Wow, I got to get in on this! For me, the Delta Blues is that really hard-hitting style that goes back to Charley Patton and Son House. Of course, they were simply the first ones to get the music on record. I read a biography of Patton in which it is reported that Patton was playing songs that dated back to the early years of the century, stuff he'd heard since being a kid. "Delta Blues" is probably what W.C. Handy heard that day in Mississippi, then took north, dressed up and made famous.
Who can say where the "Delta Blues" comes from.I'd put my money on field hollers and moans. I think "Delta" refers to Mississippi. It doesn't have the alternating bass of the Piedmont style, or the wonderful sophistication of Blind Blake's rags. Some of it sounds pre-12 bar. There's also a lot of open tuning stuff, a la Son House and his boy, Robert Johnson. About R.J. I'll say he comes in as the great synthesizer. He captures the music of his time and points it toward the future.
We'll never know the true father, or mother of the Delta Blues. But it is a distinctive style that through its players has greatly influenced popular music.
Peace.