Butyl Flooring Black Powder? We have an outdoor deck which in the order of 10 years...

We have an outdoor deck which in the order of 10 years ago we had covered beside Butyl flooring. This is a kind of rubber compound which comes contained by a flooring grade concreteness. Now when we walk on it a shroud of black dust comes off on our foot and is tramped into the house, where it is difficult to remove from the runner. In fact we hold made the outside deck a no-go area

Can anyone explain what is taking place and what we can do about it?
Air Conditioner disturbance from dipping above?
Answers:    I am not an expert , but I surmise the butyl granules are breaking away from the sticky stuff, berhaps because of sunlight degrading the adhesive.