|Geology 12 - Historical Geology|
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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:
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.