Download Chapter 23 The Geology of the Mesozoic Era

201
Chapter
23
The Geology of the Mesozoic Era
GUIDED STUDY
The text chapter should be studied one section at a time.
Before you read, preview each section by skimming it,
noting headings and boldface items. Then read the
appropriate section objectives from the following
outline. Keep these objectives in mind and, as you read
the chapter section, search for the information that will
enable you to meet each objective. Once you have
finished a section, write out answers for its objectives.
4. Describe the events that occurred with the breakup
of Gondwana during the Jurassic and Early
Cretaceous periods.
The Divisions of the Mesozoic (pp. 478-479)
1. Explain the events that both open and close the
Mesozoic Era.
5. What features indicate that Mesozoic climates were
both warmer and more stable than in the preceding
Paleozoic?
A Global Perspective (pp. 479-481)
2. Describe the geography of Pangaea at the beginning
of the Mesozoic Era.
6. What evidence suggests the occurrence of monsoon
climates in northern and southern Pangaea during
the Triassic and early Jurassic periods?
North America in the Mesozoic (pp. 482-498)
3. What happened in the initial stage of breakup of the
continent of Pangaea?
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7. Describe the tectonic activity that occurred along
the eastern margin of North America following the
formation of the Appalachian Mountains.
202
8. Why did the Gulf Coast margin accumulate such a
great thickness of sediments during the Mesozoic
Era?
9. Describe the events of the Nevadan orogeny.
CHAPTER REVIEW
When you have finished reading the chapter, work
through the material that follows to review it. Complete
the sentences. As you proceed, evaluate your
performance for each section by consulting the answers
on pages 209-210. Do not continue with the next section
until you understand each answer. If you need to, review
or reread the appropriate section in the textbook before
continuing.
Introduction (pp. 477-478)
10. Describe the effects of the Sevier orogeny on the
foreland basin sediments of the western margin of
North America.
1. The Ancestral Puebloans built their dwellings
beneath cliffs of _____________ ___________
exposed in southwestern Colorado.
2. Their structures were placed inside caves and
alcoves formed by the ______________of calcite
11. Discuss how deformation of the Laramide orogeny
differed significantly from that of the “thinskinned” Sevier tectonics.
cement in the porous rock cliffs.
3. The greatest change that occurred in North America
during the Mesozoic Era was the ________ of
Pangaea.
4. North America grew substantially larger in the
Mesozoic, primarily because of an abundance of
12. Describe the depositional environments represented
Triassic sedimentary rocks of western North
America.
accreting ____________.
Divisions of the Mesozoic (pp. 478-479)
5. The beginning of the Mesozoic is defined by a
boundary at 248 million years, which marks an
abrupt change in the _________ ______.
13. What is the significance of the Jurassic Morrison
Formation of western North America?
6. The end of the Mesozoic is marked by the mass
extinction of many animals including ___________,
which occurred 66 million years ago.
7. The __________ Period was defined in 1834 from
14. What factors caused the Western Interior Seaway to
form, and flood the North American continent to its
greatest coverage since the Paleozoic?
Germany, where three distinct rock formations are
found.
8. The Jurassic Period was named from the Jura
Mountains of ________and ___________, where
this system was first described in 1799.
15. What are the tectonic implications of the Great
Valley and Franciscan groups of western California?
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203
9. The last period of the Mesozoic is called the
22. The rotation of Eurasia caused ___________ to
____________, and was named for the chalk
move away from North America. Northward
exposures found in France and southern England.
movement of Africa narrowed the Tethys Sea.
23. The final stage of the breakup of Pangaea involved
A Global Perspective (pp. 479-481)
separation of North America, Greenland, and
_____________, and also the separation of
10. At the beginning of the Mesozoic, the continent of
_________ stretched from nearly pole to pole.
11. The worldwide ocean called ________________
had an eastern indentation called the _______ sea.
12. The breakup of Pangaea occurred in four stages that
Australia from _____________.
