Channel Belt Research Articles

Using spatial variations of grain size to reveal sediment transport in the Kumtagh Sand Sea, Northwest China

The identification of sediment transport processes is essential in understanding the accumulation and development of sand seas. However, only limited effort has been made to extract macroscale sediment transport information in aeolian science. In this study, we investigated grain-size variation to gain insight into large-scale sediment transport processes in the Kumtagh Sand Sea. Results suggest that grain-size variation is correlated to fluvial-aeolian interaction. In the central sand sea region, due to intermixed fluvial-aeolian controls, the downwind trend of grain size was significant except for the area surrounding the channel belt; but the grain-size trend in a downstream direction was not obvious. In the northeastern sand sea region, dune sand became progressively finer along a downwind direction, but sorting remained consistent. This phenomenon is ascribed to the fact that sand from upwind areas is mixed with local interdune sand. By combining evidence from dune patterns, grain sizes and mineral composition differences, we determined that sediment transport processes in the Kumtagh Sand Sea can be summarized as follows: Fluvial system transport sediments from the Altyn-Tagh Mountains to the sand sea, after which prevailing northerly winds subsequently rework these sediments and deliver them to downwind areas; meanwhile, sand from upwind areas is mixed with local sand in the northeastern sand sea region. Our findings provide insight into modern sand sea formation under the control of fluvial-aeolian interactions, while potentially offering further implications that can be used to explore paleogeographic process based on these modern processes.

Seismic geomorphology of shoal-water deltaic and mixed carbonate-siliciclastic beach-bar systems in hanging wall of rift basins: Paleogene of the Raoyang Sag, Bohai Bay Basin, China

Recent studies of ancient rift basins focus on the tectonosedimentary models, which emphasize the control of tectonics on the distribution and evolution of depositional systems in rift basins, whereas these studies seldom address stratigraphic dominated depositional models. Compared to footwall depositional systems, hanging wall depositional systems are especially underexplored due to their fine-grained, thin-layered, and widely distributed features. We integrated seismic data, cores, and well logs to define the dispersal of hanging wall depositional systems that are related to the fluctuation of lacustrine level in the late synrift and postrift stages. We identified one third-order sequence (SQ1) on the seismic reflection data and subdivided five fourth-order sequences (SSQ1–SSQ5) based on the features of parasequence sets. The strata in SQ1 record a complete regressive and progressive lacustrine process. We interpreted shoal-water deltaic systems and mixed carbonate-siliciclastic beach-bar systems in the SQ1. Within SSQ1 and SSQ2, sediments fed from the northwest, west, and southwest, and developed shoal-water deltaic systems with an average width range of the distributary channel belts within 680–1220 m. In SSQ3, beach-bar systems gradually changed from clastic beach bars to mixed carbonate-siliciclastic beach bars in a basinward direction. Clastic beach-bar systems and mixed carbonate-siliciclastic beach-bar systems were extending north–northeast with an average length of approximately 3.5–8 km and a width of 1–4 km. For those in SSQ4 and SSQ5, shoal-water deltaic systems prograded into the lacustrine, and distributary channel belts occur with an average width range within 520–880 m. We developed a spatial and temporal quantitative evaluation of deltaic and beach-bar reservoirs within a third-order sequence on the hanging wall dip slope, and it has potential worldwide implications for other hanging wall dip slopes in rift basins.

Aram Dorsum: An Extensive Mid‐Noachian Age Fluvial Depositional System in Arabia Terra, Mars

