holocene climatic and environmental changes inferred from midge records diptera chironomidae chaoboridae ceratopogonidae at lake berkut southern kola peninsula russia a radiocarbon dated sediment sequence from lake berkut in the southern part of the kola peninsula northwest russia was investigated by means of midge analysis in order to reconstruct the holocene climatic and environmental history of the region past mean july air temperatures at the study site and hypolimnetic oxygen contents of the lake water were inferred from chironomid based transfer functions the early holocene c 10 100 8400 cal yr bp is characterized by summer temperatures and hypolimnetic oxygen concentrations broadly similar to present day conditions the midge records give evidence of a lake level fall at c 7000 cal yr bp resulting in weakened thermal stratification of the lake water and improvement of the hypolimnetic oxygen conditions after c 4000 cal yr bp midge assemblages suggest a lake level rise related to increased effective moisture a secondary mid holocene climatic optimum with inferred mean july air temperatures of c 12 1 degrees c was recorded between 6000 and 4400 cal yr bp followed by minimum values c 11 3 degrees c between 3500 and 1500 cal yr bp accompanied by the onset of natural acidification of the lake the late holocene midge assemblages suggest weakly acidic conditions low hypolimnetic oxygen contents and a general warming trend during the last c 1500 years although paludification and natural acidification may have influenced the temperature reconstruction at this stage however the modern chironomid inferred mean july air temperature 12 5 degrees c is consistent with meteorological data from a nearby station in general the midge records reflect relatively warm and moist conditions at lake berkut before c 7000 cal yr bp a relatively warm and dry climate at c 7000 4000 cal yr bp and a shift to cooler and wetter climatic conditions in the region after c 4000 cal yr bp less

environmental inferences and chironomid based temperature reconstructions from fragmentary records of the weichselian early glacial and pleniglacial periods in the niederlausitz area eastern germany abstract we inferred past climate conditions from lacustrine sediments intercalated in weichselian early glacial and early pleniglacial fluvial and aeolian sediments exposed in two opencast lignite mines from the niederlausitz area eastern germany a chronology was established using radiocarbon and luminescence dating methods both lithology and chironomid fauna indicate that the former shallow lakes were situated on a floodplain palaeotemperature estimates calculated from the fossil chironomid assemblages of the early glacial lacustrine deposit indicate mean july air temperatures of ca 15 c which is in line with results derived in earlier studies from the niederlausitz area and from northwestern europe the early pleniglacial lacustrine deposits consist of an organic rich gyttja intercalated with sand and silt lenses the chironomid assemblages show that a shallow meso to eutrophic lake was present at the study site and chironomid inferred palaeotemperature estimates indicate an abrupt decline in july air temperatures from 15 16 c to ca 13 c in combination with other proxies from the same record this suggests a dansgaard oeschger like climate event

thickness of sets of cross strata and planar strata as a function of formative bed wave geometry and migration and aggradation rate cross strata and planar strata formed by the migration of ripples and dunes or low relief bed waves on upper stage plane beds respectively are the most common internal structures in fluvial sands and sandstones the thickness of cross sets or planar laminae at a given location is controlled by 1 aggradation rate relative to downstream migration rate of bed waves and 2 the succession of bed waves of varying height passing the location a quantitative understanding of this relationship is now appearing based on new theory and experimental studies with ripples dunes and upper stage plane beds in many cases the effects of control 1 can be ignored in such cases only the largest bed waves in a population form cross sets or planar laminae the ratio of mean cross set thickness mean height of formative bed waves is less than 0 4 and the ratio of mean cross set thickness mean height of all bed waves is less than 0 5 a simple quantitative model a modified form of the paola borgman model is presented for predicting the height distributions of bed waves ripples dunes low relief bed waves from the thickness distributions of cross sets or planar laminae if the aggradation rate is appreciable more of the smaller bed waves in a population can form cross sets or planar laminae and the preservation ratios increase to 1 in the case of supercritical climbing ripple cross strata in this case it is necessary to determine the angle of climb and length of the bed waves in order to use the model to predict bed wave height distributions

use of dipmeter data in clastic sedimentological studies resistivity curves from he eight measuring electrodes of schlumberger s stratigraphic high resolution dipmeter tool tm shdt can be processed to give a detailed reservoir characteriation that includes electrofacies and sedimentary dip data this conclusion is supported by evaluation of processed shdt data compared with information from over 1 000 m 3 280 ft of cores covering fluvial and eolian sedimentary environments based on three examples we give general guidelines for processing of and noise removal from shdt data to obtain satisfactory geological information foreset dips in sets as thin as 20 cm 8 in can be reliably calculated by using side by side processing options with a correlation interval of 10 cm 4 in and a step distance of 7 5 cm 3 in in many formations spurious dip readings cause serious problems these readings originate from irregularities in the formation or from processing artifacts have no directional implication and produce unsatisfactory signal to noise ratios however criteria have been defined to select relevant dips from such noisy data structural dips must be measured with a sufficient degree of confidence to accurately subtract them from sedimentary dips reliable data can be obtained by large scale interval correlation particularly when the interpretation is concentrated on suitable intervals laminated shales and horizontally bedded heterolithic sequences the shdt tool also can provide detailed information on reservoir characteristics particularly on small scale heterogeneities that escape the resolution of conventional logs boreholewide resistivity displays from interpolation of shdt traces enable the recognition of resistivity distribution patterns and may give a new scope to facies recognition from logs

subaqueous sand flow cross strata abstract subaqueous sand flow cross strata are formed by the flowage of sand down the slipfaces of submerged bedforms and isolated steps such cross strata make up the great bulk of the foreset deposits of shallow stream megaripples and bars characteristics of sand flow cross strata that form in fine to medium sand on subaqueous slipfaces less than 2 m high include steep dip angles generally 27 34 little if any curvature in dip cross sections distinct segregation of grain types downward coarsening along the cross stratum and generally upward coarsening inverse grading across the cross stratum loose gram packing absence of interbedded grainfall or other deposits small range of cross stratum thickness within a set increasing cross stratum thickness with increasing slipface heigh and great width lateral extent relative to cross stratum thickness and slipface height in coarse subaqueous sand the sand flow cross strata tend to be narrower more lenticular in horizontal sections flume experiments suggest that each cross stratum is produced by one in a series of intermittent sand flows and that the avalanching is generally not closely controlled by bedforms that spill over the brink of the slipface subaqueous cross strata that formed in fine to medium sand on relatively low slipfaces typically differ from eolian cross strata that formed under similar conditions grainfall deposits are less common on subaqueous slipfaces probably because avalanching tends to be more nearly continuous there than on eolian slipfaces another difference is that subaqueous sand flow cross strata tend to be wider more extensive laterally than eolian ones in part because avalanching tends to be more nearly continuous on subaqueous slipfaces and in part because submerged sand is even less cohesive than dry eolian sand

upscaling of small scale heterogeneities to flow units for reservoir modelling the effect of small scale heterogeneities on fluid flow through a reservoir is determined using one of so called mathematical upscaling methods that as such are fairly well established less well established however are the operations that provide their input i e construction of reservoir model and acquisition of data we thereto propose systematic description of facies and bed and systematic data sampling we upscale the ensuing model and data through a two step flow simulation i e first on the flow cell and then on the flow unit scale this work provides for a straightforward and easily applicable upscaling method that incorporates the effects of all heterogeneities

an expanded calibration model for inferring lakewater and air temperatures from fossil chironomid assemblages in northern fennoscandia chironomid temperature inference models based on an expanded data set of surface sediment and limnological data from 53 subarctic lakes in northern fennoscandia have been developed using eight different numerical techniques each based on slightly different underlying statistical models or ecological assumptions the study sites are mostly small shallow bathymetrically simple oligotrophic lakes with a ph range from 5 0 to 7 8 a total organic carbon range from 2 5 to 12 6 mg l 1 a mean july lakewater temperature ranging from 6 1 to 15 4 c and a mean july air temperature ranging from 8 5 to 14 9 c a series of redundancy analyses rda identified sediment organic content maximum lake depth and lakewater temperature as being the most important explanatory variables variance partitioning by partial rdas further suggested that each of these variables accounted for a significant fraction of variance independent from each other different cali bration models were assessed on the basis of their statisti

merging chironomid training sets implications for palaeoclimate reconstructions icelandic and norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from iceland for periods such as the early holocene the holocene thermal maximum and the little ice age when temperatures can be expected to be outside the current temperature range of the icelandic training set following taxonomic harmonisation the icelandic and norwegian data sets were compared before being merged to form a combined norwegian icelandic training set analyses showed that it was biologically and statistically valid to merge the two data sets the resulting combined inference model for mean july air temperature had improved performance statistics r2jack 0 87 rmsepjack 1 13 when compared to the best performing icelandic model r2jack 0 61 rmsepjack 0 83 due to the longer environmental gradient covered icelandic 6 11 c combined 3 5 16 c and to the increased number of samples icelandic 53 lakes combined 207 lakes and taxa icelandic 47 taxa combined 133 taxa present within the combined training set the inference models were applied to an early holocene chironomid sequence from vatnam ri north iceland and a 450 year recent record from myfluguvatn north west iceland to compare the reconstructions produced the various inference models produced similar trends and patterns of temperature reconstruction but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the icelandic model it was found that different inference models produced more variation in the reconstruction than when different training sets were used a comparison of the myfluguvatn reconstructions with meteorological observations showed that the combined norwegian icelandic inference model produced more reliable results than the icelandic or norwegian inference models alone

