Complex sentence: He was a founding member of the Minneapolis-based band The Jayhawks, and their principal songwriter and vocalist after the departure of Mark Olson; he is often credited with the band's subsequent move from folk-country toward a more progressive, poppier sound.
Split into simpler sentences: He was a founding member of the Minneapolis-based band the Jayhawks and their principal songwriter and vocalist after the departure of Mark Olson. Louris he is often credited with the band's subsequent move from folk-country toward a more progressive, poppier sound.