late quaternary paleohydrology of the madre de dios river southwestern amazon basin peru abstract late quaternary climatic and hydrologic variability triggered changes in fluvial deposition and erosion along the course of the madre de dios river peru the largest tributary basin of the madeira basin itself the largest tributary basin of the amazon three laterally extensive quaternary age terrace tracts are present within the madre de dios basin analysis of sedimentary facies present in the modern cut banks and terraced sequences along with radiocarbon dates on fossil wood and leaf material preserved in the terraced strata allow reconstruction of the late quaternary depositional history of the sedimentary sequences including determination of the approximate timing of aggradation and downcutting episodes and its relationship to the timing of past climate change in this portion of the amazon basin and beyond the quaternary sediments underlying the terraces most often recorded deposition in a coarse grained meandering fluvial system the t3 terrace the highest terrace is underlain by the miocene ipururi formation which is unconformably overlain by the late miocene pleistocene 48 000 cal yrs bp madre de dios formation a multistory coarse sandy to gravelly channel and point bar complex the latter was downcut before 29 850 100 cal yrs bp this downcut landscape was infilled by meandering fluvial strata characterized by gravelly channel deposits in a sequence dominated by floodplain and lateral accretion deposits these strata were in turn downcut to form the t2 terrace before 11 970 100 cal yrs bp a third episode of aggradation resulted in the deposition of a sand dominated meandering channel complex that infilled the t2 valley and was subsequently downcut after 3780 50 cal yrs bp this most recent terrace is infilled by the modern fluvial sediment which has been actively aggrading since at least 870 50 cal yrs bp importantly the madre de dios fluvial system actively aggraded between 30 000 and 25 000 cal yrs bp and likely much younger as dated samples were thus far only found near the base of the t2 sequence this observation implies that some combination of 1 increased precipitation and decreased temperature 2 decreased evapotranspiration and increased runoff 3 increased andean glacial erosion and increased sediment supply and 4 decreased atmospheric co 2 hence decreased rain forest primary productivity and altered rain forest physiology ecology entering the last glacial maximum period brought about increased floodplain deposition in the southwestern amazon elsewhere in the amazon basin few if any fluvial sediments of this age range have been observed the start of the next major phase of aggradation coincided with the younger dryas and suggested that floodplain sedimentation in the lowlands was again related to cold and wet conditions in the adjacent highlands and perhaps in the lowlands as well and that madre de dios history was also tied to large scale global climate this aggradation may have continued throughout the early and mid holocene until at least 3 780 cal yr bp if so and this is uncertain this episode of sedimentation took place during a dry period

facies and architectural element analysis of a meandering fluvial succession the permian warchha sandstone salt range pakistan abstract the 30 to 155 m thick early permian artinskian warchha sandstone of the salt range pakistan is a conglomerate sandstone and claystone succession within which seven lithofacies types gt st sp sr sh fl and fm occur in a predictable order as repeated fining upward cycles common sedimentary structures in the conglomerates and sandstones include planar and trough cross bedding planar lamination soft sediment deformed bedding compound cosets of strata with low angle inclined bounding surfaces and lags of imbricated pebbles structures in the finer grained facies include desiccation cracks raindrop imprints caliche nodules and bioturbation groups of associated facies are arranged into nine distinct architectural elements channels gravel bars sandy bedforms downstream and laterally accreting barforms sand sheets crevasse splays levees floodplain units and shallow lakes which is consistent with a fluvial origin for the succession the types of architectural elements present and their relationship to each other demonstrate that the warchha sandstone preserves a record of a meandering river system that drained the northern margin of gondwanaland the dominance of fine grained floodplain facies over gravel grade channel base facies and the widespread occurrence of large scale lateral accretion elements supports the interpretation of a high sinuosity meandering fluvial system in which channel bodies accumulated via the lateral accretion of point bars but in which the active channels covered only a small part of a broad floodplain at any time instant although the regional and temporal distribution of these deposits is complex in broad terms the lower part is dominated by stacked multistorey channel bodies whereas single storey channel elements isolated in abundant fine grained floodplain deposits dominate the middle and upper parts of the formation

facies architecture and depositional dynamics of the upper permian rangal coal measures bowen basin australia the upper permian rangal coal measures in the northern bowen basin australia accumulated during rapid basinal aggradation in a retroarc foreland basin setting they reflect peatland deposition towards the close of a long lived climatic regime that came to an abrupt termination at the permian triassic boundary which is well developed in the newlands mine highwall and adjoining borefield six lithofacies are represented in the newlands district 1 erosionally based vertically stacked ribbon and sheet like sandstone bodies up to 30 m thick and 1000 m wide 2 heterolithic lobes and wedges 3 interbedded siltstone and sandstone sheets 4 interlaminated claystone and coal stringers 5 laterally extensive bituminous coal sheets and 6 laterally extensive laminated carbonaceous siltstone sheets this facies assemblage is interpreted to correspond to six alluvial cold climate depositional environments 1 trunk river channels and crevasse feeder channels 2 levee bank proximal crevasse splay 3 distal splay overbank 4 marsh 5 peat mire and 6 floodbasin lake respectively the sequence architecture at newlands reveals that a prolonged period of peat deposition was progressively terminated by northward stepping lobes of fluvial sediment in the south and by lacustrine drowning in the north exceptionally well developed composite elongate crevasse splay microdeltas up to 26 m thick and 3000 m long indicate that crevassing was responsible for the localized emplacement of thick sediment packages on the proximal floodplain in the absence of active siliciclastic sedimentation peat mire environments expanded from the distal floodplain extending across abandoned depositional lobes the geometry of these deposits reflects in large part accommodation space developed by the compaction of the peat precursor of the thick and laterally extensive upper newlands seam sequential compaction of peat by clastic overburden controlled the nucleation and location of succeeding clastic packages the behavior of the peat under compactional load largely controlled the lateral facies mosaic and stacking pattern of depositional units on a district scale

levee morphology and sedimentology along the lower tuross river south eastern australia levees on the lower tuross river in south eastern australia reflect a complex interplay between depositional and erosional processes stream power conditioned primarily by valley width is the key determinant of levee morphology and sedimentology in this confined valley setting three styles of levee are described the rewlee levee is functionally linked to a flood channel in narrow valley settings 250 m these levees contain a diverse facies assemblage characterized by various scales of erosion surfaces vertical accretion on levees has produced conditions under which stream power values exceed the threshold for catastrophic floodplain stripping the levee at the mortfield site is associated with less confined settings valley width 500 600 m which present lower flood stage and stream power conditions this levee hosts a wide range of facies but erosion surfaces are seldom observed in the more open valley setting at the central site valley width 700 1000 m levees comprise uniform fine grained deposits which grade to pronounced distal floodplains with backswamps as levees reflect a combination of within channel and overbank processes both depositional and erosional these geomorphic features influence the character and sedimentology of adjacent landforms and the associated alluvial architecture of the basin

variations in natural levee morphology in anastomosed channel flood plain complexes abstract natural levees are common features of alluvial river systems yet their origin and evolution are poorly understood in this paper we present morphologic and sedimentologic data from two anastomosed rivers and offer a hypothesis of natural levee growth in these systems based on mechanisms of sediment transport in settings where floodbasins fill at the same rate as the channel levees form by turbulent diffusion of suspended sediment away from a high velocity thread into a floodbasin of relatively stagnant water the theory of diffusive transport suggests that these levees should be narrow steep and display abrupt decreases in grain size due to rapid decreases in carrying capacity with distance into the floodbasin in environments where an appreciable water surface slope is maintained between the main channel and the floodbasin levees form by advection of sediment out of the channel and into the floodbasin advective transport theory indicates that these levees should be broad and gently sloped with grain sizes gradually decreasing away from the main channel natural levees occurring in the anastomosed reach of the upper columbia river in se british columbia display significantly different morphology from levees in the cumberland marshes region of the lower saskatchewan river in east central saskatchewan at the upper columbia site the rise in stage of the floodbasin water nearly keeps up with that of the channel water because of good communication between channel and floodbasins through crevasses this inhibits the establishment of a water surface slope and the bulk of the escaping sediment is deposited close to the channel in contrast the cumberland marshes region is characterized by wide and volumetrically large floodbasins these conditions keep floodbasin water surface elevations relatively low and maintain an appreciable elevation head between the channel and its floodbasin fostering levee growth by advective transport

observations and models of inertial waves in the deep ocean the structure of the inertial peak in deep ocean kinetic energy spectra is studied here records were obtained from polymode arrays deployed in the western north atlantic ocean 40 w to 70 w 15 n to 42 n the results are interpreted both in terms of local sources and of turning point effects on internal waves generated at lower latitudes in most of the data there is a prominent inertial peak slightly above f however the peak height above the background continuum varies with depth and geographical environment three classes of environment and their corresponding spectra emerge from peak height variations class 1 is the 1500 m level near the mid atlantic ridge with the greatest peak height of 18 db class 2 includes a the upper ocean depth less than 2000 m b the deep ocean depth greater than 2000 m over rough topography and c the deep ocean underneath the gulf stream with intermediate peak height of 11 5 db class 3 is the deep ocean over smooth topography with the lowest peak height of 7 5 db near f the horizontal coherence scale is 0 60 km at depths from 200 m to 600 m and the vertical coherence scale is 0 200 m in the lower part of the main thermocline and 0 1000 m in the deep water the phase difference suggests a downward energy propagation in the lower thermocline and standing waves in the deep water a one turning point model is developed to describe inertial waves at mid latitudes based on the assumption that inertial waves are randomly generated at lower latitudes global generation where their frequency wave number spectrum is given by the model of garrett and munk 1972 1975 using the globally valid wave functions obtained by munk and phillips 1968 various frequency spectra near f are calculated numerically the model yields a prominent inertial peak of 7 db in the horizontal velocity spectrum but no peaks in the temperature spectrum the model is latitudinally dependent the frequency shift and bandwidth of the inertial peak decrease with latitude energy level near f is minimum at about 30 and higher at low and high latitudes the observations of class 3 can be well described by the model a low zonal wave number cutoff is required to produce the observed frequency shift of the inertial peak the differences between the global generation model and the observations of class 1 and class 2 are interpreted as the effects of local sources a locally forced model is developed based on the latitudinal modal decomposition of a localized source function asymptotic eigensolutions of laplace s tidal equation are therefore derived and used as a set of expansion functions the forcing is through a vertical velocity field specified at the top or bottom boundaries of the ocean for white noise forcing the horizontal velocity spectrum of the response has an inertial peak which diminishes in the far field with the forcing located at either the surface or the bottom several properties of the class 2 observations can be described qualitatively by a combination of the global and local models the reflection of inertial waves from a turbulent benthic boundary layer is studied by a slab model of given depth frictional effects are confined to the boundary layer and modeled by a quadratic drag law for given incident waves reflection coefficients are found to be greater than 0 9 for the long waves which contain most of the energy this result suggests that energy containing inertial waves can propagate over great distance as is required by the validity of the model of global generation

