historical trends in the surface temperature over the oceans based on the coads based on a new and unique compilation of surface ship data over the world ocean the comprehensive ocean atmosphere data set coads the temperature records since 1870 were thoroughly analyzed results for the air and sea surface temperature are presented for the two hemispheres and for individual 10 latitude wide belts the results support most earlier results of a relatively warm period over the oceans in the late 19th century a cool period between about 1905 and 1930 and a warm period from the 1940 s onward of considerable interest and perhaps unique in the historical record are the diverging trends in the midlatitude sea and air temperatures of the two hemispheres during the 1960 s and early 1970 s with relative cooling in the northern hemisphere and relative heating in the southern hemisphere

timescales mechanisms and controls of incisional avulsions in floodplain wetlands insights from the tshwane river semiarid south africa abstract avulsion relocation of a river course to a new position typically is assumed to occur more frequently in rivers with faster sedimentation rates yet supporting field data are limited and the influence of sedimentation rate on avulsion style remains unclear using analysis of historical aerial photographs optically stimulated luminescence dating of fluvial sediments and field observations we document three avulsions that have occurred in the last 650 years along the lower reaches of the semiarid tshwane river in northern south africa study of the modern river and abandoned reaches reveals that a downstream decrease in discharge and stream power leads to reduced channel size and declining sediment transport capacity bank erosion drives an increase in channel sinuosity leading to a decline in local channel slope and to a further decrease in discharge and sediment transport local sedimentation rates 10 mm a 1 occur within and adjacent to the channel so over time levees and an alluvial ridge develop the resulting increase in cross floodplain gradient primes a reach for avulsion by promoting erosion of a new channel on the floodplain which enlarges and extends by knickpoint retreat during periods of overbank flow ultimately the new channel diverts the discharge and bedload sediment from the older topographically higher channel which is then abandoned our findings support the assumption that avulsion frequency and sedimentation rate are positively correlated and we demonstrate that incisional avulsions can occur in settings with relatively rapid net vertical aggradation the late holocene avulsions on the semiarid tshwane river have been driven by intrinsic autogenic processes during meander belt development but comparison with the avulsion chronology along a river in subhumid south africa highlights the need for additional investigations into the influence of hydroclimatic setting on the propensity for avulsion

waterholes and their significance in the anastomosing channel system of cooper creek australia abstract cooper creek has developed a very extensive system of anastomosing channels a distinctive feature of which is the preponderance of waterholes which are readily identified as deepened and widened reaches of channel with more or less permanent water they are widely distributed over the floodplain but tend to decrease in number downstream possibly as a result of transmission losses which reduce erosive potential and to develop preferentially towards the west which has implications for the long term relocation of the system classification of waterholes according to degree of lateral restriction and flow status reveals only muted contrasts in waterhole form between the various types the one clear distinction is the unexpectedly low width length ratio of the most restricted dune flanked type its squat form being attributable to erodible banks and limited downstream confinement that waterholes have developed in abundance along cooper creek appears to be related to the presence of a more easily eroded sand sheet at depths of only 2 9 m below cohesive surface sediments sediment splays at their downstream ends indicate that waterholes can be maintained by the present regime but whether they were formed by that or a prior regime is a matter of debate some degree of inheritance cannot be discounted but a contemporary origin is favoured in view of the fact that most waterholes are located at points of flow convergence by focusing erosional energy when the floodplain is extremely broad waterholes play a significant role not only in maintaining existing channel lines but also in promoting the development of new ones as the invasion of a dune field testifies

event frequency and landscape stability on the floodplain systems of arid central australia abstract central australian floodplains contain landforms suggesting activity at three scales a set of large sand sheets sand threads and megaripple covered channels related to a few enormous floods the contemporary floodplain which consists of channels and levees floodouts unchannelled floodplains and floodbasins and erosion cell mosaics which result from local redistribution of sediment classical floodplain models do not fit these systems which behave more like low angle alluvial fans because they continue to accumulate sediment the sedimentary history of the central australian floodplains suggests that deposition in the last 10 000 years has been dominated by a few gigantic floods these events are not represented in the published slackwater deposit record but morphological evidence for them can be found in bedrock gorges as well as on floodplains since the last major flood channel levee systems have been growing slowly upwards and outwards and outwards from the mountain ranges away from these systems sediment supply is limited and the dominant process is local reworking this has intensified since the arrival of europeans 100 years ago and also as a result of increased flooding due to variations in rainfall

simple climatic indices for the tropical atlantic ocean and some applications two indices related to the sea surface temperature sst variability in the tropical atlantic are proposed one index describes the sst averaged over the whole basin 30 n to 20 s 60 w to 15 e and the other illustrates a meridional dipole between the northern and southern hemispheres the computational method for obtaining these indices is intentionally kept simple the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses monthly time series for both indices are produced from 1964 up to the present time the whole basin index exhibits principally a sustained warming which has intensified since about 1975 and it has a significant periodicity close to that of the quasi biennial oscillation the dipole index exhibits a decadal scale variation and its building up seems to be related to other worldwide climatic changes as for instance el nino southern oscillation extreme episodes rainfall variabilities over the brazilian nordeste and african sahel

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

forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction tooth s nanson g c 2004 forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction geological society of america bulletin 116 7 8 802 816 rae2008

terminal infill of eocene lake gosiute wyoming u s a abstract deposition of lacustrine sediments in the greater green river basin was progressively terminated in the middle eocene as volcaniclastic detritus prograded across the basin the lacustrine sediment of the laney member was replaced by deposition of the deltaic and fluvial sediments of the volcaniclastic bridger and washakie formations and the sand butte bed of the laney member the transition from the deposition of lacustrine to alluvial sediment also records a reversal in the direction of drainage across the basin that occurred between 49 5 ma and 48 9 ma prior to this transition drainage entered the basin from the east and the arkosic detritus of the cathedral bluffs member of the wasatch formation was deposited in the washakie and great divide subbasins at the same time evaporitic sediments of the wilkins peak member of the green river formation accumulated simultaneously in the bridger basin indicating that the clastic sediment was baffled east of the rock springs arch an intrabasinal structural high the subsequent transition to deposition of the laney member is traditionally interpreted as an isochronous expansion of lake gosiute across the greater green river basin alternatively the transition may have been diachronous with continued accumulation of the wilkins peak member in the bridger basin coinciding with the earliest deposition of the laney member in the washakie basin by 48 9 ma the dominant drainage was clearly from the west which reflects the capture of an external drainage network through the northwest corner of the basin that delivered extrabasinal volcaniclastic detritus to the greater green river basin more broadly these results illustrate that the geomorphic evolution of the landscape influenced the character of sedimentary fill in the nonmarine greater green river basin

dramatic reduction in size of the lowland macquarie river in response to late quaternary climate driven hydrologic change palaeochannels of lowland rivers provide a means of investigating the sensitivity of river response to climate driven hydrologic change about 80 palaeochannels of the lower macquarie river of southeastern australia record the evolution of this distributive fluvial system six macquarie palaeochannels were dated by single grain optically stimulated luminescence the largest of the palaeochannels quombothoo median age 54 ka was on average 284 m wide 12 times wider than the modern river 24 m and with 21 times greater meander wavelength palaeo discharge then declined resulting in a younger narrower group of palaeochannels bibbijibbery 125 m wide 34 ka billybingbone 92 m 20 ka milmiland 112 m 22 ka and mundadoo 86 m 5 6 ka yet these channels were still much larger than the modern river and were continuous downstream to the confluence with the barwon darling river at 5 5 ka a further decrease in river discharge led to the formation of the narrow modern river the ecologically important macquarie marshes and marra creek palaeochannel 31 m 2 1 ka and diminished sediment delivery to the barwon darling river as palaeo discharge fell further the hydrologic changes suggest precipitation was a driving forcing on catchment discharge in addition to a temperature driven runoff response

