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Mesozoic Earth History
245-65 Million years ago
Triassic
Jurassic
Cretaceous
Geologic Time Scale
www.geo.ucalgary.ca/~macrae/timescale/time_scale.gif
Main Happenings in Mesozoic
• Breakup of Pangaea
• Lots of mountain-building in western North America
• Appearance + extinction of dinosaurs
• More detail in the geologic record
– More climate information!
Climate information in the geologic
record
• Evaporites: precipitation < evaporation =
dry
• Coal = lots of vegetation + lots of moisture
• Sand dunes = dry
Tectonic drivers of climate
• Tectonics influences the hydrologic cycle
– Mountains can block rainfall
– Massive continents tend to have hotter, drier
cores
– Coastal regions are more moderate
• Circumpolar currents prevent heat from
reaching poles
• N/S currents move heat effectively
End Permian land and oceans
• Pangaea was shaped
like a ‘C’
• Inside ocean: Tethys
Sea
• Outside ocean:
Panthalassa
Panthalassa
Panthalassa
Tethys sea
www.ig.utexas.edu/research/projects/plates/images/pangea.jpg
Breakup of Pangea 1: Triple Junctions
• Seafloor spreading
creates a triple
junction: a point
where 3 tectonic
plates diverge
• North America split
off from S America
and Africa
Triple Junctions
Seafloor spreading raises sea
level
• Seafloor spreading causes bulges in ocean
basins
• Big enough bulges and/or lots of them
lowers the ocean volume
• This can cause flooding of the continents.
Breakup of Pangaea 2:
Opening of Gulf of Mexico
• In Middle Jurassic, North America and South
America separated
• Gulf of Mexico began to open
• Restricted basin at first – lots of evaporites deposited
Gulf of Mexico Salt
http://oceanexplorer.noaa.gov/technology/tools/mapping/media/gis_gulf.html
Paleogeography of the World
• During the Triassic Period
Paleogeography of the World
• During the Jurassic Period
Breakup of Pangaea 3:
Continued Widening of North Atlantic
• In Late Cretaceous, Atlantic widened rapidly
• Canada and Europe separated
Final Breakup
• In Late Cretaceous, Australia and Antarctica separated
• In Cenozoic, Antarctica and South America separated
Paleogeography of the World
• During the Late Cretaceous Period
At the end of the Triassic, Pangea began
to rift apart.
The supercontinent of Pangea, mostly assembled by the Triassic, allowed
land animals to migrate from the South Pole to the North Pole. Life
began to rediversify after the great Permo-Triassic extinction and
warm-water faunas spread across Tethys.
Pangea was assembled piece-wise. The continental
collisions that lead to the formation of the
supercontinent began in the Devonian and continued
through the Late Triassic.
In a similar fashion, the supercontinent of Pangea did not
rift apart all at once, but rather was subdivided into
smaller continental blocks in three main episodes.
The first episode of rifting began in the middle Jurassic,
about 180 million years ago. After an episode of igneous
activity along the east coast of North America and the
northwest coast of Africa, the Central Atlantic Ocean
opened as North America moved to the northwest. This
movement also gave rise to the Gulf of Mexico as North
America moved away from South America. At the same
time, on the other side of Africa, extensive volcanic
eruptions along the adjacent margins of east Africa,
Antarctica, and Madagascar heralded the formation of the
western Indian Ocean.
During the Mesozoic North America and Eurasia were
one landmass, sometimes called Laurasia. As the Central
Atlantic Ocean opened, Laurasia rotated clockwise,
sending North America northward, and Eurasia
southward. Coals, which were abundant in eastern Asia
during the early Jurassic, were replaced by deserts and
salt deposits during the Late Jurassic as Asia moved
from the wet temperate belt to the dry subtropics. This
clockwise, see-saw motion of Laurasia also lead to the
closure of the wide V-shaped ocean, Tethys, that
separated Laurasia from the fragmenting southern
supercontinent, Gondwana.
By the Early Jurassic, south-central Asia had assembled. A
wide Tethys ocean separated the northern continents from
Gondwana. Although Pangea was intact, the first rumblings
of continental break up could be heard.
The supercontinent of Pangea began to break apart in the Middle
Jurassic. In the Late Jurassic the Central Atlantic Ocean was a
narrow ocean separating Africa from eastern North America.
Eastern Gondwana had begun to separate form Western
Gondwana.
During the Cretaceous the South Atlantic Ocean opened. India
separated from Madagascar and raced northward on a collision
course with Eurasia. Notice that North America was connected to
Europe, and that Australia was still joined to Antarctica.
