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Economic Consequences of Geologic Structures
• Tracing Coal Seams, Aquifers, etc.
• Ore Deposits are often localized along faults and folds
• Petroleum Traps
Which Way was Up?
Sedimentary Structures are governed by:
• Gravity
• Exposure to the Surface
They all have a “right way up”
Foliation
In every case, the foliation is:
• In the direction of least resistance
• at right angles to the direction of greatest compression.
Folds and Foliation• On a small scale (microscopic to
centimeters), foliation forms by a variety of mechanisms, but always at right angles to the direction of greatest compression
• On a large scale (centimeters to kilometers), rocks fold. The axial plane of the fold is also at right angles to the direction of greatest compression
How Geologists Use These Clues
• Picture the axial plane of the fold as parallel to the foliation.
• The other side of the fold is roughly a mirror image of the side we can see.
How Geologists Use These Clues
• We can mentally fill out the sketch to get an idea of the shape of the fold.
• Note that we still have no idea how big the fold is, only what kind it is.