DETERMINING RELATIVE ROCK AGES Part 1: Using the Principles of Relative Da For e

Question

DETERMINING RELATIVE ROCK AGES Part 1: Using the Principles of Relative Da For each cross-section The oldest unit is number 1. Continue until the ing you will number the units and events in order of formation. youngest unit is numbered. 1. Number the four events form oldest to youngest Remember, 1 is the oldest. Conglomerate Shale Limestone a. Which is older, Unit A or Unit F? b. Which is older, Unit C or the erosion surface (unconformity, shown by the wavy line)? c. Number the seven events, including the unconformity, from oldest to youngest. 3. a. What is the diagonal straight line through the cross section? b. Which unit is a pluton (intrusive igneous rock)?_ c. Which is older, Unit R or the fault that cuts Unit R? d. Number the six events, including the fault, from oldest to youngest. Lecture Tutorials for Introductory Geoscience OW. H. Freeman and Company 165

Explanation / Answer

1. Principle of relative age dating follows the Principle of superposition which states that in an undisturbed sedimentary succession the oldest layer is always at the bottom. So the given figure is an sedimentary succession and the oldest layer must be the limestone followed by shale, sandstone and conglomerate. This is summerized as follows :

4. Conglomerate (youngest)

3. Sandstone

2. Shale

1. Limestone (oldest)

2. a.The older unit is F as it lies at the bottom of the given sedimentary succession.

b. Unit C is the older unit than the erosional surface as it has been cut by the erosional surface.

c. From the oldest (1) to youngest (7), the units are as follows

7. A Unit

6. B unit

5. Unconformity/ erosional surface

4. C unit

3. D unit

2. E unit

1. F unit

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