Lecture 12: Pangaea: building a supercontinent.

Question 1

Where we left it…

Answer 1

Avalonia and Baltica had collided with Laurentia in the Siluro-Devonian
Caledonian Orogeny
formed the Devonian ‘Old Red Sandstone Continent’
microplates of Armorica, Iberia and ‘the Alps’ continued north
convergence and collision by Mid-Late Devonian
Variscan (or Hercynian) Orogeny
forms Euramerica (Laurussia)
Gondwana starts to move north…

Question 2

In Carboniferous: Gondwana collides with Euramerica

Answer 2

Euramerica pushed up and north into arid climate belt
coal comes to an end
orogenic uplift and erosion produces time gap in many UK geological sequences

Question 3

Continents fully assembled by …

Answer 3

Late Palaeozoic when Siberia collides, forming the Urals

Question 4

Pangaea =

Answer 4

= ‘all the Earth’
surrounded by Panthalassia = the ‘world ocean’
V-shaped – Tethyan Ocean

Question 5

Early Carboniferous tropical limestone seas date

Answer 5

~325 Ma

Question 6

Late Carboniferous tropical coal swamps date

Answer 6

~315 Ma

Question 7

Into Permian moved north, developed arid continental interior date

Answer 7

~290 Ma

Question 8

Sediments are direct indicators of

Answer 8

Climate

late Carboniferous to early Permian ice caps

Question 9

Sediments are direct indicators of climate

warm:

Answer 9

Coal, bauxite, evaporites, calcretes

Question 10

Sediments are direct indicators of climate

cold:

Answer 10

Coal, tillites, dropstones

Question 11

By mid-late Permian very…

Answer 11

wide arid belts
ice caps gone
supercontinent: very dry interior
super-monsoons?

Question 12

Permian Rotliegend

Answer 12

German: “the underlying red”
around UK, local tectonic extension produced a flat intra-montane basin (‘between the mountain ranges’)
became a desert – ‘sand sea’
wadis & alluvial fans
salt lakes

Question 13

Wind blown sand - very pure quartz

very little cement holding grains together

Answer 13

voids in sandstone = porosity

connected voids = permeability

Question 14

Late Permian Zechstein Sea

Answer 14

Britain on Wn. edge of low-lying enclosed basin
successive marine floodings from north
5 evaporite cycles
Zechstein salt deposits

Question 15

Layer cake

Answer 15

Permian Zechstein salts: marine transgressions evaporate, form salt deposits

Permian Rotliegend sands: wind blown sand ‘sea’ surrounding a salt lake

Carboniferous coal swamps: lots of organic matter, rocks deformed, eroded

Question 16

Southern North Sea Gas Basin

Answer 16

Gas fields have restricted distribution
why?
hydrocarbon “play”
special sets of circumstances which produces hydrocarbon reserves and which can be found repeatedly in geological record

Question 17

Bury coal under more sediment

geothermal gradient ‘bakes’ it

Answer 17

when the coal is of the right type, gas is given off
just like putting coal through a coke oven
drives off methane – i.e, produces ‘natural gas’

Question 18

Sourced, sealed, delivered

Answer 18

Zechstein salt: seals the reservoir, when buried and heated salt flows over geological time (anneals)

Rotliegend sands: porous, permeable reservoir rocks

Coal Measures: natural gas (CH4) source

Question 19

Back to the beasties: “both lives”

first tetrapods return to water to reproduce:

Answer 19

amphibians
generally external fertilization
lay large numbers of small, gelatinous eggs
little parental care
little choice of mate (makes Kermit sad)
metamorphose from a juvenile water-breathing form (e.g., tadpole) to an adult air-breathing form

Question 20

Amphibians that are almost reptiles

Answer 20

‘reptilomorphs’: close to, but not yet reptiles
340Ma, Carboniferous: East Kirkton, Scotland
single, incomplete specimens

Question 21

Reptiles leave the water behind…

Carboniferous ‘reptilomorphs’ very like small living lizards

Answer 21

agile, fast, small sharp teeth
reptiles: amniotic egg
semi permeable cover (mineralized or leathery)
membranes & ‘shell’ protect embryo, deal with food & wastes

Question 22

Reptilian advantages

Answer 22

fully adapted for land
desiccation resistant
smaller numbers of eggs, better care
parental care in some cases
internal fertilisation (copulation)
mate selection becomes important
sexual display important

Question 23

Joggins, Nova Scotia

primitive amniotes: Hylonomus

Answer 23

anapsids - no skull holes
up to 17 preserved inside rotted tree trunk
not accidentally trapped
lived there, scampered in and out

Question 24

Mammals materialize

Answer 24

ancestors: synapsid reptiles
dicynodonts
cynodonts
mammals

Question 25

The synapsids

Answer 25

mammal-like reptiles
fenestra (hole) in skull behind eye
sprawling gait
the pelycosaurs – ‘sail backs’
Dimetrodon & Edaphosaurus
NOT dinosaurs!

Question 26

Dimetrodon: 3m length, carnivore (cf. teeth)
Edaphosaurus: herbivore (crushing teeth)
why the sail?

Answer 26

as animal increases size: volume3, area2
ectotherms, external heat sources
sail increases area, blood supply
solar panel, radiator

Question 27

Dinocephalians

Answer 27

evolved from the pelycosaurs
Anteosaurus (‘early reptile’): a 6m long carnivore
Moschops (‘calf face’): 5m long herbivore
10cm thick skull bone: head-butter

Question 28

Dicynodonts: ‘two dog teeth’

Answer 28

2 sabre teeth but no others
rat to hippo size
very successful herbivores, many species
large herds, slow witted
smaller ones lived communally in burrows

Question 29

Cynodonts: ‘dog teeth’

Answer 29

smaller than dicynodonts, later in Triassic
incisors, canines, cheek teeth for faster food processing
at least partially warm blooded
hairy (insulation)
mammal-like

Question 30

Earliest true mammals at close of Triassic

Answer 30

Small (10cm), large brain, good hearing & smell
teeth = insectivorous
milk teeth (suckle), whiskers
probably nocturnal, lost heat, ate lots to keep warm, furry
spent next 160 My in shadow of dinosaurs