Hello, Will you please help me with my Structural Geology Lab? We are practicing

Question

Hello,

Will you please help me with my Structural Geology Lab? We are practicing stereographic projection.

The problem I am having trouble with reads as follows; "Below an uncomformity striking N73E and dipping 32 NW, a series of planar beds strikes N18E and dips 60W. What was the strike and dip of these beds at the time the unconformity was formed? What questionable assumption have you made in arriving at your answer? (Hint: it is NOT that the unconformity was originally planar and horizontal).

I have graphed the given information (both as planes and poles) but am not sure where to go from there, especially because I am not sure what the assumption is. I think I have to utilise the relationship in where the major axis, the elliptical section, and the cylindrical axis all lie in the same plane. I may also have to use rotation (to rotate back the planes to their original position).

Any guidance would be great. Thanks!

Explanation / Answer

Hi since you have done the basic works the stepwise process I am outlining for your reference:

1- plot the unconformity and bedding planes.

2. Rotate thtracing so that unconformity lies on East West line.

3. Now bring the unconformity plane to center of the net and measure the angle, move the plane by the same amount on small circle of the net.

4. This new position of bedding plane is the original position before the deformation of the beds.

Hope this solves your problem

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