architecture of miocene overbank deposits in northern pakistan abstract understanding the geometry of sediment bodies and patterns of sediment disruption in ancient fluvial overbank successions is fundamental to interpretations of overbank deposition overbank deposits of the fluvial chinji formation siwalik group can be divided into sequences 1 20 m thick defined by the alternation of stratified sediments and paleosols preservation of stratified sequences does not support a gradual vertical aggradation of overbank sediments over the extent of the floodplain but instead indicates periods of rapid sediment deposition followed by long hiatuses and soil development rapid deposition of overbank sequences is predicted by models that hypothesize 1 episodic vertical aggradation of the entire floodplain 2 deposition controlled by the growth of alluvial ridges 3 incision and filling of local valleys 4 rapid filling of localized low areas or 5 rapid deposition associated with river channel avulsion these models also have important implications for understanding fossil preservation and floodplain paleoecology paleosol bounded sequences in the chinji formation can pinch out laterally over kilometers indicating that episodes of rapid deposition were restricted to local areas on the floodplain there is no evidence that bases of sequences are erosional and they do not appear to record valley incision and filling sequences generally do not thin and fine systematically away from the terminating margins of major channel deposits suggesting they are not related to the growth of alluvial ridges along active channels lithologic variations and patterns of sediment disruption within sequences appear to reflect the rapid tilling of low areas on the floodplain both adjacent to and distal from the major river channel this infilling of floodplain topography may reflect a continuous process whereby local areas were always being filled somewhere on the floodplain by sediments from minor tributary or crevasse channels alternatively the filling of local flood plain topography may have been caused by widespread but short lived events associated with river channel avulsion

depositional processes and stratigraphy of fluvially dominated lacustrine deltas mississippi delta plain abstract a geomorphic and stratigraphic investigation of lacustrine delta deposits in the atchafalaya basin louisiana revealed that lacustrine delta formation is rapid and cyclic in nature during the holocene thin coarse grained regionally extensive fluvially dominated lacustrine deltas filled interdistributary basins in the transition zone between the alluvial valley and the marine delta plain of the mississippi river one delta lake fausse pointe delta prograded 6 5 km partially filling the lake and covering more than 29 km2 in area in twelve years depositional processes in lake fausse pointe ranged from suspension settling of mud and organic matter during low sediment input to traction deposition of sand during floods hyperpycnal flow conditions set up by the introdu tion of sediment laden river water into the freshwater lake induced underflows that scoured the lake bottom and deposited upward coarsening lobes the low relief of the mississippi basin a constant large volume of fine grained sediment supply and prevalent fluvial processes have formed fluvially dominated lacustrine deltas that differ sedimentologically and stratigraphically from gilbert type and brackish water lacustrine deltas parallel laminated prodelta mud rippled to cross laminated delta front silty sand and very finegrained to medium grained distributary mouth bar sand are characteristic of rapidly deposited sediment whereas rooted and burrowed sediments signify periods of minimal deposition in a fluvially dominated setting delta geometry and sediment distribution patterns are controlled by river mouth processes basin shape and bathymetry thickest sand accumulations occur in linear dip elongate distributary m uth bar and natural levee lobes that are separated laterally by mud filled channels and interdistributary troughs lacustrine delta deposition is driven by basin subsidence regional downwarping and sediment compaction and the concomitant development of distributary channels in the interdistributary basins numerous lacustrine deltaic wedges each bounded by rooted backswamp clay are preserved multilaterally in atchafalaya basin sediments although lacustrine deltaic deposits constitute much of the basin s sedimentary fill each individual delta sequence records depositional events of only 100 years duration these deltaic deposits represent basin filling aggradational episodes that preceded the formation of marine delta complexes such as the maringouin teche la fourche and atchafalaya deltas of the mississippi river

base level buffers and buttresses a model for upstream versus downstream control on fluvial geometry and architecture within sequences abstract the effects of downstream base level control on fluvial architecture and geometry are well explored in several broadly similar sequence stratigraphic models cretaceous dakota group strata u s western interior have characteristics reflecting combined downstream and upstream base level controls that these models cannot address particularly three layers of amalgamated channel belt sandstone within this group thicken and are continuous for distances 300 km along dip that stretch the reasonable lengths for which these models are intended to apply as well architecture in up dip reaches records repeated valley scale cut and fill cycles this contrasts with equivalent strata down dip which record channel scale lateral migration with no such valley scale cycles apparent we here introduce the concept of buffers and buttresses to address these observations we assume that river longitudinal profiles are each anchored down dip to some physical barrier e g the sea strand etc that we refer to as a buttress buttress shift is considered the primary downstream control on base level profiles extrapolated up dip from the buttress over any modeled duration of buttress shift can range widely because of high frequency variability in upstream base level controls e g discharge etc all these potential profiles however are bounded above by the profile of highest possible aggradation and below by the profile of maximum possible incision these upper and lower profiles are buffers and they envelop the available fluvial preservation space thickness of the buffer zone is determined by variability in upstream controls and should increase up dip to the limit of downstream profile dominance dakota valley scale surfaces record repeated cut and fill cycles driven by up dip controls and are confined between thick stable buffers equivalent strata down dip record lateral reworking within a thinner channel scale buffer zone that was positioned by downstream controls regression exposed slopes similar to the buffer zone thus buffers were stable for long distances and durations this prompted dip extensive lateral reworking of strata into upstream valley scale and downstream channel scale sheets buffers and buttresses provide a broadly applicable model for fluvial preservation that captures upstream vs downstream base level controls on geometry and architecture the model lends general insights into dip oriented variations in fluvial architecture production of sheet vs lens geometry total preservation volumes for fluvial systems and variations in these factors related to contrasting climatic conditions and basin physiography the model can be amended to existing sequence stratigraphic approaches in order to capture dip oriented variations in sequence architecture

holocene floodplain soils along the rio mamore northern bolivia and their implications for understanding inundation and depositional patterns in seasonal wetland settings abstract the llanos de moxos lm in the bolivian amazon basin host one of the largest seasonally inundated savannah landscapes on earth very little is known of this area with regard to sedimentary dynamics soil formation or their relationship to longer term climatic and hydrological variability in this setting here we present a detailed study of three floodplain depositional sequences building up the inundation savannah along the mamore river in the central lm pleistocene sands and silts unit 1 are overlain by thick overbank deposits of mostly holocene age unit 2 on both sides of the mamore river and underline the importance of extensive flooding processes for the late quaternary sedimentary and geomorphic evolution of the lm the fine grained distal overbank sediments show signs of strong modification by hydromorphic processes and reflect spatial and temporal variations in flood inundation patterns in addition widespread dark gray to blackish soil and paleosol horizons are intercalated with the overbank sediments but lack evidence for significant weathering these horizons are likely the result of cumulative incorporation of organic material under conditions of particularly low sedimentation rates therefore their formation should be linked to processes such as channel migration longer term meanderbelt evolution avulsive drainage reorganization changes in sediment supply or climatically induced variations in flooding type frequency or magnitude the common occurrence of these floodplain soils in the early to mid holocene may thus reflect the combined effects of hydrological geomorphic and sedimentary changes during a drier mid holocene

middle to late holocene decreased fluvial aggradation and widespread peat initiation in the ishikari lowland northern japan this study investigated the influence of sea level and climate changes on the decreased fluvial aggradation and subsequent widespread peat initiation in the middle to late holocene in the ishikari lowland which is a coastal floodplain formed in response to the postglacial sea level change by introducing a new approach to separately evaluate the rates of organic and clastic sediment input we demonstrated that the peat began to form when the fluvial sedimentation rate was significantly decreased less than 0 6 mm yr while plant macrofossil analysis suggested that lowering of water level is also important to the peat initiation such changes in sedimentary environment may be associated with the abrupt abandonment of crevasse splays the concentrated ages of the peat initiation around 5600 5000 4600 4300 and 4100 3600 cal bp suggest that an allogenic control promoted the abandonment of crevasse splays and different onset ages can be explained by different fluvial responses of the ishikari river and i

the age and paleoenvironment of a late miocene floodplain alongside lake pannon rodent and mollusk biostratigraphy coupled with authigenic 10be 9be dating in the northern danube basin of slovakia abstract we present new age constraints for the late miocene volkovce formation of slovakia alluvial facies that accumulated adjacent to lake pannon facies analysis and authigenic 10be 9be dating was undertaken at the bernolakovo and triblavina localities while the latter outcrop also yielded additional small mammal and mollusk assemblages as well as remains of flora the results of seven radiometric dating ages yielded a weighted mean age of 9 65 0 61 ma for the triblavina outcrop and 8 85 0 32 ma for the bernolakovo outcrop the small mammal assemblage at the triblavina outcrop is indicative of the lowermost mn11 zone which in the western european standard definition suggests an age of

evaluating controls on crevasse splay size implications for floodplain basin filling abstract although crevasse splays are often considered important contributors to floodplain basin filling evidence from modern and ancient fluvial deposits indicates that they may not play a significant role in all river systems in order to better understand controls on the abundance and scale of crevasse splays produced in fluvial systems we used aerial photography to observe crevasse splay deposits along three rivers and conducted a targeted numerical modeling study to explore factors which promote widespread crevasse splay deposition on fluvial floodplains results demonstrate that splay size does not always scale directly with channel size or discharge and that hydrodynamic factors primarily sediment size and floodplain drainage conditions play a significant role in determining whether a fluvial system is likely to produce large floodplain filling splays this work suggests that widespread crevasse splays demand both a large supply of relatively coarse suspended sediment and a steep water surface slope away from the channel across the floodplain without both these conditions the role of crevasse splays in flood basin filling is limited

decadal scale riverbed deformation and sand budget of the last 500 km of the mississippi river insights into natural and river engineering effects on a large alluvial river

structure of a corystosperm fossil forest from the late triassic of argentina abstract a palaeoecological study of a standing late triassic forest containing 150 silicified stumps from the rio blanco formation of mendoza province argentina is described a mapped portion of the forest floor provides quantitative data tree density mean separation of trees and basal area per stump which along with taxonomic and sedimentologic information allowed the reconstruction of a plant community that grew along river banks and within proximal floodplain environments analysis of architectural and phenological data from monotypic forest indicates an evergreen community composed of a corystosperm genus with a canopy height of c 13 21 m the corystosperm taxon elchaxylon like rhexoxylon has polyxylic axes with centripetal secondary xylem but does not generate perimedullar bundles and the centrifugal secondary xylem produces an undivided solid pycnoxylic cylinder vegetation analysis shows that the forest has a clustered distribution pattern with high density forest density ranges between 727 and 1504 trees ha but there are first order clusters with elevated density mean nearest neighbour distance of 1 85 m the histogram of diameter classes based on 131 stumps suggests an earlier colonization by few older pioneers the largest ones followed by establishment of a large younger cohort of coeval trees based on 9 series and 139 rings the mean ring width and mean sensitivity ms were 3 47 mm and 0 31 respectively ms values and the presence of false rings indicate the forest community responded to stressed ecosystems the growth rings are very erratic and range from 0 27 to 8 94 mm for fossil growth analysis it was assumed that wider rings would suggest a warmer climate and the considerable range in growth rates would indicate variability in the limiting factors among subsequent cycles