The second phase in the breakup of Pangea began in the
early Cretaceous, about 140 million years ago.
Gondwana continued to fragment as South America
separated from Africa opening the South Atlantic, and
India together with Madagascar rifted away from
Antarctica and the western margin of Australia
opening the Eastern Indian Ocean. The South Atlantic
did not open all at once, but rather progressively
"unzipped" from south to north. That is why the South
Atlantic is wider to the south.
Other important plate tectonic events occurred during the
Cretaceous Period. These include:
- the initiation of rifting between North America and Europe,
- the counter-clockwise rotation of Iberia from France,
- The separation of India from Madagascar, the derivation of
Cuba and Hispaniola from the Pacific,
- the uplift of the Rocky mountains,
- and the arrival of exotic terranes (Wrangellia, Stikinia) along
the western margin of North America.
Globally, the climate during the Cretaceous Period, like
the Jurassic and Triassic, was much warmer than today.
Dinosaurs and palm trees were present north of the
Arctic Circle and in Antarctica and southern Australia.
Though there may have been some at the poles during
the Early Cretaceous, there were no large ice caps at
anytime during the Mesozoic Era.
These mild climatic conditions were in part due to the fact
shallow seaways covered the continents during the
Cretaceous. Warm water from the equatorial regions was
also transported northward, warming the polar regions.
These seaways also tended to make local climates milder,
much like the modern Mediterranean Sea, which has an
ameliorating effect on the climate of Europe.
Shallow seaways covered the continents because sea level
was 100 - 200 meters higher than today. Higher sea
level was due, in part, to the creation of new rifts in the
ocean basins that displaced water onto the continents.
The Cretaceous was also a time of rapid sea-floor
spreading. Because of their broad profile, rapidly
spreading mid-ocean ridges displace more water than do
slow spreading mid-ocean ridges. Consequently, during
times of rapid sea-floor spreading, sea level will tend to
rise.
50 - 55 million years ago India began to collide with Asia
forming the Tibetan plateau and Himalayas. Australia, which
was attached to Antarctica, began to move rapidly northward.
20 million years ago, Antarctica was coverd by ice and the
northern continents were cooling rapidly. The world has
taken on a "modern" look, but notice that Florida and parts of
Asia were flooded by the sea.
When the Earth is in its "Ice House" climate mode, there is ice at
the poles. The polar ice sheet expands and contacts because of
variations in the Earth's orbit (Milankovitch cycles). The last
expansion of the polar ice sheets took place about 18,000 years ago.
Where did most North American
mountain-building occur during
Paleozoic?
Where did most North American
mountain-building occur during
Paleozoic?
East Coast - Appalachians
Cordillera Orogenies
• General term refering to complex period of
mountain-building Jurassic-Cenozoic
• Farallon plate goes below N American plate
– Nevadan orogeny – Late Jurassic/Early Cretaceous
• Orogeny near the current W coast
• Slope of subducting Farallon plate decreased ->
– Sevier orogeny – Late Cretaceous
• Further east (Utah)
– Laramide orogeny – Late Cretaceous/Cenozoic
• Even FURTHER east! Rockies
Global Sea-Level Rise
• A global rise in sea level during the Cretaceous
– resulted in worldwide transgressions
– marine deposition was continuous over much of the
North American Cordillera
Cretaceous Flood
• Worldwide transgression
• 1/3 of land area of Earth submerged
• 100 Ma
• Cretaceous Interior Seaway in North America
Cretaceous Interior Seaway
• Paleogeography
of North America
during the
Cretaceous
Period
Western Interior Seaway
www.isgs.uiuc.edu/dinos/westernseaway.gif
The Effects on Global Climates
and Ocean Circulation Patterns
• At the end of the Permian Period
– Pangaea extended from pole to pole
– Covered about one-fourth of Earth's surface
– Surrounded by a global ocean that encompassed about 300 degrees of
longitude
• Such a configuration exerted tremendous influence on the
world's climate
– resulted in generally arid conditions over large parts of Pangaea's
interior
Oceanic Circulation Evolved
• From a simple pattern in a single ocean
(Panthalassa) with a single continent (Pangaea)
Oceanic Circulation Evolved
• to a more complex pattern in the newly formed
oceans of the Cretaceous Period
Areas Dominated by Seas
Are Warmer
• Oceans absorb about 90% of the solar radiation they receive
– continents absorb only about 50%
– even less if they are snow covered
• The rest of the solar radiation is reflected back into space
• Therefore, areas dominated by seas are warmer than those
dominated by continents
Mesozoic Tectonics (Key Events)
Period
North America
Orogenies
Cretaceous
Jurassic
Triassic
Devonian
Other Major Events
Separation of India
from Gondwanna
Nevadan Orogeny
(J-K)
Sevier Orogeny
(J-K)
Opening of Atlantic
Ocean
Sonoma Orogeny
(Triassic)
Opening of Gulf of
Mexico
Antler Orogeny
(Devonian)
Mesozoic Tectonics
The separation of Gondwana
and Laurentia began in the
Triassic.
