Lecture 2 Flashcards
What can shelf break also be called?
Offlap break
Draw and label a passive continental margin
see notes
Draw onlap, toplap, downlap, truncation, offlap
See notes
Offlaps are shown on chronostratigraphy graphs are what?
Triangles
Define onlap
As they build up they move onto the other surface
Define downlap
Building down onto older rock as they build out
Define offlap
Building out and downwards
Define truncation
Cross cutting one another
Define toplap
Each unit laps out in a landward direction at the top of the unit, they build progressively seaward
What 2 factors determine shoreline position
Accommodation rate (A) and sedimentation rate (S)
What does the A/S ratio determine
If the shoreline moves seaward or landward
Discuss regression
Regression is the seaward shift of the shoreline, it occurs when sediment supply exceeds accommodation rate (A
What does the A/S ratio determine
If the shoreline moves seaward or landward
Discuss regression
Regression is the seaward shift of the shoreline, it occurs when sediment supply exceeds accommodation rate A
A>S represents regression true or false?
False
A
True
A>S represents transgression or regression?
Transgression
Discuss Transgression
The landward shift of the shoreline, when accommodation rate is greater than sedimentation rate so you are creating the hole faster than you can fill it. A>S and so A/S ratio is >1. What was now in deeper water is deposited in shallower water
Does transgression cause a RSL increase, decrease or does it not affect it?
It causes a RSL increase.
Does regression need a RSL increase or decrease?
It needs a RSL increase otherwise nothing would be preserved.
Define MFS and how it relates to regression and transgression
MFS is the point between regression and transgression where the sea is furthest inland
Draw a transgressing and regressing shoreline
See page 3 of notes
Regression has what kind of sediment stacking occurring
Progradational stacking
Transgression has what kind of sediment stacking occurring
Retrogradational stacking
Discuss negative accommodation
Negative accommodation is when there is a loss of space caused by base level fall. A/S < 0 which implies erosion that can be caused by RSL fall.
What causes forced regression?
when the shoreline is lower than the previous one
What happens to the shoreline during negative accommodation?
It becomes lower than the previous one which causes forced regression to occur
How much is preserved during forced regression?
Not usually anything, small amounts can be preserved when RSL pulses up and down
what is eroded during forced regression?
The marine shelf
What happens when A=S
This is called autoretreat. When A=S, A/S =1. Although they are equal the shoreline will not remain constant, sediment will need to be distributed over a larger area so transgression occurs as the shoreline moves inland.
Define autostratigraphy
The variation in stacking if you keep everything constant, what happens naturally due to inherent characteristics and geometry.
Define a parasequence
A genetically related sequence of bedsets bounded by marine flooding sequences on top and bottom.
Define walthers law
Stacking upwards sequences represent beds that would have been side by side unless there is an unconformity.
does walthers law apply if there is an unconformity?
no
parasequences can be identified by what features on a sed log?
A rapid change from coarse - fine grained sediment.
Increase in accommodation rate causes regression or transgression?
Regression, it starts to prograde out.
Decrease in S whilst A is constant causes what?
Transgression
what are the 4 types of parasequence stacking?
Retrogradational (back towards land)
Aggradational (mainly vertical)
Progradational (building towards sea)
Degradational (seawards but downwards)
When can retrogradational stacking occur, in terms of A and S
When S is constant and A is increasing
When A is constant and S decreases.
what 2 things does degradational stacking require to occur?
Erosion to occur and an unconformity
Discuss the A and S characteristics of retrogradational, progradational, aggradational, and degradational stacking
Retrogradational stacking occurs when A = constant and S is decreasing or when S = constant and A is increasing.
Aggradational occurs when A and S keep up with one another
Progradational occurs when S = +ve and A = 0
Degradational occurs when S =+ve and A = -ve
What are the 3 types of stratal stacking patterns?
- Progradational - Aggradational (PA)
- Retrogradational (R)
- Aggradational - Progradational - Degradational (APD)