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

deglacial flood origin of the charleston alluvial fan lower mississippi alluvial valley abstract large magnitude flooding of the mississippi river from proglacial lakes agassiz and superior most likely occurred between 11 300 and 10 900 and 9900 and 9500 yr b p the charleston alluvial fan a depositional remnant of one of these floods is located at the head of a wide alluvial plain near charleston missouri the fan is an elongate convex up sand body 16 24 km composed of medium and fine grained sand at least 8 m thick this sand contrasts with the older coarse grained sand of the braided stream surface to the west and south and younger silty clay of the meandering stream level to the north and east a weakly developed soil separates the underlying braided steam deposits from the alluvial fan a bulk soil radiocarbon date of 10 590 200 yr b p from the contact between the fan and clays of the meandering stream system indicates that the charleston fan was deposited near the end of the early interval of flooding from lake agassiz about 10 900 yr b p if the charleston fan is the last remnant of deglacial flooding in the lower mississippi valley then deposition of significant quantities of sediment from largemagnitude floods between 10 000 and 9500 yr b p did not extend into the lower mississippi valley through thebes gap

alluvial architecture of the holocene lower mississippi valley u s a and a comparison with the rhine meuse delta the netherlands abstract the proportion and arrangement of channel belt deposits in alluvial successions alluvial architecture is not known in detail for most modern settings therefore the alluvial architecture of the holocene lower mississippi valley lmv between greenville mississippi and baton rouge louisiana was studied to improve estimation of parameters relevant to alluvial architecture modeling alluvial architecture parameters sand body width thickness ratio sbw sbt channel belt deposit proportion cdp overbank deposit proportion odp and connectedness ratio cr are estimated from three cross valley sections based on lithologic borings sbw sbt and cdp decrease in a downstream direction for example cdp is 0 6 upstream and 0 3 downstream odp shows an opposite trend and is at a maximum 0 7 in the downstream part of the study area cr is low throughout the study area because most channel belts in our cross sections are unconnected the alluvial architecture in the lmv also seems to change over time because late holocene channel belts tend to be wider than the early holocene channel belts the observed trends in the alluvial architecture parameters are related to the ratio between channel belt width and floodplain width variations in aggradation rate location of the cross sections relative to avulsion sites and differential subsidence the alluvial architecture of the lmv is compared to that of the holocene rhine meuse delta to identify common controls on alluvial architecture despite differences in geographic setting the alluvial architecture of the lmv is similar to that of the rhine meuse delta we conclude that alluvial architecture of both fluvial systems is strongly controlled by channel belt geometry floodplain geometry and aggradation rate these in turn are influenced by extrinsic factors i e base level discharge sediment supply tectonics and pre existing topography as well as intrinsic factors i e lateral channel migration rate subsoil erodibility differential floodplain aggradation and avulsion mechanisms therefore the interaction between extrinsic and intrinsic factors should be considered in all alluvial architecture studies

evolution of atchafalaya lacustrine deltas south central louisiana abstract the entrenched pleistocene holocene mississippi alluvial valley was cut during the last low sea level stand and alluviation of the entrenched valley occurred during the holocene sea level rise regional gulf coast structures salt domes and faults have strongly influenced the morphology of the valley valley paleotopography has controlled depositional patterns and locations of major river courses as well as partially isolated large interdistributary basins within the alluvial deltaic plain interdistributary basin formation is further enhanced by distributary channel progradation switching and abandonment in conjunction with compactional subsidence of the alluvial plain surface geomorphology and sediment cores from the atchafalaya basin louisiana revealed that this basin has alternately accumulated fine grained organic rich sediments and terrigenous clastic dominated meander belt and lacustrine deposits basin subsidence and the presence of an active distributary channel in the basin are major determinants of the lithology of the sedimentary fill prograding lacustrine deltas of the atchafalaya river are the primary mechanism for filling the atchafalaya basin these upward coarsening deltas are relatively thin 3 m but are areally extensive tens to hundreds of kilometers and because they occur so frequently during the infilling process they account for a significant volume of the basin sequence the atchafalaya basin sequence documents lacustrine deltaic episodes dating from the early holocene maringouin and teche deltas to the present atchafalaya delta continued development of the atchafalaya river will rework portions of the backswamp and lacustrine deposits into meander belt deposits upon complete filling of the atchafalaya basin sediment will mostly bypass the basin and become deposited in the marine delta in atchafalaya bay

rinded iron oxide concretions hallmarks of altered siderite masses of both early and late diagenetic origin iron bearing concretions are valuable records of oxidation states of subsurface waters but the first concretions to form can be altered drastically during later diagenetic events distinctive concretions composed of heavy rinds of iron oxide that surround iron poor mud rich cores are common along bases of fluvial cross bed sets of the cretaceous dakota formation nebraska usa concretion rinds thicken inward and cores contain 46 to 89 void space millimetre scale spherosiderites are abundant in palaeosols that developed in floodplain facies evolution of rinded concretions began when intraformational clasts were eroded from sideritic soils transported abraded and deposited in river channels alteration of siderite and formation of rinds occurred much later perhaps in the quaternary when sandstone pore waters became oxic dakota concretions are analogous to rattlestones in pleistocene fluvial channels of the netherlands and their rinded structure is analogous to that of iron rich concretions in the aeolian navajo sandstone of utah in all three deposits rinded concretions formed when pre existing siderite cemented concretions were oxidized within a sand matrix unlike fluvial examples siderite in the navajo sandstone was autochthonous and of late diagenetic origin having precipitated from carbon dioxide and methane enriched waters moving through folded and jointed strata iron rich rinds formed in all these strata because concretion interiors remained anaerobic even as oxygen accumulated in the pore waters of their surrounding permeable matrix iron oxide first precipitated at redox boundaries at concretion perimeters and formed an inward thickening rind acid generated by the oxidation reaction drove siderite dissolution to completion creating the iron poor core iron oxide rinds are indicators of the former presence of siderite a mineral that forms only under reducing conditions during either early or late diagenesis siderite is vulnerable to complete oxidation upon exposure so the distinctive rinded concretions are valuable clues that aid in deciphering diagenetic histories and for recognizing methanic floodplain palaeoenvironments and wet palaeoclimate

evolution of the holocene mississippi river floodplain ferriday louisiana insights on the origin of fine grained floodplains abstract the alluvial architecture and soil characteristics of holo cene mississippi river floodplain deposits in the southern lower mississippi valley provide evidence for significant changes in floodplain development in response to sea level rise floodplain cores acquired near ferriday louisiana show that holocene deposits consist of 15 30 m ave 20 m of sands silts and clays which overlie late wisconsin sands and gravels on the basis of differences in sediment grain size sediment body geometry and the abundance of soil features the holocene deposits are subdivided into lower and upper holocene units lower holocene deposits 5000 yr b p consist of lacustrine and poorly drained backswamp muds that contain authigenic siderite pyrite and vivianite and show little evidence of soil formation muds encase crevasse splay and floodplain channel sand bodies 1 km wide and collectively these deposits represent a mosaic of shallow lakes poorly drained backswamps and multichannel streams similar to modern examples in the atchafalaya basin 100 km south of ferriday upper holocene deposits 5000 yr b p are represented by large mississippi river meander belt sand bodies that are up to 15 km wide and 30 m thick natural levee silts and sands and well drained backswamp muds are present between meander belt sands upper holocene deposits contain abundant soil features and sandy and silty soils are entisols inceptisols and alfisols whereas clayey soils are vertisols the presence of isolated sand bodies surrounded by mud and the scarcity of soil features suggest that lower holocene sediments reflect a period of rapid floodplain aggradation during which crevassing lacustrine sedimentation and avulsion dominated floodplain construction no evidence of large meandering mississippi river channels represented by buried thick tabular sands exists near ferriday and discharge in lower mississippi valley flow was probably conveyed by a network of small multichannel floodplain streams upper holocene sediments record a dramatic change ca 5000 yr b p from rapid to slower floodplain aggradation which was accompanied by extensive lateral channel migration overbank deposition and soil formation on the basis of differences in meander belt dimensions and numbers of abandoned channels upper holocene meander belts are subdivided into simple and complex forms relative age relationships suggest that the smaller and older simple meander belts represent periods of divided mississippi river flow and early attempts to establish a large single channel meandering regime this type of meandering regime is represented by the larger and younger complex meander belts and includes the modern meander belt similarities in the timing of changes in floodplain processes and fluvial style and decreasing rates of holocene sediment accumulation in the southern lower mississippi valley strongly suggest that decelerating holocene sea level rise in the gulf of mexico affected floodplain development at least 300 km inland from the present day coast the alluvial architecture of the lower holocene deposits and the absence of large meandering mississippi river channel deposits older than 5000 yr b p near ferriday indicates that most of the floodplain muds were deposited by avulsion related crevassing and lacustrine sedimentation rather than by overbank flooding of large mississippi river channels similarities between the floodplain history of the mississippi river and those of modern and ancient rivers elsewhere further suggest that avulsion rather than simple overbank deposition contributes to the construction of fine grained floodplains to a greater degree than generally recognized

high resolution sequence stratigraphy of fluvio deltaic systems prospects of system wide chronostratigraphic correlation a basin scale numerical model with a sub grid parameterization of fluvio deltaic processes and stratigraphy was used to study the relation between alluvial sedimentation and marine deltaic deposition under conditions of time invariant forcing the experiments show that delta evolution is governed by a robust morphodynamic feedback loop which provides a link between major avulsions delta lobe switches and sequestration of sediments on the delta plain major avulsions driven by local superelevation result in abandonment of delta lobes and initiation of new lobes progradation of the delta front lengthens the fluvial profile and reduces its gradient which induces aggradation upstream the aggradation in turn causes local superelevation of the channel belt each major avulsion causes a wave of incision to migrate upstream whereas downstream of the avulsion point the rate of aggradation temporarily increases until a new equilibrium situation has been established the feedback loop explains storage and release of fluvial sediments without the need to invoke changes in upstream or downstream controls and provides a plausible mechanism for the generation of high frequency incision aggradation cycles as the sole result of compensational stacking the stratigraphic expression of a depocentre shift is an essentially isochronous surface hence the stratigraphic record of fluvio deltaic systems may be subdivided into a series of units representing intervals during which a channel belt and delta lobe were forming at a fixed location in the basin so called chronosomes fluvio deltaic chronosomes are bounded by abandonment surfaces which are clearly expressed in the marine as well as the fluvial domain the surface marking the abandonment of a particular channel belt and delta lobe correlates with the surface at the base of a new delta lobe landward this surface forms the base of an aggradational package of fluvial sediments downstream of an avulsion site associated with a lobe switch upstream of this site the conformable surface passes into a surface of fluvial incision and terrace formation onlapped by aggradational channel belt deposits identification of the isochronous bounding surfaces of chronosomes in the field offers the attractive prospect of high resolution chronostratigraphic correlation throughout fluvio deltaic systems