the chronology and long term dynamics of a low energy river system the kelvin valley central scotland the long term holocene channel and floodplain dynamics of a low gradient low energy fine grained aggradational fluvial system within a formerly glaciated landscape in central scotland the kelvin valley are described from a series of sediment stratigraphic transects and 12 14c assays in a headwater reach between kirkintilloch and kilsyth the 14c assays and dated archaeological sites on the floodplain together suggest that the river kelvin ceased to aggrade more than 2000 years ago probably much more so the 4 6 m of channel and floodplain deposits are almost entirely of early to mid holocene age the kelvin valley is characterized despite its low flow characteristics by a highly variable floodplain architecture in which some transects suggest long term channel stability and strong partitioning of floodplain sedimentation and others indicate high channel mobility this variation makes the application of general models of fluvial evolution difficult copyright 2007 john wiley sons ltd

annual cycle and depth penetration of wind generated near inertial internal waves at ocean station papa in the northeast pacific abstractthe downward propagation of near inertial internal waves following winter storms is examined in the context of a 2 yr record of velocity in the upper 800 m at ocean station papa the long time series allow accurate estimation of wave frequency whereas the continuous data in depth allow separation into upward and downward propagating components near inertial kinetic energy kein dominates the record at all measured depths energy in downgoing motions exceeds that of upward propagating motions by factors of 3 7 whereas kein is elevated by a factor of 3 5 in winter relative to summer the two successive winters are qualitatively similar but show important differences in timing and depth penetration energy is seen radiating downward in a finite number of wave groups which are tagged and catalogued to determine the vertical group velocity cgz which has a mean of about 1 5 10 4 m s 1 13 m day 1 case studies of three of these are presented in detail downward energy flux is estimated as cgz

evolution of the semidiurnal m2 internal tide on the continental slope of the northern south china sea kinetic energy spectra from a site on the continental slope in the south china sea reveal that significant peaks appear at some nonlinear interaction frequencies namely m 3 m 1 m 2 and fm 1 m 1 f where f is the inertial frequency m 1 is the diurnal internal wave and m 2 is the lunar semidiurnal internal tide a possible generation mechanism of m 3 is explored analysis of bicoherence and shear spectra suggests that strong m 3 is indirectly associated with parametric subharmonic instability psi of m 2 in another word under the effect of psi the energy of m 2 is first transferred to m 1 then via other nonlinear coupling some nonlinear waves e g fm 1 m 3 are generated moreover m 1 is also present at another site near the bottom of the continental slope the shear spectra from these two sites show for the first time that m 1 can be significantly distinguished from lunar diurnal o 1 and lunisolar diurnal k 1

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

observations of overturning in the thermocline the context of ocean mixing abstract the time sequence of events that lead to internal wave breaking and ocean turbulence is investigated data are obtained from depths 100 400 m with a repeat profiling ctd and a coded pulse doppler sonar the instruments were deployed from r p flip during february march 1995 while stationed 30 km west of point arguello california as an aspect of the marine boundary layer experiment although the water depth at the site is 1500 m both rms shear and diapycnal diffusivity as inferred from the average rate and size of overturning events increase with depth below 250 m a deep source of wave energy is implied depth time series of 6 4 m shear s 2 m strain n2 n2 where n is the buoyancy frequency 6 4 m gradient richardson number ri n2 s2 and 2 m effective strain rate the depth derivative of ctd inferred vertical velocity are obtained at 4 minute intervals over a 9 day 100 400 m domain the occurrence of overturns static instabilities of vertical scale 2 m in the observed density

controls on natural levee development in the columbia river british columbia canada natural levees of the columbia river near golden british columbia were investigated to identify the mechanisms that control levee development and morphology topographic profiles of 12 levee pairs were surveyed and measurements of water surface elevation flow velocity flow direction and turbidity were obtained during an average magnitude flood 1ae2 years recurrence interval sedimentation rates and grain size distributions were measured from sediment traps placed along levee to floodbasin transects results show that water and sediment exchange between the channel and floodbasin was mainly by advection during flooding local floodbasins behave more as efficient water pathways than water storage features resulting in down valley floodbasin flows capable of limiting basinward growth of levees levee shape results primarily from two independent factors 1 maximum channel water stage which limits levee height and 2 floodbasin hydraulics which control width in the columbia river the competence of floodbasin flows results in relatively narrow and steep levees natural levees grow under two general conditions of deposition as governed by flood stage elevation relative to levee crest elevation front loading and back loading during large floods when crests are inundated front loading preferentially aggrades the proximal portions of levees with sediment directly from the channel thus increasing levee slope during average or below average floods when many levee crests are not overtopped back loading preferentially aggrades the distal levee areas and floodbasin floor reducing levee slope in the study area a balance between front and back loading sustains these narrow and steep levee shapes for long periods reflecting an equilibrium between hydraulic regime floodplain morphology and deposition

large scale facies sequences in alluvial overbank environments abstract gradational coarsening upwards or fining upwards sequences order of meters thick in overbank environments can be produced by progressive crevasse splay levee progradation or abandonment while the channel belt remains unchanged in position in contrast meter scale facies sequences related to periodic channel bell avulsion may show relatively abrupt changes in facies and paleocurrent direction simulation models suggest that the number of such avulsion related facies changes in any overbank sequence bounded above and below by channel belt deposits is on the order of 1 to 10 this is confirmed using an ancient example in this example the average thickness of each avulsion bounded overbank facies sequence was 3 m assuming an average recurrence interval for avulsions of about 1 000 ye rs the mean overbank deposition rate was about 3 mm per year

strong inertial currents and marginal internal wave stability in the central north sea solar insolation stabilizes the water column and suppresses vertical exchange observations from the central north sea clearly show that increased heating in summer is accompanied by enhanced de stabilizing vertical current differences shear surprisingly to such extent that the equilibrium state is marginally stable under calm weather conditions the shear is predominantly generated by near inertial motions while the internal wave spectrum primarily results from nonlinear interaction between the dominating tidal and near inertial motions in terms of the associated enhanced vertical mixing across the largest vertical temperature gradients shelf seas are not different from the abyssal ocean despite the proximity to energy sources near boundaries in the former by the lack of sufficiently strong wind and tidal mixing this internal mixing is considered to be responsible for the diapycnal transport of nutrients leading to the observed increase in near surface values and triggering the late summer phytoplankton bloom

what is a fluvial levee abstract fluvial levees are elevated partitions between channels and floodplains because of their character and position levees may provide critical controls on and insights into geomorphic processes that determine the distribution of water and sediment within river systems few studies have analysed the character distribution sedimentology and processes that form levees in modern depositional environments characterisation of levee deposits from the mississippi river continues to form the basis for most levee interpretations from the rock record this discussion paper assesses the reliability of interpretations of levee deposits in numerous examples from the rock record and their associated inferences for river style this uncertainty reflects the lack of definitive sedimentological attributes for levee deposits their limited preservation potential and the fact that levee identification in the rock record is inhibited by the reliance on geometric descriptors or indirect associations between channel and floodplain facies given these concerns it is suggested that geomorphologists and sedimentologists need to recognise the limitations of our present knowledge of levees and work towards a more systematic understanding of these significant fluvial landforms in the full spectrum of modern and ancient river settings

caesium 137 in sandy sediments of the river loire france assessment of an alluvial island evolving over the last 50 years recent sedimentological and morphological evolution of an island in the river loire france was investigated using the 137cs method this study describes the morphological adjustment of the island in the last 50 years which corresponds to the increased bed incision of this sandy multiple channel environment because of among other things the increase in sediment extraction up to 1995 the results show that some 137cs can be retained by sandy particles potentially in clay minerals forming weathering features included in detrital sand grains from a morphological perspective significant lateral erosion can be observed in the upstream part of the island while a weak lateral accretion occurs in its downstream section data about 137cs and aerial photographs show that the morphology of the island margins has undergone significant changes leading to a lateral migration while the centre of the island has remained relatively stable or is slowly eroding the migration of the island depends on 1 the withdrawal of inherited preincision morphological units such as levees or the development of new units such as a channel shelf 2 water and sediment supply from surrounding channels during flood events 3 preferential sediment trapping 20 mm year 1 from the presence of riparian vegetation on the bank of the secondary channel that is subject to narrowing the sedimentological and morphological response of the island in the context of incision of the loire river bed is expressed mainly by lateral migration and secondarily by a low vertical adjustment

unconfined alluvial flow processes recognition and interpretation of their deposits and the significance for palaeogeographic reconstruction abstract palaeogeographic interpretation of the sedimentary rock record depends on correct recognition from the preserved evidence of the processes responsible for transporting and depositing the sediment this in turn depends on robust knowledge transfer from previous workers and the successful exchange of ideas between workers requires consistent use of a well defined vocabulary we have identified serious breakdowns in all these interpretation steps in the case of terrestrial unconfined flow and its deposits and these failures are leading to unreliable environmental and climatic interpretation this is significant because such alluvial deposits commonly form a majority of the rock record of continental environments working from the basic principles of geomorphology and fluid dynamics we have undertaken a wide ranging analysis of the nature of out of channel flow and from this make predictions about the characteristics of its deposits we identify the range of possible locations and conditions that lead to the development of unconfined flow review the processes operating in each case and examine the range of lithological features that can be produced by these processes this allows us to evaluate the reliability of the criteria claimed for identification of out of channel flow deposits and examine how our new insights might alter palaeoclimatic and palaeogeographic reconstructions published previously by others the sedimentary record of unconfined flows is much more diverse and complex than usually portrayed the received wisdom that the record of unconfined flow consists solely of upwards fining thin beds produced from shallow waning flows is shown to be flawed a wide range of lithofacies are possible and the variation in both flow steadiness and uniformity needs to be taken into account the previously published criteria for recognition of flows of this type are not diagnostic of process or location unconfined flow deposits cannot reliably be identified from grain size or bed thickness similar lithofacies may develop in a wide range of geomorphic and climatic settings because the deposits solely reflect the local flow conditions and sediment availability we recommend that the terms sandflat and sheetflood should not be used in sedimentological accounts because there is no longer a safe informal usage for either contradictory application of these terms and lack of robust definitions is leading to significant misunderstanding of palaeogeography and process our analysis should improve reconstruction of past terrestrial environments because it reveals more clearly the true variety of possibilities for the occurrence of unconfined flow and the resultant deposits enhanced understanding of the inherent uncertainties and realisation of the wider range of plausible alternative explanations should help resolve apparent contradictions with independent indicators of climate or geographic position

