Analyze this outcrop, photographed by geologist. Thomas McGuire. It is another natural geologic cross section with red sandstone layers on the bottom and a yellow conglomerate (gravel) rock layer on top. Notice that the red rock layers are not horizontal. They are bent up on the left and right, and down in the middle, as wave-like folds (like a crumpled rug).

1. Using a pen, trace two of the contacts henvern layers of the red sandstone as well as you can. Assuming that the red sandstone layers were originally horizontal, what may have caused than to be folded in this way?

2. On both sides of the picture. use an arrow to label the exact location of the contact hetwo?n the red sandstone and the horizontal yellow conglomerate above it. This surface is an unconformity-a surface (contact) representing erosion of layers or a brcalc in deposition of layers. like a place where pages are missing from a book. Something happened ar the time represented by the surface. but no rock layer remains as a record of the event. What sequence of events may have happened to form the unconformity?

REFLECT & DISCUSS In all of your work above, you had to figure out the relative ages (from oldest to youngest) of rack layers. fractures, folds, and clasts included in soil. Based on your work, write down throe rules that a geologist could follow to tell the relative ages of rock layers, fractures, clams. and folds in geologic cross sections.

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1 What may have caused the red sandstone to be folded in this way Compressional forces from both the ends of the sandstone may have caused it to bend ... View the full answer