2. Folds Read Davis and Reynolds, Chapter 7

3. Why is it important? fundamental to deformation of the Earth’s crust; structural traps for oil ore deposits

4. Tectonic considerations Folds, key to covergent margins, aid in resolving past stress regimes, crustal shortening, closure of sedimentary basins. Sensitive markers to tectonic forces.

5. Relevance to oil and mining Structural traps (anticlines are among the best traps Folds control ore geometry especially in strata-bound deposits

6. Descriptive analysis Basic definitions (anticline, syncline,overturned, etc.) Geometric analysis (hinge, limb, axial plane, etc) Specific geometries

7. Shapes of folds Anticlines, synclines Antiform, synform Anticlinorium, synclinorium old younger older younger

8. Antiforms, synforms, anticlinoria, synclinoria

9. Hinge, hinge zone Limb Inflection point Hinge line Do not forget axial surface Axial plane

13. Recumbent Fold lies on its side- typical for poly-deformed regions

14. Chevron Ptygmatic Cuspate

15. Geometry, size Median trace Wavelength Amplitude Width Heigth

17. Hinge line and axial plane

18. Topographic Surfaces and folds

19. Layer thickness may change during folding Didn’t here- this is a “concentric” fold This one did- it is a “similar” fold

20. Fold tightness Gentle Angle is >90 degrees

21. tight (10ish degrees opening) to isoclinal (0 degrees)

23. Symmetric, asymmetric

24. Cylindrical (there is an axial surface) and non-cylindrical (too complex to have a defined axial surface) Hinge line Poles to bedding Hinge line readings

25. Cylindrical or non-cylindrical

26. More descriptive terms?

27. Example: Analyze this alpine example: Eocene Paleocene

28. A second example

29. A final example