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

eocene hydromorphic paleosols significance for interpreting ancient floodplain processes abstract pervasive mottling iron oxide nodules and slickensides indicate that alluvial paleosols of the lower eocene willwood formation in the elk creek area of the bighorn basin wyoming were hydromorphic two basic groups of hydromorphic paleosols are present cumulative which show evidence for concurrent deposition and pedogenesis and simple noncumulative which show evidence for a single episode of deposition and pedogenesis lithologic packages consisting of vertically stacked simple paleosols and crevasse splay sandstones alternate with cumulative paleosols the simple paleosols are weakly developed indicating rapid deposition with relatively little time for pedogenesis cumulative paleosols show greater pedogenic development indicating significantly longer periods of pedogenic m dification and slower more episodic sediment accumulation differences between the simple and cumulative paleosols reflect differences in the deposition of their parent materials the packages of simple paleosols are similar to avulsion belt deposits described from the saskatchewan river and suggest that avulsion was significant in floodplain construction the upper parts of cumulative paleosols were formed on true overbank deposits which accumulated gradually after avulsion and establishment of a new channel the lower parts of many cumulative paleosols resulted from a prior episode of avulsion deposition and simple soil formation because hydromorphy is associated with texture these different depositional processes influenced lateral variations in hydromorphy of the cumulative paleosols paleosols in the elk creek area provide a simple means of identifying avulsions sediment accumulation rates suggest that avulsions occurred with a regular period of about 20 000 years and may have been induced by climatic cycles

small scale stratigraphy in a large ramp delta recent and holocene sedimentation in the volga delta caspian sea the volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient f5 cm km and by being affected by the rapid sea level changes of the caspian sea at rates up to a hundred times the global sealevel rise this paper reports 1 the morphological and facies development of part of the lower delta during the last full sealevel cycle between 1929 and 1995 as monitored using remote sensing and field mapping and 2 the holocene development of the delta from outcrop data and augered transects during a sea level fall of 3 m between 1929 and 1977 rapid progradation of levees composed of fine sand took place along over 800 distributary channels along the delta front smaller distributaries became filled with clay and organics during the 3 m sea level rise from 1977 to 1995 aggradation occurred leading to deposition of silt and clay on the levees and minor filling of the flood basins sedimentation rates as established with 137 cs dating are up to 2 5 cm year total thickness of holocene deposits in the lower delta plain is 4 10 m

volume and routing of late glacial runoff from the southern laurentide ice sheet melting of the laurentide ice sheet during the last deglaciation added large volumes of water to many rivers and lakes of north america and to the world s oceans the volume and routing of this meltwater not only helped shape the land s surface but also played a role in the evolution of late glacial climate a computerized model was prepared to quantify meltwater generation from seven drainage areas along the southern side of the laurentide ice sheet at 500 yr time slices between 14 000 and 8000 yr b p nearly all waters reaching the oceans flowed through the st lawrence hudson or mississippi river valleys discharge through the mississippi river to the gulf of mexico during late glacial time varied by more than a factor of 5 ranging between 17 400 m3 sec 1 550 km3 yr 1 and 98 200 m3 sec 1 3200 km3 yr 1 discharge entering the north atlantic ocean through the st lawrence and hudson valleys ranged between 20 300 m3 sec 1 640 km3 yr 1 and 65 300 m3 sec 1 2060 km3 yr 1 with very abrupt twofold changes at about 11 000 10 000 and 9500 yr b p as a result of the rerouting of water from the lake agassiz basin as the areal extent and mass of the laurentide ice sheet diminished the total volume of meltwater plus runoff due to precipitation from its southern side declined from 3800 km3 yr 1 at about 14 000 yr b p to 2100 to 2600 km3 yr 1 between 11 500 and 8000 yr b p no meltwater entered the gulf of mexico after 9500 yr b p after the demise of the ice sheet over hudson bay about 8000 yr b p the modern continental drainage network was established and flows through the st lawrence declined to modern values of about 320 km3 yr 1

distal alluvial deposits in a foreland basin setting the lower freshwater molasse lower miocene switzerland sedimentology architecture and palaeosols the lower freshwater molasse untere susswasser molasse crops out over a wide area of the swiss molasse basin coarse grained alluvial fan conglomerates dominate in proximal basin areas along the alpine front these conglomerates pass northwards into sandstones and mudstones of an extensive northeastward draining meandering river system which ran parallel to the basin axis sedimentological study of outcrops quarry exposures and boreholes in the basal miocene aquitanian has permitted detailed facies analysis of this distal alluvial sequence the distal aquitanian is made up of distinct architectural elements characterized by their geometries and sedimentary structures each may be assigned to a particular depositional setting meander belt levees crevasse channels and splays overbank fines and palaeosols and lacustrine meander belt sandstones were deposited in mixed load channels with a dominant bedload component sandstones commonly comprise amalgamated and locally stacked ribbon bodies 2 15 m thick and 150 1500 m wide interbedded rippled laminated and mottled fine grained levee sandstones and siltstones form lenticular packages up to 3 m thick and 30 100 m across small scale crevasse channel sandstones 2 4 m thick and 5 10 m across pass laterally into metre scale medium to fine grained crevasse sandstone sheets rare laminated lacustrine siltstones occur only in the north east part of the basin floodplain mudstones and marls make up the remainder of the succession these display a variety of pedogenic features recording cyclical palaeosol development palaeosols show strong variations in morphology and maturity both laterally across the floodplain and downstream along the basin axis reflecting local variation in aggradation rate associated with proximity to alluvial channel courses as well as regional variation in subsidence and floodplain drainage analysis of the organization and distribution of the various sediment bodies permits reconstruction of the fluvial system and allows development of a model for the sedimentary architecture of the lower freshwater molasse in the study area integration of palaeosol studies into a well defined architectural framework assists recognition of areal facies belts and may aid location of sand prone sequences in the subsurface

geometry flow and sediment transport of alluvial deposits induced by topographically driven flow expansions abstract flow expansions are a fundamental mechanism of sediment deposition here we define flow expansions as self formed alluvial expanding deposits developing over a larger experimental delta that 1 are characterized by unchannelized flow comprising a single sheet flow that covers the entire surface of the expansion and 2 do not interact laterally with still fluid and thus are not related to jets the flow spreading mechanism is transverse topographic curvature rather than mixing with ambient fluid hence we term these expansions topographic expansions to distinguish them from jet related flow expansions in topographic expansions transverse bed convexity drives lateral flow allowing topographic expansions to maintain much higher and more variable opening angles than those of jet related expansions the characteristic depositional body produced by the expansions is a relatively thin tabular sand body with a flat base and slightly convex top comparable to some sheet flood deposits in the stratigraphic record most of the deposition takes place as the topographic expansion develops followed by a longer interval of stable sediment bypass where all measured flow expansions show similar geometries this stable bypass phase is typically terminated by the flow abandoning the deposit or by channelization of the deposit itself after which the cycle can begin again one of the research questions raised by this study is the mechanism by which topographic expansions are able to maintain themselves in an unchannelized condition at flow aspect ratios that should be unstable according to current theories of bar and channel instability

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

cyclostratigraphic record of the triassic a critical examination high frequency fourth and fifth order cyclicity is a common feature of sedimentary sequencesinalldepositionalsettings whiletectonismandautocyclicprocessesare clearlyrespon sible for this cyclicity in some instances many cases are interpreted as resulting from orbitally forced variations in solar insolation at the milankovitch frequencies that is the precession and short and long eccentricity cycles at scales of tens of thousands to hundreds of thousands of years this forcing is presumed to have controlled sedimentation through periodic changes in climate or sea level examples of interpreted milankovitch frequency cyclicity occur throughout the triassic record and include much of the german triassic the alpine triassic and the newark supergroup of north america the cyclostratigraphy of these sections has been used as a tool for intrabasinal and interbasinal correlation and for chronostratigraphy these interpretations are not always without controversy however as conceptual arguments and radio isotopic age data have called some of these conclusions into question the stratigraphic record is inherently cyclical but the scale of this cyclicity varies in scale from the outcrop to the continental the largest scale or first order cycles are those that are truly continental in scope as they are thought to record changes in sea level caused by the operation of the wilson cycle at a scale of hundreds of millions of years prothero 1990 jacquin graciansky 1998 second order cycles corresponding to the sedimentary sequences of sloss 1963 last from tens of millions up to one hundred million years and are generally considered the result of long term trends in eustasy potentially in direct proportion to the activity of the mid ocean ridges the cause of the third order sea level cycles of millions of years duration is not well understood these cycles are often apparent at the basin scale and may be related to short term tectonic activity higher frequency fourth and fifth order cycles frequently are evident at the outcrop scale fourth order cycles include the classic cyclothems of the carboniferous e g heckel 1986 and have periods in the range of hundreds of thousands of years whilefifth order cyclesoperate at frequencies of tens of thousands of years these high frequency fourth and fifth order cycles are often referred to as milankovitch cycles due to the match of their interpretedperiodswiththecalculatedmilankovitch orbital frequences it is these high frequency cycles thatarethefocusofmuchmoderncyclostratigraphy and the record and application of these cycles in the triassic system is the focus of this chapter

a contemporary appraisal of some key fiskian concepts with emphasis on holocene meander belt formation and morphology abstract looking back five decades and reflecting on the contributions of harold fisk to lower mississippi valley lmv geological knowledge it is apparent that he was highly successful in making engineers aware of the critical role of glacial advance and retreat sea level changes valley slope and river gradient and time in affecting geomorphic processes sedimentary patterns and river regimes perhaps his greatest contribution to river engineering was in recognizing and elaborating on the effects of bed and bank materials on stream meandering fisk however could only work within the prevailing geological theory and method of his time with regard to glacial chronology and stratigraphy and such matters as global structure and tectonics major advances in these areas with new concepts and techniques have shown his lmv glacial response model to be oversimplified and invalid in some respects more cycles of valley filling and cutting are now known to be represented in the alluvial sequence and his concept of deep valley entrenchment as a direct response to sea level changes is untenable in light of substantial new data the presence of a regional rectilinear fracture pattern with a corresponding network of major fault zones has not been substantiated by subsurface data the most widely known aspect of fisk s work is his detailed interpretation and colorful depiction of the complex pattern of overlapping cross cutting and discontinuous holocene meander belts and their hundreds of abandoned channels however it is now recognized that fisk s elaborate chronological reconstruction is largely invalid both because of some incorrect basic assumptions and his lack of radiocarbon and other numerical dating techniques for precise control a newly emerging model of meander belt formation is more generalized and relies heavily on archaeological evidence it places emphasis on episodes of multiple active river courses partial flow channels frequent formation of distributary channels and the significant influence of mississippi river tributaries and minor basin drainage interesting regional variations over time in meander belt configurations and morphology may reflect climate changes but at present broad scale variations in the lithology of the quaternary alluvial sequence appear to be the dominant control