morphology of red creek wyoming an arid region anastomosing channel system red creek in the red desert area of the great divide basin wyoming is an arid region anastomosing stream the narrow deep and sinuous main channel is flanked by anastomosing flood channels or anabranches most anabranches are initiated at meander bends the primary mechanism of anabranch initiation is avulsion during overbank floods anabranch enlargement occurs by headward erosion anabranches act as distributary channels during floods when water and sediment from overbank flows are transported to and deposited on the floodplain via the anabranches during periods of low discharges the anabranches act as tributaries to the main channel transporting runoff from the floodplain and surrounding hillslopes to the main channel of red creek aggradation is occurring in the main channel and on the floodplain throughout the study reach infilling of the main channel occurs primarily by lateral accretion while the floodplain accretes vertically through deposition of overbank sediment from the main channel and anabranches infilling of the main channel may cause avulsion of the main channel into an anabranch the abandoned main channel segment may then fill completely or act as an anabranch because lateral migration of channels is inhibited by the high cohesion of the silt and clay channel sediment periodic avulsion is the primary form of lateral mobility in the system

evidence of remote forcing in the equatorial atlantic ocean abstract an analysis of sea surface temperature sst and surface winds in selected areas of the tropical atlantic indicates that the nonseasonal variability of sst in the eastern equatorial atlantic gulf of guinea is highly correlated with the nonseasonal variability of the zonal wind stress in the western equatorial atlantic a negative positive anomaly of the zonal wind stress near the north brazilian coast is followed by a positive negative sst anomaly in the gulf of guinea about one month later furthermore the correlation between the local wind stress anomaly and sst anomaly in the gulf of guinea is considerably smaller these preliminary results indicate that remote forcing in the western equatorial atlantic ocean is an important factor affecting the eastern equatorial atlantic sea surface temperature recent equatorial theories are consistent with these observations

stratigraphic architecture of a transtensional continental basin in low latitude semiarid conditions the permian succession of the central orobic basin southern alps italy abstract continental successions in fault controlled extensional transtensional basins store a wide range of clastic deposits from various depositional environments representing a challenging target for hydrocarbon exploration recent advances in field based facies analysis and genetic interpretation of these sediments show that these successions are characterized by great variability in terms of volume geometry facies and stacking patterns this variability derives from a number of factors that govern the sedimentary processes such as tectonic setting basin size and morphology type and amount of sediments and climate the study focuses on a well exposed early permian continental succession southern alps northern italy which was deposited in an extensional transtensional tectonic regime under a semiarid to arid climate the study area is characterized by a thick more than 1000 m succession of prevailing continental clastics with intercalations of ignimbritic flows and tuffs pizzo del diavolo formation resting on up to 800 m of prevailing pyroclastic flows cabianca volcanite these units are unconformably covered by the upper permian alluvial sediments of the verrucano lombardo sedimentological features reflect a proximal fan system where mass flow phenomena dominate a distal fan terminal setting with prevailing sandy sheet flow processes and a silty floodplain environment where sheet flood events dominate laterally continuous siltstones and dark shales with carbonate nodules and layers of microbial carbonates in the most depressed part of the basin indicate alternating conditions of shallow lake and desiccated floodplain syndepositional tectonic activity is documented in the succession by rapid vertical and lateral facies changes in this study we present a data constrained reconstruction of the depositional architecture of the basin a description of depositional processes and depositional environments and a model of facies distribution outcrop data integrated with laboratory analyses provide a detailed understanding not only of the small scale elements of the system sub seismic scale but also of the entire basin focusing on how those elements are interrelated the studied succession can be considered an interesting outcrop analogue for subsurface extensional transtensional basins potentially useful to predict reservoir properties for similar subsurface settings

unconfined flow deposits in distal sectors of fluvial distributary systems examples from the miocene luna and huesca systems northern spain abstract thin sheet sandstone beds in a continental succession may be the products of unconfined overbank flow or deposition in lacustrine environments in the distal parts of fluvial distributary systems these two settings may be intercalated recording fluctuations in lake level in response to climatic changes field studies of the luna and huesca fluvial distributary systems in the miocene of the ebro basin spain are here used to characterise sheet sandstone deposited in distal fluvial and lake margin environments in this study we document the facies and relationships between 322 individual sandbodies deposited in both alluvial settings as sheetfloods and in lacustrine settings as deltaic lobes the alluvial sandstone sheets were deposited from lateral and frontal sheetflood events when unconfined flow replaced channelised flow as the main transport mechanism the term sheetflood is used here to refer to sub aerial unconfined turbulent flow events that undergo expansion thinning and deceleration with increasing radial distance from source the depositional process is similar to modern floodouts and terminal splays of the channel country and lake eyre central australia such a process was thought to be the dominant depositional mechanism during lake lowstands the sheets formed in the lacustrine setting are interpreted as deltaic sediments deposited in a shallow gradient lake similar to the modern day volga delta caspian sea shallow water friction dominated deltaic processes are thought to have been the primary depositional mechanism in the distal sectors of the fluvial systems during lake highstands

climatology comparison and long term variations of sea surface temperature over the tropical atlantic ocean the primary aim of the present study is to compare two sea surface temperature sst climatologies produced from merchant ship observations over the tropical atlantic ocean the first climatology uses measurements taken between 1911 and 1972 the second uses 1964 1984 data the second climatology is generally warmer by a few tenths of degrees part of the difference is due to changes in the temperature measurement techniques with time the difference also shows especially along shipping routes some spatial discrepancies which are not due to instrument changes it is demonstrated the difference is mostly caused by inhomogeneity in the spatial and temporal density of the available observations used to construct the first climatology using a simple technique to eliminate spurious bias the analysis allows isolation of the long term trend of sst anomalies in the tropical atlantic ocean during this century south of the thermal equator a warming trend occurs principally during boreal summers and extends to the present with an increasing range when calculated over the past 26 year period in the north such a warming is more questionable between the 1940s and 1970s it is more evident during the past 26 year period but with a temperature range less than half of that for the southern basin thus large abnormal patterns have a tendency to straddle the thermal equator including a north south climate dipole three spatially limited areas with a cooling trend are suggested the reliability of sst anomalies along the tropical section of the europe south america shipping track in recent years is also discussed

