an early cretaceous forearc basin in the golfo de penas region southern chile a 4000 metre thick fining up succession of conglomerates sandstones and mudstones on the northwestern edge of the golfo de penas southern chile is defined as the puerto barroso formation it probably formed in a forearc basin where a fan delta built across a narrow coastal plain into a shallow marine environment during the barremian to aptian the basin is situated to the west of contemporaneous arc back are and epicratonic basins and is the only documented forearc basin of this age in southern south america

the geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the sacramento san joaquin delta california usa a multi proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic oodplain tract in the sacramento san joaquin delta california three long cores were collected from the mccormack williamson tract mwt and these cores were analyzed for bulk density loss on ignition ne clay and silt content al concentration magnetic susceptibility pollen and charcoal radiocarbon dates obtained for the cores were converted into calendar years and an age depth model was constructed long term vertical accretion and sedimentation rates were estimated from the age depth model cross core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ne sediment percentage ne and loi data show a strong linear relationship that indicates ooding is the primary mechanism for the deposition of particular organic matter on the oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5 5 per cent to the site down core grain size pro les show two hydrological domains in the cores namely millennial ne coarse uctuations superimposed on general up core ning coarse sediment is viewed as channel or near channel overbank deposits whereas ne deposits are considered to be distal overbank ood deposits the coarse ne uctuations are indicative of changing depositional settings as channels migrated laterally across mwt whereas the upward ning trend re ects a combination of self limiting overbank deposition as oodplain elevation increased and decreasing competence as sea level rise reduced ood pulse energy slopes mwt has been cross cut and incised numerous times in the past only to have the channels abandoned and subsequently lled by ne sediment the channels around mwt attained their modern con guration about 4000 years ago mwt likely came under tidal in uence at about 2500 cal bp wetlands have recently developed on mwt but they are inorganic sediment dominated copyright 2004 john wiley sons ltd

late pleistocene alluvial plain sedimentation in lower narmada valley western india palaeoenvironmental implications abstract late pleistocene fluvial sediments that were deposited in a slowly sinking basin are now exposed as 30 50 m high incised vertical cliffs all along the lower narmada valley in western india the exposed fluvial deposits have been classified into two sediment packages alluvial fan sediments overlain by alluvial plain sediments the alluvial plain sequence has not been studied previously it consists mainly of sands and silts and is dominated by overbank deposits occurrence of large scale bedforms in the alluvial plain sequence points to the existence of a large sand bed river in an alluvial plain setting the major sedimentary facies in stratigraphic order include large channel fills giant epsilon cross bedded strata overbank fines occurring in horizontal massive and undulatory stratified forms associated with crevasse splay and backswamp deposits and a reddish brown palaeosol overlain by thinly stratified sands and silts at the top of the exposed sediment succession large sized channel fills occur at two stratigraphic levels which are morphologically similar and are indicative of high rates of deposition and avulsion the large channel fill structures and the giant epsilon cross bedded strata indicate a large single channel river that was consistently 10 15 m deep and about 70 80 m wide even during the dry seasons these dimensions are larger than those of the present day narmada river at low discharge levels the overbank sediments indicate rapid deposition through frequent overbank floods and floodplain aggradation by a laterally shifting river available chronologic data suggests that the reddish brown palaeosol correlates with a regional phase of pedogenesis in the alluvial plain of gujarat prior to the last glacial maximum lgm the thinly stratified sands and silts overlying the palaeosol were deposited by a considerably depleted but perennial river during the arid phase of the last glacial maximum overall the alluvial plain sediments of the lower narmada valley particularly those below the palaeosol have been attributed to a hyper avulsive large river with low sinuosity whose high discharge levels were determined primarily by a large catchment area further to the east and not by the semiarid climate prevailing in the gujarat alluvial plain during the upper part of the late pleistocene the study concludes that the narmada river has maintained a large catchment at least since the last 100 ka however the river was characterised by a much bigger channel during much of the late pleistocene with discharge levels higher than the present day

lithostratigraphy and depositional history of the late cenozoic hominid bearing successions in the yuanmou basin southwest china abstract late cenozoic strata bearing hominids and hominoids are distributed in the yuanmou basin yunnan southwest china incisors of homo erectus discovered in these strata in 1965 reportedly show primitive features known in africa hu acta geologica sinica 1 1973 p 65 however recent paleomagnetic study has revealed that the age of the hominid correlates to the early brunhes chron hyodo et al journal of human evolution 2001 submitted the lithostratigraphy of the successions that yield many mammalian fossils including those of the hominid and the record of equus is re examined the successions are divided in ascending order into the longchuan shagou gantang newly proposed yangliuchun and daipojing members and yuanmou newly proposed dainawu and niujianbao members formations based on different lithology and sedimentary facies the newly proposed depositional systems of the formations are in ascending order alluvial fan ephemeral braided river sandy braided river ephemeral gravelly braided river and alluvial fan systems the change in facies and paleocurrents revealed in the successions suggest that the basin was initiated as a syncline basin at ca 3 5 ma and was completed as an asymmetric half graben by active movement of the eastern marginal fault in the early middle pleistocene

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

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

facies analysis of a probable large fluvial fan depositional system the upper triassic chinle formation at petrified forest national park arizona u s a abstract the upper triassic blue mesa member and the overlying sonsela member of the chinle formation consist of paleosol bearing alluvial strata whose characteristics vary markedly strata exposed within a 4 km2 study area at petrified forest national park were evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria to formulate potential depositional models that may account for varying alluvial deposition the study succession records a progressive up section increase in grain size increase in channel depth and width increase in lateral and vertical connectivity of channel deposits decrease in overbank preservation and crevasse splay and or sheetflood deposition and increase in overbank drainage mean annual precipitation from the calmag paleosol weathering proxy suggests precipitation averages approximately 1300 mm yr 1 3 m yr throughout the succession despite changing paleosol drainage these features are consistent with deposition in a progradational fluvial system such as a large fan or splay complex sediment accumulation rates in the study interval suggest decreased subsidence in the upper blue mesa member reduced rates of accommodation gain may have promoted progradation of the fluvial system an up section decrease in sandstone mineralogical maturity may be related to increasing sediment bypass in proximal fan positions or increased rates of erosion and sedimentation increasingly better drained paleosols are attributed to deposition in more upland positions during fan or avulsion complex progradation rather than changing climate

