Mode Of Sediment Transport Research Articles

Using Both Free Surface Effect and Sediment Transport Mode Parameters in Defining the Morphology of River Dunes and Their Evolution to Upper Stage Plane Beds

Dunes are common bed forms in sand bed rivers and are of central interest in water management purposes. Due to flow separation and associated energy dissipation, dunes form the main source of hydraulic roughness. A large number of dune dimension data sets was compiled and analyzed in this study—414 experiments from flumes and the field—showing a significantly different evolution of dune height and length in flows with low Froude numbers (negligible free surface effects) and flows with high Froude numbers (large free surface effects). For high Froude numbers (0.32–0.84 ), relative dune heights are observed to grow only in the bed load dominant transport regime and start to decay for u ∗ /w s (suspension number) exceeding 1. Dunes in this case are not observed for suspension numbers greater than 2.5. For low Froude numbers (0.05–0.32), relative dune heights continue to grow from the bed load to suspended load dominant transport regime. Dunes in this case are not observed for suspension numbers greater than 5. It was concluded that for reliable predictions of dune morphology and their evolution to upper stage plane beds, it is essential to address both free surface effects and sediment transport mode.

Parasequence types in shelfal mudstone strata—Quantitative observations of lithofacies and stacking patterns, and conceptual link to modern depositional regimes

Research Article| February 01, 2014 Parasequence types in shelfal mudstone strata—Quantitative observations of lithofacies and stacking patterns, and conceptual link to modern depositional regimes Kevin M. Bohacs; Kevin M. Bohacs ExxonMobil Upstream Research Company, P.O. Box 2189, Houston, Texas 77252, USA Search for other works by this author on: GSW Google Scholar O. Remus Lazar; O. Remus Lazar ExxonMobil Upstream Research Company, P.O. Box 2189, Houston, Texas 77252, USA Search for other works by this author on: GSW Google Scholar Timothy M. Demko Timothy M. Demko ExxonMobil Upstream Research Company, P.O. Box 2189, Houston, Texas 77252, USA Search for other works by this author on: GSW Google Scholar Geology (2014) 42 (2): 131–134. https://doi.org/10.1130/G35089.1 Article history received: 05 Sep 2013 rev-recd: 22 Oct 2013 accepted: 24 Oct 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kevin M. Bohacs, O. Remus Lazar, Timothy M. Demko; Parasequence types in shelfal mudstone strata—Quantitative observations of lithofacies and stacking patterns, and conceptual link to modern depositional regimes. Geology 2014;; 42 (2): 131–134. doi: https://doi.org/10.1130/G35089.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mudstone strata have a vast variety of physical, biogenic, and chemical attributes at the lamina to bed scale (approximately millimeters to decimeters thick). Our observations of more than 7 km of Paleozoic to Cenozoic mudstones revealed ordered patterns in this variety, i.e., recurrent associations of lithofacies, bedding style, sedimentary structures, and stratal architecture at bedset to parasequence scales (approximately decimeters to meters thick). We quantified characteristics of each association and their stacking patterns in vertical succession and linked them to sets of depositional processes. Most shelf mudstone strata appear to have accumulated in one of three facies association successions (FASs) that can be related to depositional regimes through characteristic modes of sediment transport and accumulation, as well as variations in benthic-energy and oxygen levels. We interpret these three FASs as records of mud accumulation on different portions of continental shelves that were dominated by storm waves, river floods, or tidal currents. Each FAS records a distinct parasequence type. This approach can help fully integrate insights from oceanographic studies into more robust interpretations of the rock record and rock-property maps. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Experimental investigation of the hydrodynamics in pockmarks using particle tracking velocimetry

