Relative dating exercise

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The letters on the other cards have no significance to the sequencing procedure and should be ignored at this time. Procedure : 1 Carefully examine the second set of cards which have sketches of fossils on them. Note on Carbon- 1. AGESGo to the Virtual. All 13 lettered events need to be included in your sequence. Fossils and relative dating Fossils are important for working out the relative ages of sedimentary rocks.

North Seattle Community College's PHYSICAL GEOLOGY 101 Instructor: RELATIVE DATING EXERCISE 2002 -- The information contained in this document is copyrighted. No reproduction may be made without prior approval from the author Dr. Relative Dating of Geologic Cross-Sections: Cliffs, road cuts, and non-vegetated landscapes allow us glimpses into geology which is often hidden from view. 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. 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. Am I getting too carried away here? 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. 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. In order to do this, we need to apply the principles of relative dating which we have learned. Complete the sequence correctly and explain the logic and principle behind your choice for each event. Your explanations are as important as the correct sequence in earning the points for this question. Again, complete the sequence correctly and explain the logic and principle behind your choice for each event. This is a much more difficult exercise than the previous two because we will find several possibilities for the sequence of geologic events. You do not need to complete the second half of this particular exercise about resolving these ambiguities in the relative dating. 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? What principle s of relative dating did you use in order to arrive at your interpretation of the relative timing of each event? The various sedimentary layers are labeled as B, E, K and W. The timing of the fault break in the rocks labeled as Q must be included in the sequence of events. Question 5 3 points : What is the sequence of events that can be inferred from the above cross-section? What principle s of relative dating did you use in order to arrive at your interpretation of the relative timing of each event? 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. Remember when we drew a topographic profile for lab manual exercise 1 page 18 on Topographic Maps? 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. 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. Take a look at the geologic cross-section below. You can open a larger version of this diagram by clicking on it. Notice that the various sedimentary layers have been labeled with letters. Also an igneous intrusion is present labeled T and a fault is present labeled A. Question 6 8 points : What is the sequence of events that can be inferred from the above cross-section? What principle s of relative dating did you use in order to arrive at your interpretation of the relative timing of each event? All 13 lettered events need to be included in your sequence. Let's return to one of the text questions we addressed as part of last week's homework. 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. Include all the events which can be inferred from the drawing. List which relative dating principles apply to the order of each event. The Geology of the Grand Canyon: Shown below is a real transect across the entire Grand Canyon in two parts. This profile is comprised of both the surface topography and the inferred geology underfoot. Notice that the rock layers are each labeled with several letters. Each rock layer was deposited at a different geologic time. We will learn more about this method of identifying rock units and geologic time periods in next week's lab. South Half -- North Half -- Question 8 2 points : On the South Half, approximately how high is Hopi Point on the Coconino Plateau? What is the approximate elevation of the Colorado River shown by the arrow pointing downwards? What is the elevation difference? Question 9 2 points : On the South Half, which rock unit is likely to be the youngest most recent? Which rock unit is likely to be the oldest? What relative dating principle tells us this? Use the letter labels to refer to the distinct rock layers. Question 10 2 points : On the South Half, we can also notice that many faults have occurred in the area of the Cheops Pyramid. These are the dark lines that slice through the rock formations. When did all this faulting take place that is, between the times of which two sedimentary layers did the faulting occur? What relative dating principle tells us this? 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. 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. Question 11 2 points : Pinpoint the time at which this tilting took place. Find the youngest layer which has been tilted and the oldest layer which has NOT been tilted. The tilting must have occurred between these two times. Between which two rock formations use the letter labels did this tilting occur? 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? Would you say that the upper rock layers in the Grand Canyon follow the Principle of Original Horizontality? I hope this first virtual trip to the Grand Canyon was a bit of fun along along with the very hard work. We will visit it again but only virtually!

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