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Question 4 - 10 points

In this case, some of the rock layers were tilted and eroded after they were laid down flat, then other rock layers were deposited on top of them, making an angular unconformity. However, we have no way of knowing how much time elapsed or how many rock layers were eroded before the current structure was developed. You needed to be sure to say that. Here's my history:

  1. Layers D, E, F, G, and H were laid down in that order.
  2. Sometime after deposition of H, the rocks were tilted.
  3. Probably at the same time, they were uplifted, and erosion kicked in.
  4. After they were eroded to a flat surface, the rock layers subsided to a level where more deposition could occur.
  5. After an unknown amount of time, layer C was laid down. Here there is an angular unconformity, and we have no way of knowing how much absolute time is missing.
  6. Next, layer B was laid down.
  7. Finally, layer A was laid down.
You could argue for a last stage, where the rocks all get raised up so that our road cut or canyon or whatever exposes the rocks, but that's not necessary for this assignment.

Greg Anderson
Tue Mar 11 18:16:04 PST 1997