The Early Paleozoic
Objectives
• Describe the Cambrian paleogeography of Laurentia.
• Discuss the concept of a passive margin.
• Describe the Cambrian fauna.
Vocabulary
– paleogeography
– passive margin
– transgression
– regression
– Burgess Shale
The Early Paleozoic
The Early Paleozoic
• Clues from the Paleozoic Era help us to
understand how the diversity of life developed.
• The Paleozoic story
explains how early
life-forms moved from
water to land, why the
Appalachians exist,
and why they contain
the vast coal deposits
that fueled the
industrial revolution.
The Early Paleozoic
Continental Setting
• Paleogeography is the ancient geographic
setting of an area.
– The supercontinent Rodinia was present at the end of
the Proterozoic.
– By the Cambrian, Laurentia had split off from Rodinia,
was located near the equator, and was surrounded
by ocean.
– Throughout the Cambrian Period, there was no plate
tectonic activity on Laurentia.
– A passive margin is an edge of a continent, or margin,
where there is no tectonic activity.
The Early Paleozoic
Continental Setting
Laurentia was positioned at
the equator during the Early
Paleozoic. Strong tropical
storms, much like today’s
hurricanes, contributed to
erosion and formation of
sandy beaches. Corals
thrived in the warm ocean
waters and ultimately
contributed to the formation
of limestone.
The Early Paleozoic
Continental Setting
Characteristic Sediments
– A characteristic pattern of sandstone-shale-limestone
deposits formed that represents increasing water depth
from the shore of a vast inland sea.
– Large, sandy beaches formed along the shoreline, claysized sediments were deposited in slightly deeper
water, and carbonate sediment accumulated in even
deeper water.
– Over time, the sandy beaches became sandstone, the
clay-sized sediments compacted to form shale, and the
carbonate sediment became limestone.
The Early Paleozoic
Changes in Sea Level
• Any changes in sediments may indicate
changes in sea level.
– A transgression occurs when sea level rises and the
shoreline moves further inland, resulting in deeperwater deposits overlying shallower-water deposits.
– A regression occurs when sea level falls and causes
the shoreline to move seaward, resulting in shallowwater deposits overlying deeper-water deposits.
– As sea level rises or falls, sediments that are lateral to
each other become stacked one on top of another.
The Early Paleozoic
Changes in Sea Level
The Early Paleozoic
Early Paleozoic Life
• Organisms representing all but one of the
major marine groups appeared during the
Cambrian Period.
• The development of mineralized
skeletons or hard parts helps
mark the beginning of the
Cambrian period.
• Burgess Shale in the Canadian
Rocky Mountains is the source
for some of the best fossilized
Cambrian organisms.
The Early Paleozoic
Section Assessment
1. Match the following terms with their definitions.
___
B paleogeography
___
D passive margin
___
C transgression
___
A regression
A. shallow-water deposits
overlying deeper-water
deposits due to a falling
sea level
B. a continental edge with no
tectonic activity
C. deeper-water deposits
overlying shallow-water
deposits due to a rising
sea level
D. the ancient geographic setting
of an area
The Early Paleozoic
Section Assessment
2. Why is the beginning of the Cambrian Period
sometimes called the Cambrian “explosion?”
The expression Cambrian “explosion”
refers to the dramatic increase in the
diversity and abundance of life-forms near
the beginning of the Cambrian Period.
The Early Paleozoic
Section Assessment
3. Identify whether the following statements are
true or false.
______
false By the Cambrian, Laurentia was connected to
Rodinia.
______
true Organisms representing all but one of the major
marine groups appeared during the Cambrian.
______
false Burgess Shale is located in the Appalachian
Mountains.
______
true During the Cambrian Period, Laurentia was
surrounded by passive margins.
The Middle Paleozoic
Objectives
• Describe the Middle Paleozoic paleogeography.
• Explain the concept of an active margin and the
formation of a clastic wedge.
• Describe the Middle Paleozoic fauna.
• Define the concept of mass extinction.
Vocabulary
– Taconic Orogeny
– Paleozoic fauna
– Caledonian Orogeny
– vascular plant
– Acadian Orogeny
– mass extinction
– Antler Orogeny
The Middle Paleozoic
The Middle Paleozoic
• The passive margin that
existed around Laurentia
continued into the Early
Ordovician Period.
