Transcript ch10x - earthjay science

THE EARTH THROUGH TIME
TENTH EDITION
H A R O L D L. L E V I N
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1
CHAPTER 10
Early Paleozoic
Events
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THE PHANEROZOIC EON

Consists of three eras (from oldest to
youngest):
 Paleozoic
= "ancient life" (542-251 m.y. ago)
 Mesozoic = "middle life" (251-65.5 m.y. ago)
 Cenozoic = "recent life" (65.5 m.y. ago - present)
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PALEOZOIC ERA
Paleozoic periods can be divided into:

Early Paleozoic = Cambrian, Ordovician and
Silurian

Late Paleozoic = Devonian, Mississippian,
Pennsylvanian, and Permian
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PALEOZOIC
OVERVIEW
FIGURE 10-1 Major events of
the Paleozoic Era.
Harold Levin
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PALEOZOIC OROGENIC BELTS
FIGURE 10-7 Cratons and orogenic belts of North America and Europe.
Orogenic belts are the result of the rebuilding of a
supercontinent during the Paleozoic.
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OROGENIC BELTS
Orogenic belts are present along the edges of
the continent.
In the orogenic belts, strata are intensely
deformed, with folding, faulting,
metamorphism, and igneous intrusions.
Deformation occurred as a result of
continental collision.
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OROGENIES
In the Appalachian region, there were three
Paleozoic mountain-building events (or
orogenies):
 Taconic
orogeny
 Acadian orogeny
 Alleghanian orogeny
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PALEOZOIC ROCKS OF THE PLATFORM
Across the
platform, in the
continental
interior, Paleozoic
strata are
relatively flat-lying
to gently dipping,
and warped into
basins, domes,
arches, and broad
synclines.
FIGURE 10-5 Central platform of the United States
showing major basins and domes.
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PALEOZOIC PALEOGEOGRAPHY

Paleogeography = "ancient geography." The
ancient geographic arrangement of the
continents.

Reconstructing the paleogeography requires
paleomagnetic, paleoclimatic,
geochronologic, tectonic, sedimentologic,
and biogeographic fossil data.
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PALEOZOIC PALEOCLIMATES

Paleoclimatic evidence comes from
environmentally-sensitive sedimentary rocks (glacial
deposits, coal swamp deposits, reef carbonates,
evaporites).

Early Paleozoic climate was affected by several
factors:



The Earth spun faster and had shorter days.
Tidal effects were stronger because the Moon was closer
to Earth.
No vascular plants were present on the land.
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NEOPROTEROZOIC PALEOGEOGRAPHY
When continents are located on a
pole, if conditions are right,
glaciers will form.
During glaciations, sea level is
lowered worldwide because the
water is tied up in the ice sheets.
Shallow epicontinental seas are
unlikely during glaciations.
FIGURE 10-2 Landmasses during the Neoproterozoic,
about 750 million years ago.
Just before Paleozoic began, the Precambrian
supercontinent, Rodinia, had rifted apart to form six large
continents and several smaller continents.
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EARLY
PALEOZOIC
CONTINENTS
1.
2.
3.
4.
5.
6.
FIGURE 10-2 Landmasses during the
Neoproterozoic, about 750 million years ago.
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Laurentia (North America,
Greenland, Ireland, and
Scotland)
Baltica (Northern Europe and
western Russia)
Kazakhstania (between the
Caspian Sea and China)
Siberia (Russia east of the
Ural Mtns and north of
Mongolia)
China (China, Indochina, and
the Malay Peninsula)
Gondwana (Africa, South
America, India, Australia,
Antarctica)
EARLY PALEOZOIC CONTINENTS
(C. R. Scotese,
2001, Atlas
of Earth History,
Vol., 1,
Paleogeography,
PALEOMAP
Project.)
By Late Cambrian, the continents moved off the pole. Some
continents lie on the equator.
Glaciers melted, sea levels rose, and shallow epicontinental seas
flooded the continents.
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EPICONTINENTAL SEAS
Wave-washed sands, muds, and carbonates
were deposited in the shallow epicontinental
seas.
The epicontinental seas were sites of major
diversification of marine life.
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TRANSGRESSIONS & REGRESSIONS
Shallow epicontinental seas transgressed (onlap
or advance onto the continent) across the
Laurentian (North American) craton during Early
Paleozoic as the glaciers melted and sea level
rose. The seas regressed (offlap or retreat off
the continent) as the glaciers enlarged and sea
level dropped.
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TRANSGRESSIVE-REGRESSIVE
SEQUENCES
The transgression and regression of the
seas deposited sequences of sedimentary
rocks that reflect the deepening and
shallowing of the waters. These are called
transgressive-regressive sequences.
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UNCONFORMITIES
During regressions, the former seafloor was
exposed to erosion, creating extensive
unconformities that mark the boundaries
between the transgressive-regressive
sequences.
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CRATONIC SEQUENCES

The unconformities can be used to correlate
particular sequences from one region to another.

