Buoyant sub-surface loading of the lithosphere in the Great Plains foreland basin

Abstract

A recent development1 in the study of foreland sedimentary basins is the recognition of the important role played by negatively buoyant sub-surface loads in the evolution of some of these basins. Models2 for the subsidence of the Apennine and Carpathian foreland basins, in particular, show that sub-surface loads can equal or exceed the topographic load of the neighbouring mountain belt. Here we show that part of the Rocky Mountain foreland is underlain by a positively buoyant sub-surface load which counterbalances almost half of the total topographic load on the western Great Plains. The presence of this load explains the shallowness of the Denver Basin and the large Bouguer gravity anomalies over the Great Plains. We suggest that this load was emplaced during the Miocene when, according to geological evidence3–5, the region underwent epeirogenic uplift. The sub-surface load may result from lithospheric thinning, which often accompanies or precedes crustal extension6,7.