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INTRODUCTION
Structural analysis proceeds through three linear stages: 1) description of the
structural geometry of a deformed field area (bedding attitudes, planar fabrics,
linear fabrics, folds, faults, joints, etc.); 2) kinematic analysis (movements
responsible for the development of structures [translation, rotation, distortion, and
dilation] and relative timing); and 3) dynamic analysis (interpretation of forces
and stresses responsible for the deformation). Stage 1, descriptive structural
analysis, is the product of careful field mapping.
Although maps are two-dimensional sheets of paper, they portray the geology in
three-dimensions. This is because most structures tend to dip or plunge and,
therefore, one can infer the direction and degree of dip or plunge through outcrop
patterns. Also, we use special geologic symbols to indicate 3-dimensionality on
our maps. Therefore, a geologic map is nothing more than the representation of
3-d structures on an arbitrary 2-d horizontal plane. Put another way, a geologic
map is a cross-section of dipping and plunging structures projected on a
horizontal plane. Clearly, it is necessary to carefully map out this 2-d view before
one can visualize the 3-d geometry of deformed rocks. A well-done geologic
map can provide a powerful down-plunge view of the 3-d structural geometry in a
“true” cross-section view that is to plunge.
Field mapping can be physically and mentally challenging. Hundreds of
questions arise, dictating that hundreds of decisions must be made during the
course of a single day. Where should I go? What unit is this? Why does this
bed abruptly end? Thus, field mapping is the ultimate application of the scientific
method – a good field mapper is constantly testing predictions about the next
outcrop and evaluating multiple hypotheses about the structure. In the midst of
this mental workout, it is important to maintain your focus and purpose by
remembering the goals of your project or research. Try to maintain a good sense
of humor and enjoy the day. After all, didn’t most of us decide to go into geology
because we like being outdoors and we like thinking about the Earth?
To get started with structural field mapping, here are some tips:
Eat a good breakfast
Drink plenty of water throughout the day
It is humanly impossible to take “too many” strike-and-dips
In structural geology, accuracy and neatness count heavily!
Force your mind to think in 3-d; with time and experience, this will come
naturally
Use your time in the field efficiently - always have a plan in the field!