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

television image of a large upward electrical discharge above a thunderstorm system an image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low light level television camera the discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher the image which had a duration of less than 30 milliseconds resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops large upward discharges may create a hazard for aircraft and rocket launches and by penetrating into the ionosphere may initiate whistler waves and other effects on a magnetospheric scale such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud to earth lightning strokes an unusually high rate of such photometric events was recorded during the night of 22 to 23 september 1989 during a storm associated with hurricane hugo

crevasse splays from the rapidly aggrading sand bed braided niobrara river nebraska effect of base level rise base level rise of 2 35 m on the niobrara river has resulted in aggradation of the channel belt and a recent avulsion overbank areas have become flooded by rising groundwaters and more than eight crevasse splays have formed between 1993 and 1997 two crevasse splays situated on the west and east sides of the niobrara have been studied using ground penetrating radar gpr shallow boreholes and topographic surveys the vibracores and gpr profiles provide a nearly three dimensional view of the architecture of crevasse splay deposits the east splay was initiated in the winter of 1993 94 and has expanded to cover an area 200 m by 1000 m with sediment up to 2 5 m thick the west splay which was initiated by the opening of a crevasse channel through a levee in the autumn of 1995 covers an area 150 m by 250 m with up to 1 2 m of sand deposited in a single year the niobrara splays are sand dominated and characterized by bedload deposition within channels 5 30 m wide and 0 5 2 m deep with the development of slipfaces where splays prograde into standing bodies of water sedimentary structures in cores include horizontal lamination ripple lamination and sets of cross stratification there is a slight tendency for splays to coarsen up but individual beds within the splays often fine up the abundance of crevasse splays on the niobrara river contrasts with other braided river floodplains in the niobrara crevasse splay formation followed aggradation within the channel belt which occurred in response to base level rise the link between crevasse splays channel aggradation and base level rise has important implications for the interpretation of ancient braided river and floodplain sequences it is suggested that crevasse splay deposits should be an important component of aggrading fluvial sediments and hence should be preserved within the rock record in this case the aggradation and crevassing have been tied to a rise in base level elevation and it is suggested that similar deposits should be preserved where braided rivers are affected by base level rise for instance during transgression and filling of palaeovalleys

anatomy and facies distribution of terminal lobes in ephemeral fluvial successions jurassic tordillo formation neuquen basin argentina in terminal fluvial fan systems characteristic proximal to distal variations in sedimentary architectures are recognized to arise from progressive downstream loss of water discharge related to both infiltration and evaporation this work aims to elucidate downstream trends in facies and architecture across the medial and distal zones of terminal fan systems which record transitions from deposits of channel elements to lobe like and sheet like elements this is achieved via a detailed characterization of ancient ephemeral fluvial deposits of the well exposed kimmeridgian tordillo formation neuquen basin argentina the fine sand prone and silt prone succession associated with the medial to distal sectors of the system has been studied to understand relationships between depositional processes and resulting architectures facies and architectural element analyses and quantification of resulting sedimentological data at multiple scales have been undertaken to characterize sedimentary facies facies transitions bed types architectural elements and larger scale architectural styles eight bed types with distinct internal facies transitions are defined and interpreted in terms of different types of flood events channelized and non channelized architectural elements are defined based on their constituent bed types and their external geometry the most common elements are terminal lobes which are composite bodies within which largely unconfined sandy deposits are stacked in a compensational manner a hierarchical arrangement of internal components is recognized proximal feeder channel avulsion events likely controlled the evolution of terminal lobe elements and their spatiotemporal shifts stratigraphic relations between architectural elements record system wide trends whereby a proximal sector dominated by channel elements passes downstream via a gradational transition to a medial sector dominated by sandy terminal lobe elements which in turn passes further downstream to a distal sector dominated by silty terminal lobe margin and fringing deposits this work enhances current understanding of the stratigraphic record of terminal fluvial systems at multiple scales and provides insight that can be applied to predict the facies and architectural complexity of terminal fluvial successions

spatial and temporal evolution of a terminal fluvial fan system the permian organ rock formation south east utah usa the recognition of terminal fluvial systems otherwise termed terminal fans or distributary fluvial fan systems preserved in the ancient rock record is based primarily on the recognition of facies characteristics indicative of a progressive downstream decrease in i fluvial discharge ii channel depth and width iii lateral and vertical connectivity of channel fill elements and iv evidence for channellized flow and a systematic increase in i evidence for sheetflood deposition ii aeolian and or playa deposits and iii channel bifurcation however despite these criteria having been applied previously to a variety of outcrop successions there is still no unifying facies model that adequately accounts for the complex stratigraphic architectural relationships expected for such systems based on the varied styles of fluvial activity and system interaction known from modern examples moreover few previous studies have given significant consideration to the long term temporal evolution of terminal fluvial fans these issues are addressed by this study of the permian leonardian artinskian organ rock formation of the paradox basin south east utah a detailed stratigraphic framework based on 84 sedimentary logs demonstrates proximal to distal variations in sedimentary style integration of these data with high resolution architectural panels depicting the geometry and facies characteristics of individual fluvial elements has enabled the development of a series of depositional models that account for both the spatial and temporal evolution of the system and which are representative of i initial progradation of the fluvial system into the paradox foreland basin ii retreat of the fluvial system and expansion of a distal aeolian dune system iii the final phase of fluvial progradation following aeolian dune deflation and iv the final retrogradation of the fluvial system back towards the hinterland

a quantitative model for deposition of thin fluvial sand sheets sheetfloods are typically invoked as the mechanism responsible for the kilometre scale transport of sand sized sediment grains in shallow gradient fluvial systems this concept is based on the lateral extent of ancient thin sheet sandstone deposits rather than on fluid dynamics which has resulted in a loosely constrained model for sheetfloods this study tested the conceptual mechanism by developing a depth averaged 2d computational fluid dynamics model the model results compare well against observations from modern deposits at lake eyre to provide a quantitative physically sound basis for sheetfloods that can be applied in ancient and modern settings to constrain otherwise qualitative interpretations

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

on the origin of crevasse splay amalgamation in the huesca fluvial fan ebro basin spain implications for connectivity in low net to gross fluvial deposits abstract floodplain deposits are abundant in low gradient dryland river systems but their contribution to connected reservoir volumes has not yet been fully acknowledged due to their poor detectability with typical wireline log suites and relatively lower reservoir quality this study presents an analysis of stacked crevasse splays in the distal part of the miocene huesca fluvial fan ebro basin spain vertical stacking of crevasse splays implies local aggradation of the active channel belt lateral amalgamation of crevasse splays created an elevated rim around their feeder channel raising its bankfull height subsequent crevasse splays were deposited on top of their predecessors creating sand on sand contact through incision and further raising the active channel belt this process of channel belt super elevation repeated until an upstream avulsion occurred amalgamated crevasse splays constitute connected reservoir volumes up to 107 m3 despite their lower reservoir quality they effectively connect channel deposits in low net to gross fluvial stratigraphy and hence their contribution to producible volumes should be considered unswept intervals of amalgamated crevasse splays may constitute a secondary source of natural gas their interval thickness can serve as a proxy for feeder channel dimensions which can in turn be used to estimate the degree of stratigraphic connectivity

the cretaceous pyonghae basin southeast korea sequential development of crevasse splay and avulsion in a terminal alluvial fan abstract the pyonghae basin early cretaceous southeast korea comprises a thick sequence of purplish siltstone with subordinate gravelstone and gravelly sandstone deposited in a terminal alluvial fan environment based on bed geometry and facies assemblage the gravelly sandstone bodies are divided into four types type a deposit consists of disorganized gravel patches and massive sandstone lenticules a few decimetres thick and a few metres wide most likely deposited from overflows type 2 deposit is characterized by crudely stratified and massive sandstone beds up to 2 m thick 20 m wide and comprises lower disorganized gravel layers and upper stratified gravelly sandstone beds forming a fining upward trend it probably represents crevasse channel distributary channel fills type 4 deposit 3 5 m thick 20 m wide consists of stratified cross stratified gravelly sandstone beds which are interpreted as main braided channel fills aggradation of the terminal fan was associated with frequent shift of channels which range from crevasse splay channel type 2 through crevasse channel distributary channel type 3 to main channel type 4 the crevassing or avulsion was preceded by overflows type 1 the avulsion processes in the terminal fan were achieved through stepwise enlargement of crevasse channels which reflect different channel responses to floods of different magnitude and frequence

