It is the floor of a sea. If it ever was part of the geologic column, it is now. And deposition is adding to it.
What is a sea:
quote:a : a great body of salt water that covers much of the earth broadly : the waters of the earth as distinguished from the land and air b : a body of salt water of second rank more or less landlocked the Mediterranean sea
quote:The sea, the world ocean or simply the ocean is the connected body of salty water that covers over 70% of Earth's surface (361,132,000 square kilometres (139,434,000 sq mi), with a total volume of roughly 1,332,000,000 cubic kilometres (320,000,000 cu mi)).
quote:sea 1. the continuous body of salt water covering the greater part of the earth's surface; ocean 2.a large body of salt water wholly or partly enclosed by land: the Red Sea, Irish Sea
quote:1. one of the larger bodies of salt water, less than an ocean, found on the earth's surface; a body of salt water of second rank, generally forming part of, or connecting with, an ocean or a larger sea; as, the Mediterranean Sea; the Sea of Marmora; the North Sea; the Carribean Sea
2. an inland body of water, esp. if large or if salt or brackish; as, the Caspian Sea; the Sea of Aral; sometimes, a small fresh-water lake; as, the Sea of Galilee
3. the ocean; the whole body of the salt water which covers a large part of the globe