TOPGRAPHIC EVOLUTION OF EXPERIMENTAL CHANNEL-SCALE ALLUVIAL ARCHITECTURE

We present results of an experiment that was designed to investigate the relationship between channel-scale alluvial architecture and the fluvial events responsible for its deposition. The experiment was motivated by the presence, in previous experimental deposits created at the St. Anthony Falls Laboratory, of both low aspect ratio (width/depth) channel (ribbon) bodies, which exhibit varying degrees of internal sorting and clinoform development, and high aspect ratio sheet deposits. Interpreting relationships between fluvial processes and resultant deposits, however, was confounded by a relative infrequency of topographic measurements. In the experiment reported here, accommodation space was created by controlled, slow base-level rise, and approximately 0.25 m of alluvial stratigraphy was preserved. Unlike previous experiments, however, we measured the topography of the fluvial system at two-minute intervals, short enough to capture stages of channel filling. This topographic data, in combination with images of the fluvial morphology throughout the experiment was compared with the resultant stratigraphy. As in previous experiments, both channel and sheet deposits were preserved. These results show how the composition and internal structure of the experimental channel deposits are strongly controlled by the fluvial processes responsible for their filling, as well as provide insight into why, of the countless events that occur in a fluvial system, only a select few are preserved.