Abstract The preservation and accretion rates of fluvial meander-belt deposits appear to vary with the time over which they are evaluated, but the drivers of this effect are not fully understood. Using channel trajectories tracking the temporal evolution of meandering rivers, constrained with data on past river planforms, a numerical model is used to simulate planform evolutions of meander-belt reaches that underwent different types of meander transformation behaviours and bend cutoffs. Sediment preservation and bar accretion rates are quantified for three hierarchies of depositional products: (i) accretion stages reflecting intervals of bend migration by a certain meander-transformation style, (ii) meander-belt segments encompassing multiple stages but no bend cutoffs and (iii) meander-belt segments that experienced one or multiple cutoffs. Results show that distinct power-law relationships between the accretion rate and the time of sedimentation exist for river systems of different magnitudes in scale. Within each order of magnitude in river-system size, a single power-law relationship fails to effectively capture all depositional hierarchies. Sediment preservation varies with the time over which it is computed, but systematic variations in accretion rates with time primarily portray an apparent dependency of river migration rates on time: these variations largely reflect the temporal resolution and timespan of the modelled examples, highlighting an inherent issue affecting studies of river evolutions.

Abstract There has been debate over the processes acting on deep-water channels, with comparisons made to the evolution of meandering fluvial systems. We characterized a three-dimensional seismic-reflection dataset of the Joshua deep-water channel–levee system located in the eastern Gulf of Mexico and interpreted 13 horizons showing its kinematic evolution over a 25 km reach. Over this reach, we documented channel migration through systematic bend expansion and downstream translation, which was sustained through channel aggradation as sinuosity increased from 1.25 to 2.3 at abandonment. An abrupt decrease in sinuosity was associated with a neck cutoff, which changed the subsequent migration direction of the channel in that locality. These processes are analogous to the evolution of meandering fluvial systems. We show that increasing channel sinuosity correlates to a reduction in channel slope and hypothesize that this promoted increasingly depositional turbidity currents that led to channel aggradation. Using a simple forward stratigraphic model in which vertical movements of the channel are governed by a stream power law, we show how aggradation can be driven autogenically. Trends in sinuosity, aggradation and slope are in broad agreement between the Joshua Channel and the model. This highlights the potential importance of intrinsic channel processes as a control on system evolution.

Abstract Intruding magma can create space by uplift and elastic bending of the overburden, which locally fractures the deforming volume and produces flat-topped or dome-like forced folds. Here, I map such fracture networks and quantify their geometry and connectivity across a range of natural and modelled intrusion-induced forced folds. I show that there is a positive relationship between forced fold length and amplitude, and all fracture networks comprise traces, with variable lengths and orientations, that are more intense and denser where fold curvature is greatest. Fracture length populations are typically best described by power-law distributions, but some fit better to log-normal or exponential distributions. Connectivity of fracture networks is low and generally increases with folding, but resurfacing by eruptive products can disrupt this trend. My work supports previous analyses of forced folds and fractures, suggesting that we can use the fracture characteristics of exposed forced folds to predict that of buried forced folds. Due to their geometry and fracture network, intrusion-induced forced folds make ideal fluid traps. As these forced folds are common in many volcanic settings and sedimentary basins, we should consider their potential as exploration targets for water, magmatic-related mineral and metal deposits, and particularly CO 2 storage.