early diagenetic minerals and variables influencing their distributions in two long cores 40 m mississippi river delta plain abstract two long 40 m continuous push cores of sediments from the mississippi delta plain one at a northern freshwater site and one at a southern marine influenced site have provided samples of individual concretions and homogenized bulk samples for a study of early diagenesis early pyrite calcite dolomite vivianite hematite siderite formed postburial and contains bands of clastic minerals and accessory diagenetic calcite and dolomite as well as ca mg and mn substituted in the lattice values for 13c increase with increasing depth to 11o oo pdb at a depth of 40 m reflecting the increasing role of methanogenesis with depth from analyses of bulk samples pyrite concentrations are higher in organic rich horizons do not vary appreciably with depth below one meter when adjusted for organic carbon control and are generally higher in the marine influenced core than at the freshwater site conversely concentrations of siderite are higher in fine grained siliciclastic horizons increase with depth to about 20 m and do not vary with the extent of marine influence in these cores to a first approximation distributions of pyrite appear to be controlled by variations in organic carbon concentration in sulfate sufficient systems that formed through marine incursion into organic rich layers that cap sediment packages in the deltaic system residual pyritic s is sulfate controlled and lower in the northern more freshwater organic rich sediments siderite formation appears to be focused in sulfate deficient systems that formed when siliciclastic wedges that constitute the central parts of sediment packages prograded into lacustrine or bay environments low sulfate levels in these horizons in both cores facilitated similar levels of siderite a juxtaposition of marine versus freshwater diagenetic mineral suites in adjacent horizons resulted from these interactions between physical and geochemical processes

sedimentology and geomorphology of overbank flows on meandering river floodplains abstract along floodplains there occurs an ordered sequence of geomorphic events during floods the following sequence occurs for individual flood events 1 the rise of floodwater and of groundwater 2 the inundation of the floodplain 3a adjustments of the overbank flow pattern to the floodplain environment 3b the flood peak 4 the initial fall of floodwaters and changes in the overbank flow pattern 5 a gradual cessation of the overbank flow 6a infiltration evaporation and a wave like motion of stagnant water and 6b postflood transformation under subaerial conditions field observations support this model for meandering rivers in the polish lowland

high frequency controls on alluvial successions an integrated sedimentological and palaeopedological approach to the plio pleistocene of argentina abstract plio pleistocene palaeosol bearing alluvial strata are continuously exposed along the marine cliffs of southeastern buenos aires province argentina the study interval was deposited by a mixed predominantly suspended load fluvial system outcrops are dominated by floodplain siltstones and mudstones that exhibit a cyclic alternation between calcic and vertic palaeosols this cyclicity is represented by meter scale alluvial cycles that show as a general trend a gradual increase in the proportion of channel fill deposits up section cyclic variations in palaeosols facies and architectural elements can be related to allogenic drivers such as climate and eustasy for the lower punta san andres alloformation the stratigraphic arrangement of the recognised palaeosols and the clay mineral distribution indicate that the palaeoclimate was subhumid average mean annual precipitation map 840 mm seasonal and temperate average mean annual temperature mat 7 85 c for at least 1 ma from ca 2 9 ma to ca 1 8 ma late pliocene early pleistocene with several intervals in which conditions became drier and probably colder even though climate was a major control on palaeosol development it is suggested here that it was not the main control on high frequency cycles variations in the orbital parameters more specifically in insolation were interpreted as having controlled the sedimentation and architectural evolution of the lower punta san andres alloformation depositional systems

sediment deposition and sources into a mississippi river floodplain lake catahoula lake louisiana floodplain lakes are important wetlands on many lowland floodplains of the world but depressional floodplain lakes are rare in the mississippi river alluvial valley one of the largest is catahoula lake which has existed with seasonally fluctuating water levels for several thousand years but is now in an increasingly hydrologically altered floodplain woody vegetation has been encroaching into the lake bed and the rate of this expansion has increased since major human hydrologic modifications such as channelization levee construction and dredging for improvement of navigation but it remains unknown what role those modifications may have played in altering lake sedimentation processes profiles of thirteen 137cs sediment cores indicate sedimentation has been about 0 26 cm y 1 over the past 60 years and has been near this rate since land use changes began about 200 years ago 210pb and 14c in tedford 2009 carbon sequestration was low 10 4 g m 2 y 1 likely because annual drying promotes mineralization and export elemental composition high zr and ti and low ca and k and low ph of recent 60 y or surface sediments suggest gulf coastal plain origin but below the recent sediment deposits 51 of sediment profiles showed influence of mississippi river alluvium rich in base cations such as k ca2 and mg2 the recent shift to dominance of coastal plain sediments on the lake bed surface suggests hydrologic modification has disconnected the lake from sediment bearing flows from the mississippi river compared to its condition prior to hydrologic alterations that intensified in the 1930s catahoula lake is about 15 cm shallower and surficial sediments are more acidic although these results are not sufficient to attribute ecological changes directly to sedimentological changes it is likely the altered sedimentary and hydrologic environment is contributing to the increased dominance of woody vegetation

nonmarine sequence stratigraphy updip expression of sequence boundaries and systems tracts in a high resolution framework cenomanian dunvegan formation alberta foreland basin canada ten allomembers labeled j a have been mapped in the deltaic dunvegan formation using 2340 wells and 63 outcrop sections each allomember spans about 200 k y is bounded by regional transgressive surfaces and consists of 3 10 component shingles apparently of autogenic origin allomembers h e are discussed in this article their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences sequences h f have a sigmoidal prismatic geometry downlap to the southeast and thin northwest onto the coastal plain no differential thickening exists toward the orogen in the southwest in contrast sequence e thickens markedly toward the northwest the tabular geometry of sequences h f suggests accommodation was controlled by sea level change whereas the wedge geometry of sequence e suggests significant tectonic tilting subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120 330 km updip into outcrop the base of each sequence is characterized by shoreline backstep of 80 150 km transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata falling stage shingles offlap seaward with little or no nonmarine equivalents updip whereas lowstand shingles show renewed coastal onlap in outcrop three nonmarine systems tracts are recognized 1 a channel dominated low accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract begin page 1968 2 a lacustrine dominated high accommodation systems tract comprises mudstone enclosing ribbon channel sandstones blankets interfluves and forms the bulk of each sequence it is equivalent to late transgressive and early highstand systems tracts 3 a paleosol dominated low accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary it is equivalent to the late highstand systems tract sequence bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation followed by fluvial entrenchment and clastic bypass and represent the late highstand falling stage lowstand and early transgressive systems tracts coastal plain deposits record only part perhaps

fluvial evolution of the rhine during the last interglacial glacial cycle in the southern north sea basin a review and look forward this paper presents the current state of knowledge on the evolution and depositional history of the river rhine in the southern part of the north sea basin during the upper middle and late pleistocene and its response to climate change sea level oscillation and glacio isostasy the study focuses on the development of the eemian interglacial lower delta in the central netherlands and its relation to records of climate and sea level rise and uses the saalian and weichselian pre and postdating periods to place its development in context the rhine fluvial system fills the gradually subsiding north sea basin but its development has strongly been affected by the saalian glaciation and its remaining topography ice pushed ridges originating off the limit of maximum glaciation basically divided the central netherlands into two sedimentary depocentres a central depocentre within the former ice limit and a southern depocentre south of it the sedimentary record of the central depocentre including an incised valley fill shows a 20 40m thick stacked sequence consisting of three units the incised valley fill consists of a late saalian to early eemian age lower fluvial unit and a weichselian age upper fluvial unit both composed of coarse grained channel deposits sandwiched in between is a 5 15m thick record composed of fine grained fluvial and estuarine tidal floodbasin and shallow marine deposits it is of eemian interglacial and early weichselian age and comprises transgressive and highstand deposits that show the drowning of a fluvial system inland parts transformed from fluvial to deltaic and estuarine environments and the most downstream parts transformed to a shallow marine embayment preservation of these units occurred despite considerable sea level fall and climate controlled erosion taking place in the last glacial preservation potential was increased by the fact that the rhine system avulsed away to the southern depocentre halfway the weichselian pleniglacial consequently the infill of the southern depocentre is of an entire different nature and last interglacial transgressive or highstand units are hardly preserved because of glaciation and resulting depocentre configuration the netherlands in nw europe thus offers a very good opportunity to study the transgressive interglacial lower deltaic records and falling stage preservation thereof both key elements for understanding sedimentary development over full 100 ky glacial interglacial cycles of climate and base level change 2014 elsevier ltd and inqua

evidence for multiple episodic mid holocene hypsithermal recorded in two soil profiles along an alluvial floodplain catena southeastern tennessee usa abstract floodplain soil paleosol successions are valuable archives for reconstructing pleistocene holocene climate changes but have been relatively unstudied in the southern appalachian region two soil profiles on a small floodplain in southeastern tennessee usa were described and sampled in detail using both pedological and geological approaches including stable carbon isotope analysis of soil organic matter som correlation between the 2 profiles was constrained by uncalibrated ams 14c ages of bulk humates and using som 13c values both mobile and immobile elements four distinct 2 5 4 shifts towards less negative 13c values for som suggest 300 yr cyclicity and transient warmer and drier climate events with either water stressed c3 vegetation or as much as 35 c4 plants present during the mid holocene these postulated multi episodic drier climate conditions have never before been documented in the southern appalachian region and are tentatively correlated with mid holocene warming and drying in the eastern us the nearly time equivalent mid holocene events documented in texas the us high plains and in the gulf of mexico high rates of floodplain sediment accumulation 0 5 3 mm yr high clay content and maintenance of poorly drained soil conditions favor preservation of high resolution climate archives in floodplain deposits by inhibiting oxidation and translocation of organic c

caprock analysis from the mihalyi repcelak natural co2 occurrence western hungary caprock integrity is one of the most important factors regarding the long term safe underground storage of co2 as a result of geochemical reactions among the caprock mineralogy and co2 saturated pore water the physical properties of caprock such as porosity permeability may change which could affect its sealing capacity natural co2 occurrences can help to understand these long term reactions under storage conditions on geological timescale our study area the mihalyi repcelak natural co2 occurrence is believed to be leak proof system on geological timescale to identify and understand the mineral reactions in the caprocks we applied xrd ftir atr and sem analysis of drill cores derived from the study area the petrophysical properties of the studied rock samples were determined from the interpretation of geophysical well logs and grain size distribution the effective porosity 4 permeability 0 026 md and clay content 80 of the drill cores imply that the studied clayey caprocks represent an adequate physical barrier to the co2 our analytical results show that dawsonite has formed within the caprocks in most cases the dawsonite crystallized after albite dissolution this implies that co2 or co2 saturated brine can penetrate into the caprock resulting in mineral reactions and most likely changing the porosity and permeability of the sealing lithology on the other hand the caprock may react as a geochemical buffer for the co2 and at least part of it can be stored within the caprock as solid phase thereby increasing the storage capacity of the system

