revision of the marine chronology in the wanganui basin new zealand based on the isothermal plateau fission track dating of tephra horizons abstract the occurrence of tephra horizons in basins adjacent to volcanic arcs provide an excellent opportunity for establishing a reliable chronostratigraphic framework for detailed sedimentological studies in this study three widespread and stratigraphically important rhyolitic tephra horizons interbedded in plio pleistocene strata of the wanganui basin new zealand are dated by application of the isothermal plateau fission track itpft technique to hydrated glass shards all glass samples were corrected for annealing and consequently yield reliable ages rangitawa tephra yielded statistically indistinguishable ages from three localities that are in excellent agreement with recently determined zircon fission track age estimates of ca 0 35 ma itpft ages of 1 05 0 05 and 1 63 0 15 ma for potaka pumice and pakihikura pumice respectively are considerably older than previous ft estimates but consistent with new magnetostratigraphic data that places the potaka within the jaramillo subchron and pakihikura within the matuyama chron between the cobb mountain and olduvai subchrons combining our fission track ages with the magnetostratigraphy the true age of sediments within the wanganui basin is found to be significantly underestimated sedimentation rates of between ca 680 630 m ma from 1 63 ma to 0 35 ma are calculated in the eastern part of the basin and are much lower than those calculated using the previous ft chronology this new itpft age data demonstrates that the existing plio pleistocene marine chronology in new zealand will require age revision and has important implications when considering the evolution of several other sedimentary basins in southern north island that contain the same itpft dated tephra horizons

eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

plant fossil distributions in some australian permian non marine sediments abstract plant remains occur in all post devonian lowland terrestrial depositional systems with distinctive assemblages characterizing discrete environments glossopterid gymnosperms dominate most australian permian coal bearing sediments herbaceous pteridophytes sphenophytes and lycophytes are best represented in lower deltaic lacustrine and paludal deposits non glossopterid gymnosperms mostly colonized drier floodplain and upland environments and are poorly represented in australian permian sequences fresh and brackish water algae are abundantly preserved in paludal and lacustrine facies in both alluvial and delta plain environments seasonal productivity and taphonomic factors undoubtedly influenced the composition of interseam compression impression floras but integration of information from these assemblages with that from permineralized peats in situ coalified plants and coal maceral and palynological analyses can assist in the interpretation of australian permian coal forming environments and the structure of plant communities

facies and cyclicity of the late permian bainmedart coal measures in the northern prince charles mountains macrobertson land antarctica the late permian bainmedart coal measures form part of the permo triassic amery group which crops out in the beaver lake area of the northern prince charles mountains macrobertson land antarctica the exposed strata are believed to have formed in graben or half graben sub basins on the western edge of the lambert graben a major failed rift system sedimentological analysis has revealed that these rocks formed in alluvial environments in which swiftly flowing rivers of low sinuosity represented by facies a1 and a2 flowed northward down the axis of the basin and were associated with waterlogged floodbasin and peat forming wetlands facies b1 b4 a third facies association comprising facies c1 c3 interpreted as the deposits of lake floor and delta environments is exclusively developed within a distinctive fine grained interval here named the dragon s teeth member the proportion of association b facies within the succession increases markedly above the level of the dragon s teeth member at about 300 m above the base of the formation flat low angle and undulatory bedding structures preserved within channel deposits are suggestive of sediment deposition in flow conditions which were often critical or supercritical presence of massive and chaotic intervals of sandstone further implies some deposition from high concentration aqueous flows alluvial channel bodies show evidence of incision into underlying substrates both during initiation and at later stages in channel belt construction the lack of interfingering between channel deposits and coals suggests that thick peats formed only in areas and at times of minimal clastic sediment supply analysis of well developed cyclicity within the coal measures suggests that the dominant control on sequence architecture was climatic related to precessional milankovitch fluctuations of c 19 kyr periodicity cycles began abruptly with the deposition of coarse grained material in high energy alluvial channels which contracted with time in response to changes in water supply rainfall upper parts of cycles are dominated by finer grained sediments and then coal indicative of progressively reduced coarse sediment input tectonic processes overprinted this pattern at least once during the period of sediment accumulation to form the dragon s teeth member

salt dynamics in well mixed estuaries importance of advection by tides abstractunderstanding salt dynamics is important to adequately model salt intrusion baroclinic forcing and sediment transport in this paper the importance of the residual salt transport due to tidal advection in well mixed tidal estuaries is studied the water motion is resolved in a consistent way with a width averaged analytical model coupled to an advection diffusion equation describing the salt dynamics the residual salt balance obtained from the coupled model shows that the seaward salt transport driven by river discharge is balanced by the landward salt transport due to tidal advection and horizontal diffusion it is found that the tidal advection behaves as a diffusion process and this contribution is named tidal advective diffusion the horizontal diffusion parameterizes processes not explicitly resolved in the model and is called the prescribed diffusion the tidal advective diffusion results from the correlation between the tidal velocity and salinity and can be explicitly calculated with

charcoal reflectance measurements implications for structural characterization and assessment of diagenetic alteration charcoal is a valuable source of archaeological and palaeoenvironmental proxy data however growing evidence suggests that production conditions can strongly influence post depositional alteration of charcoal consequently both reconstruction of production temperature and understanding of the potential for diagenetic alteration are of great interest here we use mean random reflectance r0 mean in conjunction with other chemical characterization methods to address these questions r0 mean was obtained for a suite of modern analogue charcoal produced under controlled conditions and for a series of natural charcoal samples obtained from archaeological and palaeoenvironmental deposits r0 mean proves to be a robust measure to assess formation temperature for samples produced at 400 c and above even after exposure to highly oxidizing conditions r0 mean is also useful for samples formed between 300 c and 400 c however if an assemblage of charcoals has been exposed to oxidizing conditions lower temperature charcoals may be preferentially lost it is apparent that charcoal produced at lower temperatures is more highly susceptible to chemical oxidation and that there is a continuum in charcoal degradation potential dependant upon fuel material and production conditions

