CHAPTER 13—MESOZOIC EVENTS
CHAPTER OVERVIEW
The Mesozoic Era, “Middle Life” (Triassic, Jurassic, and Cretaceous) marks a natural boundary to the end
of the Paleozoic. The mass extinctions of the late Palezoic that defined the boundary of those periods
meet the “New” changes. Those dramatic changes are noted in the continental evolution of life forms and
the crustal unrest of the continents. The breakup of Pangea is taken as a point and is discussed on a
global scale as are the configurations of the continents. A comprehensive view of the accretionary
tectonics is discussed along with the other physical processes of the Mesozoic Era that affected North
America and the rest of the world.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:
Explain the breakup of Pangea using stages (steps) in your discussion along with major
geographic features.
Discuss the conditions that account for the presence of evaporites in the Gulf Coast and how
they are related to petroleum traps in overlying cretaceous and cenozoic strata.
Discuss what is meant by the term accretionary tectonics.
Define the accretionary tectonics terms exotic terrane, obduction, tectonic collage.
Describe the major Orogenic events that affected western North America during the
Mesozoic Era including Sonoma, Nevada, Sevier, and Lamamide.
Discuss the epicontinental seas (over the continents) of the Jurassic and Cretaceous, and
give evidence for their existence.
Describe the Upper Triassic and Lower Jurassic formations that are exposed in the walls of
Zion Canyon in southern Utah.
Discuss the geologic history of the Tethys Seaway and the periods of its extent.
Describe Gondwana events including those taking place in South America, Africa, and India.
CHAPTER OUTLINE
I.
The Breakup of Pangea
II.
The Mesozoic in Eastern North America
A. Triassic and Jurassic Periods
B. Cretaceous (the “Chalk” Period)
III.
The Mesozoic in Western North America
A. Accretionary Tectonics: A Way to Grow
B. Triassic Period: Volcanism, Orogenies, and Arizona’s Petrified Logs
1. Sonoma Orogeny
C. Jurassic Period Orogenies: Nevadan, Sevier, and Laramide
1. Nevadan Orogeny
2. Sevier Orogeny
3. Laramide Orogeny
D. Jurassic Habitats for Marine Reptiles and Dinosaurs
E. The Great Cretaceous Epicontinental Sea
1. Foreland Basin and Economic Resources
IV.
The Tethys Sea in Europe
V.
Godwana Events
A. South America
B. Africa
C. India
Chapter 13—Mesozoic Events
KEY TERMS (Pages 373–403)
accretionary tectonics (380): The growth of a continent by the progressive incorporation of crustal
fragments by either obduction or subduction.
bentonite (395): Bentonite is composed of clay minerals that are formed by the alteration of volcanic ash.
Cretaceous rocks of Wyoming and Colorado include extensive beds of this soft, plastic, light-colored
clayey rock.
chalk (378): A fine-grained white, soft variety of limestone composed mainly of the microscopic
calcareous platelets (coccoliths) of golden-brown algae. The Cretaceous Period takes its name from
Creta, the Latin name for chalk.
Dakota Group (395): Lower Cretaceous sandstone beds that mark the transgressive phase of the
Cretaceous sea. The red, yellow, and brown layers of the Dakota are exposed in many places along the
eastern front of the Rocky Mountains, where the inclined beds formed prominent ridges called hogbacks.
Deccan Traps (Plateau) (401): The northwestern half of India was flooded with immense quantities of
low-viscosity basaltic lava. The now solidified lavas are flood basalts of the Deccan Traps. The
outpouring continued from Cretaceous time well into the Cenozoic. These basalt floods likely record the
passage of India across a fixed hot spot in the mantle.
exotic terranes (378): Exotic masses of rock of tectonic origin that have been displaced from their origin.
foreland basin (393): In terms of plate tectonics, the depositional basin that receives sediments (as well
as smaller amounts from the craton). The foreland basin of the western interior of North America was
immense. It extended from the Arctic to the Gulf of California, and in some places it was over 1600
kilometers wide.
Laramide Orogeny (385): In general, those pulses of mountain building that were frequent in late
Cretaceous time and were in large part responsible for producing many of the structures of the Rocky
Mountains.
mélange (384): A sequence of crumpled and altered rock that were affected by compression between
converging plates. The Franciscan fold belt of California represents a mélange.
