Sequence Stratigraphy Flashcards
What two processes control the coast?
Accommodation vs. Sediment Supply
Can move from a delta to an estuary by changing the balance between accommodation creation (aka sea level rise) and sediment supply (sand and mud input).
Draw the Turner. A Diagram that displays accommodation vs sediment supply
What is Accommodation?
The space available for potential sediment to accumulate.
How does accommodation relate to sea level rise?
If the sea level rises, then the space available becomes bigger. If the sea level falls, then the space available becomes smaller.
What is an example of accommodation subsidence?
Mississippi Delta & Norfolk - land is sinking due to fluids being pumped out.
If we create accommodation faster than can be filled…
then shoreline will move in a landward direction. Happens when we experience really high levels of sea-level rise or very low rates of deposition/transgression.
Regression is the opposite. Either falling sea level or high rates of deposition (sea level rise is outpaced by the amount of sediment being deposited).
Avulsion
The rapid abandonment of a river channel and the formation of a new river channel.
Why does avulsion occur?
The new channel slope is steeper and essentially more efficient than the current channel.
Coastal Retrogradation
- Transgression
- Landward movement of a shoreline.
How can we tell if a coastline has gone through coastal retrogradation?
Sediment core will show that environments found adjacent to each other will also have the ability to stack on top.
In the case of coastal retrogradation, you would find upland → Marsh→ Lagoon→ March→ Barrier
How could you tell if a shoreline is through a coastal progradation process?
Coarsening Upward Sequence within the sediment core.
offshore (finer sediments) at the bottom → Shoreface(medium sediments) middle → beach sediment (coarse) at the top.
Coastal Progradation
Regression - Shoreline moving seaward
A beach that has built out over its own shoreface which then has built out over its own offshore deposits.
How would you draw and shoreline that is going through normal regression- rising RSL?
Rising RSL -> Would not have a smooth transition between type of sediment.
What do you get when accommodation creation < sediment supply?
Normal Regression: Rising Relative Sea Level
depositional feature example: deltas
What are the various types of stacking patterns associated with regression or coastal progradation?
- Normal Regression - Rising RSL
- Normal Regression - Constant RSL
- Forced Regression - falling RSL
What do you get when accommodation creation = sediment supply?
Normal Regression - Constant Relative Sea Level
Wave dominated delta
Draw a Normal Regression - Constant RSL diagram
Constant RSL -> Smooth transition between type of sediment
What do you get when accommodation creation > sediment supply?
Forced Regression: falling relative sea level
How would you draw a shoreling that is undergoing a forced regression?
Falling RSL -> Never get gravel
Wy are the various stacking patterns important?
What is adjacent will stack vertically, a core sample will show how the shoreline changed over time.
Draw a transgressive shoreline
Draw a regressive shoreline
What is the basis of sequence stratigraphy?
The shifting of regressions to transgression.
Walther’s Law of Facies Succession
Sediments from depositional environments found adjacent to one another will accumulate vertically stacked atop one another when the shoreline shifts.
What are the two important concepts related to sequence stratigraphy?
- This is how continental shelves are built
- This is how we can track sea level
System Tracts
Stratigraphic units that were deposited at the same general time during phases of the sea-level cycle
- This idea of how to get sediment to form a continental rise vs a continental shelf.
Highstand System Tract (HST)
- occurs during progradation
- Sediment supply > RSL
Falling Stage System Tract (FSST)
Relative Sea Level is falling - forced regression
Lowstand Systems Tract (LST)
Sea level fall slows and is eventually exceeded by subsidence (mud sinking)
- Deep-sea canyons are very active and allow for continental rise to grow.
Transgressive Systems Tract (TST):
- Relative sea-level rise outpaces the rate of sediment supply
- Estuaries are common during the lowstand process.
Draw a diagram of the sequence associated with sequence stratigraphy