24. During the Triassic, free __________ of the
Panthalassa Ocean produced ______ deposits in the
high latitudes of Antarctica and Australia.
25. The unusually warm climate of the Jurassic and
lasted from the Late ____________ Period until
Cretaceous periods was caused by ____________
the early_____________ Era.
carrying warmer waters of the cratons and from the
13. The first stage in the breakup of Pangaea involved
_________ between Laurasia and Gondwana.
14. Faulting and stretching of the crust between eastern
elevated levels of ____________ _______ in the
atmosphere.
26. Mesozoic climates have been investigated with the
North America and Africa produced a series of
use of oxygen isotopes, aeolian sandstones, and the
_________ ______along the margins of the
examination of sedimentary structures and
separating continents.
________.
15. The separation of North and South America
North America in the Mesozoic (pp. 482-498)
allowed seawater to invade the new rift zone,
producing the ______ ___ _________.
16. The second stage of the breakup of Pangaea
involved the fragmentation of _______________.
17. The landmass of Africa-South America was
27. The geology of eastern North America was
profoundly affected by rifting form the African
continent in the early _____________. The chain of
rift basins that formed were eventually filled in by
separated from the landmass of Antarctica-
sediments to form the modern ________
____________.
___________ ________.
18. The continent of__________ moved northward and
28. The chain of rift basins that formed were eventually
was completely separated from the other land
filled in by sediments to form the modern ________
masses throughout the Mesozoic Era.
___________ ________.
19. The _______ ________ Ocean was formed between
the Late Jurassic and Early Cretaceous periods, by
the rifting of South America and __________.
20. Separation of the two above continents involve the
formation of a three-way rift or ___________.
21. The westward movement of South America caused
a _________ _______ to form on its western
margin.
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29. Erosion of the ______________ _______ _____
left a broad region of gentle topography.
30. Rifting between North America and Africa began at
the start of the _________ Period. Slivers of
African _________ underline the coastal plain of
Florida, Georgia, and South Carolina.
31. Slivers of African _________ underline the coastal
plain of Florida, Georgia, and South Carolina.
204
32. Normal faulting in the crust of the Appalachian
orogen produced down-dropped valleys called
_________ and half-grabens.
33. The normal faults that border many of the rift
clams, and deeper water facies containing shales
and ___________.
43. Petroleum deposits in the Gulf Coast region were
formed as salt squeezed upward, forming many
basins were actually________ and ______ faults
dome-shaped _______ for oil and gas by bending
formed during Paleozoic plate collisions.
and breaking overlying rock layers.
34. Many of the rift basins have been buried
44. Much of western North America is composed of
underneath the coastal plain, or lie submerged on
numerous _________ _____________, which were
the ____________ ________.
accreted to the continent at subduction zones.
35. The sedimentary rocks that accumulated in the
45. In some places, younger igneous rocks have
Mesozoic rift basins of eastern North America are
_________ older accreted terranes, confusing the
collectively known as the _________ __________.
timing of geologic events.
36. Sedimentation in the rift basins was temporarily
46. Some terranes have not remained in place where
interrupted by volcanic activity early in the Jurassic
they ________, but have been displaced along
Period. This activity included basalt flows, shallow
__________ faults.
_________, and dikes.
47. From the end of the Permian into the beginning of
37. Basement rocks of the Atlantic continental shelf
the Triassic, the accretion of a volcanic arc terrane
were ___________ by Mesozoic rifting and
that now comprises western Nevada and northern
_________ by numerous normal faults.
California and subsequent deformation was called
38. The newly formed basins were filled with detrital
sediments, overlain by __________, then by
shallow water _____________, and finally detrital
sediments shed from the erosion of the Appalachian
Mountains.
39. The Gulf Coast of North America formed through a
sequence of events in an almost identical fashion to
that of the Atlantic margin, except that sediment
thickness in the Gulf Coast was far ___________.
40. After the initial deposition of redbeds in the rift
between North and South America, thick deposits
the _____________ _________.
