-Stage 3.3-

Geological Maps

Example of Geological Map

(actual scan of the Wyndale and Holston Valley Quadrangles, Virginia)

Understanding Geological Maps

• Geological maps are topographic maps with the geological units drawn on them.

• Typically there are 2 topographic quadrangles in one geological map.

• What a geological map shows is what types of rocks are exposed on the surface.

     When no rocks are visible on the surface the type of rock is estimated

• Other features unique to a geological map:

     Faults -

            - Solid fault lines indicate where the fault is visible and/or known

            - Dashed fault lines indicated where a fault is known but the exact location is not determined

     Folds -

            - The axis for anticlines and synclines are drawn

            - Strike and Dip symbols

Geological Legend

• The legend (pictured on the right) is listed with the oldest rock units on the bottom and the youngest on the top.

     This is just like real life where the oldest rocks are on the bottom

     then progressively younger rocks get layered on top.

• The relative ages of the rocks are listed along the side of the units

     On the map they are Cambrian, Ordovician, and Quaternary

• Alluvium is loose sediment fill common to flood plains, beaches and anywhere there is active sediment movement.

Geological Cross Sections

• A cross section is a section of a map where you can look at the rock structure below the surface.

• A cross section is always related to a geological map. The cross section relates to a line that is drawn across the map.

• It is often used to enhance an interesting structure and often looks like cross between the front of the blocks in the Structures section and a topographic profile.

• The strike and dips of the rocks allow for the creation of the cross sections.

• Often there is a lot of work involved with the creation of an individual cross section.

• Very rarely does a strike and dip intersect a cross section line so a lot of estimates are required.

Understanding the Geological Profile

• The upper block represents the map.

• The lower block is the profile based from the map, similar to a topographic profile.

• The difference is the rock units are on the profile. Rock units are angled under the ground based on strike and dips determined from field work.

And related to Geological Maps - Stratigraphy

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