Fluvial Environments

• • High Energy (-flood plains)
  • During flooding even small streams can carry large boulders
  • Dry conditions - less water so energy lower
• Alluvial Fan:

  Mountain streams flow onto a flat Valley.

  Sudden decrease in gradient and Stream velocity

  Breccia - Across the back of the fan e.g due to flash flooding or from scree

  Conglomerate - Deposited in Streams. Moderately Sorted

  Arkose Sandstone - Further from the mountain. Smaller grains so transported further (granite makes up lots of mountain range - plenty of feldspar)
• Meandering Rivers:

  Channel migrates laterally. Moderately-well sorted, Sun-rounded.

  • Conglomerates: In River itself, - over a large area if flooding
  • Sandstones: From point bar (river beach) deposits
  • Clay/Mudstone - low energy floodplain
  • Muscovite and Quartz
  • Fossil tree trunk/branches in the form of lignite
  • Imbricate Structure
  • Cross Bedding
• Flood Plain Clays and Silts:

  During Floods, clay rich in organic material are deposited from the suspended load of the river.

  Siltstone

  Mudstone May have dessication cracks - any fossils terrestrial
• Braided River:

  • Semi-arid areas where discharge is low
  • Wide channels, mostly transported by reaction or saltation
  • Banks of Sand/Gravel deposited when river looses energy
  • Cross Bedding fining upwards
• Delta Environment:

  (Where River Meets Ocean)

  • If little wave action then sediment will be deposited in the mouth of the river due to loss of energy and build up over time
  • Over time the channel gets blocked and river splits into new distributary channels
  • Find Swampy Islands in between - lots of vegetarians of in tropics, main source of coal
• Topsets

  Islands -> Mudstone, Coal

  Channel -> Sandstone, Arkose

  Pebble -> Conglomerate
• Foresets

  Sandstone -> Possibly Siltstone

  Cross Bedding (asymetrical ripple marks)
• Bottomsets

  Siltstone/Mudstone
• Cyclothem


  Shows an upwards coarsening sequence

  Represent a delta building out to sea