Which map shows thickness of a specific stratigraphic interval by isopach thickness contours?

• A. Isoplets
• B. Bedrock Map
• C. Topographic Map
• D. Isopach Map

Answer: (D)

Isopach mapping focuses on showing how thick a particular stratigraphic interval is across an area, using contour lines where the thickness is the same. To build it, you measure the thickness of the interval at many locations, then interpolate between data points and draw contour lines that connect equal-thickness values. This lets you see where the layer is thicker or thinner, which is crucial for understanding sediment deposition, resource potential, and subsurface structure.

That’s why the isopach map is the best choice here. It is specifically dedicated to thickness, rather than to surface elevation or rock type.

For contrast, a bedrock map shows what rock types or formations are present at depth or at the surface, a topographic map shows the shape of the land surface and elevations, and an isopleth map (a general equal-value map) would represent lines of equal values for some other variable, not necessarily the thickness of a stratigraphic interval.