Besides backing up what Savarosa said, I think this impression of a flat disc on the back of a giant space turtle with the sun kinda hanging around is probably borrowed from Discworld (as it has shown up on the cover of a few of them), but I think Discworld initially borrowed the concept from various older theories about the shape/structure of the Earth.

Earth being on the back of a turtle is an old myth developed independently a few times. It probably has its origins in people viewing hibernating turtles emerging from under the soil.

The Disc of Discworld is also supported on the back of four elephants (possibly five since one book, The Fifth Elephant is devoted to finding the lost titular elephant), which I believe is tied to Hindu myth?