1. Economic Rock and Mineral Identification
Explanation
Lab Activity
Resources
Vocabulary
Assessment
Appendix
2. Measuring Rock Stuctures
Explanation
Lab Activity
Resources
Vocabulary
Assessment
Appendix
3. Geological Mapping
Explanation
Lab Activity
Resources
Vocabulary
Assessment
Appendix
Unit One Standards

Unit One - Geological Field Methods
3. Creating Geological Maps and Cross-Sections
Lab Activity

Objectives:   

Part 1:  Create an interpretive geologic map from an outcrop map.
Part 2:  Construct a geologic cross-section from a geologic map.

Materials:

-  Graph paper
-  Ruler with protractor
-  Pencil
-  Answer Sheet AS4B
-  Data Sheet DS2:  Geologic Map for Cross Section
-  Data Sheet DS3:  Topographic Map for Cross Section
- Teacher Supplement TS3:  Interpretive Geologic Map
- Teacher Supplement TS4:  Geologic Cross Section

Procedure:            

Part 1:  Study the example below of Map 1 (a field outcrop geologic map) and Map 2 (an interpretive geologic map of the same area).  Notice how outcrops of limestone were connected by sketching in contacts.  The same was done for outcrops of shale, sandstone and schist.  Notice how a broad area of conglomerate was mapped on the south side of the map because there is no conglomerate to the north.  Notice how a fault was drawn connecting two outcrops of sheared rocks (squiggly lines).  On the right is another different outcrop geologic map (Map 3).  You create Map 4 by drawing the contacts between different map units in Map3.  Sketch the trace of a fault where fault breccia is shown (triangles).


FIGURE F2:  Interpretive Geologic Maps  (1 & 2 from USGS,1987-192-794).

Part 2:  Examine the geologic map shown on Data Sheet DS2 and the topographic map for the same area on Data Sheet DS3.  You will construct a geologic cross-section along the section line A-B using Answer Sheet AS4B.  Construct a topographic profile (or side-view) of the topography along section line A-B as follows:

  1. Fold Answer Sheet AS 4B along the base line near the bottom.
  2. Place the fold along section line A - B on the topographic base map (DS3) with the endpoints of the base line matching the endpoints of the section line.
  3. At each spot where a contour line crosses the base line (or section line) make a small tick mark and label the tick mark with the elevation of that contour.
  4. Unfold the Answer Sheet AS 4B. 
  5. Use the vertical scale on the left side of the cross section to put a dot directly above the first tick mark at an elevation of 1800 feet.
  6. Find the next tick on the base line (1850 feet).  Likewise, place a small dot directly above this tick which corresponds to the 1850 feet elevation.  Continue the procedure for all the ticks
  7. Connect the dots with a smooth line.  This line is a profile of the topography along the section line.

Look at the geologic map on Data Sheet D2.  Again fold the Answer Sheet along the base line.  Place the fold along the section line with endpoints matching.  You will show the geology on and below the surface (ie, a profile of the geology) as follows:

  1. At each place where a geologic contact crosses the base line, make a tick mark.  Label the type of rock on each side of the tick.  Make a tick for the fault.
  2. Unfold the Answer Sheet.  Put small tick marks along the topographic profile as you did with the topographic ticks using a ruler or right triangle. 
  3. Observe the strikes and dips of bedding on the map.  Assume the geologic contacts between the units are parallel to this bedding.  Use a protractor to estimate the dip angle of the contacts, and sketch (or “project”) them below the surface.  Sketch a line dipping below the surface which matches the fault plane dip shown on the map. Sketch the fault below the surface.  Assume the contacts of the granite intrusion dip gently outward or away from the center and sketch them.  The geologic cross section you have constructed is an interpretation of the subsurface geology based on the geology observed at the surface.

 

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