Piggyback basin

A piggyback basin is a minor sedimentary basin that develops on top of a moving thrust sheet, as part of a foreland basin system, in the wedge top zone where new thrusts cut up through the existing footwall carrying older, already eroded wedge top basins. The basin is separated from the main foredeep by an anticline or by structures that grow as it is deposited, and it takes its name from the way it is carried passively toward the hinterland along with the older thrust sheet beneath it, under the push of the newer thrust behind it. Its sediment fill comes from the hanging wall ramp of the older thrust sheet, from the surrounding orogeny, or from the sides of the basin itself.