Application of flexural models to nonmarine foreland-basin evolution indicates that two different stratigraphic styles of basin fill may develop over time. Basin subsidence is most rapid during times of thrust-load emplacement; associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine-grained deposits that cover most of the basin. The distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt.
Subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin. During this postorogenic phase of adjustment, a regional unconformity develops in the proximal part of the foreland basin. Proximal deposits, along with thrust-derived sediment, are redeposited in the distal foreland basin and beyond.
This two-phase model of foreland sedimentation predicts that coarsening-upward sequences in the proximal and distal parts of the basin have reciprocal significance: the proximal sequence represents thrust-belt advance, whereas the distal sequence represents thrust-belt cessation.