The unconformity-bounded sequences are
sometimes called cratonic sequences.

Two major transgressions occurred during Early
Paleozoic in North America:
 Sauk sequence (older - primarily Cambrian)
 Tippecanoe sequence (Ordovician-Silurian)
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NORTH AMERICAN CRATONIC SEQUENCES
Green =
sedimentary deposits
Yellow = missing
strata associated
with unconformities
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WORLDWIDE SEA LEVEL CHANGE

Similar transgressive-regressive sequences are
found on other continents, suggesting that
worldwide sea level change caused the
transgressions and regressions.

Worldwide sea level changes were probably related
to glaciations and/or sea floor spreading.

During times of rapid sea floor spreading, midocean ridge volcanism displaces sea water onto
the continents.
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CAMBRIAN
PALEOGEOGRAPHY




FIGURE 10-4 North America during the Cambrian
Period.
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Laurentia is nearly covered
by shallow epicontinental
seas.
Laurentia lies on the
equator, so water is warm.
Deposition of sand &
carbonate sediments
Water deepens toward
edges of continent, where
shale is deposited
THE BASE OF CAMBRIAN


The base of Cambrian was formerly identified by
the first-occurrence of shell-bearing organisms
such as trilobites.
During the 1970s, small shelly fossils were found
below the first trilobites, and dated at 544 m.y
The base of Cambrian is now placed
at the oldest occurrence of feeding
burrows of the trace fossil
Trichophycus, and dated at 542 m.y.
FIGURE 10-8 The trace fossil Trichophycus.
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CAMBRIAN SEDIMENTARY DEPOSITS THE SAUK SEQUENCE

During Cambrian, there were no vascular plants on
the land, so the landscape was barren. Erosion was
active and severe without plant roots to hold the
soil.

After Neoproterozoic glaciation, the sea
transgressed onto the craton.

Shoreline (beach) deposition produced a vast
apron of clean quartz sand.

Carbonate deposition occurred farther from land.
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CAMBRIAN DEPOSITS OF THE
GRAND CANYON REGION
In the Grand Canyon region, the Lower Cambrian Tapeats
Sandstone is an example of the sandy beach deposits
unconformably overlying Precambrian rocks.
FIGURE 10-12 East-west section of Cambrian strata exposed in the Grand Canyon.
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CAMBRIAN DEPOSITS OF THE
GRAND CANYON REGION
Tapeats Sandstone is overlain by Bright Angel Shale, an offshore deposit.
Bright Angel Shale is overlain by Muav Limestone, deposited farther from
land. These rocks form a transgressive sequence.
FIGURE 10-12 East-west section of Cambrian strata exposed in the Grand Canyon.
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CAMBRIAN DEPOSITS OF THE
GRAND CANYON REGION
These sedimentary units are diachronous (i.e., they cut across
time lines). In each case, the sedimentary units are older in the
west than in the east. The red lines are trilobite zones, which
approximate time lines.
FIGURE 10-12 East-west section of Cambrian strata exposed in the Grand Canyon.
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CAMBRIAN DEPOSITS OF THE
GRAND CANYON REGION
The three facies (sandstone, shale, and limestone) coexisted
and migrated laterally as sea level rose. The Bright Angel Shale
is Lower Cambrian in the west, and Middle Cambrian in the
east.
FIGURE 10-12 East-west section of Cambrian strata exposed in the Grand Canyon.
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CAMBRIAN DEPOSITS OF THE
GRAND CANYON REGION
Near the end of Early Ordovician, the seas regressed (due to
glaciation). The Muav Limestone was exposed to subaerial
erosion and a widespread unconformity developed.
FIGURE 10-12 East-west section of Cambrian strata exposed in the Grand Canyon.
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COMPARISON OF CAMBRIAN
AND ORDOVICIAN PALEOGEOGRAPHY
(C. R. Scotese,
2001, Atlas
of Earth History,
Vol., 1,
Paleogeography,
PALEOMAP
Project.)
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ORDOVICIAN
PALEOGEOGRAPHY
Note the mountains and
volcanoes in the
Appalachian region.
Volcanic ash deposits
are found in Ordovician
rocks throughout the
eastern U.S. (Now
altered to a clay called
bentonite).
FIGURE 10-27 Paleogeography of Ordovician North America.
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ORDOVICIAN OROGENIES
The Taconic Orogenic Belt lay between Laurentia (North
America) and Baltica (Europe and western Russia) during
Ordovician.
(C. R. Scotese,
2001, Atlas
of Earth History,
Vol., 1,
Paleogeography,
PALEOMAP
Project.)
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ORDOVICIAN OROGENIES
Plate tectonic cross-section showing forces that caused the
Taconic Orogeny.
FIGURE 10-23
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ORDOVICIAN OROGENIES
A.
Eastern North America
during Cambrian and
Early Ordovician,
following the breakup of
Rodinia.
B.
Large volcanic island
arc nears eastern North
America.
C.
Volcanic island arc
collides with eastern
North America causing
Taconic orogeny.
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FIGURE 10-23 Plate tectonic forces that
caused the Taconic orogeny.
VOLCANIC ISLAND ARC COLLIDES WITH
EASTERN NORTH AMERICA

