Three‐dimensional forward stratigraphic modelling of the sedimentary architecture of meandering‐river successions in evolving half‐graben rift basins

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, faultbounded 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.How to cite this article: Yan N, Colombera L, Mountney NP. Three-dimensional forward stratigraphic modelling of the sedimentary architecture of meandering-river successions in evolving half-graben rift basins. Basin Res.

An integrated approach to determine three‐dimensional accretion geometries of tidal point bars: Examples from the Venice Lagoon (Italy)

“…Aggradation is modelled through the progressive vertical offset of the channel, which translates to increases in the relative elevation of the point‐bar packages at each time step, and can follow a linear behaviour or any other specified trend (Yan et al. , 2020).…”

“…In particular, a rate of increase in depth change between pool and riffle areas with increasing channel sinuosity can be specified as model input. Aggradation is modelled through the progressive vertical offset of the channel, which translates to increases in the relative elevation of the point-bar packages at each time step, and can follow a linear behaviour or any other specified trend (Yan et al, 2020).…”

“…The Point-Bar Sedimentary Architecture Numerical Deduction (PB-SAND) is a forward stratigraphic model (Yan et al, 2017;Colombera et al, 2018;Yan et al, 2019Yan et al, , 2020) that uses input on channel planform and facies, together with current understanding of relations between meander-bend planform evolution and facies organization, to predict the three-dimensional architecture arising from the evolution of pointbar bodies in response to channel migration. The PB-SAND can be constrained by data from ancient deposits and modern systems (for example, remote sensing imagery, seismic data, cores and well logs).…”

Combined inverse and forward numerical modelling for reconstruction of channel evolution and facies distributions in fluvial meander-belt deposits

“…The approach can be used to model up to three consecutive meander bends in a single run. Multiple model outputs can then be chained together to model larger river reaches (Yan et al, 2020). The accretion patterns between two successive time steps are extrapolated based on the type of meander transformation and a specified number of accretion increments.…”

“…Variations in the thickness of channel deposits might result from streamwise bathymetric variations (from riffle to pool) and temporal changes (in sinuosity or hydraulic geometry). Aggradation of the channel floor can also be modelled (Yan et al, 2020). In PB-SAND, incorporation of abandoned cut-off meander loops is achieved through integration of the outputs of separate modelling steps.…”