| Extended crust | Oceanic crust: 0–20 Ma 20–65 Ma >65 Ma |
A structural basin is a large-scale structural formation of rock strata formed by tectonic warping (folding) of previously flat-lying strata into a syncline fold. They are geological depressions, the inverse of domes. Elongated structural basins are a type of geological trough. Some structural basins are sedimentary basins, aggregations of sediment that filled up a depression or accumulated in an area; others were formed by tectonic events long after the sedimentary layers were deposited.
Basins may appear on a geologic map as roughly circular or elliptical, with concentric layers. Because the strata dip toward the center, the exposed strata in a basin are progressively younger from the outside in, with the youngest rocks in the center. Basins are often large in areal extent, often hundreds of kilometers across.
Structural basins are often important sources of coal, petroleum, and groundwater.