Mesozoic Earth History (final exam) Flashcards
(35 cards)
What timeframe is the Mesozoic? What are the 3 periods in the Mesozoic era?
Mesozoic: 251-66 Ma
Triassic, Jurassic, Cretaceous
What’s the notable sea level trend in the Mesozoic?
Mostly around modern sea levels in the first half and then in the second half the sea levels were largely above current levels (in the Cretaceous)
What are some of the main Mesozoic geologic events?
- Pangaea broke up
- Atlantic ocean formed
- Rocky Mountains formed
- Accumulation of vast salt deposits > salt domes adjacent to which oil & gas were trapped (acting as a seal for a lot of our oil deposits)
- Gold and other ore deposits
(and all of these geologic impacts had a great effect on animal evolution)
Explain Stage 1 of the breakup of Pangaea
*Triassic
- rifting between Laurasia and Gondwana
- opening of Atlantic Ocean between North America and Africa in Triassic (beginning of Atlantic ocean)
Explain Stage 2 of the breakup of Pangaea
*Late Triassic / early Jurassic
- newly formed & expanding Atlantic Ocean > separated North America from Africa
- North America rifts from South America (this narrow sea between them ends up giving lots of evaporites)
Breakup of Gondwana:
- Antarctica and Australia separate from South America and Africa
- India rifts, moving north, separating from all
Explain why we had so many evaporite deposits with the breakup of Pangaea and why is this significant?
- Pangaea rifting apart and there was thinning crust along the rift zones
- with thinning comes depressions and water flows in to these shallow seas
- oftentimes there would be barriers from regular flows in from the ocean > therefore we have evaporites
- today we see evaporite deposits as evidence that coincides with the breakup - how and where the plates pulled apart
Explain Stage 3 of the breakup of Pangaea
*Jurassic
South America and Africa begin rifting apart
- narrow basin with evaporites
Eastern Tethys Sea begins closing (due to northern movement of Africa)
- ancestor to modern Mediterranean sea
Explain Stage 4 of the breakup of Pangaea
*Cretaceous
- Australia and Antarctica rift apart
- India nears the equator > eventually flies up and hits land and forms Himalayas
- South America and Africa are widely separated (bc of seafloor spreading - divergent plate boundary)
- Greenland separates from Eurasia and North America
- sea level rises > Cretaceous interior seaway > covers 1/3 of North American continent (Manitoba under water which is why we have the marine/reptile fossil creatures)
Why was the sea level rising so much during the Cretaceous?
- at the mid-ocean ridges there was lots of rifting happening - land masses forced apart - what comes up between them is lots of magma - as lava goes on to the surface we create new ocean floor - volume of lava displaces the water
*basically it’s because of the volcanic activity happening at mid-ocean ridges
What causes Earth’s Climates?
- caused by complex interaction between wind/the atmosphere and ocean currents > can explain the temperature gradient between tropics and poles
- location of continents
- topography (shape of the earth’s surface)
ex.
- arid, dry climates on large landmasses that are remote from sources of moisture or where barriers to moist air exist (ex. mountains)
- wet climates near large bodies of water or where wind carries moist air
How can we infer past climates from these climate specific rock deposits: evaporite deposits, sand dunes & red beds, and coal
Evaporite deposits: large area of thin water with no ready supply of more water > salt deposits in rock record = infer that the climate had greater evaporation than precipitation
Sand dunes & red beds: can infer arid regions typically
Coal: typically tropical, need plant material and moisture so we can infer humid conditions
How did Pangaea impact the climate of the Permian period?
Large size of Pangaea:
- arid conditions in low latitudes (centre of continent)
- humid conditions in higher latitudes (coasts of continent)
Vast expanse of Panthalassa ocean:
- small temperature gradient because of slow oceanic circulation
How did ocean circulation patterns change from Permian to Mesozoic and how did this impact climate?