Water tank experiments were performed in order to investigate the behaviour of currents in pockmarks. A particle-seeded flow was visualised and quantified with the aid of the particle tracking velocimetry technique. The employed analogue pockmark is a 1:100 idealised scale model of a natural pockmark, while the highest Reynolds number in the experiments was one order of magnitude smaller than in nature. Interaction of the flow with the pockmark geometry resulted in an upwelling current downstream of the pockmark centre, along with enhanced water turbulence in the depression. Scaling-up the experimental measurements, it is found that the upwelling would be capable of preventing the settling of particles as large as very fine sand. Furthermore, the increased turbulence would support the suspended fine material, which can thus be transported away before settling. The net effect for a variable-direction near-bed current over long periods of time would be to winnow the settling sediments and reduce the sedimentation rate in pockmarks. These mechanisms may be responsible for the observed lack of sediment infill and the typical presence of relatively coarser sediments inside pockmarks compared to the surrounding bed. In contrast, sediments transported as bedload are likely to be deposited in pockmarks because of the weakening of near-bed currents as well as lateral flow convergence associated with the upwelling. Bedload, however, may not be the dominant mode of sediment transport in areas covered by cohesive sediments, where pockmarks are found.

The role of climate variation in delta architecture: lessons from analogue modelling

AbstractSequence‐stratigraphic models for fourth to sixth order, glacio‐eustatic sequences based only on relative sea‐level variations result in simplified and potentially false interpretations. Glacio‐eustatic sea‐level variations form only one aspect of cyclic climate variation; other aspects, such as variations in fluvial water discharge, vegetation cover, weathering and sediment supply can lead to variable sediment yield, thus adding complexity to sequence‐stratigraphic patterns normally attributed to sea‐level variations. Analogue flume models show a significant impact of water discharge on the timing and character of sequence boundaries, and on changes in the relative importance of systems tracts, as expressed in sediment volumes. Four deltas, generated under the influence of an identical sea‐level curve, and affected by different water‐discharge cycles were generated in the Eurotank facility: (1) constant discharge; (2) high‐frequency discharge variations (HFD); (3) discharge leading sea level by a quarter phase; (4) discharge lagging sea level by a quarter phase. HFD shift the parasequence stacking pattern consistently but do not alter large‐scale delta architecture. Water‐discharge changes that lead sea‐level changes result in high sediment yield during sea‐level rise and in the poor development of maximum flooding surfaces. Delta‐front erosion during sea‐level fall is expressed by multiple, small channels related to upstream avulsions, and does not result in an incised valley that efficiently routs sediment to the shelf edge. When water‐discharge changes lag sea‐level changes, sediment yield is high during falling sea level and results in rapid progradation during forced regression. Erosion from incised valleys is strong on the proximal delta top and dissipates towards the delta front. The combination of high discharge and sea‐level fall provides the most efficient mode of valley incision and sediment transport to the shelf edge. During sea‐level rise, low water discharge results in sediment starvation and well‐developed maximum flooding surfaces. Water‐discharge variations thus alter sequence‐stratigraphic patterns and provide an alternative explanation to the amplitude of sea‐level fall for generating either type 1 or 2 erosional unconformities.

The influence of coastal reefs on spatial variability in seasonal sand fluxes

The effect of coastal reefs on seasonal erosion and accretion was investigated on 2 km of sandy coast. The focus was on how reef topography drives alongshore variation in the mode and magnitude of seasonal beach erosion and accretion; and the effect of intra- and inter-annual variability in metocean conditions on seasonal sediment fluxes. This involved using monthly and 6-monthly surveys of the beach and coastal zone, and comparison with a range of metocean conditions including mean sea level, storm surges, wind, and wave power. Alongshore ‘zones’ were revealed with alternating modes of sediment transport in spring and summer compared to autumn and winter. Zone boundaries were determined by rock headlands and reefs interrupting littoral drift; the seasonal build up of sand over the reef in the south zone; and current jets generated by wave set-up over reefs. In spring and summer, constant sand resuspension and northerly littoral drift due to sea breezes allowed a sand ramp to form in the South Zone so that sand overtopped the reef to infill the lagoon. This blocked the main pathway for sand supply to downdrift zones which subsequently eroded. In autumn and winter, with the dominance of northwesterly storms and reversal in the direction of littoral drift, the South Zone eroded and sand travelled through the lagoon in the current jet to nourish the northern beaches. Inter-annual and seasonal variation in sea level, storm frequency and intensity, together with pulsational effects of local sand fluxes at Yanchep due to inter-seasonal switching in the direction of littoral drift determined marked differences in the volumes of seasonal sand transport. These seasonal ‘sediment zones’ highlighted interesting and unexplored parallels between coasts fronted seaward by coral reefs and rock formations.

