According to the Vedas, the current Kali age began 3102 BC, which ushered in disturbances both cultural and gelogical, for a two hundred or so period. I don’t think it was a sharp cutoff, but around 200 yeras. I think it very likely that a lot of the great geologic changes happened at that time.
According to the Vedic history, in between each of the four ages are great upheavals and disturbances, scattering populations, destroying traditions, cities, memories...
that reminds me of -
http://www.sacred-texts.com/cla/plato/timaeus.htm
TIMAEUS
by Plato
360 BC
excerpt:
...On one occasion, wishing to draw them on to speak of
antiquity, he began to tell about the most ancient things in our part of the world-about Phoroneus, who is called “the first man,” and about Niobe; and after the Deluge, of the survival of Deucalion and Pyrrha; and he traced the genealogy of their descendants, and reckoning up the dates, tried to compute how many years ago the events
of which he was speaking happened. Thereupon one of the priests, who was of a very great age, said: O Solon, Solon, you Hellenes are never anything but children, and there is not an old man among you.
Solon in return asked him what he meant. I mean to say, he replied, that in mind you are all young; there is no old opinion handed down among you by ancient tradition, nor any science which is hoary with age. And I will tell you why. There have been, and will be again, many destructions of mankind arising out of many causes; the greatest have been brought about by the agencies of fire and water, and other lesser ones by innumerable other causes. There is a story, which even you have preserved, that once upon a time Paethon, the son of Helios, having yoked the steeds in his father’s chariot, because he was not able to drive them in the path of his father, burnt up all that was upon the earth, and was himself destroyed by a thunderbolt.
Now this has the form of a myth, but really signifies a declination of the bodies moving in the heavens around the earth, and a great conflagration of things upon the earth, which recurs after long intervals; at such times those who live upon the mountains and in dry and lofty places are more liable to destruction than those who dwell by rivers or on the seashore. And from this calamity the Nile,
who is our never-failing saviour, delivers and preserves us. When, on the other hand, the gods purge the earth with a deluge of water, the survivors in your country are herdsmen and shepherds who dwell on the mountains, but those who, like you, live in cities are carried by the rivers into the sea. Whereas in this land, neither then
nor at any other time, does the water come down from above on the fields, having always a tendency to come up from below; for which reason the traditions preserved here are the most ancient...