Objectives Describe the Cambrian paleogeography of Laurentia. The Early Paleozoic Discuss the...

Objectives• Describe the Cambrian paleogeography of Laurentia.

The Early Paleozoic

• Discuss the concept of a passive margin.

• Describe the Cambrian fauna.

– paleogeography

– passive margin

– transgression

– regression

– Burgess Shale

Vocabulary

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• 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• Clues from the Paleozoic Era help us to

understand how the diversity of life developed.

The Early Paleozoic


Continental Setting

Paleogeography is the ancient geographic setting of an area.

The Early Paleozoic

– 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.


Continental SettingLaurentia 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

The Early Paleozoic

– 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, clay-sized 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.


Changes in Sea Level• Any changes in sediments may indicate

changes in sea level.

The Early Paleozoic

– A transgression occurs when sea level rises and the shoreline moves further inland, resulting in deeper-water deposits overlying shallower-water deposits.

– A regression occurs when sea level falls and causes the shoreline to move seaward, resulting in shallow-water 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.


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 Early Paleozoic

• 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.


Section Assessment

1. Match the following terms with their definitions.

___ paleogeography

___ passive margin

___ transgression

___ regression

The Early Paleozoic

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


Section Assessment

2. Why is the beginning of the Cambrian Period sometimes called the Cambrian “explosion?”

The Early Paleozoic


______ By the Cambrian, Laurentia was connected to Rodinia.

______ Organisms representing all but one of the major marine groups appeared during the Cambrian.

______ Burgess Shale is located in the Appalachian Mountains.

______ During the Cambrian Period, Laurentia was surrounded by passive margins.

Section Assessment

3. Identify whether the following statements are true or false.

The Early 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.

– Taconic Orogeny

– Caledonian Orogeny

– Acadian Orogeny

– Antler Orogeny

– Paleozoic fauna

– vascular plant

– mass extinction

Vocabulary

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.


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.


Sea Level Changes Again



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 minedcommercially.



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.


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 present-day eastern North America.

– the existence of a wedge of sediment, called a clastic wedge, that formed as the mountains from the Taconic Orogeny eroded.


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.



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.


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.


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.


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.


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.


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.


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.


Section Assessment


___ Taconic Orogeny

___ Caledonian Orogeny

___ Acadian Orogeny

___ 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


Section Assessment


2. What two developments in plants allowed the widespread colonization of land?


Section Assessment



______ Global cooling led to a mass extinction during the late Devonian.

______ The equator ran through present-day Alaska during the Early Ordovician Period.

______ As Earth ages, the days are getting longer.

______ Large amounts of evaporites are found in the Great Lakes region.


– Gondwana

– cyclothem

– Ouachita Orogeny

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

The Late Paleozoic

– Ancestral Rockies

– Alleghenian Orogeny

– amniote egg


The Late Paleozoic• During the Late Paleozoic, the supercontinent

Pangaea formed.

The Late Paleozoic

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


Sea Level and Deposition• The Late Paleozoic began with Laurasia still

covered by a shallow tropical sea.

The Late Paleozoic

• Mississippian rocks throughout North America are predominantly limestone.

• The end of the Mississippian was marked by a major regression of the sea.


Sea Level and Deposition• The Pennsylvanian Period began with a slow

transgression.

The Late Paleozoic

• 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.


Sea Level and Deposition

Cyclothems

The Late Paleozoic

– 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.


Sea Level and Deposition

Cyclothems

The Late Paleozoic

– 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.


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 Late Paleozoic

• 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.


Continental Collisions and Mountain Building

• The Late Paleozoic was a time of active mountain building.

The Late Paleozoic

– 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 present-day Colorado.


Continental Collisions and Mountain Building– The Alleghenian Orogeny

was the last of the three major mountain-building events to affect what is now eastern North America, and resulted in the formation of the Appalachian Mountains.

The Late Paleozoic

– Pangaea had formed.


Late Paleozoic Life• The invertebrate marine organisms that flourished

during the Middle Paleozoic continued to dominate the marine environment.

The Late Paleozoic

• One group, the crinoids, became dominant during the Mississippian.


Late Paleozoic Life

Changes in the Ocean

The Late Paleozoic

– 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.


Late Paleozoic Life

Changes in the Ocean

The Late Paleozoic

– 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 Permian Mass Extinction• The largest mass extinction in the history of life on

Earth defines the end of the Paleozoic Era.

The Late Paleozoic

• 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 Permian Mass Extinction

A Major Marine Regression

The Late Paleozoic

– 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.


Section Assessment


___ Gondwana

___ cyclothem

___ Ouachita Orogeny

___ Alleghenian Orogeny

The Late Paleozoic

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


Section Assessment

2. How does the Great Permian Reef Complex have modern commercial value?

The Late Paleozoic


Section Assessment

The Late Paleozoic


______ Trilobites became extinct during the Ouachita Orogeny.

______ Reptiles developed from the amniote egg.

______ The Pennsylvanian Period is known for its extensive deposits of limestone.

______ In some parts of Laurentia, as many as 50 cyclothems were stacked on top of each other.


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 23.1 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 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.


Chronological Order

6. Number the following periods of the Paleozoic era in the order that they occurred.

___ Silurian Period

___ Devonian Period

___ Cambrian Period

___ Pennsylvanian Period

___ Ordovician Period

___ Mississippian Period

___ Permian Period

Chapter Assessment

Short Answer

7. What is the process of overturning?

Chapter Assessment

True or False


______ The Late Ordovician mass extinction may have

been caused by an episode of global cooling.

______ The Antler Orogeny primarily affected the southeastern part of Laurasia.

______ Amphibians were the first to have amniotic eggs.

______ Throughout the Cambrian, there was no plate

tectonic activity on Laurentia.

______ Paleozoic fauna refers to animals that dominated the Cambrian seas.

Chapter Assessment

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