W5 - Early Mesozoic

Question 1

What is Plate Tectonic Theory?

Answer 1

Theory that says that Earth’s surface is divided into a series of large plates that move around, allowing continents to change position

Question 2

How was the Plate Tectonic Theory Developed?

Answer 2

Alfred Wagner published ideas on continental drift in 1912 - proposed and ancient supercontinent: Pangea

Question 3

What is a supercontinent?

Answer 3

Assembly of most, if not all, of Earth’s continental blocks or cratons to form a single large landmass
Cratons are continuously converging and diverging over time

Question 4

What were the 4 pieces of evidence that support the existence of Pangea?

Answer 4

1) Continents fit together like puzzle pieces
2) Fossils of creatures unable to swim are found oceans away
3) Glacial sediments are found on continents close to the equator - suggest that they were located closer to the poles in the past
4) Similar geological features are found on different continents (ex: Appalachian and Caledonian mountains)

Question 5

What are mid-ocean ridges?

Answer 5

Seafloor mountain system formed by plate tectonics

Question 6

What is geomagnetism?

Answer 6

Study of the Earth’s magnetic field
Magnetic field is a vector quantity with strength and direction
Magnetic field is constantly changing in strength and direction

Question 7

How does the magnetic pole move?

Answer 7

Moved 1100km between 1831 and 2001
Has accelerated since 1970 and is currently moving more that 40km/year
Will reach Siberia in ~50 years (may change course or slow down instead - erratic)
Last reversal occured 780 000ya - reversals take 1000-8000y to occur

Question 8

How do rocks record magnetic field?

Answer 8

Magnetic minerals (like magnetite) are ‘fixed’ in the rock
Record the magnetic field when it solidifies (cools) or lithifies (changes to sedimentary rock)
Reset by heating

Question 9

What is paleomagnetism?

Answer 9

The study of magnetic field fixed in the rock
Measured with a magnetometer
Magnetic reversals have been documented for the past 330my
Anomalies = changes in magnetic properties

Question 10

How was paleomagnetism used to confirm sea floor spreading at Mid-Ocean Ridges?

Answer 10

Magnetometer surveys of ocean floor identified patterns of anomalies on each side of midge ocean ridges - patterns matched pattern of magnetic reversals
Confirmed formation of sea floor at MORs and movement away from ridges (cms/y)
Allowed age of sea floor to be predicted

Question 11

What is the oldest ocean crust?

Answer 11

340 my
Stretch of the eastern Mediterranean Sea between Cyprus, Crete, and Egypt
Called the Herodotus Basin

Question 12

How did Pangaea form?

Answer 12

410mya
Laurentian (NA), Baltican (NW Eurasia), and Avalonian (British Islands) cratons collided to create Euramerica
Laurassia (current Russia) fused with Gondwana to form Pangaea by late Carboniferous (~310mya)
Euramerica and Gondwana collided by late Devonian / early Permian
Completely formed by end of Permian (~250mya)

Question 13

When did Pangaea begin breaking up?

Answer 13

~200mya

Question 14

What are Wilson Cycles?

Answer 14

Model that describes the opening and closing of ocean basins and the subduction and divergence of tectonic plates during the assembly and disassembly of supercontinents
Developed by Canadian geologists J. Tuzo Wilson

Question 15

What did Wilson hypothesize about the formation of Pangaea?

Answer 15

Noted that Eastern NA contianed fossils more akin to the West Atlantic and hypothesized that the Iapetus ocean once laid between suture between the welded blocks
Harol Williams, his grad students, tested his hypotheses, focusing on searching for a lost ocean on the island of Newfoundland

Question 16

What did William identify while mapping out Newfoundland?

Answer 16

Initially identified 4 major zones:
1) Humber = ancient
2) Laurentian = continental margin
3) Dunnage and Gander = part of the ancient Iapetus ocean
4) Avalon = old Eastern continent
Extended his maps into mainland Canada, the USA, and Western Europe

Question 17

How was the geology of Newfoundland formed?

Answer 17

Precambrian basement characterizes ancient eastern margin of Laurentia
Basement rocks were covered by shallow water limestones (carbonates), indicating a passive continental margin that faced East (originally South) - interpreted as Cambrian-Ordovician reefs
Carbonates are overlain by westerly derived deep-water deposits (represented as tilted shales and sandstones with graded beds and ripples - formed by waning turbidity currents) - produced by erosion of uplifted areas
Eventually as compression continued, fluvio-deltaic deposits overlaid deposits
Ophiolites present

Question 18

What are ophiolites?

Answer 18

Pieces of oceanic plate that have been thrusted (obducted) onto the edges of continental plates

Question 19

What ophiolites can be observed in Newfoundalnd?

Answer 19

Table mountains with silica-poor, magnesium rocks (olivine rich) that inhibit vegetation - originally sea floor
Sheeted dikes and pillow basalts present

Question 20

How did Table Mountains (NFL) form?

Answer 20

Originated as oceanic crust
Thrust onto the eastern margin of Laurentia as Iapetus closed due to compression caused by convergence
Allocthonous = out-of place origin (vs autocthonous)

Question 21

What is a sedimentary basin?

Answer 21

Open volume of space that can be infilled with sediment
Different types are associated with different tectonic settings

Question 22

What are the types of sedimentary basins?

Answer 22

a) Extensional = rifts and passive margins
b) Compressive = trenches and foreland basins

Question 23

What is the Carskill Delta?

Answer 23

Found in Pennsylvania and New York
Consists of deltaic, channel and floodplain redbeds, and alluvial conglomerate
Crustal thickening pushed foreland area into mantle by isostasy
Fluvio-deltaic sediments overlie deepwater facies as uplift and compression proceeded
Zig-zag pattern indicates folds due to compression that formed Pangaea

Question 24

What orogenic events define the formation of Pangaea?

Answer 24

750mya = rifting of Rodinia and creation of Iapetus
540mya = formation of Iapetus Ocean
450mya = Taconic orogeny
350mya = Acadian orogeny
260-250mya = Pangaea formed
175mya = Pangaea broke up