VFE: Wind River Canyon, Wyoming

Rock Types

Here are three samples of rock collected at Wind River Canyon, Wyoming. Examine each sample in detail by zooming in and exploring its composition and texture.

Sample A:

Sample B:

Sample C:

Now answer these interpretive questions:
1) Identify the rock type that makes up each sample:
A) _________________________________
B) _________________________________
C) _________________________________

2) Which of these three rock samples is sedimentary? (answer A, B, or C) _________________________________

3) Which of these three rock samples is metamorphic? (answer A, B, or C) _________________________________

4) Which of these three rock samples is igneous? (answer A, B, or C) _________________________________

5) Is the igneous sample plutonic or volcanic? __________________________________
Explain how you know: ______________________________

Outcrops

Now, let’s explore the larger context in which these rocks were collected. We will do this by exploring some outcrops.

The samples were collected at Wind River Canyon, Wyoming, at these sites:

Site 1:

Site 2:

Now answer these interpretive questions:

6) Site 2 shows all three rock types, but Site 1 only shows two. Which two are present at Site 1? (answer ‘A and B,’ ‘B and C,’ or ‘C and A’) _________________________________

7) Based on the principles of relative dating, which of these three rocks is the oldest? _________________________________
Cite your rationale (which principle of relative dating you used for your previous answer): _________________________________

8) Based on the principles of relative dating, which of these three rocks is the youngest? _________________________________
Cite your rationale (which principle of relative dating you used for your previous answer): _________________________________

9) Therefore, what sort of surface divides samples B and C from sample A? ________________________________

10) Sample B includes zircon crystals. Imagine you collected some of these zircons and ran them through a mass spectrometer. The analysis produced a ratio of ²³⁸U to ²⁰⁶Pb of 3:1. How many half-lives have elapsed since the formation of the rock? ____________________________

11) Considering that the half-life of ²³⁸U is 4.468 billion years, calculate the crystallization age of sample B: _________________________________

12) Sample A is found to include these fossil specimens: Lingulepis is an inarticulate brachiopod. According to the Paleobiology Database, it has a geologic range from 516.0 to 449.5 Ma. What period(s) is/are included in that range? _______________________________ (Feel free to consult a geologic timescale.)

13) Which of the major North American cratonic sequences was Sample A deposited as part of? _____________________________________

14) Constrain the amount of time missing along the surface you noted in your answer to question #8 above. Record your answer as a minimum and a maximum number of millions of years missing:
“Between _________________________________ minimum and _____________________________ maximum are missing.”

Please submit your answers to the instructor.