A comparison of foreland and rift margin sedimentary basins

Abstract

Foreland and rift margin basins are compared on the basis of (1) their tectonic setting, (2) reasons for subsidence, and (3) their large-scale geophysical and geological characteristics. The thermal and mechanical properties of the underlying lithosphere are shown to be fundamental to the form of tectonic subsidence. The lithosphere beneath foreland basins is flexurally downwarped by the loading of the adjacent fold-thrust belt, whereas tectonic subsidence at rifted margins is caused by mass replacement at depth, during lithospheric extension on rifting, and subsequent thermal contraction as the lithosphere cools. The effects of rheology, thermal maturity, and lateral changes in properties of the lithosphere are outlined for foreland basins, as is the topographic effect of possible phase changes beneath the fold-thrust belt. The thermal and rheological consequences of lithospheric extension at rift margins makes flexural subsidence relatively less important than in foreland basins. Flexure may, however, be partly responsible for uplift landward of the hinge line that is associated with rifting. Other mechanisms that could cause such uplift include depth-dependent extension and thermal expansion due to the lateral diffusion of heat. The models describing the evolution of these basins are shown to predict characteristics that are in accord with observations. The superposition of foreland and rift margin basins as a result of ocean closure can lead to an overall basin stratigraphy that is complex. Such phases of basin subsidence must be separated according to the tectonic environment in which they formed in any analysis of the cause and consequences of basin evolution.