CHAPTER 10—EARLY PALEOZOIC EVENTS
CHAPTER OVERVIEW
Rocks of the Phanerozoic are more accessible, less altered, and more fossiliferous than rocks of the
earlier eons and therefore they give us a more complete picture of Earth’s history. The Phanerozoic Eon
is divided into the Paleozoic (“ancient life”), the Mesozoic (“middle life”), and Cenozoic (“recent life”). This
chapter looks specifically at the early Paleozoic and specifically the oldest three geologic periods: the
Cambrian, the Ordovician, and the Silurian. These three periods together lasted about 126 million years.
The geologic history of the Paleozoic is characterized by long periods of sedimentation, punctuated by
intervals of mountain building. In North America, the mountain-building events are called Taconic,
Acadian, and Allegheny orogenies.
Late in the Neoproterozoic, the supercontinent Rodina broke up into six large continents and several
smaller microcontinents. As these continents drifted, ocean tracts opened and closed and subduction
zones developed that led to multiple thrust faults and orogenies. There was relatively little activity on the
interior of the continents with the site of intense deformation, igneous activity, and earthquakes at the
orogenic belts. Fossils of carbonate secreting marine organisms indicate that shallow seas were common
throughout much of the Earth during this period. The chapter discusses the transgression of major seas
that led to a variety of deposits. These sequences of transgression and regression of the seas are named
Sauk, Tippecanoe, Kaskaskia, and Absaroka. Each of these is described in detail. With no evidence of
compressional deformation, it is clear that western North America was a passive margin during the early
Paleozoic. Orogenic activity was more or less continuous at one place or another during the Silurian and
the Devonian.
While generally warm conditions dominated Laurentia during the early Paleozoic, there were some
periods of aridity. Extensive glacial deposits suggest frigid conditions in the region of today’s Sahara
Desert. Other factors that affected the climate included shorter days, stronger tidal effects, and the
absence of vascular plants.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:
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Describe the breakup of the supercontinent Rodina including the resulting land masses
and their locations.
Discuss the continental framework of the Early Paleozoic using the events of the more
stable interiors. Consider the terms craton, platform, dome, basin, and orogenic belt.
Explain the approximate duration of the Sauk, Tippecanoe, Kaskaskia, and Absaroka
sequences and how they correspond to Paleozoic Orogenic events.
Describe the events in the Cordillera including any deformational activities.
Discuss dynamic events in eastern North America including deposition and the
development of the Taconic Orogeny.
Discuss aspects of the Early Paleozoic climates including indicators such as glacial
deposits, evaporites, fossiliferous limestones, extensive reefs, massive limestone
deposits, etc.
CHAPTER OUTLINE
I.
Dance of the Continents
II.
Some Regions Tranquil, Others Active
A. The Stable Interior
B. Orogenic Belts
III.
Identifying the Base of the Cambrian
IV.
Early Paleozoic Events
Chapter 10—Early Paleozoic Events
V.
Cratonic Sequences: the Seas Come In, the Seas Go Out
VI.
The Sauk and Tippecanoe Sequences
A. The First Major Transgression
B. Islands in the Inland Sea
C. Cambrian Rocks in the Southwest: A Transgressive Succession
D. The Second Transgression
E. Evaporites Mark the Sea’s “Last Stand”
VII.
Way Out West: Events in the Cordillera
A. In the Beginning, a Passive Margin
B. Early Paleozoic Rocks
C. Orogeny Begins
VIII.
Deposition in the Far North
IX.
Dynamic Events in the East
A. Taconic Orogeny
1. Northern Appalachian Region
2. Southern Appalachian Region
X.
The Caledonian Orogenic Belt
A. Ocean Expansion
B. Ocean Contraction
XI.
Aspects of Early Paleozoic Climate
Chapter 10—Early Paleozoic Events
KEY TERMS
(Pages 267–293)
Absaroka Sequence (275): A sequence of Permian-Pennsylvanian sediments bounded both above and
below by a regional unconformity and recording an episode of marine transgression over an eroded
surface, full flood level of inundation, and regression from the craton.
Acadian Orogeny (267): An episode of mountain building in the northern Appalachians during the
Devonian Period.
