University of Colorado GEOLOGY 1010

Class Note 10

Geologic Structures


Stress and Strain

Stress is the applied force. Strain is the resultant deformation.

Stress can be compressional, tensional, shear, or isostatic.

All applied stresses cause rock (or any other solid) to deform (strain).

Strain can be elastic or plastic.

If a material undergoes continuous plastic deformation, it is said to be ductile. If it fractures, it is said to be brittle.


Rock Folds

Fig 16.1. Split Mountain Anticline, Dinosaur National Monument, Colorado. This is an example of a plunging, anticlinal fold in Paleozoic and Mesozoic sedimentary rocks. The river is the Green just below its confluence with the Yampa. There are also some pre-Cambrian sediments exposed in the core of this classic anticline, upstream of this photo.

Sedimentary rocks that deform plastically are said to form folds.

The orientation of the strata (beds) at any point in a fold can be described by the strike and dip.


Rock Fractures

If no movement has occurred on a fracture it is called a joint.

If movement has occurred on a fracture it is called a fault.

Movement on a fault is described as dip-slip, strike-slip, or oblique-slip.


Unconformities

Any break in the sedimentary geologic record is an unconformity,
GEOL 1010 Syllabus

Class Note 9

Class Note 11

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