Chapter 20

Question 1

What is the difference between geochronological and a chronostratigraphic unit?

Answer 1

Time = geochron
Space = Chronostrat

Question 2

Main geochronological units from largest to smallest

Answer 2

Eons, Eras, Periods, Epochs, Ages

Question 3

Main chronostratigraphic units from largest to smallest

Answer 3

Systems, Series, Stages

Question 4

Why do some geologists not want to distiguish between geochron and chronostrat?

Answer 4

Now that we have better methods of dating the rocks, it seems redundant to distiguish the two

Question 5

What is the purpose of the Global Standard Section and Point (Golden spike)?

Answer 5

Internationally agreed upon standard for geochronological boundaries to be used as a reference.

Question 6

What criteria are used to establish a golden spike?

Answer 6

Accessible
Usually fossil based
Adequate thickness
Not effected by tectonics
Continuous sedimentation

Question 7

What are the major rules for defining relative stratigraphic postion? What is up?

Answer 7

a) Superposition
b) Unconformity: All rocks under the unconformity must be older than those above it
c) Cross-cutting relationship
d) Inclusions and fragments
e) way up indicators

Question 8

4 ways to determine “up”

Answer 8

Mudcracks
Sharp crests
asymptotic cross-bedding
Fossils (tree trunks, worm holes)

Question 9

how is the top unit of the rock defined when it is gradational?

Answer 9

It is arbitrary, but when you have about a 50/50 split, that is the transition line

Question 10

What is the purpose of a type section

Answer 10

To have a standard to reference that has all the notable features.

Question 11

What are the rules for naming lithography?

Answer 11

Has to be geography based and with a lithologic term (Jacobsville Sandstone)