GSC 111 Lecture Notes - Lecture 18: Western Interior Seaway, Nevadan Orogeny, Sevier Orogeny

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The Cretaceous World and K/T Mass Extinction
1. Paleogeography of the Cretaceous
a. Early Triassic
i. Pangaea is still fully assembled
ii. Subduction zone along western margin of Pangaea
b. Late Jurassic
i. North America being separated from South America and Africa
ii. India and Antarctica being rifted from Africa
c. Late Cretaceous
i. Look more like present-day conditions
ii. We have started to rift open South America and Africa
1. Narrow seaway between them
iii. Foreland basin in western margin of South America
iv. Colombia is completely underwater
v. India is broken up from Africa but still connected to Madagascar
vi. Antarctica in Australia are attached to each other
vii. Middle East is still open
1. Tethys Seaway still there
viii. Still have a tropical current, so the oceans and the climate are very
different from today
d. Latest Cretaceous
i. New oceanic crust being created
ii. Fast seafloor spreading in Atlantic and Pacific
iii. Subduction all over the place
e. Radiometric dating of oceanic crust
i. Most oceanic crust today is from the Cenozoic and Mesozoic
1. Produced following the breakup of Pangaea
2. Tectonic Events of North America
a. Nevadan orogeny of the Late Jurassic
i. Western coast of North America
ii. Created plutons
iii. Subducting and forming volcanism close to the coast
b. Sevier Orogeny
i. Subducting slab changes its angle from fairly steep angle in Late Jurassic
to fairly shallow angle
1. Volcanism moves further east
2. We get a fold-and-thrust belt all the way to Colorado
3. When rates of sea floor spreading and subduction increase, we are
subducting warmer crust
a. It is warmer and less dense, so it does not penetrate as
much into the mantle
ii. Continuation of the Nevadan Orogeny
3. Cretaceous Interior Seaway
a. Cretaceous climate and sea level
i. Much warmer than it is now
1. Subtropical plants found in the Arctic circle
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