48. Although the accretion of Sonomia ended
westward-dipping subduction of the North
American plate, oceanic crust of the ___________
plate was subducted underneath the continent from
the Late Triassic onward.
49. The sequence of Mesozoic mountain-building
events in western North America is called the
_________________ orogeny.
50. ___________ The formation of a large igneous arc
parallel to the coastline of North America from Late
Triassic to Early Cretaceous time is called the
_____________ orogeny.
51. The deeply-eroded remnants of this magmatic arc
of ________ formed by evaporation of marine
are seen as numerous ____________ composed of
waters that flowed in between the new Pacific and
granite and granodiorite.
Atlantic oceans.
41. Gulf Coast sediments were supplied from the
continental interior, the western end of the
Appalachian-Ouachita fold belt, and the rising
mountains of the _____________.
42. Cretaceous sediments of the Gulf Coast included
shallow water shelf edge reefs made of _______
52. Compression east of the magmatic belt caused
sedimentary rocks to be folded and thrust tens of
kilometers eastward. This deformation is called the
_____________ orogeny.
53. Compression east of the magmatic belt may have
been caused by the docking of a series of crustal
blocks known as ______________.
54. Vertical and lateral uplift of Precambrian basement
rocks, forming broad uplifts, steep-sided folds, and
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205
deep basins is assigned to a period of deformation
called the _____________ orogeny.
55. Igneous activity in the Sevier orogeny ended at the
end of the Cretaceous, suggesting a change in the
____________ process.
56. The North American plate may have overidden the
oceanic Farallon plate, thereby causing it to flatten
out in a process called ________ ____________.
57. The drag of the underlying ocean plate on the base
of the overriding continental plate may have caused
it to pile up in blocks that were pushed _________.
58. Much deposition along the margin of western North
America occurred in the ___________ _______ that
formed inland from the orogenic belt.
59. River channels, floodplains and lakes located on an
alluvial plain are the depositional environments
characteristic of the __________ _________ of late
Triassic age in the Four Corners area.
60. The eolian deposits of the _________ __________
represent sand dunes that migrated across a coastal
desert.
61. Braided and meandering stream deposits, as well as
intervening floodplain sediments gradually filled
the Sundance Sea as a clastic wedge called the
___________ __________.
62. Early to Late Cretaceous worldwide transgression,
caused by rapid rates of sea-floor spreading flooded
North America with the _________ __________
_________.
63. Sediments of the _______ __________ ________
were deposited in the forearc basin seaward of the
magmatic arc.
64. Sediments of the ______________ _______
represent oceanic sediments scraped off the
subducted oceanic plates, mixed with slivers of
oceanic plates and volcanic arc sediments.
PRACTICE TESTS
After you thoroughly understand the correct answers of
the Chapter Review, answer the following questions and
check them with the answers on pages 210-211. If your
answer is incorrect, consult the appropriate pages of the
text.
Multiple Choice Questions
Circle your answers to the following questions.
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1. The sandstone cliffs that support the top of Mesa
Verde represent a sedimentary environment of:
a. coastal sand dunes.
b. lowland river floodplains.
c. barrier islands.
d. alluvial fans.
2. The three periods of the Mesozoic were all defined
from exposures in:
a. North America.
b. Europe.
c. Africa.
d. Australia.
3. The Wilson cycle that marked the assembly of the
supercontinent of Pangaea continued to operate
during the:
a. Cretaceous Period.
b. Jurassic Period.
c. Triassic Period.
d. Permian Period.
4. The polar regions of the supercontinent Pangaea
were unusually warm because of:
a. oceanic circulation.
b. large landmasses over the poles.
c. large mountain ranges near the poles.
d. large freshwater lakes near the poles.
5. The initial rifting of Pangaea involved separation
between North America and:
a. Europe.
b. Asia.
c. South America.
d. Africa.
6. The initial Atlantic Ocean was much like today’s:
a. Gulf of Mexico.
b. Red Sea.
c. Mediterranean Sea.
d. Atlantic Ocean.