revealing the late pliocene to middle pleistocene alluvial archive in the confluence of the western carpathian and eastern alpine rivers 26al 10be burial dating from the danube basin slovakia abstract the danube basin located in the junction of the eastern alps and western carpathians comprises up to 600 m thick alluvial succession which was previously assigned to the quaternary without geochronological constraints the internal stratigraphy and timing of the succession remained unknown although it has potential to provide an important record of geological evolution of the region the present study involves 26al 10be burial dating of 17 samples from wells along with facies correlation from the nw margin towards the basin centre with the purpose of recovering the pliocene quaternary depositional archive obtained ages ranging from 0 58 0 06 to 3 39 2 11 ma allow for four separate members to be distinguished the lowermost kolarovo fm with inferred depositional age of 5 2 6 ma shows lateral variability with gradual shift of channel fills composed of sands and gravelly sands across the floodplain pond facies from nw to se an abrupt increase of sediment supply accommodation ratio was observed at 2 6 ma and led to the dominance of amalgamated gravelly channel fills in the centre of the basin another sharp increase of sediment supply was observed at 1 2 ma reflected in a brief period of dominance of gravelly channel fill facies across the basin this highly supplied environment then gradually occupied the whole basin after 0 9 ma petrographic study implies a distant provenance for the period 5 0 2 6 ma the subsequent interval is characterised by sediment sourcing from uplifting mountains of the western carpathians on the margins of the danube basin drained by the vah river a notable change appeared after 0 9 ma when the eastern alpine provenance of clasts brought by the danube river prevailed based on a review of existing data about regional tectonics and climate the changes in this depositional record are interpreted as an interplay of climate changes 2 6 ma and 1 2 ma and local vertical movements affecting both sediment input and drainage network patterns the accommodation space was formed without contribution of fault activity according to the observed settings a noteworthy observation is time transgressive shift of facies boundaries in the pliocene quaternary succession

avulsion deposits in lower eocene alluvial rocks bighorn basin wyoming abstract eocene alluvial rocks in the northern bighorn basin can be subdivided into three major kinds fine grained deposits on which cumulative paleosols developed lithologically heterogeneous packages associated with immature paleosols and major sheet sandstone bodies the heterogeneous packages which alternate vertically with the cumulative paleosols are dominated by fine grained deposits and also contain ribbon sandstone bodies and thin 1 m sheet sandstone bodies most ribbon sandstones are less than 3 m thick and are more common in the middle and upper parts of the packages cut and fill deposits with fine grained fills are locally important because the lithologic packages are readily apparent in the field because of the immature or simple paleosols developed on the fine grain d facies they are referred to as simple paleosol packages the major sheet sandstones were deposited by meandering trunk rivers and locally overlie and truncate the other deposits contrary to classical models of meandering streams only a portion of the fine grained rocks in the study area were deposited by overbank flooding of a trunk channel on the basis of their stratigraphic position and few ribbon sandstones the upper parts of some simple paleosol packages are interpreted as ancient levee deposits associated with a trunk channel farther from the trunk channel overbank floods deposited alluvium on which the cumulative paleosols formed the greater parts of the simple paleosol packages including their fine grained deposits were deposited rapidly during channel avulsion ribbon sandstone bodies represent ancient splay channels on the avulsion belt simple paleosol packages in the willwood formation support the contention of smith et al 1989 that n many meandering river systems a significant portion of the fine grained deposits were deposited as the trunk channel avulsed deposits that resemble the simple paleosol packages may provide a means of recognizing avulsion episodes in other alluvial sequences

field strength variations of lf radio waves prior to earthquakes in central italy abstract the electric field strength of the lf radio broadcasting rmc principality of monaco which operates at 216 khz has been recorded since january 1991 by two receivers in central italy during the monitoring period we observed two evident attenuations of the field strength in one receiver with durations of 6 10 days the geomagnetic and ionospheric observations carried out in the same time interval do not seem able to explain the attenuation of the radio signal an analysis of the seismic activity occurring in the area between transmitter and receiver has revealed that some days after the attenuations the energy released by earthquakes reaches a maximum the observed attenuation might therefore be precursors of earthquakes we also checked meteorological conditions and found that advections of warm air occurred during both the two anomalous periods it seems possible that these conditions can help the action of preseismic effects in generating irregularities in the vertical gradient of the tropospheric radio refractivity able to produce defocusing of lf radiobroadcast propagation

holocene floodplain evolution in the shiribeshi toshibetsu river lowland northern japan abstract the influence of sea level and climate changes on the evolution of coastal floodplains is an important problem in fluvial geomorphology and geology however few studies have constructed detailed chronologies of floodplain evolution and the influence of sea level and climate changes at submillennial time scales is not clear this study investigated the holocene evolution of the floodplain in the shiribeshi toshibetsu river lowland hokkaido northern japan based on 13 auger cores 15 radiocarbon ages and 2 cross sections made using existing columnar sections in the study area peat beds 3 6 m thick in the uppermost holocene sediments are underlain by fluvial sediment that mainly consists of sand beds resulting from crevassing or progradational avulsion age elevation plots of the bases of these peat beds suggest that fluvial aggradation was continuous until peat formation began which in turn suggests that peat beds began to form with the cessation of fluvial deposition the chronology of floodplain sediments based on radiocarbon ages indicates that peatlands began to develop locally before ca 6500 cal bp and became moderately widespread before 5600 cal bp peatlands then became more extensive after two periods of rapid expansion during ca 5300 5000 and 4100 3900 cal bp comparison with sea level and regional climate changes suggests that the initiation of these peat beds before 5600 cal bp was associated with the deceleration of sea level rise at ca 7000 cal bp the two later periods of peatland expansion may have been strongly influenced by reduced fluvial activity due to decreased precipitation from a weakened east asian summer monsoon this interpretation suggests that floodplain evolution was controlled by sea level and climate changes and that the response to climate change occurred at submillennial time scales a comparison with the ishikari lowland on hokkaido showed that the two floodplains have slightly different histories possibly because of differences in internal characteristics of the fluvial systems such as the number and size of tributary rivers water discharge and sediment supply although their responses to sea level and climate changes were similar the fluvial response to sea level and climate changes revealed in this study has implications for studies of the holocene evolution of other coastal floodplains

diagenetic siderite and other ferroan carbonates in a modern subsiding marsh sequence abstract mineralogical and carbon and oxygen stable isotope compositions in siderite rich concretions from a marsh within the mississippi river deltaic plain are highly variable the concretions have sideritic interiors and become more calcitic and dolomitic ankeritic near their margins 13c values of these concretions range from 10 0 to 7 4 pdb and 1 o values range from 2 4 to 8 9 pdb the stable isotope compositions exhibit two general trends one is a growth trend that shows 13c an 18o depletion from the centers to the margins of the nodules and bands the other is a progressive burial trend that shows 13c enrichments and 18o depletions at the centers of the concretions with depth a zonal model for carbonate precipitation with emphasis on an early fresh water non sulfidic methanic phase followed by a sulfidic stage associated with marine inundation of the marsh explains much of the observed carbon isotopic variations mixing of fluids plus precipitation in a partially closed chemical microsystem accounts for most of the oxygen isotope fractionations documented between growth layers and casts doubt on the utility of change in 18o shifts as an indicator of depth or relative temperature of concretion formation for concretions that form in coastal environments

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

kosi megafan historical records geomorphology and the recent avulsion of the kosi river abstract it has been proposed that the kosi river continuously migrated 113 km westward across the surface of the megafan over the last two centuries examination of a number of old maps published between 1760 and 1960 shows that during most of this period the kosi river occupied a position slightly east of the megafan axis the apparent channel movement shown in these maps is oscillating in nature and not unidirectional instead of encountering deposits left behind by a sweeping braided kosi like stream a preliminary study of the uppermost 2 5 m succession in the north central part of the megafan reveals overwhelming dominance of meandering stream deposits assuming the existing notion of kosi river migration the rate of deposition averaged over 100 200 years for the uppermost 5 10 m of megafan deposits works out to be unusually high 50 mm y all these observations question the soundness of the hypothesis of rapid westward migration of the kosi river over the last two centuries the existing facies model for the uppermost 8 10 m of the megafan deposits also appears untenable the three dimensional geometry of the kosi megafan is similar to those of typical alluvial fans but with much gentler gradient 0 05 0 01 and with larger area 10 000 km 2 based mainly on the patterns of paleo and modern channels recognised in the satellite images three major accretionary lobes can be identified on the kosi megafan relative age of the lobes determined from the truncating relationship of the paleochannels indicates a random shift of the trunk channel forming these lobes similar multilobate form and evidences of random switching of the loci of lobe aggradation are also found to be common in the tista and taquari megafans the factors known to favour avulsion and the results of the recent simulation studies of alluvial deposits are inconsistent with the notion of unidirectional shift of the channels for more than 100 km across the entire megafan surface this study suggests that the relocation of the kosi river in the past was through random nodal avulsion rather than systematic unidirectional shift the recent avulsion of the kosi channel by a large distance to the east follows this expected pattern further study and age dating is required for a comprehensive understanding of the depositional dynamics of the megafan and the pattern of channel movement on it future flood predictions and disaster management plans should be based on such comprehensive understanding

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

middle to late holocene delta plain evolution of the kimotsuki lowland kyushu southern japan abstract the evolution of delta plains and coastal floodplains is commonly believed to be influenced by sea level and climate changes however regional climate change influences on the evolution of delta plains and floodplains are poorly understood compared with responses to rapid sea level rise since the last deglaciation this study investigated the kimotsuki lowland delta plain evolution kyusyu southern japan including allogenic controls based on 28 auger cores and 28 radiocarbon ages large scale crevasse splay deposition occurred at 7000 6000 cal yr bp in response to sea level rise or increased sediment supply following a volcanic eruption afterwards widespread peat was formed in the absence of substantial fluvial sedimentation decreased precipitation from a weakened east asian summer monsoon may have dried the peatlands around 4000 cal yr bp with increasing precipitation and storminess around 2000 cal yr bp peat formation resumed at areas further from the kimotsuki river while increased overbank flows deposited organic rich mud near the river these changes may reflect an increased frequency of la nina events and higher ocean surface temperatures of the kuroshio extension the increased storminess around 2000 cal yr bp may have produced similar influences on delta plain and coastal floodplain evolution across the east asia region the results of this study suggest that regional climate change in the late holocene has a potential to control the evolution of coastal floodplains and delta plains

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

sedimentology floods of record research on two bolivian rivers provides explanations of how and when they flood it also gives pointers for interpreting earth s history as recorded by the sediments left behind by flood waters

micromorphology and sequence stratigraphy of the interfluve paleosols from the ganga plains a record of alluvial cyclicity and paleoclimate during the late quaternary

multiproxy studies of early miocene pedogenic calcretes in the santa cruz formation of southern patagonia argentina indicate the existence of a temperate warm vegetation adapted to a fluctuating water table abstract the lower miocene santa cruz formation in southern patagonia austral basin argentina contains several horizons of pedogenic calcretes which record 17 5 myr old vegetation adapted to a shallow and fluctuating water table at paleolatitude of 56 s to reconstruct the paleoenvironment paleoclimate and paleoecosystem we performed a multiproxy study of the calcretes examining abiotic and biotic components the calcretes exhibit a variety of morphologies horizontal and vertical rhizoliths laminar structure nodules massive crusts microfabrics beta predominant over alpha microfabrics and 18o and 13c values that fluctuate within each morphotype and throughout the analysed interval microfossils and phytoliths in the host material of the calcretes indicate fluctuating terrestrial freshwater and marine conditions and record an ecosystem dominated by herbaceous plants and arboreal elements in association with a typical coastal santacrucian vertebrate fauna we propose that the calcretes developed in soils in a coastal fluvial setting during pauses in floodplain aggradation that typically lasted between 8 25 ka and 400 ka years variable sedimentation rates in different parts of the coastal fluvial floodplain the fine texture of the host sediment and the influence of a fluctuating water table also influenced the formation of the calcrete a high water table in low relief areas of the floodplain created the conditions necessary to form a horizontally extended rhizolithic system that jointly with the biotic proxy can be correlated with a radicular pattern similar to the arboreal elements from coastal settings abiotic and biotic proxies of the studied interval attest to environmental fluctuations recorded at different scales that took place under temperate warm and subhumid climates with a marked rainfall seasonality with a slight increase in the aridity towards the top of the studied interval under these conditions a subtropical fauna and a c3 dominated ecosystem developed coincident with the onset of the mid miocene climatic optimum in patagonia

applying dem srtm for reconstructing a late quaternary paleodrainage in amazonia abstract remote sensing is a particularly invaluable tool that has helped the detection of paleomorphologies produced by river dislocation in a variety of landscapes which has contributed in reconstructing the geological evolution of many fluvial systems this technique might provide useful information to discuss the evolution of large fluvial systems in special those located in areas of difficult access where the acquisition of field data is difficult application of remote sensing for paleodrainage characterization in densely vegetated tropical areas is scarce in the literature this work records processing of the digital elevation model dem derived from the shuttle radar topography mission srtm which succeeded in revealing an ancient drainage complex of the madeira river one of the main amazonas tributaries where other remote sensing products failed the detection analysis of this paleodrainage and of its modern counterpart within the geological framework available for this region leads to propose that activity along pre existent faults during the latest quaternary would have promoted the southeastward dislocation of a nearly 200 km long segment of the madeira river during this process an impressive paleodrainage network was left behind which was only able to be detected using the dem srtm application of this technique might be of great help to the detection of paleodrainage morphologies in densely vegetated areas similar to the amazonas lowland the dynamics of channel migration in this and many other large scale tropical river systems might benefit from the investigation based on data derived from dem srtm

geostatistical analysis of overbank deposits of anastomosing and meandering fluvial systems rhine meuse delta the netherlands the architecture of overbank deposits of anastomosing and meandering rivers in the central rhine meuse delta the netherlands is analysed by geostatistical investigation of three detailed cross sections in two study areas the thickness of the overbank deposits in the cross sections were examined by semivariogram analysis the cross sections show that two different types of overbank deposits are found at different depths at the same location at greater depths lithologically complex overbank deposits with many crevasse splays and a varying thickness are found at shallow depths lithologically uniform overbank deposits with a more or less constant thickness are found the semivariogram analysis serves as a tool to distinguish between these two types of overbank deposits semivariograms of the lithologically complex overbank thicknesses strongly differ from the semivariograms of the more uniform overbank deposits the former show large nugget values combined with large sill values and a small range the latter show small nugget values and a clear trend and no sill is reached the complex overbank deposits are thought to be deposited by anastomosing rivers the uniform overbank deposits by meandering rivers maximum boring intervals for mapping of the overbank deposits can be derived from the semivariograms if a complete understanding of the fluvial architecture in the study areas is needed e g for reservoir characterization a sampling grid of 25 m perpendicular and 100 m parallel to main flow direction is necessary

石狩低地内陸部で採取された ik1 コアが示す完新世の堆積環境 堆積速度の変化

channel floodplain geomorphology along the solimoes amazon river brazil across the cratonic landscape of brazil the solimoes amazon river transports to its delta plain 1240 mt of suspended sediment derived from andean erosion and reworks another 3200 mt of floodplain sediments distribution of these sediments has resulted in a variable along stream pattern of geomorphology the upstream reaches are characterized by sediment erosion in the main channel and deposition in floodplain channels that are an order of magnitude smaller in discharge than the main channel sediment deposition in and migration of the floodplain channels erases oxbow lakes of the main channel and yields an intricate scroll bar topography that forms the boundaries of hundreds of long narrow lakes in contrast downstream reaches are characterized by channels restricted by stabilizing long term levee building and floodplain construction dominated by overbank deposition overbank deposition buries the scroll bar topography resulting in a flat floodplain covered by a patchwork of large more equant shallow lakes on the basis of estimated rates of recycling of floodplain sediments the modern floodplain of the brazilian amazon could have been recycled in 5000 yr and is recycled more rapidly in the upstream than the downstream reaches the cratonic interior is interrupted by structural arches that bound intracratonic basins four of these arches cross the valley of the main river system at intervals of several hundred kilometres and impart a tectonic imprint on the channel floodplain geomorphology at this spatial scale structural arches appear to exert a primary influence by promoting entrenchment of the river as it passes through zones of deformation thus restricting channel movement for example as the river crosses the purus arch the valley narrows to 20 km compared to an average of 45 km the water surface gradient decreases sediment is deposited and yet the rate of channel migration is negligible hence the effect of the arches is to create a landscape where on the spatial scale of hundreds of kilometres the river is confined and entrenched in its valley is straight and is relatively immobile local valley tilting apparently unrelated to the arch structures also imprints the geomorphology in particular a tilted valley in the upstream reaches appears to have caused avulsions which have left behind the only large scale oxbow type features on the brazilian amazon river floodplain

sediment load and floodplain deposition rates comparison of the fly and strickland rivers papua new guinea 1 rates of aggradation and infilling of accommodation space along lowland channels in response to postglacial sea level rise should depend on sediment supply the strickland and fly rivers join at just 6 m above sea level and have experienced the same holocene sea level rise historically the strickland has carried about 7 times the sediment load and 1 4 times the water discharge as the fly therefore we hypothesize that the lowland strickland floodplain should be more developed and consequently should presently be capturing proportionately less sediment than the floodplain of the lowland fly river we use mine derived elevated pb and ag concentrations in 111 shallow 1 m floodplain cores collected in 2003 to determine deposition rates across the lower strickland floodplain sediment deposition rates decrease across the floodplain with distance from the channel bank and the average rate of deposition is 1 4 cm a over the first 1 km overbank deposition along the lowland sandbedded strickland results in 13 loss of the total load 0 05 km of channel length of the main stem deposition rates over the first 1 km from the channel bank on the strickland are about 10 times those on the fly for estimated natural sediment loads however the proportional loss per channel length on the strickland is less than that on the fly 0 09 km of main stem channel length because of an extensive network of tributary and tie channels that convey sediment to the floodplain on the fly furthermore the lateral migration of the strickland channel is 5 times that on the fly such that most overbank deposits on the strickland are returned to the channel causing the net loss of sediment to the floodplain to be small we conclude that the strickland river which has a much higher overbank deposition rate than the fly river as a function of distance from channel bank nonetheless has significantly less net accumulation than the fly because 1 a large proportion of the sediment load is conveyed up tributaries and tie channels on the fly and 2 lateral migration which presumably results from the higher load on the strickland sweeps sediment back into the channel hence our field observations support our initial hypothesis though the primary reason for this is because of active lateral migration rather than low overbank deposition rates

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

holocene flood plain soil formation in the southern lower mississippi valley implications for interpreting alluvial paleosols holocene mississippi river flood plain soils in central louisiana provide important insights on alluvial pedogenesis in an aggradational setting insights that are useful for interpreting alluvial paleosols the flood plain soils are younger than ca 5400 yr b p and are grouped into two categories 1 meander belt and 2 backswamp soils meander belt soils are entisols inceptisols and alfisols developed on point bar ridges and natural levee crests they consist of 3 5 m thick brown silty and sandy moderately well drained profiles with multiple parent materials common yellow brown and gray mottles and a few iron and calcite nodules backswamp soils are vertisols formed in flood plain depressions away from active and abandoned mississippi river channels and consist of up to 10 m thick gray clayey poorly drained profiles that have abundant yellow brown mottles iron and calcite nodules gypsum accumulations and slickensides the thickness of the soils and the presence of multiple parent materials show that as the flood plain aggrades concurrent or alternating episodes of sedimentation and pedogenesis produce cumulative profiles profile thickness is more closely related to sediment accumulation rates than to the depth of chemical weathering and the cumulative nature of the soils explains the difficulty of recognizing discrete paleosol profiles in many ancient alluvial deposits comparisons of soils formed on the three youngest holocene mississippi river meander belts saucier and snead 1989 show that the soils record episodes of meander belt growth abandonment and relocation meander belt 1 soils form as the active meander belt develops and consist of either vertically stacked entisols or a single inceptisol the soils contain few calcite nodules and form over intervals of a few hundred years meander belt 2 soils are alfisols lack free carbonates and form over intervals of a few thousand years following meander belt abandonment and soil leaching meander belt 3 soils are alfisols or vertisols that contain common calcite nodules and the profiles are developed in 1 to 2 m of backswamp mud that overlies meander belt silt and sand the mud inhibits profile leaching and leads to poor drainage and calcite precipitation this change in soil hydrology complicates interpretations of the effects of time on meander belt soil development backswamp soils are strongly influenced by seasonal episodes of soil wetting and drying as demonstrated by the gray colors and the abundance of mottles nodules and slickensides in the soils the distribution of calcite nodules in the backswamp and meander belt soils is more closely related to seasonal water table position than to mean annual precipitation which suggests that not all calcic paleosols in ancient alluvial deposits represent semiarid or arid climates slickensides attest to seasonal rainfall but the composition of the backswamp soils primarily reflects source area lithology and depositional influences rather than the effects of chemical weathering in general these soils provide an incomplete record of the humid subtropical climate of louisiana although short term sediment accumulation rates decrease away from mississippi river channels the backswamp soils are not better developed i e more mature than the meander belt soils because poor drainage and slow but continuous sedimentation inhibits weathering collectively these observations suggest that flood plain soils that developed in aggradational settings such as that of the mississippi river flood plain are best suited for interpreting depositional and hydrologic histories of ancient alluvial deposits rather than paleoclimates

