Deltas Flashcards
1
Q
Why do deltas form?
A
- Form where flowing water enters relatively still water
- Loss of velocity results in deposition of sediment
- Max deposition at river mouth which can expand lengths of channel and shallows gradient so you get avulsion
2
Q
Zones of deposition in a delta:
A
- Deltas are made up of 3-4 different zones
- Delta plain domainated by river/floodplain processes - flat line dip
- Delta front dominated by shoreline and river mouth - lip dip
- Delta slope dominated by slope + slumping - dipping down hill
- Prodelta dominated by ocean/lake floor with occasional slope processes - flattening out dip
3
Q
Delta Slope
A
- Get lots of slumps, sediment, gravity flows, and mud diapirs/dikes on slope
4
Q
Delta Plain = fluvial system
A
- Will have some depositional facies
- low gradient = meandering
- Steep gradient = braided
- Primarily river processes -> all deltas have a river feeding it
5
Q
Delta front = river mouth processes
A
- Zone of maximum deposition
- Competing processes of river flow, waves and tides
- specific to deltas
- current from channels
- If entering ocean it will meet wave processes that will redistribute sediment from oscillatory movement
- Tide-dominated might take sediment and redistribute it with tidal currents
- Current - if there is no active processes in water body
- Most of deposition is occurring at the river mouth
6
Q
Delta types by dominant delta front processes:
A
- Fluvial
- Waves
- Tides
7
Q
River dominated deltas:
A
- Loss of velocity so deposition of sediment
- Fan shaped
- Deposition at river mouth
- Forms a bar at the river mouth so channel splits again and again
- Channel avulses
- Advancement of delta front outwards over time
- Have swamps etc along low lying shorelines
8
Q
Typical Stratigraphy from a fluvially dominated prograding delta
A
- Land develops and you get roots, river avulses and it becomes swampy until it moves back the process restarts
