loma, San Diego
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Turbidity Current Deposits, Point Loma, CA
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Graded Bedding
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Submarine Turbidity Current
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Burrows, St. Lawrence Fm., Homer, MN
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Great Sand Dunes, Colorado
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Braided River Deposition
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River and Floodplain
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Mississippi River Delta
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Nile River Delta
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Outer Banks, North Carolina
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Nags Head, Outer Banks, North Carolina
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Barrier Island and Lagoon, Galveston, Texas
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Lagoon at Low Tide
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South Padre Island, Texas
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Carbonate Rocks

• Classified by minerals present
• Calcite Ca(CO3) - Limestone
• Dolomite CaMg(CO3)2 - Dolostone
• Dolostones have crystalline textures (crystals
  interlock as in a mosaic)
• Limestones have either crystalline or clastic
  textures
• Clastic limestones are named according to grains
• Fossil fragments - Fossiliferous limestones
• Oolites (spherical sand sized grains of calcite
  with concentric laminations around a nucleus -
  oolitic limestones
• Intraclasts (fragments of limey sediment ripped
  from bed while still semi-soft) - Intraclastic
  limestones

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Oneota Dolomite, Homer, Minnesota
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Carbonate Sedimentation - Great Bahama Bank
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Coral Reefs and Lagoon, Bora Bora, South Pacific
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Carbonate Environments, Florida Keys
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Fossils - Decorah Limestone
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Oolites in thin section
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Stromatolites, Willow River Dolomite, Chatfield,
MN
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Facies and Stratigraphy
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Transgression, Regression, and Stratigraphy
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Stratigraphy in Southeastern Minnesota
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Minnesota Paleogeography
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Cross Section of Cambrian Strata