Dazed and Brutal
Yall About to Witness
Examples? Most Magma I've heard is really jazz-funky which is basically the opposite of black metal.
Sonically, you could make the argument that their more frenetic moments have an almost feverishly occult sound.
I was think more in the terms of post-second wave visual aesthetics. All their album cover's seem to convey a similar vibe. Sorry I don't have anything more concrete for ya. I'll run through their catalog this weekend and try to make some stronger parallels.