AbstractA major debate in Mars science is the nature of the early Mars climate, and the availability of precipitation and runoff. Observations of relict erosional valley networks have been proposed as evidence for extensive surface runoff around the Noachian‐Hesperian boundary. However, these valley networks only provide a time‐integrated record of landscape evolution, and thus, the timing, relative timescales and intensity of aqueous activity required to erode the valleys remain unknown. Here, we investigate an ancient fluvial sedimentary system in western Arabia Terra, now preserved in positive relief. This ridge, “Aram Dorsum,” is flat‐topped, branching, ~85 km long, and particularly well preserved. We show that Aram Dorsum was an aggradational alluvial system and that the existing ridge was once a large river channel belt set in extensive flood plains, many of which are still preserved. Smaller, palaeochannel belts feed the main system; their setting and network pattern suggest a distributed source of water. The alluvial succession is up to 60 m thick, suggesting a formation time of 105 to 107 years by analogy to Earth. Our observations are consistent with Aram Dorsum having formed by long‐lived flows of water, sourced both locally, and regionally as part of a wider alluvial system in Arabia Terra. This suggests frequent or seasonal precipitation as the source of water. Correlating our observations with previous regional‐scale mapping shows that Aram Dorsum formed in the mid‐Noachian. Aram Dorsum is one of the oldest fluvial systems described on Mars and indicates climatic conditions that sustained surface river flows on early Mars.

Integrated seismic and well-log analysis for the exploration of stratigraphic traps in the Carbonera Formation, Llanos foreland basin of Colombia

The Llanos foreland basin of Colombia is the country's most prolific oil producer, with the most known oil fields found in normal fault traps created during flexure of the foreland basin. The objective of the study is to evaluate the potential of stratigraphic traps in the Late Eocene-Early Miocene Carbonera Formation, a 400-1800 m-thick reservoir unit with numerous traps related to unfaulted, sand-prone fluvial deposits. We integrated 700 km2 of 3D seismic data with eight wells near the ~8600 bcd Cubiro field in the central area of the Llanos foreland. Interpretations of well logs and stratal slices through multi-attribute and iso-frequency amplitude cubes show that the Carbonera Formation contains tectonically-controlled, sinuous channel belts seen on seismic lines as strong, high-amplitude, concave reflections with variable width-to-depth ratio. Well logs through the Carbonera Formation record two regressive-transgressive cycles with greater preservation of non-reservoir, shaly transgressive deposits within the intermediate Carbonera members 5 and 3, and sandy, lowstand deposits in the lower and uppermost Carbonera members 7 and 1, respectively. Seismic and gamma-ray facies analyses allowed the distinction of prospective, sand-rich point bars, scrolls, and basal lag deposits from non-prospective, mud-rich abandoned channels. Stratal slices within the Carbonera Formation show changes from Late Eocene-Early Oligocene, northeast-flowing channel belts of a main axial fluvial system -proposed to be the proto-Meta River-, to a Late Oligocene southeast-flowing tributary channels interpreted as a result of eastward flexural migration, enhanced accommodation from loading of the Eastern Cordillera and a shift from an underfilled to overfilled foreland basin.

Facies analysis relationships depositional environments of the subsurface stratigraphy of the Snake Cave Interval in the Bancannia Trough, western Darling Basin, New South Wales, SE Australia

Abstract This work presents the first detailed research on the subsurface stratigraphy of the sedimentary Snake Cave Interval (late Early to late Middle Devonian) in the Bancannia Trough, the westernmost component of the Darling Basin, in western New South Wales, Australia. The study is based on data from wireline-log responses (especially gamma-ray and sonic logs), and core and cuttings descriptions in three exploration wells that are used to develop a model for depositional environments in the Bancannia Trough. This study provides re-evaluation and re-interpretation of the positions of the top and bottom boundaries of the Snake Cave Interval using distinct patterns changes in gamma-ray and sonic log signatures in relation to lithological characteristics in the Bancannia South-1, Bancannia North-1 and Jupiter-1 wells. The log facies interpretation of the Snake Cave Interval section enabled the detailed facies description of four lithostratigraphic units (A, B, C and D, in ascending order) in the study area. The Snake Cave Interval displays units with ten distinct sedimentary facies identified from core and then tied to the gamma ray log characteristics, forming facies associations that are visible in both vertical and lateral sections. Five facies associations have been identified: FA-I, braided fluvial multistory channel belt complex deposits; FA-II, meandering fluvial distributary channel sandstone complex deposits; FA-III, sandy braided fluvial distributary channels deposits; FA-IV, meandering fluvial deposits; and FA-V, fluvial channel-fill association with fluvio-tidal transition zone complex deposits. Detailed comparison of lithologic logs with wireline-log suite signatures (mainly gamma-ray logs) that are dominantly braided fluvial and meandering fluvial deposits, with minor fluvio-tidal transition zone complex deposits in this trough. This article presents a new depositional model that will promote exploration and discovery of potential petroleum resources and stratigraphic-trap configurations in this trough and adjacent regions of the Darling Basin.

