What kind of black marks? Circular depressions? Like sooty deposits on the leaf surface? Circular black spots on the surface? I'd ask for a photograph, but I expect most of the leaves have fallen by now anyway.

As said above, many leaves before they drop develop blotches or marks and this can be just part of the natural beak down of the leaves as food is drawn out of them before the tree seals the base of the leaf stalk and they drop. I have to say that both of our native species, Quercus petraea and Q. robur are well known for the plethora of organisms that live on them and are considered great for wildlife because of it. If I was making a wild stab in the dark, I would say they could be the left over marks from a gall wasp such as the Spangle Gall. These will turn black at the end of the year and are relatively harmless to the overall health of the tree.