natural levee evolution in the rhine meuse delta the netherlands during the first millennium ce this paper presents reconstructions on natural levee development in the rhine meuse delta the netherlands during the first millennium ce covering the full delta plain it is the first study that performs this on a delta scale which allows seeing the delta wide trends on levee forming controls and their feedbacks we mapped the levee morphology and elevation by combining lidar imagery lithological borehole data soil mapping radiocarbon dates archaeological data and gis reconstruction techniques from the detailed levee reconstructions we quantified natural levee dimensions and evaluated the temporal changes therein the dimensions and the changes therein were then linked to external forcings increasing suspended sediment load variable flooding intensity and to natural preconditions e g delta plain width flood basin configuration we show that natural preconditions are an important control on levee shape this is demonstrated for the upper delta where the relatively narrow delta plain combined with strong compartmentation i e the occurrence of many alluvial ridges and enclosed flood basins caused the flood levels to be amplified allowing the natural levees to grow relatively high compartmentation also seems to have stimulated trapping of coarse grained overbank sediments explaining the clear downstream trend in levee width this effect was probably further aided by the clearance of the riparian forests mainly in the upstream and central delta which caused the coarser fraction of the suspended load to be further dispersed into the flood basin leading to wider levees in the first millennium ce several new river courses formed that avoided the areas of natural levee relief of abandoned alluvial ridges on these fossil alluvial ridges the topographical expression gradually reduced because of widespread flood basin trapping of overbank sediment which led to topographic levelling the natural levees that formed during this period along the new courses appear to be relatively high compared to precursor generations in the upper and central delta this is most likely related to the increased suspended sediment supply and intense flooding regime during their formation the hypotheses generated with this new delta wide overview help to better understand the controls in the development of levees which are important elements in river landscapes and in fluvial sedimentary records 2017 elsevier b v

moored observation of abyssal flow and temperature near a hydrothermal vent on the southwest indian ridge four moorings were deployed near dragon flag an active hydrothermal vent in the valley of the southwest indian ridge the goal was to examine the variability of currents and temperature which will guide the trajectory of spreading plumes the mean current was cross isobath and the circulation was characterized by a submesoscale circulation observed currents also showed fluctuations with periods of 1 15 days the inferred phase speed and wavelength for the wave with a period of 4 4 day are 10 4 km d 1 and 45 8km respectively which are consistent with the topographic rossby wave theory the persistent warming tendency with corresponding variation of salinity based on background s properties may be caused by background circulation and divergence of the water column the warming or cooling episodes were most likely as signatures of isopycnal surface depression or uplifting induced by the moving of mesoscale eddies well resolved rotary spectra exhibited important nonlinear interactions between inertial and semidiurnal tide in the velocity and temperature records amplification of near inertial currents in the near bottom is also exposed these discoveries provided new evidence for the nonlinear interaction and trapped near inertial waves by the ridge which occurred in the deep ocean of the southern hemisphere such nonlinear interaction may represent a significant energy loss pathway for the internal waves and part of the decay of such motion would likely result in increased mixing to maintain the abyssal stratification enhanced near inertial motions can play a major role for the local advection of hydrothermal plumes

the effect of a bottom shelf front upon the generation and propagation of near inertial internal waves in the coastal ocean abstract a three dimensional nonlinear baroclinic model in cross sectional form is used to study the generation and propagation of wind forced near inertial internal waves in a coastal region in the presence of a bottom front initially calculations are performed with the front in an infinite domain region by this means coastal effects are removed the initial response is in terms of inertial oscillations in the surface layer however in the frontal area these are modified by interaction through the nonlinear momentum terms with regions of positive and negative vorticity associated with the alongfront flow this leads to a change in amplitude phase and frequency of the inertial current and a resulting ekman pumping that drives near inertial internal waves in the frontal region on the positive vorticity side of the front these waves are at the superinertial frequency and rapidly propagate away on the negative side they are at the subinertial frequency and are trapped and inertial energy leaks to dep

elevation adjustments of paired natural levees during flooding of the saskatchewan river natural levees control the exchange of water between an alluvial channel and its floodplain but little is known about the spatial distribution and evolution of levee heights the summer 2005 flood of the saskatchewan river cumberland marshes east central saskatchewan inundated large areas of floodplain for up to seven weeks forming prominent new deposits on natural levees along main stem channels measurements of flood deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre flood levee in 80 of the sites though no clear relationship exists between deposit thickness and magnitude of height difference only 16 of the pairs displayed thicker deposits on the higher levee half of which occurred at sites where relatively clear floodbasin waters re entered turbid channels during general flooding difference in crest elevation e between paired levees is approximately log normally distributed both before and after the flood though with different mean values supplemental observations from tank experiments indicate that during near bankfull flows temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension during floods preferential deposition in lows tends to even out crest heights copyright 2009 john wiley sons ltd

fluvial architecture and reservoir compartmentalization in the oligocene middle frio formation south texas abstract seeligson stratton and agua dulce fields south texas are being studied as part of a gas research institute department of energy state of texas cosponsored program designed to develop and test methodologies and technologies for gas reserve growth in conventional reservoirs in mature gas fields over the last five decades each field has produced approximately 2 tcf of gas from middle frio reservoirs alone recent drilling old well workover results and reservoir pressure data however point to the possibility of additional reserves within these fields the middle frio oligocene is composed of sand rich channel fill and splay deposits interstratified with floodplain mudstones all forming part of the gueydan fluvial system channel fill deposits are 30 ft 9 m thick and 2 500 ft 76 m wide splay deposits are as much as 20 ft 6 m thick proximal to channels and extend as much as 2 mi 3 km from channels channel fill and associated splay sandstones are reservoir facies porosity 20 percent permeability 10 s to 100 s md floodplain mudstones and levee sandy mudstones impede or obstruct flow and separate individual reservoirs and compartments both vertically and laterally deposition on an aggrading coastal plain resulted in a continuum of fluvial architectural styles that has important implications for reservoir compartmentalization relatively slow aggradation resulted in laterally stacked channel systems whereas more rapid aggradation resulted in vertically stacked channel systems in seeligson field laterally stacked architecture alternates with vertically stacked architecture through the 2 000 ft 610 m thick middle frio section in stratton and agua dulce fields the same general alternation in architectural modes exists through the 2 500 ft 763 m thick middle frio section in stratton and agua dulce however the reservoir zones composed of laterally stacked architecture are not laterally continuous instead the laterally stacked architecture locally changes into a vertically stacked architecture because laterally stacked sandstone bodies lead to separate but potentially leaky reservoir compartments and vertically stacked sandstone bodies favor more isolated reservoir compartments a high potential for reserve growth through the identification of untapped poorly drained and bypassed gas reservoir compartments exists in each of these fields differences in reservoir architecture also must be taken into account as part of exploitation strategies

influence of coastal fronts on near inertial internal waves 1 a numerical model with a coastal boundary and near shore surface or bottom front is used to examine the role of the coast and front upon the generation and propagation of wind induced near inertial internal waves when stratification extends to the coast near inertial internal waves are produced at the coastal boundary however when the near shore region is well mixed the source of near inertial internal wave production is the front near inertial internal waves generated on the positive vorticity side of the front propagate away in the horizontal those generated on the negative vorticity side are trapped although some vertical propagation occurs when a coastal boundary is included significant inertial currents are found at depth phase shifted by 180 from the surface this goes some way to explain the recent observed distributions of inertial energy found in near coastal measurements

a suburban inter dike river reach of a large river modern morphological and sedimentary changes the bratislava reach of the danube river slovakia abstract the paper outlines contemporary geomorphic and sedimentary changes 1949 2007 in the suburban inter dike reach of the danube river in bratislava underpinning requirements of its management the studied river reach represents the right bank inter dike area of a tectonically determined bend of the danube river which is about 5 km long with a radius of 1 5 km the landform and floodplain roughness classification schemes show variations in hydraulic and depositional conditions during flooding investigation of landform and floodplain roughness changes and the bank retreat rate is based on the multitemporal interpretation of aerial photographs sedimentological analysis of 10 borings and 20 pit exposures helped to delimit the morphostratigraphic units the process and the rate of the vertical accretion of the modern floodplain were investigated by sedimentological and dendrochronological methods the behaviour of the study reach is dependent on upstream dams in austria dams produce changes in the suspended load regime and a steady riverbed erosion of 2 to 3 5 cm occurs upstream of the study river reach near the slovak austrian border the cunovo dam downstream expediates upstream channel filling in spite of the ongoing channel gravel mining in the danube channel this has resulted in channel bed aggradation of about 1 m since 1992 the bank retreat of about 100 m during 1949 2007 was caused by the natural bank erosion processes as well as by channel straightening as a flood control measure for bratislava the bank shift resulted in the development of the new levee the current overbank deposits differ from the older gravels consisting of a fine grained alluvium varying in thickness from 0 5 m to 1 m the lithofacies of three flood deposits march 2002 august 2002 and september 2007 were examined overbank sediments differentiate with distance from the bank and vertically suburban settings of the study reach and the flood control measures along with the external forcing dams induced changes in channel morphology as well as in floodplain roughness variability this has resulted in changes in the present floodplain sedimentary conditions channel forms and biodiversity the landscape evolved through three distinct evolutionary phases

