Which map type is used to depict thickness variations of a stratigraphic unit across a region?

• A. Facies map
• B. Structure map
• C. Isopach map
• D. Thickness map

Answer: (D)

The concept here is how we represent how thick a stratigraphic unit is across an area. An isopach map is designed for this exact purpose: it uses contours that connect points with equal thickness, so you can see where the unit thickens or thins across the region. This helps interpret depositional patterns, subsidence, erosion, and tectonic effects that controlled thickness.

Facies maps show where different rock types or environmental conditions occur, not how thick they are. Structure maps focus on the elevation or depth to the top or base of a unit to reveal faults and folds. A thickness map is a less precise term; the standard, widely used way to depict thickness variation is the isopach map.