Here. This video explains the setting, more or less…
…but the basic idea is this: imagine an America riven in two during the Civil War by black magic and necromancy. The Deadlands setting was the Old West in such a milieu: explicitly horror, with a lot of weird technology and magic and whatnot. The Deadlands Noir setting, in contrast, is same world decades later, with a hard-boiled pulp detective edge to it. I’ll have to see if I can free up the cash for this one.