prediction of channel connectivity and fluvial style in the flood basin successions of the upper permian rangal coal measures queensland predicting the presence and connectivity of reservoir quality facies in otherwise mud prone fluvial overbank successions is important because such sand bodies can potentially provide connectivity between larger neighboring sand bodies this article addresses minor channelized fluvial elements crevasse splay and distributary channels and attempts to predict the connectivity between such sand bodies in two interseam packages of the upper permian rangal coal measures of northeastern australia channel body percent as measured in well logs was 2 in the upper aries castor interseam and 17 in the lower castor pollux interseam well spacing were too great to allow accurate correlation of channel bodies the ob river siberia was used as a modern analog to supply planform geometric measurements of splay and distributary channels so that stochastic modeling of channel bodies was possible the resulting models demonstrated that 1 channel body connectivity is more uniform between minor distributary channels than between crevasse splay channels 2 relatively good connectivity is seen in proximal positions in splays but decreases distally from the source as channel elements diverge and 3 connectivity tends to be greater down the axis of splays with more isolated channel bodies occurring at the margins

sedimentology of pennsylvanian quartzose sandstones of the lee formation central appalachian basin fluvial interpretation based on lateral profile analysis abstract lateral profiling including bounding surface and architectural element analyses are utilized to demonstrate a fluvial origin for the quartzose sandstones of the lee formation internal architecture of the sandstones consists primarily of multistorey and multilateral channel bodies individual channel elements up to 20 m thick contain a complex hierarchy of bedform deposits the primary depositional elements within the channels were downstream accreting mid channel macroforms channel elements frequently contain deposits of more than one macroform reconstruction of the macroforms reveals accretion primarily by superposed bedforms that migrated down a low angle front steeper giant foresets transitional along flow with the low angle facies indicate that the macroform episodically developed a steep slipface the uppermost channels within the rockcastle member contain macroform elements with components of lateral accretion interpreted as deposits of alternate bank attached macroforms other depositional elements recognized within channel fill deposits are minor channel sandy bedform gravity flow attributed to bank slumping and channel bottom elements the latter element is contained within a facies sequence that suggests rising to flood to waning stage deposition in general deposition probably occurred during relatively high stage little evidence of low stage flow was recognized subordinate fine grained facies are interpreted as levee and overbank deposits the greater part of the lee formation was deposited in deep low sinuosity bedload dominated fluvial channels strongly unimodal paleocurrents lack of facies that suggest low stage reworking and paucity of lateral accretion features indicate deposition in a single channel system i e a low braiding index

on the interaction of internal tides over two adjacent sills in a fjord 1 the problem of to what extent two topographic features namely adjacent sills in a fjord interact to modify the internal waves between the sills is considered using a two dimensional vertical slice nonhydrostatic model motion is generated by forcing with a barotropic tide at the m2 frequency calculations are performed with a range of sill depths hs and sill separations l initially a single sill is considered and a progressive internal tide lee waves and a baroclinic jet are formed in the region of the sill when a second sill is introduced the intensity of the sill jet is reduced and a standing internal tide is generated between the sills with an associated increase in mixing and change in tidal energy flux however as the sill separation increases the energy flux increases toward its single sill value for higher harmonics of the tide which have a wavelength shorter than the intersill separation their magnitude is increased for certain sill separations l due to focusing with an associated broadband resonance in essence nonlinear interaction of waves between the sills increases mixing which explains the observed enhanced mixing found in observations made in such regions

variations in fluvial deposition on an alluvial plain an example from the tongue river member of the fort union formation paleocene southeastern powder river basin wyoming u s a abstract the tongue river member of the paleocene fort union formation is an important coal bearing sedimentary unit in the powder river basin of wyoming and montana we studied the depositional environments of a portion of this member at three sites 20 km apart in the southeastern part of the basin six lithofacies are recognized that we assign to five depositional facies categorized as either channel or interchannel wetlands environments 1 type a sandstone is cross stratified and occurs as lenticular bodies with concave upward basal surfaces these bodies are assigned to the channel facies interpreted to be the product of low sinuosity streams 2 type b sandstone occurs in parallel bedded units containing mudrock partings and fossil plant debris these units constitute the levee facies 3 type c sandstone typically lacks internal structure and occurs as tabular bodies separating finer grained deposits these bodies represent the crevasse splay facies 4 gray mudrock is generally nonlaminated and contains ironstone concretions these deposits constitute the floodplain facies 5 carbonaceous shale and coal are assigned to the swamp facies we recognize two styles of stream deposition in our study area laterally continuous complexes of single and multistoried channel bodies occur at our middle study site and we interpret these to be the deposits of sandy braided stream systems in the two adjacent study sites single and multistoried channel bodies are isolated in a matrix of finer grained interchannel sediment suggesting deposition by anastomosed streams a depositional model for our study area contains northwest trending braided stream systems avulsions of these systems created anastomosed streams that flowed into adjacent interchannel areas we propose that during late paleocene a broad alluvial plain existed on the southeastern flank of the powder river basin the braided streams that crossed this surface were tributaries to a northward flowing basin axis trunk stream that existed to the west

influence of stratification and topography upon internal wave spectra in the region of sills 1 a non hydrostatic model in vertical cross section form is used to examine the role of sill width and buoyancy upon the energy cascade into the internal tidal band and higher frequencies in sill regions power spectra analysis of computed time series show that as sill width is reduced the energy transfer from the baroclinic tide to its higher harmonics is reduced however there is an increase in energy at higher frequencies corresponding to lee wave periods in addition internal mixing on the lee side of the sill increases the addition of small scale topography on the sill slope produces a similar spectral change in the internal wave distribution and mixing for a narrow sill the addition of a surface buoyant layer with a higher buoyancy frequency significantly reduces the energy cascade to higher frequencies with a corresponding reduction in mixing the associated spectra have characteristics resembling wide sill topography

natural levee deposition during the 2005 flood of the saskatchewan river abstract in summer 2005 a controlled flood of the saskatchewan river east central saskatchewan canada resulted in general floodplain inundation and extensive natural levee deposition along a 60 km reach extending from 40 km below the e b campbell dam to cumberland lake levee crests along channel banks were inundated for up to 7 weeks in some areas of the floodplain new deposits on levee crests varied from 0 to 70 cm in thickness displaying large variations both along reach and in opposing sites across channels mean grain sizes mainly silt and very fine sand likewise varied considerably among sample sites pre and post flood surveys of channel cross sections along the flooded reach permitted assessments of relationships between channel area changes and patterns of levee sedimentation in this system in which virtually all new flood sediment was derived by channel scour results show that both net deposition and net erosion occurred within the channel cross sections but that on average net channel enlargement of 4 2 prevailed over the entire survey reach when weighted by cross section size over the 60 km flooded reach zones of thick levee deposition occur at or just downstream of two areas of major channel enlargement and an intermediate zone of thin levee deposits is associated with an intermediate area of net channel aggradation this bimodal distribution of flood deposit thickness is inferred to have resulted from differences in sediment supply produced locally by the different extents of channel perimeter erosion two other factors 1 position of interfacial zones between clear floodbasin water and turbid channel water and 2 difference in pre flood levee heights contributed to the poor correspondence in thickness and grain size between opposing levees at some sites additional features of the new levee deposits including increases in transverse slopes abrupt basinward fining and paucity of deposition in distal areas due to clear floodbasin waters are characteristic of strong front loading that results when suspended sediment production is restricted to channel erosion processes

integration of channel and floodplain suites i developmental sequence and lateral relations of alluvial paleosols abstract the lower eocene willwood formation of the bighorn basin northwest wyoming consists of about 770 m of alluvial rocks that exhibit extensive mechanical and geochemical modifications resulting from eocene pedogenesis willwood paleosols vary considerably in their relative degrees of maturity maturity is defined as stage of development as a function of the amount of time required to form five arbitrary stages are proposed to distinguish these soils of different maturities in the willwood formation stage 1 soils the least mature are entisols stage 2 and stage 3 soils are intermediate in maturity and are probably alfisols and stage 4 and stage 5 soils the most mature are spodosols these stages are not only time progressive elements of an in situ maturation sequence for w llwood soil formation but in the lateral dimension they are also usually distributed sequentially study of willwood paleosols indicates that an inverse relationship exists between soil maturity and short term sediment accumulation rate the least mature willwood paleosols formed in areas of relatively high net rates of sediment accumulation on 1 channel levee and crevasse splay sediments of the proximal alluvial ridge and 2 deposits filling large and small paleovalleys formed by major episodes of gullying lowered baselevels in contrast the fine grained sediments of the distal floodplain where net sediment accumulation rates were relatively low experienced development of much more mature soils soils of intermediate maturities occur in the order of their stage on intervening proximal floodplain and distal alluvial ridge sediments adjacent bodies of sedimentary rock that differ in their ancient soil properties because of distance from areas of relatively high sediment accumulation are denoted by the new term pedofacies the remarkable sequence of paleosols in the willwood formation clearly illustrates several important principles of soil sediment interrelationships in aggrading alluvial systems that have broad application to other deposits this is especially true in view of the widespread distribution of paleosols in nearly all ancient fluvial rocks further study of willwood paleosols will not only enable precise lateral correlation of coeval alluvial sediments and thereby fluvial sedimentary events from the distal to the proximal realms of the floodplain but will also contribute to increasingly informative evaluations of the nature tempo and mode of alluvial succession

variability of sea ice draft off hokkaido in the sea of okhotsk revealed by a moored ice profiling sonar in winter of 1999 1 using a moored ice profiling sonar along with an adcp a spatial section of draft across 855 km of sea ice was obtained for the first time in the southwestern part of the okhotsk sea near hokkaido in winter of 1999 the draft evolved from 0 20 m in mid february to 1 45 m in late march with the overall value of 0 72 m the draft characteristics were quite different between february and march before and after the period of strong winds the increase of the mean draft from february to march was associated with the increase of deformed ice the maximum draft observed was 17 m ice volume was dominated by the contribution from portions of deformed ice especially in march these results suggest that deformed ice dominated in the region of observation and dynamical processes were mainly responsible for the evolution of draft