Planform and stratigraphic signature of proximal braided streams: remote-sensing and ground-penetrating-radar analysis of the Kicking Horse River, Canadian Rocky Mountains

ABSTRACTBraided rivers have accumulated a dominant fraction of the terrestrial sedimentary record, and yet their morphodynamics in proximal intermountain reaches are still not fully documented—a shortcoming that hampers a full understanding of sediment fluxes and stratigraphic preservation in proximal-basin tracts. Located in the eastern Canadian Cordillera near the continental divide, the Kicking Horse River is an iconic stream that has served as a model for proximal-braided rivers since the 1970s. Legacy work on the river was based solely on ground observations of small, in-channel bars; here we integrate field data at the scale of individual bars to the entire channel belt with time-lapse remote sensing and ground-penetrating-radar (GPR) imaging, in order to produce a more sophisticated morphodynamic model for the river.Cyclical discharge fluctuations related to both diurnal and seasonal variations in melt-water influx control the planform evolution and corresponding stratigraphic signature of trunk channels, intermittently active anabranch channels, and both bank-attached and mid-channel bars. Three-dimensional GPR fence diagrams of compound-bar complexes are built based on the identification of distinct radar facies related to: i) accretion and migration of unit bars, ii) both downstream and lateral outbuilding of bar-slip foresets; iii) buildup of bedload sheets, iv) channel avulsion, and v) accretion of mounded bars around logs or outsized clasts. Trends observed downstream-ward include decreases in gradient and grain size decreases, trunk-channel shrinkage, intensified avulsion (with increase in abundance for anabranch channels), and a shift from high-relief to low-relief bar topography. The integration of ground sedimentology, time-lapse remote sensing, and GPR imaging demonstrates that proximal-braided streams such as the Kicking Horse River can be critically compared to larger systems located farther away from their source uplands despite obvious scale differences.

Architecture, process, and environmental diversity in a late Cretaceous slope channel system

ABSTRACT Arroyo San Fernando, on the Pacific coast of Baja California, Mexico, provides a superb view of the architecture of a Maastrichtian active margin slope channel system and the record of its evolution through a third-order sea-level cycle. The succession is organized into architectural building blocks (channel-complex sets) consisting of a channel belt with an axial region and a channel-belt margin of terraces and internal levees. The channel belt is confined by an external levee on one side and by an erosion surface into the slope on the other. Each channel-complex set can be subdivided into three stages of evolution: Stage I consists of highly amalgamated coarse-grained channel complexes, Stage II consists of gravelly meander belts with marginal and stratigraphically intervening thin-bedded turbidites, and Stage III consists of mudstones representing abandonment. This succession is associated with repeated and therefore predictable changes in architecture, facies distribution, inferred seafloor morphology, and sedimentary process. We describe variability in the sedimentology, ichnology, palynology, provenance, and inferred sedimentary processes between and within these architectural elements. Channel formation and fill are attributed to erosion, sediment transport, and deposition by turbidity currents and lesser debris flows. Ichnology indicates enhanced oxygenation and supply of organic material, substrate type, and turbidity within the channel belt; the axial region can be differentiated from the terraces by differing response to turbidity-current intensity. Levee environments show ichnological gradients away from the channel towards background slope. Palynology reflects confinement of the supply of terrigenous material to the channel belt, but is also indicative of stratification within the turbidity-currents, as is the distribution of heavy minerals. Provenance is from the extinct part of the continental-margin arc to the east, via high-gradient gravelly streams and across a steep shoreline, with direct supply of coastal material to deep water. Architectural hierarchy bears comparison with other slope channel systems, but in common with them the fill represents only a small fraction of the time that the system was active.