Morrison Formation (387): Formation formed when the Sundance Sea regressed, leaving behind a vast,
swampy plain across which meandering rivers build floodplains. The Morrison Formation extends across
millions of square kilometers of the American West. Enclosed within these floodplain deposits are the
bones of more than 70 species of dinosaurs.
Nevadan Orogeny (383): In general, those pulses of mountain building, intrusion (magmatism), and
metamorphism (deformation) that were most frequent during the Jurassic and early Cretaceous along the
western part of the Cordilleran Orogenic belt. During the Triassic, and increasing in frequency during the
Jurassic and Cretaceous, graywackes, mudstones, cherts, and volcanics that had been swept into the
subduction zone were severely folded, faulted, and metamorphosed.
Niobrara Formation (395–396): Cretaceous carbonate formation including soft, clayey limestones and
chalky shales. The Niobrara has yielded the remains of a variety of marine creatures, including enormous
numbers of oysters, a large Cretaceous diving bird, marine reptiles, and the large flying reptile
Pteranodon.
obduction (380): The process whereby one rock mass rides up and over another (the opposite of
subduction).
rudistid (378): Peculiarly specialized Mesozoic bivalva often having one valve in the shape of a horn
coral, covered by the other valve in the form of a lid.
Chapter 13—Mesozoic Events
salt dome (375): Huge, cylindrical domes that are economically important structures in that they help
entrap oil and natural gas.
Sevier Orogeny (385): A second phase of the tectonic development of the Cordillera which primarily
affected shallow-water carbonates and terrigenous clastics deposited over a time span from Middle
Jurassic to earliest Cenozoic. During the Sevier Orogeny, strata were sheared from underlying
Precambrian rocks and broken along parallel planes of weakness to form multiple, imbricated, low-angle
thrust faults. Decollement (unsticking) is the term used to describe this kind of structure in which older
rocks are thrust on younger in multiple, nearly parallel slabs of crust.
Sonoma Orogeny (385): Middle Permian orogenic movements, the structural effects of which are most
evident in western Nevada. It occurred when an eastward-moving volcanic arc, called the Golconda arc,
collided with the Pacific margin of North America (western edge of Nevada).
Sonoma Terrane (381): Triassic rocks of the far western Cordillena include volcanics and graywackes
derived from the island arc. The Sonoma Terrane originated in the Pacific Ocean.
Sundance Formation (387): Famous for its fossil content of Jurassic marine reptiles. Sediment in the
Sundance Formation and overlying younger Jurassic rock units was derived from the Cordilleran
highlands that lay to the west.
Sundance Sea (487): A great embayment occurring during the Middle Jurassic. Marine conditions
became more widespread. The entire west-central part of the continent was flooded by a wide seaway
that extended well into central Utah. Within the Sundance sea were deposited the sand and silts of the
Sundance Formation.
tectonic collage (380): An analogous region of displaced terranes.
Tethys Sea (396–398): Sea between Eurasia and Africa that began to narrow as a result of compression
from the northwardly-moving African plate.
Chapter 13—Mesozoic Events
MULTIPLE-CHOICE QUESTIONS
1.
During the Mesozoic, the westward motion of the North American continent was a result of the
a. opening of the Iapetus sea.
c. opening of the Pacific Ocean.
b. opening of the Tethys Sea.
d. opening of the Atlantic Ocean.
2.
What was the geologic period during which the Sundance Sea occupied a large region of the
western United States?
a. Carboniferous
c. Jurassic
b. Triassic
d. Cretaceous
3.
The geographic (and geologic) separation between the Triassic faulted sedimentary basins and
crystalline rocks of the east coast of the United States and the flat-lying Cretaceous sediments of
the Atlantic coastal plain is called the
a. Newark Basin.
c. Mississippian Embayment.
b. Fall Line.
d. Palisade Sill.
4.
The shells of these bivalves form the basic framework of many Cretaceous reefs. They have high
porosity and permeability, making their reefs some of the world’s greatest Cretaceous oil reservoirs.
They are termed
a. coccoliths.
c. accretions.
b. rudists.
d. chalk reefs.
5.
