I have no idea, I'm not a geologist.
However, logic dictates in order for the Earth to experience an ice age, it can't get radiation from the sun. So either the sun magically turned off for a while, the distance between the Earth and sun dramatically changed for a bit, or something kicked up in the atmosphere to block the sun's radiation.
I don't know, but I'm going to guess on the latter. Asteroids crashing into the Earth, kicking up debris, blocking the sun. That tends to seem more plausible than the sun turning on / off, or the sun and Earth changing distance from each other.