Deep‐water sediment transport patterns and basin floor topography in early rift basins: Plio‐Pleistocene syn‐rift of the Corinth Rift, Greece

AbstractOur current understanding on sedimentary deep‐water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio‐Pleistocene deep‐water sedimentary system (Rethi‐Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep‐water syn‐rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast‐count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone‐dominated sheets, B—conglomerate‐dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone‐dominated broad shallow lobes, F—sandstone‐dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland‐fed Mavro delta, with minor contributions from a transverse system of conglomerate‐dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep‐water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin‐floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large‐scale subaqueous landslides and eventual uplift of the whole fault block.

Application of seismic attribute analysis in fluvial seismic geomorphology

Seismic attributes can be important predictors, either qualitative or quantitative, of reservoir geometries when they are correctly used in reservoir characterization studies. This paper discusses seismic attribute analyses and their usefulness in seismic geomorphology study of Moragot field of Pattani Basin, Gulf of Thailand. Early to Middle Miocene fluvial channel and overbank sands are the reservoirs in Pattani Basin. Due to their limited horizontal and vertical distribution, it is not always possible to predict the geometry and distribution of these sands based on the conventional seismic interpretation. This study utilized various seismic attributes, e.g., RMS amplitude analysis, spectral decomposition, semblance and dip-steered similarity, RGB blending to image the geometry and the spatial distribution of sand bodies in horizon and stratal slices at different stratigraphic intervals. Attribute analyses reveal, at shallow stratigraphic levels, RMS and semblance can successfully identify channel-shaped sand bodies and mud-filled channels associated with channel belts. On the other hand in deeper stratigraphic intervals, sand distribution can be imaged more effectively by using spectral decomposition and dip-steered similarity volumes. High-frequency spectral decomposition slices can image thin sands, and low-frequency slices can image thick sands quite effectively in deeper intervals. RGB blending of different frequency slices is particularly useful in delineating channel systems of various dimensions at deeper intervals. These images show the distribution of sands and mud-filled channels at various stratigraphic levels. The width of channel belts varies from 200 m to 3 km. These channel belts are N–S or NW–SE oriented. From the channel pattern and their dimensions, depositional environments can be predicted. Mud-filled channels identified in the horizon slices will act as a connectivity barrier between sand bodies at either side of the channel. They can also act as lateral and up-dip seal to form stratigraphic traps. The seismic attribute analyses clearly show the geometry and spatial distribution of sand bodies. Hence, this method for predicting sand body geometry might help in field development planning as well as in reducing exploration risk.

Morphotectonic analysis of two axial tributary basins of the San Juan river controlled by the Precordillera fold and thrust belt, Central Andes of Argentina

Analysis of several morphotectonic tools (longitudinal river profiles, knickpoints, swath profiles, and geomorphic indices) together with geomorphological, lithological, and structural data provided objective and quantifiable elements to improve the knowledge of the Quaternary tectonic activity in a region. In this study, we analyzed and compared two large intermountain basins located in the Precordillera of the Central Andes of Argentina. Local distortions in longitudinal river profiles and river patterns may reflect resistant lithology, an increase in shear stress, or differential surface uplift. Both basins have similar shapes, although one mirrors the other producing a large-scale broom-shaped drainage pattern. The values of the Asymmetry Factor and Transverse Topographic Symmetry Factor show opposite signs and almost identical values, suggesting that both basins have mirror symmetry independently of order and scale. The asymmetry in both basins would be a result of the progressive migration of the Andean orogenic front towards the east. Knickpoints were mainly associated with resistant rocks, faults with the scarp facing upstream, or both. In the reaches where the rivers flow across areas with presumed higher rates of uplift, we observed a reduction in the width of the active channel belt by lateral confinement and river pattern changes. The results presented in this paper constitute one of the first attempts to apply geomorphic indices to large drainage basins in the Precordillera fold-and-thrust belt.

