I would second that it is a Buckthorn, as to the species...I will defer to those who know the family better than I. I'm 100% that its not a prunus. My only
experience with Buckthorn like that is some work I did in southern Minnesota farm country. They grow all over the edge of corn fields and have a very similar form. They seems to grow well disturbed areas and deal with wet feet very well. They were most commonly growing along side
native cherries and box elder maples. I don't know of any real uses for the tree, but I don't know much in the realm.
J