late quaternary dynamics of the tisza river evidence of climatic and tectonic controls abstract the focus of this study is to understand a dramatic avulsion event on the tisza river during the late pleistocene the river course switched by about 80 km from the east to west of the great hungarian plain ghp through the zahony bend to its present meander belt the aim of this study is to date this zahony avulsion based upon radiocarbon and pollen samples from six cores in the polgar study area situated in the west of the ghp at the middle course of the tisza river in addition a grain size composition and heavy mineral analysis has been performed the results of these analyses reveal a sequence of paleochannels and have been plotted on a high resolution digital elevation model illustrating the paleochannel form and age relationships the study suggests that the age of this major avulsion event is significantly older than it was previously supposed instead of 10 to 11 ka it is according to our new data 16 18 ka and definitely predates the last glacial maximum lgm the river cut into the previous contiguous surface and formed at least one climatic terrace then drifted gradually westward as a response to a tilt or the differential subsidence of tectonic origin

carbonate lake deposits associated with distal siliciclastic perennial river systems abstract the genesis of thick accumulations of carbonate lake deposits on the siliciclastic floodplains of perennial rivers situated below the regional spring line requires 1 a significant source for calcium in the watershed and 2 a protected area to accumulate calcite the phanerozoic record of fluvial deposits shows that anastomosing rivers with carbonate rich provenance situated in distal areas below the spring line are the best environments for floodplain accumulation of significant carbonate lake deposits anastomosing rivers exist below the regional spring line and have isolated flood basins generally protected from bedload by high levees receiving suspended and dissolved load during flooding events numerical modeling to test the rate of accumulation for these carbonate sediments was performed using stratigraphic data from the pennsylvanian succession containing floodplain limestones of the stewart quadrangle of athens county in ohio usa limestone volumes for six limestone units upper pittsburgh fishpot sewickley benwood arnoldsburg uniontown and waynesburg limestones were calculated with the assumption of overland input of dissolved calcite from carbonate source areas in comparing the calcium input rate to the amount of calcium calculated from limestone unit volumes overland transport of calcium ions not spring input can supply sufficient ions to accumulate thick carbonates over the short lifetime of floodplain lakes within anastomosing river systems

the tectono sedimentary evolution of a major seismogenic zone with low slip rate activity a geochronological and sedimentological investigation of the dobra voda depression western carpathians abstract seismically active fault zones receive a great deal of attention due to their potential for quantification of seismic hazards zones with low slip rates pose a challenge however since their poor topographic expression is related to difficulties in the quantification of fault movement this study focuses on the dobra voda depression an area with the highest level of seismic activity in the western carpathians the quaternary tectono sedimentary evolution of the small intramontane basin was investigated with the use of facies analysis of cores dated with the use of cosmogenic nuclide depth profiles 10be 26al and 36cl together with 26al 10be burial dating and radiocarbon dating a set of archived boreholes and geoelectric survey data was used for the correlation of results with those from new boreholes across the depression four facies associations were distinguished fa1 colluvial deposits that comprise subaerial debris flows and mudflows fa2 fluvial deposits with high sediment supply accommodation ratio composed mostly of sandy gravelly channel fill facies fa3 fluvial deposits with low sediment supply accommodation ratio consisting mostly of floodplain muds overbank heterolithic facies and minor sandy gravelly channel fills and fa4 swamp deposits which are mostly made up of peat geochronological results suggest that the studied part of fa3 was deposited before 1 0 ma due to a rise in the base level following a major incision event overbank dominated deposits of fa3 covered an incision surface resulted in a difference of ca 65 m of elevation of these strata which represents the minimal thickness of fa3 the second phase of incision was related to reactivation of miocene normal faults resulting in further topographic differentiation the initiation of fault activity is recorded by the deposition of colluvial fa1 before ca 250 ka fa2 accumulated between ca 160 and 100 ka mostly at the toes of slopes bounding the fault scarps on the basin margins the last documented phase of evolution represents an increase of accommodation which was connected to the deposition of holocene peat in swamps as well as floodplain muds of fa4 above fa2 the observed settings imply that variation between incision and accumulation in a scale of hundreds of thousands of years is characteristic for low relief tectonically active zones the presented research demonstrates the significance of sedimentological analysis for reconstruction of tectonic evolution in areas with low slip rate activity

holocene evolution of the western orinoco delta venezuela the pristine nature of the orinoco delta of eastern venezuela provides unique opportunities to study the geologic processes and environments of a major tropical delta remote sensing images shallow cores and radiocarbon dating of organic remains form the basis for describing deltaic environments and interpreting the holocene history of the delta the orinoco delta can be subdivided into two major sectors the southeast sector is dominated by the rio grande the principal distributary and complex networks of anastomosing fluvial and tidal channels the abundance of siliciclastic deposits suggests that fluvial processes such as overbank flooding strongly influence this part of the delta in contrast the northwest sector is represented by few major distributaries and overbank sedimentation is less widespread relative to the southeast sector peat is abundant and occurs in herbaceous and forested swamps that are individually up to 200 km 2 in area northwest directed littoral currents transport large volumes of suspended sediment and produce prominent mudcapes along the northwest coast mapping of surface sediments vegetation and major landforms identified four principal geomorphic systems within the western delta plain 1 distributary channels 2 interdistributary flood basins 3 fluvial marine transitional environments and 4 marine influenced coastal environments coring and radiocarbon dating of deltaic deposits show that the northern delta shoreline has prograded 20 30 km during the late holocene sea level highstand progradation has been accomplished by a combination of distributary avulsion and mudcape progradation this style of deltaic progradation differs markedly from other deltas such as the mississippi where distributary avulsion leads to coastal land loss rather than shoreline progradation the key difference is that the orinoco delta coastal zone receives prodigious amounts of sediment from northwest moving littoral currents that transport sediment from as far away as the amazon system 1600 km late holocene progradation of the delta has decreased delta plain gradients increased water levels and minimized overbank flooding and siliciclastic sedimentation in the northwest sector these conditions coupled with large amounts of direct precipitation have led to widespread peat accumulation in interdistributary basins because peat forming environments cover up to 5000 km 2 of the delta plain the orinoco may be an excellent analogue for interpreting ancient deltaic peat deposits

middle to late holocene paleochannels and migration of the palar river tamil nadu implications of neotectonic activity abstract geomorphic tectonic and sedimentary investigations have been carried out to understand the landscape evolution of the palar river basin southern peninsular india for this purpose satellite data interpretations coupled with field investigations fluvial architecture and optically stimulated luminescence osl dating methods were adopted to infer climatic variations and neotectonic deformation that took place during the mid to late holocene period several paleochannels have been identified in the northern part of the present day palar river the distribution pattern of the palar paleochannels and its present course indicate its migration towards the south leaving behind the old palar river streams as paleochannels significant changes in the morphological characteristics channel width and river pattern in the successive paleochannels reveal evidences of channel movement by avulsion largely controlled by reactivation of pre existing lineaments and intensified ne monsoon based on osl ages two major phases of migration have been identified that occurred between 4 83 ka to 1 88 ka first phase occurred between 3 59 ka to 3 26 ka due to intensified monsoon accompanied with small scale neotectonic activity the second phase took place between 2 42 ka to 1 88 ka which occurred probably due to the rapid upstream avulsion this rapid avulsion is due to the close proximity of mpa and the reactivation of the pre existing lineaments moreover the present palar river basin exhibits evidences of neotectonic activity such as soft sediment deformation structures anomalous drainage deflections and reactivation of lineaments and faults further indicating that the palar river is still draining a tectonically active region thus neotctonics and fluctuations in the intensity of monsoon are largely responsible for sculpting the present landscape

an approximation of the sediment budget of the lower mississippi river prior to major human modification a sediment budget is constructed for the lower mississippi river prior to the introduction of most human modifications components of the budget are derived from historical data including mississippi river commission hydrographic survey maps for the period from 1877 to 1924 a quantitative estimate of major sediment sources sinks and storage locations in the lower mississippi valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short term channel storage than in longer term overbank storage the budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated the magnitude and variability of these sediment budget components are discussed the results of the study suggest that prior to modifications the river was aggrading over much of its length

fine grained splay deposition in the avulsion belt of the lower saskatchewan river canada abstract in or about 1883 a northward avulsion of the meandering lower saskatchewan river at the cumberland marshes initiated a broad belt of alluvial sedimentation that has continued to evolve to the present and now covers some 500 km2 the avulsion belt comprises a complex alluvial terrain dominated by individual and coalesced splays and associated wetlands connected by networks of active and abandoned channels of various sizes the windy lake splay a predominantly fine grained feature typical of large parts of the avulsion belt was examined to investigate the relationships between splay evolution and facies development the splay now largely inactive mostly formed over a 35 year period depositing nearly 2 m of sediment over a 7 2 km2 area the splay surface is ch racterized by stable well defined anastomosed distributary channels that separate interchannel wetland basins heights of channel levees diminish downstream and the levees merge with channel mouth bars whose progradation forms the locus of lakeward channel extension and the base for subsequent subaerial levee deposition the anastomosed channel pattern was created when the mouth bars of separate distributary channels merged during progradation vibracore and soil probe profiles show the splay to be dominated by upward coarsening lacustrine prodeltaic mouth bar facies sequences capped by levees and organic rich interchannel wetland deposits channels now containing sand only sporadically in narrowed or slightly migrated reaches will eventually fill with fine sediment when abandonment s complete the windy lake splay is typical of stage iii splays smith et al 1989 whose deposits and associated lacustrine fills form at least half of the avulsion belt thin widespread predominantly upward coarsening sequences capped by either nondepositional horizons or true overbank fines may be characteristic of many avulsive suites in the ancient alluvial record

