Chapter 10 Early Paleozoic Events
Chapter 10—Early Paleozoic Events
Chapter 10—Early Paleozoic Events
CHAPTER OVERVIEW
Phanerozoic rocks 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 eon we call Phanerozoic is divided into Paleozoic (“ancient life”), Mesozoic (“middle life”), and Cenozoic (“recent life”). This chapter looks specifically at Early Paleozoic and specifically the oldest three geologic periods: Cambrian, Ordovician, and Silurian. These three periods together lasted about 126 million years. The geologic history of the Paleozoic is characterized by long periods of sedimentation, and punctuated by intervals of mountain building. In North America, the mountain-building events are called Taconic, Acadian, and Allegheny.
During Late 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 time interval. 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 Silurian and Devonian.
While generally warm conditions dominated Laurentia during Early Paleozoic, there were some time intervals 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:
· Describe the breakup of the supercontinent Rodina, including the resulting land masses and their locations.
· Discuss the continental framework of 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 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
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
Key Terms (pages given in parentheses)
Absaroka Sequence (283): A sequence of Permian-Pennsylvanian sediments bounded both above and below by a regional unconformity and providing a record an episode of marine transgression over an eroded surface, full flood level of inundation, and regression from the craton.
Acadian Orogeny (277): An episode of mountain building in the northern Appalachians during the Devonian Period.
Alleghenian orogenic belt (277): The belt of rocks formed by mountain building tectonics of the Allegheny Orogeny in North America.
Allegheny Orogeny (277): Late Paleozoic episodes of mountain building along the present trend of the Appalachian Mountains. Likely caused by the collision, occurring during Late Carboniferous, of northwest Africa and the southern part of the Appalachian belt. The third of the orogenies that built the Appalachian Mountains of North America.
barred basin (287): A basin which had its opening to the sea restricted by a raided sill (or possibly also by a submerged bar).
bentonite (293): 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 (296): An orogenic belt extending from Ireland and Scotland northwestward through Scandinavia. Created by the Caledonian Orogeny during Early Paleozoic episode of mountain building in Europe.
Caledonian Orogeny (277, 297): 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 (287): 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 (283): 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 (287): Extinct colonial marine invertebrates considered to be protochordates. Graptolites range from the Late Cambrian to the Mississippian.
Hercynian orogeny (277): The belt of rocks formed by mountain building tectonics of the Hercynian Orogeny in Europe.
Iapetus ocean (277): During 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 (283): 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 (280): Belt of crustal compression, mountain building, and metamorphism.
Ouachita-Marathon trough (296): 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.
Ouachita orogenic belt (277): The belt of rocks formed by mountain building tectonics of the Ouachita Orogeny in North America.
Queenston clastic wedge (286, 294): A clastic wedge of red beds shed westward from highlands elevated in the course of the Taconic Orogeny.
Rheic Ocean (277): An ocean that began to form as the Iapetus began closing during Ordovician and Silurian. Located north of Iapetus, between Laurentia and Africa.
Sauk sequence (283): 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.
Taconic Orogeny (277, 291): 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 (283): 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.
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 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 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 c. Devonian
b. Cambrian d. Precambrian
7. During 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 Cambrian rocks is marked by the lowest (oldest) occurrence of feeding burrows of this trace fossil.
a. Arthropod (trilobite) c. Porifera
b. Brachiopoda d. Trichophycus
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 cratonic sequence of which the St. Peter Sandstone is a part
a. Sauk. c. Kaskaskia.
b. Tippecanoe. d. Absaroka.
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 Ordovician dark shales in Europe and North America are called
a. mollusks. c. graptolites.
b. brachiopods. d. peleypods.
18. The break up of 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 eon we call Phanerozoic includes these three eras.
a. Proterozoic, Mesozoic, Cenozoic. c. Paleozoic, Mesozoic, Cenozoic.
b. Proterozoic, Jurassic, Cenozoic. d. Paleozoic, Jurassic, Cenozoic.
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 during Early Ordovician and continued with intense deformation through 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 is made mainly of 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 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 Silurian strata exposed along the walls of a gorge where a river flows from Lake Erie into Lake Ontario is called .
14. 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 .
15. In North America the mountain building events are called the ______, ______, and ______orogenies.
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.