sorting in grain flows at the lee side of dunes abstract sediment sorting at the lee side of ripples dunes and bars has already been recognized long ago a predictive model of the sorting is necessary but unavailable for implementation in sediment transport models for sediment mixtures relevant processes in sedimentological and physical literature are reviewed and compared to the sparse data of sediment sorting a synthesis is given of the most important variables governing the sorting processes for the benefit of future experimentation and modelling these variables are the sorting standard deviation skewness and bimodality of the sediment mixture delivered to the brink point the height of the dune or bar relative to the average grain size of the mixture the velocity of the flow above the brink point relative to the settling velocity for all grain size fractions and the frequency of the grain flows in addition the initiation mechanism and frequency of the grain flows affect the pattern and effectiveness of sorting

sampling procedure for small scale heterogeneities crossbedding for reservoir modelling sampling permeability from individual laminae in crossbedded rocks is very well possible by making use of a so called probe permeameter the methodology and calculation of permeabilities from the output of this instrument are fairly well established however what is hardly established is a sampling strategy that guarantees adequate representation of permeability contrast between laminae especially so because finer foreset and bottomset are difficult to sample yet their permeabilities are critical to fluid flow through a crossbed therefore we propose to systematically sample laminae to this end we suggest a sampling strategy that is adapted to the heterogeneity under study namely to the thickness of the finer foreset

a late glacial chironomid record from hawes water northwest england this paper presents the results of a high resolution late glacial chironomid stratigraphy from hawes water a small carbonate lake in northern lancashire the samples were from a core taken from the terrestrialised margin of the present lake which represents an intermediate depth between the true littoral and the profundal the chironomid assemblage showed a high degree of sensitivity to both broad scale and short term temperature changes comparison with an existing proxy temperature record 18o for the site confirmed the presence of four temperature inversions within the late glacial interstadial a mean july air temperature inference model derived from acid soft water lakes in norway and svalbard was applied to the data despite the absence of carbonate lakes within the norwegian training set there was a close similarity between trends in estimated july air temperature and the 18o trace with a particularly strong correspondence in the periods of clay deposition this suggests that this model is highly robust the inferred maximum interstadial temperature was 13 4 c dropping initially to 7 5 c in the loch lomond stadial temperatures reach a maximum of nearly 10 c in this period cool for a short period before rising rapidly to 13 2 c at the start of the holocene these temperatures are similar to but slightly higher than those estimated for whitrig bog southeast scotland and lower than those inferred from coleopteran based models for sites in south wales

scales and causes of heterogeneity in bars in a large multi channel river rio parana argentina to date published studies of alluvial bar architecture in large rivers have been restricted mostly to case studies of individual bars and single locations relatively little is known on how the depositional processes and sedimentary architecture of km scale bars vary within a multi km reach or over several 100s km downstream this study presents ground penetrating radar gpr and core data from 11 km scale bars from the rio parana argentina the investigated bars are located between 30 km upstream and 540 km downstream of the rio parana rio paraguay confluence where a significant volume of fine grained suspended sediment is introduced into the network bar scale cross stratified sets with lengths and widths up to 600 m and thicknesses up to 12 m enable the distinction of large river deposits from stacked deposits of smaller rivers but are only present in half the surface area of the bars up to 90 of bar scale sets are found on top of finer grained ripple laminated bar trough deposits bar scale sets make up as much as 58 of the volume of the deposits in small incipient mid channel bars but this proportion decreases significantly with increasing age and size of the bars contrary to what might be expected a significant proportion of the sedimentary structures found in the rio parana is similar in scale to those found in much smaller rivers in other words large river deposits are not always characterised by big structures that allow a simple interpretation of river scale however the large scale of the depositional units in big rivers causes small scale structures such as ripple sets to be grouped in thicker co sets which indicate river scale even when no obvious large scale sets are present the results also show that the composition of bars differs between the studied reaches upstream and downstream of the confluence with the rio paraguay relative to other controls on downstream fining the tributary input of fine grained suspended material from the rio paraguay causes a marked change in the composition of the bar deposits compared to the upstream reaches the sedimentary architecture of the downstream reaches in the top 5 m of mid channel bars shows i an increase in the abundance and thickness up to m scale of laterally extensive 100s of metres fine grained layers ii an increase in the percentage of deposits comprised of ripple sets to 40 in the upper bar deposits and iii an increase in bar trough deposits and a corresponding decrease in bar scale cross strata

cross strata and bedforms of probable transitional dune to upper stage plane bed origin from a late precambrian fluvial sandstone northern norway a late precambrian fluvial sandstone sequence in northern norway is dominated by large scale cross sets that show either lenticular or tabular geometries in the streamwise sections the lenticular sets interdigitate and in places show nearly symmetrical formsets the tabular sets are in places solitary but are mainly grouped in cosets in both cross set types the cross strata range from concave up to sigmoidal in shape with the latter variety comprising subhorizontal to gently inclined topset strata with parting lineation that merge uninterruptedly downflow into the steeper 10 2 foresets within the cross sets the geometry and dip azimuths of the foresets are conspicuously consistent although the concave up and sigmoidal strata commonly alternate downcurrent the cross strata characteristics suggest flood stage deposition from relatively high velocity steady currents heavily laden with suspended sand both cross set types are interpreted as representing bedforms generated by flow in the dune to upper stage plane bed transition the lenticular cross sets probably represent periodic dunes but it is far less clear whether the long bedforms represented by the tabular sets should be classified as dunes or rather as solitary to quasi periodic bars

a chironomid based reconstruction of summer temperatures in nw iceland since ad 1650 few studies currently exist that aim to validate a proxy chironomid temperature reconstruction with instrumental temperature measurements we used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since ad 1650 for nw iceland through a transfer function approach and validated the record against instrumental temperature measurements from stykkisholmur in western iceland the core was dated through pb 210 cs 137 and tephra analyses hekla 1693 which produced a well constrained dating model across the whole study period little catchment disturbance as shown through geochemical itrax and loss on ignition data throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within lake variables particularly cold phases were identified between ad 1683 1710 ad 1765 1780 and ad 1890 1917 with relative drops in summer temperatures in the order of 1 5 2 c the timing of these cold phases agree well with other evidence of cooler temperatures notably increased extent of little ice age lia glaciers our evidence suggests that the magnitude of summer temperature cooling 1 5 2 c was enough to force lia icelandic glaciers into their maximum holocene extent which is in accordance with previous modelling experiments for an icelandic ice cap langjokull

summer temperature gradients in northwest europe during the lateglacial to early holocene transition 15 8 ka bp inferred from chironomid assemblages abstract we present a series of summer air temperature isotherm maps based on chironomid inferred temperatures from northwest europe covering the lateglacial and early holocene 15 8 ka bp these maps are the first of their kind and use data derived from 22 lateglacial sites and 34 early holocene sites the isotherms are generated by weighted spatial interpolation kriging the major patterns of chironomid inferred summer temperatures are spatially well resolved in both the lateglacial and early holocene the isotherm maps indicate that there was a strong west to east gradient during the lateglacial interstadial gi 1 due to the influence of thermohaline circulation in the regions bordering the north atlantic which diminishes eastwards a strong north to south temperature gradient is also apparent particularly in eastern regions influenced by the extent of the scandinavian ice cap peak temperatures are achieved early in the interstadial in the south of the region but occur towards the end of the interstadial in the north holocene warming varies spatially and temporally and is earliest in the south and east but later in the north and west during the period covered in our study maximum warmth is reached ca 10 ka bp the chironomid based lateglacial isotherm maps are compared with previously published isotherm maps from the same region based on beetle inferred temperatures while the trends shown in the two datasets are similar beetle inferred temperatures are often warmer than chironomid inferred temperatures this is especially marked in gi 1e and may be due to microclimatic effects causing the chironomids to underestimate air temperatures and or the beetles to over estimate air temperatures the spatial coherence between sites in both the lateglacial and early holocene suggest that the chironomid based temperature estimates are largely reliable although data testing suggests that estimates from southern scandinavia may be less reliable perhaps due to high topographical relief influencing local climate more data points are required particularly from northwest scotland southwest england and wales northeast france denmark finland and the baltic states to confirm trends and provide even coverage and a denser network of sites

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

chironomid inferred air temperatures from lateglacial and holocene sites in north west europe progress and problems abstract non biting midges insecta diptera chironomidae are now widely recognised as powerful biological proxies for inferring past climatic change in this paper the response of chironomid assemblages to lateglacial and holocene climatic change from sites in scotland and norway is discussed analyses have shown that midge assemblages have responded to major and minor climatic fluctuations during the last 15 000 yr such as the aegelsee oscillation gerzensee oscillation and younger dryas in the lateglacial and the thermal optimum little ice age and cooling events at 8 2 and 2 0 cal ka bp in the holocene in an attempt to quantify these and other climatic fluctuations a chironomid mean july air temperature inference model based on a modern calibration set of 109 lakes in norway and svalbard has been developed the 3 component weighted averaging partial least squares inference model performs well with a root mean squared error of prediction of 0 90 c and a maximum bias of 0 59 c both based on leave one out cross validation which is lower than chironomid temperature inference models developed in canada switzerland and finland however while temperature inference models perform well in the lateglacial the more subtle climatic changes of the holocene are more difficult to reconstruct because the likely temperature changes are close to the limits of the prediction errors of the existing models to address this problem future work is required to refine and develop the calibration set by further improving taxonomic resolution by adding more lakes to the calibration set and by investigating the influence of other environmental variables on chironomid distributions and abundances

bottomset architecture formed in the troughs of dunes and unit bars abstract bottomsets are formed in the troughs of migrating bedforms the flow and sediment dynamics downstream of bedforms differ and consequently the thickness grain size and internal structure of bottomsets vary greatly a classification of the controls on bottomset formation is proposed related to two and three dimensional processes flow and sediment unsteadiness and pre existing deposits structures and deposits created by flow and sediment unsteadiness as well as pre existing deposits are also considered in relation to changes they can induce in subsequent trough processes the classification is illustrated by observations from laboratory flumes the modern burdekin river australia and the rock record the roaches grit england and hawkesbury sandstone australia in bottomset examples described in this paper internal variability both vertically and laterally was much greater than that within the dominant foreset component complex compound structures were created by the interaction and predominance of different bottomset controls this combined with their high preservation potential makes them a highly useful paleoenvironmental indicator bottomset variation e g changes in the abundance of mud laterally will influence the permeability heterogeneity of fluvial reservoir rocks bottomsets formed under relatively steady conditions are likely to be laterally extensive and have similar characteristics over their entire length they may act as significant barriers to vertical flow conversely bottomsets generated in unsteady regimes tend to be highly variable potentially creating conduits between cross bed sets aiding inter set permeability