River scale model of a training dam using lightweight granulates

Replacing existing river groynes with longitudinal training dams is considered as a promising flood mitigation measure in the main Dutch rivers, which can also serve to guarantee navigability during low flows and to create conditions favourable for ecological development. Whereas the bed response in the streamwise uniform part of a river trained by a longitudinal dam can be readily predicted, the bed response at the transition zones is unclear. In the present study, we investigate the local morphological effects resulting at the intake section of a longitudinal training dam, where the flow is distributed over the main channel and a side channel in between the dam and the river shore. A sediment recirculating model with a nearly undistorted geometry with respect to the prototype was setup. Lightweight polystyrene granulates were used as a surrogate for sediment, to properly scale the Shields parameter without compromising Froude scaling, and reach dynamical similarity. A laser scanner allowed collecting high-resolution bed elevation data. Results obtained under typical low flow and high flow conditions show a general deepening of the bed in the area adjacent to the training dam, in response to narrowing of the main channel. Scour at an upstream river groyne embedded in the model showed a scour hole which was deeper than realistic. Throughout the entire domain, bedforms developed featuring geometrical properties that reproduced the prototype conditions appropriately. Based on a comparison with characteristics from the River Waal, regarded as the prototype without a longitudinal dam, lightweight sediments were considered to be a proper choice for this study, in which bedload is the main sediment transport mode. The main conclusion regards the absence of significant morphodynamic developments at the intake section, both during the high flow experiment and during the low flow experiment, which can be attributed to the alignment of the dam with the local streamlines.

AN ENERGETIC TYPE MODEL FOR THE CROSS-SHORE DISTRIBUTION OF TOTAL LONGSHORE SEDIMENT TRANSPORT

This paper presents an energetic-based simple approach for the computation of cross-shore distribution of total longshore sediment transport (LST) rates. The proposed approach (Baykal 2012) follows similar assumptions with the given formula of Bayram et al. (2007) for the total LST rate (Qlst,t) across the surf zone and is applied to investigate the relation between the rate of dissipation in wave energy flux due to wave breaking and total longshore sediment flux using the available laboratory measurements of Wang et al. (2002) and Gravens and Wang (2007) and the field measurements carried out at Duck site, North Carolina, USA between years 1995-1998 (Miller 1999). The proposed approach is also compared with some of the available distributed total load models. From the comparative studies, it is found that the proposed approach shows good agreement with both the laboratory and field measurements, using a single empirical constant, both qualitatively and quantitatively, especially for the cases where the wave conditions are highly energetic (both for plunging and spilling type breakers) and the suspended load is the main mode of sediment transport in the surf zone.

하구둑에서의 하폭축소 방법을 이용한 퇴사저감 효과 분석

In this study, the methods of sedimentation reduction for the estuary barrage were analyzed using the CCHE2D bed change model. Especially, the effectiveness of sediment dredging currently applied in the field was evaluated quantitatively and also the channel contraction method which is a substitute method was analyzed for the Nakdong River Estuary Barrage (NREB). The numerical model was calibrated and validated for the sediment transport equations and transport modes. In the NREB case, the Ackers and White formula and bed load type was the most similar to the field condition. As a results of the dredging simulation, there was the sedimentation reduction effect of 0.2 m in the bed changes. Furthermore, the analysis result of the channel contraction method represented that the sedimentation reduction effects of the average 0.4 m and the maximum 2.0 m were produced.

