Folds Read Davis and Reynolds, Chapter 7 Why is it important? fundamental to deformation of the Earth’s crust; structural traps for oil ore deposits.

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Presentation transcript:

Folds Read Davis and Reynolds, Chapter 7

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

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

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

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

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

Antiforms, synforms, anticlinoria, synclinoria

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

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

Chevron Ptygmatic Cuspate

Geometry, size Median trace Wavelength Amplitude Width Heigth

Hinge line and axial plane

Topographic Surfaces and folds

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

Fold tightness Gentle Angle is >90 degrees

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

Symmetric, asymmetric

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

Cylindrical or non-cylindrical

More descriptive terms?

Example: Analyze this alpine example: Eocene Paleocene

A second example

A final example