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

effect of bed permeability and hyporheic flow on turbulent flow over bed forms this paper uses particle imaging velocimetry to provide the first measurements detailing the flow field over a porous bed in the presence of bed forms the results demonstrate that flow downstream of coarse grained bed forms on permeable beds is fundamentally different to that over impermeable beds most significantly the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface such that reattachment of the separated flow does not occur and the reynolds stresses bounding the separation zone are substantially lessened these results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bed forms water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers yet mass and momentum exchanges across the bed interface are not routinely incorporated into flow models our observations suggest that ignoring such exchange processes in coarse grained rivers may overlook important implications these new results also provide insight to explain the distinctive morphology of coarse grained bed forms the production of openwork textures in gravels and the absence of ripples in coarse sands all of which have implications for modeling and prediction of sediment entrainment and flow resistance

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

flume experiments on lower flow regime bed forms in coarse sand thirty five runs were made in a recirculating channel 11 5 m long and 0 92 m wide with four sizes of very well sorted coarse sand to study geometry migration and hydraulics of bed configurations in equilibrium with steady uniform open channel flows at flow depths of about 15 cm equilibrium energy slope and sediment transport rate were measured as well bed phases kinds of bed configurations studied were ripples low flow velocity flat beds with sand transport and dunes identical with megaripples current velocities in none of the runs were high enough for development of an upper flow regime flat bed a plot of mean flow velocity versus sand size for all the runs shows that at low flow velocities the ripple field narrows with increasing sand size and pinches out at about 0 7 mm the field for flatbed transport narrows with decreasing sand size and pinches out at about 0 5 mm just above the ripple field at high flow velocities dunes are the stable phase for all sand sizes studied dune configurations are divided into two subphases two dimensional dunes 2d dunes with fairly straight continuous even crests and no strong localized scour in troughs are formed at relatively low flow velocities three dimensional dunes 3d dunes with strongly sinuous discontinuous uneven crests and strong localized scour pits in troughs are formed at relatively high flow velocities 3d dunes tend to be higher than 2d dunes have larger height spacing ratios and show less variability in height spacing and migration rate dunes can be viewed as kinematic shock waves differences between 2d dunes and 3d dunes lie in the differing importance of shock wave coupling and of sand transport in bed form troughs in both geometry and hydraulic ralationships the 2d dunes and 3d dunes in our flume runs correspond to the relatively regular megaripples at low flow velocities and relatively irregular megaripples at high flow velocities described by other authors from intertidal environments

bedform development in mixed sand mud the contrasting role of cohesive forces in flow and bed abstract the majority of subaqueous sediment on earth consists of mixtures of cohesive clay and cohesionless sand and silt but the role of cohesion on the development and stability of sedimentary bedforms is poorly understood the results of new laboratory flume experiments on bedform development in cohesive mixed sand mud beds are compared with the results of previous experiments in which cohesive forces in high concentration clay flows dominated bedform development even though both series of mixed sand mud experiments were conducted at similar flow velocities the textural and structural properties of the bedforms were sufficiently different to permit the designation of key criteria for identifying bedform generation under cohesive flows against bedform generation on cohesive substrates these criteria are essential for improving bedform size predictions in sediment transport modelling in modern sedimentary environments and for the reconstruction of depositional processes in the geological record the current ripples developing on the cohesive mixed sand mud beds with bed mud fractions of up to 18 were significantly smaller than equivalent bedforms in noncohesive sand moreover the bedform height showed a stronger inversely proportional relationship with initial bed mud fraction than the bedform wavelength this is in contrast with the bedforms developing under the cohesive clay flows which tend to increase in size with increasing suspended clay concentration until the flow turbulence is fully suppressed selective removal of clay from the mixed beds i e clay winnowing was found to be an important process with 82 100 clay entrained into suspension after 2 h of bedform development this winnowing process led to the development of a sand rich armouring layer this armouring layer is inferred to have protected the underlying mixed sand mud from prolonged erosion and in conjunction with strong cohesive forces in the bed may have caused the smaller size of the bedforms winnowing was less efficient for the bedforms developing under the cohesive clay flows where bedforms consisting of muddy sand were more characteristic the winnowed sand was also found to heal irregularly scoured topography thus reestablishing classic quasitriangular bedform shapes in cohesive flows the bedforms had more variable shapes and the healing process was confined to lower transitional plug flows in which strong turbulence is only present close to the sediment bed furthermore the bedforms on the cohesive beds tended to form angle of repose cross lamination whereas low angle cross lamination was more common in bedforms under cohesive flows in general terms erosional bedforms prevail when cohesive forces in the bed dominate bedform dynamics whereas depositional bedforms prevail when cohesive forces in the flow dominate bedform dynamics empirical relationships between the proportion of cohesive mud in the mixed sand mud bed and the development rate and size of the bedforms are defined for future use in field and laboratory studies

early holocene temperature variability inferred from chironomid assemblages at hawes water northwest england this paper presents the first high resolution chironomid inferred mean july air temperature c it reconstruction for the early holocene from england the reconstruction is based on a core recovered from a terrestrialised carbonate bench at hawes water a small hard water lake in northwest england the record shows that temperatures rose rapidly after the younger dryas with temperatures reaching 14 0 c at the beginning of the holocene over millennial timescales the temperature record points to a slight rise in temperatures towards the top of the sequence at around 8000 years before the year 2000 b2k the trend is punctuated by a series of cool oscillations at 11 200 11 400 10 700 10 400 9300 and 8300 b2k and by a short period 11 300 to 10 250 b2k when temperatures were considerably warmer up to 14 9 c the five cool oscillations coincide with temperature reversals found elsewhere in the north atlantic region and in the greenland ice core records these cool events correlate well with both me

lateglacial summer temperatures in the northwest european lowlands a chironomid record from hijkermeer the netherlands lateglacial environments at hijkermeer northwest netherlands were reconstructed by means of chironomid diatom and pollen analyses diatom assemblages indicate that hijkermeer was a shallow oligo to mesotrophic lake during this period pollen assemblages reflect the typical northwest european lateglacial vegetation development and provide an age assessment for the record from the beginning of the older dryas ca 14 000 calibrated 14c yr bp into the early holocene to ca 10 700 calibrated 14c yr bp the chironomid record is characterized by several abrupt shifts between assemblages typically found in mid latitude subalpine to alpine lakes and assemblages typical for lowland environments based on the chironomid record july air temperatures were reconstructed using a chironomid temperature transfer function from central europe mean july air temperatures of ca 14 0 16 0 c are inferred before the older dryas of ca 16 0 16 5 c during most of the allerod of ca 13 5 14 0 c during the younger dryas and of ca 15 5 16 0 c during the early holocene two centennial scale decreases in july air temperature were reconstructed during the lateglacial interstadial which are correlated with greenland interstadial events gi 1d and 1b the results suggest that vegetation changes in the netherlands may have been promoted by the cooler climate during gi 1d immediately preceding the older dryas biozone and gi 1b the hijkermeer chironomid inferred temperature record shows a similar temperature development as the greenland ice core oxygen isotope records for most of the lateglacial and a good agreement with other temperature reconstructions available from the netherlands this suggests that chironomid based temperature reconstruction can be successfully implemented in the northwest european lowlands and that chironomids may provide a useful alternative to oxygen isotopes for correlating european lake sediment records during the lateglacial 2007 elsevier ltd all rights reserved

standard flow cells to incorporate small scale heterogeneity crossbedding in a reservoir model small scale heterogeneities like crossbedding hamper fluid flow and cause oil to be capillary trapped at the intersections of coarser to finer lamina these effects are fairly well established but less well established is the method to construct an adequate flow cell model containing critical hydraulic properties like bed shape and size lamina shape angle and boundaries nor is it trivial how to obtain those features from well and core we therefore propose to systematically describe geometry and distribution of beds to this end we make use of standard flow cell models that a priori contain all elements and boundaries of beds for a number of bedding types

standard facies models to incorporate all heterogeneity levels in a reservoir model abstract the construction of reservoir models is frustrated by the fact that core and well cover only a fraction of the reservoir volume and it is therefore difficult to determine features like facies shape size and distribution inter and intra facies boundaries and lateral trends from them these features are however critical to fluid flow and they should necessarily be incorporated in the reservoir model and we therefore propose to systematically describe geometry and distribution of facies to this end we make use of standard facies models that a priori contain all elements and boundaries of facies for a number of typical depositional environments

icelandic coastal sea surface temperature records constructed putting the pulse on air sea climate interactions in the northern north atlantic part i comparison with hadisst1 open ocean surface temperatures and preliminary analysis of long term patterns and anomalies of ssts around iceland abstract a new comprehensive record of long term icelandic sea surface temperature measurements which have been updated and filled in with reference to air temperature records is presented the new sst series reveal important features of the variability of climate in iceland and the northern north atlantic this study documents site histories and possible resulting inconsistencies and biases for example changes in observing sites and instruments a new 119 yr continuous time series for north iceland sst is presented which should prove particularly useful for investigating air sea ice interactions around northern iceland as this is the only part of the country to be regularly engulfed by winter and or spring sea ice it is therefore highly sensitive to climatic change the coastal series correlate well overall with independent hadley centre sea ice and sst dataset version 1 hadisst1 series from the adjacent open ocean mean r 0 59 although correlations are generally higher in summer than winter