7. The Jurassic breakup of Gondwana completely
isolated the continent of:
a. Antarctica.
b. Australia.
c. India.
d. Africa.
8. The aulacogen occupied by the Niger River Valley
of Africa formed during its rifting from
a. South America.
b. India.
c. Australia.
d. Antarctica.
206
9. The final stage of Pangaean breakup involved the
rifting from both Europe and North America of :
a. Laurentia.
b. Laurasia.
c. Africa.
d. Greenland.
10. The seasonal climate of the Pangaean interior is
indicated by:
a. coal deposits.
b. paleosols.
c. subtropical plants.
d. chalk deposits.
11. Jurassic rifting in eastern North America ultimately
produced a:
a. foreland basin.
b. forearc basin.
c. passive plate margin.
d. backarc basin.
12. The sediments of the Newark Supergroup filled:
a. the subsiding foreland basin.
b. the subsiding backarc basin.
c. the subsiding forearc basin.
d. the down-dropped rift basins.
13. Igneous activity along the eastern margin of North
America erupted into:
a. the subsiding foreland basin.
b. the subsiding backarc basin.
c. the subsiding forearc basin.
d. the down-dropped rift basins.
14. A Mesozoic sedimentary deposit unique to the Gulf
Coast is:
a. salt.
c. oil.
b. coal.
d. gas.
15. The great thickness of Gulf Coast sediments
accumulated in the Mesozoic is attributed to:
a. rifting.
b. subsidence.
c. sea level change.
d. volcanism.
16. The oil deposits of the Gulf Coast can largely be
attributed to traps involving:
a. faulting.
b. stratigraphic change.
c. salt domes.
d. compressional deformation.
17. North America’s western margin was enlarged by:
a. accretion of displaced terranes.
b. continental collision.
c. rifting.
d. sea-floor spreading.
18. The formation of a magmatic arc along the western
margin of North America that began in the Late
Triassic resulted from :
a. rifting of the Farallon plate.
b. rifting of the Sonoma plate.
c. subduction of the Sonoma plate.
d. subduction of the Farallon plate.
19. Activity of the Nevadan orogeny was responsible
for the formation of the present-day:
a. Cascade Range.
b. Sierra Nevada.
c. Ouachita Mountains.
d. Appalachian Mountains.
20. The cause of the Sevier compressional deformation
may be with:
a. Sonomia.
b. Avalonia.
c. Wrangellia.
d. Klamathia.
21. The major effects of the Laramide orogeny were
seen in:
a. thin-skinned thrusts.
b. rifting.
c. broad uplifts and steep-sided folds.
d. intrusions of granite and granodiorite.
22. The major site of deposition at the western margin
of North America was the:
a. foreland basin.
b. forearc basin.
c. backarc basin.
d. rift basins.
23. The Chinle Group of the Four Corners area
represents:
a. arid tidal flats.
b. a coastal desert.
c. a highland region.
d. a broad alluvial plain.
24. The Navajo Sandstone of Jurassic age represents:
a. arid tidal flats.
b. a coastal desert.
c. a highland region.
d. a broad alluvial plain.
25. The Sundance Sea represents the:
a. Absaroka transgression.
b. Kaskaskia transgression.
c. Zuni transgression.
d. Western Interior transgression.
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207
26. The Western Interior Seaway resulted from :
a. global warming.
b. glacier formation.
c. slowed rates of sea-floor spreading.
d. accelerated rates of sea-floor spreading.
27. Sediments of the Great Valley Group were
deposited in the:
a. forearc basin
b. foreland basin.
c. backarc basin.
d. rift basins.
____ 17.
Mesozoic sedimentation on the western
margin of North America occurred mainly in
the foreland basin inland from the orogenic
belt.
_____ 18. The Western Interior Seaway was a result of
the greatest transgression since the early
Paleozoic.
Essay Questions
Write a brief essay on a separate sheet of paper
answering each of the following questions.
