Did you buy weed treated turf? If so perhaps these got too much? Why not ring the supplier they may well have the answer?

Could be as it was treated. I'll give them a call. Thanks

You think if it's gone black, it's dead?

Depends what the problem is? may not be dead? Also have you watered as per instructions? but you do have rights with the supplier. One other thought did you treat the ground before the turfs went down?

Yeah. We used pre turf fertilizer!

That should be ok.