lacustrine evidence of early holocene environmental change in northern iceland a multiproxy palaeoecology and stable isotope study early holocene warming in iceland caused rapid glacial ice melt which led to exposed landscapes on which soils developed and floras quickly established our chironomid based records from northern iceland suggest temperatures were up to 2 2 5 c warmer than present throughout the first two millennia post deglaciation 10 500 to 8500 cal bp while sedimentary and isotopic data indicate the development of soils within the local environment throughout this period before catchment conditions started to stabilise around 8400 cal bp the warming trend over this period was not uniform however but punctuated by a series of relatively short lived climatic events specifically inwash events are suggested by the 13corganic toc and c n data around 9600 cal bp and 8250 cal bp and are seen at two independent sites there is also evidence from the 18ocarbonate and 13ccarbonate records which suggests that progressive evaporation of the study lakes occurred from 8200 cal bp the timing of which accords well with other isotopic records of drier conditions from around the north atlantic

supply limited sediment transport in a high discharge event of the tropical burdekin river north queensland australia interactions between catchment variables and sediment transport processes in rivers are complex and sediment transport behaviour during high flow events is not well documented this paper presents an investigation into sediment transport processes in a short duration high discharge event in the burdekin river a large sand and gravel bed river in the monsoon and cyclone influenced semi arid tropics of north queensland the burdekin s discharge is highly variable and strongly seasonal with a recorded maximum of 40 400 m s sediment was sampled systematically across an 800 m wide 12 m deep and straight reach using helley smith bedload and us p 61 suspended sediment samplers over 16 days of a 29 day discharge event in february and march 2000 peak 11 155 m s about 3 7 10 tonnes of suspended sediment and 3 10 tonnes of bedload are estimated to have been transported past the sample site during the flow event the sediment load was predominantly supply limited wash load included clay silt and very fine sand the concentration of suspended bed material including very coarse sand varied with bedload transport rate discharge and height above the bed bedload transport rate and changes in channel shape were greatest several days after peak discharge comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport and that antecedent weather is an important control on suspended sediment concentration neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload e g ackers white 1973 nor observations of sediment transport characteristics in ephemeral streams e g reid frostick 1987 are directly applicable to this river

imaging and quantification of spreading and trapping of carbon dioxide in saline aquifers using meter scale laboratory experiments the role of capillary forces during buoyant migration of co2 is critical toward plume immobilization within the postinjection phase of a geological carbon sequestration operation however the inherent heterogeneity of the subsurface makes it very challenging to evaluate the effects of capillary forces on the storage capacity of these formations and to assess in situ plume evolution to overcome the lack of accurate and continuous observations at the field scale and to mimic vertical migration and entrapment of realistic co2 plumes in the presence of a background hydraulic gradient we conducted two unique long term experiments in a 2 44 m 0 5 m tank x ray attenuation allowed measuring the evolution of a co2 surrogate fluid saturation thus providing direct insight into capillarity dominated and buoyancy dominated flow processes occurring under successive drainage and imbibition conditions the comparison of saturation distributions between two experimental campaigns suggests that layered type heterogeneity plays an important role on nonwetting phase nwp migration and trapping because it leads to i longer displacement times 3 6 months versus 24 days to reach stable trapping conditions ii limited vertical migration of the plume with center of mass at 39 versus 55 of aquifer thickness and iii immobilization of a larger fraction of injected nwp mass 67 2 versus 51 5 of injected volume as compared to the homogenous scenario while these observations confirm once more the role of geological heterogeneity in controlling buoyant flows in the subsurface they also highlight the importance of characterizing it at scales that are below seismic resolution 1 10 m

flood behaviour of the burdekin river tropical north queensland australia strongly seasonal rainfall in north queensland australia causes extremely variable fluvial discharge and tropical cyclones commonly produce high magnitude short duration floods in the burdekin river catchment 129 500 km2 of eastern queensland rapid runoff and channel floodplain configuration lead to very fast flood wave speeds up to 4 34 m s 1 calculated the large catchment and varying tropical cyclone paths result in extreme variations in flood history at different sites changes in channel conditions bed elevation vegetation bedforms sediment surface character in successive events combined with complex rainfall patterns and highly unsteady flow make flood estimates extremely difficult because of the short duration of flow events and very rapid rate of change in discharge during individual events sediment transport rate bedforms and bed elevation change continuously for most of the year the channel is occupied by an underfit stream but this small perennial stream does not significantly rework the deposits or change channel form before the next major discharge event consequently there is little channel form recovery between major discharge events successive events have very variable size and consequently the bedforms and channel morphology are normally out of equilibrium with the flow and record the result of the most recent major events high magnitude floods transport coarse sediment onto the floodplain and the short duration of flooding and rapid runoff results in relatively low preservation of mud in the channel or overbank environment the holocene flood deposits include thick coarse sand and medium sand units and generally thin fine grained units

transfer of nonsorbing solutes to a streambed with bed forms theory a theoretical analysis of the exchange of nonsorbing solutes between a permeable streambed and the overlying water of a stream or river is presented in this paper in a companion paper elliott and brooks this issue the results of experimental studies of such exchange are presented the analysis focuses on water movements into within and out of the bed which result from the presence of bed forms ripples and dunes and highlights the mechanisms of pumping and turnover pumping is the movement of fluid through the bed induced by steady dynamic pressure variations over bed forms turnover occurs as moving bed forms trap and release interstitial fluid the detailed analysis was used to generate the distribution of the residence time of solute within the bed which can be used to calculate the net mass exchange due to pumping and turnover

widespread nearshore and shallow marine deposition within the lower jurassic precipice sandstone and evergreen formation in the surat basin australia abstract in the surat basin of eastern australia the lower jurassic precipice sandstone and evergreen formation are a highly prospective reservoir seal pair for notional future carbon capture and storage however the succession remains poorly constrained from a paleodepositional standpoint and this has impacted the capacity to construct predictive reservoir models here we integrate sedimentological ichnological and palynological data from ten cores located across a large region of the northern and central basin to produce conceptual depositional models for the interval our analysis shows that the lower jurassic series consists of fifteen recurring sedimentary facies that are arranged into six facies associations braidplain lower delta plain subaqueous delta delta influenced shoreface tidally influenced shoreline and restricted marine shoals the facies associations occur in the context of large scale fluvio deltaic systems that occupied the basin these results are supported by ichnological indications of marine and brackish water a coastal suite of palynomorphs and marine palynomorphs including rare dinocysts acritarchs and copepod fragments the very low abundance of marine palynomorphs are confined to the upper portion of the evergreen formation and in combination with the sedimentology and ichnology suggest that marine influence increased through time as the basin was filled the elucidation of marine influenced deposition contravenes all but the most recent facies interpretations of the precipice sandstone and evergreen formation and suggests that the paleogeography of the mesozoic of eastern australia needs to be reconsidered importantly the nearshore and shallow marine depositional affinity has important implications for the size orientation and distribution of geobodies when building geologically realistic static reservoir models for dynamic flow simulation

a first chironomid based summer temperature reconstruction 13 5 ka bp around 49 n in inland europe compared with local lake development temperature reconstructions for the end of the pleistocene and the first half of the holocene based on biotic proxies are rare for inland europe around 49 n we analysed a 7 m long sequence of lake deposits in the vihorlat mts in eastern slovakia 820 m a s l chironomid head capsules were used to reconstruct mean july temperature tjuly other proxies diatoms green algae pollen geochemistry were used to reconstruct local environmental changes that might have affected the climate reconstruction such as epilimnetic total phosphorus concentrations tp lake level changes and development of surrounding vegetation during the younger dryas yd temperature fluctuated between 7 and 11 c with distinct decadal to centennial scale variations that agree with other palaeoclimate records in europe such as 18o content in stalagmites or greenland ice cores the results indicate that the site was somewhat colder than expected from the general south to north yd temperature gradient within europe possibly because of north facing exposition the warmer phases of the yd were characterised by low water level or even complete desiccation of the lake 12 200 12 400 cal yr bp at the late glacial holocene transition tjuly steeply increased from from 11 to 15 5 c 11 700 11 400 cal yr bp the highest tjuly for entire sequence this rapid climate change was reflected by all proxies as a compositional change and increasing species diversity the open woodlands of pinus betula larix and picea were replaced by broad leaved temperate forests dominated by betula later by ulmus and finally by corylus ca 9700 cal yr bp at the same time input of eroded coarse grained material into the lake decreased and organic matter loi and biogenic silica increased the early holocene climate was rather stable till 8700 cal yr bp with temporary decrease in tjuly around 11 200 cal yr bp the lake was productive with a well developed littoral as indicated by both diatoms and chironomids a distinct decline of tjuly to 10 c between 8700 and 8000 cal yr bp was associated with decreasing chironomid diversity and increasing climate moistening indicated by pollen tychoplanktonic and phosphorus demanding diatoms increased which might be explained by hydrological and land cover changes later a gradual warming started after 7000 cal yr bp and representation of macrophytes periphytic diatoms and littoral chironomids increased our results suggest that the holocene thermal maximum was taking place unusually early in the holocene at our study site but its timing might be affected by topography and mesoclimate we further demonstrated that temperature changes had coincided with variations in local hydrology

use of sedimentological information for geometric simulation of natural porous media structure a geometric simulation method was used to develop a three dimensional highly detailed synthetic representation of point bar sediments in the wabash river system geometric simulation methods in comparison to well known second order stochastic methods offer the advantage of being more closely related to depositional processes which are often similarly conceptualized i e described in terms of shapes of discrete bed forms trends in grain size and spatial relationships of defined geologic facies multiple scales of geometric variation were defined within a sedimentologically prescribed framework and shapes of discrete geometric elements were established at each scale the selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments the parameterization of the shapes allowed for random variability of the shape descriptors discrete shapes were then generated and assimilated by computer hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity the synthetic model referred to as a numerical aquifer is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport

late glacial chironomid based temperature reconstructions for lago piccolo di avigliana in the southwestern alps italy chironomid headcapsules were used to reconstruct late glacial and early holocene summer temperatures at lago piccolo di avigliana lpa two training sets northern sweden north america were used to infer temperatures the reconstructed patterns of temperature change agreed well with the grip and ngrip 18o records inferred temperatures were high during the bolling ca 19 c slowly decreased to ca 17 5 c during the allerod reached lowest temperatures ca 16 c during the younger dryas and increased to ca 18 5 c during the preboreal the amplitudes of change at climate transitions i e oldest dryas bolling 3 c allerod younger dryas 1 5 c and younger dryas preboreal 2 5 c were smaller than in the northern alps but similar to those recorded at another site in northeastern italy our results suggest that 1 allerod temperatures were higher in the southern alps and 2 higher during the preboreal 1 c than during the allerod these differences might provide an explanation for the different responses of terrestrial vegetation to late glacial and early holocene climatic changes in the two regions other sites on both sides of the alps should be studied to confirm these two hypotheses

capturing and modelling metre scale spatial facies heterogeneity in a jurassic ramp setting central high atlas morocco each simulation algorithm including truncated gaussian simulation sequential indicator simulation and indicator kriging is characterized by different operating modes which variably influence the facies proportion distribution and association of digital outcrop models as shown in clastic sediments a detailed study of carbonate heterogeneity is then crucial to understanding these differences and providing rules for carbonate modelling through a continuous exposure of bajocian carbonate strata a study window 320 m long 190 m wide and 30 m thick was investigated and metre scale lithofacies heterogeneity was captured and modelled using closely spaced sections ten lithofacies deposited in a shallow water carbonate dominated ramp were recognized and their dimensions and associations were documented field data including height sections were georeferenced and input into the model four models were built in the present study model a used all sections and truncated gaussian simulation during the stochastic simulation for the three other models model b was generated using truncated gaussian simulation as for model a model c was generated using sequential indicator simulation and model d was generated using indicator kriging these three additional models were built by removing two out of eight sections from data input the removal of sections allows direct insights on geological uncertainties at inter well spacings by comparing modelled and described sections other quantitative and qualitative comparisons were carried out between models to understand the advantages disadvantages of each algorithm model a is used as the base case indicator kriging model d simplifies the facies distribution by assigning continuous geological bodies of the most abundant lithofacies to each zone sequential indicator simulation model c is confident to conserve facies proportion when geological heterogeneity is complex the use of trend with truncated gaussian simulation is a powerful tool for modelling well defined spatial facies relationships however in shallow water carbonate facies can coexist and their association can change through time and space the present study shows that the scale of modelling depositional environment or lithofacies involves specific simulation constraints on shallow water carbonate modelling methods

outcrop analog for an oolitic carbonate ramp reservoir a scale dependent geologic modeling approach based on stratigraphic hierarchy considerable effort has been devoted to the development of simulation algorithms for facies modeling whereas a discussion of how to combine those techniques has not existed the integration of multiple geologic data into a three dimensional model which requires the combination of simulation techniques is yet a current challenge for reservoir modeling this article presents a thought process that guides the acquisition and modeling of geologic data at various scales our work is based on outcrop data collected from a jurassic carbonate ramp located in the high atlas mountain range of morocco the study window is 1 km 0 6 mi wide and 100 m 328 1 ft thick we describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest 1 stacking pattern of high frequency depositional sequences 2 facies association and 3 lithofacies five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data the surface based model shows a low angle profile with modest paleotopographic relief at the inner to middle ramp transition facies associations were populated using truncated gaussian simulation to preserve ordered trends between the inner middle and outer ramps at the lithofacies scale field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation this study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks the selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings this study demonstrates that a scale dependent modeling approach should be a common procedure when building subsurface and outcrop models

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

new aspects of deformed cross strata in fluvial sandstones examples from neoproterozoic formations in northern norway abstract extensive 20 200 m long exposures of tabular cross sets in neoproterozoic fluvial sandstone in northern norway demonstrate that deformed cross strata in the form of recumbently folded cross strata with associated massive sand are localized features passing in both up and down current direction into undeformed concave upward or sigmoidal cross strata the deformation occurs in down current inclined tangential wedge shaped zones beneath reactivation surfaces and less commonly as flat topped lenticular zones the localized nature of the sediment deformation is attributed to local liquefaction below the top of the bed in the case of the flat topped lenses and at the dune front in the case of the more common tangential wedges the position of the flat topped lenses suggests deformation by the shear stress of high velocity suspension laden currents although liquefaction of the dune front implies the action of gravity forces it is argued that the fluvial currents were the main driving force at the instant of bed liquefaction post folding gravitational shearing probably enhanced the deformation within the upper part of the wedges with their long flat lying toeset resulting from redeposition of downslope moving liquefied sand the down current alternation of deformed tangential wedges and undeformed cross strata suggests that the mechanism that triggered the liquefaction of the dune lee side was related to the fluvial system itself and hence was of autokinetic origin the tabular cross sets have previously been interpreted as a product of the dune upper stage plane bed flow regime in this flow context it can be speculated that the liquefaction and deformation occurred when the flow conditions approached the plane bed phase probably inducing a highly differential turbulent pattern and pressure fluctuations sufficient to liquefy the fine medium sand the small flat topped deformation lenses also suggest liquefaction by cyclic loading whereas the solitary nature of the large lenses may alternatively be the result of impulsive loading from bank collapse in less well exposed fluvial successions the auto or allokinetic origin of recumbently folded cross strata may be difficult to determine however the common occurrence of recumbent folds in cross stratified fluvial sandstones and their virtual absence in marine cross stratified deposits suggests strongly that in the majority of cases the deformation was autokinetic resulting from flow phenomena typical of river channels this kind of deformation structure should thus not be attributed to an allokinetic seismic triggering mechanism unless independent evidence of fault activity can be documented

fracture pattern analysis as a tool for constraining the interaction between regional and diapir related stress fields poza de la sal diapir basque pyrenees spain during diapir evolution the local stress field results from the interaction between diapirrelated and remote regional stress fields the fracture pattern hosted in the overburden can register this evolving interaction providing significant insights for the unravelling of the diapir kinematics in this work we present the example of the poza de la sal diapir which is a salt diapir that pierces the synorogenic deposits of the basque pyrenees the integrated analysis of mesostructural data which includes field collected faults joints and fracture traces digitalized on high resolution orthophotos allowed us to establish an evolutionary model for the stress field around diapirs the presented data support the idea that during diapir evolution stress fields evolve from mostly regional related to mostly diapir related contrasting with other geological data seismic data geological map and cross section we observe that different methods provide complementary information coherent with the proposed evolutionary model of the poza de la sal diapir the study of fracture development associated with the growth of salt diapirs is of interest for both academic and industrial purposes in fact fractures play an important role in fluid flow and its accumulation in salt diapir related reservoirs johnson bredeson 1971 koestler ehrmann 1987 davison et al 2000a b on the other hand the analysis of fracture patterns is useful to constrain the host structure evolution thorbjornsen dunne 1997 tavani et al 2008 and accordingly can provide useful information for understanding diapir kinematics alsop 1996 stewart 2006 yin groshong 2007 yin et al 2009 the fracture pattern associated with salt diapirs and in general with doming structures is characterized by two classes of elements radial and concentric fig 1a b e g parker mcdowell 1955 withjack 1979 squyres et al 1992 branney 1995 malthe sorenssen et al 1999 rowan et al 1999 2003 davison et al 2000a b freed et al 2001 stewart 2006 this pattern is documented in simple structures where the remote stress field is negligible in relation to the diapir related stress fields when such a condition is not verified the interaction of these two stress fields leads to the development of more complex patterns ode 1957 withjack scheiner 1982 studies of interacting regional and punctual stress fields e g ode 1957 indicate that the influence of diapir induced stress progressively reduces away from the dome i e the punctual structure as a consequence far from the diapir the fracture pattern responds to the remote stress field and approaching the diapir the fracture pattern tends to be radial and concentric fig 1c although these patterns have been observed by several authors in different structures withjack scheiner 1982 mege masson 1996 ernst et al 2003 there are no detailed field studies focusing on this topic in this work we present a simple 2d theoretical stress field model where the stress tensor resulting from the interaction between remote and diapirrelated stress fields is assumed to be for a fixed distance from the diapir centre a 2 2 matrix provided by the sum of the horizontal components of the two stress tensors the eigenvectors associated with this matrix are assumed to be the principal axes of the local stress field the working hypothesis is that if the stress field changes the azimuth of fractures joints developed under these stress fields also change by understanding interactions between diapir related and regional stress fields we can predict the azimuth of the developed fractures to test the validity of this theoretical model we have applied it to a well exposed salt diapir located at the western pyrenees poza de la sal diapir this is a near circular diapir with a mainly carbonate overburden affected by a complex pattern of fractures results of this comparison indicate that despite its simplicity the provided stress model is a useful tool for understanding the kinematics of salt diapirs accordingly in this paper we provide from alsop g i archer s g hartley a j grant n t hodgkinson r eds 2012 salt tectonics sediments and prospectivity geological society london special publications 363 521 532 http dx doi org 10 1144 sp363 25 the geological society of london 2012 publishing disclaimer www geolsoc org uk pub ethics guidelines to obtain a fracture pattern using the theoretical model presented to complement other techniques of investigation such as field work or 3d seismic interpretations

