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FOLDS
1. Anticline-upfold of crust of earth
a. beds dip away from the axis (hinge line)
b. oldest beds are located in interior
2. Syncline-downfold in crust of earth
a. beds dip toward the hinge or axis
b. youngest rocks are located in center
**both anticline and synclines are compressional features
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3. Shapes of Folds
a. Symmetrical
-hinge vertical beds dip away (toward) at same angle
b. Asymmetrical
-hinge inclined beds dip away (toward) at different angles
(1) overturned fold--one limb overturned
(2) Recumbent (lying down)
-hinge horizontal one limb overturned
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STRUCTURAL FEATURE INTERPRETATIONS
I. Compressional
a. Folding
b. Thrusting or reverse faulting
c. Trenching
d. Thickening
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II. Tensional
a. Rifting
b. Downdropping or Normal Faults
e.g.
East African Rift
Gulf of California
c. Crustal Thinning
Death Valley
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III. Shearing (sliding past one another)
Before
Left lateral strike slip motion
Right lateral strike slip motion
SPECIAL TYPE OF STRIKE SLIP FAULT
Called Transform Fault
Mid Ocean Ridge
Transform fault (one type ) defined as:
*That section located between ridge segments where the offset of ridge is opposite to spreading direction
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UNCONFORMITITES are breaks or gaps in the geologic record; a time period that is missing in
the rock record
1. ANGULAR UNCONFORMITY: beds above and below the unconformity meet at an angle
a. 1 through 5 deposited horizontally
b. Tilted (implies uplift, tectonics)
c. Erosion leaves undulatory surface
d. Beds 6-8 deposited horizontally
2. NONCONFORMITY: when sedimentary rocks are in unconformable contact with Igneous or
metamorphic rocks
3. DISCONFORMITY: series of parallel beds with an unconformable surface between
side view