• The paleogeography of
Laurentia was still
equatorial, with the
paleo-equator running
from approximately
modern-day New
Mexico through
Minnesota.
The Middle Paleozoic
Sea Level Changes Again
• Sea level rose during the Early Ordovician and,
once again, a beach environment covered much
of Laurentia’s margins.
• The resulting sandstone is overlain by minor
amounts of shale and by extensive limestone
deposits that include the first corals that built
organic reefs.
• Organic reefs are structures composed of
carbonate skeletons made by living organisms.
• Reefs affect the environments in which they grow.
The Middle Paleozoic
Sea Level Changes Again
The Middle Paleozoic
Sea Level Changes Again
• The Great Lakes
area of North
America contains
huge deposits of
Silurian-aged
evaporite minerals,
including halite,
anhydrite, and
gypsum that
are mined
commercially.
The Middle Paleozoic
Middle Paleozoic Tectonics
• During the Middle Ordovician, an ocean-continent
collisional boundary, an active margin, developed
in what is now eastern
North America.
• The Taconic Orogeny, a
mountain-building event
named for the Taconic
Mountains of eastern New
York State, occurred during
the Middle Ordovician.
The Middle Paleozoic
Middle Paleozoic Tectonics
• We know that this Taconic Orogeny occurred
because of:
– the existence of angular unconformities.
– the existence of lava flows, volcanic ash deposits,
igneous intrusions, and regional metamorphic features
that are Middle-to-Late Ordovician in age in presentday eastern North America.
– the existence of a wedge of sediment, called a clastic
wedge, that formed as the mountains from the Taconic
Orogeny eroded.
The Middle Paleozoic
Middle Paleozoic Tectonics
Orogenies and Deformation
– Tectonism continued
during the Late Silurian
and into the Devonian
when Laurentia collided
with Baltica.
– This collision joined
Laurentia and Baltica into
a larger continent known
as Laurasia.
The Middle Paleozoic
Middle Paleozoic Tectonics
Orogenies and Deformation
– Caledonian Orogeny, the collisional tectonic event that
occurred when Laurentia and Baltica collided, closed the
ocean that had separated these two continents.
– The Acadian Orogeny was the result of a
microcontinent called Avalonia, which is now
Newfoundland, colliding with the southeastern margin
of Laurasia.
– The Antler Orogeny was a collisional tectonic event
during the Late Devonian, and into the early
Mississippian, that affected the passive western
margin of Laurentia.
The Middle Paleozoic
Middle Paleozoic Tectonics
The Middle Paleozoic
Middle Paleozoic Life
• The Middle Paleozoic seas
were dominated by animals
that are collectively called
the Paleozoic fauna.
• The animals that dominated
the Cambrian seas were
replaced during the Early
Ordovician by a variety of
new organisms.
The Middle Paleozoic
Middle Paleozoic Life
• Corals deposit thin layers of carbonate, called
growth lines, to their skeletons each day.
• Corals indicate
that Earth was
rotating more
rapidly during
the Paleozoic
and has been
slowing ever
since.
The Middle Paleozoic
Life Moves to Land
• For the first time in the history of life on Earth,
land was colonized during the Middle Paleozoic.
• Fossilized plant parts and spores suggest that
some form of land plant existed during the
Late Ordovician.
• Vascular plants have tissue for circulating water
and nutrients through their stems and leaves.
• The development of vascular tissue allowed
plants to spread out on land.
The Middle Paleozoic
Life Moves to Land
New Plants Emerge
– By the Late Devonian, three important groups of
vascular spore-bearing plants were living on land: ferns,
sphenopsids, and lycopods.
– During the Late Devonian, the seed ferns developed.
– The most important aspect of these plants was the
development of seeds, which allowed plants to spread
out and colonize dry land.
The Middle Paleozoic
Mass Extinctions
• Two of the greatest extinction events in Earth’s
history occurred during the Middle Paleozoic.
• A mass extinction is when an unusually large
number of organisms becomes extinct over a
relatively short period of geologic time.
– The first mass extinction occurred at the end of the
Ordovician Period when approximately 57 percent of all
marine genera became extinct.
– An episode of global cooling caused the extinction of
many species that were adapted to warm environments.
The Middle Paleozoic
Mass Extinctions
Global Cooling and Overturning
– A second mass extinction occurred during the late
Devonian when approximately 50 percent of the marine
genera were wiped out.
