Three-dimensional forward stratigraphic modelling of the sedimentary architecture of meandering-river successions in evolving half-graben rift basins |
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| Authors: | Na Yan Luca Colombera Nigel P Mountney |
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| Institution: | Fluvial & Eolian Research Group, School of Earth and Environment, University of Leeds, Leeds, UK |
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| Abstract: | The spatial organisation of meandering-river deposits varies greatly within the sedimentary fills of rift basins, depending on how differential rates of fault propagation and subsidence interplay with autogenic processes to drive changes in fluvial channel-belt position and rate of migration, avulsion frequency and mechanisms of meander-bend cut off. This set of processes fundamentally influences stacking patterns of the accumulated successions. Quantitative predictions of the spatio-temporal evolution and internal architecture of meandering fluvial deposits in such tectonically active settings remain limited. A numerical forward stratigraphic model—the Point-Bar Sedimentary Architecture Numerical Deduction (PB-SAND)—is applied to examine relationships between differential rates of subsidence and resultant fluvial channel-belt migration, reach avulsion and channel-deposit stacking in active, fault-bounded half-grabens. The model is used to reconstruct and predict the complex morphodynamics of fluvial meanders, their generated channel belts, and the associated lithofacies distributions that accumulate as heterogeneous fluvial successions in rift settings, constrained by data from seismic images and outcrop successions. The 3D modelling outputs are used to explore sedimentary heterogeneity at various spatio-temporal scales. Results show how the connectivity of sand-prone geobodies can be quantified as a function of subsidence rate, which itself decreases both along and away from the basin-bounding fault. In particular, results highlight the spatial variability in the size and connectedness of sand-prone geobodies that is seen in directions perpendicular and parallel to the basin axis, and that arises as a function of the interaction between spatial and temporal variations in rates of accommodation generation and fault-influenced changes in river morphodynamics. The results have applied significance, for example, to both hydrocarbon exploration and assessment of groundwater aquifers. The expected greatest connectivity of fluvial sandbody in a half-graben is primarily determined by the complex interplay between the frequency and rate of subsidence, the style of basin propagation, the rates of migration of channel belts, the frequency of avulsion and the proportion and spatial distribution of variably sand-prone channel and bar deposits. |
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| Keywords: | forward stratigraphic modelling half-graben meandering river point bar sand connectivity stacking pattern |
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