True or False Items
Write true or false on the line in front of each statement.
_____ 1. The sandstones of the Mesa Verde area were
deposited 75 million years ago.
_____ 2. All three of the Mesozoic periods were
defined from outcrops in Germany.
_____ 3. The Pangaean supercontinent was
surrounded by the Tethys global ocean.
_____ 4. The mid-Atlantic ridge system had formed in
by the Middle of the Jurassic Period.
_____ 5. Rifting of North America from Africa caused
North and South America to collide.
_____ 6. Antarctica and Australia remained together
throughout the Mesozoic Era.
_____ 7. The northward migration of India was
tectonically quiet.
_____ 8. Africa separated from Arabia in the Late
Cretaceous Period.
_____ 9. The northward drift of Pangaea during the
early Mesozoic warmed the southern polar
regions once covered by glaciers.
_____ 10. Fossils from the polar regions of Pangaea
indicate a severe climate.
_____ 11. Crustal extension that formed the Mesozoic
rift basins in eastern North America moved
along previously formed thrust and reverse
faults.
_____ 12. Initial sedimentation in the Gulf of Mexico
involved deposition of evaporites.
_____ 13. Rapid filling of the Gulf of Mexico rift zone
by sediments produced a shallow shelf by
Cretaceous time.
_____ 14. The Nevadan orogeny included the formation
of a magmatic arc parallel to the coastline.
_____ 15. The “thin-skinned” tectonics of the Sevier
orogeny were probably a result of collision
with the displaced terrane called Sonomia.
_____ 16. Broad uplifts, steep-sided faults, and deep
basins were formed as a result of the
Laramide orogeny.
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1. Describe the breakup of the Pangaean World.
2. Discuss the three phases of the Cordilleran
orogeny.
3. Explain the tectonic significance of the Great
Valley and Franciscan Groups of California.
CHALLENGE TEST
Answer these questions the day before an exam as a
final check on your understanding of the chapter’s terms
and concepts. Check your responses with the answers on
pages 211-212. If your answer is incorrect, consult the
appropriate pages of the text.
Completion
Fill in the correct answers.
1. Cretaceous sandstones of the Mesa Verde region
represent ____________ and _________ ________
depositional environments.
2. The series of collisions between North America and
accreted terranes produced vast ___________
___________.
3. The Triassic Period began_____ million years ago,
and the Cretaceous Period ended ____ million years
ago.
4. The assembly of Pangaea ended the ________
_____ that began in the Late Proterozoic with the
breakup of Rodinia.
5. Rifting between Laurasia and Gondwana began in
the ______ ___________.
6. Fragmentation of Gondwana began in the
__________ Period.
208
7. The opening of the south Atlantic Ocean between
Africa and South America occurred between Late
Multiple-Choice Questions
Circle the correct answer.
Jurassic and _______ _____________ time.
8. Sedimentary structures such as __________ and
various types of paleosols indicate that Triassic
climates in the interior of Pangaea were ______ and
seasonal.
9. The eastern edge of North America is called the
modern ____________ _________. It was the site
of several orogenies during the Paleozoic Era.
1. The sandstone cliffs that support the top of Mesa
Verde are of :
a. Cretaceous age.
b. Jurassic age.
c. Triassic age.
d. Permian age.
2. Which Mesozoic period’s upper boundary marked
the greatest extinction event of the era?
a. Permian .
c. Jurassic.
b. Triassic .
d. Cretaceous.
10. Thrust and reverses faults that were active in the
Allegeheny orogeny were reactivated by
____________ forces associated with the rifting of
continents.
11. Sediments of the Newark Supergroup occupied
Mesozoic ______ ________ in eastern North
America.
12. The greater thickness of sediments in the Gulf
Coast region of North America was due to the rapid
____________ of the shelf following rifting.
3. A new Wilson cycle of rifting and drifting began in
the:
a. Permian Period
c. Jurassic Period.
b. Triassic Period.
d. Cretaceous Period.