– The cooling of Earth’s atmosphere may have caused a
tremendous disturbance in the ocean system.
– This disturbance created overturning, a process in which
oxygen-poor, deep ocean water rises up, creating
surface waters that contain little or no oxygen.
The Middle Paleozoic
Section Assessment
1. Match the following terms with their definitions.
___
C Taconic Orogeny
___
B Caledonian
Orogeny
___
D Acadian Orogeny
___
A Antler Orogeny
A. collisional tectonic event that
affected the passive western
margin of Laurentia
B. collisional tectonic event that
occurred when Laurentia and
Baltica collided
C. a mountain-building event that
occurred during the Middle
Ordovician along what is now
eastern North America
D. tectonic event resulting from
Avalonia colliding with the
southeastern margin of Laurasia
The Middle Paleozoic
Section Assessment
2. What two developments in plants allowed the
widespread colonization of land?
The development of vascular tissue and the
emergence of seeds allowed the widespread
colonization of land.
The Middle Paleozoic
Section Assessment
3. Identify whether the following statements are
true or false.
______
true Global cooling led to a mass extinction during
the late Devonian.
______
false The equator ran through present-day Alaska
during the Early Ordovician Period.
______
false As Earth ages, the days are getting longer.
______
true Large amounts of evaporites are found in the
Great Lakes region.
The Late Paleozoic
Objectives
• Describe the formation of Pangaea.
• Explain how cyclothems formed.
• Identify the importance of amniote eggs.
• Discuss the causes of the Late Permian mass extinction.
Vocabulary
– Gondwana
– Ancestral Rockies
– cyclothem
– Alleghenian Orogeny
– Ouachita Orogeny
– amniote egg
The Late Paleozoic
The Late Paleozoic
• During the Late Paleozoic, the supercontinent
Pangaea formed.
• Gondwana was a large continent in the
southern hemisphere that formed as a result of
collisional events between South America,
Africa, India, and Antarctica.
The Late Paleozoic
The Late Paleozoic
The Late Paleozoic
Sea Level and Deposition
• The Late Paleozoic began with Laurasia still
covered by a shallow tropical sea.
• Mississippian rocks throughout North America
are predominantly limestone.
• The end of the Mississippian was marked by a
major regression of the sea.
The Late Paleozoic
Sea Level and Deposition
• The Pennsylvanian Period began with a slow
transgression.
• The Pennsylvanian and Permian rocks in central
and eastern North America are predominantly
river and delta deposits.
• The Pennsylvanian Period is known for the coal
deposits that accumulated in heavily vegetated
lowland swamps.
The Late Paleozoic
Sea Level and Deposition
Cyclothems
– A cyclothem is a repeating
cyclic pattern of sediments
stacked one on top of another,
as found in Pennsylvanian
rocks in North America.
– A regression is represented
by layers of marine limestone
and sandstone.
– A transgression is represented
by sandstone, clay, coal, shale,
and marine limestone.
The Late Paleozoic
Sea Level and Deposition
Cyclothems
– In some parts of Laurentia, as
many as 40 to 50 cyclothems
were stacked one on top of
the other.
– Most geologists hypothesize
that glaciation was responsible
for the varying sea levels that
caused the cyclothems.
The Late Paleozoic
Reefs and Evaporites
• During the Permian, sponges and algae built a
reef complex, known as the Great Permian Reef,
in what is now western Texas, southeastern New
Mexico, and northern Mexico.
• The pore spaces in Permian reefs and in the
surrounding coarse-grained rocks are filled with
oil, making these reefs important oil reservoirs.
• The thick salt deposits that also formed have
very low permeability, making them an excellent
environment for long-term storage of nuclear
waste.
The Late Paleozoic
Continental Collisions and Mountain Building
• The Late Paleozoic was a time of active
mountain building.
– During the Ouachita Orogeny, Gondwana collided
with the southeastern margin of Laurasia, forming the
Ouachita Mountains of Arkansas and Oklahoma and
the mountains in the Marathon area of West Texas.
– The Ancestral Rockies were created during the
Ouachita Orogeny as the collision was so intense that
it caused the crust to uplift inland as far as presentday Colorado.