Chalk is composed of the shells of what organism?
a. diatoms
c. radiolaria
b. rudists
d. coccoliths
6.
During plate collisions, the process that occurs when low-density rocks (and sediments) from a
subducting oceanic plate are emplaced on the continental plate is called
a. accretion.
c. reduction.
b. obduction.
d. shortening.
7.
During the Triassic, and increasing in frequency during the Jurassic and Cretaceous, graywackes,
mudstones, cherts, and volcanites that had been swept into the subduction zone were severely
folded, faulted, and metamorphosed. The intensely crumpled and altered rock sequences that were
affected by compression between the plates are appropriately termed
a. mélange.
c. batholiths.
b. decollement.
d. strata.
8.
The Moenkopi, Shinarump and Chinle Formations all formed in what geologic period?
a. Permian
c. Jurassic
b. Triassic
d. Cretaceous
9.
The initial orogenic event that marked the development of the Cordillera region was the
a. Sevier Orogeny.
c. Laramide Orogeny.
b. Nevadan Orogeny.
d. Sonoma Orogeny.
10.
The Nevadan Orogeny that resulted in the intrusions of the granite batholiths that formed the Sierra
Nevada Mountains took place during what geologic period?
a. Triassic
c. Cretaceous
b. Jurassic
d. Permian
11.
During which orogeny were strata sheared from underlying Precambrian rocks and broken along
parallel planes of weakness to form multiple, imbricated, low angle thrust faults?
a. Sevier Orogeny
c. Nevadan Orogeny
b. Sonoma Orogeny
d. Laramide Orogeny
12.
Cretaceous rocks of Wyoming and Colorado contain rocks composed of clay minerals formed by
the alteration of volcanic ash. These clayey rocks are called
Chapter 13—Mesozoic Events
a. bentonites.
b. flysch.
c. molasses.
d. mélanges.
13.
Besides the extensive mountain-building events of the late Cretaceous, this period of geologic time
is also noted for
a. widespread marine regressions.
c. widespread glaciation.
b. widespread marine transgressions.
d. increase in global temperatures.
14.
What Cordilleran Orogeny occurred in the Cretaceous and was characterized by eastward directed,
low-angle thrust faults?
a. Sonoma
c. Sevier
b. Nevadan
d. Laramide
15.
The flood basalts of the Deccan Plateau (Traps) in India suggest that
a. the Indian continent experienced a failed rifting event.
b. the Indian continent was struck during the late Cretaceous by a meteorite.
c. the Indian continent passed over a “hot spot” on its voyage toward Laurasia.
d. they are the eroded remnants of once extensive volcanoes.
16.
The dismemberment of Pangea occurred in four stages. The first stage occurred in the __________
with rifting and volcanism along normal fault systems.
a. Permian
c. Jurassic
b. Triassic
d. Cretaceous
17.
The second stage in the dismemberment of Pangea involved the opening of narrow oceanic tracts
between southern Africa and _____________.
a. Europe
d. Antartica
b. North America
e. Asia
c. South America
18.
The final stage in the breakup of Pangea occurred early in the Cenozoic Era and took an estimated
______________ years for Pangea fragmentation.
a. 25 million
d. 100 million
b. 45 million
e. 150 million
c. 65 million
19.
The orogenic event of the Cordilleran region occurred at or near the Permian-Triassic boundary
when an eastward-moving volcanic arc collided with the North American Pacific margin is called the
a. Laramide Orogeny.
d. Nevadan Orogeny.
b. Seiver Orogeny.
e. Acadian Orogeny.
c. Sonoma Orogeny.
20.
This organic event shifted eastward to the Cratonic region where today’s Rocky Mountains of New
Mexico, Colorado, and Wyoming are located. The move-eastward disturbances constitutes the
a. Laramide Orogeny.
d. Nevadan Orogeny.
b. Seiver Orogeny.
e. Acadian Orogeny.
c. Sonoma Orogeny.
Chapter 13—Mesozoic Events
FILL IN THE BLANK
1.
The orogeny that occurred when an eastward-moving volcanic arc collided with the Pacific margin of
North America during the Permian-Triassic is called the
.
2.
The geologic features that extend from the Cretaceous into the Cenozoic and mark the passage of
India across a fixed hot spot in the mantle is
3.