4. The large indentation in the eastern region of the
Pangaea coastline was occupied by:
a. The Mediterranean Sea c. The Tethys Sea.
b. The Atlantic Ocean.
d. The Black Sea.
5. Late Triassic separation of North America from
Africa produced:
a. a foreland basin.
c. a mountain belt.
b. a volcanic arc.
d. a line of rift basins.
13. In western North America, displaced terranes
accreted to the continental margin at__________
________.
14. The volcanic arc terrane that was added to the
western margin of North America between the end
of the Permian and the beginning of the Triassic
Period was called _____________.
15. The Nevadan orogeny formed a large, _________
6. The Gulf of Mexico formed between North and
South America as a:
a. rift zone.
c. foreland basin.
b. backarc basin.
d. trench.
7. The two Gondwana continents that remained
attached throughout the Mesozoic were:
a. Africa and South America.
b. Antarctica and Australia.
c. Africa and India.
d. South America and Antarctica.
_____ parallel to the coastline.
16.
In the Laramide orogeny, large blocks of
Precambrian__________ rocks were pushed
vertically and laterally.
17. The Late Jurassic landscape of western North
America contained a low-relief alluvial plain that
bordered the ___________ _______.
18. Rocks of the Franciscan Group represent an
___________ _________ formed above the trench
to the west of the volcanic arc.
8. The Tethys Sea was narrowed in the Cretaceous by
the northward movement of:
a. India.
b. Australia.
c. Antarctica.
d. Africa.
9. Warm climates that existed in the high latitudes of
Mesozoic Pangaea are indicated by polar:
a. coal beds.
b. fossil subtropical plants
c. fossil dinosaur remains.
d. All of the above.
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209
10. Mountain building ended on the eastern margin of
North America with the Pennsylvanian-Permian:
a. Sonoma orogeny.
b. Nevadan orogeny.
c. Allegeheny orogeny.
d. Antler orogeny.
11. The actual separation of continental crust between
North America and Africa occurred:
a. far to the east of the rift basins.
b. far to the west of the rift basins.
c. right along the rift basins themselves.
d. None of the above.
12. The source of sediments shed onto the Gulf Coast
shelf was from:
a. the western Appalachian-Ouachita fold belt.
b. the continental interior.
c. the rising western Cordillera.
d. All of the above.
13. The accreted terrane of Sonomia includes parts of:
a. Montana and Wyoming.
b. California and Nevada.
c. Oregon and Washington.
d. Utah and Idaho.
14. Activity of the Sevier orogeny in western North
America was mainly:
a. normal faulting.
c. thrust faulting.
b. volcanism.
d. rifting.
15. The cause of Laramide mountain building may be a
process called:
a. a arid tidal flats.
b. a coastal desert.
c. a highland region.
d. a broad alluvial plain.
16. The Morrison Formation of Late Jurassic age
represents:
a. arid tidal flats.
b. a coastal desert.
c. a highland region.
d. a broad alluvial plain.
17. Regression during latest Cretaceous time was due in
part to:
a. rapid deposition from eroding mountains.
b. global warming.
c. rapid coastal subsidence.
d. accelerated sea-floor spreading.
18. Sediments of the Franciscan Group represent
deposits of the:
a. foreland basin .
b. accretionary wedge beyond the volcanic arc.
c. backarc basin.
d. rift basins.
Copyright © Houghton Mifflin Company. All rights reserved.
True or False Items
Write true or false on the line in front of each statement.
_____ 1. The greatest geologic change that North
America experienced was the buildup of the
supercontinent Pangaea.
_____ 2. The Triassic Period was the first of the three
Mesozoic periods to be established.
_____ 3. The land surface of Pangaea was unusually
high because of numerous mountain ranges.
_____ 4. Pangaea was not completely assembled until
the Late Triassic Period.
_____ 5. Rifting began between North America and
Africa.
_____ 6. Central America was a crustal fragment that
remained between North and South America.
