GSC 111 Lecture 17: The Early Mesozoic age of Dinosaurs
13 Jan 2017
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The Early Mesozoic age of Dinosaurs (Triassic and Jurassic)
1. Paleogeography of the early Mesozoic
a. Early Triassic
i. Pangaea is still assembled but we do start seeing the opening of the Tethys
Ocean
ii. Warm dry conditions
iii. Strong seasons
b. Middle Triassic
i. Earliest staging of rifting
ii. Rift basins are starting to form
c. Late Triassic
i. Basins are starting to elongate, Caribbean starting to form
d. Early Jurassic
i. More separation
e. Middle Jurassic
i. A fully developed seaway between North America and Africa
1. narrow
f. Late Jurassic
i. Well-developed reefs
ii. Oceans are forming
1. Caribbean sea has opened up
iii. Rifted North America from South America
2. Tectonic Events of North America
a. Fault block basins in the east
i. Early Mesozoic Rifting in North America
1. Late Triassic
a. Early stages of rifting
b. Continents being pulled apart
c. Formation of normal faults
2. Latest Triassic
a. Basins get flooded with marine sediments
b. May fill in and then evaporate out, forming evaporate
deposits
3. Early Jurassic
a. North American basin stops subsiding and we get a passive
continental margin
ii. Basins fill in with sediments, get flooded, we get evaporates
1. As they pull apart, we get a marine shelf developing on the margin
iii. Evidence is all along margin of eastern North America
1. We see fault block basins where one part is dropped down relative
to the other
2. As they are subsiding, they are being filled in with sediments that
are being eroded off the uplifting environments
3. Form alluvial fans
4. Record mass extinction event
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iv. Igneous and metamorphic rocks that have been heavily metamorphosed
during Alleghenian. We pull things apart and we see the fault blocks. Full
of sediments from highland areas. Sometimes we see dikes or sills that get
intrudeds
b. Westward expansion
i. Series of accreted island arcs and microcontinents
1. Devonian and early Carboniferous
a. Antler orogeny accretes Roberts Mountain terrain
2. Permian and Triassic
a. Sonoma orogeny accretes Sonomia microcontinent to
Western North America
3. Jurassic
a. Andean type subduction zine formed from Alaska to Chile
b. Volcanoes formed in present day Sierra Nevadas followed
by the accretion of a forearc accretionary prism
ii. Nevadan Orogeny
1. Jurassic
2. Subduction zone from Alaska to Chile
3. Oldest Sierra Nevada plutons
a. Granites that are deep in the Earth’s crust
4. Accretion of Great valley sequence and Franciscan Melange
3. Marine recovery from the Permo-Triassic Extinction
a. 96% of all marine species went extinct in Permo-Triassic extinction
i. Marks the transition from Paleozoic fauna (crinoid, trilobites rugose and
tabulate coral, bryozoan, brachiopod) to the “Modern fauna” (bivalve,
gastropod, echinoid)
b. Life on the seafloor
i. Epifaunal and infaunal sea urchins
ii. Scleractinian corals- modern coral
iii. Bivalaves and gastropods
c. Triassic Reefs- coralline sponges and scleractinian corals
i. Rugose and tabulate coral were the dominant reef builder from the
Ordovician to the Permian
1. Decline during Carboniferous
a. Switching to an aragonite sea
2. Wiped out in Permian mass extinction
d. Jurassic Reefs- Scelreactinian Corals, silicious sponges
i. Europe and North American tropical environment
e. Other marine invertebrates
i. Dinoflagellates
ii. Calcaereous nannoplankton
iii. Ammonoids and belemnoids
4. Gymnosperms and the age of Dinosaurs
a. Ferms and gymnosperms dominate the Mesozoic flora
i. Replace lycopods and sphenopsids
b. Three main groups of gymnosperms
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