comparison of observed hf radar and adcp measurements and computed tides in the north channel of the irish sea abstract a three dimensional high resolution grid of order 1 km model of the north channel of the irish sea incorporating a one equation turbulence energy submodel to parameterize vertical mixing is used to compute the m2 s2 n2 k1 and o1 tides elevations and currents are compared with observations with particular emphasis on a detailed comparison with current profiles recorded by two acoustic doppler current profilers adcps and hf radar measurements of the surface current the comparison with the hf radar shows small scale spatial variations in both modeled and observed currents superimposed upon the larger scale tidal currents these small scale changes appear to be associated with variations in bottom topography and can only be resolved by using fine grid models or detailed measurements computed m2 current profiles derived from a multiconstituent calculation are in excellent agreement with profiles measured by the adcps however in a single constituent m2 calculation the magnitude of the

geomorphic and vegetative characteristics along three northern virginia streams geometry sediment and woody vegetation data were collected from bottomland geomorphic surfaces at valley sections along three gaged perennial streams of northern virginia the basins of the streams differ widely in topography and physiography mean discharges vary from 0 196 to 323 m3 per sec prevalent surfaces identified were the depositional bar the active channel shelf the flood plain and terraces the stages corresponding to active channel shelf levels were equivalent to flow durations of 5 to 13 stages corresponding to flood plain levels were equivalent to discharges with 1 4 to 2 0 yr recurrence intervals the discharge data and statistical tests of geomorphicsurface sediment and vegetative data suggest that the various alluvial features are formed and maintained by hydraulically controlled sorting processes analysis of woody plant and geomorphic data shows that each surface supports characteristic species some of which are nearly unique to a surface tests of sediment type with species distribution showed lower correlation than that of geomorphic surface with species it is inferred that plant distributions largely are controlled by flow frequency and intensity and that plants may help to identify geomorphic levels and potential for flood damage

the role of advection in determining the temperature structure of the irish sea abstract the temperature structure of the irish sea is investigated using a 3 yr simulation with a high resolution 1 8 km three dimensional baroclinic model the proudman oceanographic laboratory coastal ocean modelling system and ctd and advanced very high resolution radiometer observations this paper focuses on the extent to which horizontal advection determines the temperature structure it is found that it has a significant effect on the depth mean temperatures throughout the region and on the vertical profiles in seasonally stratified areas such as the celtic sea and western irish sea there is depth mean advective heating during the summer in these stratified regions whereas in well mixed regions advection tends to reduce the amplitude of the seasonal cycle through an analysis of the terms in the temperature equation the warming of the cool pool waters of the western irish sea can be attributed to the advection of partially well mixed waters into the stratified region from the north th

correspondence between glass ft and 14 c ages of silicic pyroclastic flow deposits sourced from maninjau caldera west central sumatra abstract paroxysmal pyroclastic flow deposits sourced from maninjau caldera in west central sumatra are dated at 50 3 ka n 3 using the isothermal plateau and diameter corrected fission track itpft and dcft respectively techniques on glass shard constituents in addition charcoal obtained from tall trees in position of growth within the paroxysmal flow deposit on the upper flanks for the caldera are also dated at 52 3 2 14c ka n 2 and 51 1 3 2 14c ka n 1 using an acid base wet oxidation stepped combustion abox sc and standard acid base acid aba 14c techniques respectively the close correspondence in 14c ages of charcoal sample splits analysed at two laboratories australian national university australia and waikato university new zealand verifies the reliability of these 14c techniques up to at least 50 ka based on concordant ages derived from glass ft and 14c techniques an age of 52 3 ka is assigned to the latest silicic eruptive activity at maninjau caldera this chronology is further confirmed by the occurrence of a silicic tephra bed that closely underlies paroxysmal maninjau deposits at two sections and is correlated with youngest 75 ka toba tephra ytt erupted from toba caldera in north central sumatra this study not only provides a much needed regional chronological reference point for quaternary deposits in west central sumatra but also extends the minimum age range of the glass ft technique from 75 ka down to c 50 ka that is now for the first time within the extended maximum age range of the 14c technique

a three dimensional model of diurnal and semidiurnal tides on the european shelf a three dimensional hydrodynamic model of the continental shelf is used to examine the sensitivity of computed diurnal k1 and o1 and semidiurnal m2 s2 and n2 tidal elevations and currents to changes in eddy viscosity profile friction coefficient and water depth the influence of the tide generating potential is also considered the model uses a standard finite difference grid in the horizontal with a functional approach in the vertical thereby giving a continuous tidal current profile from sea surface to seabed the magnitude of the vertical eddy viscosity depends upon the flow field comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical a detailed examination of these comparisons shows that frictional effects in the near bed region are particularly important in determining near bed shear and that an accurate specification of water depth is critical for tidal current magnitude the spatial distribution of computed current ellipses shows that the semidiurnal currents are strongest in shallow water with the diurnal currents exhibiting an intensification in the shelf edge region the inclusion of the equilibrium tide is particularly important for the correct determination of the magnitude of the k1 tidal current as well as k1 elevations in the north sea the detailed comparisons show that the magnitude of the tidal currents is correctly determined to within 5 cm s 1 at 220 locations with the model accurately to within 2 cm s 1 reproducing the vertical variation the most sensitive test of a three dimensional model of the tidal current at most locations

processes influencing storm induced currents in the irish sea abstract although the problem of predicting storm surge elevations has received significant attention the simulation of currents has suffered because of lack of current observations during surges current measurements made during surge conditions are presented here and are used in combination with three dimensional models to understand processes producing storm currents in the irish sea a coarse grid resolution of order 7 km model of the west coast of britain together with a fine grid of order 1 km model of the eastern irish sea is used to examine the processes namely open boundary forcing of the west coast model and wind fields that produced flows within the eastern irish sea during the storm surge of november 1977 simulations of the surge show that the fine grid model nested within the west coast model can reproduce observed coastal changes in surge elevation however an observed major inflow that was recorded by current meters in the region prior to a storm surge elevation peak is not repr

a high resolution three dimensional model of the m2 m4m6 s2 n2 k1and o1tides in the eastern irish sea abstract the spatial distribution of the m 2 s 2 n 2 m 4 m 6 k 1 and o 1 tidal elevations and currents in the eastern irish sea is examined using a high resolution three dimensional model of the region the model uses a functional representation of the current in the vertical and can resolve the near bed high shear bottom boundary layer comparison of computed and observed tidal elevations and currents shows that the grid is sufficiently fine of order 1 km and the near bed region sufficiently well resolved to enable tidal elevations and currents particularly near bed currents to be accurately reproduced in order to accurately reproduce the near bed currents its is essential to reduce eddy viscosity close to the bed and enhance the bottom friction coefficient above that used in two dimensional models calculations of the m 2 m 4 and m 6 tidal currents with and without the other tidal constituents show that it is essential to include the other constituents if tidal elevations and currents are to be determined with a high level of accuracy with the m 6 tide being significantly influenced by the presence of the other constituents the presence of other tidal constituents not only increases bottom friction in an analogous manner to a two dimensional model but because the model involves a flow dependent viscosity they increase its magnitude which affects current structure the calculation of parameters such as the maximum bed stress which is important in sediment transport can be severely underestimated if the other tidal constituents are not included

