Sequence Stratigraphy

Question 1

What is sequence stratigraphy and what does it show?

Answer 1

Shows packages of strata each of which was deposited during a cycle of sea level change or change in sediment supply

Question 2

Name four uses of sequence stratigraphy

Answer 2

1. Understand and predict gaps in the sedimentary record.
2. Divide the sedimentary record into time related units used fro stratigraphcal correlation
3. Help determine rates and amplitude of past sea level change
4. Help understand sedimentary cycles in the stratigraphical record

Question 2

What does onlap and offlap show in terms of changeing sea level

Answer 2

Onlap shows sea transgression

Offlap shows sea regression

Question 3

What is meant by base level?

Answer 3

Base level is the imaginary equilibrium between erosion and deposition at the shoreline.

Question 3

What is meant by forced regression?

Answer 3

Lowering in sea level, shore moves out into sea.

Question 4

List 4 characteristics of forced regression

Answer 4

• Sea level fall
• Fluvial incision to meet new base level
• Progradation of sediment deposition
• Wave erosion of previous shoreline deposits

Question 4

How do forced regression deposits appear?

Answer 4

Progradation of sediment with downstepping. Driven by base level fall regardless of sediment supply.

Question 5

How do normal regression deposits appear?

Answer 5

Progradation driven by sedimentation outpacing baselevel rise. Progradation with aggradation

Question 6

How do transgression deposits appear?

Answer 6

Retrogradation driven by base level rise outpacing sedimentation

Question 7

Define what is meant by the maximum flooding surface

Answer 7

The deposition at the time of maximum transgression, flooding of land

Question 8

Define the transgressive surface

Answer 8

The surface that marks the onset of when the rate of generation of accommodation space is greater than the rate of sediment supply

Question 8

Define what is meant by sequence boundaries and give examples

Answer 8

Significant erosional unconformities produced by regression, e.g. subaerial unconformity, basal surface of forced regression or maximum regressive surface

Question 9

What is a system tract?

Answer 9

A specific set of sedimentary features or stratigraphic deposits characteristic of a section of the base level curve.

Question 9

Describe a highstand system tract (HST)

Answer 9

Low rate of progradation into basin,
Aggradation at basin margin with deltaic deposits,
Max flooding surface,
Normal regression - downlap

Question 10

Describe a falling stage system tract (FSST)

Answer 10

High rate progradation,
Turbidite and debris flow, Subaerial erosion of exposed features
Basal surfaces of forced regression
Offlap present

Question 10

Describe a lowstand system tract (LST)

Answer 10

Low grade progradation and aggradation
Maximum regressive surface
Normal regression, may see fluvial onlap

Question 11

What is the difference between low stand and high stand?

Answer 11

LS - accelerating relative to sea level rise, decreased progradation increased aggradation
HS - decelerating relative to sea level rise, increased progradation decreased aggradation

Question 11

Describe a transgressive system tract (TST)

Answer 11

Retrogradation and aggradation
Maximum flooding surface
Transgression, fluvial and coastal onlap