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

a quantitative approach to soil occurrence in alluvial deposits and its application to the old red sandstone of britain palaeosols fossil soils are a major component of alluvial deposits in the geological record not only do these typically show considerable variations in their degrees of development within single formations but they also exhibit highly complex stratigraphic relationships with one another a simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil palaeosol development within a sequence with calcic or petrocalcic horizons to illustrate the approach a range of palaeosols from the siluro devonian old red sandstone of britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation in particular two alluvial suites from the manorbier area of south wales are analysed using this approach the technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates

depositional environments of overbank sedimentation in the lignite bearing grey clays member new evidence from middle miocene deposits of central poland abstract a detailed sedimentological study of polish lignite bearing successions has not previously been undertaken this contribution focuses on the lignite lithotypes and lake and crevasse splay lithofacies that together constitute the grey clays member this lithostratigraphic unit strictly refers to the middle miocene overbank fluvial environments in central poland it mostly consists of the first mid polish lignite seam mpls 1 in the tomislawice lignite opencast mine this lignite seam containing four lithotypes is interbedded by sandy and silty clayey lithofacies the lithotype associations are characteristic of the low lying mires representing fen or open water 2 m lakes in the mire area this is additional evidence of the relatively long lasting and slow sedimentation of these very fine grained clastics from suspension in standing lake water conversely the sandy lithofacies associations representing crevasse splays were deposited suddenly during overbank flooding crevasse splay deposits are typical of initial stages of avulsion and are moderately diverse both texturally and structurally exceptions here are slurry flow deposits that contain rip up clasts of paleosol aggregates these crevasse splay deposits provide the first evidence of the fluvial environments of the mid miocene mires backswamp in central poland and they split the currently exploited lignite seam mpls 1 in the study area thus identification and description of lithofacies and lithotypes and determination of their spatial distribution can contribute to a better understanding of the mire development of which the examined lignite seam arose

hydrogeomorphological differentiation between floodplains and terraces floodplains and terraces in river valleys play important roles in the transport dynamics of water and sediment while flat areas in river valleys can be identified from lidar data directly characterizing them as either floodplain or terraces isnot yet possible to address this challenge we hypothesize that since geomorphic features are strongly coupled to hydrologic and hydraulic dynamics and their associated variability there exists a return frequency or possibly a narrow band of return frequencies of flow that are associated with floodplain formation and this association can provide a distinctive signature for distinguishing them from terraces based on this hypothesis we develop a novel approach for distinguishing between floodplains and terraces that involves transforming the transverse cross sectional geometry of a river valley into a curve named river valley hypsometric rvh curve and linking hydraulic inundation frequency with the features of this curve our approach establishes that the demarcation between floodplains and terraces can be established from the structure of steps and risers in the rvh curves which can be obtained from the dem data further it shows that these transitions may themselves be shaped by floods with 10 to 100 yr recurrence we additionally show that when floodplain width and height above channel bottom are normalized by bankfull width and depth the ratio lies in a narrow range independent of the scale of the river valley

analysis of floodplain sedimentation avulsion style and channelized fluvial sandbody distribution in an upper coastal plain reservoir middle jurassic ness formation brent field uk north sea

sequence stratigraphic analysis of cenomanian greenhouse palaeosols a case study from southern patagonia argentina abstract the aim of this contribution is to analyse extrinsic i e tectonics climate and eustasy and intrinsic i e palaeotopography palaeodrainage and relative sedimentation rates factors that controlled palaeosol development in the cenomanian mata amarilla formation austral foreland basin southwestern patagonia argentina detailed sedimentological logs facies analysis pedofeatures and palaeosol horizon identification led to the definition of six pedotypes which represent histosols acid sulphate histosols vertisols hydromorphic vertisols inceptisols and vertic alfisols small and large scale changes in palaeosol development were recognised throughout the units small scale or high frequency variations identified within the middle section are represented by the lateral and vertical superimposition of inceptisols vertisols and hydromorphic vertisols lateral changes are interpreted as the result of intrinsic factors to the depositional systems such as the relative position within the floodplain and the distance from the main channels that condition the nature of parent material the sedimentation rate and eventually the palaeotopographic position vertical stacking of different soil types is linked to avulsion processes and the relatively abrupt change in the distance to main channels as the system aggraded the large scale or low frequency vertical variations in palaeosol type occurring in the mata amarilla formation are related to long term changes in depositional environments the lower and upper sections of the studied logs are characterised by histosols and acid sulphate histosols and few hydromorphic vertisols associated with low gradient coastal environments i e lagoons estuaries and distal fluvial systems at the lower boundary of the middle section a thick palaeosol succession composed of vertic alfisols occurs the rest of the middle section is characterised by vertisols hydromorphic vertisols and inceptisols occurring on distal and proximal fluvial floodplains respectively the palaeosol succession for the mata amarilla formation can be analysed within a sequence stratigraphic scheme considering changes in depositional environments in relation to accommodation supply conditions the results contrast with classical models mainly in that the palaeosols of the mata amarilla formation are relatively well developed throughout the whole sequence including transgressive periods of relatively high aggradation rate also even when during regressive episodes when a thick palaeosol succession that marks the sequence boundary is developed in the classical models the lack of incised valleys in this succession led to the preservation of thick palaeosol successions during lowstand conditions the vertical and lateral palaeosol distribution identified in the mata amarilla formation could be eventually extrapolated to other sequences deposited during climate optimums

