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in geology, a complex of relatively more ancient, usually strongly folded, regionally metamorphosed, and granitized rocks that constitute the lower structural stage of a craton or constitute a roughly equivalent formation in a geosynclinal region or ocean.
A basement is a formation of the precratonic, or geosynclinal, stage of development of the earth’s crust. The basement of an ancient craton is often called a crystalline basement because it is composed predominantly of Precambrian schists, gneisses, and granites. The basement of a young craton is called a folded basement because, unlike the cratonic mantle, it consists of strongly folded rocks. In the Baikalian and Phanerozoic folded geosynclinal regions, the basal complex, which underlies the main geosynclinal complex, corresponds to the basement of an ancient craton. The main geosynclinal complex is associated with the primary stage of development of the particular geosynclinal system, a stage that preceded the principal folding and orogeny.
In a geophysical sense, a basement corresponds to the consolidated part of the earth’s crust, and the surface of the basement coincides with the surface of the granitic layer on the continents and with the upper margin of magnetically active bodies. The surface of a basement is an important refracting surface for seismic compressional waves, or P waves, with boundary velocities of 5.5–6.4 km/sec.
In the oceans, an acoustic basement, which underlies the crustal sediment, is distinguished. Reflected seismic waves are not detected beneath the surface of the acoustic basement. The upper part of the acoustic basement corresponds to the second layer of the oceanic crust, a layer composed of thick basalts and intercalated sediments.
V. E. KHAIN
What does it mean when you dream about a basement?
Unless one’s dream flows directly out of associations with an actual basement, the connotations of an underground room are obvious enough, which is that a basement represents the unconsciousness. (Freudians view basements as symbols of sexual energy.) Being afraid of going into a basement in a dream, for example, often symbolizes fear of the unknown or fear of repressed aspects of oneself. And being locked in the basement can indicate feeling immobilized by the power of the unconscious.