Quantifying the distributions of channel geometry and channel belt properties for single-thread and braided rivers

Abstract:

Distinguishing the two main alluvial river morphologies, single-thread and braided, is straightforward in the modern environment as they can be directly observed or predicted using hydrological data. However, distinguishing channel patterns in the sedimentary rock record has proven more difficult, as only remnants of the river channels are preserved and they only account for a small fraction of the overall stratigraphy. Identifying channel patterns in geologic records is useful for predicting the quality and heterogeneity of groundwater and hydrocarbon reservoirs. Moreover, this distinction is important for testing the hypothesis that single-thread rivers were rare prior to the arrival of land plants in the Silurian. Previous studies have used reconstructed paleohydraulic data to distinguish channel patterns in the rock record, but such results have uncertainties that range up to an order of magnitude due to compounded calculation errors. Here, we develop new quantitative metrics using distributions of channel geometry (e.g., width and depth) and channel belt properties (e.g., width, sinuosity, radius of curvature, and wavelength), measured from modern fluvial systems worldwide via remote sensing techniques, with the aim for distinguishing channel types in the rock record. Specifically, we test the hypothesis that braided and single-thread rivers have distinct distributions of channel geometry and channel belt properties as supported by theories on river branching. Preliminary data indicates that channel width of single-thread and braided rivers are normally and lognormally distributed, respectively. Distributions of channel belt properties for the two river types, such as radius of curvature and sinuosity, also appear different, each with distinct modes. Analyses presented here will aid improved interpretation of sedimentary deposits on Earth and other planets to infer past surface conditions.