the influence of a large anthropogenic sediment source on the fluvial geomorphology of the knabeana kvina rivers norway abstract molybdenum mining at knaben discharged more than eight million tonnes of tailings into two lakes in the upstream end of the knabeana river southern norway during the period 1918 1973 a dam was built downstream of the lakes in 1976 to stop the fluvial dispersion of tailings bulk samples were collected from the tailings pond n 30 natural sediment sources n 7 sandbars n 98 and overbank sediments 0 25 cm depth n 79 along the 55 km river reach downstream of the mining area in addition overbank sediment samples of 1 cm thickness were collected at depth intervals of 1 5 cm in 19 vertical profiles n 497 sedimentological properties were recorded in 17 of the profiles chemical analysis icp aes after hot nitric acid or aqua regia extraction has shown that a minimum of 420000 tonnes of tailings with a median molybdenum content of 80 ppm are presently stored in the fluvial sediments the major volumes are present in sandbars in a 6 km long low gradient reach that acts as a bedload trap under normal flood conditions however bedload may be flushed into the steeper reaches by repeated major events on the floodplains 14 c dating has shown that the average sedimentation rate in one profile has increased from 0 5 to 4 3 mm year due to deposition of tailings since lateral channel instability has only been detected in a few locations the floodplains are regarded as semi permanent sinks for tailings however extreme floods that strip off vegetation or undercut the floodplains may increase the availability of tailings from these deposits the results from the knabeana kvina rivers indicate that construction of weirs may stop the dispersion of bedload sized contaminated sediments while construction of dams may be necessary to trap contaminated sediments transported in suspension in each case the benefit and disadvantages of such constructions must be evaluated according to the local conditions

facies and architectural analysis to interpret avulsion style and variability upper cretaceous blackhawk formation wasatch plateau central utah u s a abstract sequence stratigraphic models emphasize the role of external allogenic controls such as relative sea level tectonic subsidence and climate on alluvial to coastal plain stratigraphic architecture at the expense of internal autogenic behaviors such as avulsion these models are tested via sedimentologic analysis of fine grained floodplain deposits and their relationship to channelized fluvial sandbodies in a well exposed alluvial to coastal plain succession developed under progressively increasing distance from the coeval shoreline and an accompanying decrease in the rate of accommodation creation late cretaceous blackhawk formation wasatch plateau central utah u s a the studied alluvial to coastal plain succession contains fourteen lithofacies which are grouped into four associations and eight architectural elements facies associations consist of 1 channelized fluvial sandstone bodies 2 nonchannelized fluvial sandstone and siltstone bodies 3 fine grained floodplain deposits and 4 brackish floodplain deposits paleosols are immature and are classified as entisols inceptisols and histosols integrated analysis of paleosol character facies analysis and architectural element analysis indicates deposition on a rapidly aggrading floodplain that was subject to frequent crevassing and channel belt switching the character relative abundance and vertical stacking of the paleosol types architectural elements and the first three facies associations exhibit little variation stratigraphically from base to top of the blackhawk formation c 250 m or paleogeographically between the northern and southern limits of the outcrop belt c 100 km local stratigraphic architectures record three styles of avulsion representing avulsion by reoccupation avulsion by progradation and avulsion by incision avulsion style displays no consistent pattern with stratigraphic position or paleogeographic location in combination these results suggest that floodplain sedimentation and local stratigraphic architecture are dominated by autogenic avulsion the three observed avulsion mechanisms operated in apparent uniformity over a range of tectonic subsidence rates c 80 700 m ma and distances from the coeval shoreline c 0 100 km

genetically related alluvial deposits across active fault zones an example of alluvial fan terrace correlation from the upper quaternary of the southern po basin italy integrated studies of alluvial fan systems and related intramontane valley deposits provide potentially useful tools for understanding the character of alluvial sedimentation and its control in fault controlled piedmont zones an example is reported from the uppermost quaternary alluvial deposits of the northern apennines and the southern margin of the po basin a distinctive cyclicity characterizes both the outcropping and the buried units in the study area in intramontane valleys individual cycles consist of regular alternations of sections displaying high and low terrace preservation in the subsurface a rhythmic alternation of coarse grained bodies and laterally extensive pelitic horizons occurs at various scales and represents the basic cyclic motif of the depositional system the correlation between the terrace sequences and the depositional cycles in the subsurface allows the differentiation of distinct sequences with a characteristic internal architecture in the lower part of sequences poorly preserved terrace deposits are laterally correlatable with alluvial fan gravel bodies whereas highly preserved terrace deposits are correlated laterally with predominantly floodplain sediments in the upper part of sequences reliable correlation lines have been constructed using 14c dating thrust tectonics and climate exerted a major control on sequence development deep valley excavation with subsequent low terrace preservation occurred in response to relief rejuvenation during successive thrusting events on the other hand decreasing erosion related to periods of minor tectonic activity led to terrace preservation in the intramontane valleys the coeval episodes of alluvial fan growth and abandonment recorded at the basin margin are interpreted to reflect changes in the efficiency of the drainage system due to variations of tectonic uplift in the adjacent areas alternating phases of deglaciation and renewed glaciation however are inferred to have played a major role in controlling the amount and type of sediment delivered to the alluvial fan complexes

