Here is some excellent and extended bibliography in AFRICAN-AMERICAN TRADITIONS IN SONG, SERMON, TALE, AND DANCE 1600s - 1920, by Southern & Wright:

   http://books.google.com/books?id=GQC7pBjAsCAC&pg=PA45&dq=Aaron,+The+Light+and+Truth+of+Slavery&lr=&cd=7#v=onepage&q=Aaron%2C%20T

This link gives you the beginning of the section on "The Song", which includes many references to worksongs.

The title of Dena Epstein's book, referred to above is SINFUL TUNES AND SPIRITUALS: BLACK FOLK MUSIC TO THE CIVIL WAR. See Chapter 9.