restoration of floodplain topography by sand splay complex formation in response to intentional levee breaches lower cosumnes river california restoration of sustainable geomorphic processes that create floodplain topography through development of sand splay complexes at intentional breaches is one method to promote variability in physical structure needed for habitat restoration the topography of splay complexes provides a range of floodplain elevations that creates local variability in i inundation duration and frequency and depth to ground water that influence riparian vegetation establishment and ii flow depth and velocity that create refuge for fish two intentional levee breaches along the lowland cosumnes river central valley ca were evaluated during water years 1999 and 2000 in order to document changes in morphology and relief associated with deposition of sandsplay complexes during the study period annual peak flow recurrence intervals ranged from 1 to 3 years and water flowed through the breaches for a minimum of 55 days during water year 1999 and 53 days during water year 2000 at the two study sites rapid vertical accretion and scour occurred within the first several years after intentionally breaching the levee at the accidental forest floodplain constructed in 1995 and at the corps breach floodplain constructed in 1997 splay complexes are organized into a variety of landforms including lateral levees and lobes separated by new floodplain channels maximum deposition measured on the splay surface is 0 36 m year while maximum scour in channels is 0 27 m year juxtaposition of floodplain splay deposition and adjacent channel scour creates relief ranging from 1 6 to 0 25 m that decreases with distance from the breach and that becomes more pronounced over time as higher magnitude floods scour channels in the old floodplain sediment and deposit new sand and silt onto the surface of the splay the ratio of splay complex height to depth of formative flow is estimated as 0 4 progradation of main and secondary splay channels takes place by down floodplain sand transport 25 m year maximum large wood recruited onto the floodplain through the breach promotes local scour and deposition that enhances topographic variability at one of the study sites initial grading of a low setback berm prior to opening the breach forced a change in floodplain flow direction and the geometry of the splay complex additionally progradation of the complex is arrested by an excavated pond that creates a sediment trap we present a conceptual model that describes the importance of floods in constructing and modifying sand splay complexes that create floodplain topography the potential habitat variability created as floodplain topography evolves is the linkage between physical and ecological processes that are critical for restoration d 2002 elsevier science b v all rights reserved

effects of the 1997 flood on the transport and storage of sediment and mercury within the carson river valley west central nevada abstract intense warm rains falling on a heavy snowpack in the sierra nevada at the end of december 1996 produced some of the largest floods on record in west central nevada within the carson river basin a peak discharge of 632 cm was recorded at the fort churchill gaging station on january 3 1997 a flow exceeding the 100 yr event geomorphic impacts of the event and the redistribution of mercury hg released to the carson river valley by comstock mining operations during the mid to late 1800s were assessed by combining field data with the interpretation of aerial photographs geomorphic impacts included significant increases in channel width measuring up to 280 of preflood conditions and large scale shifts in channel position ranging from 10 to 110 m both changes in channel width and position vary as a function of valley morphometry width and slope and differ from the long term trends measured from 1965 to 1991 the 1997 flood also produced widespread overbank deposits that vary morpholo

recent observations of lightning discharges from the top of a thundercloud into the clear air above a note of inquiry published in a magazine read by airplane pilots has elicited 15 new observations of a rare form of lightning that comes out of the cloud top goes up vertically and terminates in the clear air above these confirm previous observations showing that this phenomenon usually occurs above very large and energetic thunderclouds however small clouds with tops at 15 000 ft mean sea level 5000 m have been observed to exhibit this rare form of lightning also one of the more spectacular observations was made over the severe storm system that produced the devastating tornadoes of april 11 1965

cascades of sub decadal channel floodplain changes in low gradient non vegetated reaches near a dryland river terminus salar de uyuni bolivia

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

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

sprite observations above the u s high plains in relation to their parent thunderstorm systems transient luminous events sprites blue jets elves above large mesoscale convective systems mcss over the u s high plains have been routinely monitored from the yucca ridge field station near fort collins colorado using ground based low light video systems we analyzed 36 sprites above the nebraska mcs of august 6 1994 the results lend further support to the hypothesis that sprites are almost uniquely associated with positive cloud to ground cg lightning flashes sprite associated cgs also averaged substantially larger peak currents than the remaining cg population 81 ka versus 30 ka in this storm system there is some evidence that sprite associated cgs also have higher stroke multiplicity this study yields no evidence of sprites associated with negative cg events in the central united states an additional requirement appears to be that the parent mcs has a contiguous radar reflectivity area exceeding 20 25 000 km 2 the majority of the sprites occur above the large stratiform precipitation region and not the high reflectivity convective core of the mcs triangulation of a limited number of paired images from september 7 1994 suggests that the sprite is generally centered within 50 km of the parent cg assuming the cg provides the range single image photogrammetric analyses provide estimates of the maximum vertical extent of the sprites for this storm the sprite tops averaged 77 km with a maximum of 88 km the bases averaged 50 km but with a few sprite tendrils extending as low as 31 km

anabranching rivers on the northern plains of arid central australia anabranching rivers are a widespread feature of the northern plains in the alice springs region of central australia but their unusual characteristics previously have not been described on the northern plains anabranching occurs on rivers transporting bedloads of coarse sand and gravel and is characterised by channels of variable size and shape which occur within a broader typically well defined channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands ridges and islands are either depositional features formed in situ by accretionary processes or erosional features formed by excision from once continuous areas of floodplain vegetation plays a key role in the initiation survival and growth of depositional forms through its influence on flow sediment transport and ridge and island stability anabranching is also related to the influence of tributaries for some large rivers alternate from single thread to anabranching along their length in response to tributary inputs of water and sediment tributary inputs occur during flow events that are either independent from or in concert with floods in the trunk channel ridges and islands form in association with tributaries as a result of various hydrological depositional and erosional processes including irrigation of enhanced numbers of in channel trees and resulting lee side sediment accretion floodplain scour and the formation and maintenance of deferred junction tributaries the change from single thread to anabranching downstream of tributary junctions occurs in the absence of any significant change in channel gradient or degree of channel confinement on the northern plains anabranching appears to be a stable river pattern that helps to maintain the throughput of relatively coarse sediment in low gradient typically 0 0005 0 002 channels characterised by an abundance of within channel vegetation and subject to declining downstream discharges

distribution of palaeosols and deposits in the temporal evolution of a semiarid fluvial distributary system bauru group upper cretaceous se brazil abstract the stratigraphic and sedimentological knowledge of the bauru group upper cretaceous se brazil is still generally insufficient and controversial a sedimentological and palaeopedological study allowed to interpret the south eastern portion of the bauru group according to the model of a fluvial distributary system this work has two objectives 1 to include palaeosols in the interpretation of a fluvial distributary system and 2 to give detailed information on the sedimentological and stratigraphic features of the se portion of the bauru group in order to support biostratigraphical taphonomic and palaeoecological studies in the south eastern portion of the bauru group three genetic stratigraphic units were described and interpreted here informally called lower intermediate and upper units the lower unit is constituted of muddy sandstone salt flat deposits and sandstone sheet deltas deposits and is interpreted as a basinal part of a fluvial distributary system the intermediate unit is formed of very fine to fine grained sandstone filled ribbon channel and sandy sheet shaped beds suggesting a distal or medial portion of a fluvial distributary system the upper unit does not match with the present models of the fluvial distributary system because mostly constituted of moderately developed well drained medium to fine grained sandstone palaeosols which testify pauses of sedimentation to the order of 104 years preserved features of sedimentary structures suggest that the parent material was formed by occasional catastrophic unconfined flows this unit may represent the most distal portion of a fluvial distributary system generated by retrogradation of the alluvial system due to aridification of the climate the upper unit may be interpreted also as proximal portion of fluvial distributary system if considering the coarser grained and the well drained palaeosols however the absence of channel deposits makes this interpretation unconvincing

splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia abstract splays are common features of many rivers and deltas forming as a result of overbank flooding and sediment deposition but they have rarely been described from modern dryland settings this paper investigates splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia here splays vary from small lobate or tongue shaped features 1 km long to larger elongate features up to 4 km long and are supplied with rare floodwater and sediment through well defined breaches in the upper parts of the main channel banks in proximal and medial parts splay channels are incised up to 2 m into pre splay fine grained floodplain sediments but remain elevated between 0 5 m and 2 m above the main channels only in the very distal parts are splay channels less deeply incised either grading into the floodplain surface or terminating as sediment lobes that are deposited upon the floodplain aerial photographs and field observations indicate that many splays develop rapidly during large floods and are modified during infrequent subsequent floods four main stages of splay development are proposed 1 aggressive overbank flow results in bank line breaching and channel scour on the floodplain but little sediment deposition 2 coarse bed sediment is diverted from the main channel preventing further deepening at the bank line breach and slowing channel scour 3 increasing coarse sediment transport through the bank line breach and scoured channels leads to the formation of distal sediment lobes 4 subsequent floods divert around these distal lobes sometimes leading to further channel scour and lobe formation on the northern plains splays contribute to downstream decreases in the discharge and size of the main channels and splay deposits form local accumulations of gravelly sand in the predominantly fine grained floodplain successions some splays ultimately may evolve into distributaries or anabranches the dominantly erosional bases of these splay channels contrast with typical descriptions of many humid region splays but they do not display any geomorphological or sedimentological features that are necessarily diagnostic of formation in a dryland setting

morphology and sediment dynamics of ephemeral stream terminal distributary systems in the kobo basin northern welo ethiopia channel morphology bedforms and sedimentary structures of the distributary systems of ephemeral streams in the structural basin of kobo northern ethiopia are analysed the basin is characterised by a semi arid monsoon affected climate most of the rivers originate in the western margin range and dry up in the middle of the basin where they form large distributary systems they show characteristics different from those of the terminal fans and floodouts previously reported in the literature no flow data are available but bankfull discharge for several study reaches has been obtained by field survey of a number of cross sections hydraulic geometry streambed gradient and bed material grain size distribution in both the main stems and the distributary channels two different types of terminal distributary systems have been identified bird foot and lobate the first type by far predominates in the kobo basin bird foot distributary systems were recognized to consist of five distinctive reach units while the lobate splays have a simpler morphology and are thought to evolve into the former more complex type a description of channel morphology bedforms and sedimentary structure distribution is given and these characteristics are compared to those of other similar depositional systems reported in the literature other features such as the lack of scour pockets around boulder particles scattered on the streambed surface and the interaction of individual large particles with massive or horizontal laminated sand on top of typical upward fining channel sequences are also highlighted

spillage sedimentation on large river floodplains active deposition across the floodplains of large rivers arises through a variety of processes collectively these are here termed spillage sedimentation three groups of 11 spillage sedimentation styles are identified and their formative processes described form presences on large river floodplains show different combinations of active spillage styles only some large floodplains have prominent levees some have coarse splays many have accessory channel dispersion and reworking while still water sedimentation in lacustrine environments dominates some lower reaches infills are also commonly funnelled into prior and often linear negative relief forms relating to former migration within the mainstream channel belt 2016 the authors earth surface processes and landforms published by john wiley sons ltd shuttle radar topography mission srtm and landsat 8 data are used to map spillage form types and coverage along a 1700 km reach of the amazon that has an active floodplain width of up to 110 km with a systematic character transformation down valley spillage forms associated directly with mainstream processes rarely account for more than 5 of the floodplain deposits there is a marked decrease in floodplain point bar complexes pbc over 1700 km downstream from 34 to 5 and an increase in the prevalence of large water bodies 2 to 37 and accompanying internal crevasses and deltas 0 to 5 spillage sedimentation is likely within the negative relief associated with these forms depending on mainstream sediment laden floodwater inputs 2016 the authors earth surface processes and landforms published by john wiley sons ltd spillage style dominance depends on the balance between sediment loadings hydrological sequencing and morphological opportunity down river form sequences are likely to follow gradient change prior up river sediment sequestration and the altered nature of spilled loads but also crucially local floodplain relief and incident water levels and velocities at spillage times considering style distribution quantitatively as a spatially distributed set of identifiable forms emphasizes the global variety to spillage phenomena along and between large rivers 2016 the authors earth surface processes and landforms published by john wiley sons ltd

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

a small alluvial crevasse splay abstract a crevasse splay deposited on the floodplain of the clarence river in northeastern new south wales australia by a small ephemeral tributary provides a guide to the geometry and sedimentary structures of crevasse splays in general and to the processes affecting their final form the splay consists of a main lobe of sand with smaller sand fingers that end in slipfaces around its edges water seeping out of the channel reworks part of the splay into a gently thinning sheet small scale facies models derived from different parts of this splay explain the origins of solitary planar cross sets and gently inclined bedding in some ancient crevasse splay sandstones

crevasse splay morphodynamics in a dryland river terminus rio colorado in salar de uyuni bolivia high resolution satellite imagery in combination with field investigation enables the analysis of splay morphological developments in time and space at the low gradient terminus of the modern rio colorado dryland river system in the salar de uyuni bolivia two sets 2004 2005 2010 2011 of satellite images are used to visualize splay morphological developments and three types of crevasse splays are identified based on temporal changes 1 new crevasse splays ncs refers to those splays that are not observed in the first set of images but can be observed on the second sets of images 2 changing crevasse splays ccs representing those splays that are found on the first set of images but their geometry has changed between two satellite observation periods and 3 inactive crevasse splays ics referred to those splays that are found on the first set of images but on the second set of images they remain the same or are partially overlapped by adjacent expanding crevasse splays the density or frequency of these three types of crevasse splays has no correlation with the distance to the starting point of the river or the local slope the cross sectional area of the studied river steadily decreases downstream and frequency analysis shows a downstream increase in the number of crevasse splays and suggests an exponential relationship with the river cross sectional area development of crevasse splays is often attributed to topographic lows between adjacent crevasse splays and they fill in the depression by compensational stacking e g li et al 2014 these amalgamated splays are capable of forming a large area of sheet sands and potentially provide an analogue for thin bedded hydrocarbon reservoirs

