One of the levels in Chaorix has a moving boat as floor. If that was developed for the Genesis, no background would have been used. Only two planes are available on the Genesis. One for the foreground and one fro the background. The moving boat is inbetween the foreground and the background. Sky Sanctuary in S&K has a simular moving ground like the boat in Chaotix, but it is using the background for that, and the background is made up of the backdrop as well as cloud sprites.