[Fred Nerks]

The change in the burial method indicates a change in the ideology or religion of the people. The cremation of the dead is tied with people's belief in the existence of the soul.

methinks the change in the burial method indicates a wide-scale catastrophic event - if the celestial 'gods' saw fit to cremate mankind, the survivors simply followed suit.

[SunkenCiv]

For that matter, maybe they were faced with a situation where either A) they had so many dead to dispose of, fire seemed to be just what was needed or B) they only needed to finish the job after gathering the many charred bodies.