16.5: How Do I Construct a Geologic Cross-section?

How Do I Construct a Geologic Cross-section?

Follow these steps to successfully create your own geologic cross-section (Figure 16.5):

  1. Locate the points between which you will be constructing a cross-section for. Observe the geologic map in this region. Pay close attention to any strike and dip symbols, geologic contacts, and ages of the rock types.
  2. Take a sheet of scrap (scratch) paper. Place the paper along the map where you want to draw a cross-section.
  3. At each geologic contact, make a mark on the scratch paper. Position the marks in the direction you believe the rocks are dipping. To determine this, use any strike and dip symbols. If they are not provided, use the Rule of V’s or the ages given to help determine the geologic structure.
  4. Transfer the marks from your paper to a provided diagram.
  5. Sketch in and complete any structures, paying careful attention to dip angles (if provided). Structures may be drawn in with a dotted line above the Earth’s surface to indicate rocks that were formerly present but that have since been eroded.
  6. Incorporate a legend into the cross-section to explain the types of geologic materials present.
  7. Include vertical and horizontal scales along with the statement of vertical exaggeration.
The top figure displays the geologic map, with different rock units of different colors, and age symbol provided. In the second figure, the scratch sheet of paper is stretched along the bottom of the cross-section, and a mark is made at each geologic contact. The oldest bed is in the middle which indicates this structure is an anticline, so beds have been drawn so that they dip away from the axis. In the bottom image, the scratch paper has been superimposed and contacts have been drawn in (as indicated by the dashed lines on each end mark). Beneath the surface, contacts have been drawn in using a solid line. The beds above the surface that have since eroded have been drawn in with a dashed line.

Figure 16.5: How to construct a geologic cross-section from a geologic map. (CC-BY-SA 3.0; Randa Harris)

Need more information? Watch the construction of a cross-section in the YouTube video below,