Module 8, Stratigraphy

Question 1

What is Stratigraphy?

Answer 1

the study of the layered characteristics of sedimentary rocks in outcrop , well logs and core

Question 2

Why is Stratigraphy used?

Answer 2

in the correlation of petroleum bearing zones

Question 3

What do stratigraphic sequences describe?

Answer 3

The order in which bodies of sediments were deposited and their geometrical relationship to each other

Question 4

What two cycles can sediments be of?

Answer 4

Single or multiple and this is found out VIA stratigraphic sequences

Question 5

What is a vertically stacked association?

Answer 5

A sequence

Question 6

What are the sedimentary strata related to in the belly river?

Answer 6

the mode of seidment accumulation (deltaic) as well as the changes in sea level (eustasy)

Question 7

Eustatic/Absolute Sea-Level is based off of what?

Answer 7

A fixed Datum - example: the Centre of the Earth

Question 8

Relative Sea-Level is based off of what?

Answer 8

A local datum

Question 9

When do Absolute (eustatic) base -level fluctuations occur

Answer 9

on a global scale and are controlled by major climatic or tectonic events such as glacial episodes and inflation / deflation along spreading centers

Question 10

What are included in Relative base-level fluctuations?

Answer 10

Both, eustatic and local signals. Major local factors include basin subsidence and sedimentation rates

Question 11

What is a Base-Level?

Answer 11

The level below which erosion cannot occur and above which deposition does not take place.

Question 12

What is the ultimate base level?

Answer 12

Sea level

Question 13

Global sea-level fluctuation occurs on a variety of scales. What are they?

Answer 13

Tectonic and climatic processes

Question 14

What is Accommodation?

Answer 14

“Space” available for sediment accumulation

Question 15

How is sediment accumulation limited?

Answer 15

By the amount of space available below base-level. This is referred to as accommodation space.

Question 16

What determines the amount of accommodation?

Answer 16

a combination of eustatic sea -level fluctuation and basin subsidence and can be either positive or negative

Question 17

What controls the thickness and type of a sedimentary deposit?

Answer 17

Sediment supply and base level and accommodation space

Question 18

What is sequence stratigraphy?

Answer 18

The analysis of cyclic patterns in sedimentary successions developed through time

Question 19

Name the four key principles of stratigraphy?

Answer 19

1) Original Horizontality
2) Stratigraphic superposition
3) Cross-cutting relationship
4) Lateral Continuity

Question 20

What does an unconformity indicate?

Answer 20

An uplift and erosion of the surface of the older bed before the younger bed was laid down resulting in the geological record

Question 21

Describe a nonconformity

Answer 21

a surface of erosion that separates younger sedimentary strata above from older igneous or metamorphic rocks below

Question 22

Describe angular unconformity

Answer 22

A surface of erosion between two groups of sedimentary rocks in which the orientation of older strata, below , are at and an angle to younger strata above

Question 23

Describe disconformity

Answer 23

a surface of erosion in which the orientation of older strata , below , are parallel to younger strata, above.

Question 24

Describe a paraconformity

Answer 24

parallel beds and no erosion surface (pinpointed by relative dating method such as fossil succesion)

Question 25

What is a diastem?

Answer 25

short break or gap between similar depositional events such as floods, storms, etc. They can be pinpointed by radiometric dating.

Question 26

In a fluvial system the equilibrium state is called what? What is it called in a marine system?

Answer 26

graded profile

base level

Question 27

How are ichnofacies commonly used as a stratigraphic tool?

Answer 27

To interpret both lateral and vertical changes in depositional environments.

Question 28

What are 3 examples of ichnofossils?

Answer 28

Tracks

Happy Snails Trails

Question 29

what well logs are used for correlation?

Answer 29

Gamma Ray

Spontaneous Potential

Question 30

What 2 methods can be used to correlate stratigraphy?

Answer 30

Lithostratigraphy

Chronostratigraphy

Question 31

Name 6 reasons why seismic is an essential exploration tool?

Answer 31

Determines:
Tectonic setting adn the depositional environments
Hydrocarbon Traps (structural or stratigraphic)
Structural elevation and dip
Isopach variations
Potential reservoirs and seals
Source rock and reservoir estimation

Question 32

What factors does accommodation depend ?

Answer 32

The sea level
the movement of sea floor (subsidence)
Changes in rates of sediment supply ( for examples, progradation during sea - level rise)

Question 33

What has caused the sea level to change over time?

Answer 33

The effects of plate tectonics
Eustacy
Glacial events (isostacy)

Question 34

What is happening to the sea level during transgression?

Answer 34

The relative sea - level increases

Question 35

What is happening to the sea level during regression?

Answer 35

The relative sea - level decreases

Question 36

Explain progradation and what is an example of it

Answer 36

occurs when the sediment accumulation rate is higher than the creating of new accommodation space. The Mississippi River Delta is an example

Question 37

What is the difference between conformable and unconformable strata?

Answer 37

Conformable is when there is no significant break in deposition (rocks have been deposited in a continuous succession through time).

Unconformable is when an interruption exists - an episode of erosion between deposition (the boundary between the older and younger rocks is unconformable)