interplay between longitudinal fluvial and transverse alluvial fan systems and growing thrusts in a piggyback basin se pyrenees abstract the integration of sedimentological and structural data in the western end of the ripoll syncline allows a clearer understanding of the palaeogeography of the area between the oblique termination of the pedraforca thrust sheet and the frontal vallfogona thrust during middle eocene times in this region a 2 5 km thick clastic succession corresponding to the bellmunt and milany sequences infilled the ripoll syncline this succession evolved from fluvio deltaic to alluvial the long lived and west prograding longitudinal fluvio deltaic system was parallel to the axis of the syncline the fluvio deltaic deposits are found interfingered with others which correspond to transverse alluvial fans of northern provenance which are increasingly important towards the top of the section the persistent and uniform wsw palaeoflow direction of the fluvio deltaic system together with the position of open marine conditions to the south indicate that the southern boundary of the system was constrained by a tectonic barrier which is attributed to the emergence of the vallfogona thrust the ramp of this thrust above the foreland basin strata formed the ripoll piggyback basin from middle lutetian times on several millions years earlier than previously proposed the western end of the ripoll syncline is thus an example of a complex partitioning of a foreland basin over time and space by structures of differing growth duration and different trend the interaction of the oblique system of thrusts corresponding to the eastern termination of the pedraforca thrust sheet and the vilada anticline and the frontal system of the vallfogona thrust controlled the position of the bellmunt river dominated delta which acted as the outlet of the ripoll piggyback basin

sedimentation patterns across a coastal plain floodplain the importance of hydrogeomorphic influences and cross floodplain connectivity abstract the floodplains of large coastal plain rivers in the southeastern u s are important long term storage sites for alluvial sediment and nutrients yet considerable uncertainty surrounds sediment dynamics on many large river floodplains and in particular the local scale factors that affect the flux of sediment and nutrients from rivers onto their floodplains and their subsequent deposition this research quantifies short term rates of sediment deposition from 2012 to 2014 on floodplain sites at congaree national park using feldspar pads sediment deposition rates ranged from 0 1 to 15 6 cm median 1 46 cm and were closely associated with inundation frequency and geomorphic position cross floodplain distributary channels served as particularly important conduits for moving sediment onto the floodplain physical and chemical analyses of soil samples demonstrated that the most flood exposed sites had higher major nutrient and micronutrient levels especially of phosphorus and more diverse nutrient compositions this research advances current understandings of lateral floodplain connectivity by demonstrating the complex effects of regional hydrology and local floodplain environmental characteristics on the supply of sediment and nutrients

sequence stratigraphic analysis of the youngest nonmarine sequence in the cretaceous ferron notom delta south central utah u s a abstract this study evaluates the nature and internal complexity of high frequency fluvial aggradational cycles and linked paleosols that were previously not recognized in nonmarine sequences of the turonian ferron notom delta in central utah detailed facies analysis of the 33 meter thick youngest nonmarine sequence sequence 1 reveals 11 depositional facies that build 33 fluvial aggradational cycles 9 fluvial aggradation cycles sets and 3 sequences in what was previously classified as a single 100 ka 4th or 5th order sequence fluvial aggradation cycles in the succession are either simple floodplain bedsets or single channel stories that are bounded by paleosols or erosional surfaces they represent depositional events that likely do not span more than 2 ka depositional periods are followed by short hiati 10 to 400 a characterized by subaerial exposure and soil development possibly reflecting floodplain abandonment or short term river avulsions fluvial aggradational cycle sets show systematic stacking of fluvial aggradational cycles and are analogous to parasequence sets they are represented by either compound floodplain bedsets or multi story channel sandstones bounded by relatively mature paleosols or erosionally top truncated they represent multiple small scale depositional events that span not more than 14 ka followed by relatively long 100 a to 1 ka hiati characterized by subaerial exposure and soil development which suggest a relationship to longer term floodplain abandonment due to either longer term avulsion or fluvial entrenchment during base level falls fluvial aggradational cycle sets are often capped by coals and carbonaceous strata marine trace fossils and dinocysts above coal beds suggest marine transgression due to compactional subsidence or sea level rise the scale of cyclicity of the fluvial aggradation cycle sets 14 ka is similar to underlying marine parasequences 10 to 15 ka and suggests that nonmarine and marine cycles have a similar control fluvial sequences are aggregates of fluvial aggradational cycle sets that are bounded by unconformities or their correlative conformities that represent longer periods 1 to 5 ka of subaerial exposure and pedogenic development cyclicity on the sequence scale in this succession is attributed to high frequency milankovitch scale 20 ka 40 ka rises and falls in sea level

modelling the depth of penetration of the wind s momentum at super inertial frequencies due to non linear effects in frontal regions 1 a numerical model with a coast and density front is used to examine the influence of the front upon the depth of penetration of the wind s momentum we find that non linear processes associated with spatial variations in vorticity play an important role in driving wind induced currents at depth internal wave generation and propagation also occur in the frontal region for a bottom front the downward propagation of internal waves in the frontal region is inhibited by the presence of sloping isotherms and a region of enhanced current magnitude develops at depth at the front s edge on the stratified side for a surface front the presence of enhanced surface vorticity on the well mixed side of the front means that the wind s energy is trapped in the surface layer these calculations help to explaining the large spatial variability of wind forced energy found in observations

variability in the internal wave field induced by the atlantic deep western boundary current at 16 n abstractfive years of continuous mooring data combined with conductivity temperature depth ctd lowered acoustic doppler current profiler ladcp measurements from five cruises are used to investigate the influence of the deep western boundary current dwbc on the internal wave field and associated vertical mixing at the continental slope at 16 n in the western atlantic the mooring data include 2 hourly rotor current meter measurements and temperature conductivity time series with a high temporal resolution of 5 20 min thus the data resolve time scales ranging from the low frequency variability of the large scale dwbc that generates internal waves due to interactions with the topography to frequencies greater than that of internal waves that are associated with vertical mixing estimates of the vertical mixing induced by the breaking of the observed internal waves show elevated diapycnal diffusivities of up to 10 3 0 4 10 3 m2 s 1 in the bottommost 1500 m during times of a strong dwbc maximum ve

morphology of fluvial levee series along a river under human influence maros river hungary abstract the development and morphometry of fluvial levees reflect the connection between channel and overbank processes which can be altered by various human activities the aims of this study are to investigate the morphology and spatial characteristics of fluvial levees and evaluate the role of some local and catchment scale human activities on their medium term 150 years development this study applies lidar data along a 53 km long reach of the maros river in hungary six fluvial levee types are identified based on the beginning and end of their evolution these levee types were generated by local nineteenth century channel regulation works cutoffs and mid twentieth century channel narrowing which was caused by gravel mining and water impoundment in the upstream sections however other human activities also influenced the development of active fluvial levees because their horizontal evolution could have been limited by embanked flood protection levees or the widening of low lying floodplain benches that were generated by channel narrowing additionally revetment constructions influenced their vertical parameters as higher fluvial levees developed along the fixed banks generally the older active fluvial levees are wider while the younger active levees are narrower with steeper slopes but not always lower on the low lying floodplain levels benches the youngest fluvial levees evolved quite rapidly and consist of coarser material currently only 9 8 to 38 year return period floods could cover the fluvial levees contributing to their evolution this fact and the development of fluvial levee series with two three members reflect a gradual decoupling of the channel from the floodplain

anatomy and dimensions of fluvial crevasse splay deposits examples from the cretaceous castlegate sandstone and neslen formation utah u s a abstract crevasse splay deposits form a volumetrically significant component of many fluvial overbank successions up to 90 in some successions yet the relationships between the morphological form of accumulated splay bodies and their internal facies composition remains poorly documented from ancient successions this work quantifies lithofacies distributions and dimensions of exhumed crevasse splay architectural elements in the campanian castlegate sandstone and neslen formation mesaverde group utah usa to develop a depositional model fluvial crevasse splay bodies thin from 2 1 m average to 0 8 m average and fine from a coarsest recorded grain size of lower fine sand to fine silt away from major trunk channel bodies internally the preserved deposits of splays comprise laterally and vertically variable sandstone and siltstone facies associations proximal parts are dominated by sharp and erosional based sandstone prone units which may be structureless or may comprise primary current lineation on beds and erosional gutter casts medial parts comprise sets of climbing ripple strata and small scale deformed beds distal parts comprise sets of lower stage plane beds and complex styles of lateral grading into fine grained floodbasin siltstones and coals lithofacies arrangements are used to establish the following i recognition criteria for crevasse splay elements ii criteria for the differentiation between distal parts of crevasse splay bodies and floodplain fines and iii empirical relationships with which to establish the extent ca 500 m long by 1000 m wide and overall semi elliptical planform shape of crevasse splay bodies these relationships have been established by high resolution stratigraphic correlation and palaeocurrent analysis to identify outcrop orientation with respect to splay orientation this permits lateral changes in crevasse splay facies architecture to be resolved facies models describing the sedimentology and architecture of crevasse splay deposits preserved in floodplain successions serve as tools for determining both distance from and direction to major trunk channel sandbodies

natural levees and human settlement in the song hong red river delta northern vietnam the song hong red river delta northern vietnam is characterized by huge natural levees in an area of the delta plain known as the west floodplain where fluvial sedimentation predominates the natural levees along the day river a major distributary of the song hong are comparable in size with those of the main course of the song hong the day river levees are 3 8 km wide and rise 2 5 m above the adjacent backswamps and have played an important role in human settlements since the late metal age we discussed the relationships among the natural levees of the day river delta progradation and the distribution of archaeological sites on the delta plain during the early holocene the accumulation of sediment discharged by the song hong enhanced both aggradation of the floodplain and river mouth progradation within the drowned valley of the song hong radiocarbon dates from cores trench exposures and archaeological sites record a dramatic slowing of aggradation when sea level stabilized during 6 4 cal

on the behavior of internal waves in the wakes of storms abstract the rossby adjustment process in the wake of a storm is studied with a view to finding within the context of linear theory how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer comparisons are made between three cases 1 a periodic storm on the f plane where dispersion is purely vertical 2 a bounded storm on the f plane and 3 a bounded storm centered 2700 km from the equator on an equatorial beta plane particular attention is paid to the initial rate of loss of energy from the mixed layer and some simple formulas which work very well in the cases studied are derived these show that the rate of loss goes up when the mixed layer depth is increased and also that the rate scales as the square of the wavenumber values of the rates are sufficient to provide a major source of energy for internal waves below the mixed layer the often observed tendency for phase lines to propagate upward is found in all case

