In a 1954 issue of Geological Society of America, Bulletin, Bruce Heezen and others reported on a seamount - an underwater mountain - that has been named Atlantis by geologists and is in the Atlantic Ocean. It has been found to have been an island about 12,000 years - exactly the time specified by Plato! This abstract is given:
The Atlantis, Cruiser, and Great Meteor seamounts rise from a broad ridge or plateau which extends from the Mid-Atlantic Ridge to 37°N. 32°W. southeast to Great Sea mount at 30°N. 28°W. The Atlantis Sea mount, briefly explored 1947 and 1948, was found by echo sounding and submarine photography to have a fairly flat bedrock summit area at about 180 fathoms covered in some cases by current-rippled sand. Its slopes are covered with sand or ooze symmetrically rippled at 400 fathoms and marked by slump features in 570 fathoms. A small piece of volcanic agglomerate was dredged from 400 fathoms on the north slope. About a ton of flat pteropod limestone cobbles was dredged from the summit area. One of the cobbles gave an apparent radiocarbon age of 12,000 years ±900 (J.L. Kulp). The state of lithification of the limestone suggests that it may have been lithified under subaerial [i.e. above water, on land surface] conditions and that the sea mount may have been an island within the past 12,000 years. (Heezen, Bruce C., et al, "Flat-Topped Atlantis, Cruiser, And Great Meteor Sea Mounts" in Geological Society of America, Bulletin, 65:1261, 1954 (Protogonos issue 9))
In later studies, evidence was found for the remnants of a "sunken block of continent" in the middle of the Atlantic Ocean. An articlein New Scientist 1975 summarizes the result. (Anonymous, New Scientist, 66:540, 1975)
Although they make no such fanciful claim from their results as to have discovered the mythical mid-Atlantic landmass, an internationa group of oceanographers has now convincingly confirmed preliminary findings that a sunken block of continent lies in the middle of the Atlantic Ocean. The discovery comes from analysing dredge samples taken along the line of the Vema offset fault, a long east-west fracture zone lying between Africa and South America close to latitude 11øN.
The article describes the first report of "shallow-water limestone fragments" from the Vema Fracture in the Atlantic:
Four years ago two University of Miami workers, J. Honnorez and E. Bonatti, first reported the recovery of shallow-water limestone fragments from the Vema fracture zone. This limestone contained minerals indicative of a nearby granitic source unlikely to occur on the ocean floor. Neither water currents, nor more esoteric transport systems, could explain the presence of these rocks so far from the modern boundaries of the continents. The two researchers believed that, instead, the granitic grains must have been deposited close to their source.
Then the recent researchers are noted:
Now, with C. Emiliani of Miami, Paul Bronniman of the University of Geneva, M.A. Furrer of Esso Production Research, Begles, and A.A. Meyerhof, a consulting geologist from Tulsa, USA, they have carried out a more searching analysis of the dredge samples (Earth and Planetary Science Letters, vol. 26, p.8)
Finally he notes the evidence for activity in less than 30 meters of water, and even some evidence for activity in soil.
The Limestones include traces of shallow-water fossils - foraminifera, green algae, bits of gastropods, and crab coprolites - implying formation in water, in one instance, less than 30 m deep. Furthermore, the limestones have been recrystallized from a high to low-magnesium form of calcite. Oxygen and carbon-isotope ratios prove conclusively that this process must have taken place subaerially [on land surface] "through the action of meteoric water enriched in light carbon while passing through a soil zone ..." A pitted limestone sample bears evidence of tidal action. Some 50 km east of the dredge site along the Vema fracture the team also recovered a thick-shelled, shallow-water, bivalve fossil from a depth of over 2000 m.
The coprolites in the sample indicate a Mesozoic age for the limestone which may well be the sedimentary capping on a residual continental block left behind as the [??] spread out into an ocean. The granitic minerals could thus have come from the bordering continents while the ocean was still in its infancy. Vertical movements made by the block appear to have raised it above sea level at some period during its history.
(from Unknown Earth: A Handbook of Geological Enigmas by William R. Corliss.)