recognition of the sedimentary architecture of dryland anabranching anastomosing rivers abstract the application of rigorous criteria for identifying fluvial style from sedimentary deposits is crucial if environmental reconstructions from stratigraphy are to be reliable from modern observations it appears that anabranching anastomosing rivers can be divided into separate humid and dryland classes each class has dissimilar characteristics to the other necessitating different criteria for their recognition in the rock record the criteria being used by sedimentologists to recognize deposits of anabranching rivers are derived solely from modern examples in humid regions heavily biased to a few specific cases in canada these criteria are dominated by the concept of ribbon sandstone bodies encased in fine grained floodplain sediment with an overall low sand to mud ratio in the succession there has been a general failure to appreciate that dryland anabranching rivers have characteristics significantly different from these and almost certainly leave a sedimentary record quite dissimilar to that previously expected avulsion or obtrusion the gradual formation of an alternative channel are the characteristic dynamic of anabranching rivers forming and maintaining coexisting multiple anabranch channels avulsion or obtrusion require stream banks to have a high resistance to erosion usually achieved by cohesive bank sediments or the reinforcement of banks by vegetative root mats in some drylands riparian vegetation can be sparse and bank resistance may depend in large part on a high clay content here channel fills are mud dominated and floodplains have a uniform fine grained character which is usually structureless because of intense pedoturbation and some bioturbation the evidence from such present day dryland anabranching rivers suggests that their sedimentary record is likely to be one of laterally extensive mud rich beds with weak or enigmatic fluvial indicators elsewhere dryland anabranching systems are sand dominated their banks reinforced with riparian gallery forests sustained by infrequent flow and a shallow water table though the stratigraphy of these has barely been investigated they are clearly different from humid region anabranching systems for their channels and islands are predominantly sandy anabranching rivers with prominent channel sandbodies separated by muddy islands have never been described from contemporary drylands the interpretation of a dryland origin for ancient stratigraphic successions with this form is made therefore without evidence that they can actually exist in the light of this such interpretations should be reevaluated

possible climate variability in the lower old red sandstone conigar pit sandstone member early devonian south wales uk abstract the early devonian conigar pit sandstone member cpsm of the freshwater west formation lower old red sandstone lochkovian age at freshwater west in south wales comprises a heterolithic predominantly alluvial suite mudstones fine to coarse grained sandstones conglomerates with varying depositional architecture a number of discrete facies associations are observed the fine grained inclined and non inclined heterolithic association is dominant within the cpsm it represents dryland sinuous channelized flow ihs bedsets and unconfined flow non inclined bedsets at terminal and intermediate floodouts deposited under semi arid conditions mudstones were deposited in two distinct environments associated with this semi arid river system laminated and burrowed reddish brown mudstones were deposited in shallow semi permanent lakes or pools on the floodplain massive mudstones were deposited as within channel muddy braid bars with sedimentary structures being lost during subsequent compaction the mudstones exhibit vertisol pedogenesis reflecting the seasonal wetting and drying associated with the semi arid climate periods of intense desiccation are indicated by deep desiccation cracks and associated rubbly surfaces possible though unproven tidal conditions influenced a small percentage of the heterolithic channels at freshwater west the extent of these channels is uncertain the coarser grained multi storey sandstone association was deposited by low sinuosity rivers with a fluctuating but perennial discharge associated with these laterally extensive sandbodies was a high water table with surface ponding wetlands that enabled the preservation of plant detritus during high discharge events flow expanded over the contemporaneous floodplain depositing the sheet sandstone association within splay complexes the interpretation that perennial discharge may have been triggered by basin wide climate change challenges the long held view that the lower ors climate was continuously semi arid in nature the spatial temporal extent of this climate change is uncertain as it is possible that the multi storey sandbodies were deposited by allogenic rivers draining a distant possibly uplifted source area a decrease in the observed frequency and maturity of vertisol profiles and a corresponding increase in multi storey sandbodies upward through the succession may reflect a long term episodic pattern of climate change

fluvial fans myths misconceptions and the end of the terminal fan model we propose that the so called terminal fan facies model should be abandoned since it is flawed on several counts and it is leading to misunderstanding and poor communication rivers in drylands may experience excessive down stream discharge reduction such that they terminate subaerially rather than reach the sea or a lake the facies model predicts that the distal reaches of such rivers form a network of bifurcating distributary channels producing a fan shaped sediment body with downstream thinning and fining of sedimentary units ending in sand filled ribbons encased in mud extensive review of modern rivers has failed to turn up convincing examples that fit the model rivers in drylands do not ubiquitously end in fans fan shaped fluvial bodies are common wherever rivers are released from confinement and the discharge conditions promote frequent avulsion channels on such fans generally do not repeatedly bifurcate downstream where they are seen to do so it can usually be shown they are lacustrine deltas inherited from wetter times the term distributary is being used carelessly and is conveying incorrect understanding of sediment geometry and architecture the proposed synonym of fluvial distributary systems is unsatisfactory as it perpetuates the same misunderstandings reliance on planform alone in analogue selection is highly risky the fluvial fan is a composite sediment body resulting from frequent nodal avulsions in a setting without horizontal constraints channels on fans range in planform as much as any other river the resultant sedimentary record differs little from that expected from non fan fluvial systems except having a regionally radiating orientation when viewed over geological time scales contrary to the implications of the facies model there is no distinctive terminal fan sedimentary succession

tropical atlantic thermal structures along the europe brazil ship line beginning in 1981 expendable bathythermograph xbt temperature sections down to 460 meters have been made two to three times per month between 20 n and 20 s along the ship of opportunity line from europe to brazil three thermal zones are described the guinea dome at 10 n 15 n the equatorial region and the brazilian warm waters between 2 s and 18 s the guinea dome is characterized by a shallow thermocline with little seasonal cycle and a doming or surfacing of the isotherms in the equatorial region the thermocline is almost flat but moves up and down with the season and the changes in the trade winds in the brazilian warm waters the mixed layer is always thick with some seasonal cycle and the thermocline spreads from 100 meters down to the maximum depth of the measurements the presence of absence of the major currents is infered from the slopes of the thermocline the most striking event of the period is the development of a warm anomaly in conjunction with light trade winds during the southern hemisphere warm seasons of 1982 1983 and 1984 reaching 1 5 c over a large area in april 1984

the 1870s avulsion of the saskatchewan river several major avulsions of the saskatchewan river have occurred in the cumberland marshes east central saskatchewan during the past few thousand years the most recent avulsion occurred in about the 1870s converting over 500 km2 of floodplain into a belt of anastomosing channels splay complexes and small lakes a region that is still evolving today the avulsion began near the tip of a large meander bend by following a small outflowing creek sturgeon river which in turn followed an abandoned former channel of the saskatchewan river flow began to permanently divert out of the saskatchewan when a narrow strip of floodplain separating the sturgeon river from the nearby torch river became breached diversion into the connected sturgeon torch began to increase sometime in the 1870s and probably culminated around 1882 the triggering event for the avulsion may have been a chute cutoff of the meander bend shown by numerical modeling experiments to have significantly raised water surface elevations at th

digital elevation models for topographic characterisation and flood flow modelling along low gradient terminal dryland rivers a comparison of spaceborne datasets for the rio colorado bolivia abstract many dryland rivers are terminal systems with small channels undergoing prominent downstream size reductions before ending on channelless floodplains in wetlands or at playa margins spaceborne digital elevation models dems provide potential for assessing subtle topographic and hydrodynamic changes in these low gradient low relief settings but challenges are posed by limitations in vertical and horizontal accuracy this study evaluates the use of different spaceborne dems for topographic characterisation and flood flow modelling of the low gradient