anastomosing river deposits sedimentation rates and basin subsidence magdalena river northwestern colombia south america situated in a tectonically active foreland basin the magdalena river consists of vertically accreting levee confined channels and adjacent extensive wetlands which are interpreted as an anastomosing river sedimentary system equivalent rates of basin filling and subsidence average 3 8 mm yr 1 based on 18 14c dates from five bore holes drilled to depths of 55 m and sediment transport budgets from 35 years of measurement located in a savanna tropical climate anastomosing river deposits of the magdalena are remarkably similar to the anastomosing deposits of the upper columbia river in a temperate cold climate in western canada suggesting that climate is not a controlling factor of anastomosis the geometry of anastomosing channel fills in the magdalena consists of stratigraphically non uniform low sinuous narrow stringers of sand up to 30 m thick by 600 m wide a width depth ratio of 20 thin 1 2 m off channel crevasse splay sand sheets extend laterally up to 10 km distance when buried both sand deposits become encased by lacustrine or marsh mud to form stratigraphic traps while there are few modern anastomosing river systems as compared to braiding and meandering there may be a disproportionately large number of ancient anastomosed fluvial rock sequences due to the rapid rate of vertical accretion such a different depositional style and geometry of sand bodies have considerable significance in the interpretation of some ancient fluvial rock sequences because it provides an alternative to the meandered and braided river deposition models

internal tide spatial variability off western portugal detected by current meter observations 1 long term 10 12 months current meter observations from the western iberian continental margin are analyzed focusing on oscillations in the internal gravity wave band kinetic energy spectra are characterized by background falloff rates with frequency ranging from 1 to 2 superposed by energetic narrow bands at specific frequencies significant spectral peaks are found at some of the inertial tidal nonlinear interaction frequencies m2 f and m4 f and at higher semidiurnal harmonics m4 m6 and m8 semidiurnal internal tide kinetic energy reveals a spatial distribution with a maximum coherent contribution 44 cm2 s 2 at 1200 m depth on the mid continental slope and a maximum relative incoherent signal 60 of the total semidiurnal tidal band energy at intermediate levels 650 to 1200 m depth and 30 to 130 km from the shelf break

quantitative model of the growth of floodplains by vertical accretion a simple one dimensional model is developed to quantitatively predict the change in elevation over a period of decades for vertically accreting floodplains this unsteady model approximates the monotonic growth of a floodplain as an incremental but constant increase of net sediment deposition per flood for those floods of a partial duration series that exceed a threshold discharge corresponding to the elevation of the floodplain sediment deposition from each flood increases the elevation of the floodplain and consequently the magnitude of the threshold discharge resulting in a decrease in the number of floods and growth rate of the floodplain floodplain growth curves predicted by this model are compared to empirical growth curves based on dendrochronology and to direct field measurements at five floodplain sites the model was used to predict the value of net sediment deposition per flood which best fits in a least squares sense the empirical and field measurements these values fall within the range of independent estimates of the net sediment deposition per flood based on empirical equations these empirical equations permit the application of the model to estimate of floodplain growth for other floodplains throughout the world which do not have detailed data of sediment deposition during individual floods copyright 2000 john wiley sons ltd

human induced sedimentation patterns of a channelized lowland river channelization of the severely polluted odra and vistula rivers in poland induced intensive accumulation of fine grained deposits rich in organic matter and heavy metals these sediments have been identified in vertical profiles in a narrow zone along river banks both in groyne created basins and on the floodplain grain size organic matter zinc zn lead pb copper cu content and cesium 137 137cs was used for sediment dating and stratigraphy and chemistry have been diagnostic features for these deposits named industrial alluvium in the most polluted river reaches stabilized by bank reinforcements and groynes 2 m thick slack water groyne deposits are composed of uniform strata of polluted silts with organic matter content over 10 zn content over 1000 mg kg and average cu and pb over 100 mg kg the average rate of sediment accretion in groynes is higher than on the floodplain and reaches 5 cm yr stratification which appears at higher levels in the groyne fields and on the levees reflects a change from in channel to overbank deposition and is typified by dark layers separated by bright sandy and less polluted strata stratified 4 m thick sediment sequences have been found in groyne fields of incised river reaches the average rate of sediment accretion in these reaches is of the order of 5 cm yr in stable and relatively less polluted river reaches vertical accretion organic deposits are finely laminated and the average rate of deposition amounts to a few millimeters per year investigations indicate that groyne construction favors conditions for long term storage of sediments at channel banks for this reason groynes should be considered as structures that efficiently limit sudden release of sediment associated heavy metals stored in channels and in floodplains of the historically polluted rivers copyright 2014 john wiley sons ltd

observations of inertial wave events near the continental slope off goban spur near inertial waves were observed during the ocean margin exchange omex i experiments with current meters over the continental slope near goban spur the strongest inertial motion was observed in the bottom layer about 50 m above the 1000 m isobath there the waves were slightly 1 7 superinertial and the bottom slope appeared to be critical for the near inertial peak frequency allowing the velocity vector to follow the sloping bottom the vertical velocity component of this motion was responsible for the near inertial spectral peak in the temperature spectrum which was also observed in the bottom layer evidence was found supporting the speculative hypothesis that high energy near inertial wave events were produced during geostrophic adjustment in the variable deep eastern boundary current over the slope near goban spur

spatial variability of deep ocean motions above an abyssal plain 1 near bottom current observations are discussed from an array of moorings separated by 8 40 km horizontally in the madeira abyssal plain north atlantic ocean the area is topographically smooth but observed currents varied strongly over short distances across horizontal scales o 10 km incoherent internal wave properties were retrieved such as conservation of relative frequency bandwidth and internal wave polarization at inertial tidal and higher harmonics frequencies in the vertical between 10 110 110 650 m above the bottom mab at 5000 m the current differences shear were predominantly at the local inertial frequency f near f the largest variance was found at 110 mab with peaks in power at 0 99f and 1 03f as stratification was weak n 2f the subinertial frequency peak was well within the combined internal inertio gravity wave band at 650 mab n 4f and smaller peaks at 1 00f and 1 03f were observed toward the bottom subinertial currents increased in magnitude the horizontal scale of variation of subinertial and inertial motions was small 30 km the magnitude of horizontal current differences in these frequency bands was equal to that in the tidal band although the energetically dominant highly deterministic tidal currents were predominantly barotropic confirming a previous study their horizontal scale of variation was 300 km due to small bottom relief results are discussed relevant for matching records from nearby moorings to generate extra long time series

late jurassic fluvial eolian deposits from the tianchihe formation ningwu jingle basin shanxi province china abstract eolian systems were widespread in china in the cretaceous however the reports of pre cretaceous eolian and its related systems are scarce which prohibits studying the construction accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors in this paper we report on fluvial eolian successions from the late jurassic tianchihe formation in the ningwu jingle basin these successions represent the oldest reported inland fluvial eolian systems in china fourteen lithofacies types are recognized in the tianchihe formation and have been grouped into six facies associations including meandering fluvial channel levee and overbank in the lower part and eolian sandsheet eolian dune ephemeral fluvial channel and floodplain in the upper part the fluvial system comprises a series of wetting upward cycles which indicate humid climate culminating in high precipitation and shallow water table level eolian dune deposits composed of grainflow grainfall wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface suggesting compound dunes or draas eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination the association of eolian dune and eolian sandsheet is development of a dry eolian system twelve drying upward cycles mainly composed of eolian sandsheet eolian dune successions and four wetting upward cycles consisting of eolian sandsheet dune ephemeral fluvial channel floodplain successions occur in the eolian system these repeated cycles likely reflect an evolving erg system directly controlled by sediment supply sediment availability and relative water table the vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions which may be related with the uplift of the east china plateau in the late jurassic

lithofacies and palaeosol analysis of the middle and upper siwalik groups plio pleistocene haripur kolar section himachal pradesh india abstract the middle upper siwalik groups plio pleistocene are exposed at haripur kolar himachal pradesh india the succession is 2800 m thick and has been subdivided into unit m1 of the middle siwalik and four units u1 u4 of the upper siwalik group on the basis of facies associations and type and degree of development of palaeosols the available magnetostratigraphic ages for bases of units u1 u3 and u4 are 5 5 2 6 and 1 77 ma respectively the top of the section has been dated as 19 ka lithofacies association and palaeocurrent analysis indicates that the middle and upper siwalik groups were formed mainly by a basin transverse fluvial system two types of river systems which differ in their size can be documented in unit m1 unit u1 and unit u2 one trunk river system similar to the modern kosi and the other smaller river system which formed tributaries to the former the large rivers were mainly braided in nature the unit u3 and lower part of unit u4 were deposited in the piedmont depositional system mainly by small braided streams and the upper part of the unit u4 was deposited during a period of arid climate by sediment gravity flows integration of fluvial lithofacies and pedofacies helps to identify two fluvial depositional systems from the modern indo gangetic plains the lowland system involved deposition on alluvial megafans and interfan areas which resulted in sand rich and mud rich sequences with weekly developed soils the upland system allowed large tracts to act as high ground for thousands of years thereby giving rise to sandstone poor intervals with moderately to strongly developed soils occurrence of moderately to strongly developed soils was controlled by uplifting and tilting of large tectonic blocks without any relation to distance from the main channels rate of subsidence apparently controlled the occurrence of lowland and upland systems deposition of the unit m1 unit u1 and unit u2 took place under upland and lowland systems very similar to those identified from the modern indo gangetic plains the warm and humid climate between 5 3 and 2 6 ma led to the formation of red alfisols with calcrete nodules at places slightly cooler and drier climate starting at about 2 6 ma and approximately coinciding with the onset of global scale glaciation produced poorly developed yellow soil with common development of nodular calcretic horizon and calcitc material disseminated in the groundmass at ca 0 9 ma a probable significant change to still drier and cooler climate produced typical sediment gravity flows in the piedmont system that continued until at least up to 19 ka

late quaternary stratigraphy of the yeongsan estuary southwestern korea abstract the 18 820 m long sediment core mw 1 from the yeongsan estuary consists of five primary unconsolidated to semi consolidated units ranging in age from late pleistocene to holocene overlying a cretaceous aged basement from oldest to youngest these units include units 1 2 3 fluvial units unit 4 paleosol unit and unit 5 holocene estuarine deposits units 1 2 and 3 are interpreted as in channel or overbank deposits plant materials included within the units and the toc tn total organic carbon total nitrogen ratios 11 14 are also indicative of terrestrial origin unit 2 yields radiocarbon date of 37 700 14 c yrbp unit 4 the paleosol unit is estimated to be originally deposited in fluvial setting such as the area of floodplain or backswamp away from the main channel based on the sporadic distribution of the stagnant freshwater acritarch pseudoschizaea and algae spirogyra the timing of deposition of the original sediments of the paleosol unit is constrained by radiocarbon age of underlying fluvial sediments unit 2 the timing of pedogenesis is around the last glacial maximum when sea level of the yellow sea was lowered temperature was lowered rainfall was reduced and the inland was sparsely vegetated estuarine deposits unit 5 are interpreted to be deposited during the holocene marine transgression

