Origin of line of color change in Red Bed deposition

The line of color change in Pennsylvanian and Permian sediments, extending from south-central Kansas across Oklahoma into north-central Texas, is produced by a facies change in which a nonmarine and marine series of sediments were deposited contemporaneously during a differential downwarp that changed their initial strike. Later truncation to the present erosional surface has cut the facies change and gives rise to the seeming anomaly that the line of color change transects the present strike of the sediments.