lower cretaceous tides revealed by cross bedding with mud drapes the sand dominated folkestone beds widely exposed around the weald of south east england are of upper aptian to lower albian lower cretaceous age and range in thickness up to 84 m refs 1 3 their content of ammonites bivalves and sponges indicates a marine origin while their relative coarseness and the incorporation of drifted timber point to a shallow water deposition near land one striking sedimentary facies is formed by medium to coarse grained cross bedded sands in which several foreset and or bottomset surfaces support mud drapes although it was suggested4 that this facies may have been formed by the storm induced movement of sand waves i now consider that the facies is best explained by the migration of sand waves under the influence of strongly asymmetrical tides and that the mud drapes are formed at slack water a model of this process has been described elsewhere5 and i now describe measurements of a section which supports my earlier conjecture6that the separation of the mud drapes is systematically related to the phase of the spring neap tidal cycle at the time of deposition although criteria for recognizing tidal deposits have long been available it has not previously been possible to analyse a series of ancient sediments with a view to characterizing the tidal regime

early holocene climate variability and the timing and extent of the holocene thermal maximum htm in northern iceland the magnitude and timing of holocene maximum warmth in the arctic and sub arctic has been the subject of considerable recent interest particularly in the context of future climate change although lying at a crucial location in the north atlantic close to significant atmospheric and oceanic boundaries terrestrial holocene climatic data from iceland are few and predominantly derive from glacial and palaeoecological evidence here we present new datasets from trollaskagi based on chironomid inferred temperatures ci t using sub fossil chironomids from the same lake sediments supplemented by pollen data july air temperatures have been derived using an icelandic training set and the data suggest optimal temperatures at sea level up to 1 5 c above current levels around 8 k cal yr bp a time when birch woodland was well developed in trollaskagi but when woodland had still not fully developed in the more isolated nw peninsula our data thus suggest that optimal summer warmth did not occur in iceland until 8 kcal yr bp at the earliest possibly lasting until 6 7 kcal yr bp the amount of warming for july was therefore at least 1 5 c but possibly up to 2 3 c higher than the 1961 1990 average on the basis of the tree line data comparison with data from elsewhere in adjacent arctic regions greenland and eastern arctic canada show peak warmth to be later in iceland and less pronounced it also appears that there were enhanced temperature gradients during the first half of the holocene between the two study areas trollaskagi and the nw peninsula and that they influenced patterns of vegetation colonisation with current spatial temperature patterns only developing as holocene climate deteriorated after around 6 kcal yr bp

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

structures and textures in triassic braided stream conglomerates bunter pebble beds in the sherwood sandstone group north staffordshire england in the northern parts of the needwood and stafford eccleshall basins england the pebble beds of the sherwood sandstone group contain thick successions of texturally mature fluvial pebble cobble conglomerates which are organized into either horizontal or cross stratified sets the horizontally lying sets generally coarser grained and more poorly sorted than the cross bedded sets are usually disorganized and either matrix or clast supported although thin lenses of well sorted occasionally openwork units interpreted as falling stage phenomena are often present the cross stratified conglomerates have foresets exhibiting remarkable textural organization with a coarse bimodal sometimes matrix supported part grading upwards or being abruptly overlain by a finer well sorted occasionally openwork part and finally capped by sandstone these rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions the most common types of vertical association are thick successions of horizontally bedded conglomerates up to 20 m and sequences of an upwards coarsening nature 2 12 m in which cross stratified sets are overlain by flat lying sets the environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains proglacial or alluvial fan but shallower than depths associated with the pleistocene catastrophic floods from which texturally mature giant gravel bars have been recorded recent braided streams with relatively confined channels and considerable bar channel relief are better analogues in particular medial or mid channel bars with a two tier structure subaqueous and partly emergent portions may explain the upward coarsening sequences in which horizontally lying conglomerates overlie cross stratified conglomerates the thicker sequences of horizontally stratified conglomerates represent proximal longitudinal bar deposits sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates and commonly occurring towards the top of the succession largely represent deposition from sandwaves and dunes finer interbedded argillaceous sandstones siltstones and mudstones are interpreted as overbank and waning flood deposits basin forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the midlands and the hercynides account for the upwards fining of the upper part of the succession

bed material movement in hyperconcentrated flow a series of experiments were made in a closed rectangular conduit with bentonite as fine particles and plastic beads as coarse particles compared with that in clear water in bentonite suspensions coarse particles settle more slowly and start moving at a higher flow intensity due to the larger threshold velocity and smaller settling velocity the bed load is smaller and the suspended load is larger as a result the total load consisting of the bed load and the suspended load is smaller in the low flow intensity region but larger in the high flow intensity region the increase of the suspended load favors the transition from dunes to plane bed so in clay suspension dunes are lower flatter and change to plane bed at lower flow intensity correspondingly the form resistance is smaller in clay suspension

radar architecture and evolution of channel bars in wandering gravel bed rivers fraser and squamish rivers british columbia canada abstract the alluvial architecture and evolution of two kilometer scale compound bars in the wandering gravel bed fraser and squamish rivers british columbia canada are described integrating ground penetrating radar bathymetry and aerial photographs enables the internal architecture to be linked to the evolution of the gravelly barforms over the previous 50 years these linkages reveal the sedimentary mechanisms that formed the various architectural packages within compound bars and unit bars growth of compound bars is controlled by the accretion of unit bars onto discrete segments along their gravelly edges the attachment of unit bars deflects the thalweg to impinge on and erode specific portions of bars and channel banks bar growth leads to the stabilization of bars vegetation colonization of bar interiors and island formation it is the formation of islands along with channel avulsions that maintains channel division in wandering rivers seven styles of gravelly deposition are imaged in the alluvial architecture vertical accretion deposits formed from the deposition of gravelly bedload sheets are the most common strata a moderate abundance of slipface deposits preserves high relief bar margins lateral accretion dominates point bar deposits downstream accretion deposits govern some phases of down bar growth partial and complete channel fill and chute fill deposits are eroded into underlying sediments as are scour and fill deposits upstream accretion deposits are uncommon a depositional model of gravelly channel bars in the two rivers is presented and reveals that the architecture is made up of depositional styles similar to those observed in braiding river successions although the sedimentary packages are preserved in different proportions differences in braiding river and wandering river sedimentology largely reflect the relatively frequent migration of channels and bars in braiding rivers which preserve high proportions of channel fill and chute fill and confluence scour and fill deposits conversely the moderately stable island and channel network in wandering rivers limits channel shifting and consequently preserves a low number of channel fills moderate proportions of slipface strata and coherent patterns of sand deposition along bar tops provide evidence of comparatively uniform flow patterns in independent channel segments divided by islands these patterns of bar sedimentation and channel shifting preserved in the alluvial architecture appear to be signature characteristics of wandering rivers the occurrence of similar architecture in both the fraser and squamish rivers suggests that the model likely applies to most wandering gravel bed rivers

an experimental study of subaquaeous slipface deposition abstract a flume study indicates that grainflow on slipfaces accounts for most cross strata formed in unidirectional shallow water flows the slipfaces studied were on small megaripples and delta like steps 0 06 0 28 m high during intermittent avalanching at relatively low flow velocities periods between avalanches were marked by grainfall onto the slipface the intensity of which was greatest near the brink of the slipface and increased with current velocity nearly all grainfall deposits however were incorporated into subsequent grainflows grain flow cross strata were made up of relatively distinct layers at least near the base of the slipface continuous avalanching at high flow velocity was marked by a steady stream of grains forming more poorly defined cross strata although the fundamental cause of grain flow is the gradual buildup of sediment on the upper slipface to the angle of initial yield four other processes were recognized as promoting avalanching 1 migration of superimposed bedforms to the brink 2 generation of turbulent pulses upstream of the brink 3 lee eddy impingement on the lower slipface and 4 extension of the lee eddy above the brink the lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow regression analyses showed that the slipface advance per avalanche sa is strongly correlated with the slipface height h expressed approximately by sa 0 060h in addition sa is a direct function of the rate of slipface advance vb the relationship among sa h and vb can be expressed as sa h 0 0385 1 0 134 min cm vb 1 cross strata dip angles between 28 and 34 show no systematic relation to h and vb but dip angles greater than 34 occurred only when both h and vb were small and dip angles less than 28 occurred only when both h and vb were large

predicting erosion resistance of muds abstract when measured or apparent yield stress of cohesive muds is assumed to reflect average particle particle bond strength in network structures critical bed shear stress required for grain by grain entrainment can be predicted from an analysis of the forces acting on component grains of geometrically flat mud beds erosion resistance is then defined in terms of cohesive yield stress as well as nominal particle size shape relative density and packing geometry predicted values of critical bed shear stress compare favorably with existing data from selected studies in which appropriate yield stress and hydrodynamic parameters have been reported

formation and preservation of open framework gravel strata in unidirectional flows open framework gravel ofg in river deposits is important because of its exceptionally high permeability resulting from the lack of sediment in the pore spaces between the gravel grains fluvial ofg occurs as planar strata and cross strata of varying scale and is interbedded with sand and sandy gravel the origin of ofg has been related to 1 proportion of sand available relative to gravel 2 separation of sand from gravel during a specific flow stage and sediment transport rate either high falling or low 3 separation of sand from gravel in bedforms superimposed on the backs of larger bedforms 4 flow separation in the lee of dunes or unit bars laboratory flume experiments were undertaken to test and develop these theories for the origin of ofg bed sediment size distribution sandy gravel with a mean diameter of 1 5 mm was kept constant but flow depth flow velocity and aggradation rate were varied bedforms produced under these flow conditions were bedload sheets dunes and unit bars the fundamental cause of ofg is the sorting of sand from gravel associated with flow separation at the crest of bedforms and further segregation of grain sizes during avalanching on the steep lee side sand in transport near the bed is deposited in the trough of the bedform whereas bed load gravel avalanches down the leeside and overruns the sand in the trough the effectiveness of this sorting mechanism increases as the height of the bedform increases infiltration of sand into the gravel framework is of minor importance in these experiments and occurs mainly in bedform troughs the geometry and proportion of ofg in fluvial deposits are influenced by variation in height of bedforms as they migrate superposition of small bedforms on the backs of larger bedforms aggradation rate and changes in sediment supply if the height of a bedform increases as it migrates downstream so does the amount of ofg changes in the character of ofg on the lee side of unit bars depend on grain size sorting in the superimposed bedforms dunes and bedload sheets thick deposits of cross stratified ofg require high bedforms dunes unit bars and large amounts of aggradation these conditions might be expected to occur during high falling stages in the deeper parts of river channels adjacent to compound bar tails and downstream of confluence scours increase in the amount of sand supplied relative to gravel reduces the development of ofg such increases in sand supply may be related to falling flow stage and or upstream erosion of sandy deposits

