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<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Tidal channels exert a crucial control on sediment transport and drive geomorphic changes in the tidal environment. Despite their ubiquitous occurrence, long-term morphodynamics and processes driving the morphologic changes remain less well understood than fluvial counterparts. Spanning from straight to dendritic, Korean tidal channels become more sinuous and densely populated with elevation due to higher mud content. Mutually evasive current patterns resulted in a cuspate meander bend, where flood barb develops at the seaward side of the bend. Multiannual observation revealed that tidal channels migrate up to 80 m per year in the lower intertidal zone of open-coast sandy tidal flats to nearly stationary for several years in the upper intertidal zone of protected muddy tidal flats. Migration rates are temporarily pronounced during the summer monsoon when heavy rainfall-induced surface runoff intensifies ebb tidal asymmetry and promotes headward erosion. Meander bends are mostly landward-skewed and shift downstream, implying that ebb currents primarily drive the long-term channel morphodynamics. Tidal point bars commonly display ebbwardly dipping, inclined heterolithic stratification (IHS), dominated by bedforms formed by subordinate flood tidal currents. An overall ebb-dominance and mutually evasive current patterns account for the counterintuitive stratigraphic architecture of the point bars in Korean tidal channels.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Faults and folds are the clearest expressions of deformation we can observe directly in the rock record. This is visualised on 2D maps through the geometry of outcrop patterns and lines or polygons with marker symbols indicating different kinematics. But the record of deformation is 4D, and faults and folds represent only the products of deformation, not the processes responsible. Understanding the evolution of the 3D structural framework through time is fundamental for all forms of subsurface exploration across the energy transition. The aim of this paper is to show how 2D geospatial databases can represent the 4D deformational record. This is by capturing the three components of deformation: the initial state of the crustal architecture to be deformed (the pre-deformational crustal facies and structural framework), the processes responsible for the deformation (geodynamics), and the products of the deformation (folds, faults, magmatism, and crustal facies). Deformation is not limited to a single tectonic cycle. Within each cycle, it is time-transgressive and highly variable spatially. By evolving these 2D geospatial databases through time using restoration and plate modelling, we can better understand the 4D complexity of deformation and how this impacts exploration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> Cutoffs, which include neck and chute cutoffs, are the results of the fluvial processes that fundamentally influence evolution of meandering rivers. A neck cutoff happens when the two limbs of a highly sinuous bend touch, whereas a chute cutoff refers to the formation of a shortcut channel passing through a meander bend. In this review, we begin by distinguishing the morphological and hydrological conditions of the two cutoff types. Mechanisms driving the development of a neck cutoff are embodied in a variety of kinematical and hydrodynamic models simulating processes governing the long-term evolution of meandering rivers. These models adopt a morphological threshold for judging the occurrence of a neck cutoff, <jats:italic>b</jats:italic> = <jats:italic>αw</jats:italic> , where <jats:italic>α</jats:italic> is a constant ranging between 0 and 1, <jats:italic>b</jats:italic> is the bend neck width and <jats:italic>w</jats:italic> is the mean channel width. The potential underestimation of the evolutionary period during the late stage of bend evolution toward a neck cutoff when using this morphological threshold and the uncertainties in quantifying the migration–curvature relationship limit the abilities of existing models to predict the occurrence of neck cutoffs. We then suggest three possible directions for future research on meander neck cutoffs. Mechanisms controlling chute cutoffs are relevant to six key factors representing the meander hydrological regime, planform morphology, bed topography and floodplain characteristics. The combination of these factors gives rise to four distinguishable triggering mechanisms: headward-erosion, embayment, mid-channel bar and scroll–slough chute cutoffs, though the initiation of the chute cutoff may be caused by some combination of these. However, the hydraulic and morphological characteristics of meander bends under these triggering mechanisms are so complex that they are often site-specific, making it extremely challenging to generalize the known morphodynamic and hydrodynamic processes driving the formation of chute cutoffs in individual meander bends. We close the review by recommending three possible research directions on chute cutoffs for tackling the existing challenges in the future. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> Fluvial point-bar deposits are described from the <jats:italic>c.</jats:italic> 1 Ga Diabaig Formation, representing some of the most compelling architectural evidence of planform sinuosity recognized in pre-vegetation sedimentary strata to date. The stratigraphical architecture of the deposits indicates different planform transformations in response to meander-bend expansion and downstream migration. Point-bar architectural motifs are locally abundant in the unit and this is attributed to elevated amounts of mud-calibre cohesive sediment. Mud afforded landscape stability that, together with limited stream power, was sufficient to corral sediment into single-thread, sinuous channels. Significant volumes of fine-grained sediment were encouraged to accumulate by the local basin setting of several topographically confined endorheic depressions. These conditions ceased once the hydrologically closed valleys were filled, with the overlying sandstone-dominated Applecross Formation subsequently deposited by low-sinuosity, braided rivers that bypassed fine-grained sediment oceanward. Other endorheic basins conducive to the formation of depositional meanders should be expected to have been relatively widespread on pre-vegetation Earth, though many individually limited in size, confined by their inherited topographies. Depositional architectures representative of sinuous channel planforms remain scarce within more extensive, externally drained basins. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Neck and chute cutoffs along meandering rivers are near-instantaneous morphodynamic perturbations that drive modification of planform channel geometry and kinematics at the cutoff site and in adjacent bends. Despite their ubiquity, quantitative and predictive linkages between post-cutoff planform bend geometry and subsequent bend kinematics remain limited. Here, using a 37-year record of Landsat-derived river channel centerlines from a meandering reach of the Trinity River in Texas (USA) and a newly developed directed graph-based approach for high-resolution channel tracking, we identify a linkage between post-cutoff bend curvature and the magnitude, spatial extent, and temporal duration of cutoff influence on local and nonlocal channel bend kinematics. We further explore this relationship using a kinematic model of meandering applied to synthetically generated river reaches and the Landsat-derived Trinity River centerlines. While the model captures the observed linkages between post-cutoff bend curvature and resultant bend kinematics, it underpredicts the magnitude of cutoff influence observed in the real centerline data, particularly at the cutoff site, by up to one order of magnitude. Our results provide a promising advance in the characterization and prediction of the spatiotemporal impact of cutoffs on local and nonlocal post-cutoff channel bend kinematics.</jats:p> <jats:p content-type="supplementary-material"> Supplementary material at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" specific-use="dataset is-supplemented-by" xlink:href="https://doi.org/10.6084/m9.figshare.c.6906126">https://doi.org/10.6084/m9.figshare.c.6906126</jats:ext-link> </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Geological maps document knowledge of considerable value (economic, cultural and aesthetic) for societies, enterprise and people in general. Knowledge illustrated in geological maps also helps us to foresee how landscape interventions and climate change may affect our living ground and make us vulnerable to geohazards. The present paper presents an overview of geological mapping carried out by the Geological Survey of Norway since 1858 and focuses on mapping activities and products produced in the present millennium. Key issues to consider are how we are moving into the digital worlds, how we use geological mapping to follow up on national agendas like Green Shift and Blue Growth, and how national agreements and cooperations help us to make geological and other geographic information available to everyone through Open access web-portals and services.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many present-day alluvial floodplains display traces of abandoned meandering channel belts developed during the past millennia (i.e. mid to late Holocene). Deposits of these ancient rivers represent preferential pathways for groundwater flows and related environmental issues, such as contaminant propagation or saltwater intrusion in coastal areas. However, since formative bankfull flows in such old and abandoned routes are hard to estimate, fossil meanders have not been commonly addressed by morphodynamic numerical models, and most of them have been investigated following classical sedimentological approaches based mainly on punctual data derived from sedimentary cores. This study aims at investigating the sediment distribution within different fossil bends on the southern Venetian Plain (NE Italy), and relating such distribution to numerically modelled bed shear stresses used herein as a proxy of sediment sorting patterns. For this purpose, formative flows in the studied palaeomeanders are first inferred from measured sediment grain size and estimates of bend widths. Then, shear stress distributions are computed along the studied palaeobends using a 2D linearized model. Model results are finally compared with conductivity distributions gauged directly in the field through electromagnetic induction investigations in the frequency domain. Our results suggest significant correlations between shear stress distributions and sediment sorting estimated from conductivity data. We deem that the integration between sedimentological reconstructions and state-of-the-art numerical modelling can provide a solid contribution to predicting the spatial distribution of sediment properties within ancient meandering channel belts, with relevant implications for the understanding of shallow aquifer dynamics and soil management.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Since the term was coined in 1873, paleogeography has provided a powerful map-based tool for synthesising, visualising, and testing diverse regional data and hypotheses, but there are problems in deducing the palaeogeography of areas with few data points. As an example, the Scottish Highlands are better mapped and more studied than almost any other ancient orogen, yet questions remain on the persistence of topography since the Caledonian orogeny and the possibility of Cretaceous marine inundation. This paper reviews the data available on Scottish Cretaceous outcrops using published geological maps and memoirs to extract data: outcrop length, stratigraphic thickness and component units, elevation range of the outcrop, and subcrop formations. All Cretaceous rocks in western Scotland were deposited in shallow marine and shoreline environments; deposits thin northwards and appear to be close to a feather edge. Elevation data are used to construct a Cretaceous surface which intersects present-day topography at low to intermediate altitudes. It is concluded that the Scottish Highlands were largely emergent during the Late Cretaceous, confirming previous palaeogeographic studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Fault mapping is essential for understanding subsurface geological structure. However, effective training of students in developing and understanding fault patterns in 3D seismic imagery is impeded by the time-investment needed to acquire competence using software and then creating depth-structure maps of stratal horizons. Here an exercise is laid out that can achieve the desired experience – using the young fault systems of Afar (Djibouti), where former land-surface-defining basalt flows are offset by arrays of normal faults. The top-basalt surface, displayed on GoogleEarth, is in effect a depth-structure map and the gaps (‘fault-loss’) in this surface approximate to exposed fault surfaces. The mapping exercise is described and illustrated here step-wise. The fault system is gradually mapped out to reveal examples of long-continuous faults, branching patterns, relaying faults and isolated fault segments. Alternative criteria for identifying faults can be examined, with analogies in seismic interpretation. This can inform discussion of the approaches and uncertainties inherent in mapping faults in the subsurface. The study may be extended to consider the pattern of early–syn-rift depositional systems. Collectively these tasks can be progressed within an hour or so, providing effective insights into the structure of normal fault systems that cannot be replicated by conventional fieldwork.</jats:p>