influence of multiple sills upon internal wave generation and the implications for mixing a cross sectional non hydrostatic model of a fjord is used to examine to what extent the internal tide is modified by two closely spaced sills the model is forced with an m2 barotropic tide and internal tides unsteady lee waves and a jet are generated at the sills in contrast to an isolated sill calculations with two closely spaced sills show that the presence of the second sill leads to standing internal wave generation with associated changes in wave spectrum and richardson number in the inter sill region associated with these there is a cascade of energy towards short waves leading to enhanced mixing between the sills this increase in mixing is consistent with enhanced mixing between closely spaced sills found in observations it is also relevant to enhanced oceanic and lake mixing and suggest that future mixing measurements in both oceans and lakes should focus on these regions

anatomy and dynamics of a floodplain powder river montana u s a abstract centimeter scale measurements on several powder river floodplains provide insights into the nature of overbank depositional processes that created the floodplains during a 20 year period after a major flood in 1978 rising stages initially entered across a sill at the downriver end of the floodplains later as stages continued to rise water entered the floodplains through distinct low saddles along natural levees the annual maximum depth of water over the levee crest averaged 0 19 m from 1983 through 1996 and the estimated flow velocities were approximately 0 15 m s 1 water ponded in the floodplain trough a topographic low between the natural levee and the pre flood riverbank and mud settled as thin layers of nearly constant thickness mud layers alternated with sand layers which were relatively thick near the channel together these beds created a distinctive natural levee in some locations individual flood deposits began as a thin mud layer that gradually coarsened upwards to medium grained sand coarsening upwards sequences form initially as mud because only the uppermost layers of water in the channel supply the first overbank flows which are rich in mud but starved of sand at successively higher stages fine sands and then medium sands increase in concentration in the floodwater and are deposited as fine and medium sand layers overlying the initial mud layer theoretical predictions from mathematical models of sediment transport by advection and diffusion indicate that these processes acting alone are unlikely to create the observed sand layers of nearly uniform thickness that extend across much of the floodplain we infer that other transport processes notably bedload transport must be important along powder river even with the centimeter scale measurements of floodplain deposits daily hydraulic data and precise annual surface topographic surveys we were unable to determine any clear correspondence between the gauged flow record of overbank floods and the depositional layers mapped in the floodplain these results provide a detailed example of floodplain deposits and depositional processes that should prove useful for interpreting natural levee deposits in a variety of geologic settings

internal wave trapping and mixing in a cold water dome 1 a cross sectional nonlinear numerical model of a shallow sea basin containing a cold water dome is used to examine the influence of wind frequency and dome characteristics upon internal waves and mixing at superinertial forcing frequencies nonlinear effects in the frontal regions of the dome give rise to propagating internal waves which are reflected by the dome s fronts this reflection gives a standing internal wave trapped within the dome the spatial variability of the wave is determined by forcing frequency stratification and dome length the magnitude of the internal wave and the length of the dome are related to the horizontal distribution of density in the frontal region at the inertial frequency there is little internal wave propagation while at subinertial forcing frequencies the internal wave is trapped in the frontal region and energy cannot radiate away consequently vertical mixing is enhanced in the frontal regions while in the center of the dome the mixed layer increases due to the vertical diffusion of the wind s momentum to depth as in a single point model in the case of wind forcing at a superinertial frequency there is less mixing in the frontal region with internal wave propagation leading to mixing in the center of the dome these calculations suggest that the breakdown of cold water domes in response to winter wind events may be due to a number of mixing processes depending upon wind frequency

doppler sonar observations of internal waves wave field structure abstract during may of 1980 an internal wave measurement experiment was conducted from the research platform flip off the california coast this paper discusses an 18 day sequence of velocity profiles obtained during the experiment using a pair of doppler sonars the sonars profile to a depth of 700 m with approximately 20 m depth resolution plots of the velocity and shear field indicate the dominance of near inertial motions much of the near inertial variance can be ascribed to a few identifiable wave groups the progress of these groups can he tracked for many days the shear at the base of the mixed layer is often dominated by near inertial motions propagating vertically through the thermocline rather than wind forced motions in the mixed layer itself power spectral analysis suggests that the low frequency component of the wave field is dominated by the near inertial and tidal peaks and their harmonics the wisdom in modeling the low frequency wave field as an equivalent continuum is questioned

on the nature of internal wave spectra near a continental slope 1 amongst the most energetic motions in the deep ocean are internal waves supported by stable vertical stratification in density previously these waves were considered freely propagating as described by a smooth continuum internal wave band iwb frequency spectrum we studied details of the iwb using yearlong current observations from the bay of biscay instead of observing continuum iwb spectra near a continental slope we show that at least the first half decade of the iwb is dominated by motions at localized frequencies determined by strong non linear interactions between waves at the fundamental semidiurnal tidal and atmospherically induced inertial frequencies

on the influence of a surface coastal front on near inertial wind induced internal wave generation 1 a numerical model is used to examine the wind induced near inertial internal waves in the coastal region in the presence of a surface front initial calculations with the front separating a well mixed coastal region from a stratified offshore area in an infinite sea domain showed that away from the front surface inertial oscillations are dominant near the front on the positive vorticity side superinertial internal waves are generated and propagate offshore in an analogous manner to that found when stratification intersected a coastal boundary however in the case of a coastal boundary the no flow condition at the coast produced inertial oscillations at depth phase shifted by 180 from those at the surface on the negative vorticity side of the front internal waves at the subinertial frequency are trapped between the well mixed region and the front some inertial energy is found at depth in the frontal region although the large scale features of the distribution of inertial energy are independent of vertical eddy viscosity parameterization its magnitude depends upon it in the case of a stratified nearshore region and an offshore front near inertial waves generated at the coast were trapped between the coastal boundary and the front which results in a surface region of enhanced inertial energy this gradually decreased with time as inertial energy diffused to depth this timescale depended upon vertical eddy viscosity magnitude

fluvial channel and overbank deposits from the westphalian of the durham coalfield ne england the westphalian upper carboniferous coal measures of the durham coalfield in ne england were deposited in lower and upper delta plain environments distributary channels crossed the plain and were separated by shallow interdistributary lakes and bays detailed observation of three dimensional 3 d opencast surface mine exposures in collaboration with subsurface borehole analysis has revealed the existence of five varieties of channel deposits and two associated overbank facies within the durham coal measures major distributary channels were the major avenues of sediment transport across the coal measures plain were variably sinuous mostly 1 2 km wide and deposited elongate belts of sand mostly up to 5 km wide proximal major crevasse splay channels formed by the breaching of major channel banks during flood events were straight sand filled and up to 400 m wide minor distributary channels formed by the sustained operation of such crevasses varied from straight to highly sinuous and deposited shoestring sand mud belts up to a few hundred metres wide minor crevasse channels generally straight and up to 50 m wide were formed through bank breaching of minor and in a few cases major distributaries distal feeder channels formed down palaeocurrent extensions of minor distributaries which supplied interdistributary minor delta subsystems were generally straight and up to 200 m wide of the two types of channel overbank levee deposits recognized one comprising thinly interbedded fine grained sandstone and siltstone claystone is mostly though not exclusively associated with major distributary channels the other consisting of massive siltstones with regularly spaced thin claystone bands is uniquely developed at the margins of minor distributary channels the lower part of the westphalian a succession in the northern pennines records a change in the depositional environment upwards from a lower to upper delta plain through this transition major channel deposits show evidence of having evolved from being of dominantly low sinuosity to being more variable in morphology channel sedimentation was profoundly influenced by regular possibly seasonal variations in flow stage and sediment load

inquiry of levee formation by grain size analysis a case study from the warta river central poland abstract levees were the most easily recognised depositional forms developed after two subsequent floods that occurred in summer 2010 and winter 2010 2011 in the warta river valley central poland the levees are built of mainly by fine grained well sorted massive or climbing ripple laminated sands the forms were sampled in 3 pits 0 75 1 1 m deep samples were collected every 5 cm in vertical profiles the main aim of the study was to investigate changes in the grain size of the sands deposited during one flood episode analyses indicated slight differences in the grain size of the deposits with a mean ranging from 1 9 to 2 5 phi however a detailed grain size analysis of sand samples showed that a single flood event was represented by a coarsening upward sequence it is generally assumed that such a trend indicates an increasing energy of the transporting medium therefore the deposits recorded the rising flood stage in scatter plots of mean vs skewness and mean vs kurtosis the examined deposits show a v shaped point arrangement it may indicate the mixing of grain subpopulations differences in flow energy observed mainly within the channel banks resulted in mixing sediment transported in saltation with sediment transported in graded suspension the paper proposes a model sequence for levee deposition during flood event it is directly related to the flood progress 1 beginning of the flood fine grained sand 2 rapid rise of water level up to the inflection point inverse grading deposits and 3 slow rise and stabilisation of the water level up to the culmination point fining upward deposits the subsequent phase of falling water level does not involve deposition therefore a single flood particularly the rising phase is represented by a pensymmetric sequence however the uppermost part of the sequence is sometimes lacking in the fossil record which results in an upward coarsening sequence

first report of sauropod tracks from the upper jurassic tianchihe formation of guxian county shanxi province china abstract this paper presents the first report of sauropod tracks from the upper jurassic of shanxi province china dinosaur tracks appear concentrated in five trackways in different stratigraphic levels of the late jurassic tianchihe formation tracks are dominantly small and medium size sauropod tracks and are tentatively assigned to brontopodus based on preserved track morphology trackway pattern and statistical analysis the tianchihe formation in which the tracks appear shows a gradual change from meandering fluvial to sandy braided fluvial depositional systems developed in a seasonally arid environment comparisons of the evaluated speed of bipedal to quadruped trackways indicate that the slower walk more easily produces pes dominated overprints trackways in the guxian tracksite appear following different orientations suggesting that these trackways were produced by different sauropods at different times an unusual trackway following a curved pattern has been identified in the site and could represent a special locomotion character or a social behavior the presence of eolian deposits in central shanxi province could have acted as a paleogeographic and paleoenvironmental barrier for the dispersion of the yanliao biota that survived in northern hebei western liaoning and northestern shanxi province to the ordos basin during the late jurassic

