The Earth Through Time, 10th Edition
by Harold L. Levin
CHAPTER 10—EARLY PALEOZOIC EVENTS
CHAPTER OUTLINE FOR TEACHING
I.
Early Paleozoic Periods
A. Cambrian: began 542 million years ago
B. Ordovician
C. Silurian: ended 416 million years ago
II. Overview
A. Larger Continents of Early Paleozoic
1.
2.
3.
4.
5.
6.
B.
Laurentia
Baltica
Kazakhstania
Siberia
China
Gondwana
Plate Tectonic Events (in order)
1. Breakup of Rodinia (proto-Pangaea)
2. Oceanic closing and orogeny to form Pangaea
a. Taconic orogeny
b. Acadian orogeny
c. Alleghenian orogeny
d. Caledonian orogeny
e. Hercynian orogeny
C. Paleogeographic Areas
1. Stable Interiors
a. domes
b. basins
2. Orogenic Belts
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III. Base of the Cambrian
A. Former Marker: First appearance of shelly animals
B. Current Marker: Lowest occurrence of trace fossil Trichophycus
IV. Early Paleozoic Events
A. Cratonic Sequences and Sea-Level Change
1. Sauk
a. first major transgression
b. transgressive sedimentary sequence
2. Tippecanoe
a. second major transgression
b. transgressive sequence terminated by evaporites
3. Kaskaskia
4. Absaroka
B. Lithologic Evidence
1.
2.
3.
4.
5.
6.
7.
Limestone (shallow marine, subtropical)
Evaporites (equatorial dry conditions)
Lithic sandstone and graywacke (mountain uplift)
Arkose (arid conditions)
Tillites (glacial deposits)
Quartz sandstone (shorelines, deserts)
Shales (deep marine; graptolite-bearing deposits)
C. Orogenies of Early Paleozoic
1. Cordilleran orogeny begins
2. Rifting and displacement of Rodinia
3. Eastern U.S. orogeny begins
a. Taconic orogeny
b. vast bentonites from volcanic ash deposition
4. Ouachita-Marathon trough deformation
5. Caledonian orogenic belt
a. Iapetus ocean expansion
b. subsequent ocean contraction
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V. Early Paleozoic Climates
A. Transgressions = mild climates, windswept low terrains
B. Regressions and Orogenic Episodes = harsher more diverse climates; winds
diverted by mountains
C. Earth Rotation was Faster (days shorter, tidal effects greater)
D. No Land Plants (Cambrian-Ordovician)
1. solar radiation reflected, not absorbed
2. severe temperature differences resulting
E. End of Late Proterozoic Glacial Cycle: cool beginning for Early Paleozoic
Answers to Discussion Questions
1. Book your vacation for Laurentia, Baltica, Kazakhstania, Siberia, China, and Gondwana.
2. Rock formations thin and (or) pinch out along the transcontinental arch indicating that it was a
feature above sea level during most of Early Paleozoic.
3. A barred basin is a low area below sea level wherein sea water inflow and outflow is
restricted by organic reefs, a raised sill, or a submerged bar. These kinds of basins are
particularly effective in producing evaporite deposits because they generally restrict both
inflow and outflow of water. Such a basin developed in the area of the lower peninsula of
Michigan during Silurian.
4. A clastic wedge is a great mass of sedimentary rock representing sediments which have
been shed off a rising mountain range during and after an orogenic event. The Queenston
clastic wedge was shed off the Taconic Mountains during Early Paleozoic.
5. Sequence-bounding unconformities are the result of global changes in sea level as indicated
by their development on all the world’s continents. If they were the result of an uplift of the
North American craton, all other cratons would have had to move simultaneously for the
same result.
6. The Sauk regression and Tippecanoe transgression were not instantaneous events but
occurred over several million years thus an age difference across the unconformity surface,
which separates the two sequences.
7. A dome is a radial symmetrical uplift of crust which was active during deposition. A basin is a
similarly symmetrical feature which is negative or subsiding during deposition. In dome
stratigraphy, strata thin toward the center or axis and unconformities become more
numerous and notable toward the center or axis. In a basin, strata thicken toward the center
and unconformities occur near the margins. On a geologic map, both may show a “bull’s
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eye” pattern, but the oldest layers will be in the center of a dome, the youngest at center of a
basin.
8. Trace fossils are indirect evidence of life such as trails, tracks, burrows, borings, etc. Trace
fossils may be more susceptible to destruction than other fossils under some conditions.
Further, two or more organisms may make a very similar trace, thus confusing identification.
9. The paleoequator may be determined by paleomagnetic studies with precision, or by studies
of rock and fossil distribution (e.g., reefs). Arid regions might be identified by deposits of
evaporites and quartz sandstone with eolian cross-bedding. Glacial episodes would be
identified by tillites, glacial lake deposits, glacial striations, moraines, and melt-water
deposits. Mountain building due to plate collision produces folded and thrust-faulted strata,
ophiolite belts, and great clastic wedges. Volcanics are also associated with these events.
10. Graptolites were attached to floating masses that allowed them to float widely through
Cambrian and Ordovician seas. Graptolites evolved rather quickly and were dispersed widely
in a short time.
11. d
12. a
Chapter Activities
Student activities for in-depth learning.
1. The current marker for the bas of the Cambrian System is the elongate trace fossil,
Trichophycus. Take a look at the discussion and images available at this German university web
page (in English) and look for images of this fossil:
http://www.palaeontologie.uniwuerzburg.de/Stuff/casu8.htm. Write a short summary of the global significance of this trace
fossil both as a basal marker for the Cambrian and also as a fossil of evolutionary significance.
There are other pages featuring images and discussion of Trichophycus, so take a look at those
as well. Make a sketch of this trace fossil and the type of organism that you think might have
made this trace. What is the significance of Fortune Head, Newfoundland? Why are such places
so important in paleontology and stratigraphy?
2. Using the various links at this climate page (http://www.scotese.com/climate.htm), which is
maintained by the PaleoMap Project, describe the climates that persisted over the Early
Paleozoic (Cambrian-Silurian). What is the basis for the climatic interpretation (see links on the
left side of the page)? Make a diagram showing how global average temperature is thought to
have fluctuated over the Cambrian-Silurian time interval.
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