Allegheny Orogeny (267): The late Paleozoic episodes of mountain building along the present trend of
the Appalachian Mountains. Likely caused by the collision, occurring during the late Carboniferous, of
northwest Africa and the southern part of the Appalachian belt.
barred basin (278): A basin which had its opening to the sea restricted by a raided sill (or possibly also
by a submerged bar).
bentonite (284): Bentonite is composed of clay minerals that are formed by the alteration of volcanic ash.
Cretaceous rocks of Wyoming and Colorado include extensive beds of this soft, plastic, light-colored
clayey rock.
Caledonian orogenic belt (288): An orogenic belt extending from Ireland and Scotland northwestward
through Scandinavia. Created by the Caledonian Orogeny during an early Paleozoic episode of mountain
building in Europe.
Caledonian Orogeny (269, 290): A major early Paleozoic episode of mountain building affecting Europe,
which created an orogenic belt, the Caledonides, extending from Ireland and Scotland northwestward
through Scandinavia.
Cordillera (278): The region of North America that consists of the entire system of more-or-less parallel
mountain ranges that extend westward from the Rocky Mountains to the Pacific coast. It includes the
Rocky Mountains, Sierra Nevada, and Coast Ranges.
cratonic sequences (275): Repeated advances (transgressions) and retreats (regressions) of
epicontinental seas. The regressions exposed old seafloors to erosion, creating extensive unconformities
that mark the boundaries of each transgressive-regressive cycle of deposition.
graptolites (280): Extinct colonial marine invertebrates considered to be protochordates. Graptolites
range from the Late Cambrian to the Mississippian.
Iapetus ocean (269): In the early Cambrian, rifts were forming between once firmly-adjoined land
masses. The ocean flooded into the broadening rift zones, one of which separated North America and
what is now northern Europe. The Paleozoic ocean is know as Iapetus.
Kaskaskia sequence (275): A sequence of Devonian-Mississippian sediments, bounded above and
below by regional unconformities and recording an episode of transgression followed by full flooding of a
large part of the craton and by subsequent regression.
orogenic belt (273): Belt of crustal compression, mountain building, and metamorphism.
Ouachita-Marathon trough (287): This trough extends across the southern margin of the North
American craton. Although over 1500 kilometers long, only about 300 kilometers of its folded strata are
exposed.
Queenston clastic wedge (285): A clastic wedge of red beds shed westward from highlands elevated in
the course of the Taconic Orogeny.
Sauk sequence (275): ): A sequence of upper Precambrian to Ordovician sediments bounded both
above and below by a regional unconformity and recording an episode of marine transgression, followed
by full flooding of a large part of the craton, and ending with a regression from the craton.
Chapter 10—Early Paleozoic Events
Taconic Orogeny (269): A major episode of orogeny that affected the Appalachian region in Ordovician
time. The northern and Newfoundland Appalachians were the most severely deformed during this
orogeny.
Tippecanoe sequence (275): A sequence of Ordovician to Lower Devonian sediments bounded above
and below by regional unconformities and recording an episode of marine transgression, followed by full
flooding of a large region of the craton and subsequent regression.
Chapter 10—Early Paleozoic Events
MULTIPLE-CHOICE QUESTIONS
1.
The Paleozoic ocean that separated North America and what is now northern Europe when the
supercontinent Rodinia formed rifts that split the land mass was known as
a. Iapetus.
c. Proto-Pangea.
b. Mirovia.
d. Laurasia.
2.
The sequence of sediment deposition on the North American craton during the Paleozoic, from
oldest to youngest, is
a. Sauk, Tippecanoe, Kaskaskia, Absaroka. c. Tippecanoe, Kaskaskia, Sauk, Absaroka.
b. Absaroka, Kaskaskia, Tippecanoe, Sauk. d. Sauk, Absaroka, Kaskaskia, Tippecanoe.
3.
A large-scale, lithostratigraphic unit that represents a major transgressive-regressive cycle and is
bounded by a regional unconformity is called a
a. platform.
c. cratonic sequence.
b. shield.
d. cyclothem.
4.
During the Cambrian, the North American continent was
a. domed upward and experienced extensive erosion.
b. submerged beneath an epeiric sea except for the Transcontinental Arch region.
c. rifted apart along the present day Mississippi River region.
d. combined into a great supercontinent called Pangea.