The Late Paleozoic
Continental Collisions and Mountain Building
– The Alleghenian
Orogeny was the last of
the three major mountainbuilding events to affect
what is now eastern North
America, and resulted in
the formation of the
Appalachian Mountains.
– Pangaea had formed.
The Late Paleozoic
Late Paleozoic Life
• The invertebrate marine organisms that flourished
during the Middle Paleozoic continued to
dominate the marine environment.
• One group, the crinoids, became dominant
during the Mississippian.
The Late Paleozoic
Late Paleozoic Life
Changes in the Ocean
– Following the extinction of many fishes during the Late
Devonian, sharks and other ray-finned fishes became
more abundant.
– Lobe-finned fishes appeared during the Late Devonian,
but became more abundant during the Late Paleozoic.
– The true ferns, sphenopsids, lycopods, and seed ferns
had thoroughly invaded the swampy land of the
Pennsylvanian, ultimately giving rise to the great coal
swamps of the Pennsylvanian.
– Swamps were a breeding ground for insects as well
as plants.
The Late Paleozoic
Late Paleozoic Life
Changes in the Ocean
– Amphibians, the top carnivores on the land, had to
remain close to water because their eggs had no
protective coating to prevent them from drying out.
– Reptiles that evolved from the early amphibians during
the Late Mississippian developed a new type of egg.
– The amniote egg has a shell that protects the embryo,
which is surrounded by a liquid-filled sac that contains
a food sac and a waste sac.
– During the Permian, reptiles became abundant on
land and displaced the amphibians as the top land
carnivores.
The Late Paleozoic
The Permian Mass Extinction
• The largest mass extinction in the history of life on
Earth defines the end of the Paleozoic Era.
• The Permo-Triassic Extinction Event marks the
end of nearly 95 percent of all species, and
affected terrestrial as well as marine animals.
• More than 65 percent of the amphibians and
reptiles did not survive, nor did almost one-third
of all insects.
The Late Paleozoic
The Permian Mass Extinction
A Major Marine Regression
– A major marine regression is one possible cause of the
Permo-Triassic Extinction Event.
– Now, as then, most marine animals live in the relatively
shallow water called the continental shelf.
– During regression, the continental shelf became very
narrow, leaving little space for marine animals to live.
– Life on Earth was irrevocably changed at the end of
the Paleozoic.
The Late Paleozoic
Section Assessment
1. Match the following terms with their definitions.
___
A Gondwana
___
D cyclothem
___
B Ouachita
Orogeny
___
C Alleghenian
Orogeny
A. large supercontinent that was
located in the southern hemisphere
B. mountain-building event that
was caused when Gondwana
collided with the southeastern
margin of Laurasia
C. the last of the three major
mountain-building events to affect
what is now eastern North America
D. a repeating cyclic pattern of
sediments stacked one on top
of another
The Late Paleozoic
Section Assessment
2. How does the Great Permian Reef Complex
have modern commercial value?
The pore spaces in Permian reefs and in the
surrounding course-grained rocks are filled with
oil, making these reefs important oil reservoirs.
The thick salt deposits that formed behind the
reefs have very low permeability, making them
an excellent environment for the storage of
nuclear waste.
The Late Paleozoic
Section Assessment
3. Identify whether the following statements are
true or false.
______
false Trilobites became extinct during the
Ouachita Orogeny.
______
true Reptiles developed from the amniote egg.
______
false The Pennsylvanian Period is known for its
extensive deposits of limestone.
______
true In some parts of Laurentia, as many as 50
cyclothems were stacked on top of each other.
Chapter Resources Menu
Study Guide
Section 23.1
Section 23.2
Section 23.3
Chapter Assessment
Image Bank
Section 23.1 Study Guide
Section 23.1 Main Ideas
• The ancient North American continent of Laurentia was
located near the equator and surrounded by ocean
during the Cambrian Period. A shallow sea covered most
of Laurentia.
• Laurentia was completely surrounded by passive
margins throughout the entire Cambrian Period.
• Many new organisms developed during the Cambrian
explosion. Fossils of trilobites and articulate brachiopods
are particularly common in Cambrian rocks.
• When environments change position laterally due to
changes in sea level, adjacent depositional facies overlie
each other in vertical succession.