linked sequence stratigraphy and tectonics in the sichuan continental foreland basin upper triassic xujiahe formation southwest china abstract intracontinental subduction of the south china block below the north china block in the late triassic resulted in formation of the transpressional sichuan foreland basin on the south china block the upper triassic xujiahe formation was deposited in this basin and consists of an eastward tapering wedge of predominantly continental siliciclastic sedimentary rocks that are up to 3 5 km thick in the western foredeep depocenter and thin onto the forebulge and into backbulge depocenters five facies associations a e make up the xujiahe formation and these are interpreted respectively as alluvial fan transverse and longitudinal braided river meandering river overbank or shallow lacustrine and deltaic deposits this study establishes a sequence stratigraphic framework for the xujiahe formation which is subdivided into four sequences sq1 2 3 and 4 sequence boundaries are recognized on the basis of facies tract dislocations and associated fluvial rejuvenation and incision and systems tracts are identified based on their constituent facies associations and changes in architectural style and sediment body geometries typical sequences consist of early to late transgressive systems tract deposits related to a progressive increase in accommodation and represented by facies associations a b and c that grade upwards into facies association d regionally extensive and vertically stacked coal seams define maximum accommodation and are overlain by early highstand systems tract deposits represented by facies associations d e and c late highstand systems tract deposits are rare because of erosion below sequence boundaries sequence development in the xujiahe formation is attributed to active and quiescent phases of thrust loading events and is closely related to the tectonic evolution of the basin the sichuan basin experienced three periods of thrust loading and lithospheric flexure sq1 lower sq2 and sq3 two periods of stress relaxation and basin widening upper sq 2 and sq3 and one phase of isostatic rebound sq4 paleogeographic reconstruction of the sichuan basin in the late triassic indicates that the longmen mountains to the west consisting of metamorphic sedimentary and pre neoproterozoic basement granitoid rocks was the major source of sediment to the foredeep depocenter subordinate sediment sources were the xuefeng mountains to the east to backbulge depocenters and the micang mountains to the northwest during the late history of the basin this study has demonstrated the viability of sequence stratigraphic analysis in continental successions in a foreland basin and the influence of thrust loading on sequence development

on the interaction between internal tides and wind induced near inertial currents at the shelf edge 1 numerical calculations are performed at the shelf edge to examine the role of nonlinear processes in transferring energy from the m2 tide and wind induced currents close to the inertial frequency f into a wave at the sum of their frequencies termed the fm2 frequency a numerical model of the hebrides shelf edge represented by a cross section initially with idealized topography and subsequently with realistic topography is used in these calculations results show that in the near coastal ocean currents at the fm2 frequency are primarily due to coupling between wind induced inertial oscillations and the m2 internal tide a major source is associated with vertical shear in the inertial oscillations and the vertical velocity due to the internal tide a secondary source is due to the nonlinear momentum advection term in the case in which eddy viscosity is computed from a turbulence energy model shear across the thermocline is larger than when a constant viscosity is used the reduction in shear with a constant viscosity reduces the role of the nonlinear term involving vertical shear and hence the magnitude of the fm2 current in the region of the thermocline increasing the wind stress leads to a deeper thermocline and hence the location of maximum fm2 current in the water column changing the vertical stratification influences the intensity of the inertial oscillations in the surface layer and the distribution of the internal tide and hence changes the pattern of fm2 currents results with realistic topography confirm the major conclusions

paleoflooding reconstruction from holocene levee deposits in the lower meuse valley the netherlands this study investigates the holocene levee deposits and paleoflooding history of the lower meuse in the netherlands based on archeological investigations and sedimentary analyses grain size end member modelling magnetic susceptibility and thermogravimetric analyses the levee on the left bank in the study area near ooijen contains a continuous sedimentary record in the nw downstream part the archeological evidence and sedimentary results including a grain size based flood energy index lfei indicate that the lower meuse experienced a quiescent flooding period and low sedimentation rates during the mid late mesolithic when the levee was low and human influence was minor deposition during the mesolithic shows a fining upward trend and a highly developed soil containing abundant artefacts during the neolithic and bronze age the flooding intensity was low but gradually increased to a moderate level probably because of deforestation and increased runoff limited bronze age findings may reflect decreased human activity because of the increased flooding starting from the iron age the meuse experienced a generally enhanced flooding regime which is reflected by erosion and coarsened sedimentation in the iron age and roman period the high peak discharges during the iron age may have re opened a low lying paleochannel near to the levee during the intensified floods this general increasing trend is interrupted by the lower flooding phase in the early middle ages dark ages from the middle to the late middle ages the floods intensified again the coarsening deposition and higher sedimentation rates since the iron age resulted from increased floods and higher sediment supply by deforestation and soil erosion the findings of this study agree with a recent paleoflood reconstruction for the lower meuse by using a floodplain archive implying that levee sediment records have potential in paleohydrological studies if the completeness of the record and chronological information is guaranteed 2019 elsevier b v

formation of a cohesive floodplain in a dynamic experimental meandering river field studies suggest that a cohesive floodplain is a necessary condition for meandering in contrast to braided rivers however it is only partly understood how the balance between floodplain construction by overbank deposition and removal by bank erosion and chutes leads to meandering this is needed because only then does a dynamic equilibrium exist and channels maintain meandering with low width depth ratios our objective is to understand how different styles of floodplain formation such as overbank deposition and lateral accretion cause narrower channels and prevent chute cutoffs that lead to meandering in this study we present two experiments with a self forming channel in identical conditions but to one we added cohesive silt at the upstream boundary the effect of cohesive silt on bank stability was tested in auxiliary bank erosion experiments and showed that an increase in silt reduced erosion rates by a factor of 2 the experiment without silt developed to a braided river by continuous and extensive shifting of multiple channels in contrast in the meandering river silt deposits increased bank stability of the cohesive floodplain and resulted in a reduction of chute cutoffs and increased sinuosity by continuous lateral migration of a single channel overbank flow led to deposition of the silt and two styles of cohesive floodplain were observed first overbank vertical accretion of silt e g levee overbank sedimentation or splays and second lateral point bar accretion with silt on the scrolls and in the swales the first style led to a reduction in bank erosion while the second style reduced excavation of chutes we conclude that sedimentation of fine cohesive material on the floodplain by discharge exceeding bankfull is a necessary condition for meandering

evolving fluvial architecture during a marine transgression upper buntsandstein triassic central spain abstract the sedimentation in central spain during the late anisian middle triassic limos y areniscas de rillo formation recorded the evolution from an alluvial environment into a coastal one with a diversity of environments this evolution was the result of one of the episodes of the tethys sea transgression over iberia during the first and second stages of this evolution mixed load low sinuosity channels evolved upwards into a distal braidplain with ephemeral run off and poorly defined channels during a third stage the characteristics of the sediments indicate the existence of both continental and marine waters in a transitional zone with seasonal hydrological fluctuations the fourth stage records the sedimentation in an upper intertidal to supratidal environment in a semiarid coastline with the presence of thin cryptalgal sheets and chicken wire textures the final evolution consists of an environment with a high percentage of fluvial channel deposits probably related to a meandering pattern this evolution has been correlated with the depositional sequences established for the ne of spain where the anisian transgressive event resulted in the formation of an inter to supratidal carbonate ramp so lowstand transgressive and highstand system tracts from depositional sequence 1 have been recognized in the centre of spain

evolution of devonian alluvial systems in an oblique slip mobile zone an example from the broken river province northeastern australia abstract the lower 1500 m of the late devonian bulgeri formation was deposited in a tectonically active foreland basin in response to a major late devonian orogeny in the broken river province northeastern australia the basin was bounded to the east by an uplifted belt of palaeozoic sedimentary and volcanic rocks that was deformed east of an active thrust zone gray creek fault to the south the basin was bounded by igneous and metamorphic basement rocks uplifted along a major oblique slip fault zone clarke river fault facies analysis and mapping of alluvial stratigraphy has resulted in the recognition of compositionally distinct coalescing axial and transverse alluvial drainage systems the axial drainage system flowed to the northeast approximately parallel to the gray creek fault and away from the clarke river fault the system drained the cratonic basement to the south and west and accumulated mainly feldspathic and quartzose sediments a lower fine grained succession and an upper coarse grained succession are recognised the lower succession rockfields alluvial system was deposited in broad sandy low sinuosity channels and semi permanent floodplain lakes these rivers drained ultimately northward into a retreating coastal plain and shallow sea that lay over the georgetown province the upper succession bulgeri alluvial system was deposited in gravelly and sandy braided rivers emanating from south of the clarke river fault the transverse distributary system stopem blockem alluvial system accumulated mainly lithic coarse grained sediments deposited in gravelly braided rivers sourced from the uplifted orogenic belt to the east these rivers flowed towards the northwest before coalescing with the axial drainage system where they changed to a northerly orientation uplifted fault blocks of devonian limestone within the basin locally contributed limestone gravel to these rivers between the coalescing axial and transverse river systems lay extensive floodplains which received a slow but compositionally mixed supply of mainly fine grained sediments long periods of weathering resulted in the development of reddened palaeosols with well developed calcrete horizons the palaeogeography and fluvial style of the lower bulgeri formation is compared to the gulf of carpentaria in northeastern australia analysis of the architecture of these alluvial systems has led to recognition of at least three subsidence driven tectonic cyclothems and this is supported by simple quantitative modelling the lower part of each cycle begins with a thin conglomeratic succession above an unconformity and is overlain by thick relatively fine grained syn tectonic alluvial facies deposited during maximum subsidence the upper part of each cycle is marked by increasingly coarse grained post tectonic alluvial facies these were deposited by gravel progradation following cessation of uplift or thrusting in the source areas and concomitant slowing of subsidence rates

reliability based three dimensional assessment of internal erosion potential due to crevasse splays abstractgeomorphic features in the soil layers underlying a structure often have a significant effect on the underseepage behavior and the potential for initiating internal erosion based on the as