paleovalley morphology and fluvial system evolution of eocene oligocene sediments auriferous gravels northern sierra nevada california implications for climate tectonics and topography in the northern sierra nevada california eocene oligocene fluvial sediments the auriferous gravels rest unconformably in well defined basement incised paleovalleys providing a record of paleolandscape geomorphology and drainage system evolution paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad terraced paleovalley segments which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition high gradient high energy deposits are present near the edges of these areas suggesting that tributaries and outlets resided in steeper narrow paleovalleys multiple strath terraces are common in broad paleovalleys indicating that incision events occurred both before deposition and during paleovalley widening followed by periods of aggradation broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system multiple upward fining cycles bounded by erosional surfaces are composed of alternating coarse grained channel belt and fine grained floodplain packages an overall upward fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys paleochannel slope estimates of 0 004 0 055 were obtained based on average grain sizes of coarse channel fills anomalously thick up to 11 m laterally continuous 1 3 km floodplain units containing kaolinite rich clay and oxisol intervals record high fine grained sediment supply driven by high rates of chemical weathering in the warm eocene climate based on sedimentary characteristics combined with floral and detrital zircon data braided stream deposition within the basin occurred from the late early eocene through late eocene and aggradation primarily occurred in broad lower gradient reaches behind a major bedrock knickpoint created in the late mesozoic early cenozoic possibly due to asymmetric batholith unroofing the diachronous localized nature of paleovalley incision and braided stream aggradation within the northern sierra nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients both internal and external drivers influenced the evolution of the fluvial system through 1 the pattern of basin filling as the locus of deposition migrated east to west 2 the warm eocene climate which increased chemical weathering and contributed a high sediment supply and 3 changes in base level due to eustasy and or laramide tectonism this record of laramide tectonics in the sierra nevada and basin and range is important for the timing of sierra nevada uplift for tectonic reconstructions of western north america and for studies of landscape evolution in tectonically active orogens

contrasting development patterns of crevasse channel deposits in cretaceous alluvial successions korea abstract the eumsung and pyonghae basins both of cretaceous age in korea comprise a thick alluvial sequence of conglomerate sandstone and purplish siltstone laterally impersistent gravelly sandstone beds can be classified into two types based on bed geometry internal structure and occurrence a vertically stacked sheetlike bodies facies 1 and b migratory ribbon shaped bodies facies 2 facies 1 is characterized by symmetrical channel geometry with a large ratio of width to thickness of sandstone beds which are mostly stratified and bounded by relatively distinct lower and upper boundaries they are frequently found in aggradational style facies 2 shows asymmetric geometry with a relatively small ratio of width to thickness of sandstone beds it comprises massive cross stratified units bounded by sharp basal contacts and gradational upper boundaries which resulted from laterally shifting mode both types represent crevasse distributary channels developed in floodplain environments facies 1 is suggestive of gradual migration of crevasse distributary channels under the conditions of overall aggradation whereas facies 2 represents discrete abrupt diversion of crevasse channels these features are due to differences in floodplain gradients paleohydrology and trunk channel behaviour

geochemistry of the floodplain sediments of the kaveri river southern india abstract the floodplain sediments of the kaveri river southern india derived from archean gneissic and charnockitic source regions show interbedding of silty 4 4 7 and sandy units 1 4 3 7 the geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of nearly 250 km the sandy beds have more variable chemical compositions yet are comparable to those of silty beds except for the diluting effect of quartz silty sediments retain the geochemical signature of prominently exposed source rocks for almost all elements and provide evidence of tectonic instability in the source region the floodplain sediments contain all size grades sand silt and clay which may have resulted in minimizing the biases imposed on suspended and bedload sediments due to sorting the low chemical index of alteration cia the dominance of unweathered primary minerals and the minor proportion of smectitic clay all suggest that the region has been subjected to little chemical weathering this is possible if the region has undergone recent uplift exposing fresh archean rock to surface denudation the formation of fertile farmland along the kaveri river course and its delta is related to these recent geological processes

crevasse splay processes and deposits in an ancient distributive fluvial system the lower beaufort group south africa abstract up to 12 of the mud prone ephemeral distributive fluvial system stratigraphy in the permo triassic lower beaufort group south africa comprises tabular fine grained sandstone to coarse grained siltstone bodies which are interpreted as proximal to distal crevasse splay deposits crevasse splay sandstones predominantly exhibit ripple to climbing ripple cross lamination with some structureless and planar laminated beds a hierarchical architectural scheme is adopted in which 1 m thick crevasse splay elements extend for tens to several hundreds of meters laterally and stack with other splay elements to form crevasse splay sets up to 4 m thick and several kilometers in width and length paleosols and nodular horizons developed during periods or in areas of reduced overbank flooding are used to subdivide the stratigraphy separating crevasse splay sets deposits from crevasse splays differ from frontal splays as their proximal deposits are much thinner and narrower with paleocurrents oblique to the main paleochannel in order for crevasse splay sets to develop the parent channel belt and the location where crevasse splays form must stay relatively fixed during a period of multiple flood events beaufort group splays have similar geometries to those of contemporary perennial rivers but exhibit more lateral variability in facies which is interpreted to be the result of more extreme fluctuations in discharge regime sharp based crevasse splay packages are associated with channel avulsion but most are characterized by a gradual coarsening upward interpreted to represent progradation the dominance of progradational splays beneath channel belt deposits may be more characteristic of progradational stratigraphy in a distributive fluvial system rather than dominated by avulsion processes in a trunk river system this stratigraphic motif may therefore be an additional criterion for recognition of distributive fluvial systems in the ancient record

