The Role of Fluvial Morphodynamic Hierarchy in Shaping Bedform Deposits

Abstract

Fluvial cross strata are fundamental sedimentary structures that record past flow and sediment transport conditions. Bedform preservation can be significantly influenced by the presence of larger-scale topographic features that cause spatial gradients in flow. However, our understanding of the controls on cross strata preservation in the presence of a morphodynamic hierarchy is limited. Here, using high-resolution bathymetry from a physical experiment, we quantify bedform evolution and cross strata preservation in a zone of flow expansion and deceleration. Results show that the size and celerity of superimposed bedforms decreases along the host-bedform lee slope, leading to a systematic downstream increase in the sediment accumulation rate relative to bedform celerity. This increase in local bedform climb angle results in the preservation of a larger fraction of formative bedforms. Our results highlight the need to revise current paleohydraulic reconstruction models, and demonstrates that fluvial morphodynamic hierarchy is a fundamental determinant of sedimentary strata.