Lecture 2

Question 1

Who first observed unconformity and when

Answer 1

Hutton and playfair in 1788

Question 2

Siccar point unconformity

Answer 2

a surface with horizontal Devonian sandstones on top of almost vertical silurian slates

Question 3

Geological cycle

Answer 3

• Sedimentation
• Burial
• Folding, faulting, mountain-forming and igneous intrusion
• Erosion
  Back to sedimentation as eroded rocks transported by rivers

Question 4

What is lithophagia

Answer 4

when organisms gain nutrients from rocks—>form of erosion

Question 5

What did Ussher work on

Answer 5

He was an archbishop and in 1654 estimated the creation of the earth at 4004 BC based on the bible

Question 6

Lord kelvin’s contribution

Answer 6

Using loss of heat from a sphere he estimated 40-100 million years old—>however made many invalid assumptions

Question 7

Stratigraphy

Answer 7

The study of rock layers in order to determine relative ages and therefore form a relative geological timescale

Question 8

4 laws of stratigraphy

Answer 8

1. Superposition, so rocks on top are newer
2. Lateral continuity, so if rocks eroded away then lateral construction can be formed as originally continuous
3. Initial horizontality, assumption that strata were formed relatively horizontally
4. Cross-cutting relations

Question 9

Biostratigraphy

Answer 9

Stratigraphy with fossils and fossil zones as these are generally more uniform than the differing conditions across the surface of earth which leads to different rock types

Question 10

Facies

‘fash-ees’

Answer 10

environment of deposition. SO different environments can exist in different places at the same time, so mud and sand on river estuary and beach.

Question 11

Problems with biostratigraphy

x5

Answer 11

1. facies
2. Many rocks lack fossils, especially continental ones
3. Fossil zones may not extend beyond a single continent, if that far
4. Few useful fossils prior to Cambrian and evolution of hard parts and almost 90% history before that
5. Gaps are common—>called an unconformity

Question 12

Unit Ma

Answer 12

Means million years before present

Question 13

What is chalk formed of

Answer 13

Mainly coccolithophores, which are formed of CaCO3

Question 14

Break between proterozoic and cambrian

Answer 14

Evolution of ‘hard’ parts, bone, shells and other less fleshy parts

Question 15

Paleozoic to Mesozoic

Answer 15

Volcanic eruption in siberia

Question 16

Mesozoic to Cenozoic

Answer 16

Asteroid impact removed charismatic megafauna

Question 17

Pliocene to Pleistocene

Answer 17

Development of ice sheets in the northern hemisphere

Question 18

The decay of parent, P, isotopes to stable daughter, D, isotopes gives us a clock, what equations do we use.

Answer 18

GRAPH 5

Question 19

What are the most common systems used in radioactive dating

Answer 19

Rb—>Sr
Thorium and uranium to lead
Potassium to argon
Carbon to nitrogen

Question 20

Best crystal to test

Answer 20

Zircons in Jack Hills
4.4B
No lead when formed but some uranium so any lead present was due to decay

Question 21

Only closed systems are dated. Why?

Answer 21

IF the daughter atoms are lost we need to reset the clock as it makes it look younger than it is.
Closure occurs when below closure temp which changes due to isotope system and mineral involved.

Question 22

Why is zircon a good closed system

Answer 22

Closes at >750 degrees so very close to actual formation time

Question 23

What do we actually mean by date?

—why do we have to ask that question?

Answer 23

Age of deposition of the sediment may be much younger than the formation of the crystals within it

Question 24

Estimate of the earths age using U-Pb system

Answer 24

~4560Ma

Question 25

How good is stratigraphic correlation?
Using the example between deep-sea boreholes in the Southern Ocean
-GRAPH

Answer 25

1. Magnetic polarity, rock types and fossil zone shown
2. Rock type does not correlate at all (variability of facies)
3. Magnetic polarity reversals are effectively synchronous everywhere
4. Sedimentation rates very variable
5. Fossil zone correlate quite well with the magnetic reversals