GEO 11 - Sed Environments

• Mass of sedimentary rock which can be defined and distinguished from another by its geometry, lithology, sedimentary structure, paleocurrent patterns, and fossils


  facies

  
• Facies


  • Geometry
  • Lithology
  • Sedimentary structure
  • Paleocurrent patterns
  • Fossils

  
• Fossils lived where they were buried
• Habitat of fossils is deduced by their morphology
• Trace fossils are also used to define facies
• Terrestrial environments


  • Alluvial fans
  • Fluvial (rivers)
  • Lacustrine (lakes)
  • Paludal (marsh and swamps)
  • Aeolian (desert)
  • Glacial
• Transitional environments


  • Delta
  • Beach
  • Lagoon
  • Tidal flats
• Marine environments


  • Reef
  • Continental margin (slope, shelf, rise)
  • Abyssal plain

  
• Alluvial fans


  • Fan-view shape (top view)
  • Found in tectonically-active region
  • Formed by mudflow and debris flow
• Alluvium


  Freshly-eroded sediments
• Size and extent of alluvial fans depends on area of basin, climate, lithologies, and tectonic activity
• Alluvial fans


  • Poorly-sorted, coarse sediments due to proximity from source
  • Coarser sediments are found in the apex and fining towards the toe
• Fluvial


  Elongated bodies of water that flow though channels

  
• Fluvial systems are the most active transported of sediments
• Fluvial systems are dependent on energy and velocity (Hjulstrom diagram)
• Types of river channels


  • Meandering
  • Braided
  • Anastomosing
  • Straight

  
• Meandering rivers


  • Consist of a single channel and a thalweg (deepest point in a channel)
• Braided rivers


  • Consist of multiple bars and thalwegs within a single low sinuosity channel
  • Poorly sorted, coarse-sediments

  
• Anastomosing rivers


  • Multiple, interconnected, coexisting channel belts on alluvial plains
  • Laterally stable than braided channel
  • May consist of individual channels that may be braided, meandering, or straight

  
• Straight rivers


  • More of a hypothetical end member and not often found in nature
  • Low sinuosity index
  • May be produced by tectonic controls
• Drainage patterns


  • Dendritic
  • Trellis
  • Radial
  • Centripetal
  • Rectangular
  • Deranged
• Ephemeral lakes


  Land-locked body of standing water usually formed as a result of water filling depressions
• Depressions that form ephemeral lakes may be caused by subsidence, isolation due to sediment deposition, glacial erosion and deposition, volcanic processes, landslides, or meteorite impacts
• Lacustrine environments


  • May be freshwater or salt water
  • Good paleoclimate indicator
  • Special stratification - varves (alternating light and dark layers of sediments)
• Paludal environments


  • Constant flooding of water, organic material, and fine sediments
  • Wet climates near the equator and temperate higher latitudes
  • High organic content favorable for coal formation
• Aeolian


  Ability of the wind to shape the surface of the Earth (and other planets) by erosion, transportation, and deposition
• Deflation


  Removal of loose particle by the wind
• Abrasion


  Cannonading of rock and other surfaces by particles carried by the wind
• Deserts


  • Generally formed in areas with little to no rain (<250 mm/year)
  • Low precipitation - scarce vegetation
  • Scarce vegetation - high wind velocity

  
• Formation of deserts


  • By-product of global atmospheric circulation
  • Rain-shadow effect
  • Coastal deserts
  • Continental interior desert
  • Polar desert
• Aeolian sediment erosion and deposition

  • Ventifacts
  • Lag deposits
  • Desert pavement
  • Loess
  • Sand dunes

  
• Types of sand dunes


  • Barchan
  • Parabolic
  • Traverse
  • Linear/longitudinal
  • Star

  
• Glacial


  • Snow falls greater than which melts during summer
  • Permanent (on a human scale) body of ice that shows evidence of movement due to gravitational pull
• Glacial drift


  Sediment deposited as result of glacial erosion
• Glacial sediments are usually poorly sorted and varied in size

  
• Tillite


  Sedimentary rock formed from glacial till
• Transitional environments


  • Delta
  • Lagoon
  • Tidal flats
  • Beach
• Deltas


  • Formed when rivers empty into larger bodies of water
  • Shaped like Greek letter delta (Δ)
• Types of deltas


  • River-dominated
  • Tide-dominated
  • Wave-dominated
• River-dominated deltas


  • Significant sediment input from rivers
  • Protrude into the sea
  • Lobate in shape (moderate sediment supply)
  • Bird's foot shape (large sediment supply)