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

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

relating small scale sedimentary structures and permeability in a cross bedded aquifer summary the objective of this study is to investigate the relation between small scale sedimentary structures and permeability in the brussels sands formation an early middle eocene shallow marine sand deposit in central belgium that constitutes a major groundwater source in the region a field campaign was carried out consisting of field observations of the sedimentary structures and in situ measurements of air permeability the sedimentary structures were interpreted sketched digitally photographed and measured in a representative outcrop additionally a total of 2750 cm scale air permeability measurements were carried out in situ analysis of the spatial distribution of sedimentary structures and permeability shows that clay rich sedimentary features such as bottomsets and distinct mud drapes exhibit a different statistical and geostatistical permeability distribution compared to the other lithofacies in the cross bedded sands spatial analysis of the air permeability data shows that permeability anisotropy in the cross bedded lithofacies is dominated by the foreset lamination orientation these results show that small scale sedimentary heterogeneity strongly influences the local spatial distribution of the hydraulic properties and results in permeability heterogeneity and stratification that would produce anisotropy in upscaled permeability values

a kinematic model for the structure of lee side deposits a kinematic model for the structure of the lee side deposit of a dune like bedform gilbert type delta or similar step is developed based on the assumptions that initial deposition is entirely by grainfall that the rate of deposition decreases as a power function of distance downflow from the brink of the slipface and that the resulting steepening of the slipface is periodically interrupted by avalanching the parameters used in the model are 1 the deposition rate at a given distance from the brink 2 the exponent in the equation relating the deposition rate to distance from the brink 3 the bedform migration rate 4 the bedform height 5 the avalanche speed 6 the angle of initial yield and 7 the residual angle after avalanching from these parameters can be calculated structural characteristics such as the proportions of bottomset and foreset deposits the proportions of avalanche and grainfall deposits in the foreset deposit and the spacing of avalanche grainfall couplets the model correctly predicts the trends of changing avalanche activity and changing structural character with changes in flow character grain size and bedform height in both air and water moreover the model correctly predicts certain consistent structural differences between aeolian and subaqueous lee side deposits quantitative evaluation of the model requires more accurate data on the values of the input parameters than are presently available

in channel woody vegetation controls on sedimentary processes and the sedimentary record within alluvial environments a modern example of an anabranch of the river loire france a multidisciplinary approach was used to analyse the role of pioneer trees populus nigra on bar formation in the modern fluvial system of the river loire france data were collected on seven plots located on a secondary channel chosen for their vegetation cover and their sedimentary context physical features of vegetation topographical evolution sediment grain size and flow velocity were investigated during and after floods between 2001 and 2003 woody vegetation responds morphologically to fast flowing waters and sediment deposition these adaptations influence the role played by trees on local sedimentary processes some morphological types of trees exert a strong influence during flood events by deflecting reducing or increasing the flow energy as a consequence the evolution of bedforms distribution of sediment grain size and slopes are controlled by the flood type the morphological context i e high or low energy zones the morphology of the vegetated bar and the characteristics of vegetation conceptual models are proposed to account for local processes and evolution of tree groves the first model which describes the behaviour of groves during a single flood underlines the sediment deposition downstream of the trees and the trapping of bedload sediments during the falling stage of the flood the reorientation of current streams constrained by both local bed topography and woody vegetation induces transverse sediment fluxes for these water levels the control exerted by trees on small scale sedimentary processes becomes significant the second model shows the evolution of vegetation bands over several flood events in particular it describes the influence of vegetation on the fixing and reworking of bedload sediments during the falling limb of the hydrograph the coalescence of vegetation induced bedforms and the resulting morphological changes increase the deflection power of the vegetated bar inducing the deposition of finer sediments

back flow ripples in troughs downstream of unit bars formation preservation and value for interpreting flow conditions back flow ripples are bedforms created within the lee side eddy of a larger bedform with migration directions opposed or oblique to that of the host bedform in the flume experiments described in this article back flow ripples formed in the trough downstream of a unit bar and changed with mean flow velocity varying from small incipient back flow ripples at low velocities to well formed back flow ripples with greater velocity to rapidly migrating transient back flow ripples formed at the greatest velocities tested in these experiments back flow ripples formed at much lower mean back flow velocities than predicted from previously published descriptions this lower threshold mean back flow velocity is attributed to the pattern of velocity variation within the lee side eddy of the host bedform the back flow velocity variations are attributed to vortex shedding from the separation zone wake flapping and increases in the size of and turbulent intensity within the flow separation eddy controlled by the passage of superimposed bedforms approaching the crest of the bar short duration high velocity packets whatever their cause may form back flow ripples if they exceed the minimum bed shear stress for ripple generation for long enough or if much faster may wash them out variation in back flow ripple cross lamination has been observed in the rock record and by comparison with flume observations the preserved back flow ripple morphology may be useful for interpreting formative flow and sediment transport dynamics

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

regional consistency in lateglacial chironomid inferred temperatures from five sites in north west england abstract high resolution lateglacial ice core records from greenland show both millennial and centennial scale change and have been used as a benchmark for lateglacial climatic stratigraphy throughout the north atlantic region and beyond in this study we assess the local reflection in north west europe of climatic events recognised in ice cores and identify differences in the climate signature between greenland uk and sites in continental europe this study uses chironomid inferred temperature analysis and loss on ignition data from five carbonate lakes in north west england to determine the pattern of lateglacial climatic change and demonstrates the reproducibility of chironomid inferred temperature reconstructions both within a catchment and from sites within a small area at both millennial and centennial scales our results show statistical similarities between sites giving a clear regional signal chironomid assemblages pick out the rapid shifts at the major event boundaries at all sites and indicate temperatures of between 12 and 13 c for the region at the beginning of greenland interstadial 1 a rapid fall of around 4 c into the younger dryas and a rise of around 5 c in the early holocene at a finer scale four centennial cooling events are identified within the interstadial together with an oscillation in the early holocene which we tentatively identify as the pre boreal event the records were analysed statistically using redundancy analysis and sequence slotting techniques differences in the impact of individual climatic events demonstrate that subtle changes in the chironomid inferred temperatures reflect the local geographical setting and morphology of the lakes with more marked impact registered in higher altitude and more wind exposed sites whilst the overall pattern of lateglacial climate can be recognised from greenland to central europe important regional differences that can be attributed to marine influence and perhaps changes in atmospheric circulation are beginning to emerge

aeolian stratification and facies association in desert sediments arran basin permian scotland abstract permian aeolian sediments on the island of arran are divisible into dune including draa and interdune deposits both types display a distinctive and unusually wide variation in grain size the dominant features of the dune deposits are grainfall lamination sandflow lamination and inverse graded lamination associated with ripple form lamination and normal graded lamination the flat lying aeolian interdune deposits are characterised by granule and sand ripples horizontal lamination in coarse sand and granules plane bed lamination and inverse graded lamination associated structures include ripple form lamination and deflation lags three types of trace fossil associated with completely bioturbated horizons occur in some low angle dune and interdune deposits the aeolian facies interfinger with alluvial fan deposits giving rise to three recognizable facies belts marginal aeolian deposits are associated with fluvial conglomerates and are dominated by interdune deposits and occasionally very thin barchan deposits set height 3 37 cm intermediate aeolian deposits are characterized by interbedded crescentic dune small draa dune set height 5 cm 4 5 m and interdune deposits and rare fluvial and lake sediments basinal aeolian deposits are dominated by draa deposits dune set height 0 2 28 m associated with rare interdune sediments transverse dunes and draas were moved by north eastern palaeowinds towards the foot of the alluvial fans the aeolian sediments were deposited in a fault bounded desert basin

stochastic prediction of sediment transport in sand gravel bed rivers classical deterministic bedload transport predictors are applied to sand gravel bed rivers the turbulent bed shear stress is modeled according to a probability distribution to obtain realistic bedload transport rates at incipient motion in extending the predictors to stochastic predictors for nonuniform sediment many parameters that represent near bed turbulence and the particle size distribution must be chosen the parameters that give realistic results are chosen by analyzing the results of a new experimental flume dataset with relatively large water depths choosing other combinations of parameters may give equal total bedload transport rates but at the cost of large errors in fractional transport rates attention is given to the hiding exposure phenomenon and a hindrance effect related to nonuni form sediment validation based on two independent field datasets shows that successful predictions of particle sizes near the threshold for motion are feasible using the stochastic approach while the deterministic approach gives successful predictions well above incipient motion

