Alluvial fans and fluvial fans at the margins of continental sedimentary basins: geomorphic and sedimentological distinction for geo-energy exploration and development

Abstract

Abstract Alluvial fans and fluvial fans are the most common depositional landforms along the margins of continental sedimentary basins. Their occurrence is determined by the area, relief and hydrology of the catchment, which ultimately control the relative ratios of sediment v. flow discharge and runoff regimes. Fundamental morphological and process distinctions exist between these two kinds of deposystem, which are seen as essentially different facies associations and internal architectures for the corresponding deposits. Alluvial fans commonly develop over short radial distances (hundreds of metres to a few kilometres) and are constructed by ephemeral, flash flow events that lead to poor organization of the sedimentary facies and overall architecture of the corresponding deposits. By contrast, fluvial (mega)fans are fed by proper river systems, which aggrade much larger volumes of clastic sediment over distances of up to a few hundred kilometres. Distinct channel belt and overbank domains are developed with a marked heterogeneity in the distribution of sedimentary facies, represented by hierarchically well-organized fluvial deposits. The general properties of alluvial and fluvial fans reflect the different potentials for the corresponding successions to host economically attractive oil and gas resources and the different approaches required in exploration and prediction.