Drawing Structural and Isopachous Maps

Janis Treworgy, Principia College
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This activity has 3 maps with real stratigraphic data recorded adjacent to drill holes in the Illinois Basin. Students contour the structural data. They may also contour the associated thickness data or they can just look at the trends of the thickness data relative to the structures on their completed structure map.

Used this activity? Share your experiences and modifications



I use this with undergraduate students who are minoring in geology (we have no major)and taking Sedimentary Geology 330. The only prerequisites are Physical Geology and Historical Geology.

Skills and concepts that students must have mastered

They need to understand how to interpret map patterns and be able to visualize the 3rd dimension of the structures they map. The structures are anticlines and synclines, no faults, in the Illinois Basin. If they have not done any contouring before, you might want to start them on a simpler map with fewer datum points. They should understand the basics of depositional environments for coal-bearing strata.

How the activity is situated in the course

This is part of a sequence on geologic maps and cross sections that I do with teaching the basics of geophysical log interpretation, stratigraphic correlation, and types of geologic maps. I do this in the last 3rd or 4th of the course on Sedimentary Geology.


Content/concepts goals for this activity

1. To become familiar with drawing contour maps, both structural and isopachous (thickness)
2. To learn to interpret structural contour maps
3. To learn to interpret changes in thickness relative to the structure of an area

Higher order thinking skills goals for this activity

They have to be thinking about the regional structural picture (I show them a structure map of the Illinois Basin) as they contour the data. After they draw the structure map on the 2nd map, they have to look at thickness data for a coal and an interval between two coals and see if there is any correlation between the thickness trends and the structure. They will find that there is. They have to explain why there is this correlation.

Other skills goals for this activity

You could have them write their explanation, discussing the tectonic activity of the region at that time and the impact of that activity on the depositional setting.

Description and Teaching Materials

I am including 2 Word files that give the purpose, directions (methods), and questions. One file is for students and one has notes to instructors on how I have used the activity and has answers.
I am including 3 pdfs of maps with the data plotted on them.
I am also including 3 Excel files with the raw data so that maps can be generated to your liking.
I do not include my structure maps, but I could if that would be helpful.
drawing structure map-student (Microsoft Word 2007 (.docx) 15kB May24 14)
drawing structure map-instructor (Microsoft Word 2007 (.docx) 16kB May24 14)
Lawrence Co Base Map for Structure Contouring-student (Acrobat (PDF) 100kB May24 14)
Fayette Co Base Map for Structure Contouring-student (Acrobat (PDF) 104kB May24 14)
Marion Co Base Map for Structure Contouring-student (Acrobat (PDF) 106kB May24 14)

Lawrence Co. location & stratigraphic data (Excel 119kB May24 14)

Fayette Co. location & stratigraphic data (Excel 96kB May24 14)

Marion Co. location & stratigraphic data (Excel 161kB May24 14)

Teaching Notes and Tips

I would not use these maps for their first experience in contouring data. My students have had some experience in contouring data in Historical Geology so this activity works well for them, although they need a quick review.
I will have the students finish the contouring as homework if we run out of time, but it is important that they understand how to do it so they don't waste time going in a wrong direction.
I printed the maps on 11x16 sheets of paper.


I compared their structural contour map to mine to see how they varied and if their differences were valid or not, using the guideline that the simplest interpretation is the best if data are lacking. I look for honoring all the data and neatness. I expect them to use pencil and refine their lines as they develop their map. I sometimes have them watch me how I contour data because I am constantly erasing and refining my lines.
The questions we addressed as a class (my class size is only 6 students), so I am looking for engagement in the discussion and thought process.

References and Resources