*Greater ocean = slower circulaion = less of a temperature gradient because it’s all moving around and mixing together
End Permian > arid climates across much of Pangaea
Mesozoic and during the breakup of Pangaea:
- change in circulation patterns - more humid
- more circulation of oceans in between land masses - more complicated circulation
- Temperature gradient from equator to poles increased (but still relatively warm at mid to high latitudes due to warm waters from Tethys ocean)
- STRONGER SEASONALITY and SEVERITY OF WEATHER CHANGES with the season (still mild compared to what we see today though)
For the cratonic sequences of North America, what is the broad category of mountain-building episodes on the west margin and what are they on the east margin
west = cordilleran mountain-building episodes
east = appalachian mountain-building
What are the notable Mesozoic Cratonic sequences?
- Absaroka sequence regression
- Zuni sequence
What are the main points about the Absaroka sequence and Zuni sequence from the Mesozoic?
Absaroka sequence regressing in beginning Mesozoic:
- lead to nearshore marine and nonmarine sediments
Zuni sequence:
- formation of the Sundance Sea in Jurassic
- Sundance Sea regression led to deposition of
Jurassic Morrison formation > famous for dinosaur fossils
- Mid Cretaceous sea level rise *Western Interior Seaway
What were the main events happening on the west and east margins of North America in the Triassic
West:
- Cordilleran mobile belt continuing to form a chain of volcanic islands (which began in the Permian)
East:
- exposed craton above sea level - uplift
- erosion, block faulting, and igneous activity in the Appalachians as North America separated from Africa
Explain in more detail the impacts of the Appalachian Mountain Erosion > what occurred from the separation of North America and Africa?
*late Triassic - North America separating from Africa
- fault-block basins
- extensive lava flows on the fault-block basins > dikes and sills intruded in the basins
*Erosion of fault-block mountains produced the deposition sediments of the Newark Group (famous for dino footprints)
Explain why faults form and what are dikes and sills?
Faults:
- cold rocks behave differently from warm > more jarred movements, more brittle, will break and form faults (shown by thin lines on maps with arrows along them - 2 going opposite ways)
- Dikes:
- formed when faults get filled with lava > cross-cuts other cracks
Sill:
- sheet of igneous rock intruded between and PARALLEL with the existing strata
What are the main events in the Jurassic (regarding bodies of water)
- Gulf of Mexico widening and depositing extensive evaporites in the shallow sea as North America separated from South America
- Sundance sea flooded inland
What is the significance of the Gulf Coastal Region in the Jurassic and Cretaceous
It was above sea level until the separation of North and South America (became a newly flooded area)
- shallow and restricted leading to evaporites
- transitioned to normal marine by late Jurassic
REEFS during the Cretaceous
- bivalves = main reef building organism
- reefs = major oil reservoirs in the gulf region
Main events/sequences of North America during the Cretaceous
What’s going on with Manitoba?
- sea level rising steadily through the Cretaceous > **global transgressive sequences
- The North American continental interior, though inundated somewhat by seaways, was largely above sea level > Zuni Sequence
- Manitoba is completely underwater
Explain the stages of the Cretaceous Interior Seaway forming through the early, middle, and late Cretaceous
Early Cretaceous: Arctic waters spread southward over the North American craton to form a large inland sea in the Cordilleran region
Middle Cretaceous: global transgressions occurred due to expansion of oceanic ridges > widespread deposition of black shales (anoxic conditions)
Late Cretaceous: the Cretaceous Interior Seaway formed, extended from the Arctic to the Gulf of Mexico
What are Terranes? How do they differ from each other and from continents?
Terranes: small, exotic lithospheric blocks
- accreted onto larger continental blocks
- include island arcs, oceanic crust, small fragments of continents (analogous to cratons)
(exotic means it was formed in a different geologic setting from the main north american continent)
Differ from each other and continents in:
- fossil content, stratigraphy, structural trends, paleomagnetic properties
