If your gg-grandmother was born about 1838 or '39, then Marion was one of her brothers. One reason you might have been having trouble finding a link is that in many places Marion is listed (incorrectly) as Marvin. He was the 3rd child of Miles B. Abernathy and Charlotte E. Capps, and Sarah Jane was the 4th child and 2nd daughter.
Miles B. and Charlotte are found on the 1860 Census in Mecklenburg County NC, with most of their children. Those children, in order, are:Catherine, Columbus Washington, Marion Calvin, Sarah Jane, Janette or Mary, John A., Lockie Josephine, Susan, Elizabeth, and Nancy. I have some descent info on a few of these children and would love to add your line to what I have, despite the fact that I'm only a cousin from a collateral line in the next county west.