In the latest WHFB Daemon codex, there is a map of the Realm of Chaos. There are several crossover connections between Fantasy and 40k: this map shows the Eye of Terror, for example.
An interesting landscape feature, however, is in Slaanesh's domain: The Bad Moon. It's a blue crescent moon with a pointed nose and an open mouth. It looks a LOT like the Bad Moons icon, but there's nothing else describing it in the book. And since Slaanesh is the god of avarice, and the Bad Moons are known for greed...it feels like there's a connection here. An Ork klan that has been vaguely tainted by Chaos, and might turn whole-heartedly to Slaanesh in the future!