Atlantis: The Land Beyond The Pillars proposes a new theory based solely on Solon's geographical specifications for Atlantis as recorded in Plato's dialogues, Timaeus and Critias. Solon set forth a complex and very specific array of geographical features comprising alignments, relative positioning and dimensions, which limits the site for Atlantis to only one possible location: South America and Argentina's Mesopotamian Plain.
Not only is
Argentina's Mesopotamian Plain the only sizable rectangular plain in the world defined by waterways on all four sides, which is in accordance with Solon's description, its perimeter is only 50 miles off from the stated 1,150-miles, or 10,000 stadia. Further, the plain lies in the center of the continent, is oriented with its narrower width extending from the coast inland, is surrounded by mountains on three sides, but open toward the south, and lies within 14.5 miles of the sea, all per Solon's specifications.
Here's a more complete list of geographical specifications this theory meets which can also be found in the article along with much more detail and further insights:- A continent sized island (South American 'nesos' [see article for explanation])
- Opposite the Pillars of Hercules (The Strait of Gibraltar) and
- Located in the Atlantic Ocean with
- Associated islands (the Caribbean Islands)
- Forming a distinct path to a continent (North America) at the opposite end.
- Having a lofty precipitous coastline (South America's Brazilian Highlands) transitioning to
- A flat even rectangular plain (Argentina's Mesopotamian Plain)
- Located at the center of the island (center of South American 'nesos')
- Within 14.5-miles of the sea that is
- Delineated on all four sides by channels of water (the Parana and Uruguay rivers) with
- A perimeter of approximately 10,000 stadia (10,455 stadia or 1,200 miles actual. Only 50 miles longer than the specified 10,000 stadia or 1,150 miles.) and
- Oriented with its narrower width extending from the coast inland, and also having
- A climate conducive to biannual harvests.
- Pocketed in by mountains to the west (Andes), north, and east (Brazilian Highlands), but open toward the sea in the south with
- River ways from the surrounding mountain ranges feeding the rivers that flow around the plain, converge, and then empty into the sea in the south. (Rio Pilcomayo, Rio Bermejo, Rio Salado and Rio Dulce flowing down from the Andes in the west. The Parana and Uruguay Rivers dropping down onto the plain from the Brazilian Highlands in the north and the Rio Ibicui, Rio Arapey Grande, and Rio Queguay sourced from smaller mountains in the east, to name just a few.)
There also exists a circular landform positioned per Solon's specifications which measures exactly the diameter of Atlantis' capital city: 
Figure 15 - Lines A, B, and C represent Solon's specified 14.5-mile distance extending
between the plain and the sea with a center point at 7.25 miles representing the center point of the
island city. Lines A and C represent extreme placements where the island city would lie closest to the
Parana and the confluence of the Parana and Uruguay rivers. Line B aligns the channel so that the
center point is equidistant from the Mesopotamian plain and the sea. Multiple other channel placements
would find the city's center located between these three points along or near arc ABC. Equidistant
point B mysteriously sits atop a circular landform while line B itself lies near channels of similar
lengths matching those stated to lead from the plain to the sea.

Figure 16 - Satellite image of the circular landform in the Parana Delta (top). Same image (below)
with a 2.50-mile dimension set with Google Earth™ to establish scale. The yellow overlain
rings conform to the concentric rings of Atlantis and have been scaled to the image. While
the circular landform does not appear to have any demarcations suggesting the existence of
inner zones, the outside diameter of Atlantis’ outermost land zone at 2.41 miles (21 stadia) is
an extraordinarily close match with this Parana Delta landform. The waterway surrounding the
landform also conforms closely to Atlantis’ outer zone of water, which was to have had an
outside diameter of 3.10 miles (27 stadia).
The delta location would be susceptible to liquefaction during a quake, which could explain why the warlike men are described as having "
sank into the earth" and not the sea.
There occurred violent earthquakes and floods; in a single day and night of misfortune all your warlike men in a body sank into the earth, and the island of Atlantis in like manner disappeared in the depths of the sea. - (Timaeus)
While tsunamis or additional liquefaction saw the city isle completely sinking beneath the sea.
-Doug