5.
The lithology of the Tippecanoe sequence, from oldest to youngest, is
a. black shales, limestones, and sandstones. c. conglomerates, limestones, and dolomites.
b. sandstones, conglomerates, and limestones.d. limestones, dolomites, and evaporates.
6.
The first occurrence of shell-bearing multi-cellular animals was in what system?
a. Silurian System
c. Devonian System
b. Cambrian System
d. Precambrian System
7.
During the Early Paleozoic the North American craton was bounded on four sides by orogenic belts.
They were
a. Ouachita, Cordilleran, Franklinian, and Caledonian.
b. Franklinian, Caledonian, Appalachian, and Cordilleran.
c. Caledonian, Michigonian, Appalachian, and Cordilleran.
d. Willistonian, Franklinian, Michigonian, and Caledonian.
8.
The boundary of the base of the Cambrian System is marked by the lowest (oldest) occurrence of
feeding burrows of this trace fossil.
a. Arthropod (trilobite)
c. Porifera
b. Brachiopoda
d. Phycodes Pedum
9.
A basin where evaporation produced heavy brines that sank to the bottom and were prevented from
escaping because of the sill or bar is called
a. the Cordilleran Region.
c. Sauk Deposition.
b. Barred Basin.
d. Appalachian Basin.
10. An extensive accumulation of mostly clastic sediments that are deposited in an area adjacent to an
uplifted region is called a(n)
a. depositional basin.
c. structural dome.
b. clastic wedge.
d. alluvial fan.
11.
During what geologic system were extensive evaporite minerals deposited in the Michigan Basin?
a. Proterozoic
c. Silurian
b. Cambrian
d. Ordovician
12.
The sequence during which the St. Peter Sandstone was deposited is the
a. Sauk.
c. Kaskaskia.
b. Tippecanoe.
d. Absaroka.
Chapter 10—Early Paleozoic Events
13.
The principle that postulates that sediments deposited during transgression (or regression) do not
necessarily correlate in geologic age throughout their areal extent is called
a. uniformitarianism.
c. the principle of original horizontality.
b. the principle of lateral continuity.
d. the principle of temporal transgression.
14.
In the Cordilleran region, the earliest deposits were sands, which graded westward into finer
clastics and carbonates. An excellent place to study this Sauk transgression is along the walls of
the
a. Niagara Escarpment.
c. St. Peter Sandstone.
b. Grand Canyon of the Colorado River.
d. Niagara Falls.
15.
Paleozoic rocks of the Ouachita Belt are noted for their
a. shelly facies.
c. large mineral content.
b. abundant supply.
d. unusually siliceous and cherty derived from
submarine weathering of ash.
16.
Ash beds, associated with the great volcanism that occurred during the rising of the Taconic ranges
have been weathered to a clay called
a. bentonite.
c. graptolites.
b. siliceous shales.
d. zircon.
17.
The most often associated fossil that contain stipes (branches) that is common in dark shales of the
Ordovician age in Europe and North America are called
a. mollusks.
c. graptolites.
b. brachiopods.
d. peleypods.
18.
The break up of the Neoproterozoic supercontinent Rodina produced Laurnetia which was
composed of North America and parts of all of the following except
a. Greenland.
c. North Western Ireland.
b. Scotland.
d. Africa.
19.
The six major continents derived from the breakup of Rodinia were
a. Laurentia, Baltica Kayalchstania, Siberia, China, and Gondwana.
b. Laurasia, Baltica, Kayalchstania, Siberia, China, and Gondwana.
c. Laurentia, Baltica, Kayalchstania, Siberia, China, and Gowganda.
d. Laurasia, Baltica, Kayalchstania, Siberia, China, and Gowganda.
20.
The Phanerozoic Eon includes these three eras.
a. Proterozoic, Mesozoic, Cenozoic.
c. Paleozoic, Mesozoic, Cenozoic.
b. Proterozoic, Jurassic, Cenozoic.
d. Paleozoic, Jurassic, Cenozoic.
Chapter 10—Early Paleozoic Events
FILL IN THE BLANK
1.