Prediction of local scour depth at bridge piers under clear-water and live-bed conditions: comparison of literature formulae and artificial neural networks

The scouring effect of the flowing water around bridge piers may undermine the stability of the structure, leading to extremely high direct and indirect costs and, in extreme cases, the loss of human lives. The use of Artificial Neural Network (ANN) models has been recently proposed in the literature for estimating the maximum scour depth around bridge piers: this study aims at further investigating the potentiality of the ANN approach and, in particular, at analysing the influence of the experimental setting (laboratory or field data) and of the sediment transport mode (clear water or live bed) on the prediction performances. A large database of both field and laboratory observations has been collected from the literature for predicting the maximum local scour depth as a function of a parsimonious set of variables characterizing the flow, the sediments and the pier. Neural networks with an increasing degree of specialization have been implemented – using different subsets of the calibration data in the training phase – and validated over an external validation dataset. The results confirm that the ANN scour depths' predictions outperform the estimates obtained by empirical formulae conventionally used in the literature and in the current engineering practice, and demonstrate the importance of taking into account the differences in the type of available data – laboratory or field data – and the sediment transport mode – clear water or live bed conditions.

The abrasion of modern and archaeological bones by mobile sediments: the importance of transport modes

Fresh, weathered, archaeological and fossilized bones were subjected to a series of abrasion experiments using fine sand in an annular flume in order to link bone-surface abrasion to flow regimes and sediment transport modes, compare these effects on bones of different states, and quantify the extent and types of wear occurring. Flow velocities were chosen to replicate the predominant transport modes of bedload, saltation and suspension. Comparative scanning electron microscopic image analysis was performed to assess the degree and type of wear occurring on each bone type for the different transport modes over a range of exposure periods from 24 to 72 h. These preliminary investigations have shown that both the amount and type of wear experienced was related to the bone type, duration of exposure and the mode of sediment transport with wear being the result of deformation, rather than cutting wear. The formation of scour pits in the sand bed on the upstream side of the bone samples significantly reduced wear, and appears to be an important control mechanism for impact related wear that has been overlooked until now.

Sediment transport constraints on river response to regulation

We demonstrate that alluvial channel response to regulation depends on the characteristic mode of sediment transport in a channel and, thus, for a channel in supply-transport equilibrium, on the caliber of sediment mantling the channel bed, as well as changes in characteristic water discharge and sediment load. We find that regulated, coarse gravel- and cobble-bed alluvial rivers dominated by bedload transport are predicted and observed to preserve the value of a dimensionless ratio of characteristic water discharge, channel slope, width, and size of sedimentary particles mantling the bed associated with the critical conditions required for the onset of significant sediment transport. The covariant geomorphic adjustment of such rivers to regulation is independent of the degree of sediment impoundment, although the nature and rate of changes in any specific characteristic appear to be sensitive to changes in sediment supply. In contrast, covariant geomorphic changes in sand- and fine gravel-bed alluvial rivers dominated by weak suspension transport are predicted and observed to be dependent on the degree of sediment impoundment and commensurate with the change in the sediment concentration of characteristic, formative flows. In both cases, specific geomorphic characteristics of alluvial rivers exhibit varied responses to regulation in different rivers, but across all rivers a systematic covariation in channel slope, width, and grain size is observed that, for a given mode of sediment transport, preserves a characteristic value of the Shields number.

