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.