This clastic wedge of red beds shed westward from highlands elevated during the Taconic Orogeny
and was called the
.
2.
A basin which had its opening to the sea restricted by a raised sill (or possibly by a submerged bar)
is called a
.
3.
The name of the orogeny where initial activity began in the Early Ordovician and continued with
intense deformation through the middle and late Ordovician is
.
4.
The St. Peter Sandstone, which is pure quartz and used in the manufacture of glass, was deposited
during which sequence of deposition?
5.
The Taconic and Acadian orogenies were the result of plate convergence associated with the
narrowing of the
Ocean.
6.
The closure of the Iapetus and crumpling of the Caledonian marine basin began in what time
period?
7.
The Caledonian Orogeny reached in climax during what two periods?
to
8.
The mobile belt that contains rocks that are well exposed not only in the British Isles but also across
northeastern Greenland and Spitzbergen is called the
9.
Clinton iron ore from the Silurian Clinton group near Birmingham, Alabama represents what oxide
mineral?
.
10.
The shales noted for their rich content of fossil colonial organisms used to subdivide the Ordovician
and Silurian into biostratigraphic zones are called the
.
11.
The relatively stable part of a continent that consists of a Precambrian shield and the buried
extension of the shield known as the platform is called the
.
12.
One of the largest of the highland regions during the Cambrian (Sauk sequence) that was a vast
upland area composed of previously formed Precambrian igneous and metamorphic rocks was
called
.
13.
The classic example of the American Silurian System exposed along the walls of a gorge where a
river flows from Lake Erie into Lake Ontario is called
14.
15.
.
The effects of the Taconic orogeny are represented by remnants of an activity in the Taconic
mountains of New York in ash beds now weathered to clay is called
In North America the mountain building events are called the _____________, ___________, and
________________ orogenies.
.
.
Chapter 10—Early Paleozoic Events
TRUE/FALSE
1.
The ocean formed during the rifting between North America and the remainder of the
Proterozoic craton was called Rodinia Ocean.
2.
The principle of temporal transgression stipulates that sediments deposited by
advancing or regressive seas are of correlative geologic age throughout their aerial
extent.
3.
The St. Peter Sandstone is characterized as a “mature” sandstone because of good
sorting and an abundance of well-rounded grains of stable minerals.
4.
The Sauk and Tippecanoe cratonic sequences record the transgressive-regressive
cycles of the early Paleozoic.
5.
The Iapetus ocean formed during the Early Paleozoic as a response to the rifting of
Pangea.
6.
During the Ordovician, extensive evaporite deposits were forming in the Michigan
Basin.
7.
The Tippecanoe and Kaskaskia represent sequences of deposition on the North
American craton during the early Paleozoic.
8.
The Queenston Clastic Wedge was formed as a result of the Taconic orogeny.
9.
In North America the mountain-building events in the Early Paleozoic are called the
Taconic, Acadian, and Allegheny orogenies.
10.
In the early Paleozoic, there were four large continents.
Chapter 10—Early Paleozoic Events
ANSWER KEY
Multiple Choice
1. a
2. a
3. c
4. b
5. d
6. b
7. b
8. c
9. b
10. b
11. c
12. b
13. d
14. b
15. d
16. a
17. c
18. d
19. a
20. c
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Queenston Clastic Wedge
barred basin
Taconic Orogeny
Tippecanoe
Iapetus
Middle Ordovician
Late Siburian
Early Devonian
Caldonian Belt
hematite
Gaptolite Facies
craton
Transcontinental Arch
bentonite
Taconic, Acadion,
Allegheny
True/False
1. F
2. F
3. T
4. T
5. F
6. F
7. F
8. T
9. T
10. F
Chapter 10—Early Paleozoic Events
RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES
FIGURE 10–4 (p. 271) Among the possibilities for your location, you might select beneath the Cordilleran
or Appalachian seaway, on lowlands of the Canadian Shield, beneath a shallow epicontinental sea, or on
an island along the Transcontinental Arch.
FIGURE 10–11 (p. 276) The “fining-upward” sequence from sandstone (Tapeats Sandstone) to shale
(Bright Angel Shale) to limestone (Mauv Limestone) indicates a rise in sea level.