Download Homework #2 - Relative dating excercise

Name _______________________
Geol 101.02 Physical Geology
Homework #2 – Relative dating
Due: Friday, Feb 18
Principles of Relative Dating:
-Principle of Original Horizontality— Sedimentary rocks and lava flows are deposited in
horizontal or nearly horizontal layers. When rock layers are found in nonhorizontal
positions, they were affected by some geologic process(es) following deposition.
-Principle of Superposition— In any horizontal sequence of rock layers, the youngest
layer is at the top and the oldest is at the bottom (as long as the sequence has not been
overturned).
-Principle of Cross-Cutting Relationships—Any intrusive magma must be younger than
the rock it cuts across. Faults must be younger than the rocks they cut and displace.
-Principle of Continuity — Sedimentary layers were deposited as single units
-Principle of Fossil Successions—specific groups of fossils follow, or succeed, one
another in the rock record in a definite order (won’t use in this assignment)
Anytime you have regional metamorphic rocks near the surface, you know they’re older
than any neighboring igneous or sedimentary rocks. You know this because they
were metamorphosed at depth and the neighboring igneous or sedimentary rocks
would have also been metamorphosed.
Unconformities (marked by squiggly lines):
-Nonconformity—separates non-layered rock (metamorphic rock or an igneous intrusion)
from layered rock (sedimentary rocks, extrusive lava flows).
-Disconformity—separates parallel layers of layered rock — erosion and gap in time
separates the two sets.
-Angular Unconformity—separates a block of layered rock from another block of layered
rock, with some angle between the two sets.
Assignment:
Using the principles above, determine the relative ages of the rock layers, intrusions,
faults and unconformities in the block diagrams on the following pages. Be sure to
examine all the relationships between layers.
PLEASE USE PENCIL (with erasure) – be neat!
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List the order of events from youngest to oldest.
1.
Youngest
________________
________________
________________
________________
________________
________________
________________
________________
Oldest
a What type of unconformity separates N from U?
b. What two principles are necessary to interpret this column?
2.
Youngest
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
Oldest
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3. List the letters in chronological order from youngest to oldest.
Youngest
____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____
A = granite (6 ma)
E = granite (9 ma)
____
Oldest
____
J = Limestone
a. What type of unconformity separates layer F from the layers below?
b. What type of unconformity separates layer N from layer J?
c. A fossil was found in layer C. The fossil was determined to be from a species that
lived from about 7.5 ma to 8.5 ma. Use this new information to determine the age
constraints on layer L. (What are the maximum and minimum ages that layer L can be?)
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4. List the letters in chronological order from youngest to oldest.
Youngest
Oldest
____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____
K
a. What type of unconformity separates E from A, H, R, and B?
c. Absolute dating reveals that M, a granite intrusion, is about 6 million years old. What
does this tell us about the age of H?
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5. List the letters in chronological order from youngest to oldest.
Youngest
Oldest
____ ____ ____ ____ ___ ___ ___ ____ ____ ____ ____ ___ ____ ____
T
B
O
a. What type of unconformity separates N from L?
b. What type of unconformity separates D from layers K and A?
c. Layer K contains fossils of organisms known to have gone extinct 500,000 years
ago. Charcoal found in layer D was analyzed and found to be about 35,000 years
old. What is the minimum time gap of the unconformity between D and K?
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Extra credit: List the letters in chronological order from youngest to oldest.
Youngest
Oldest
____ ____ ____ ____ ____ ____ ____ ____ ____ ____
____ ____ ____ ____ ____ ____ ____ ____ ____ ____
Z
A = intrusive (0.6 ma) S = intrusive (14 ma)
V = metamorphic (89 ma)
E = intrusive (
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