Relative Age Dating Name ______________________________ Date _______________ The diagram below shows a section of Earth’s crust exposed at the surface. Different rock units are labeled with letters A through H. Refer to the diagram and the key to rock types to answer the following questions.

1. List the letters of the sedimentary rock layers in order from oldest to youngest.

___ ___ ___ ___ ___ 2. What stratigraphic principle(s) allowed you to determine the sequence listed in question 1? 3. Determine the relative ages of the fault and the three intrusions.

__________ __________ __________ __________ 4. Use a colored pencil to trace the unconformity and identify the type(s) of unconformity. 5. What are two ways that you can tell that intrusion C is younger than all of the other rocks in the

section?

6. Outline the sequence of geologic events that has occurred in the area represented by this cross section.

The diagram below shows geologic sections from three different locations X, Y and Z, all underlain by sedimentary rocks. Some layers contain important index fossils. Refer to the diagrams to answer the following questions.

7. Which rock layer is the oldest? 8. What type of unconformity can be observed at location Z? 9. What rock layer(s) was apparently removed by erosion during the time represented by the

unconformity? 10. Fossils provide useful information for inferring depositional environments. Based on the fossil

evidence, indicate whether the following formations were deposited in marine or nonmarine environments. a. the green shale at location X: b. the red sandstone at location Y:

11. Explain how you can use relative age dating principles to infer that the black shale at location X is the same rock formation as the black shale at locations Y and Z.

Interpreting the Geologic History of the Grand Canyon from Poort & Carlson, 2005, Historical Geology: Interpretations & Applications The Grand Canyon in northern Arizona is one of the most spectacular examples of stream erosion in the United States. The walls of the canyon are nearly 100 miles long and 1 mile deep. These excellent exposures of Paleozoic strata in the canyon make this one of the best areas in the world for illustrating geologic history. Attached are a map and cross section of the Grand Canyon. 12. Go through the cross section and determine the relative ages of the rock units exposed in the canyon.

Begin with #1 for the oldest unit. Write the numbers on the cross section.

13. Locate all of the unconformities in the Grand Canyon. Use a color to highlight them on the canyon. Identify and label the type of unconformity represented by each surface. What type of unconformity would be the most difficult to recognize if you were looking at the real rocks in the Grand Canyon? Give a specific example of this type of unconformity in the canyon:

14. What is the name of the oldest rock unit in the cross section? 15. Which is older, the Zoroaster granite or the Grand Canyon Supergroup?

How can you tell?

16. Is the Tapeats sandstone part of the Grand Canyon Supergroup? How can you tell?

17. Did the faulting in the Inner Gorge of the canyon occur before or after the intrusion of the Zoroaster

Granite? What stratigraphic principle enables you to make this determination?

18. Where in the cross section are the youngest sedimentary rock formations exposed, on the North side

or on the South side? During what geologic ERA were those rocks deposited? On the other hand, most of the older sedimentary rocks in the Grand Canyon were deposited during the ERA.

19. What evidence do you have that most of the sedimentary rock units exposed in the Grand Canyon

have NOT undergone substantial folding and deformation? Use stratigraphic principles to support your answer.

20. What evidence does the cross section provide that erosion by the Colorado River began more

recently than the Triassic Period?