morphodynamics of the erosional phase of crevasse splay evolution and implications for river sediment diversion function abstract despite being a primarily depositional landform a crevasse splay experiences an initial evolutionary phase that is primarily erosional as sediment laden river water spills from a main river channel and incises a new route through the river banks and levee into an interdistributary basin or floodplain this phase sets the dimensions and the conveyance properties of the crevasse which in turn influences the continued expansion or closure of the crevasse channel however little is known about the controlling morphodynamics or how the erosional processes transition to depositional processes during this phase the objective of this study is to investigate these phenomena at the west bay sediment diversion louisiana usa using coupled field observations and numerical modeling the west bay diversion was cut into a lower mississippi river levee to mimic the function of a crevasse splay i e to divert river water and sediment to an adjacent receiving basin for land building purposes bathymetric measurements show that the diversion channel experienced significant natural morphologic evolution during the initial decade 2004 2014 hydrodynamic and sediment transport modeling suggests that this evolution initially increased the discharge of flow and sediment through the crevasse as the channel became wider and deeper and altered its orientation relative to the main river flow direction after 5 years the model results predict that further evolution led to monotonically reduced diversion discharges during this time natural and engineered sediment deposition in the receiving basin decreased predicted basin flow velocities and promoted a backwater effect that reduced the sediment transport capacity of the diversion channel observations during the final 2 years show that much of the initial erosion around the diversion had abated indicating that diversion morphology may have stabilized a modeling sensitivity analysis confirmed that the observed changes to channel geometry and orientation likely promoted flows of water and sediment through the diversion while increases in basin bed elevation would have had a contrary effect the morphodynamic evolution of the west bay diversion documented in this study presents a model indicative of the erosional phase of crevasse splay evolution in a deltaic distributary fluvial network study results offer an analogue on how an engineered river sediment diversion constructed for coastal restoration may function during its first years of operation and suggest that the desired land building processes may take time to become established

avulsions channel evolution and floodplain sedimentation rates of the anastomosing upper columbia river british columbia canada ages of channels of the anastomosing upper columbia river south eastern british columbia canada were investigated in a cross valley transect by c 14 dating of subsurface floodplain organic material from beneath levees the avulsion history within the transect was deduced from these data and morphological stages in channel development were recognized additionally floodplain sedimentation rates were established the new data demonstrate that the upper columbia river is a long lived dynamic anastomosing system results show that anastomosis at the study location has persisted since at least 2700 cal years bp with avulsions occurring frequently at least nine channels have formed in the studied cross valley transect within the past 3000 years channel lifetimes from formation to abandonment appear to be highly variable ranging from approximately 800 to 3000 years log jams provoking avulsions and or silting up of old channels are proposed as reasons for this variability long term average floodplain sedimentation rates appear to be significantly lower than previously proposed by smith 1983 int assoc sedimentol spec publ 6 155 168 a long term 4550 years average of 1 75 mm per year after compaction was based on c 14 dates whilea short term sedimentation rate of 0 8 mm was determined for a single relatively small seasonal flood in 1994 using sediment traps however short term sedimentation rates vary considerably over the floodplain with levees aggrading up to four times faster than floodbasins channels of the upper columbia river anastomosed reach follow a consistent pattern in their development with each stage being characterized by different morphology and processes channel evolution comprises the following succession 1 avulsion stage in which a crevasse splay channel deepens by scour and levee sedimentation 2 widening and deepening stage in which bank slumping and bed scouring dominates 3 infilling stage in which either channel narrowing bank accretion or channel shallowing bed accretion takes place and 4 abandonment stage in which the residual remnant channel is filled exclusively by silt clay and organic material vertical stacking super imposition of active channels on recent channel fill sand bodies is a notable feature of the upper columbia river which suggests that reoccupation of residual channels is a common process

facies partitioning and stratal pattern in salt controlled marine to continental mini basins examples from the late oligocene to early miocene of the sivas basin turkey the sivas basin turkey records a complex interaction between sedimentation salt tectonics and regional shortening leading to the formation of numerous mini basins the segmentation into mini basins was initiated during the oligocene by the deposition of the fluvio lacustrine karayun fm this continental succession is overlain abruptly by an oligo miocene shallow marine succession karacaoren fm which comprises two main sub environments i mixed deltaic and carbonate ramp ii coastal plain and lagoon the karacaoren fm forms a marine succession more than 1500 m thick that passes vertically upwards into a continental succession the fluvial dominated benlikaya fm these two formations are the focus of the present study during the period of marine sedimentation the competing accumulation of carbonates and clastics is related not only to the topography inherited from salt tectonics but also to relative sea level variations expressed by two large scale transgressive regressive cycles we analyse these complex facies and stratal relationships to illustrate the modifications induced by salt tectonics this study is based on extensive fieldwork and mapping making use of numerous measured stratigraphic sections and aerial photos over a large area comprising more than fifteen adjacent outcropping mini basins the aim of this study is to provide a detailed description of the stratigraphic relationships correlations and sedimentary systems distribution in mini basins during deposition of the oligo miocene shallow marine and continental successions we first clarify the vertical stratigraphic succession of the oligo miocene marine and continental deposits and establish correlations between the studied mini basins these correlations then allow us to characterize and assess the local effects of salt withdrawal in relation to the regional forcings associated with flexural subsidence tectonic shortening and relative sea level changes an improved understanding of the complex interactions of these variables provides a framework to distinguish the mechanisms that control facies distribution and stratal geometry in salt basins

changes in global surface temperature from 1880 to 1977 derived from historical records of sea surface temperature abstract a preliminary analysis based primarily on historical records of sea surface temperature sst gives estimates of the change since 1880 of global hemispheric and zonal average surface temperatures the global change with time is roughly similar in shape and magnitude to that derived by mitchell from land station data alone but lags the mitchell curve by 10 20 years that is the present data show a minimumof temperature somewhere between 1900 and 1925 and a maximum somewhere between 1945 and 1970 comparing the means of these 25 year periods the rise from minimum to maximum was roughly 0 6 k for the northern hemisphere and 0 9 k for the southern hemisphere comparing the means of the 50 years before 1930 and the 48 years from 1930 to 1977 the rise was 0 3 k for the northern hemisphere and 0 6 k for the southern hemisphere the figures do not take into account the polar regions which on linear extrapolation from lower latitudes may have risen in temperature by twice the hemispheric averages

environmental character and history of the lake eyre basin one seventh of the australian continent abstract one of the world s largest internally drained endorheic basins the 1 14 million km 2 lake eyre hydrological basin leb covers nearly 15 of the australian continent palaeoclimatic and associated flow regime variations are recorded in an archive of fluvial aeolian and lacustrine sediments that are particularly accessible for deposits from the past 300 ka and are especially relevant for the past 50 ka during which humans have inhabited australia due to its great size economic resources and diverse latitudinal extent it has for over six decades been the focus of environmental scientific and resource based studies across numerous disciplines with an emphasis on assessing the scientific and environmental research over this period this paper is divided into four parts part a provides an introduction and background part b provides the geological history including evidence of substantial tertiary and quaternary climate change part c covers the contemporary environmental conditions and part d presents a conclusion and summary this not only represents the first comprehensive review of current knowledge of any of the world s truly large dryland drainage basins but also highlights how more multi disciplinary research is required key remaining questions revolve around the impact of global weather systems on the leb the lake level story in relation to a more precise picture of late quaternary climate change the role of humans and climate in the demise of the megafauna modern hydrological changes the role of vegetation in altering channel morphology and flow efficiencies and nature of flood transmissions

