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The Earth Through Time, 10th Edition
by Harold L. Levin
CHAPTER 13—MESOZOIC EVENTS
CHAPTER OUTLINE FOR TEACHING
I.
Overview of Mesozoic (251 to 65.5 million years ago)
A. Spans Three Periods
1. Triassic: spans 51 million years
2. Jurassic: spans 55 million years
3. Cretaceous: spans 80 million years
B. Evolution
1. Many new families of plants and animals
2. Two new vertebrate classes (birds and mammals)
C. Supercontinent of Pangaea: rifted apart over a span of 150 million years.
II. Breakup of Pangaea: 4 stages (three of those 3 during Mesozoic)
A. Stage One: Triassic
1. Rifting and volcanism, normal faulting
a. tensional stresses separated North America from Gondwanaland
b. similarly Mexico from South America
c. similarly eastern North America from northern Africa
2. Sea-floor generation during opening of oceans (basaltic volcanism)
B. Stage Two: Triassic-Jurassic
1. Rifting of narrow oceans between South Africa and Antarctica, Africa and India
2. Massive outpouring of basaltic lavas (covering 7 million km 2)
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C. Stage Three: Jurassic-Cretaceous
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Atlantic Ocean rift extended northward
Clockwise rotation of Eurasia (Europe)
Closing of eastern Tethys Sea (pre-Mediterranean)
South America-Africa split apart
Australia-Antarctica remained intact
Eastern North America-Greenland-Baltica remained intact
D. Stage Four: post-Mesozoic
1. Complete North America-Eurasia (Laurentia-Baltica) split
2. Antarctica-Australia split
III. Mesozoic History of North America
A. Triassic and Jurassic (eastern and southern areas)
1. Normal fault-bounded basins developed due to rifting: Nova Scotia to
North Carolina
a. troughs filled with terrestrial sediments and volcanics
b. Newark Group (Upper Triassic-Lower Jurassic)
c. Palisades basalts of NJ and NY (190 million years ago)
2. Fall Line: boundary of rift-faulted rocks, a prominent physiographic feature
3. Development of Gulf of Mexico
a. occupied areas opening south of Appalachian-Ouachita folded mountains
b. filled with Upper Triassic-Lower Jurassic salts and evaporites (indicating aridity);
over 1000 m deposited; origin of Gulf coast salt domes of today
B. Cretaceous (eastern and southern areas)
1. Flooding of coastal lowlands due to high sea levels
a. Atlantic and Gulf Coastal Plains inundated as they acted as subsiding shelves at
this time
b. thick deposits of deltas, barrier islands, shelves, reefs, etc. formed
c. Florida: shallow submarine bank for limestones
d. reefs made of rudistid bivalves rimmed Gulf Coastal area during Early
Cretaceous
e. extensive chalk deposits of Cretaceous sea due to massive production of
microscopic calcareous plankton (coccoliths); creta = chalk
2. Rifting and ocean opening on eastern side led to closure and compression on the
western side of continent; subduction resulted
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C. Triassic (western areas)
1. Accretionary tectonics - characteristic of west coast subduction at this time
a. steeply dipping subduction zone
b. volcanic arcs and micro-continents carried to western margin (displaced, exotic,
or alien terrains—as many as 50 now known)
c. massive accretion by subduction (including volcanism), obduction, and tectonic
accretion of displaced terrains
d. tectonic collage of displaced terrains may be 70% of total western accretion;
termed accretionary tectonics
2. Cordilleran region divisions
a. western belt: volcanics and siliceous deposits (800 m)
b. eastern belt: stable interior sediments
3. Sonoma orogeny: Permian-Triassic, Nevada
a. island arc collided with west coast
b. then a west-dipping subduction zone
c. added 300 km new area to west
d. massive thrust faulting
e. Sonoma terrain: additional rocks added during accretion
4. Eastern belt deposition
a. sandstones and limestones (shallow marine, 1000 m in Idaho, Early Triassic)
b. Lower Triassic continental red-bed facies farther east
c. Upper Triassic sediments: from rivers flowed west across area
d. Upper Triassic-Jurassic stratigraphy (Arizona): Moenkopi Fm. (oldest), Shinarup
Fm., Chinle and Kayenta Fms., Navajo Sandstone, Wingate Sandstone
D. Jurassic-Early Tertiary (western area)
1. Nevadan orogeny: eastward shift in orogenic effect
a. formation of convergent mélange deposits
b. Franciscan belt of California (classic mélange)
c. great volumes of granodiorite intruded: Sierra Nevada, Idaho, and Coast Range
batholiths
2. Sevier orogeny: Middle Jurassic-earliest Tertiary