variations in character and preservation potential of vegetation induced obstacle marks in the variable discharge burdekin river of north queensland australia abstract vegetation induced obstacle marks are described from dalrymple bend in the burdekin river of queensland australia and their preservation potential is discussed the bend is divided into a sand and gravel covered lower bar and a vegetated upper bar obstacle marks comprising an erosional scour and a depositional sediment tail are recognised on the lower bar and the lower margin of the upper bar two types of obstacle marks are dominant in the lower part of the lower bar sediment tail dominated obstacle marks associated with inclined trees of melaleuca argentea silver leaved paperbark and comparatively small obstacle marks around stranded driftwood obstacle marks in the upper part of the lower bar are formed around grass clumps armoured with mud and gravel at the lower margin of the upper bar scours and gravelly sediment tails are recognised around mature tall trees in these cases the scour is 4 m in width and covered with alternating beds of fine sand and mud among the obstacle marks described sediment tail dominated obstacle marks around groves of m argentea have the highest preservation potential obstacle marks in the lower margin of the upper bar are also considered to have high preservation potential obstacle marks around stranded driftwood have the lowest preservation potential obstacle marks around grass clumps survive more than 1 year but their long term preservation potential is nonetheless low implications for the stratigraphic record are also discussed

woody vegetation and channel morphogenesis in low gradient gravel bed streams in the ozark plateaus missouri and arkansas woody vegetation affects channel morphogenesis in ozark streams of missouri and arkansas by increasing local roughness increasing bank strength providing sedimentation sites and creating obstructions to flow variations in physiographic controls on channel morphology result in systematic changes in vegetation patterns and geomorphic functions with increasing drainage basin area in upstream reaches streams have abundant bedrock control and bank heights that typically are less than or equal to the rooting depth of trees in downstream reaches where valleys are wider and alluvial banks are higher vegetation has different geomorphic functions at drainage areas of greater than 100 200 km2 ozarks streams are characterized by longitudinally juxtaposed reaches of high and low lateral channel migration rates referred to as disturbance reaches and stable reaches respectively whereas stable reaches can develop stable forested floodplains if they are not farmed disturbance reaches are characterized by dynamic vegetation communities that interact with erosion and deposition processes disturbance reaches can be subdivided into low gradient and high gradient longitudinal zones low energy zones are characterized by incremental unidirectional lateral channel migration and deposition of gravel and sand bars the bars are characterized by prominent bands of woody vegetation and ridge and swale topography channel monitoring data indicate that densely vegetated bands of woody vegetation formed depositional sites during bedload transporting events the same floods caused up to 20 m of erosion of adjacent cutbanks scoured non vegetated areas between vegetation bands and increased thalweg depth and definition in high energy or riffle zones channel movement is dominantly by avulsion in these zones vegetation creates areas of erosional resistance that become temporary islands as the channel avulses around or through them woody vegetation on islands creates steep root defended banks that contribute to narrow channels with high velocities calculation of hydraulic roughness from density and average diameter of woody vegetation groups of different ages indicates that flow resistance provided by vegetation decreases systematically with group age mainly through decreasing stem density if all other factors remain constant the stabilizing effect of a group of woody vegetation on a gravel bar decreases with vegetation age

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

all toba tephra occurrences across peninsular india belong to the 75 000 yr b p eruption abstract a controversy currently exists regarding the number of toba eruptive events represented in the tephra occurrences across peninsular india some claim the presence of a single bed the 75 000 yr old toba tephra others argue that dating and archaeological evidence suggest the presence of earlier toba tephra resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples allowing comparison of the indian samples to those from the toba caldera in northern sumatra malaysia and importantly the sedimentary core at odp site 758 in the indian ocean a core that contains several of the earlier toba tephra beds in addition two samples of toba tephra from western india were dated by the fission track method the results unequivocally demonstrate that all the presently known toba tephra occurrences in peninsular india belong to the 75 000 yr b p toba eruption hence this tephra bed can be used as an effective tool in the correlation and dating of late quaternary sedimentary sequences across india and it can no longer be used in support of a middle pleistocene age for associated acheulian artifacts

riparian vegetation and fluvial geomorphic processes abstract riparian vegetation and fluvial geomorphic processes and landforms are intimately connected parts of the bottomland landscape relations among vegetation processes and landforms are described here for representative streams of four areas of the united states high gradient streams of the humid east coastal plain streams great plains streams and stream channels of the southwestern united states vegetation patterns suggest that species distributions in the humid east are largely controlled by frequency duration and intensity of floods along channelized streams vegetation distribution is largely controlled by variation in fluvial geomorphic processes cycles of degradation and aggradation in response to increases in channel gradient associated with channelization similarly riparian vegetation of great plains streams may be controlled by fluxes in sediment deposition and erosion along braided streams patterns of riparian vegetation in semi arid regions may be most closely related to patterns of water availability unlike most other streams in more humid environments channel equilibrium conditions control stability of the coincident fluvial landform and attendant vegetation pattern throughout the continent in most situations riparian vegetation patterns are indicative of specific landforms and thus of ambient hydrogeomorphic conditions