Section 23.2 Study Guide
Section 23.2 Main Ideas
• High evaporation rates in lagoon settings cause the water to
become oversaturated with calcium and sodium. These
elements combine with other elements or compounds in the
water and precipitate out of solution as the evaporite minerals.
• Clastic wedges provide evidence for orogenic events.
• The seas were dominated by articulate brachiopods, corals,
mollusks, bryozoans, crinoids, graptolites and conodonts.
Fishes were the top predators of the seas during the Devonian.
Ferns, sphenopsids, and lycopods covered the landscape by
the Late Devonian.
• Two mass extinctions occurred. A mass extinction occurs when
an unusually large number of organisms becomes extinct over a
relatively short period of geologic time.
Section 23.3 Study Guide
Section 23.3 Main Ideas
• Pangaea formed as Laurasia (North America + Europe)
collided with Gondwana (South America, Africa, India,
Australia and Antarctica).
• Cyclothems consist of transgressive and regressive rock
sequences stacked one on top of another. They represent
cycles of glacial-interglacial periods.
• Seeds evolved and allowed plants to colonize dry land.
The amniote egg evolved and allowed reptiles to colonize
dry land.
• One possible cause of the Permo-Triassic Extinction Event
was regression. Marine habitats around Pangaea shrank.
Feedback from this event caused global warming, which
affected organisms on land as well as in the sea.
Chapter Assessment
Multiple Choice
1. A(n) ____ occurs when sea level rises and the
shoreline moves inland.
a. passive margin
c. orogeny
b. regression
d. transgression
A passive margin refers to a continental edge that is not
tectonically active. Orogeny is a mountain-building
process. A regression occurs when sea level falls and
causes the shoreline to move seaward.
Chapter Assessment
Multiple Choice
2. What was the last mountain-building event along
what is now the eastern coast of North America?
a. Antler Orogeny
c. Ouachita Orogeny
b. Alleghenian Orogeny d. Taconic Orogeny
The Alleghenian Orogeny was the result of a collision
between Laurasia and Gondwana during the Late
Pennsylvanian. It resulted in the formation of the
Appalachian Mountains and finalized the formation
of Pangaea.
Chapter Assessment
Multiple Choice
3. Where do some of the best fossilized Cambrian
organisms come from?
a. Burgess Shale
c. coal
b. Great Lakes region
d. Great Permian Reef
Burgess Shale is found in the Canadian Rocky
Mountains. The reefs in the Great Lakes region were
prevalent during the Middle Paleozoic. The organisms
and swamps that are responsible for coal are from the
Pennsylvanian Period. The Great Permian Reef
Complex was created during the Permian Period.
Chapter Assessment
Multiple Choice
4. Nearly ____ percent of all species became extinct
during the Permo-Triassic Extinction Event.
a. 55
c. 88
b. 72
d. 95
The Permo-Triassic Extinction Event was the largest
mass extinction in the history of life on Earth. It defines
the end of the Paleozoic Era.
Chapter Assessment
Multiple Choice
5. Laurasia was formed during which period?
a. Devonian
c. Pennsylvanian
b. Cambrian
d. Mississippian
Laurasia was formed when Laurentia collided with
Baltica, an ancient continent that consisted of what are
now northern Europe and Russia west of the Ural
Mountains. This collisional tectonic event is known as the
Caledonian Orogeny.
Chapter Assessment
Chronological Order
6. Number the following periods of the Paleozoic
era in the order that they occurred.
___
3 Silurian Period
___
4 Devonian Period
___
1 Cambrian Period
___
6 Pennsylvanian Period
___
2 Ordovician Period
___
5 Mississippian Period
___
7 Permian Period
Chapter Assessment
Short Answer
7. What is the process of overturning?
Overturning is a process in which oxygen-poor
deep ocean water rises up, creating surface
waters that contain little or no oxygen.
Chapter Assessment
True or False
8. Identify whether the following statements are
true or false.
______
true The Late Ordovician mass extinction may have
been caused by an episode of global cooling.
______
false The Antler Orogeny primarily affected the
southeastern part of Laurasia.
______
false Amphibians were the first to have
amniotic eggs.
______
true Throughout the Cambrian, there was no plate
tectonic activity on Laurentia.
______
false Paleozoic fauna refers to animals that
dominated the Cambrian seas.
Image Bank
Chapter 23 Images
Image Bank
Chapter 23 Images
Image Bank
Chapter 23 Images
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