In contrast to subduction, the process that occurs when one rock mass rides up and over another is
called
.
4.
The Laramide Orogeny at the end of the Cretaceous resulted in the formation of what range?
5.
The orogenic event that marked the formation of low-angle detached thrust faults and which
resulted in over 100 kilometers of crustal shortening in the Nevada Utah area is called
.
6.
The formation that is well known for the presence of Jurassic terrestrial reptiles and dinosaurs and
that strongly suggests that the fossils of this formation were terrestrial in origin is
.
7.
The Cretaceous formation that has yielded the remains of a variety of marine creatures, a large
Cretaceous diving bird, marine reptiles and the large flying reptile Pteranodon is called
.
8.
The basin at the southern end of Africa that formed late in the Carboniferous but is known for its
wealth of fossilized mammal-like reptiles is called
9.
The Painted Desert of Arizona is developed mostly with what formation?
.
10.
Chalk is composed of the shells of what organism?
11.
The growth of a continent by progressive incorporation of crustal fragments and exotic terranes is
called ______________ __________________.
12.
The crumpled, altered rock sequences that are trapped between converging plates are called a
______________.
13.
In plate tectonic terms, the depositional basin that received terrigenous clastics supplied by streams
from the Cordilleran highlands is called a ______________ _____________.
14.
In geology, an analogous region of displaced terranes is called a ____________ _____________.
15.
During the Cretaceous Period invertebrates called ________________ contributed their skeletal
substance to reefs.
.
Chapter 13—Mesozoic Events
TRUE-FALSE
1.
Evaporative conditions were prevalent in the Gulf Coast region during the late Triassic
and Jurassic, resulting in the deposition of thick layers of salt that contributed to the
formation of salt domes.
2.
The supercontinent of Pangea first started to rift apart in the early Jurassic.
3.
The rifting of a supercontinent such as Pangea is often signaled by outpourings of lava
and other volcanic activity.
4.
Obduction occurs when high-density rock material is stripped off and emplaced on lowdensity rock material during continent-continent plate collisions.
5.
Most of the structures of the present-day Rocky Mountains are a result of the Sevier
Orogeny.
6.
The Deccan Plateau (also called the Deccan Traps) may record the passage of a drifting
India over a “hot spot” in the mantle.
7.
The poor sorting and high content of unweathered rock and mineral fragments suggests
that the sediments of the Newark Group were transported only a short distance from the
source of the sediments.
8.
The upward motion of the salt from evaporite layers in the Gulf Coast deforms and
fractures the overlying rock, providing structural traps for petroleum and natural gas.
9.
The Jurassic Morrison Formation has provided excellent fossil remains of many large
marine reptiles.
10.
The sequence of formations that are exposed in the walls of Zion Canyon in southern
Utah is upper Triassic: Chinle Group, Moenkopi, Shinarump, followed by Lower Jurassic
Navajo sandstone, Wingate sandstone, Kayenta Formation.
Chapter 13—Mesozoic Events
ANSWER KEY
Multiple Choice
1. d
2. c
3. b
4. b
5. d
6. b
7. a
8. b
9. d
10. b
11. a
12. a
13. b
14. c
15. c
16. b
17. d
18. e
19. d
20. d
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Sonoma Orogeny
Deccan Traps
Obduction
Rocky Mountains
Sevier Orogeny
Morrison Formation
Niobrara Formation
Kavoo basin
Chinle Formation
Coccoliths
accretionary tectonics
mélange
foreland basin
tectonic collage
rudistids
True/False
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
T
F
T
F
F
T
T
T
F
F
Chapter 13—Mesozoic Events
RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES
FIGURE 13–2 (p. 376) Faulting along the eastern margin of North America was a consequence of the
separation of North America from the Moroccan region of northwestern Africa.
FIGURE 13–7 (p. 379) Examination of the map should reveal whether the location of your college was on
land, beneath a shallow sea, or in the open ocean.
FIGURE 13–10 (p. 381) The fault is a normal or tensional fault, such as would be expected along the
trailing passive margin of a tectonic plate.
FIGURE 13–22 (p. 390) An ophiolite suite would have been developed just east of the trench.