1. n. [Geology]
The rock layer below which economic hydrocarbon reservoirs are not expected to be found, sometimes called economic basement. Basement is usually older, deformed igneous or metamorphic rocks, which seldom develops the porosity and permeability necessary to serve as a hydrocarbon reservoir, and below which sedimentary rocks are not common. Basement rocks typically have different density, acoustic velocity, and magnetic properties from overlying rocks.