How Plate Tectonics and Climate Shape the Geological Record P2 - Lec 13

Question 1

How many years ago was Ireland at the equator and went from deserts to coal swamps?

Answer 1

420-300mya

Question 2

What occurred following the closing of the Rheic Ocean as Gondwana moved northwards?

Answer 2

The supercontinent of Pangea formed (Devonian period)

Question 3

What occurred in what time periods to lead to the formation of Pangea?

Answer 3

Cambrian and Ordovician: Laurentia and Gondwana/Avalonia split by Iapetus Ocean
Silurian: Avalonia drifts and collides with Laurentia, opening the Rheic ocean and leaving Gondwana alone
Devonian: Laurussia (Laurentia, Avalonia and Baltica) collides with Gondwana to form Pangea

Question 4

What was the 3 names for the amalgamation of Laurentia, Avalonia and Baltica?

Answer 4

Euramerica, Laurussia and Old Red Sandstone Continent

Question 5

Where was the transition from marine sediment to terrestrial sediment?

Answer 5

Low palaeolatitudes south of the equator

Question 6

What was the result of this amalgamation? (7)

Answer 6

Red beds, desert environment, alluvial fans (scree slopes and debris flows), unconfined sheet folds over floodplains, aeolian (wind-blown) deposits, lacustrine deposits

Question 7

What occurred in the Early Devonian? (400mya)

Answer 7

Localised lacustrine systems in NE Scotland
Marine influence restricted to southern Britain
Prominent topography: extensive alluvial fan sedimentation and major river systems flowing length of topographic lows
Eg. Cushendun, Co. Antrim and Sandeel Bay (old red sandstone), Co. Wexford

Question 8

What occurred in the Middle Devonian? (380mya)

Answer 8

Decrease in alluvial fan sedimentation (reduced topography/mountains)
Development of major lacustrine systems in NE Scotland (eg. Orcadian Bay)
Marine influence has migrated further North

Question 9

What occurred in the Late Devonian? (370mya)

Answer 9

Alluvial plains and aeolian facies important (ie. further north and more arid)
Rivers: some meandering not braided (reduced topography)
Locally lacustrine deposits and evaporites
Major coastal plain has developed in the south

Question 10

What occurred in the Lower Carboniferous? (350-325mya)

Answer 10

Ireland was on the equator and covered by a tropical ocean. It was located to the north of ‘Variscan Mountains’

Question 11

What occurred in the Early Carboniferous? (355mya)

Answer 11

Marine influence further north than before
Carbonate platforms - limestone deposition in southern Britain and Ireland
Deeper water facies to south
Major transgression (migration of seaway) underway
Sea level from south floods northwards

Question 12

What occurred in the Middle Carboniferous? (328mya)

Answer 12

Coal swamps and deltas becoming established in NE Britain with some marine influence during short scale transgressions
Significant marine limestone deposition across much of southern and central Ireland and Britain
Localised deeper basins eg Dublin Basin

Question 13

What occurred in the Late Carboniferous? (313mya)

Answer 13

Extensive terrestrial (emergent) surfaces in northern part of Britain and Ireland
Coal swamps - burial of carbon

Question 14

What is the summary of the Devonian period?

Answer 14

400-350mya

Terrestrial Old Red Sandstone continent

Question 15

What is the summary of the Early-Mid Carboniferous?

Answer 15

Extensive limestone platforms
Flooding onto land surfaces
Transgression
Rise in sea level

Question 16

What is the summary of the Mid-Late Carboniferous?

Answer 16

Major phase of deltas and coal swamps

Global sea level fall as ice sheets build up

Question 17

Describe the Orcadian Basin from the Middle Devonian.

Answer 17

Cyclical patterns of sedimentation as lake levels rise and fall
Astronomical forcing of sediment patterns (axis tilt, orbital eccentricity, eccentricity rotation)
Lake geometry reflects local physiography and tectonics (illustrates nature of sequence for only 70m out of 750m thickness)
One deep lake phase resulted in laminated sediments from Shetlands Islands to Scottish mainlands

Question 18

What was the low lake stands?

Answer 18

When the lake level is low and the system is dry

Question 19

Describe the low lake stands

Answer 19

Playa type environments: evaporites (eg. salt)
Deposition of fluvial sediments
Stromatolites
Dessication-cracked horizons
(Orkney period)

Question 20

What are high lake stands?

Answer 20

When the lake level is high and the system is wet

Question 21

Describe the high lake stands

Answer 21

Deep permanent lake
Fish faunas preserved under oxygen-free locations (at lake bottom)
Finely laminated quiet-water sediments (at lake bottom)
No infauna can survive anoxic conditions of lake bottom
One deep lake phase resulted in laminated sediments from Shetland Islands to Scottish mainland
Possible intensification of monsoonal system

Question 22

Describe and give examples of Carboniferous Limestone

Answer 22

Fossiliferous carbonate muds
Examples are crinoids (stem with tentacles that falls and runs or polo mints), corals, brachiopods (shells) and foraminifera

Question 23

What led to the formation of the Lead and Zinc deposits?

Answer 23

Approx. 345mya - Ireland stretched N-S to form wide rift
Stretching formed fault-controlled basins
Led to formation of Irish Zn-Pb Orefield

Question 24

Describe the Irish Zn-Pb Orefield

Answer 24

All deposits contained within limestone-dominated successions
Faults provided pathways for upward flow of mineral rich fluids from deep within crust
Ireland - one of largest producers Zn in world

Question 25

What is the Central Clare Group in Western Ireland?

Answer 25

The last part of the infill of a deep water basin resulting from a series of repeated delta deposits (cyclical sedimentation)

Question 26

How did the cycles go in the Central Clare Group in Western Ireland?

Answer 26

Cycle started with offshore marine sediments and shallows upwards, ending with delta top environments including channels and floodplains (modern analogue=Mississippi). Sea level then rises and sequence starts again.

Question 27

How many cycles occurred in Central Clare Group?

Answer 27

5

Question 28

What did the Central Clare Group cycles result in?

Answer 28

Major economic deposits (eg. coal deposits)

Question 29

What does the formation of sedimentary organic deposits, such as coal and oil, do?

Answer 29

It removes CO2 from atmosphere and buries carbon is deep storage reservoirs

Question 30

During the Late Palaeozoic (Carboniferous), what were conditions in Europe and N America like?

Answer 30

Much of Europe + N America in shallow water environments at appropriate low-intermediate latitude (coal-forming environments)

Question 31

What did the removal of organic carbon (from coal formation) during the Carboniferous lead to?

Answer 31

It led to global cooling (greenhouse effect as CO2 warms planet so without it the planet cools)

Question 32

How do coal swamps effect the global climate?

Answer 32

Coal swamps=burial of carbon
Reduced carbon=global cooling
Cooling=glaciation at high latitudes
Glaciation=sea levels fall
Current global warming from burning fossil fuels
UK and Ireland - Carboniferous coal important source of energy

Question 33

How was CO2 removed from the atmosphere during this time?

Answer 33

Through coal swamps as they buried the carbon in storage reservoirs

Question 34

From largest to smallest, what is the list of 5 geological chronostratigraphical terms?

Answer 34

Eon, Era, System, Series, Stage