a three dimensional model of diurnal and semidiurnal tides and tidal mixing in the north channel of the irish sea the spatial variability of the m2 s2 n2 k1 and o1 tides are examined using a high resolution model of the north channel of the irish sea the sensitivity of computed currents and elevations to two formulations of the vertical eddy viscosity one involving a turbulence energy submodel and another in which it is computed from the flow field are examined tidal elevation amplitudes and phases are compared at 20 gauges and shown to be in good agreement with observations root mean square rms errors of 7 85 cm 32 turbulence energy model and 7 93 cm 41 flow dependent viscosity model were found for the m2 tide comparable errors were found for the other semidiurnal tides differences in the amplitude errors between the two models are below the uncertainty associated with open boundary forcing and measurement errors and are therefore not statistically significant computed cotidal charts showed good agreement with published cotidal charts derived from observations comparison with observed m2 tidal current profiles suggests that at some locations a more accurate profile is determined with the turbulence model while at others the flow dependent solution is more accurate a comparison of m2 tidal current shear in the vertical showed that the turbulence energy model had a slight bias to underestimate this shear this bias was not found in the flow dependent viscosity model for the other tidal constituents the uncertainty in the accuracy of the currents prevented such a comparison also it is not possible to decide with any confidence which closure method is more accurate due to possible errors in the data and the small number of locations where significant shear is found in the vertical the spatial variability of tidal elevations and currents shows an amphidromic point for the semidiurnal tides but none for the diurnal tides in the northern part of the north channel significant differences in tidal current are found between the north channel and the clyde sea where tidal currents are strong and weak respectively this difference is related to the tidal energy flux in the region which is confined to the north channel the spring neap temporal and spatial variability of tidal turbulence shows a close correlation with tidal current magnitude and water depth this in part explains why the simple flow related viscosity model gives comparable results to those from the turbulence model

fluvial sedimentology of an upper jurassic petrified forest assemblage shishu formation junggar basin xinjiang china abstract a remarkable petrified forest assemblage is preserved in the upper jurassic shishu formation of the northeastern junggar basin xinjiang uygur autonomous region china discovered in 1965 the silicified wood occurs as two horizons of fallen logs and a group of rooted stumps in growth position coincident with the upper log horizon the largest log is 25 3 m in length the largest stump is 2 5 m in diameter the enclosing strata are fluvial silts sands and gravels wood characteristics indicate that climate was mild with seasonal variation in precipitation temperature or light paleohydrology and stratigraphy of the shishu formation suggest a wide shallow low sinuosity mixed load meandering stream regime that drained southward into the junggar basin during the late jurassic

isothermal plateau fission track ages of hydrated glass shards from silicic tephra beds abstract the age of silicic tephra beds that have experienced a simple thermal history can be accurately and precisely determined by application of the isothermal plateau fission track technique to hydrated glass shards age estimates obtained by this means compare very well with those based on co existing mineral phases using the k ar 40ar 39ar external detector fission track and thermoluminescence techniques this concordance contradicts the popular belief that hydrated glass shards give unreliable ages distal tephra beds many of which are difficult to date because of their fine grainsize low abundance of crystals and common presence of detrital grains are readily dated by the isothermal plateau glass fission track method this new advance should greatly facilitate the development of detailed chronologies of tephra bearing sedimentary sequences located far from volcanic centres

flow separation a physical process for the concentration of heavy minerals within alluvial channels flow separation is a common feature within alluvial channels that occurs at abrupt changes in the bed geometry at a wide range of scales it is a process that can exert considerable control over the segregation and deposition of heavy mineral grains fluid separation generates a region of high bed shear stress that can entrain heavy minerals and a region of low velocity that is a preferred site for the deposition of denser particles significant concentrations of heavy minerals sometimes up to eight times the background value may be formed by flow separation processes a review of the occurrence of flow separation illustrates that it may be responsible for the accumulation of heavy mineral grains at a range of geomorphological scales

the wind induced circulation and the interaction of wind forced and tidally driven currents on the european shelf abstract a three dimensional hydrodynamic model of the continental shelf is used to examine the wind induced flow on the shelf produced by uniform northerly and westerly wind stresses the model has a functional approach in the vertical and a finite difference grid in the horizontal a flow dependent eddy viscosity is used to parameterize vertical mixing of momentum initial calculations of the wind driven flow in the absence of tides are used to examine the spatial variability of the currents in response to uniform northerly and westerly winds and the time taken to reach a steady state results of subsequent calculations including tidal turbulence show that the wind induced flow is modified by the non linear interaction between tidal and wind driven currents arising from the flow dependent eddy viscosity term and bottom friction effects the spatial variability of wind induced currents on the shelf is related to topographic features and used to explain some of the variability found in the flow fields on the shelf that have been deduced from measurements a comparison of tidal current ellipses at the fundamental frequency and higher harmonic derived from a harmonic analysis of tidal and wind driven flows shows that the surface current ellipses particularly those of the higher harmonic are modified by the presence of the wind driven flow the processes giving rise to this modification are the time variability of the eddy viscosity and the near surface shear produced by the wind stress

tephrochronology of late cenozoic loess at fairbanks central alaska nineteen distinctive distal tephra beds from the gold hill loess in the fairbanks region central alaska are divided into two groups based on their color mineralogy glass shard morphology and the major and trace element composition of their glass shards this dichotomy in tephra composition is believed to reflect the two source regions namely the eastern aleutian arc alaska peninsula region and the wrangell volcanic field despite the fragmentary nature of the preserved loess record which contains many local unconformities these tephra beds can be used to link the numerous loess exposures in the fairbanks region in their proper time sequence establishing thereby a comprehensive reliable time stratigraphic framework because these distal tephra beds are related to large magnitude volcanic eruptions given the long distance to the nearest possible source vent they will also enable correlation of the late cenozoic sedimentary sequence at fairbanks to those of adjacent regions of alaska and the yukon tephra beds with bubble wall or chunky glass shards have been dated by the isothermal plateau fission track method results demonstrate that the gold hill loess spans a long interval of time from late pliocene time to the last interglacial about 125 ka however the age of the basal part of this formation is not well constrained due to the apparent absence of tephra beds paleomagnetic studies suggest that loess deposition in the fairbanks region began about 3 ma

a finite element multi scale model of the scheldt tributaries river estuary and rofi w e report on the development and validation of a coupled two and one dimensional finite element model for the scheldt tributaries river estuary and region of fresh water influence rofi the hydrodynamic equations are solved on a single unstructured multi scale mesh stretching from the shelf break to the scheldt tributaries the tide is forced on the shelf break and propagates upstream in the riverine network upstream boundaries lie on sluices or outside of the region of tidal dominance where daily averaged discharges are imposed two dimensional depthaveraged shallow water equations are solved by means of the discontinuous galerkin dg method over the marine and estuarine parts of the computational domain in the rivers however one dimensional equations are dealt with using the dg method with the addition of a technique to cope with confluence points model parameters are carefully calibrated leading to the simulation of wind and tide forced flows that are in excellent agreement with available data the diffusivity in the transport equation is calibrated using timeseries of salinity at various locations in the estuary finally the lagrangian residual transport in the estuary an the adjacent coastal zone is investigated this work is a major step towards an integrated model for studying the dynamics of waterborne contaminants and the water renewal timescales in the scheldt land sea continuum