palaeoenvironment and ecology of the middle cretaceous grebenka flora of northeastern asia the grebenka flora from the main exposure of the albian cenomanian krivorechenskaya formation in northeastern russia represents a range of plant communities from pioneer to mature forest that grew close to the mid cretaceous north pole 72degreesn the diversity of this flora is dominated by angiosperms followed by conifers ferns and other plant groups the age is constrained by ar 40 ar 39 analyses of associated volcaniclastics similar to 96 5 ma coupled with biostratigraphic correlation of the plant bearing non marine beds with marine units of the krivorechenskaya formation and the overlying dugovskaya formation limited palaeosol development and pronounced episodic floodplain aggradation indicate that the 100 m thick plant bearing volcaniclastic floodplain succession was deposited rapidly resulting in excellent trapping and preservation of the plant communities but dilution of the palynoflora analysis of the megaflora 100 foliage taxa plus woods and fructifications provides a snapshot of the mid cretaceous climate and offers reliable quantitative climatic signals of conditions near the mid cretaceous north pole multivariate analysis of leaf physiognomy climate leaf analysis multivariate program on the whole flora suggests that the plants experienced a mean annual temperature of 13 0 1 8degreesc and a cold month mean temperature of 5 5 3 3degreesc however analyses of individual florules yield slightly different results that help constrain the uncertainties inherent in such an approach these and other foliar physiognomic data are compared across the arctic less

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

the cretaceous pyonghae sequence southeast korea terminal fan facies abstract the cretaceous pyonghae sequence southeast korea comprises a nonmarine clastic sequence of dominant purplish siltstone with subordinate gravelstone and sandstone the sequence consists of eight sedimentary facies which can be organized into three facies associations facies association i occurs along the basin margins and is represented by disorganized gravelstone facies g1b and g2 and stratified gravelly sandstone facies gs the gravelstone and sandstone facies are interpreted as debris flow deposits and braided stream deposits respectively formed in alluvial fans n facies association ii mainly occurs in the central part of the basin and comprises sheet like sandstone bodies facies gs s1 and s2 intercalated with purplish siltstone beds facies m1 the sheet like sandstone beds show a fining upward trend with sharp base and lateral margins and are often horizontally stratified these features most likely result from frequent diversion of ephemeral shallow stream channels on floodplain and subsequent infilling with coarse grained sediments facies association iii is characterized by thick siltstone beds facies m1 with lenticular sandstone and gravelstone beds the siltstone beds contain calcareous nodules the facies association iii is well developed in the southern part of the basin where it represents floodplain environments alluvial fans facies association i and adjacent floodplain facies association iii which are connected by ephemeral stream channel networks facies association ii can be referred to as terminal fan system autocyclic processes such as spasmodic floods under semi arid climatic conditions are important for the development of terminal fan systems

evolving fluvial style in the kekiktuk formation mississippian endicott field area alaska base level response to contemporaneous tectonism the hydrocarbon reservoir at endicott field offshore from the sagavanirktok delta in northeastern alaska is found in the upper mississippian visean kekiktuk formation the trap is bounded by the northwest southeast trending tigvariak and mikkelson bay faults and the younger east west trending niakuk fault the kekiktuk comprises sandstones siltstones and mudstones with locally significant coals and conglomerates and is subdivided into three major reservoir zones based on the relative dominance of these lithologies zone 1 the lowest comprises mudstones siltstones and coals with subordinate isolated sandstones and represents deposition within a low lying swamp plain with very low net to gross ratio this zone is considered to be effectively nonreservoir major movement on the mikkelson bay and tigvariak faults created a half graben with uplift to the north and east and a very significant drop in base level this change resulted in fairly widespread deposition of zone 2 medium to coarse grained sandstones from sandy bed load braided streams however those sandstones thin significantly to the west away from the faults continuing tectonism at this time created local shifts in base level manifest as diversion of streams widespread abandonment and subsidence leading to the creation of a arge lake the lacustrine deposits are widespread and effectively divide zone 2 into two subzones those subzones are mappable sheet sandstones and constitute the best reservoir at endicott field in terms of net to gross ratio porosity permeability and sandstone connectivity base level shows evidence of rising dramatically at the end of zone 2 this rise is attributed to continuing tectonism within the basin and is particularly associated with the east west trending mid field fault system at endicott field as well as ongoing activity on the tigvariak mikkelson bay fault system thus at the base of zone 3 subzone 3a in the southern and eastern parts of the field the rocks are mudstones and widespread coals and contain at least one unequivocally marine mudstone these rocks are lower delta plain interdistributary bay fill deposits with rare distributary channel sandstones north and west of the mid field fault system the marine mudstone is absent and the facies changes significantly with the loss of dominant coal and a concomitant increase of dist ibutary channel sandstones reservoir properties of subzone 3a including connectivity are significantly different in this area subzone 3b is a thick accumulation of fine grained alluvial overbank deposits within which occur rare isolated anastomosed channel sandstones of limited connectivity this subzone makes minimal contribution to endicott field reserves subzone 3c is characterized particularly in its upper part by well developed fining upward cycles indicating mature meandering streams the relationships between these two highest subzones of the kekiktuk at endicott field indicate they represent an aggradational episode initiated by tectonically induced avulsion and set against a background of rising base level to the west at some distance from the tigvariak mikkelson bay f ult system zone 3 is much thinner than at endicott field and is dominated by mudstones and coals this evidence emphasizes the control that contemporaneous tectonism related to those faults had on sediment especially sandstone distribution within the kekiktuk formation base level changes can be identified within the end page 1723 kekiktuk formation in the north slope subsurface by careful lithofacies analysis and an awareness of key constraining indicators such as are revealed by palynology paleontology and structural geology by analogy with shallow marine rocks sequence stratigraphic concepts may be extended to continental successions however one must approach such problems with a full awareness of the impact of tectonism on base level and basin development

early new world maritime technologies sea grass cordage shell beads and a bone tool from cave of the chimneys san miguel island california usa recent excavations at cave of the chimneys ca smi 603 located on san miguel island revealed well preserved sea grass knots twined cordage olivella spire ground beads and a bone gorge the assemblage dated to roughly 8000 years ago is dominated by s twist cordage and includes an assortment of strands loops and knotted pieces wrapped sea grass knotted balls including some stained red suggest they may have had a decorative function unique among paleocoastal assemblages of the area these artifacts offer a rare glimpse into the non lithic technologies of early native americans on the pacific coast of north america