a. precedes batholith intrusion
b. basement-involved tectonics: multiple imbricated thrust faults (low-angle
décollement structures)
c. mainly seen in NV and UT, also MT, BC, Alberta
d. crustal shortening by 100 km
3. Jurassic sedimentation
a. Navajo Sandstone (Lower Jurassic, MT, WY, NV, Alberta): clean recycled eolian
sands deposited in coastal dune and shoreline environments; covers 50,000 km 2
b. Sundance Formation (Middle) Jurassic, famous for fossil reptiles): deposits of the
Sundance Sea
c. Morrison Formation (Upper Jurassic, famous for dinosaurs): swampy plain
deposits formed as Sundance Sea regressed upon rising of Cordilleran highlands
to the west
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4. Laramide orogeny: Cretaceous-Paleogene
a. eastward shift in deformation
b. high-angle reverse faults
c. domes and anticlines
d. Rocky Mountain structures
5. Cretaceous sedimentation
a. foreland basin sedimentation
b. Early Cretaceous Seaway: seas withdrew during Middle Cretaceous regression
c. Late Cretaceous Seaway: greatest of marine intrusions (transgressions); flooded
area = foreland basin
(i) Dakota Group: transgressive-phase clastics (Great Plains area)
(ii) Niobrara Formation: carbonates of high sea level (limestones and marls)
d. bentonites: altered volcanic ash layers
IV. Mesozoic History of Eurasia (Europe) and the Tethys Seaway History
A. Triassic
1. Limestone deposition
2. Highlands developed to north (Vindelician arch)
3. New Red Sandstone deposited as clastic wedge
B. Jurassic: period of quiet
C. Cretaceous
1. Africa moves north toward Eurasia (Europe)
2. Compression during collision deforms Tethys sediments
3. Many great transgressions of the sea
V. Gondwanaland’s Continents
A. South America
1. Triassic: 3 depositional areas
a. western tract: turbidites, conglomerates, and siliceous sediments
b. eastern tract: deeper water carbonates and shales
2. Jurassic
a. widening split of South America and Africa
b. Andean belt deformation and volcanism
c. great outpourings of andesite in volcanic chain
d. emplacement of large batholiths
B. Africa
1. Early Triassic: Africa still joined to South America
2. Triassic-Jurassic: Karoo basin filled with fossiliferous continental clastics, then
1000 m of basalt flows due to rifting
3. Jurassic-Cretaceous: Africa is a stable continent
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C. India
1. Triassic-Cretaceous: moved continually north
2. Jurassic: interior sedimentation (dinosaurs well represented)
3. Cretaceous: vast outpourings of basaltic lava in northern regions (Deccan Traps
covering 500,000 km 2, as much as 1 million km3 of basalt makes it Earth’s greatest
known outpouring)
Answers to Discussion Questions
1. Rifting generally precedes the separation of continental crustal segments. Examples of
Mesozoic rifting include Triassic rifting of eastern North America and Gondwanaland and the
Jurassic-Cretaceous rifting of South America and Africa.
2. The Triassic Newark Group of the east coast of North America was formed in a tensional
stress environment that caused rifting with associated normal faulting and basaltic volcanism.
The rifts filled with alluvial and lacustrine sediments shed from adjacent fault-block
mountains. The normal faults originated from gravity effects after crustal stretching and
fracturing. Reverse faults were not produced for lack of requisite compression. Older lateral
strike-slip faults and reverse faults provided sites for reactivation of crustal movement during
rifting.
3. The Sevier orogeny involved basement crystalline rocks which were displaced laterally along
imbricate thrust faults. These low-angle features represent a décollement where extensive
amounts of crust become “unstuck” and are displaced laterally many kilometers. The most
well known structure is the Lewis Thrust with over 65 km displacement.
4. Arid conditions are accountable for producing extensive evaporation to produce 1000 m of
salt and gypsum. The tectonic setting also contributed such that a limited amount of
seawater could enter the basin, evaporate, and then be recharged by another influx of
seawater. The lighter specific gravity (density) of salt and gypsum and salt’s tendency to be
plastically deformed under great pressure help create conditions so that deeply buried salt
flows upward in the form of salt domes. Gulf Coast salt domes deform overlying strata as
they migrate upward and thus create structural conditions for accumulation of migrating
hydrocarbons in “petroleum traps.”