tidal energy fluxes and dissipation on the european continental shelf the spatial distribution of the energy flux energy dissipation current magnitude and surface elevation amplitude of the major tidal constituents over the northwest european shelf are examined in detail these distributions are obtained from the harmonic analysis of a 6 month three dimensional simulation of 28 tidal constituents the model currents are validated by a comparison of computed tidal harmonics against those derived from a harmonic analysis of up to 278 current time series a similar comparison is performed for tidal elevations based on 257 tide gauges calculations show that for the most significant tidal constituents e g m2 s2 and k2 there is a major energy flux in the deep water along the shelf edge off the northwest of scotland with some energy leaking onto the shelf and into the north sea a second source of energy is across the shelf edge at the southern end of the celtic sea with this energy flux propagating into the irish sea and southern north sea where the majority of the energy is dissipation in the shallow regions significantly different distributions are found for the diurnal and shallow water constituents and the spatial distributions of energy flux and dissipation of the various constituents are considered the accuracy of separating tidal current harmonics using model data of less than a synodic period is examined with reference to the s2 and k2 tide calculations suggest that the accuracy of computed currents comparable to those obtained from observations can be obtained from an analysis of a 60 day period compared with the synodic period for s2 and k2 of 182 days a significant saving in computer time

implications of the diffuse deformation of the indian ocean lithosphere for slip partitioning of oblique plate convergence in sumatra oblique plate convergence between indian ocean lithosphere and continental crust of the sunda plate is distributed between subduction on the sunda megathrust and upper plate strike slip faulting on the sumatran fault zone in a classic example of slip partitioning over the last decade a destructive series of great earthquakes has brought renewed attention to the mechanical properties of these faults and the intervening forearc crustal block while observations of forearc deformation over the earthquake cycle indicate that the forearc crust is fundamentally elastic the spatial pattern of slip vector azimuths for earthquakes sourced by rupture of the sunda megathrust is strongly inconsistent with relative motion of two rigid plates permanent and distributed deformation therefore occurs in either the downgoing lithospheric slab or the overriding forearc crust previous studies have inferred from geodetic velocities and geological slip rates of the sumatran fault that the forearc crust is undergoing rapid trench parallel stretching using new geological slip rates for the sumatran fault and an updated decadal gps velocity field of sumatra and the forearc islands we instead show that permanent deformation within the forearc sliver is minor and that the sumatran fault is a plate boundary strike slip fault the kinematic data are best explained by diffuse deformation within the oceanic lithosphere of the wharton basin which accommodates convergence between the indian and australian plates and has recently produced several large earthquakes well offshore of sumatra the slip partitioning system in sumatra is fundamentally linked with the mechanical properties of the subducting oceanic lithosphere

confirmation of carboniferous clastic swamp communities tropical lowlands dominated by arborescent lycophytes are the principal foci for our understanding of carboniferous peat and non peat accumulating coastal swamps1 2 suggested palaeoeco logical interpretations of various lycophytes and accessory vegetation have been based on transported compression assemblages3 4 and palynomorphs5 6 or in situ permineralized peats7 where transported macrodetritus resulting in compression assemblages is used to reconstruct past vegetational patterns taphonomic factors tend to bias the preserved flora8 11 taken alone or out of depositional context the heterogeneity of an assemblage most probably bears little or no relationship to that of the original contributing communities gastaldo9 suggests that reconstructions should be based on the autecology of erect in situ plants because with peats permineralized in situ precise resolution in time of laterally equivalent vegetation is difficult here i document an erect in situ early pennsylvanian lycophyte swamp which provides the first confirmatory evidence for previously hypothetical ecological amplitudes

isothermal plateau fission track age and revised distribution of the widespread mid pleistocene rockland tephra in west central united states a tephra bed in southeastern idaho is correlated to rockland tephra a widespread silicic air fall unit previously identified in northern california and western nevada correlation of proximal rockland tephra and its distal correlative is based on glass chemistry determined by electron microprobe and neutron activation analysis an age estimate of proximal rockland tephra is precisely determined by application of the isothermal plateau fission track itpft technique to its hydrated glass shards a weighted mean age of 0 47 0 04 ma compares well with age estimates based on co existing mineral phases using the external detector fission track and additive dose thermoluminescence techniques the presence of rockland tephra 800 km east of its presumed eruptive source will improve the development of detailed chronologies and correlation of pleistocene sedimentary sequences located in coalescent intermontane basins of west central united states

the correlation between reduction in fission track diameter and areal track density in volcanic glass shards and its application in dating tephra beds abstract the relationship between the reduction in fission track diameter and the reduction in areal track density in hydrated glass shards has been investigated under varying annealing and etching conditions a near 1 1 relation is observed for adequately etched tracks following laboratory heating of induced tracks the partially reduced areal track density was renormalized with error

a three dimensional model of the principal tides on the european shelf abstract a three dimensional hydrodynamic model of the continental shelf is used to examine the spatial distribution both elevations and currents of 28 of the major tides in the region tidal constituents in the diurnal and semi diurnal band together with higher harmonics and long period tides are used to illustrate the magnitude and spatial variability of the tides over the shelf comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical observed and computed tidal elevation amplitudes and phases are also compared at up to 257 shore based and off shore tide gauges these detailed comparisons are used to determine any bias in the model and the accuracy of predicted elevations and currents derived with the model results of these comparisons show that although the diurnal and semi diurnal tidal elevations and currents can be accurately reproduced using a 12 km grid the error in the higher harmonics is significantly larger the fact that the model contains all the non linear terms advection quadratic friction wave drift time varying viscosity necessary to generate these harmonics together with a full set of tidal harmonics in order to have the correct level of friction suggests that potentially it should reproduce these constituents however a rigorous comparison was found to be very difficult because of the rapid variation of the higher harmonics in shallow water which cannot be adequately resolved in the model and possible inaccuracy in the measurements of the small currents associated with the higher harmonics