palaeosols as indicators of geomorphic stability in two old red sandstone alluvial suites south wales palaeosols fossil soils are abundant in the alluvial late silurian early devonian moor cliffs formation and rat island mudstone freshwater west formation of south dyfed south wales the palaeosols occur in thick mudstones deposited on floodplains under a seasonal semi arid climate and represent vertisol type soils simple single profiles are rare and most of the mudstone intervals exhibit complex overprinted profiles however a major difference exists between the palaeo vertisols in each of the two units studied the moor cliffs formation contains thick floodplain intervals with evidence of frequent erosion and reactivation of earlier soil horizons the associated coarser channel deposits mainly represent ephemeral streams the alluvial system was unstable flashy and prone to extensive stripping of stored floodplain sediment arroyos unstable ephemeral stream channels probably developed during this interval evidence for any marine influence on soil development is missing and previous speculations that the formation may represent deposition in an upper intertidal or supratidal system are not supported the rat island mudstone represents a complete contrast in that there was little or no stripping of floodplain sediments the channel deposits are typically of the fining upwards type representing more stable low sinuosity channels and with ephemeral stream floods by integrating the palaeosols a more detailed picture of the geomorphic history of these units can be formulated comparison with contemporary drainage basins indicates that a change in climate was a possible cause for the differences between the two units less frequent and more severe storms occurring during the deposition of the rat island mudstone

lacustrine records of holocene flood pulse dynamics in the upper paraguay river watershed pantanal wetlands brazil abstract the pantanal is the world s largest tropical wetland and a biodiversity hotspot yet its response to quaternary environmental change is unclear to address this problem sediment cores from shallow lakes connected to the upper paraguay river pr were analyzed and radiocarbon dated to track changes in sedimentary environments stratal relations detrital particle size multiple biogeochemical indicators and sponge spicules suggest fluctuating lake level lowstand conditions between 11 000 and 5300 cal yr bp punctuated by sporadic and in some cases erosive flood flows a hiatus has been recorded from 5300 to 2600 cal yr bp spurred by confinement of the pr within its channel during an episode of profound regional drought sustained pr flooding caused a transgression after 2600 cal yr bp with lake level highstand conditions appearing during the little ice age holocene pr flood pulse dynamics are best explained by variability in effective precipitation likely driven by insolation and tropical sea surface temperature gradients our results provide novel support for hypotheses on 1 stratigraphic discontinuity of floodplain sedimentary archives 2 late holocene methane flux from southern hemisphere wetlands and 3 pre colonial indigenous ceramics traditions in western brazil

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

volcaniclastic resedimentation in distal fluvial basins induced by large volume explosive volcanism the ebisutoge fukuda tephra plio pleistocene boundary central japan the ebisutoge fukuda tephra plio pleistocene boundary central japan has a well recorded eruptive style history magnitude and resedimentation styles despite the absence of a correlative volcanic edifice this tephra was ejected by an extremely large magnitude and complex volcanic eruption producing more than 400 km 3 total volume of volcanic materials volcanic explosivity index 7 which extended more than 300 km away from the probable eruption centre remobilization of these ejecta occurred progressively after the completion of a series of eruptions resulting in thick resedimented volcaniclastic deposits in spatially separated fluvial basins more than 100 km from the source facies analysis of resedimented volcaniclastic deposits was carried out in distal fluvial basins the distal tephra 100 300 km from the source comprises two different lithofacies primary pyroclastic fall deposits and reworked volcaniclastic deposits the resedimented volcaniclastic succession shows five distinct sedimentary facies interpreted as debris flow deposits facies a hyperconcentrated flow deposits facies b channel fill deposits facies c floodplain deposits with abundant flood flow deposits facies d and floodplain deposits with rare flood deposits facies e resedimented volcaniclastic materials at distal locations originated from unconsolidated deposits of a climactic large ignimbrite forming eruption factors controlling inter and intrabasinal facies changes are 1 temporal change of introduced volcaniclastic materials into the basin 2 proximaldistal relationship and 3 distribution pattern of pyroclastic flow deposits relative to drainage basins thus studies of the ebisutoge fukuda tephra have led to a depositional model of volcaniclastic resedimentation in distal areas after extremely large magnitude eruptions an aspect of volcaniclastic deposits that has often been ignored or poorly understood

depositional controls in a bedload dominated fluvial system internal architecture of the lee formation kentucky abstract sandstones of the early pennsylvanian lee formation central appalachian foreland basin were deposited in a low sinuosity bedload dominated fluvial system the internal architecture of the sandstones consists of a six fold hierarchy of bounding surfaces which are evaluated with respect to depositional controls minor first second and third order surfaces generally less than a few hundred meters in extent separate deposits of small to intermediate scale bedforms third order surfaces which dip gently in the downflow direction represent reactivation surfaces of downstream accreting macroforms major surfaces fourth fifth and sixth order are hundreds of meters to kilometers in extent fourth order surfaces separate deposits of individual macroforms fifth order bounding surfaces are erosional boundaries of major system scale channels individual sandstone members of the lee formation are bound by sixth order surfaces erosional at the base and gradational at the top deposits overlying major surfaces contain fining upward sequences the trends are more apparent with increased scale of the deposit these sequences represent responses of the fluvial system to various mechanisms that controlled sedimentation both fourth and fifth order surfaces are interpreted as results of autocyclic controls the nature of the lee formation fluvial system was such that a solitary major channel was relatively stable in one position within the alluvial plain for a significant period of time during this time the channel aggraded with the passage of one or more downstream accreting macroforms creating a fourth order erosional surface the channel eventually diverted its flow to another portion of the alluvial plain by avulsion creating a fifth order surface a gross fining upward trend and upward change in fluvial style for individual sandstone members both characteristic of paleovalley fills indicate that sixth order surfaces were controlled by allocyclic processes these characteristics and the stair step positioning of the sandstone members younger away from the alleghenian mountains to the east suggest that tectonic processes were the ultimate control on the system