Effects of spatially variable accommodation rate on channel belt distribution in an alluvial sequence: Authigenic 10Be/9Be-based Bayesian age-depth models applied to the upper Miocene Volkovce Fm. (northern Pannonian Basin System, Slovakia)

Relationships between spatially variable accommodation rate and the distribution of channel belt deposits are important issues in alluvial stratigraphy. This segment of sedimentology still records important progress using experimental models and field examples. This study focuses on the alluvial stratigraphy of the Volkovce Fm. which was deposited between ~9.0–6.0 Ma in the northern Pannonian Basin System, and it provides an excellent natural laboratory to study this topic. The spatial variability of channel belt distribution was determined in 809 borehole logs drilled to 200–300 m depths while the facies associations were defined on the outcrops. A significant variance in channel belt content was observed, since it reaches 10–40% of the stratigraphic column in the southwestern part of the study area and only 0–15% in the northeastern portion. Moreover, the transition between the areas of different channel belt distribution is oriented perpendicular to the paleo-drainage network axis. Geochronology was then established by applying the authigenic 10Be/9Be dating method to three borehole cores. The Bayesian age-depth models used herein proved a decrease in average accommodation rates from ~200 m/Myr to ~50 m/Myr towards the area with <15% of channel belts. The results indicate that the four times higher subsidence caused dominant deposition of channel belts in the area of maximum subsidence and avoided the basin-scale avulsion to relocate the channels in the area of lower accommodation rate. This was most likely caused by topographic confinement. The deposition of poorly-drained floodplain and swamp facies appeared in the area of lower accommodation rate, where absence of channels caused low sediment supply. The study highlights that authigenic 10Be/9Be dating Bayesian age-depth models can provide a strong geochronological framework for the late Cenozoic alluvial depositional record necessary for interpretation of the influence of allogenic factors on stratigraphic architecture.

Does fluvial channel-belt clustering predict net sand to gross rock volume? Architectural metrics and point-pattern analysis of a digital outcrop model

ABSTRACTSpatial point-pattern analyses (PPAs) are used to quantify clustering, randomness, and uniformity of the distribution of channel belts in fluvial strata. Point patterns may reflect end-member fluvial architecture, e.g., uniform compensational stacking and avulsion-generated clustering, which may change laterally, especially at greater scales. To investigate spatial and temporal changes in fluvial systems, we performed PPA and architectural analyses on extensive outcrops of the Cretaceous John Henry Member of the Straight Cliffs Formation in southern Utah, USA. Digital outcrop models (DOMs) produced using unmanned aircraft system-based stereophotogrammetry form the basis of detailed interpretations of a 250-m-thick fluvial succession over a total outcrop length of 4.5 km. The outcrops are oriented roughly perpendicular to fluvial transport direction. This transverse cross-sectional exposure of the fluvial system allows a study of the system's variation along depositional strike. We developed a workflow that examines spatial point patterns using the quadrat method, and architectural metrics such as net sand to gross rock volume (NTG), amalgamation index, and channel-belt width and thickness within moving windows. Quadrat cell sizes that are ∼ 50% of the average channel-belt width-to-thickness ratio (16:1 aspect ratio) provide an optimized scale to investigate laterally elongate distributions of fluvial-channel-belt centroids. Large-scale quadrat point patterns were recognized using an array of four quadrat cells, each with 237× greater area than the median channel belt. Large-scale point patterns and NTG correlate negatively, which is a result of using centroid-based PPA on a dataset with disparately sized channel belts. Small-scale quadrat point patterns were recognized using an array of 16 quadrat cells, each with 21× greater area than the median channel belt. Small-scale point patterns and NTG correlate positively, and match previously observed stratigraphic trends in the fluvial John Henry Member, suggesting that these are regional trends. There are deviations from these trends in architectural statistics over small distances (hundreds of meters) which are interpreted to reflect autogenic avulsion processes. Small-scale autogenic processes result in architecture that is difficult to correlate between 1D datasets, for example when characterizing a reservoir using well logs. We show that 1D NTG provides the most accurate prediction for surrounding 2D architecture.

A multi‐method approach to dating the burial and skeleton of Kiacatoo Man, New South Wales, Australia

ABSTRACTKiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley &amp; Sons, Ltd.