gravel antidunes in the tropical burdekin river queensland australia the geological record is punctuated by the deposits of extreme event phenomena the identification and interpretation of which are hindered by a lack of data on contemporary examples it is impossible to directly observe sedimentary bedforms and grain fabrics forming under natural particle transporting high velocity currents and therefore their characteristics are poorly documented the deposits of such flows are exposed however in the dry bed of the burdekin river queensland australia following tropical cyclone induced floods long wave length up to 19 m gravel antidunes develop during short days high discharge flows in the upper burdekin river maximum recorded discharge near the study reach over 25 600 m s in february 1927 flood water levels fall quickly metres in a day and flow is diverted away from raised areas of the river bed into subchannels exposing many of the high stage bedforms with little reworking by falling stage currents gravel bedforms were observed on the dry river bed after the moderate flows of february 1994 max 7700 m s and january 1996 max 3200 m s the bedforms had wave lengths in the range 8 19 m amplitudes of up to 1 m with steeper stoss than lee faces and crest lines generally transverse to local peak discharge flow direction the gravel fabric and size sorting change systematically up the stoss and down the lee faces the antidune deposits form erosive based lenses of sandy gravel with low angle downstream dipping lamination and generally steep upstream dipping a b planes the internal form and fabric of the antidune gravel lenses are distinctly different from those of dune lee gravel lenses the erosive based lenses of low angle cross bedded gravel with steep upstream dipping a b planes are relatively easy to recognize and may be diagnostic of downstream migrating antidunes the antidune gravel lenses are associated with thick to 1 m high angle cross bed sets ancient antidune gravel lenses may be diagnostic of episodic high discharge conditions and particularly when they are associated with high angle cross bedded gravelly sand they may be useful for palaeoenvironmental interpretation

plant material deposition in the tropical burdekin river australia implications for ancient fluvial sediments abstract in the deposits of the burdekin river north queensland australia plant material character and directional fabric together with the sedimentary facies character are generally diagnostic of depositional environment plant material is selectively entrained transported and deposited in all flow conditions ranging from dry season minimal flow

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

influence of wave current interaction and high frequency forcing upon storm induced currents and elevations abstract a high resolution of order 1 km grid three dimensional model of the eastern irish sea including wave current interaction effects is used to examine the surges of november 1977 computed surge elevations and currents are compared with observations taken at the time the inclusion of wave current interaction effects in which the amplitude of the surface wind wave field changes over the period of the storm is shown to influence computed surge elevations in shallow regions the inclusion of wave current interaction effects also influences currents particularly in the near bed region an increase in air sea drag coefficient reflecting an enhanced sea surface roughness due to increased wave heights at the time of the storm is shown to improve the computed storm surge elevation in shallow regions the effects of including a high frequency component based on observations into the lower frequency meteorological forcing usually used to drive the model is examined such fluctuations produce high frequency variations in the near surface currents however such changes are not found at depth the introduction of similar high frequency changes into the currents along the open boundary of the model is also considered this produces high frequency variations throughout the water column within the interior of the eastern irish sea which are similar to those found in the observations

alkali extraction of archaeological and geological charcoal evidence for diagenetic degradation and formation of humic acids charcoal forms a crucial source of archaeological and palaeoenvironmental data providing a record of cultural activities past climatic conditions and a means of chronological control via radiocarbon 14c dating key to this is the perceived resistance of charcoal to post depositional alteration however recent research has highlighted the possibility for alteration and degradation of charcoal in the environment an important aspect of such diagenesis is the potential for addition of exogenous humic acids has to affect the accuracy of archaeological and palaeoenvironmental reconstructions based upon chemical analyses of ha containing charcoal however the release of significant quantities of ha from apparently pristine charcoals raises the question whether some ha could be derived via diagenetic alteration of charcoal itself here we address this question through comparison of freshly produced charcoal with samples from archaeological and geological sites exposed to environmental conditions for millennia using elemental c h o and isotopic 13c measurements fourier transform infrared spectroscopy ftir and proton liquid state nuclear magnetic resonance 1h nmr the results of analyses show that the presence of highly carboxylated and aromatic alkali extractable ha in charcoal from depositional environments can often be attributable to the effects of post depositional processes and that these substances can represent the products of post depositional diagenetic alteration in charcoal

fluvial process and the establishment of bottomland trees the effects of river regulation on bottomland tree communities in western north america have generated substantial concern because of the important habitat and aesthetic values of these communities consideration of such effects in water management decisions has been hampered by the apparent variability of responses of bottomland tree communities to flow alteration when the relation between streamflow and tree establishment is placed in a geomorphic context however much of that variability is explained and prediction of changes in the tree community is improved the relation between streamflow and establishment of bottomland trees is conditioned by the dominant fluvial process or processes acting along a stream for successful establishment cottonwoods poplars and willows require bare moist surfaces protected from disturbance channel narrowing channel meandering and flood deposition promote different spatial and temporal patterns of establishment during channel narrowing the site requirements are met on portions of the bed abandoned by the stream and establishment is associated with a period of low flow lasting one to several years during channel meandering the requirements are met on point bars following moderate or higher peak flows following flood deposition the requirements are met on flood deposits high above the channel bed flood deposition can occur along most streams but where a channel is constrained by a narrow valley this process may be the only mechanism that can produce a bare moist surface high enough to be safe from future disturbance because of differences in local bedrock tributary influence or geologic history two nearby reaches of the same stream may be dominated by different fluvial processes and have different spatial and temporal patterns of trees we illustrate this phenomenon with examples from forests of plains cottonwood populus deltoides ssp monilifera along meandering and constrained reaches of the missouri river in montana

review of recent developments in tidal hydrodynamic modeling i spectral models in this paper we present a brief overview with a comprehensive set of references to recently published papers for detail of a range of techniques used in tidal hydrodynamic modeling and recent progress in the field although the paper aims to introduce the topic to someone new to the area the main emphasis is on new developments in near coastal shallow sea tidal modeling and consequently we concentrate on three dimensional modeling which has progressed significantly in recent years the paper gives a brief account of methods used to discretize the hydrodynamic equations in the horizontal namely finite difference finite element and boundary fitted coordinates and through time the representation of tidal current structure in a three dimensional model using a spectral method in the vertical is also described in this method the subgrid scale vertical diffusion of momentum which has a major influence on tidal current profiles is parameterized using a flow dependent eddy viscosity recent work on

