Notice that the various sedimentary layers have been labeled with letters. Am I getting too carried away here? Again, complete the sequence correctly and explain the logic and principle behind your choice for each event. Use the letter labels to refer to the distinct rock layers. Now let's practice on a couple more imagined cross-sections: Question 4 3 points : What is the sequence of events that can be inferred from the above cross-section? We will learn more about this method of identifying rock units and geologic time periods in next week's lab. This is a much more difficult exercise than the previous two because we will find several possibilities for the sequence of geologic events.
Would you say that the upper rock layers in the Grand Canyon follow the Principle of Original Horizontality? What is the elevation difference? Click to access the activities related to the interpretation of geologic sequences. The number of each question below corresponds to the questions on our submission form for this week's lab assignment. When did all this faulting take place that is, between the times of which two sedimentary layers did the faulting occur? Question 5 3 points : What is the sequence of events that can be inferred from the above cross-section? The Geology of the Grand Canyon: Shown below is a real transect across the entire Grand Canyon in two parts. Question 12 1 point : Approximately how much higher are the upper rock layers on the North side of the Grand Canyon the Kaibab Plateau than they are on the South side? These are the dark lines that slice through the rock formations. The timing of the fault break in the rocks labeled as Q must be included in the sequence of events. What relative dating principle tells us this? Just as Sherlock Holmes used his power of observation to decipher the clues to a suspect's past actions, we will let the blemishes and behaviors of the rocks tell us their past story.
In the next lab, we will learn how to use local geologic information from outcrops to begin to build such regional geologic maps and geologic cross-sections, but for now we just want to practice how to read them. Notice that the rock layers are each labeled with several letters. The earlier sequence of rock formations had to have been tilted before the more recent sequence of rock formations was deposited on top of it. Let's return to one of the text questions we addressed as part of last week's homework. Question 10 2 points : On the South Half, we can also notice that many faults have occurred in the area of the Cheops Pyramid. To review our principles of relative dating as applied to such geologic cross-sections, we will make use of a neat learning tool available on the Internet.
Take a look at the geologic cross-section below. You do not need to complete the second half of this particular exercise about resolving these ambiguities in the relative dating. List which relative dating principles apply to the order of each event. Remember when we drew a topographic profile for lab manual exercise 1 page 18 on Topographic Maps? What do conglomerates generally tell you about geologic history? This is not labeled as such -- but see how the rocks at the bottom of the profile have been tilted while the younger rocks on top are horizontal. What is the approximate elevation of the Colorado River shown by the arrow pointing downwards? Each rock layer was deposited at a different geologic time. No reproduction may be made without prior approval from the author Dr. All 13 lettered events need to be included in your sequence.
What principle s of relative dating did you use in order to arrive at your interpretation of the relative timing of each event? What relative dating principle tells us this? We could draw such a profile across several miles of landscape so we would see a side-view of the land's surface over which we might be hiking. Question 6 8 points : What is the sequence of events that can be inferred from the above cross-section? What is the youngest rock in the area? Relative Dating of Geologic Cross-Sections: Cliffs, road cuts, and non-vegetated landscapes allow us glimpses into geology which is often hidden from view. In order to do this, we need to apply the principles of relative dating which we have learned. Also an igneous intrusion is present labeled T and a fault is present labeled A. This profile is comprised of both the surface topography and the inferred geology underfoot. Kurt Friehauf — Geology of National Parks Questions for relative dating practice problem Questions Which is older and why? We will visit it again but only virtually! The tilting must have occurred between these two times.
. Events can be the deposition of a sedimentary layer, the eruption of a lava flow, the intrusion of magma to form a batholith, a fault break in the rock that shifts one side relative to the other side and causes an earthquake , a fold that bends and distorts rock layers, or any number of other geologic processes. What principle s of relative dating did you use in order to arrive at your interpretation of the relative timing of each event? What is the oldest rock in the area? Question 9 2 points : On the South Half, which rock unit is likely to be the youngest most recent? What is the name of the geologic feature at the base of the Friehauf conglomerate and what does it indicate about the geologic history of the area? Question 11 2 points : Pinpoint the time at which this tilting took place. Between which two rock formations use the letter labels did this tilting occur? Which rock unit is likely to be the oldest? Question 7 8 points : Using the relative dating method you have now practiced, derive the history of the hypothetical landscape on page 173 also shown below. You can open a larger version of this diagram by clicking on it. South Half -- North Half -- Question 8 2 points : On the South Half, approximately how high is Hopi Point on the Coconino Plateau? The various sedimentary layers are labeled as B, E, K and W.
Your explanations are as important as the correct sequence in earning the points for this question. Complete the sequence correctly and explain the logic and principle behind your choice for each event. I hope this first virtual trip to the Grand Canyon was a bit of fun along along with the very hard work. In the same way, such a transect could also show the inferred profile of the geology underfoot -- the expected rock layers and structures beneath the land from the northwest corner to the southeast corner of the map. Include all the events which can be inferred from the drawing. .
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