낙동강하구둑 상류 접근수로에서의 유사량 공식 및 유사 이송형태에 따른 하상변동 수치모의에 관한 연구

본 논문에서는 2차원 하상변동 수치모형인 CCHE2D 모형을이용하여 유사량 공식과 유사이송형태별 이류-확산 방정식의 선택이 하상변동 수치모의결과 값에 미치는 영향을 분석하고 실제 현장자료와 비교하였다. 또한 이러한 분석을 기초로 낙동강하구둑 상류 접근수로에서의 최적의 유사량 공식과 유사 이송형태별 이류-확산 방정식을 제안하였다. 낙동강하구둑 상류 접근수로에 대해 Ackers and White와 Engelund and Hansen의 유사량 공식과 소류사와 부유사 유사 이송형태에 따른 이류-확산 방정식을 각각 다르게 적용하여 모의한 결과, Engelund and Hansen 공식을 적용한 경우에는 Ackers and White 공식을 적용한 경우와 비교했을 때, 평수 및 홍수 조건에서 모두 하상변동량이 거의 없는 것으로 나타났다. 또한 Ackers and White 공식으로 2002년에 발생한 실제 수문사상을 적용하여 하상변동 모의한 결과, 소류사 이송형태의 이류-확산 방정식을 적용한 모의결과가 부유사 이송형태를 적용했을 경우 보다 실제 하상변동에 더 근접한 것으로 나타났다. The effects of the selection for sediment transport equations and advection-diffusion equations according to different sediment transport modes on the modeling results of bed changes were analyzed using the CCHE2D and compared with field data in this paper. The most suitable sediment transport equation and sediment transport mode for advection-diffusion equation were suggested for the upstream approached channel of the Nakdong River Estuary Barrage. The bed changes simulated by the Engelund and Hansen formula were very small in the modeling case for the low and high flow discharges compared with the case of the Ackers and White formula. Also, the numerical modeling with the actual hydraulic event in 2002 presents that the bed change result with the bed load transport type for advection-diffusion equation was close to the field measurement more than the suspended load type.

서해안 안면도 사질 조석대의 퇴적환경

This study investigated the depositional environment of the area of Anmyeondo in the mid-western coast of Korea. A total of 142 surface sediments were analyzed, and leveling survey was conducted as well in 12 transects at the sandy tidal flat in the area. The surface sediments are classified into several different types (slightly gravelly Sand, Sand, slightly gravelly sandy Mud, etc.) and they show fining-distribution toward the offshore. Textural parameters are characterized by being coarse, well sorted, positively skewed in the supratidal and intertidal flat, whereas being finer, poorly sorted, negatively skewed in the subtidal flat. According to the C-M diagram, the sediment transport modes are characterized by the mixed mode of bedload and graded suspension in supratidal and intertidal flat, and by graded suspension or uniform suspension in the subtidal flat. Histogram shows a bimodal distribution in the lower subtidal flat which is indicative of two sediment transport modes.

Palaeoflow reconstruction from fan delta morphology on Mars

Alluvial fans and deltas on Mars record past hydrological conditions. Until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models (DTMs), and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels. Neither method can distinguish between dilute (river-like) flows and dense (sediment-laden) flows, however, while the formation time scales for these two sediment transport modes differ by orders of magnitude. The objective of this paper is to compare DTM data quantitatively with a morphological model to infer sediment transport mode and formative duration. We present a quantitative morphological model for fan and delta formation that assumes as little as possible. The model calculates the growth of a sedimentary body in a crater lake, represented by a low-gradient, subaerial cone on top of a high-gradient, subaqueous cone. The volume of the cone is constrained by the influx of sediment while the elevation of the break in slope, that is, the shoreline, is constrained by the influx of water. The water and sediment fluxes were calculated with physics-based predictors based on the feeder channel. Small-scale morphology, such as crater wall irregularities, concavity of the fan surface and channel avulsion, is ignored. The model produces alluvial fans, stair-stepped fan deltas and Gilbert fan deltas as well as hitherto unidentified crater wall drapes. The parameters that determine which morphology emerges are the supply of sediment and water to the basin, the size of the basin and the duration of the flow. A direct comparison between the cone model and HRSC DTM data for five deltas and an alluvial fan demonstrates that single-event dilute flows of short duration (days to years) have created all of the deposits. Two Gilbert fan deltas were formed in overspilling crater lakes from long low-gradient upstream channels. One alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding. Three stair-stepped deltas were formed from short high-gradient upstream channels that only partially filled the crater lakes.

