Barb, my husband descends from Robert Black and Susanna Shaw and while I am still trying to learn their parents names, I have obtained verficiation that Susanna/Susan's maiden name was Shaw per her daughter's (Mollie Black Brown Renfro) death cert.
I also have obtained copy of a marriage between Robert Black and Susan Shaw in Clark Co IL on 22 May 1837 and will be most happy to share a copy with you. I am thinking this is our Robert and Susan even tho it states Robert is a minor and his mother gives her approval...as does Susan's mother because she too was a minor. Unfortunately it does not list their mother's names.
I also have a copy of your Robert A. Black and Samantha I. Clark's marriage cert and again will share a copy with you. I wanted to post the above info for others researching this line, but welcome talking with you or any one else researching this line via my personal email of email@example.com