sedimentology of the upper burdekin river of north queensland australia an example of a tropical variable discharge river the burdekin river is an example of a class of tropical streams which experience two to four orders of magnitude variation in discharge in response to seasonal but erratic monsoonal rainfall floods of the burdekin rise abruptly reaching peak discharges of up to 40 000 m s in less than 24 h maintain peak flow for up to a few days and recede exponentially the geomorphology and deposits of these rivers reflect the extreme discharge fluctuations and have not previously been described a stretch of the upper burdekin river comprising four bends and one straight reach was examined near the town of charters towers the river bed is largely exposed for most of any year with a small misfit perennial channel carrying low stage flow major geomorphic elements of bends include point bars with ridge and swale topography three distinct types of chute channels avalanche slipfaces up to 5 m or more high around the downstream edges of bars and on the outer part of one point bar an elevated vegetated ridge straight reaches are flat or gently inclined sand and gravel covered surfaces much of the river bed is covered by well sorted in places gravelly coarse to very coarse grained sand with local accumulations of pebble to boulder gravel lower parts of the river bed are periodically draped by mud which is desiccated on exposure dunes and plane beds are the most commonly occurring bedforms with local development of gravelly antidunes most bank tops and upper vegetated bars are covered by silt and fine grained sand the river bed also hosts a low diversity but locally high abundance flood tolerant flora dominated by the paperbark tree melaleuca argentea which plays an important role in controlling the distribution of sediment the gross geomorphology of the river bed and most of the sedimentary features are interpreted as having formed during major bankfull or near bankfull flows which have a recurrence of about 18 years based on 65 years hydrographic data the initial rapid drop in discharge following flood peaks appears to preserve flood peak features on upper bars more or less intact whereas lower areas are subjected to variable degrees of modification during falling stage and by more frequent non bankfull discharge events

fluvial islands first stage of development from nonmigrating forced bars and woody vegetation interactions abstract fluvial islands can develop from the channel bed by interactions between pioneer trees and bars although vegetation recruitment and survival is possible on all bar types it is easier for trees to survive on nonmigrating bars developed from a change in channel geometry or to the presence of a steady perturbation this field study details the first stages of development of a vegetated mid channel nonmigrating or forced bar and its evolution toward an island form over six years analysis of bed topographical changes vegetation density and roughness scour and fill depths sediment grain size and architecture and excess bed shear stress highlighted a specific signature of trees on topography and grain size segregation two depositional processes combining the formation of obstacle marks and upstream shifting deposition of sediments led to the vertical accretion of the vegetated bar during the first stage of the bar accretion bedload sediment supply coming from surrounding channels during floods was identified as a key process modulated by the presence of woody vegetation and a deflection effect induced by the preexisting topography grain size segregation between vegetated and bare areas was also highlighted and interpreted as an important process affecting the development of surrounding channels and the degree of disconnection and hence the speed of development of a growing island the heterogeneity of bedload supply can explain why sediment deposition and density of trees are not strictly related a general conceptual model detailing the first stages of evolution from a bar to an established island is proposed for relatively large lowland rivers

three dimensional reconstruction of an in situ miocene peat forest from the lower rhine embayment northwestern germany new methods in palaeovegetation analysis palaeovegetation reconstructions particularly of fossil forests are generally restricted to scant information on the taxonomic composition relative abundance of individual taxa or on tree density we have developed new techniques for the analysis of stump horizons that result in a relatively detailed three dimensional reconstruction of ancient forests in addition a rough estimate of their above ground standing biomass can be calculated these techniques are applied to an in situ miocene peat forest preserved in the lower rhine embayment northwestern germany in a study area of 2500 m2 476 stumps were mapped and used in the forest reconstruction additionally pollen samples and leaf remains have been analysed the peat forest consists primarily of conifers in particular taxodiaceae and pinaceae with sciadopitys being the most common genus the only angiosperms in the wood flora were palms but in the pollen flora evidence for the myricaceae mastixiaceae ericaceae and a few other angiosperms is also present the forest was relatively dense with 1904 trees ha and a basal area of 164 m2 mean trunk diameter was 28 cm while mean tree height is calculated to have been 9 9 m height diameter and density distribution are illustrated using contour and three dimensional surface plots estimated above ground biomass is 750 t ha but this value also includes dead or partly dead trees this peat forest does not closely compare with previous reconstructions of miocene peat forests its three dimensional structure and biomass differ from those of modern bald cypress swamps

a widespread ca 1 1 ma tvz silicic tephra preserved near wellington new zealand implications for regional reconstruction of mid pleistocene vegetation abstract a sequence of terrestrial pollen bearing sediments exposed in transmission gully tg near wellington new zealand contains a prominent ca 20 cm thick silicic tephra bed dated at 1 09 0 12 ma based on itpft dating of glass shards such occurrences are rare in the wellington region the associated palynology overlying tg tephra represents vegetation totally different from any modern assemblage with both warm climate taxa e g lygodium articulatum toronia toru and cool climate taxa e g acaena apiaceae epilobium gentiana lycopodium australianum taraxacum and wahlenbergia occurring together a pollen assemblage 0 4 m above the base of tg tephra comes from a southern beech forest existing under warm temperate conditions with both fuscospora and nothofagus menziesii beeches and an abundance of ferns and lycopods represented beeches rapidly disappeared from around the site of deposition until at 0 6 m above the base of tg tephra beech pollen were rare and the pollen assemblages were dominated by grass ferns and lycopods were still well represented but the dramatic increase in grass pollen suggests that the environment outside the immediate depositional site had become much drier a ca 0 64 m thick gravel layer was then deposited which impeded drainage associated pollen assemblages were then dominated by sedges and grasses in approximately equal percentages although conditions may have still been relatively dry overall the pollen assemblages are indicative of a sedge swamp surrounded by grassland with distant beech forest since the glass itpft age range 1 sd for tg tephra extends over oxygen isotope stages ois 37 to 26 the fossiliferous sequence overlying the tephra should be any of the five periods of relative warmth in spite of the lack of tree pollen and dominance in the profile of herbaceous taxa however geochemical comparison of tg tephra with those preserved in odp site 1124 and two equivalent age sequences in auckland region patiki core site okariha suggest a correlation with ois 35 on this basis the presence of beaupreaidites diversiformis 0 4 m above the base of tg tephra provides a date for the final extinction of the modern new caledonian genus beauprea in new zealand pollen from toronia toru occurs throughout the sequence far further south than in any other pleistocene sequence so far analysed