“Grain-size bookkeeping,” a new aid for siliciclastic systems with examples from paralic environments

ABSTRACTSedimentary logs form the foundation of many studies of ancient and modern sedimentary successions. In siliciclastic settings in particular, vertical grain-size trends are important records of past depositional processes and environments, so that they are recorded with care and are often central to final interpretations. It is rare for the actual grain size to play a similar role. Yet there is significant value in (i) digitizing sedimentary logs to produce statistical grain-size data and (ii) the deliberate study of grain size, a process described here as “grain-size bookkeeping.” To illustrate this, over 5.9 km of sedimentary logs have been digitized from the Miocene to Pliocene paleo–Orinoco delta, the Cretaceous Ferron Last Chance and Notom deltas, and the Jurassic Ravenscar Group. The digital data reveal how grain size partitions into distinct sedimentary facies, proximal-to-distal changes, changes related to stratigraphy and base level, and the overall grain size of paralic systems. It emerges that fluvio-distributary channels are the coarsest-grained sediment bodies in each of the studied systems. The coarsest material does not reach the shoreline, though the grain sizes of fluvio-distributary channels and shoreline sand bodies overlap, in accordance with the concept that the former feeds the later. By contrast, overbank sediments are relatively fine-grained, suggesting that, with the exception of channel belts, coarse sediment can largely bypass the delta plain. Grain-size changes occur across some key stratigraphic surfaces, but not consistently so. Channels in valleys are, on average, coarser than similar channels in unconfined systems, but, in the presented datasets, valleys do not contain the coarsest channels. The data have also allowed the analysis of down-system fining rates in ancient, sandy fluvio-distributary systems, with grain size being measured to decrease at rates ranging from 0.7 to 7.7 μm/km—values that compare favorably with modern rivers. Such large-scale trends are ornamented by, and link to, smaller-scale spatial changes associated with, for example, channel bars, crevasses, and mouth bars, and an initial dataset of associated fining rates has been collected. In general, very large systems (rivers) have low fining rates because of their great size, whereas the converse is true for small systems, especially if the grain size range is large. Consideration of downstream fining rates has led to the insight that avulsion initiates an unequal race to the shoreline. Suspended very fine sand and silt is likely to reach the shoreline with the avulsion flood waters, but bedload will advance far more slowly, perhaps too slowly to reach the shoreline before the river avulses again. Some avulsions may lead to notable temporal variations in the caliber of sediment supplied to shorelines. As expected, the largest system, the paleo-Orinoco, is the finest grained. The Ferron deltas have catchment areas 12 and 22 times smaller than the Orinoco, and are the coarsest grained. Remarkably, though their catchment areas differ by a factor of two, they have almost identical sand grain-size distributions. The data have also proved powerful in refining paleogeographic reconstructions, in particular suggesting “missing” depositional elements needed to complete local sediment routing systems. Careful tracking of grain size is also beneficial in that it is a key control on permeability, the description of which is crucial to the prediction of subsurface fluid flow.

Morphometric diversity of supply-limited and transport-limited river systems in the Himalayan foreland

The Indo-Gangetic basin exhibits highly diverse hydro-geomorphic settings that influence the hydrology, sediment production, and transport rates of the rivers draining this region, and this, in turn, is manifested in morphometric diversity of river systems. The rivers draining the western Gangetic plains (WGP) show incised channels attributable to high stream power and low sediment yield. In contrast, the rivers draining the Eastern Gangetic Plains (EGP) have formed aggradational landforms such as megafans due to low stream power and high sediment yield. For a better process understanding of the causal factors of such spatial inhomogeneities in a river basin, a morphometric characterization of its hinterland is necessary. In this work, a set of morphometric parameters such as stream network, longitudinal profile, and hypsometric curve have been integrated with data on sediment connectivity and stream power index to establish the form-process relationships in two contrasting basins, the upper Ganga basin (UGB) and the upper Kosi basin (UKB). The results of this study suggest that high sediment flux in the UKB is attributed to high rainfall, steep topography, unstable channel longitudinal profiles, and high sediment connectivity. A large part of these sediments gets deposited within the channel belt in the alluvial reaches and is remobilized during high flow events. However, the UGB produces fewer sediments due to low rainfall, mild topography, stable channel longitudinal profile, and low sediment connectivity. Also, the presence of a major dam at Tehri further reduces the functional sediment connectivity in the Upper Ganga Basin.

