Basement (geology)

In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover. "The surface beneath which no sedimentary rock is found".
More generally, it is any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way the sediments and/or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover".