Question 5 - 20 points

Oh, boy, this is the complicated case. Here there are angular unconformities, faults, and intrusive bodies. If you properly unraveled this one, you should be proud (though perhaps a bit pissed off at me). Here's my history of the area:

1. Layers F, G, H, I, J, K, L, and M were laid down in that order.
2. Sometime after deposition of M, these layers were tilted back.
3. Probably at the same that they were tilted, these layers were uplifted and erosion kicked in.
4. After they were eroded to a flat surface, these layers subsided to a level where more depositon could occur.
5. After an unknown amount of time, layer E was laid down. Here there is an angular unconformity, and we have no way of knowing how much absolute time is missing.
6. After layer E was laid down, but before layer D, an active fault broke layers E, I, H, and G. We know it had to start after layer E, because the fault broke that layer, and it had to stop before layer D, because that layer is not broken by the fault. Layers G, H, and I are broken because they are older than the fault and just happen to be in the ``right'' spot.
7. Next, layer D was laid down. It is thicker on the right side of the fault because the right side of the fault moved downward, leaving a spot to be filled in by sediments.
8. Next, layers C and A were laid down in that order.
9. After layer A was laid down, a granitic body was intruded between layers A and C, doming A upward.

Complicated, yes -- but certainly not impossible.

You were asked to answer two further questions in this problem. My answers are:

1. The fault shown in the sketch is a normal fault, because the ``hanging wall'', which is on the right in this case, is downdropped relative to the ``foot wall.''
2. The granitic body (layer B) which was intruded between layers A and C is a sill, because it is intruded between the beds, which are horizontal. If the body had cut across the beds and been tabular, the body would have been a sill.

   You could argue that the granitic body is actually a laccolith, which is a sort of mushroom-shaped body of igneous rock, which usually domes up the layer(s) above it (as with layer A). I wouldn't take points off for such an answer -- in fact, I'd be impressed.