High‐resolution stratigraphy of a Quaternary fluvial deposit based on magnetic susceptibility variations (Jászság Basin, Hungary)

Quaternary fluvial succession of the Jászság Basin (Hungary) was investigated, challenging the stratigraphical potential of ‘early postglacial fluvial magnetic susceptibility episodes' recognized earlier in the Körös Basin. Low field magnetic susceptibility (MS) was measured in four boreholes from the basin centre and margins, representing channel and flood‐plain environments. Statistical distributions of MS data contain significant sets of outliers, regardless of facies conditions. The downhole distribution of these outliers produces magnetic susceptibility cycles. Supported by magnetic susceptibility cycles, high‐resolution facies correlations were performed reflecting a steady palaeohydrographical situation in the area, with a trunk river to the southeast and tributaries to the northwest. SEM‐EDX data revealed that ferromagnetic grains are responsible for the outlying MS values. The heterogeneous association of magnetite indicates a catchment area with volcanic and metamorphic rocks, while the group of small (&lt;5 μm) magnetite octahedrons originated from nearby rhyolitic tuff formations. Magnetic grains were transported along channel belts, while small (&lt;2 μm) magnetic particles were floated onto flood‐plains attached to clays. Climatic control is indicated by peaks at ~100 ka frequency in spectra of MS records and was also detected in palaeosol development and in flood frequency using the spectra of measured colour (~100 ka) and logged resistivity (~100 ka, ~41 ka), respectively. The climate‐dependent MS signal traceable far into the basin in both channel and flood‐plain environments can be summoned when the Quaternary fluvial succession of the Pannonian Basin is investigated, assuming some sources of magnetite in the catchment areas. According to the concept of ‘fluvial magnetic susceptibility episodes’, the early postglacial escape and spreading of the magnetite fraction control the MS signal that can support mapping of the unconformable Quaternary base and building of high‐resolution models of aquifers.

Persistent mercury hot spot in Central Europe and Skalka Dam reservoir as a long-term mercury trap.

This study aimed to evaluate the relevance of the floodplain pollution sinks of the legacy mercury (Hg) hot spot in Kössein-Röslau river system (east Bavaria, Germany) for further mobilisation and fluvial transport of mercury in suspended particulate matter (SPM), as an important transport medium of Hg in aquatic systems. The channel belt fluvial erosion as the secondary pollution pathway was also considered. The hot spot has originated from the production of Hg compounds such as C2H5HgCN and C6H5HgCl in Chemical Factory Marktredwitz, and even more than 30years after the factory abandonment, the Kössein and the Röslau rivers still export polluted fine grained SPM (median 25-35μm) with mean annual concentrations of 17.4mg/kg. SPM sampling was performed by floating samplers, supported by floodplain drill cores and by recent channel sediments manually collected along the polluted rivers further. Based on long-term monitoring data set from state enterprise Povodí Ohře, fish in the Skalka Reservoir have had Hg concentrations in their muscles up to 6mg/kg for at least the last 14years, exceeding the European maximal limit of 0.5mg/Hg/kg. In addition, the Hg inventory in the Kössein-Röslau river stretches was therefore calculated; it produced an estimate of ca. 21tHg in a 22-km-long channel belt, prone to fluvial remobilisation during floods. Although a major portion of the fluvially transported Hg has yet been trapped by the Skalka Reservoir, the Hg content in the SPM exported farther downstream still varies between 2 and 10mg/kgHg. Due to the considerable Hg inventory in the Kössein-Röslau rivers, an improvement will not occur downstream unless specific measures target the secondary pollution mechanism(s).

