Geology 12 - Historical Geology
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Potential Exam Questions, Exam #2

Potential Short Answer Questions

1. What kind of plate boundary is a(n) (rift valley, passive margin, intracratonic, foreland, forearc, trench, ophiolite) tectonic basin associated with? How do you recognize this tectonic basin (environments and lithologies)?
2. Characterize the sedimentary deposits found in one of these plate settings: rift valley, subduction zone, suture zone, ophiolite.
3. Why do we think the earth, planets and sun all had a common origin? Cite three lines of evidence.
4. How are Archean rocks different from Proterozoic rocks? Be sure to describe both the rocks and their plate tectonic setting.
5. What evidence supports the interpretation that a supercontinent 1) formed in Late Proterozoic time, and 2) broke up just at the beginning of the Cambrian?
6. Cambrian rocks in North America are dominated by quartz sandstones; Ordovician rocks are mostly limestones. What can you say about depositional environments during the Cambrian and Ordovician? What caused the change from sandstone deposition to limestone deposition?
7. Describe the history of the Earth's atmosphere and oceans.  Include a description of ALL of Earth's atmospheres over time, where the air and water came from, and the evidence for each atmosphere.
   
8. How does our model of the origin of the solar system explain these phenomena?

• There is an asteroid belt between Mars and Jupiter
• All the planets go around the sun in the same direction
  
• The major planets are in roughly circular orbits
• The overall density of the Earth is the same as the overall density of meteorites.
• The density and composition of the surface rocks of the Earth are different than the density and composition of meteorites.

Potential Essay Questions

1.  For the exam, I will choose at least one of the following geologic settings for analysis. Your job is to do ALL FIVE of these things:

• to identify the sedimentary environments represented by these rocks.
• Then identify the tectonic basin these rocks belong to (rift valley, passive margin, intracratonic, foreland, forearc, trench, ophiolite) and
• identify what the plate tectonic setting was at the time these rocks were formed.
• Suggest what other geologic features you might look for to test your hypothesis.
• Explain your reasoning at every step.

a. A large portion of the Middle Paleozoic rocks in the Eastern U.S. are red shales and arkosic sandstones. Interbedded with the redbeds are thick layers of bentonite, which is weathered of volcanic ash (assume it was volcanic ash in the Middle Paleozoic). The sequence of redbeds is thickest in the east, and thins westward. Further west are found deposits of gray shales with thin layers of limestone.

b. In the middle of North America are some very ancient rocks, about a billion years old. At the bottom of this stack of rocks are basalt flows. On top of the basalt flows are red sandstones and shales, then white sandstones and conglomerates. These rocks occupy a strip about 100 miles wide and 800 miles long through the center of the continent, though over most of that extent they are buried by younger rocks.

c. The Middle Paleozoic rocks of New England are typified by gray and brown sandstones and shales. The sandstones are graywackes with graded bedding that contain fragments of andesite. The shales are finely laminated and contain marine fossils. 

d. The Coast Range of California contains greenschists of Mesozoic to Cenozoic age. Mixed into the greenschists are large chunks of blueschist (boulder to hill-sized), and chert that is found in both layers and discontinuous boulder-sized blobs. The green schists are folded and reverse faulted.

e.  The Late Paleozoic rocks of the Mid-Atlantic region are composed of immensely thick layers of red sandstones with ripple marks and red conglomerates with metamorphic pebbles.  Further west are red-brown shales with mudcracks.   To the east are granite bodies of about the same age.

f.  The middle Paleozoic rocks of Colorado include flat-lying carbonates and shales full of marine fossils.  These rocks are essentially undeformed.