Comparison of stratigraphic and paleo-topographic slope statistics of experimental laboratory deltas
Description
Recent work demonstrates differences between channelized topography and resulting stratigraphic surfaces at various spatial resolutions, however, at present we lack a description of how channel mobility influences this architecture. Our goal is to develop a quantitative understanding of how information pertaining to paleo-topography and morphodynamics is stored in stratigraphy. To better understand the role of channel mobility in transferring topographic information into stratigraphy we examine three physical deltaic experiments, a key difference between each being the inclusion and amount of a polymer. The polymer enhances sediment cohesion and promotes channelization from subcritical Froude number flows. To quantitatively compare topographic and stratigraphic surfaces, we measure the decay of mean absolute surface slope as a function of measurement window. In all experiments we observe steeper average slopes in the stratigraphy compared to the topography over length scales less than a channel width. The difference between stratigraphic and topographic average mean slope is the least pronounced in the weakly cohesive experiment, which is associated with the highest channel mobility. As cohesion increases and channel mobility decreases, the difference between the slopes increases. In all experiments, stratigraphic and topographic statistics converge at a length scale approximately equal to one channel width. These results suggest that channel mobility, influenced by sediment cohesion, strongly influences the storage of paleo-topographic information in stratigraphy. Specifically, we predict that systems with low channel mobility, such as vegetated river deltas, have the greatest difference in topographic and stratigraphic statistics, while this difference is minimized in high mobility systems, such as alluvial fans.