I don't think it should target the mark slot. To me, the mark slot should be indestructible in order to help prevent being quanta locked by poor draws or denial or whatever. I do like the card, though, and the fact that it doesn't specify opponent's permanents means it could hit your own. In light of that, I don't think it really needs to drain all your gravity quanta. (if you meant it only to affect opponent's permanents, then I agree that it should drain all gravity quanta, and then the card text should be updated to reflect this)