The Energon Pub

I hope the presequel tells us more about how Megatron got in ice.

Urrrrr.... what more do you need to know?
Seriously, the Prequel basically spells it out for you. Megatron is burning through the atmosphere, so close to the allspark he can practically reach out & grab it, he gets to wrapped up in fantasy & hits the frozen Antarctic (??) & burns his way through a good few feet of Ice & stays frozen...
Do you really need more than that???