_____ 7. The Niger River aulacogen formed as
Greenland pulled away from North America.
_____ 8. Australia finally separated from Antarctica in
the early Cenozoic Era.
_____ 9. Mesozoic paleotemperatures can be
determined from an analysis of the oxygen
isotopes contained in fossil shells.
_____ 10. Sedimentary structures such as mudcracks
indicate an arid climate in the interior of
Pangaea throughout the year.
_____ 11. Erosion of the Appalachian Mountains by the
Jurassic Period had reduced the eastern
margin of North America to a broad region
with a gentle topography.
_____ 12. Mesozoic rift basins in eastern North
America formed west of where North
America and Africa rifted apart.
_____ 13. Salt beds in the Gulf of Mexico contain vast
quantities of oil.
_____ 14. The Mesozoic mountains of the western
margin of North America were formed by
continental collisions.
_____ 15. The Cordilleran orogeny has been divided
into three separate events.
_____ 16. The dinosaur-bearing sediments of the
Morrison Formation represent coastal deserts
and shallow-shelf environments.
_____ 17. The late Mesozoic plate margin of western
North America is represented by an
accretionary wedge, a forearc basin, and a
magmatic arc.
ANSWERS
CHAPTER REVIEW
1.
2.
3.
4.
5.
Cretaceous sandstones
dissolution
breakup
terranes
fossil biota
210
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
dinosaurs
Triassic
France; Switzerland
Cretaceous
Pangaea
Panthalassa; Tethys
Triassic; Cenozoic
rifting
sedimentary basins
Gulf of Mexico
Gondwana
Australia
India
South Atlantic; Africa
aulacogen
subduction zone
Greenland
Europe; Antarctica
circulation; coal
transgressions;greenhouse gases
paleosols
Mesozoic
passive continental margins
Appalachian mountain belt
Jurassic
terrane
grabens
thrust; reverse
continental shelf
Newark Supergroup
sills
stretched; broken
evaporites; carbonates
greater
salt
Cordillera
rudists; chalk
traps
displaced terranes
intruded
docked; transform
Sonoma orogeny
Farallon
Cordilleran
Nevadan
batholiths
Sevier
Wrangellia
Laramide
subduction
buoyant subduction
upward
foreland basin
Chinle Group
Navajo Sandstone
Morrison Formation
western Interior Seaway
Great Valley Group
64. Franciscan Group
PRACTICE TESTS
Multiple-Choice Questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
c
b
c
a
d
b
c
a
d
b
c
d
d
a
b
c
a
d
b
c
c
a
d
b
c
d
a
True or False Items
1. True.
2. False. Only the Triassic Period was defined from
outcrops in Germany.
3. False. Panthalassa was the global ocean surrounding
Pangaea.
4. True.
5. False. Rifting between North America and Africa
caused separation between North and South
America as well.
6. True.
7. False. India moved northward over a hot spot in the
Cretaceous, producing tremendous outpourings of
basalt.
8. False. Africa separated from Arabia early in the
Cenozoic.
9. True.
10. False. Fossils from the polar latitudes of Pangaea
indicate a mild climate.
11. True.
12. False. Initial sedimentation in the Gulf of Mexico
involved continental redbeds.
13. True.
14. True.
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211
15. False. The displaced terrane involved in the Sevier
orogeny was probably Wrangellia.
16. True.
17. True.
18. True.
Essay Questions
1. The breakup of the Pangaean world occurred in a
series of four stages:
a. The initial stage of separation involved rifting
between the eastern margin of North America and
Africa. The modern Atlantic began as a narrow sea,
but by the Middle Jurassic, had developed a midocean ridge system, and each continental edge had
become a passive plate margin. The initial rifting
also caused North America to pull away from South
America, opening the Gulf of Mexico. Fragments of
crust between the two continents became parts of
Cuba and Central America.
b. The second stage of Pangaean fragmentation
involved the rifting of Gondwana. Africa and South
America split apart from Antarctica and Australia,
and India was left to move northward by itself.
