Strabo reports that in ancient times there was a large lake ( sea ) in Araratian plain.

 Strabo reports that in ancient times there was a large lake ( sea ) in Araratian plain. It must be added that this is true. But it was in Neolithic times and not in Iron Age. Somehow the memory about this lake was kept. 

Then it disappeared. Maybe due to earthquakes? Who knows.

----

The Araxes also in Armenia, descending from the mountains, is said to have spread itself in ancient times, and to have overflowed the plains, like a sea, having no outlet; that Jason, in imitation of what is to be seen at Tempe, made the opening through which the water at present precipitates itself into the Caspian Sea; that upon this the Araxenian plain, through which the river flows to the cataract, became uncovered. This story which is told of the river Araxes contains some probability; that of Herodotus15 none whatever. For he says that, after flowing out of the country of the Matiani, it is divided into forty rivers, and separates the Scythians from the Bactrians. Callisthenes has followed Herodotus. [14]

http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0239%3Abook%3D11%3Achapter%3D14#note-link15