Lecture 9 - Stratigraphy and Geochronology

Question 1

A definitio of stratigraphy

Answer 1

The studied of stratifed rocks especially thier sequenxe in time, the character of the local rocks and the correlation of beds in different localities.

Question 2

What is geochronology

Answer 2

The measurement of time interbals on a geological scale

Question 3

Explain relative dating, an example

Answer 3

“bed A is older than bed B”

Question 4

What is abosulte dating, an example

Answer 4

“bed B is 33million years old”

Question 5

What is absolute dating important

Answer 5

its needed to calculate the rates of procresses

Question 6

Explain half life

Answer 6

The time is takes for half the initial radioactive atoms to decay

Question 7

Measuring abunce of what and using the half life what can you calculate

Answer 7

If you know the half life you can count how many parent and daughter nucleotides thier are to calculate the age

Question 8

What is chronostratigraphy

Answer 8

the use of half lives and radioactive elements in aging rocks

Question 9

What is Biostratigraphy

Answer 9

Its used to calculate the age of beds from looking at rock and having prior knowledge of the age of extiction

Question 10

What are the benefits to this (5)

Answer 10

Distictive
Widespread
Abundant
Independent of facies
Short ranging

Question 11

Fossil assemblages as oppose to single fossil species

Answer 11

Fossils assemblages reduces reliance on a single fossil and improves precision of these biostratigraphic dating

Question 12

Disadvantages?

Answer 12

Are they truel syncronous
Are they instantenous
Need to date the biostratific events anyways
Age estiments are ALWAYS being updated

Question 13

What is geophysical correlation

Answer 13

comparision of the formation of thess rocks and comparing them to another set of rocks to see if theere is a comparison

Question 14

What is Chemostratigraphy

Answer 14

An element is defined by its atomic number, using stable isotopes of stronituim

Question 15

Why use stronituim

Answer 15

There are stable isotopes, we know their have been changes of the ratio of 87 and 86 isotopes and we can work out how seawater ratios have change throug time

Question 16

Using this on fossils

Answer 16

Using the ratio can calcuate the age of these fossils

Question 17

What is magnetostratigraphy

Answer 17

Earths magnetic field acts as a powerful magment bar, this has rotated 100s of times and these flips can be used to calcuate age of rocks

Question 18

Ignous rocks and magnetostratigraphy

Answer 18

Preserve a strong magnetic signal are easy to date radiometrically, using igneous rocks has createda a histrory of the earths magnetic field

Question 19

Sed rocks and magentostratigraphy

Answer 19

Tiny rocks in the deposit become aligned to the earths field.These are then matched to the magentic timescale

Question 20

Advantages magento

Answer 20

Truly sunchronois events can be correlated world wide

Question 21

Disadavantes of mageneto

Answer 21

Must be used in conjuction with other methods, need to work out which flip it iwas

Question 22

What is cyclopstratigraphy

Answer 22

Changes in the earths orbit mean diferent solar radiation is recieved by earth, this can then be used to calcuate ages.