sedimentology of a fine grained aggrading floodplain abstract historical land use changes accelerated both soil erosion and subsequent floodplain alluviation within the galena river basin wisconsin a cross valley transect in a low gradient downstream section of this watershed permitted documentation of the lateral and vertical sedimentological properties occurring during this aggradational phase mechanical and statistical analyses of 97 sediment samples reveal two dominant controls determining the resulting floodplain sedimentology firstly the initial fine grained loessial texture dominated the particle size of the early post settlement alluvium generally yielding fine textured sediments across the valley bottom further landscape de stabilization promoted upland gullying into coarser textured residuum below the loess with a concomitant particle size increase in the foodplain alluvium thus the resulting foodplain stratigraphy exhibits a coarsening upward sequence secondly distance from the stream channel exerts a strong control on overall sedimentological properties distal settings possess massive high clay content sediments usually with less than 1 sand samples become coarser and more stratified near the modern stream channel with channel fill facies containing approximately 20 sand in the upper sections the fine grained loessial sediment source affected numerous sedimentological properties of the deposited alluvium sorting correlates negatively with particle size because all particle sizes were entrained during large overbank floods dominance of silt in this loess mantled basin maintains the maintains the median of the particle size distribution within a fairly narrow range only the tails of the distribution vary and they are primarily controlled by the distance to the stream channel in distal settings the fine tail emerges whereas the coarse tail appears in the channel fill and proximal settings although all sediments were deposited in an overbank floodplain environment passega s cm diagrams erroneously indicate a pelagic depositional environment

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

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

the spatial distribution of heavy metal contaminated sediment across terraced floodplains abstract deposits of fine alluvial sediment contaminated by heavy metals derived from mining provide an opportunity to reconstruct the alluvial histories of mineralised catchments field data were collected to identify the spatial distribution of heavy metal contamination in surficial floodplain sediments and establish the relationships between terrace height terrace age and metal concentrations floodplain terrace morphology was mapped and terrace heights were measured for three separate study reaches in the upper sevem basin mid wales concentrations of pb ba and zn were determined in 97 samples taken from fine overbank units capping these terrace surfaces between the three study reaches element concentrations showed wide ranges pb 11 964ppm ba 141 1118 ppm zn 73 1134 ppm they also exhibited significant spatial variation across the floodplain at each study reach e g at llandinam pb 36 964ppm ba 141 1118 ppm and zn 173 1134 ppm peak metal concentrations at morfodion pb 399 ppm ba 474 ppm and welsh pool pb 149 ppm ba 558 ppm were found on terrace surfaces 1 5 2 5m and 2 0 3 0 m above present river level respectively lower concentrations reflect natural background levels of contaminants higher terraces and post mining reworking of spoil heaps and floodplains lower terraces in general the spatial distribution of floodplain contaminants is more significantly correlated with terrace height than with terrace age different flooding mechanisms and styles of channel instability in relation to the timing and mode of sedimentation have resulted in different patterns of floodplain contamination focused deposition particularly in palaeochannels is also an important mechanism for creating strongly contaminated sites within the floodplain environment

early holocene alluvial stratigraphy chronology and paleoindian early archaic geoarchaeology in the loup river basin nebraska u s a abstract the preservation of alluvium dictates the discovery of archaeological sites in valleys we address two questions in our study of the loup river basin in the midcontinent of north america 1 what is the alluvial chronology of the loup river basin between about 10 300 and 7700 bp and 2 what is the potential for preservation and exposure of paleoindian and early archaic sites cleaned cut banks walls of backhoe trenches and archaeological test units cores collected with a trailer mounted giddings soil probe and bucket auger samples were described buried a horizons organic enriched alluvial strata peat and charcoal were sampled for radiocarbon dating dating was supplemented by temporally diagnostic cultural materials we recognize the absence of 14 000 10 300 bp alluvium in the loup river basin floodplain stability very slow aggradation occurred from 10 300 10 000 bp rapid floodplain aggradation is inferred between 10 000 and 9450 bp between 9450 and about 9250 bp erosion initially produced the kilgore creek terrace the valley floor landscape stabilized from about 9250 to 9100 bp before an episode of rapid aggradation overwhelmed floodplains and alluvial colluvial fans the fans stabilized about 8600 8500 bp while floodplains in larger valleys 5th order stabilized shortly after about 8400 8200 bp renewed valley bottom aggradation after 8200 was interrupted at about 7750 the absence of alluvium dated between 14 000 and 10 300 bp in the loup river basin precludes discovery of early paleoindian sites in valleys and contrasts with the presence of alluvium and buried soils containing clovis and folsom paleoindian sites in other drainage basins in the u s central great plains although the distribution of the kilgore creek terrace is an excellent proxy of preservation of 10 300 9450 bp alluvium in the loup river basin and thus late paleoindian sites very few remnants of this terrace have been preserved two early holocene erosional episodes have been documented in the loup river basin at 9450 9250 bp and again immediately before 8300 8200 bp alluvium deposited between 10 300 and 9450 contains one archaeological site and alluvium deposited 9250 8200 contains five other paleoindian sites five early archaic sites are documented in three alluvial colluvial fans and on a terrace remnant in the north loup river valley but have not been discovered in an alluvial stratigraphic context outside of fans although stable surfaces are much more likely to accumulate a greater density of artifacts than sedimentary units that are deposited rapidly we document three paleoindian components that are in alluvium between buried soils

