The origin and tectonic significance of asymmetrical meander-belts

In the Hebgen lake area of SW Montana, the Madison and South Fork Rivers occupy the northeast sides of their respective meander-belts. The form of the abandoned meander-loops within these asymmetric meander-belts indicates that they were produced by gradual northeast migration of the active channels. This progressive migration can be related to tectonic tilting produced by regional extensional faulting at a high angle to the original channel-belt axis which ran down a gently sloping outwash cone. Asymmetric channel sandstone bodies in the rock record can be recognized by the preferred dip of successive lateral accretion units in meander loops. Together with soft sediment deformation, facies and thickness variations they may indicate tectonic deformation of the sedimentary surface.