How Plate Tectonics and Climate Shape the Geological Record P1 - Lec12

Question 1

Where is Hutton’s Unconformity and what is it?

Answer 1

Scotland

It is a mixture of Silurian sandstones an shale (marine) and the Devonian conglomerate (fluvial)

Question 2

What is the time period for the Cambrian age?

Answer 2

550-500mya

Question 3

What is the time period for the Ordovician age?

Answer 3

500-450mya

Question 4

What is the time period for the Silurian age?

Answer 4

450-400mya

Question 5

What is the time period for the Devonian age?

Answer 5

400-350mya

Question 6

What is the time period for the Carboniferous age?

Answer 6

350-300mya

Question 7

What is the time period for the Permian age?

Answer 7

300-250mya

Question 8

List the 6 geological time periods in order from oldest to youngest

Answer 8

Cambrian - Ordovician - Silurian - Devonian - Carboniferous - Permian

Question 9

What was the time period for the death of the Iapetus Ocean?

Answer 9

Cambrian-Silurian

Question 10

What continent was Avalonia originally attached to?

Answer 10

Gondwana

Question 11

What ocean separated Laurentia and Avalonia?

Answer 11

The Iapetus Ocean

Question 12

What ocean opened as Avalonia drifted towards Laurentia?

Answer 12

The Rheic ocean

Question 13

In the Early Cambrian (550mya) where were northern and southern Ireland located?

Answer 13

Northern: part of Laurentia
Southern: part of Gondwana

Question 14

In the early Ordovician (490mya) what happened to the southern parts of Ireland?

Answer 14

They began to rift away from Gondwana as part of the micro-continent called Avalonia

Question 15

In the middle Ordovician (470mya) what happened to Avalonia and the ocean?

Answer 15

Avalonia drifts northwards and the Rheic ocean opens between Avalonia and Gondwana

Question 16

In the early Silurian (440mya) what happened to Avalonia and the ocean?

Answer 16

Avalonia accretes (joins) onto the margins of Laurentia (and Baltica) and the Iapetus ocean closes

Question 17

What occurs in the Devonian (395mya)?

Answer 17

Gondwana begins to drift northwards towards Laurentia as a result of subduction

Question 18

What occurs in the Carboniferous (350mya)?

Answer 18

Gondwana joins with the mass of Laurussia/Avalonia which leads to the formation of the supercontinent Pangea

Question 19

What mountain belt was formed as a result of the collision of Avalonia and Laurentia (what orogeny?)? Where did they stretch?

Answer 19

The Caledonian/Acadian mountain chains (the Caledonian-Appalachain Orogen)
Stretches into Scandinavia, Greenland, Scotland, N. America and Europe

Question 20

When did the the Caledonian/Acadian mountain chain begin to form?

Answer 20

The early Devonian

Question 21

Ocean’s are not usually just open, what do they usually contain?

Answer 21

Island arcs, micro-continents, seamounts - these can build up to form future mountain belts

Question 22

When was the collision between North and South Ireland? What did this ccollision cause?

Answer 22

400mya
It caused trends in the direction of NE-SW of intermediate accreted terranes (Valleys and Uplands) that can override the plate margins

Question 23

What evidence is there that the Iapetus Ocean ever existed and the plate tectonic history of Avalonia? (3)

Answer 23

Palaeomagnetism
Faunal Provincialism
Sedimentology (Southern Uplands Terrane)

Question 24

Palaeomagnetism evidence

Answer 24

The orientation of the magnetic field can be retained in rocks at the time they form
It is shown through a plaeolatitude graph by Mac Niocaill (2000) - illustrates the movement of Avalonia through time towards Laurentia (be familiar- slide 20)

Question 25

What is thermoremanent magnetisation?

Answer 25

Magnetic minerals become aligned in igneous rock as they cool

Question 26

What is depositional remanent magnetisation?

Answer 26

Detritic magnetic minerals settle out during deposition sympathetic to the orientation of the magnetic field

Question 27

Faunal Provincialism evidence - benthic

Answer 27

Living on/within floor of water body

Question 28

Faunal Provincialism evidence - pelagic

Answer 28

Water not at/close to floor of water body, nor its margins (eg. shore)

Question 29

Faunal Provincialism evidence - planktonic

Answer 29

Drift or swim weakly

Question 30

Faunal Provincialism evidence - nektonic

Answer 30

Free swimming in water column

Question 31

Faunal Provincialism evidence - epifaunal

Answer 31

Living on surface of sediment column

Question 32

Faunal Provincialism evidence - infaunal

Answer 32

Living within sediment column

Question 33

Faunal Provincialism evidence - sessile versus motile

Answer 33

Can be different between juvenile and adult stages

Question 34

Faunal Provincialism evidence - describe the different depths of the evidence.

Answer 34

At the top of the water - open ocean plankton
On the continental shelf - shallow marine sessile infaunal benthos proximal to landmass
On the abyssal plain (very bottom) - deep marine benthos independent of position of landmass, less variation in environmental conditions, wider latitudinal sprea

Question 35

Faunal Provincialism evidence - What are trilobites?

Answer 35

Marine anthropods (Phylum Anthropoda)
Extinct
Date from Cambrian to Permian

Question 36

Faunal Provincialism evidence - What are graptolites?

Answer 36

Phylum Hemichordata
Colonial, marine, invertebrates
Date from Middle Cambrian to Upper Carboniferous
Organic periderm
Extant hemichordates

Question 37

Faunal Provincialism evidence - give 2 examples of Early Ordovician pelagic trilobites that had strong latitudinal control (Arenig)

Answer 37

Cyclopygid trilobites: high southerly latitudes, enlarged eyes fo wider view, both horizontal and vertical
Opipeuter: low latitudes visual adaptation for nektonic style
(And Carolinites)

Question 38

Faunal Provincialism evidence - give 3 examples of Late Ordovician trilobites (Caradoc-Ashgill)

Answer 38

Ampyxina, Calyptaulax, Panderia
Benthos
Possible W-E variations, larvae possibly spread through ocean currents, overlap with Avalonia and Baltica

Question 39

Faunal Provincialism evidence - Ordovician Graptolites

Answer 39

Some types have cosmopolitan distribution
Atlantic Province: mid-high palaeolatitudes of Gondwana and Avalonia
Pacific Province: low-equatorial palaeolatitudes of Laurentia
Siberia and Baltica=mid latitudes so a mix of both

Question 40

Faunal Provincialism evidence - Through Time

Answer 40

As Iapetus Ocean closed, faunal provincialism
Graptoloid faunas were among the first to lose a distinctive faunal provincialism
Be familiar with graph on slide 29

Question 41

Sedimentology evidence - AccretionaryWedge (accretion and mtn builidng)

Answer 41

Deep marine sediments (graywackes-muddy sandstones) deposited as event beds from turbidity currents
Associated with black shales and cherts (open ocean sediments)
Various subduction + orogenic events creates Caledonian orogeny
The Southern Upland terrane represents deep-
marine sediments obducted in an accretionary wedge during final closure of Iapetus Ocean (wedge developed north of suture)

Question 42

Recap

Answer 42

Look over recap slides 33-34 and slides 2-4 of next lecture