5. Accretionary tectonics probably accounts for most of the increase in size of North America
during Mesozoic. Accretionary tectonics encompasses all active margin processes which
add continental crust via subduction (including volcanism), obduction (including mélange
accretion), and welding of displaced terrains (both micro-continents and island arcs). In
North America during Mesozoic, accretionary tectonics characterizes the western belt of the
Cordilleran area during Triassic. The Sonoma Orogeny specifically is an example of such
tectonics. Likewise, with Jurassic the Nevadan Orogeny represents accretionary tectonics of
western North America. Allochthonous terrains contribute displaced continental crust
(perhaps 70% of total western Mesozoic accretion) and the energy of accretionary collision
produces structural effects and regional metamorphism. Passive margin sedimentation
accounts for the other part of North American size growth during Mesozoic.
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6. Deccan volcanism would have contributed significant amounts of greenhouse gasses
(especially CO2) in a relatively short period of time. Such an imbalance in atmospheric gas
mixture could have temporarily strongly elevated global temperatures.
7. Obduction involves off-scraping and thrusting of lighter rock, especially sediments, and in
some places, pieces of denser seafloor (ophiolites) onto continental crust as a process in
tectonic accretion. Subduction involves decent and re-melting of denser seafloor at a
convergent boundary. Examples of Triassic obduction are common. Examples of subduction
abound: the entire Mesozoic history of the western U.S. is dictated by continual subduction
as the Pacific Ocean closes.
8. Chalk is a sedimentary rock composed of microscopic calcareous plankton compressed
together. Cretaceous strata are especially rich in chalk deposits. The marine plankton-chalk
connection dictates composition and physical properties of the rock. The profusion of
coccoliths during Cretaceous is key to chalk’s domination of the marine sediment record of
that period.
9. Mesozoic Era lasted approximately 179 million years. Cretaceous Period lasted the longest
of the Mesozoic periods, 78 million years.
10. Cordilleran highlands adjacent to the retreating Sundance Sea were the likely sources of
clastic sediments comprising the Morrison Formation of the Rocky Mountain region. The
Morrison Formation shows evidence of fluvial (river) deposition and includes abundant traces
and bones from terrestrial vertebrates, especially dinosaurs.
11. Epicontinental (epeiric) seas were most extensive during Cretaceous and least extensive
during Triassic according to Mesozoic paleogeographic maps.
12. When the breakup of Pangaea began about 180 million years ago, the Tethys seaway was
located between Gondwanaland and Laurasia on the eastern side of Pangaea. Later, the
Tethys occupied the region between Africa-India-Australia (as a southern continent) and
Eurasia or Europe (as a northern continent). The Tethys was closed by northward movement
of Africa-India-Australia and subduction of Tethys seafloor beneath Eurasia (Europe). The
Mediterranean Sea, Adriatic Sea, Aegean Sea, and Black Sea occupy the former position of
the Tethys, and thus may be part of the former Tethys. Rocks deposited within the Tethys,
which extended from Japan to the western Mediterranean, may be formed in the Alps and
Himalayan Mountains.
13. The Late Cretaceous development of a “great embayment” of the Tethys resulted in a
connection of the Tethys and the northern Atlantic Ocean. Using the Western Interior
Seaway of North America as an example, the distribution of many sea creatures, for example
the abundant oysters of that time, could be used as evidence of a connection during that
time.
14. c
15. B
16. d
17. b
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Chapter Activities
Student activities for in-depth learning.
1. Some of the best-known and best-preserved early dinosaurs come from a locality in South
America at Ischigualasto, Argentina. Look at the University of California, Berkeley, Museum of
Paleontology web page on this famous locality and describe the age and types of dinosaur
remains that are found here http://www.ucmp.berkeley.edu/mesozoic/triassic/ischigualasto.html.
Why do you think that this is such a good place to look for dinosaur bones?
2. The Palisades basalts of the Hudson River area are remarkable volcanic features. Look at the
background information on these basalts at http://en.wikipedia.org/wiki/Palisades_Sill and answer
these questions. When were the Palisades basalts formed? Where do they lie relative to the
Hudson River today? How were they formed? What was going on in the geological history of
Pangaea that contributed to the outpouring of basalts that became the Palisades?
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