I found an outcrop of sandstone interbedded with claystone which strike/dip is N 195 E/42. Then, around 4 km at the south of previous outcrop, i found another outcrop with similar characteristic, but the strike/dip is N 132 E/79. The question is what should I do to make a cross section? should I connect the bed layer, considering their similar characteristic, or make a new layer, considering the distinct strike/dip? (could it be angular discontinuity?)

  • $\begingroup$ Try and collect more data and/or check and refine your existing measurements. Also consider that the rocks may have been folded. $\endgroup$ – bon Apr 20 '16 at 9:25
  • $\begingroup$ A quick note: your strike designation is backwards. Right hand rule strike for east dip should be north, as you have, but you give a southward orientation. Should be 015 N / 42 E strike/dip, correct? $\endgroup$ – Shawn Dec 20 '16 at 10:24
  • $\begingroup$ Next point: 4km is far enough for quite a lot to happen. If you invoke folding as the cause of this change in bedding orientation, you should look carefully for evidence of solid state deformation fabrics in outcrop: cleavage, mineral foliation, mineral lineations, etc. Do you have these? Otherwise, faulting may be a better means to explain the change $\endgroup$ – Shawn Dec 20 '16 at 10:27

Is this a homework question?

These are quite steep dips, strongly implying that substantial deformation (folding) has taken place. The interlayering of steep mudstone pretty much rules out your outcrops as being original bedding structure. Draw your examples in plan, using the normal dip and strike notation. Sketch in some possible continuation of the strike (as curved lines). Then consider what style of folding could have created this pattern. Consider also the possibility that the fold could be steeply plunging.

When you have an idea of the structure from the plan view, this should guide you in deciding the orientation of the cross section.

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  • $\begingroup$ Ha! Now I see: it does look like a second or third year mapping assignment $\endgroup$ – Shawn Dec 20 '16 at 10:30

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