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

evolution of lower jurassic coastal plain and fan delta sediments in the beryl embayment north sea coastal plain and fan delta sediments accumulated throughout the sinemurian to late pliensbachian in the beryl embayment area north sea these sediments represent a marginal clastic fringe along the southern extension of the boreal ocean into the northern north sea two informal formations are recognized in these predominantly sandy deposits the lower formation comprises interbedded sandstones siltstones and coals of minor fluvial channel and associated coastal floodbasin marsh lake and sheetflood origin the overlying formation represents a fan delta system possibly generated as a result of footwall uplift and associated erosion this formation is dominated by probable channel sandstones with marine influenced debris flow deposits developed at a number of levels indicating an active coastal fan setting fan sediments are capped by a marine sandstone beds of which interfinger with the overlying offshore siltstones thickness variations are related to major normal faults suggesting at least a limited fault control on the deposition and distribution of facies during a time conventionally regarded as tectonically quiescent in the northern north sea there is no clear evidence for a eustatic control on sedimentation although deposition of post fan delta shallow marine siltstones may have been principally controlled by eustatic sea level rise recording the acme of the early jurassic expansion of boreal waters into the viking graben

geomorphological and sedimentological analysis of flash flood deposits the case of the 1997 rivillas flood spain on the basis of the description of the 1997 rivillas flood deposits a morphosedimentary feature classification is proposed mapping of the main morphosedimentary deposits in seven reaches along the basin has provided abundant data for each defined typology and for a better adjustment of their stability fields because of their unstable preservation environment immediate post flood field surveys with descriptions of erosive and depositional features were undertaken up to 18 features were classified as either sedimentary or erosive and mapped according to their genetic environments anthropic interference such as land use changes produce modification of sediment supply and in channel and floodplain erosive processes causing flash floods to be more catastrophic erosive features are dominant over sedimentary ones as the sedimentary budget in the river is negative by means of hec ras hydrologic engineering center modelling we were able to obtain mean values of the main variables limiting feature stability velocity depth stream powers and shear stress these provide information regarding maximum stability threshold and peak flood discharge the ephemeral nature of riverine flash flood deposits in this type of setting does not mean that they are not significant and their interpretation after recent floods can significantly improve interpretation of the event dynamics and its flood hydrology and also be useful for flood risk mapping

climatic and tectonic controls on the sedimentary processes of an alluvial fan of the western ganga plain india detailed facies analysis and morphotectonic investigations of the malin river9s alluvial fan in the western ganga plain india reveal that the morphology of the fan is largely tectonically controlled whereas the sedimentary processes are mainly climatically controlled the sedimentation occurred in two distinct evolutionary cycles which are separated by a time gap the older cycle deposited thick gravelly units up to the distal fan area whereas the sediment fill of the younger cycle is gavel dominated in the proximal fan area gravel sand dominated in the middle fan area and sand mud dominated in the distal fan area the gravels of the older cycle were emplaced by intense sediment gravity flows during periods of strengthened monsoon and steeper regional gradient during the younger cycle the proximal to distal parts of the fan were dominated by different sedimentary processes this was a time of relatively weaker monsoon and gentler regional slopes when gravels could travel only up to the middle fan area the gravels in the proximal fan area have mainly been deposited by sediment gravity flows and channel processes in the middle fan area channel processes sheetfloods and sediment gravity flows have been the main sedimentary processes and in the distal fan area fluvial processes of channel migration and overbank deposition have been the main sedimentary processes

late pleistocene fluvial sedimentary facies the dhadhar river basin western india abstract the late pleistocene fluvial succession is exposed as 18 20 m high incised vertical cliffs all along the dhadhar river basin in western india the major fluvial sedimentary facies of the late pleistocene deposits in the dhadhar river basin have preserved evidence of palaeodrainage and could provide an important link between the sub humid narmada basin in the south and the semi arid mahi basin in the north the sedimentary facies documented include overbank fines which are associated with crevasse splays fine grained overbank sediments are interpreted as having formed by sheet flow of sediments over the banks of minor distributary channels during the flood stage the overlying thinly stratified fluvial sands and silts at the top of the exposed sediment succession show a thin cap of aeolian sediments suggesting less intense aeolian activity than that observed in sabarmati mahi and orsang basins though a significant reduction in fluvial activity is suggested during the arid phase of the lgm however the river may still have been perennial assuming that it retained the larger part of the catchment

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

comparison of expert estimates of number of undiscovered mineral deposits with mineral deposit densities abstract the difficult and critical problem of estimating numbers of undiscovered mineral deposits has long been addressed by experts making subjective judgments few tests of the quality of such estimates have been made due to long lag times before exploration results are available estimates made by expert teams in 100 published permissive tracts are compared to those made by mineral deposit density equations the density equations developed from 109 well explored control tracts containing 10 different deposit types provide a robust basis for comparison to ground truth approximately 90 percent of the experts estimates of median number of deposits are within 1 time the density equation estimate where experts estimates were lower than the density estimates the experts probably had relevant information about negative exploration in the tract in tracts where experts median estimates were remarkably higher than the density estimates there were many known deposits two exceptionally high estimates by experts appear to be due to unawareness of how unusual the estimates were in one tract an exceptionally high estimate by experts may be due to not properly using an aggregation of adjacent deposits rule for the grade and tonnage model because the number of known deposits was improbably high also some of 100 expert estimates of expected number of undiscovered deposits are close to the median estimate a result not consistent with known densities of deposits the density equations can be improved by adding new deposit types in proper control tracts having analysts familiar with resource statistics as part of the assessment team and using the density equations in all assessments would identify flawed estimates needing corrections or situations where explanations would improve quantitative assessments