1. Geologic Cross-Sections

2. Cross Sections are Based on Surface and Sub-Surface Data

3. Sub-Surface Interpretation (3-D)

4. Constructing a Cross-Section
choose a line of section (perpendicular to structures)

5. Cross-Section Construction Cont…
2. transfer topographic data
(topographic profile with no vertical exaggeration)

6. Structural Data – (Apparent) Dips
3. add structural data to the topographic profile

7. Add the Geology!
4. add geologic data (contacts) to the profile; dash in eroded structures above present-day topography

8. Apparent Dip

9. True Dip & Apparent Dip

10. Apparent to True Dip Trigonometry
= apparent dip
= angle between strike
and apparent dip
direction
= true dip

11. Calculating Apparent Dip from True Dip( )

12. Apparent Dip “Nomogram”

13. True Dip to Apparent Dip – the Easy Way!

14. Cross Section “Rules”
calculate apparent dips of beds that are not perfectly perpendicular to your section line
DO NOT use vertical exaggeration
don’t extrapolate structural data too far from your section line
dash in eroded structures above the present-day topography
don’t extend dip data more than a few hundred meters in depth