--> Prediction of Fluvial Point-Bar Internal Architecture and Heterogeneity From Outcrop and System-Independent Morphometric Analysis of Meander Bends

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Prediction of Fluvial Point-Bar Internal Architecture and Heterogeneity From Outcrop and System-Independent Morphometric Analysis of Meander Bends

Abstract

River bends are complicated and dynamic features of meandering fluvial systems; understanding point-bar deposits in seismic and at outcrop is challenging as successions represent partially preserved remnants. Predictive tools to capture geomorphological details of the internal architecture and heterogeneity of meander-fills, and to classify them in a meaningful way for comparison is important in understanding the geologic record. This research uses an integrated GIS and quantitative sedimentological approach to predict and classify the geometry and internal architecture of components of meandering fluvial systems from different settings to better understand scroll-bar development and modes of growth. A classification scheme identifies end-member models, which can be used to interpret the origin of ancient point-bar accumulations from their internal heterogeneity and architecture. To achieve this, a novel ‘Intersection Shape Method’ has been developed that allows quantitative comparison of meanders with markedly differing morphologies. Measurements of 35 morphometric parameters of 390 meander bends from 13 different rivers (13,650 in total) have been acquired using Google Earth Pro. Studied rivers were selected to isolate the effects independent variables (e.g., climatic zone, valley slope and discharge); systems strongly modified by anthropogenic activity have been avoided. Analyses of ancient point-bar successions (Pennsylvanian, Wales; Jurassic, England) serve as test data sets for the reconstruction of meander morphology from preserved stratal architectures; distributions of 19 lithofacies and 2500 palaeocurrent readings highlight subtle yet predictable variations in ripple, dune and bar growth histories. The approach has yielded the following novel findings: (i) climatic regime exerts a primary control on meander morphology through its role in determining mean annual discharge, sediment supply, and vegetation type and density; (ii) fluvial systems with different gradients, sediment calibers, channel sizes, accumulation rates and climate regime all exhibit different yet predictable trends in meander and scroll-bar development. This method can also be applied to high-resolution seismic slices (e.g., Cretaceous McMurray Formation, Alberta, Canada; Triassic Mungaroo Formation, NW Shelf, Australia) to help infer river characteristics and predict internal architectures and heterogeneity.