Mid-ocean ridges to its south, and subduction zones
to its north caused India to move towards Asia. As
it moved over a hot spot, large volumes of basalts
were erupted during the Cretaceous Period.
c. The third stage of Pangaean breakup came from
the opening of the South Atlantic Ocean between
South America and Africa. This separation involved
at least one three-way rift, or aulacogen. As South
America drifted westward, it experienced a
subducted oceanic plate to its west, forming the
Andes magmatic arc.
d. The final stage of rifting caused separation
between North America, Greenland, and Europe.
This allowed a further widening of the North
Atlantic Ocean. Also, Australia separated from
Antarctica, and Arabia separated from Africa.
These events occurred during the early Cenozoic
Era, and have given the world its modern
appearance.
2. Mountain-building events along the western margin
of North America during the Mesozoic Era have
been described as the Cordilleran orogeny. The
collision and accretion of various terranes derived
from an eastward-subducting oceanic plate resulted
in large-scale intrusions of granite and granodiorite,
which caused uplift and eastward-directed thrust
faulting. The events of the Nevadan orogeny also
produced a foreland basin developed inland from
the region of uplift. Intense crustal compression
resulting from extensive intrusions cause rocks of
the foreland basin to be folded and thrust many
miles eastward. The Sevier orogeny is an example
of “thin-skinned” tectonics, where deeper crustal
rocks were not invoved in the deformation. Docking
Copyright © Houghton Mifflin Company. All rights reserved.
of the displaced terrane called Wrangellia also may
have played a part. The Laramide orogeny involved
uplift and faulting of basement Precambrian rocks
into steep-sided folds, deep basins, and broad
uplifts. Because of the deep-seated movement
involved, a process called buoyant subduction may
have caused oceanic crust to pile up underneath the
continental crust, resulting in upward pressure and
uplift.
3. The sediments deposited on the seaward side of the
magmatic arc provide valuable information about
Mesozoic tectonics on the western margin of North
America. The Great Valley sediments represent
over 16, 000 meters of sediments shed into the
forearc basin west of the magmatic arc. Farther
west, over 7, 000 meters of highly deformed
sediments of the Franciscan Group represent a
mélange of oceanic sediments scraped off the
oceanic plate, slivers of oceanic crust, and volcanic
sediments from the magmatic arc to the east. This
sediment formed an accretionary wedge above the
trench to the west of the magmatic arc. The Late
Mesozoic plate margin of the western United States
consisted of a trench, accretionary wedge, forearc
basin, and magmatic arc closed to shore.
CHALLENGE TEST
Completion
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
shoreline; barrier islands
mountain ranges
248; 66
Wilson cycle
Late Triassic
Jurassic
Early Cretaceous
mudcracks; dry
Atlantic margin
extensional
rift basins
subsidence
subduction zones
Sonomia
igneous arc
basement
Sundance Sea
accretionary wedge
Multiple-Choice Questions
1.
2.
3.
4.
5.
6.
7.
a
d
b
c
d
a
b
212
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
d
d
c
a
d
b
c
d
d
a
b
True or False Items
1. False. The greatest geologic change to North
America in the Mesozoic was the breakup of the
supercontinent of Pangaea.
2. False. The Triassic Period was the last of the three
Mesozoic time periods to be established.
3. True.
4. False. Pangaea began to rift apart in the Late
Triassic Period.
5. True.
6. True.
7 False. The Niger River aulacogen formed as Africa
pulled away from South America.
8. True.
9. True.
10. False. Mudcracks indicate a seasonal climate with
alternating wet and dry periods.
11. True.
12. True.
13. False. Salt domes of the Gulf Coast trap large
quantities of oil and gas contained in other rocks.
14. False. The Mesozoic mountains of the western
margin of North America were formed by accretion
of displaced terranes at subduction zones.
15. True.
16. False. Dinosaur-bearing sediments of the Morrison
Formation represent stream channel and floodplain
deposits.
17. True.
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