Hudson Valley Fold and Thrust belt Field Trip (Structural Geology)

Martha Growdon
SUNY Oneonta


This activity is designed to help students identify and observe ramp-flat geometry faults and associated flexural-slip folding.

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Required Jr/Sr level course in structural geology.

Skills and concepts that students must have mastered

Students should have seen, had practice with, read about, or heard in lecture the following topics:
  • Strike and dip measurements
  • flexural-slip folding
  • ramp-flat geometry (thin-skinned deformation)

How the activity is situated in the course

This is a field-activity situated about mid-way through the course. A full day trip is best; my students found much more to see/do at this outcrop than they expected.


Content/concepts goals for this activity

This activity emphasizes field observations of folded and faulted rocks. It reinforces practice with strike and dip, recognizing bedding, identifying cross-cutting relationships, and visualizing folding and faulting.

Higher order thinking skills goals for this activity

Students use their observations and sketches of the rocks to make interpretations of the geologic and structural history.

Other skills goals for this activity

Students become more comfortable with taking attitude measurements. Students can plot their measurements on Stereonets to reinforce plotting lines and planes. This can also hone their stereonet interpretation skills.

Description of the activity/assignment

This structural geology field trip in the Hudson Valley region reinforces class discussions about fold and thrust belts and thin-skinned tectonics. Students observed a ramp anticline over a ramp-flat geometry fault. The anticline has minor faulting and veining in the hinge zone and folding occurred by flexural slip (evident from down-dip slickenlines on bedding surfaces). Students make observations and sketches of the outcrop and take strike and dip measurements of bedding and fault surfaces. Students can also look for a very weak cleavage. Students can use attitude measurements to reinforce key principles of stereonets including plotting lines, planes, and poles and interpreting the orientation of the fold axis (or other information) from these nets.

Determining whether students have met the goals

I collect the students field notebooks and handouts at the end of the field day and grade them based on:
  1. Quality of observations, including key features on sketches (don't have to be good quality sketches, even line drawings can capture folded beds truncating against a fault surface);
  2. Observations and interpretations are clearly separated; interpretations are based on observations;
  3. Strike and Dip measurements and other records are neat and readable;
  4. Thoughtful answers to questions in the field-guide include logical arguments.

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