Homework Assignment 2
This exercise will hopefully give you a better understanding
of geologic time as represented by sedimentary rocks now exposed in the
Grand Canyon. In order to complete the exercise you will need to
refer to Figure 2-14 (page 32) in your text, and the Geologic Time Scale
I handed out in class.
1. Estimate the approximate number of years required for the
accumulation of that part of the Grand Canyon sequence (Fig. 20-4) extending
from the base of the Tapeats Sandstone to the top of the Kaibab Limestone.
Assume that the base of the Tapeats represents the Cambrian - PreCambrian
boundary, and that the top of the Kaibab is at the Triassic - Permian boundary.
Use absolute ages from the Geologic Time Scale for these rock units.
2. Given that the thickness of this part of the rock sequence
is 1.2 kilometers, estimate the average rate of accumulation of sediment
during this time interval. State whether you believe your estimate is a
minimum, maximum or accurate figure.
3. Would any of the rocks exposed in the Grand Canyon be good
candidates for radiometric dating? Briefly explain your reasoning.