| Our understanding of sedimentation in alluvial basins is best for very short and very long time-scales. Between these end members, the intermediate time-scales of stratigraphic assembly are especially difficult to constrain. The dissertation is focused on these 'mesoscale' fluvial dynamics---reporting results from two experiments conducted at the St. Anthony Falls Laboratory, University of Minnesota.; Three results from the first experiment are emphasized here. First, the deposits of the experiment comprise low width:depth ribbon bodies and high width:depth sheet bodies. Second, ephemeral flows are disproportionately important in basin filling. And third, there is a characteristic time required for individual depositional events to average to basin-scale stratal patterns. The second experiment shows that a characteristic sequence of (1) initial incision, (2) abandonment and reoccupation of channel topography, and (3) burial and preservation by a topographically convex-up deposit, is preserved in all experimental channel bodies. This sequence may be common in field-scale subaerial and submarine channel bodies. Two time-scales---one that measures fluvial channel lateral mobility, and another that measures the rate at which tectonics becomes morphologically significant---govern whether fluvial channels may be tectonically steered. Application to experimental results shows that the first experiment was arranged such that tectonic deformation was dominated by sedimentation. However, tectonics commonly dominates sedimentation in natural examples. There is a long-term lateral cyclicity to experimental sedimentation, related to the fact that the fluvial system fills the basin in a piecemeal manner, which suggests the possibility of ordered channel body distribution in the subsurface. Statistical comparison between experimental channel deposit distribution and random channel deposit distribution suggests that the two are more similar than one might intuitively expect, but that the channel body formation and preservation sequence leads to channel body anti-clustering.; The conclusion of the dissertation is that an understanding of mesoscale dynamics, which are not so cryptic as study of modern or ancient individually might suggest, is crucial to interpretation of ancient deposits. Insight into the mesoscale improves our ability to characterize alluvial strata given limited exposure. Indeed, physical experiments provide unparalleled data sets with which to investigate the assembly of alluvial stratigraphy. |