necessary conditions for a meandering river avulsion there is as yet no rational basis for predicting the conditions leading to avulsion of a meandering river here we present a conceptual model and quantify it under simplifying assumptions as a first step toward the construction of a stability diagram for avulsion initiation it is assumed initially that a rectangular crevasse channel of arbitrary depth is cut into the levee of a meandering river because the water entering the crevasse channel is derived from relatively high in the main flow it contains low concentrations of suspended solids consequently the crevasse flow is under capacity and the entrance is eroded deepening of the entrance increases the crevasse channel discharge and the concentration of suspended solids supplied because more sediment laden waters are tapped from the deeper flow in the main channel the crevasse entrance is predicted to deepen until its sediment carrying capacity is satisfied by the suspended solids entering from the main channel whether an avulsion will occur for a particular combination of initial conditions depends upon whether there exists steady state hydraulic and sediment transport conditions for crevasse channel depths that are equal to or less than the main channel depth this conceptual model is quantified by writing the unsteady gradually varied one dimensional conservation of mass and momentum equations for water and sediment transport through a main and crevasse channel sediment transport is computed as the integral of a cross sectional mean velocity and a rouse concentration profile solutions show that stable crevasse channels exist only for particular combinations of the initial height of the crevasse bed relative to the water depth in the main channel and the ratio of initial crevasse bed slope to main channel slope

a shifting river of sand the profound response of australia s warrego river to holocene hydroclimatic change abstract in dryland river catchments palaeochannels provide some of the key records for understanding the changes in river character and behaviour that can occur in response to different extrinsic and intrinsic controls here we combine modern hydroclimatic datasets satellite imagery field surveys and optically stimulated luminescence osl dating of palaeochannels to investigate the response of the 850 km long warrego river located in central eastern australia to holocene hydroclimatic change the modern warrego is an intermittent to ephemeral low energy river unit stream power 4 w m 2 and is characterised by low sinuosity straight narrow

downstream changes in dryland river channels the northern plains of arid central australia abstract many dryland rivers undergo marked downstream changes owing to factors such as infrequent floods flow transmission losses and typically few tributary inflows beyond the headwaters along the sandover bundey sandover bundey and woodforde rivers on the northern plains of arid central australia downstream channel changes are broadly similar in upland zones small rocky channels transporting sand and gravel gradually increase in size before entering piedmont zones where channels and narrow floodplains are confined by bedrock alluvial terraces or aeolian dunes in lower gradient lowland zones channels and floodplains remain confined and in the absence of tributary inflows channel cross sectional areas and discharges decrease downstream confining landforms are not present in floodout zones which results in splay formation increased floodplain widths and marked overall downstream decreases in cross sectional areas eventually channelised flow and bedload transport terminate although occasional large floods continue across extensive unchanneled alluvial surfaces termed floodouts these broad similarities apart downstream changes along the three rivers differ in detail the sandover is largely a single thread channel whereas many reaches of the sandover bundey and woodforde are anabranched on the small woodforde river downstream decreases in parameters such as cross sectional area and width are roughly linear on the larger sandover and sandover bundey downstream changes are more irregular particularly through the floodout zones where there are marked fluctuations in widths depths and bed slopes the irregular downstream changes typical of the lower reaches of these large rivers may be due to the reduced influence of vegetation on bankline stability and width adjustment relative to that of smaller rivers on the northern plains as in other drylands complex interactions between discharge sediment transport slope patterns of tributary drainage bank sediment type and vegetation result in variable patterns of downstream channel change

sedimentology and architecture of the douglas creek terminal splay lake eyre central australia douglas creek terminal splay sited on the western shoreline of lake eyre north central australia covers a surface area of approximately 4 km2 with a down system length of 2 5 km from the distributary channels terminus to the splay fringe two distributary channels feed two sediment lobes which have amalgamated to form the terminal splay three primary facies associations have been identified sub dividing the creek terminus into distributary channel proximal and distal splay sections proximal splay sediments are characterized by erosionally based relatively thick 100 mm stacked sheets of coarse to medium sand which commonly display trough and planar cross bedding whereas the distal splay is characterized by thin generally 50 mm massive beds of very fine sand silt and clay the change in splay sedimentology is interpreted as reflecting the transition from bedload dominated deposition to suspended load dominated deposition from decelerating sheetfloods as they spread out from the channel onto the dry lake bed a proximal to distal splay transition zone is also noted where deposits of both facies associations interfinger laterally and vertically in scale geometry and facies associations the douglas creek terminal splay is very different to the often cited neales terminal splay complex located 70 km to the north it is suggested that these architectural differences reflect variations in discharge volume input sediment distribution and the degree of vegetation cover understanding the variation in terminal splay architecture has very significant implications for the modelling of analogous subsurface petroleum systems which at present relies on few modern day analogues

unusual conditions in the tropical atlantic ocean in 1984 au cours de la 1ere moitie de 1984 les conditions oceaniques et atmospheriques dans l atlantique tropical ont ete a bien des egards similaires a celles dans le pacifique au cours de l el nino l ocean superieur a ete inhabituellement chaud dans sa partie orientale les pluies ont ete abondantes sur des regions normalement arides au sud de l equateur et l upwelling cotier a ete contrarie dans une region sud ouest africain ou il constitue un phenomene saisonnier le changement de tsm sst qui apparait lorsque d inhabituels courants portant a l est au sud de l equateur transportent de l eau chaude de surface vers l afrique contribue au changement des conditions atmospheriques ces dernieres en retour contribuent au changement de la circulation oceanique et de la tsm

controls on the genesis sedimentary architecture and preservation potential of dryland alluvial successions in stable continental interiors insights from the incising modder river south africa abstract interpretations of the allogenic and autogenic controls on dryland alluvial successions are commonly hampered by incomplete knowledge of the sedimentology of modern dryland river floodplains in part because of the limited subsurface sediment exposures available in typically stable or aggrading riverine settings along many valleys in the south african interior however river incision and associated formation of dongas gullies and badland type settings provides extensive exposures of cenozoic alluvial successions which enable assessment of the controls on their genesis sedimentary architecture and preservation potential this paper focuses on the incised modder river at erfkroon free state located 1480 km river distance inland from the atlantic ocean at erfkroon numerous dongas have formed in an 15 m thick alluvial succession deposited within a narrow 500 m valley carved predominantly in erodible fine grained sedimentary rocks shales facies associations include channel deposits that vary in texture from sandy gravel to silty sand and overbank deposits consisting predominantly of sandy mud to muddy sand that have varying degrees of pedogenic overprinting younger deposits are stacked upon crosscut or onlap older deposits indicating a complex history of cut and fill changing assemblages of associated fossil fauna and archaeological artifacts luminescence ages and paleosol characteristics demonstrate net sediment accumulation over at least the last 42 ka under humid to arid climatic conditions by contrast the present day situation of deep channel and donga incision into bedrock appears to represent a new phase of sediment evacuation and valley deepening comparison with other incising dryland rivers in the south african interior suggests that 1 while phases of cut and fill are driven largely by climatic fluctuations major phases of incision into bedrock are controlled by breaching of downstream resistant rock barriers 2 long term sediment preservation is limited in narrow valleys that are subject to extended periods of base level stability followed by episodic major incisional phases but is greater along broader valleys where rivers are undergoing lateral migration and more progressive long term incision study of incising rivers such as the modder can yield important insights into the controls on alluvial successions in stable continental interiors beyond the range of sea level changes which may help with the interpretation of inland alluvial valleys preserved in the geological record