Introduction and stratigraphic methods

Question 1

What can stratigraphy be used for?

Answer 1

Determining tectonic, biological, and climatic events

Question 2

What are the two ways to determine geological age?

Answer 2

Relatively or numerically

Question 3

Define relative geological aging

Answer 3

Placing rocks and events in their proper sequence of formation/occurence
Lithostratigraphy

Question 4

Define numerical (absolute) geological aging

Answer 4

Specifying absolute number of years since an event
Geochronology

Question 5

Describe the principle of superposition

Answer 5

Relative aging
Each bed is younger than the one below it
Thrust faulting can invert the order

Question 6

Describe the principle of cross-cutting

Answer 6

Relative aging
A bed or unit is younger than the one it cuts across

Question 7

Describe the principle of original horizontality

Answer 7

Relative aging
Consolidated strata that are now tilted were originally deposited horizontally

Question 8

Describe the principle of continuity

Answer 8

Relative aging
In a basin, the same bed is of identical age in every part, beds terminate were deposition was not possible or where they have been eroded or deformed after deposition

Question 9

Describe the principle of inclusion

Answer 9

Relative aging
If an element A is included in an element B, A is older than B

Question 10

Describe palaeontological identity

Answer 10

Relative aging
All beds including the same fossils are of the same age
Relies of the principle of faunal succession
Not applicable where there has been reworking

Question 11

Describe an unconformity

Answer 11

Relative aging
A break in the geological record produced by erosion and/or non-deposition

Question 12

Describe an angular unconformity

Answer 12

Relative aging
Tilted rocks are overlain by flat-lying rocks

Question 13

Describe a disconformity

Answer 13

Relative aging
Strata on either side a parallel, there have been a period of erosion

Question 14

Describe a non-conformity

Answer 14

Relative aging
Metamorphic or ignous rocks in contact with sedimentary strata

Question 15

Describe isotopic ratios

Answer 15

Relative aging
Applicable when changes are globally synchronous
O2 linked to temp
C linked to biological activity
S linked to igneous processes
Correlates within basin
Supported by absolute age dates

Question 16

Define uniformitarianism

Answer 16

The same processes operating today were active in the past

Question 17

Define numerical (absolute) geological aging

Answer 17

Specifying the absolute number of years since an event

Question 18

Describe radioactive decay

Answer 18

Absolute aging
Time that it takes U to decay to Pb (parent to daughter isotope)

Question 19

What does the use of radioactive decay for absolute dating require?

Answer 19

A closed system that contains no original daughter nuclides

Question 20

Describe mangetostratigraphy

Answer 20

Absolute aging
Magnetic minerals orient to the pole
Pole changed from S to N ~700,000 ya
Minerals formed before this will orient to old pole

Question 21

When do magnetic minerals orient to the pole?

Answer 21

Below the Curie point, ~570C, above this they orientate in random directions

Question 22

Describe radiocarbon (C-14) dating

Answer 22

Absolute aging of organic material
Upper limit of ~70,000 years

Question 23

Define chronostratigraphic units

Answer 23

The relative relations and ages of rock bodies

Question 24

Define geochronological units

Answer 24

Dating and determining the time sequnce of depositional/deformity events
Provides absolute ages

Question 25

Give an example of how a bed can be destroyed

Answer 25

By compaction during lithification
This compaction can make it so the bed’s thickness no longer indicates geological time

Question 26

What is the subdivision of stratigraphic units based on?

Answer 26

Their lithological character and stratigraphy
Boundaries are placed at lithological changes (can be sharp/gradational)

Question 27

Give the subdivision of stratigraphic units, in order from smallest to largest

Answer 27

Bed, member, formation, group, supergroup

Question 28

Describe a bed subdivision

Answer 28

Smallest unit, can be a key/marker bed, a thin distinctive bed that is widely distributed

Question 29

Describe a member subdivision

Answer 29

Part of formation with distinguishing traits

Question 30

Describe a formation subdivision

Answer 30

Fundamental unit

Question 31

Describe a group subdivision

Answer 31

Expresses natural relations beween formations
Small to regional scale

Question 32

Describe supergroup subdivsion

Answer 32

Assemblage of related or superposed groups
Regional to provincial scale

Question 33

What does biostratigraphy depend on?

Answer 33

Species evolve into new forms and have a discreet duration before becoming extinct

Question 34

What defines a biozone?

Answer 34

The assemblage of index fossils

Question 35

What is a limitation of biostratigraphy?

Answer 35

The biases of the rock record and taphonomy
Organisms can evolve at different rates around the world

Question 36

Describe radiometric dating

Answer 36

Absolute aging
Radioactive clock measures time of crystallisation

Question 37

Give four requirement of geochronology that can limit its efficacy

Answer 37

Requires a closed system with no original daughter nuclides (Pb), fresh samples, and a variety of minerals