Foreland basins

Abstract

The characteristic pattern of the subsidence, deformation, uplift and erosion of foreland basins, or exogeosynclines, has long been recognized by geologists as an integral part of the geosynclinal cycle yet only descriptive models have been proposed. This evolution is quantified in terms of a model of regional isostatic adjustment of the lithosphere under the mass load of the adjacent migrating fold-thrust mountain belt. It is shown that the foredeep, which received the clastic wedge of detritus from the core of the orogen and the fold-thrust belt, owes its existence to downward flexure of the lithosphere by the fold-thrust belt. Additional depression occurs in response t o the infilling sediment. The scale of the basin therefore reflects the degree of shortening in the orogen and the rheological properties of the underlying lithosphere. Subsidence reflects mass that accretes at a faster rate than mass wasting from the orogen, whereas regional uplift and erosion of the basin is attributed to the large-scale erosion of the fold-thrust belt that has been depressing the lithosphere. There is a complete coupling between the evolution of the foreland basin and its adjacent mountain belt through the lithospheric flexure. Lateral migration of the fold-thrust belt accounts for the progressive overriding and disruption of some foreland basins.