Geologic dating exercise
Question 2: What is the sequence of events that can be inferred from the above cross-section?
The two intrusions are labeled as X and Z; the surrounding rock (called the "country rock") is labeled as D.
Refer to the geologic time scale on page 219 for the names of each of the geologic time periods, as well as the absolute dates attached to each Period. Four major unconformities are evident in the Grand Canyon cross-section.
Remember that unconformities represent sections of missing time, either through non-deposition of rocks for a period of time, or through an interval of erosion which has removed some strata.
This means that the remains of living things are useful for carbon-14 dating.
Most rocks, however, are not useful for carbon-14 dating (either not enough carbon, or didn't derive its carbon from the atmosphere-shallow water reservoir).
The various sedimentary layers are labeled as B, E, K and W.
What principle(s) of relative dating did you use in order to arrive at your interpretation of the relative timing of each event?
In Part 2 you will use the principles of relative dating to determine sequences of geological events as indicated by the layers and structures in the rocks.
Part 2 ends with an application of the principles of relative dating to the rocks of the Grand Canyon.
View the above image, a cross-section (side-view of a cut-out through the crust) of the Grand Canyon.
Study this diagram carefully, noting the orientation of individual rock layers, as well as the type of rock in each layer, and the age of the rock in each layer. IS TO CLEARLY IDENTIFY FOUR MAJOR UNCONFORMITIES IN THE GRAND CANYON SEQUENCE.