Coupled fluvial and shoreline dynamics: Experiments and theory

The morphodynamics of the sediment-fluid interface are influenced by both depositional mechanics and environmental forcing and often can be cast as a moving boundary problem. Subsurface architecture records the "fossilized" dynamics of this moving boundary. The shoreline is a moving boundary that partitions fluvial and submarine sediment transport regimes, onshore and offshore deposits, and topset and foreset geometries. Migration of this shoreline position in sedimentary rocks is a sensitive recorder of the interplay of several controlling factors. The causes of shoreline migration can be divided into allogenic processes, which are externally forced, and autogenic processes, which originate within the sedimentary system. The former, often thought to be the "stratigraphic trinity" (eustatic sea level, tectonic subsidence and sediment supply), are usually considered as the most important determinants of an evolving sedimentary basin in a long-term, large-scale framework. The latter are often associated with changes in the position and planform pattern of channels that deliver sediments in the fluvial system, which are defined within a short-term, regional-scale framework.; This dissertation is focused on the study of the allogenic and autogenic origins of the shoreline dynamics and their imprint on the stratigraphic record by conducting physical laboratory experiments and developing theoretical models. A unique facility at St. Anthony Falls Laboratory, the Experimental EarthScape (XES) basin allows for studying sedimentation over space and time scales that are inaccessible in the field. Five chapters (1) Experimental measurement of the relative importance of controls on shoreline migration, (2) Shoreline response to autogenic processes of sediment storage and release in the fluvial system, (3) Net pumping of sediment into deep water due to base-level cycling, (4) Long-period cyclic sedimentation with constant tectonic forcing in an experimental relay ramp, and (5) Steering of experimental channels by an active relay ramp, present findings from coupled experimental observation, mathematical models, and application to field conditions to improve interpretation of paleoenvironments.