Structure-Contour Map

(or structure map), a map portraying a subterranean structural surface. Examples of such surfaces include the top or bottom of a stratigraphic unit; marker beds and horizons; and surfaces of unconformity, of fractures, of mineral deposits, and of aquifers.

The data used in constructing a structure-contour map may be obtained from geological surveys, the drilling of holes, mining, or geophysical investigations. On the basis of these data, the depth of the structural surface is established at various points in the area under study. The form and depth of occurrence are portrayed by means of structure-contour lines, which are constructed in much the same way as contour lines on a topographic map; the structure-contour lines take into account all the data on the geologic structure of the area (see Figure 1). The scale used depends on the map’s purpose. Small-scale maps (1:1,000,000) are generally used for depicting the surface of the foundation of a craton. Large-scale maps (1:50,000, 1:10,000, or larger scales) are employed for determining modes of occurrence, planning exploration, and calculating mineral reserves.

Figure 1. (1) Block diagram of an anticline with an oil-bearing stratum, (2) structure-contour map (top) and block diagram (bottom) of the same section with the roof of the oil-bearing stratum removed; the numbers indicate the absolute depths of the structure-contour lines in meters

Geologic structure-contour maps are of great practical importance. They are used in searching and exploring for minerals and in extracting the minerals. Such maps combine structure-contour maps and maps of the geologic structure of an area or some underground horizon. (See alsoGEOLOGICAL MAPS.)