Initial flooding of the “Atlantic
Ocean” began in the Jurassic.
This was the start of a new drift
direction for North America;
WNW
Mesozoic Tectonics
Into the Triassic, many more
“terranes” (mostly island arcs)
began to be scooped up by
North America as it drifted
WNW
Mesozoic Tectonics
Into the Triassic, many more
“terranes” (mostly island arcs)
began to be scooped up by
North America as it drifted
WNW
•Brooke Range Terrane (Alaska)
•Stikine Terrane (British Columbia)
•Sonoma Terrane (Nevada)
Mesozoic Tectonics
Into the Triassic, many more
“terranes” (mostly island arcs)
began to be scooped up by
North America as it drifted
WNW
•Brooke Range Terrane (Alaska)
•Stikine Terrane (British Columbia)
•Sonoma Terrane (Nevada)
Mesozoic Tectonics
The Sonoman Orogeny in the
Triassic marks the start of the
formation of the Cordilleran
Mountains and the current
active margin
Mid-Triassic Paleogeography
(source
Mesozoic Tectonics
In the Jurassic, we start to see
terranes with mixed lithologies
docking with North America
(e.g., Klamath Terrane)
•Major (felsic) intrusions
begin
Mesozoic Tectonics
The culmination of several
“hits” and docking events
as well as major phases of
felsic intrusions is
collectively called the
Nevadan Orogeny
Mid-Jurassic Paleogeography
(source
Mesozoic Tectonics
In the Cretaceous, more hits
and more intrusions. More
uplift
•Wrangellia Terrane docks
Mesozoic Tectonics
The culmination of several
“hits” and docking events
from the Jurassic to the
Cretaceous produced
major phases of thrust
faulting and is collectively
called the Sevier Orogeny
Early Cretaceous Paleogeography
(source
Mesozoic Paleogeography
 Most continents were
isolated
 Seas opened:
 South Atlantic; Gulf of
Mexico; Caribbean
Sea
 Mid-Cretaceous sea
level high
 Tethys Seaway
Mesozoic Climate
 Wind belt
– Evaporite
deposition
Mesozoic Climate
 High latitudes were
warm
– 50°F / 10°C
– Dinosaurs near south
pole
Mesozoic Climate
 Period of high sea
level
 Associated with rapid
sea floor spreading
 Long period without
reversal
Mesozoic Climate
• Oceans stagnated
 Epicontinental black
muds when seas spilled
over
 Normally thin oxygen
poor zone expanded
This will change in the
early Cenozoic (Late
Eocene)
Cenozoic Climate
 Oxygen isotopes
 Late Eocene cooling
 Deep sea foraminifera
Cenozoic Climate
Paleocene-Middle Eocene:
•No circumpolar current
Late Eocene-today:
•Circumpolar current
–Permitted development of
glaciers on Antarctica
Cenozoic Climate
Cenozoic Tectonic Events
Final breakup of Gondwana (Australia separated from Antarctica in the Latest
Paleocene – earliest Eocene epochs)
India began to collide with Asia forming the Himalayan Mountain Range
(Oligocene to Recent)
Africa started to shift northward, gradually sliding under Europe and uplifting
the Alps (Oligocene to Recent)
Continued westward movement of North America and South America formed
an on again off again land bridge between the two continents. This gave rise to
some interesting animal exchanges.
North American orogenies become dominated by strike-slip faulting and
uplift. Mountain building in the northern part of the Cordilleran mountains
(mostly Canada) slows down stop during the Oligocene. Activity shifts to the
southern part of the mountain chain (Colorado, Nevada etc.).
Major late Tertiary flood basalt eruptions occur in Oregon and Washington
state. Hot spot volcanism occurs in the area of Yellowstone (Pliocene to
present). Composite volcanic eruptions (some incredibly explosive)
periodically occurred and still do (e.g., Mt St Helen’s).
Himalayan Mountains
 Indian craton collided
with Eurasia