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

alluvial pedogenesis in pleistocene and holocene mississippi river deposits effects of relative sea level change comparison of pleistocene and holocene soils developed in mississippi river meander belt deposits in louisiana illustrates the influence of relative sea level change on pedogenesis holocene and pleistocene meander belts have similar landscape morphologies lithofacies and soil characteristics and probably formed under similar hydrologic regimes the pleistocene avoyelles prairie meander belt is now terraced but it was originally graded to a lower relative sea level position than the holocene flood plain holocene alluvial soils are generally weakly expressed cumulative profiles with abundant redoximorphic features and formed on an aggrading flood plain with a shallow fluctuating water table the soil morphology varies with respect to landscape position and overbank lithofacies pleistocene alluvial paleosols show evidence for two stages of pedogenesis during the first stage of pedogenesis water table fluctuations and flood plain aggradation produced profiles with color mottles iron and carbonate nodules and weak b and c horizons similar to holocene flood plain soils the second stage of pedogenesis occurred after the avoyelles prairie was terraced and the regional water table fell a minimum of 30 m improved soil drainage created oxidizing and acidic conditions removed free carbonates dehydrated iron oxides and transformed clay minerals this stage produced pleistocene profiles with brighter matrix and mottle hues lower ph values larger and harder iron nodules and greater kaolinite contents than comparable holocene flood plain soils the primary influence on regional water table lowering in the southern lower mississippi valley was relative sea level fall mississippi river flood plain lowering adjacent to the avoyelles prairie most likely occurred between the end of oxygen isotope stage 3 and the maximum period of valley entrenchment during oxygen isotope stage 2 water table fall affected pedogenic processes a minimum of 400 km upvalley of the continental shelf margin pleistocene mississippi river paleosols represent excellent analogs for interpreting ancient alluvial paleosols formed during episodes of base level fall and valley incision as fluvial entrenchment terraced the meandering avoyelles prairie a pedogenic threshold was crossed that altered the pathway of chemical weathering the complexity of a multiple step pedogenic history also highlights the fact that interpretation of relative profile development as a function of time can be problematic

continental sequence stratigraphy of the upper triassic norian rhaetian chinle strata northern new mexico u s a allocyclic and autocyclic origins of paleosol bearing alluvial successions abstract two age equivalent upper triassic fluvial successions deposited on the continental interior of the southwestern united states were evaluated using an adapted marine stacking pattern analysis methodology a three tier cyclic hierarchy is present in the strata at both study areas meter scale fining upward fluival aggradation cycles facs comprise fluvial aggradational cycle sets facsets 4 15 m thick avg 8 4 m facsets in turn stack into four fluvial sequences 26 48 m thick avg 41 m within these sequences transgressive systems tract equivalents te are characterized by channel sands and associated minor overbank deposits and relatively immature paleosols i e high rates of deposition whereas highstand to falling stage systems tract equivalents hfe are dominated by overbank muds and relatively well developed paleosols i e lower rates of deposition these two fluvial successions which are 200 km apart contain age equivalent fluvial sequences that record similar histories of deposition and pedogenesis sequence 1 contains only an incomplete hfe sequence 2 includes both the te and hfe sequence 3 is an hfe and sequence 4 contains only a te fluvial sequences likely accumulated in response to pulses of source area uplift and or basin subsidence which resulted in changes in accommodation conversely higher frequency facs and facsets that occur within sequences do not correlate between study areas and are likely the products of autocyclic processes such as channel avulsion floodplain aggradation and channel migration these results suggest that regionally significant tectonic episodes may be discernible in suspended load fluvial deposits that accumulated over a broad area

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

fluvial sequence stratigraphy the wapiti formation west central alberta canada abstract outcrop exposures and high resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the campanian maastrichtian wapiti formation western interior foreland basin alberta canada this framework defines four unconformity bounded depositional sequences a d based on sequence stratigraphic methodology well log patterns and facies analysis in ascending order sequence a records the transition from the underlying marine facies of the puskwaskau formation into the wapiti fluvial facies and consists of strongly progradational and aggradational stacking patterns sequences b and c show a similar pattern of basal amalgamated channel fill deposits that grade upwards into floodplain dominated strata finally sequence d is dominated by channelized sediments and extensive overbank facies an aggradational stacking pattern suggests deposition under high accommodation conditions maximum flooding surfaces are interpreted within fine grained deposits in the upper portions of sequences c and d they are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline this study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream controlled fluvial realm furthermore the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine wapiti formation into depositional sequences and component systems tracts

rapid evolution of coastal lagoons in response to human interference under rapid sea level change a south caspian sea case study this research is part of the phd of the first author entitled evaluation of sefidrud delta south west caspian sea during the last millennium which was funded by brunel university london grant no r85104 the publication is a contribution to the inqua quicklakeh project no 1227 and to the european project marie curie climseas pirses ga 2009 247512

lower cretaceous paleo vertisols and sedimentary interrelationships in stacked alluvial sequences utah usa the yellow cat member of the cedar mountain formation in poison strip utah usa consists of stacked erosionally bounded alluvial sequences dominated by massive mudstones lithofacies fm with paleo vertisols sediment bodies within these sequences grade vertically and laterally into each other at pedogenic boundaries across which color texture and structures sedimentary vs pedogenic change slickensides unfilled sealed cracks carbonate filled cracks and deeper cracks filled with sandstone the latter features suggest thorough desiccation during aridification thin sandstones sms in some sequences typically as well as laminated to massive mudstones flm with which they are interbedded in some cases are interpreted as avulsion deposits the termini of many beds of these lithofacies curve upward parallel to nearby pedogenic slickensides as the features we call turnups turnups are overlain or surrounded by paleosols but strata sheltered underneath beds with turnups retain primary sedimentary fabrics turnups were produced by movement along slickensides during pedogenesis by differential compaction alongside pre existing gilgai microhighs or by a combination of both palustrine carbonates lithofacies c appear only in the highest or next highest alluvial sequences along with a deep paleo vertisol that exhibits partially preserved microrelief at the base of the overlying poison strip member the attributes of the yellow cat member suggest comparatively low accommodation slow accumulation long hiatuses in clastic sedimentation and substantial time intervals of subaerial exposure and pedogenesis it appears to be distinct among the members of the cedar mountain formation in these respects

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

basin scale reconstruction of the geological context of human settlement an example from the lower mississippi valley usa abstract large river valleys integrate hydroclimatic change differently than smaller ones whereas sedimentary deposits in smaller valleys serve to record temporally short lived and or low amplitude hydrological and geomorphic responses larger valleys are relatively insensitive to changes at these scales however because of their size larger valleys archive sedimentary records of longer term geographically extensive flooding and climate related landscape evolution recent work in the upper tensas basin of the lower mississippi river valley usa demonstrates the utility of analyzing sediments from a large geomorphically and fluvially complex river basin as a proxy for significant climatic and landscape changes and their relation to human history a 6000 year sedimentary archive is used to explore the interplay between climate change landscape evolution and human responses to changing environmental parameters once the mississippi river basin stabilized following glacial retreat and deceleration of sea level rise the history of the river and its inhabitants was dominated by long periods of landscape stability punctuated by episodes of significant landform alteration modifications of the landscape are correlated with intervals of rapid climate change recorded in globally distributed multiproxy data sets periods of significant landscape instability and fluvial re adjustment are recorded for the periods ca 4800 3800 3000 2500 and 1000 800 cal bp these punctuations in the history of the lower mississippi valley are related to periods of major cultural transformation and suggest climate change plays a significant role in the long term history of human occupation in this river valley this research demonstrates how geoarcheology can provide information on human environmental relationships and long term landscape histories at temporal and spatial scales relevant to understanding cultural responses to climate change

effects of spatially variable accommodation rate on channel belt distribution in an alluvial sequence authigenic 10be 9be based bayesian age depth models applied to the upper miocene volkovce fm northern pannonian basin system slovakia abstract relationships between spatially variable accommodation rate and the distribution of channel belt deposits are important issues in alluvial stratigraphy this segment of sedimentology still records important progress using experimental models and field examples this study focuses on the alluvial stratigraphy of the volkovce fm which was deposited between 9 0 6 0 ma in the northern pannonian basin system and it provides an excellent natural laboratory to study this topic the spatial variability of channel belt distribution was determined in 809 borehole logs drilled to 200 300 m depths while the facies associations were defined on the outcrops a significant variance in channel belt content was observed since it reaches 10 40 of the stratigraphic column in the southwestern part of the study area and only 0 15 in the northeastern portion moreover the transition between the areas of different channel belt distribution is oriented perpendicular to the paleo drainage network axis geochronology was then established by applying the authigenic 10be 9be dating method to three borehole cores the bayesian age depth models used herein proved a decrease in average accommodation rates from 200 m myr to 50 m myr towards the area with

variability of channel belt dimensions and the consequences for alluvial architecture observations from the holocene rhine meuse delta the netherlands and lower mississippi valley u s a abstract over the past decades many studies have focused on the dimensions of channel belt sand bodies referred to as channel belts in fluvial deposits because of their relevance for hydrocarbon exploration and production some field studies have revealed a significant downstream decrease of channel belt width and width thickness ratio along the length of the channel belt to verify whether this is a common feature in fluviodeltaic settings eight holocene channel belts in the rhine meuse delta the netherlands were selected and one in the lower mississippi valley u s a we determined channel belt geometry width or width thickness ratio using geological geomorphological maps and detailed cross sections based on borings it was found that the width of channel belts encased in cohesive deposits decreases by a factor of 4 to 6 5 in a downstream direction along the length of the channel belts the width thickness ratio decreases by a factor of 2 5 to 5 on the other hand the width of a channel belt incised in a noncohesive substrate remains constant along its entire course these observations are related to longitudinal changes in bank erodibility and stream power it is suggested that bank erodibility is the dominating factor determining the geometric properties of channel belts and the variability therein at least in the rhine meuse delta the currently available alluvial architecture models most likely overestimate sand quantities and connectedness in alluvial successions because channel belt dimensions are held constant in all models we therefore propose that the factors bank erodibility and stream power which influence width and width thickness ratio of channel belts should be incorporated in future alluvial architecture models in order to make more realistic estimates of sand quantities in river deltas

episodic sediment accumulation on amazonian flood plains influenced by el nino southern oscillation continental scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains the spatial extent and depths of such deposits have been described and flood plain accumulation has been determined at decadal timescales but it has not been possible to identify discrete events or to resolve deposition on near annual timescales here we analyse 210 pb activity profiles from sediment cores taken in the pristine beni and mamore river basins which together comprise 720 000 km2 of the amazon basin to investigate sediment accumulation patterns in the andean amazonian foreland we find that in most locations sediment stratigraphy is dominated by discrete packages of sediments of uniform age which are typically 20 80 cm thick with system wide recurrence intervals of about 8 yr indicating relatively rare episodic deposition events ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with la nina events which debouch extraordinary volumes of sediments from the andes we conclude that transient processes driven by the el nino southern oscillation cycle control the formation of the bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon nutrients and pollutants to the amazon main stem

surprisingly small increase of the sedimentation rate in the floodplain of morava river in the stražnice area czech republic in the last 1300 years abstract sediment profiles from the floodplain of morava river in the czech republic have been collected from exposed river banks 4 6 m long sections and cores 2 4 m deep and investigated using a set of geochemical proxies validated by granulometry and conventional geochemical analysis outlined in our previous paper the work was conducted to evaluate the increase in sedimentation rate during medieval and modern time periods correlation of sediments along the current channel belt allows identification of two most important synchronous changes in the channel structure over the past 1300 years in the 13th century and at the end of the 16th century these changes could be related to central european climatic extremes rather than to land cover land use practises analysis of the pollen record in peaty deposits at the floodplain edge allows excluded dramatic deforestation in medieval times maps of the area from the last five centuries revealed direct and indirect signs of past avulsions and clearly show how the original multichannel system was transformed into a single meandering channel in the early 20th century the extrapolated aggradation rate net vertical accretion of floodplain fines except for levee sediments increased from 0 2 0 3 cm year in 700 ad to 0 3 0 4 cm year in 2000 ad depending on the grain size of the sediment this is the smallest yet reported enhancement of siliclastic deposition although morava river watershed has been intensively used for agriculture and its land cover has changed in a manner similar to west and central european rivers