As the Iapetus Ocean narrowed, a volcanic
island arc approached and collided with the
North American craton, causing folding,
faulting, metamorphism, and mountain
building.

This mountain-building event in the
Appalachian region is called the Taconic
orogeny (480 - 460 m.y. ago).
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UPPER ORDOVICIAN
SEDIMENTARY DEPOSITS
As the Taconic mountain belt
eroded, Upper Ordovician to
Lower Silurian red
sandstones and shales were
deposited to the west in huge
delta systems.
FIGURE 10-26 Great wedges of
clastic sediments spread westward.
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UPPER ORDOVICIAN
SEDIMENTARY DEPOSITS
FIGURE 10-26 Great wedges of
clastic sediments spread westward.
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These sediments formed a
wedge-shaped deposit
known as the Queenston
clastic wedge, or the
Queenston delta. Red deltaic
sediments coarsen and
thicken to the east (toward
the mountainous source
area), and become thinner
and finer grained to the west.
UPPER ORDOVICIAN
SEDIMENTARY DEPOSITS


FIGURE 10-26 Great wedges of
clastic sediments spread westward.
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The size of the clastic wedge
suggests that the mountains
may have been more than
4000 m (13,100 ft) high.
There were two main
highland areas; the higher of
the two was in the northern
Appalachians.
CALEDONIAN OROGENIC BELT
The Caledonian orogenic belt (which extends along the
northwestern edge of Europe) is part of the same trend
as the Taconic orogenic belt.
The Caledonian orogeny reached its climax slightly later,
during Late Silurian to Early Devonian.
The Caledonian event is
recognized in the
Canadian Maritime
Provinces, northeastern
Greenland, northwestern
Great Britain, and
Norway.
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FIGURE 10-7 Cratons and orogenic belts of
North America and Europe.
COMPARISON OF ORDOVICIAN
AND SILURIAN PALEOGEOGRAPHY
(C. R. Scotese,
2001, Atlas
of Earth History,
Vol., 1,
Paleogeography,
PALEOMAP
Project.)
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SILURIAN GLOBAL CONDITIONS

Silurian sea levels were high worldwide.

In Laurentia (North America), much of the
craton was flooded, indicating melting of
Late Ordovician glaciers.

This was the second major transgression
during Paleozoic, which deposited the
Tippecanoe Sequence.
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SILURIAN
PALEOGEOGRAPHY





FIGURE 10-31 Silurian North America
Paleogeography.
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Mountains in eastern N.
America are eroding.
Sandstone &
conglomerate deposits.
Widespread carbonate
deposition.
Deep marine deposits in
NW and SE U.S.
Reefs and evaporites.
SILURIAN SEDIMENTARY DEPOSITS

As the Tippecanoe Sea flooded North America in
the late Ordovician to Silurian, deposition began
with nearshore sands.

These include the famous St. Peter Sandstone, an
unusually pure, well sorted, well rounded quartz
sandstone.
The purity of the St. Peter Sandstone is the result
of reworking of older sedimentary rocks.


