Sedimentological Effects of a Moving Terrain

Abstract

To investigate the sedimentologic effects of changing rheology and boundary conditions on lithospheri cflexure due to thrust loading, the following simple linear models for flexure have been examined: the infinite elastic plate to represent thrusting on the craton, the semi-infinite plate to represent thrusting near a plate boundary, and the infinite viscoelastic plate to consider simple time-dependent effects. These models make the following sedimentological predictions: (1) periodic thrust motion on the infinite and semi-infinite elastic plates produces periodic regressions and transgressions on the orogenward and cratonward side of the basin, respectively; (2) periodic thrust motion on a viscoelastic plate with a small relaxation constant produces out of phrase transgressions and regressions on both sides of the basin; and (3) for a given set of flexural parameters the flexure size for these models, in order of decreasing amplitude, are the semi-infinite elastic plate, the infinite viscoelastic plate, and the infinite elastic plate. With cratonward movement of the thrust terrain the deflection of the semi-infinite plate becomes indistinguishable from the infinite plate. In the Western Overthrust belt of Idaho and Wyoming, some sedimentologic indicators are consistent with an infinite viscoelastic plate with a small relaxation time. The sedimentation history in the "Sevier Shale" basin of Tennessee suggests that lithospheric boundary conditions in thrust belts may change with time.