Practice Questions #2
Figure shows a sketch of a rock outcrop where bedding and cleavage are visible. It is known that the bedding is folded in this area, and that the cleavage is axial planar to these folds. What can be deduced about these folds from the information at this outcrop?
Overturned fold?
We look first at the dip of the cleavage. This dips moderately to the left (west) and from this we should visualize folds occurring within the area with axial planes having the same dip. Some possible folds with westerly dipping axial planes are drawn in Fig shown below.
https://uploads.disquscdn.com/images/7f823ffe7160fc942a0e81b71510d6dbbce3ee599b578372349574b5ea7a741c.png
If we consider one such fold of antiformal type, we find that the bedding/cleavage relationship on its east limb matches that observed at the outcrop. We can conclude from this that the outcrop is situated on the east limb of an antiformal fold. In other words, we have deduced that the next fold hinge to the west of the outcrop is an antiform. We are, of course, not able to say how far to the west the antiform is.