Silurian Tuscarora Sandstone was deposited in the
central Appalachian region.
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SILURIAN SEDIMENTARY DEPOSITS


Sandstone is overlain by extensive limestone
deposits, locally replaced by dolomite.
In eastern U.S., limestones are overlain by and
interbedded with shales along the periphery of the
Queenston delta. Niagara Falls is a classic locality
where these rocks are exposed.
FIGURE 10-15 Niagara Falls
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SILURIAN MICHIGAN BASIN EVAPORITES



Near the end of the Tippecanoe sequence, reeffringed basins developed, such as the Michigan
Basin.
Evaporation led to the precipitation of immense
quantities of rock salt and gypsum within the
basin, indicating an arid paleoclimate.
Evaporite minerals total over 2500 ft (750 m)
thick in the Michigan Basin.
 Thick accumulation of salt it is likely the
result of a restricted basin where a structure
such as a organic reef would periodically
allow communication with the ocean.
FIGURE 10-17 Isopach map shows
thickness of late Silurian evaporite
basins.
FIGURE 10-18 Cross
section shows a
deposition model for
evaporites in a barred
basin.
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SILURIAN IRON ORE




Economically important sedimentary
iron ore deposits accumulated
during Silurian in the southern
Appalachians, particularly around
Birmingham, Alabama.
Steel was produced for many years
in Birmingham from this iron ore.
Fuel was supplied by nearby Late
Paleozoic coal deposits.
Limestone, also found nearby, was
used as flux in the blast furnace.
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SILURIAN OROGENIC ACTIVITY

Orogenic activity (mountain building) was more or
less continuous at one place or another during
Silurian and Devonian.

The Caledonian orogeny was most intense in
Norway, as the Iapetus Ocean closed.

The folded rocks of the Caledonians end in Ireland,
but can be traced to NE Greenland, Newfoundland,
and Nova Scotia, Canada.
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EARLY PALEOZOIC CORDILLERA

Passive margin during early Paleozoic


Tentional basins deposits – Belt Supergroup (Montana-Idaho-British
Columbia, Uinta (Utah), Pahrump (California)
Starting in the Ordovician and Silurian the passive margin
gave way to an active margin. Subduction zone

Thick sequences of graywackes and volcanic rocks deposited in a
trench
FIGURE 10-20 Interpretive
cross section of conditions
across the Cordilleran region
during early Paleozoic time.
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PALEOZOIC
REVIEW
FIGURE 10-1 Major events of
the Paleozoic Era.
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IMAGE CREDITS
• FIGURE 10-1 Major events of the Paleozoic Era. Source: Courtesy R. F. Dymek.
• FIGURE 10-7 Cratons and orogenic belts of North America and Europe. Source: Harold Levin.
• FIGURE 10-5 Central platform of the United States showing major basins and domes. Source: Harold Levin.
• FIGURE 10-2 Landmasses during the Neoproterozoic, about 750 million years ago. Source: Harold Levin.
• TABLE 10-1 Cratonic Sequences of North America. Source: Sloss, L., 1965, Bulletin of the Geological Society
of America 74:93-114.
• FIGURE 10-8 The trace fossil Trichophycus. Source: Jensen, S., The Proterozoic and Earliest Cambrian
Trace Fossil Record; Patterns, Problems and Perspectives, Integrative and Comparative Biology: Oxford
University Press.
• FIGURE 10-12 East-west section of Cambrian strata exposed in the Grand Canyon. Source: After E. D.
Mckee, 1945, Cambrian Stratigraphy of the Grand Canyon Region, Washington, Carnegie Institute, Publication
563.
• FIGURE 10-27 Paleogeography of Ordovician North America.Source: Harold Levin.
• FIGURE 10-23 Plate tectonic forces that caused the Taconic orogeny. Source: Harold Levin.
• FIGURE 10-26 Great wedges of clastic sediments spread westward. Source: Harold Levin.
• FIGURE 10-7 Cratons and orogenic belts of North America and Europe. Source: Harold Levin.
• FIGURE 10-31 Silurian North America Paleogeography. Source: Harold Levin.
• FIGURE 10-15 Niagara Falls (A) stratigraphic section and (B) block diagram. Source: Harold Levin.
• FIGURE 10-17 Isopach map shows thickness of late Silurian evaporite basins. Source: After Alling, H. and
Biggs, L., AAPG (c) 1961, 45:515–547. Reprinted by permission of AAPG, whose permission is required for
further use.
• FIGURE 10-18 Cross section shows a deposition model for evaporites in a barred basin. Source: Einsele, G.,
2000, Sedimentary Basins: Evolution, Facies, and Sediment. New York, p. 261. With kind permission of
Springer Science+Business Media.
• FIGURE 10-20 Interpretive cross section of conditions across the Cordilleran region during early Paleozoic
time. Source: Harold Levin.