Grain size dependency in sandbank modeling for the case of uniform sediment

A 2‐D depth‐integrated stability analysis designed for marine tidal sandbanks is developed to investigate the relative influence of the grain size–dependent parameters on the simulated dynamics of the sandbanks for the case of uniform sediment. The model is applied to a real case in the North Sea. Assuming that the model is valid mainly in an area where bed load is the dominant sediment transport mode, the model taking into account the grain size dependencies gives a better prediction of sandbank occurrence than models neglecting these dependencies. All the grain size–dependent parameters are investigated separately. Focusing on the morphological time and wavelength of the sandbanks, this paper demonstrates that neglecting the grain size dependencies, especially the transport threshold, has a drastic influence on the dynamics of modeled sandbanks, especially on the sandbanks growth rate. The influence on the geometrical properties (wavelength and orientation) is less pronounced.

Effect of Time Scale on the Performance of Different Sediment Transport Formulas in a Semiarid Region

This note compares the performance of various sediment transport formulas for a semiarid region of southern Italy (Puglia region). The sediment transport that occurs in the main streams of the region has been monitored for about 30 years (1958–1986) and the measured data are available at monthly intervals. The field data were compared with those predicted from four formulas (Ackers-White, Engelund-Hansen, Yang, and Van Rijn) selected on the basis of the sediment transport mode, the theoretical aspects, and the sensitivity to basic physical properties. The study examines the ability of the formulas to adapt to local conditions, the influence of time scale on predictions, and the accuracy of the prediction varying the discharge. The Engelund-Hansen and Van Rijn formulas (suspended sediment transport) estimate well the sediment load and are largely unaffected by variations in time scale. For low sediment loads, these formulas were less reliable.

Variations in downstream grain-sizes to interpret sediment transport in the middle-lower Yangtze River, China: A pre-study of Three-Gorges Dam

In 2000 and 2003 before the closure of 3-Gorges Dam, numerous sediment samples were taken from the middle-lower Yangtze River channel to examine sediment transport processes and associated hydromorphological nature of the river. Analytical results show that the riverbeds consist mostly of medium to coarse sands and gravelly sands, and fine sand occurs locally, especially near the river coast. The results further indicate a downstream fining trend in riverbed sediment from Yichang to the river mouth, totaling about 1900 km long with 12 sediment zones (I-XII). These were identified as alternate coarse- and fine-grained sediment on the riverbed, although the zonation of I–III below Three-Gorges Dam site is weaker. The mode of sediment transport in the river is dominated by saltation (20–80%), followed by bed-load transport with 3–15%; transport by suspension is quite low. Grain-sizes associated with hydrological parameters have greater values in the Jingjiang Reaches (from Yichang to Chenglingji; unit stream power: 5–18 N m − 1 s − 1 , boundary shear stress: 14 Nm − 2 and mean flow velocity: 2–3.2 ms − 1 ), whereas the values obtained from Chenglingji downstream are considerably low (< 5 N m − 1 s − 1 , 1–4 Nm − 2 and < 0.7–1.5 ms − 1 ). These values, when compared with on-site measured velocity of the ADP flow column, revealed the erosive riverbed sediment transport in the Jingjiang Reaches, and the accumulative riverbed transport downstream, from Wuhan to the river coast. Hydrological parameters together with distribution of grain-sizes indicate a coarsening riverbed in the Jingjiang river, largely because damming peaked since the last half-century. This corroborates the weakening sediment zonation in the Jingjiang Reaches, which is expected to extend further downstream towards the river coast in response to the potential impact of 3-Gorges Dam in the coming decades.

Particle resuspension in the Columbia River plume near field

Measurements of suspended sediment concentration, velocity, salinity, and turbulent microscale shear in the near‐field region of the Columbia River plume are used to investigate the mechanisms of sediment resuspension and entrainment into the plume. An east‐west transect was occupied during spring and neap tide periods in August 2005 and May 2006, corresponding to low and high river discharge conditions, respectively. During the high‐discharge period the plume is decoupled from the bottom, and fine sediment resuspended from the bottom does not leave the benthic boundary layer. The primary modes of sediment transport associated with the plume are advection of sediment from the estuary and removal of sediment from the plume by gravitational settling and turbulent mixing. In contrast, the plume is much less stratified during low‐discharge conditions, and large resuspension events are observed that entrained sediment through the water column and into the plume. Our measurements indicate that two factors control the magnitude and timing of sediment resuspension and entrainment: the supply of fine sediment on the seabed and the relative influence of tidal turbulence compared with buoyancy input from the river. The latter is quantified in terms of the estuary Richardson number RiE. The magnitude of vertical turbulent sediment flux is correlated with RiE during the low‐flow period when there is a sufficient supply of bottom sediment in the near‐field region. Such sediment resuspension may be an important mechanism for the delivery of bioavailable micronutrients to the plume during the summer.

