Stratigraphy of the Lower Pierre Shale (Campanian): Implications for the Tectonic and Eustatic Controls on Facies Distributions

Figure 13

Model of the forebulge migration in the Black Hills region. (1) With initial thrusting, the forebulge migrates cratonward, producing a regional unconformity (the top of the Gammon Ferruginous Member, Figure 11). (2) Continued thrusting and cratonward migration of the forebulge results in overlap of the forebulge of the foreland basin and the peripheral bulge of the Williston Basin, causing yoking of the two basins. (3) Relaxation of thrusting results in deposition of coarse clastics in the basin, causing the basin to deepen and narrow, with thrustward migration of the forebulge. (4) Continued deposition of coarse clastics into the basin results in cratonward migration of the foreland basin and forebulge.