preservation of in situ arborescent vegetation and fluvial bar construction in the burdekin river of north queensland australia abstract in sub humid parts of north queensland ne australia certain types of trees are well adapted to living in river bed habitats the bed of the tropical variable discharge upper burdekin river hosts a community dominated by the paperbark melaleuca argentea trees grow preferentially in flow parallel linear groves and engineer their own environment by deflecting currents building sand and gravel bars and stabising banks this is the first study to document in channel bar development resulting from vegetation growth rather than the reverse which has been inferred by previous workers in the burdekin river study site individual melaleuca range from seedlings to mature trees over 100 years old these trees survive regular partial to total submergence and impact damage during wet season runoff events often reaching over 20 000 m3 s 1 at peak discharge partly by adopting structural and growth modifications these modifications include a reclined downstream trailing habit multiple stemmed form modified crown with weeping foliage development of thick spongy bark root regeneration and group strategies notably development of flow parallel linear groves following death in situ remains of trees are preserved within the mainly coarse sand to gravel channel fill either as reclined stems trunks stripped of branches and foliage or as more upright trunks snapped at a height of typically 1 2 m above base both with roots the morphological adapations and styles of preservations of in situ vegetation within the burdekin river are considered distinctive of variable discharge rivers and may be useful in the identification of facies formed in such environments in the rock record particularly when associated with bar development

lead isotope ratios of volcanic glass by laser ablation inductively coupled plasma mass spectrometry application to miocene tephra beds in montana usa and adjacent areas abstract recent improvements in spatial resolution and sensitivity of laser ablation inductively coupled plasma mass spectrometry allow exploration of the tephrochronologic potential of pb isotope ratios of volcanic glass in particular their use in characterization and provenance detection of distal tephra beds measurements have good accuracy and precision as determined by comparison with reference materials a test suite of samples was taken from miocene tephra beds in montana and sw saskatchewan all of which come from the yellowstone hotspot track yhst but only those tephra beds of known age were used because of the need to track any temporal changes in the pb isotope ratios samples of a few quaternary tephra beds from the yellowstone plateau volcanic field were also included the pb isotope ratio analyses form three distinct clusters on a 207 pb 208 pb 206 pb 208 pb plot with ages of 0 6 2 0 ma 5 5 7 8 ma and 7 4 11 1 ma the same pb isotope age clusters were reproduced when published pb isotope information on dated rocks from the yhst is used rocks from the heise volcanic field and from a core recovered between the heise and picabo volcanic fields all fall within the younger miocene group whereas rocks from the bruneau jarbidge volcanic field plot in the older miocene group therefore pb isotope ratios of glass shards do help in provenance detection of distal tephra beds at least in the tectono volcanic setting of the yhst and will be a useful addition to the criteria necessary to establish a reliable miocene tephrostratigraphic framework for montana and adjacent areas

flow and sediment dynamics in the vegetated secondary channels of an anabranching river the loire river france this study investigates the hydrological and sedimentological mechanisms occurring in the vegetated secondary channels of an anabranching river affected by incision the loire river france during and after flood events that occurred between 2000 and 2003 observations and measurements were performed on a vegetated secondary channel located in the study site of brehemont 790 km downstream the source morphological changes and sediment dynamics were analysed using low elevation airborne photographs topographic and bathymetric surveys and scour chains the hydraulic behaviour of the channel was also analysed by measurements performed on flow velocity and direction during different flood stages in order to quantify the influence of woody vegetation on flow resistance the roughness of bands of trees was determined from measurements performed on the field the impact of the disruption of armour layers on bedload pulses the variation of sedimentary processes during a single flood event and the fixation of bedforms by vegetation are all identified as key processes influencing the behaviour of the study channel topographic surveys demonstrate that sediment dynamics is substantial in the upstream part of the channel and that sediment budgets are different according to the temporal scale considered moreover an asymmetrical behaviour of the secondary channel is demonstrated reduced quantities of sediment deposited and preserved in the vegetated zones contrast with material by passing observed in the third order channels flow velocity and direction measurements indicate that these parameters vary according to the water level and to the morphological units of the channel pools riffles vegetated areas during low flows scouring and export of particles from the secondary channel are a consequence of reduced sediment supply from the main channel of the loire river for these water levels sedimentation occurs in pools where velocity and turbulence decrease whereas third order channels are subjected to erosion during high discharges large quantities of sediment available in the main channel feed the temporary stores formed by riffles and bars in the secondary channel the vegetated area located in the downstream part of the secondary channel deflects current trickles at low discharges and decreases flow velocity during high water levels the sedimentary accretion observed in this area exerts a feedback on flow and sedimentary processes d 2005 elsevier b v all rights reserved

a detailed comparison of a range of three dimensional models of the m2 tide in the faeroe shetland channel and northern north sea abstract a three dimensional hydrodynamic model of the faeroe shetland channel and northern north sea is used to investigate the spatial variability of m2 tidal elevations and currents in the region this area is chosen because it covers a range of water depths also there is a significant database of tidal elevations namely 41 gauges and current meters namely 89 observations with which comparisons can be made with the exception of a couple of measurements made at the shelf edge which may be influenced by the internal tide namely a 180 phase shift across the thermocline due to a first mode internal tide the observations correspond to those of a barotropic tide two different approaches are used to represent the profile of tidal currents in the vertical in the first a spectral functional method is used while in the second a finite difference grid is applied a range of parameterizations of vertical eddy viscosity suitable for deep water regions are used from ones in which viscosity is relate

implications on the paleoecology of autochthonous lycopods in clastic sedimentary environments of the early pennsylvanian of alabama abstract numerous correlative localities throughout the upper cliff coal interval lower pennsylvanian blount county alabama have been observed in which lycopod forests are preserved these assemblages are present in lower delta plain facies interpreted to represent 1 the abandonment phase of a distributary channel system with resultant bayou development 2 non peat accumulating swamps capping interdistributary bay deposition 3 possible terminal phase of peat accumulating swamps and 4 crevasse splay deposits field observations in combination with sedimentological preservational and biological evidence support the conclusion that these autochthonous carboniferous lycopods represent a taphonomically biased assemblage of aquatic or semi aquatic swamp communities interpretations derived from the present study in conjunction with published accounts of erect lycopods suggest that these plants could tolerate all waters from fresh to saline conditions periodic drying of swampy habitats may have subjected lycopods to subaerial and aerial conditions but bulk replaced erect lycopods predominantly inhabited water stressed conditions the monotypic character of the lycopod forests supports the hypothesis that in the tropical lowlands of the tropical lowlands of the carboniferous lycopods held a relatively unique physiologically stressed position in the delta flood basin these arborescent lycopods became established in any depositional site subject to flooding and standing water when conditions prevailed which allowed for the establishment and development of individuals