Depositional variability of an ancient distributive fluvial system: The upper member of the lower cretaceous Bima Formation, Northern Benue Trough, Nigeria

The upper Bima Formation in the Northern Benue Trough has been interpreted as a distributive fluvial system. Previous stratigraphic studies on the Bima Formation were focussed on localized, qualitative, sedimentary facies analysis without regional context or quantitative information about sand-body scale and architecture. This study quantitatively analysed sand-body thickness variations in the upper member of the Bima Formation across the Northern Benue Trough, documented the spatial variations in channel dimensions. Photo-realistic virtual outcrops were generated for four study sites using data acquired with an unmanned aerial vehicle and processed photogrammetrically. Analysis of the virtual outcrops illustrated spatial variation in the thickness of channel infill components, a downstream decrease in proportion of multi-storey channel belt facies association (from 98% to 5%), an increase in floodplain facies association (from 0% to 13%), an increase in the proportion of isolated channel fill facies association (from 2% to 80%) and a slight decrease in average grainsizes of channel fill sandstone. These observations are interpreted to represent evidence of a distributive fluvial system (DFS) or mega-fan with the proximal part of system at Tula, Ture and Tashan Alaji to the medial part at Hinna having an increase in frequency and thickness of the flood plain facies association and abundance of isolated channel fill facies associations. This study demonstrates the regional facies variability of the upper Bima Formation and has provided a basis for comparison with other ancient distributive fluvial system.

Integration of channel meander abandonment age uncertainty into a stochastic channelized system reconstruction method

The logic of sedimentary channelized systems is only partly preserved in the depositional record. We propose a new method to reconstruct 3D channelized systems from incomplete observations made on surface or subsurface images that integrates the uncertainty on meander abandonment chronology. Starting with the youngest channel path observed and the abandoned loops in the meander belt, the method generates local relative chronologies using cross-cutting analysis. It thus proposes a possible global chronology of channel meander abandonments by going back in time while updating the system configuration. This global chronology is obtained through a stochastic procedure that orders the youngest abandoned meanders with regard to their position and orientation relative to the current channel path. Ordered abandoned meanders are then integrated in the main channel path during the reverse migration process so that the global stochastic ordering is made at each time step of the migration algorithm consistently with the updated channel belt. The proposed approach is parameterized by the spatio-temporal density of meander cutoff along the channel belt, which can be inferred from analog databases. The application of our tool on a seismic stratal slice of the McMurray Formation in Canada provides various possible global chronologies of the abandoned meanders. We analyze the variability of these chronologies and highlight its impact on the various possible subsurface 3D global architectures of the paleo-system and on the associated subsurface heterogeneity.

Controls on the lateral channel‐migration rate of braided channel systems in coarse non‐cohesive sediment

AbstractLateral movements of alluvial river channels control the extent and reworking rates of alluvial fans, floodplains, deltas, and alluvial sections of bedrock rivers. These lateral movements can occur by gradual channel migration or by sudden changes in channel position (avulsions). Whereas models exist for rates of river avulsion, we lack a detailed understanding of the rates of lateral channel migration on the scale of a channel belt. In a two‐step process, we develop here an expression for the lateral migration rate of braided channel systems in coarse, non‐cohesive sediment. On the basis of photographic and topographic data from laboratory experiments of braided channels performed under constant external boundary conditions, we first explore the impact of autogenic variations of the channel‐system geometry (i.e. channel‐bank heights, water depths, channel‐system width, and channel slope) on channel‐migration rates. In agreement with theoretical expectations, we find that, under such constant boundary conditions, the laterally reworked volume of sediment is constant and lateral channel‐migration rates scale inversely with the channel‐bank height. Furthermore, when channel‐bank heights are accounted for, lateral migration rates are independent of the remaining channel geometry parameters. These constraints allow us, in a second step, to derive two alternative expressions for lateral channel‐migration rates under different boundary conditions using dimensional analysis. Fits of a compilation of laboratory experiments to these expressions suggest that, for a given channel bank‐height, migration rates are strongly sensitive to water discharges and more weakly sensitive to sediment discharges. In addition, external perturbations, such as changes in sediment and water discharges or base level fall, can indirectly affect lateral channel‐migration rates by modulating channel‐bank heights. © 2019 The Author. Earth Surface Processes and Landforms published by John Wiley &amp; Sons, Ltd. © 2019 The Author. Earth Surface Processes and Landforms published by John Wiley &amp; Sons, Ltd.