The idea of an elephant/elephants standing upon a giant turtle which supports the world is a part of numerous different cultures mythologies, mainly Hindu but this myth has similaritiesinsimilarities in other cultures such as;as China:
In Chinese mythology the creator goddess Nüwa cut the legs off the giant sea turtle Ao (鳌) and used them to prop up the sky after Gong Gong damaged the Buzhou Mountain that had previously supported the heavens.
In North America although elephants were not apart of the myth, the idea of the world residing on the back of a turtle is constant.
Although this myth has developed into the phase where it is believed that the world resides on the back of a varying number of elephants on one gigantic turtle I believe Pratchett was using the Hindu version of the myth. One interesting thing to think about is that in the beginingbeginning this mythology did NOT state that the disc the elephaphantselephants were carrying was the world, some people believe that it was actually refers to the creation of the universe and the 'Milky Way's place in the galaxy.
Here are some websites that go into a little more detail on the Elephant/turtle myth.
Good Luck.
Explains the different myths and talks about the meaning behind them.Explains the different myths and talks about the meaning behind them.
Another elephant and turtle mythAnother elephant and turtle myth