Clinoform Progradation by Turbidity Currents: Modeling and Experiments

Abstract Clinoform morphologies and growth patterns are typically viewed as the product of a particular mode of sediment transport, but process-specific models for their generation from turbidity currents are few, despite observations of turbidity currents on modern clinoforms and turbidites in ancient clinoform deposits. We present a simple morphodynamic model, supported by laboratory experiments, which shows how net-depositional turbidity currents can build sedimentary clinoforms. Most conceptual models for clinoform evolution assume that under constant (sea level, sediment supply) forcing progradation occurs via continuous basinward migration of a depocenter localized near the clinoform rollover. Abrupt basinward shifts in depocenter location are therefore an indication of allogenic variability in forcing. In contrast, our results document a unique style of progradation driven by autogenic cycles of slope steepening, sediment bypass, and depositional backstepping on the foreset slope. In experiments designed to investigate this slope–flow feedback, deposition from a continuous turbidity current transporting fine sand and silt repeatedly steepened a clinoform foreset to a graded slope which bypassed sediment to the slope base, depositing a sediment lobe. Continued deposition then caused the lobe to backstep up the slope, building a lower-slope foreset and eventually reinitiating the cycle. Our model shows how this cyclic depositional pattern arises from a morphodynamic feedback between the foreset gradient and the rate of sediment resuspension by the overriding turbidity current. Using our model to scale experimental results to the field, we predict gradual foreset steepening in prograding turbidity-current- dominated clinoform strata, with slope grading and cyclic deposition favored where these clinoforms build over steep basin slopes under conditions of high sediment supply and/or lateral confinement. We demonstrate how our results can add new insight to process-based interpretation of clinoform strata by application to a modern and an ancient field example.

Deep-water and fluvial sinuous channels—Characteristics, similarities and dissimilarities, and modes of formation

High-resolution 3D seismic data of several subsurface examples reveal significant differences in internal architecture and evolution of fluvial and deep-water sinuous channel systems, although there are many similarities in external morphologies of both systems. Channel migrations or shifts in fluvial systems, with point-bar scrolls, are relatively continuous laterally and show a downstream component; they are commonly a single seismic phase thick, with flat tops. In deep-water systems, channel migrations or shifts, with or without point-bar scroll-like features, may be lateral, either continuous or discrete, and laterally to vertically aggrading, again either continuous or discrete; they are single to multiple seismic phases thick, with or without a downstream component. Even the most laterally migrated channel complex commonly aggrades, to varying degrees, from the inside to the outside of sinuous loops. Similarities between fluvial and deep-water sinuous channel systems discussed here imply that sinuosity enhancements in both cases are the result of gradual processes, involving interaction of flows, sediments and alluvial plain or seafloor in attempts to build equilibrium profiles. Flat gradients, high width to depth ratios of valleys/channel belts, fine sediment grain sizes, a certain degree of bank cohesiveness, and presence of secondary circulations in flows were pre-requisites in both systems. However, a number of factors appear to have caused major differences in the internal architecture and modes of evolution of fluvial and deep-water channels. These include differences in (1) density contrasts of flows relative to ambient fluids, (2) entrainments of ambient fluids into flows, (3) effects of centrifugal and Coriolis forces on flows, (4) frequency, volume and duration of steady vs. catastrophic flows, (5) modes of sediment transport, and (6) effects of sea level changes on deposition. Furthermore, within deep-water systems, changes in flow parameters and sediment grain size can cause erosion, bypassing or deposition in space and time and result, through cuts and fills, in sinuous channels with lateral migrations, vertical aggradations and combinations thereof.