stratigraphy petrochemistry and quaternary depositional record of the songaksan tuff ring jeju island korea abstract the songaksan tuff ring str is one of several recent hydrovolcanic centers on jeju island korea which provides an excellent example of proximal to distal facies changes in wet pyroclastic surge deposits a multidisciplinary study has been carried out on the str and adjacent lithostratigraphic units to constrain absolute age geochemical characteristics and quaternary depositional history a number of rock units were identified inside the crater of the str including scoria deposit i trachybasalt lava scoria deposit ii and a late stage basaltic tuff indicative of a rather complex sequence of magmatic and phreatomagmatic eruptions after the construction of the tuff ring petrochemical analysis shows that the str was generated from different magma batches that fractionated from a homogenous magma chamber and the early erupted magma was more evolved and volatile rich reworking of the str commenced shortly after the hydromagmatic eruption in a high energy nearshore environment resulting in deposition of the hamori formation the formation is composed of planar stratified and low to high angle cross stratified tuffaceous pebbly sandstones and occurs up to an altitude of about 4 m above present sea level 14c dating of molluscan shells beneath the formation indicates that it began to be deposited after about 4000 yr bp detailed sedimentary logging reveals that the formation consists of several stratal packages bounded by laterally persistent and distinct lithologic boundaries probably formed by millennial scale sea level fluctuations occurrence of another hydrovolcanic sequence the sinyangri formation on the opposite side of jeju island having similar sedimentary characteristics and ages suggests that the sea level fluctuations as seen in the hamori formation have affected a wide area of jeju island probably related to the high frequency sea level oscillations during the post 6 ka bp regression period in the east asian region it can be concluded that the formation of the str was possible because of the holocene transgression which made the present coastal areas water saturated and adequate for hydrovolcanic eruptions the str in turn contributed to record high frequency sea level fluctuations during the holocene via acting as a local and short lived but affluent source of loose sediment

methodology for reconstructing wind direction wind speed and duration of wind events from aeolian cross strata 1 a methodology for reconstructing wind direction speed and event duration from aeolian dune cross strata was developed from analysis of crescentic dunes at white sands new mexico during wind events dune lee faces were surveyed lee face deposits mapped deposition rates measured grain size sampled by stratification type and winds characterized from meteorological and field data the spatial distribution of lee face stratification styles is a function of the incidence angle formed between the wind and the brinkline with secondary controls by wind speed and dune sinuosity and height sets of wind ripple strata form at incidence angles of 25 40 grainfall grainflow foresets over wind ripple bottomsets at 40 70 and grainflow grainfall foresets at 70 90 erosional reactivation surfaces form at incidence angles up to 15 bypass surfaces up to 25 the total sediment load is fractionated within lee face stratification types wind speed can be reconstructed from relationships between grain size transport mode shear velocity and grain settling velocity where the full range of grain transport modes occurs and grain size is limited by shear stress the shear velocity and grain size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep and the coarse fraction in grainfall traveled in saltation the minimum duration of a wind event can be estimated using measures of shear velocity dune height and dune forward migration method limitations arise with source area control on grain size extremes in wind events and severe truncation of sets of cross strata

turbulent flow and drag over fixed two and three dimensional dunes 1 detailed measurements of turbulent flow were obtained over a fixed flat bed two dimensional 2 d dunes and four types of three dimensional 3 d dune morphologies including 1 full width saddles 2 full width lobes 3 sinuous crests and 4 irregular shaped crests the time averaged turbulence structure over the fixed flat bed was dynamically similar to flow over a flat bed with active sediment transport the flow field over 2 d dunes conforms with previous observations of flow over mobile and fixed bed forms bed form three dimensionality significantly altered the flow field observed over the 2 d dunes lobe shaped dune crest lines curved crests with topographic highs that bowed downstream enhanced the level of turbulence producing a better defined wake structure and more vigorous mixing in the separation cell than observed over 2 d dunes saddle shaped dune crest lines curved crests with topographic highs that bowed upstream diminished the level of turbulence suppressing a well defined wake structure and mixing in the flow separation cell flow over sinuous crested bed forms with lobes and saddles was dynamically similar to flow over full width bed forms development of in line paired saddles and lobes in the downstream direction appears to be controlled by near bed velocity gradients which were larger over saddles and smaller over lobes these gradients control local boundary shear stress patterns that should promote scour and high transport rates over saddles and deposition on lobes two dimensional and 3 d bed forms with the same height and length offered different levels of flow resistance the flow observations support the idea that saddles decrease flow resistance and lobes increase flow resistance relative to a 2 d dune bed form crests composed of irregularly spaced lobes and saddles suppressed turbulent flow structure development and reduced drag by 20 below levels for 2 d or sinuous crested dunes the results suggest that bed form crest shape needs to be accounted for in flow resistance calculations and that a single drag coefficient is inadequate where the bed can evolve through 2 d 3 d and irregular 3 d bed form states

large eddy simulation of three dimensional dunes in a steady unidirectional flow part 1 turbulence statistics we performed large eddy simulations of flow over a series of three dimensional dunes at laboratory scale reynolds number based on the average channel depth and streamwise velocity was 18 900 using the lagrangian dynamic eddy viscosity subgrid scale model the bedform three dimensionality was imposed by shifting a standard two dimensional dune shape in the streamwise direction according to a sine wave the statistics of the flow are discussed in 10 cases with in phase and staggered crestlines different deformation amplitudes and wavelengths the results are validated qualitatively against experiments the three dimensional separation of flow at the crestline alters the distribution of wall pressure which in turn may cause secondary flow across the stream which directs low momentum fluid near the bed toward the lobe the most downstream point on the crestline and high momentum fluid near the top surface toward the saddle the most upstream point on the crestline the mean flow is characterized by a pair of counter rotating streamwise vortices with core radius of the order of the flow depth however for wavelengths smaller than the flow depth the secondary flow exists only near the bed and the mean flow away from the bed resembles the two dimensional case staggering the crestlines alters the secondary motion the fastest flow occurs between the lobe and the saddle planes and two pairs of streamwise vortices appear a strong one centred about the lobe and a weaker one coming from the previous dune centred around the saddle the distribution of the wall stress and the focal points of separation and attachment on the bed are discussed the sensitivity of the average reattachment length depends on the induced secondary flow the streamwise and spanwise components of the channel resistance the skin friction and the form drag and the contribution of the form drag to the total resistance are also studied three dimensionality of the bed increases the drag in the channel the form drag contributes more than in the two dimensional case to the resistance except for the staggered crest case turbulent kinetic energy is increased in the separated shear layer by the introduction of three dimensionality but its value normalized by the plane averaged wall stress is lower than in the corresponding two dimensional dunes the upward flow on the stoss side and higher deceleration of flow on the lee side over the lobe plane lift and broaden the separated shear layer respectively affecting the turbulent kinetic energy

holocene environmental history recorded in lake lyadhej to sediments polar urals russia an 1180 cm long core recovered from lake lyadhej to 68 15 n 65 45 e 150 m a s l at the nw rim of the polar urals mountains reflects the holocene environmental history from ca 11 000 cal yr bp pollen assemblages from the diamicton ca 11 000 10 700 cal yr bp are dominated by pre quaternary spores and redeposited pinaceae pollen pointing to a high terrestrial input turbid and nutrient poor conditions existed in the lake ca 10 700 10 550 cal yr bp the chironomid inferred reconstructions suggest that mean july temperature increased rapidly from 10 0 to 11 8 c during this period sparse treeless vegetation dominated on the disturbed and denuded soils in the catchment area a distinct dominance of planktonic diatoms ca 10 500 8800 cal yr bp points to the lowest lake ice coverage the longest growing season and the highest bioproductivity during the lake history birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the holocene mean july temperature was likely 11 13 c and annual precipitation 400 500 mm the period ca 8800 5500 cal yr bp is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment the pollen and chironomid inferred temperatures reflect a warm period ca 6500 6000 cal bp with a mean july temperature at least 1 2 c higher than today birch forests disappeared from the lake vicinity after 6000 cal yr bp the vegetation in the lyadhej to region became similar to the modern one shrub betula nana salix and herb tundra have dominated the lake catchment since ca 5500 cal yr bp all proxies suggest rather harsh environmental conditions diatom assemblages reflect relatively short growing seasons and a longer persistence of lake ice ca 5500 2500 cal yr bp pollen based climate reconstructions suggest significant cooling between ca 5500 and 3500 cal yr bp with a mean july temperature 8 10 c and annual precipitation 300 400 mm the bioproductivity in the lake remained low after 2500 cal yr bp but biogeochemical proxies reflect a higher terrestrial influx changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake however chironomid based reconstructions reflect a period with minimal temperatures during the lake history

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

multi scale three dimensional distribution of fracture and igneous intrusion controlled hydrothermal dolomite from digital outcrop model latemar platform dolomites northern italy abstract in recent years fracture controlled hydrothermal dolomitization in association with igneous activity has gained interest in hydrocarbon exploration the geometry and distribution of dolomite bodies in this setting are of major importance for these new plays the latemar platform presents a spectacularly exposed outcrop analogue for carbonate reservoirs affected by igneous activity and dolomitization light detection and ranging lidar scanning and digital outcrop models doms of outcrops offer a great opportunity to derive geometrical information only a few analysis methods exist to quantitatively assess huge amounts of georeferenced three dimensional lithology data this study presents a novel quantitative approach to describe three dimensional spatial variation of lithology derived from doms this approach is applied to the latemar platform to determine dolomite body geometry and distribution in relation to crosscutting dikes a high resolution photorealistic dom of the latemar platform allows description of dolomite occurrences in three dimensions with high precision at platform scale this results in a unique lithology dataset of limestone dolomite and dike positions this dataset is analyzed by true three dimensional variography for the geospatial description of dolomite distribution in most studies three dimensional geostatistics is the combination of two dimensional horizontal and one dimensional vertical variation in this study the dolomite occurrences are extensive in three dimensions and cannot be reduced to a two dimensional one dimensional case therefore the concept of two dimensional variogram maps is expanded to a three dimensional description of lithology variation three dimensional anisotropy detection is used to derive principal directions in the occurrence of dolomite two small scale

bar top hollows a new element in the architecture of sandy braided rivers abstract discrete hollows in the bar tops of the south saskatchewan river are described that form a newly recognized morphological element of sandy braided rivers these bar top hollows which are up to 1 7 m deep and may extend for 10 30 m down and across flow have a circular to ovoid planform and are shown through use of ground penetrating radar to be filled by a series of distinct often angle of repose foresets the hollows form by both erosion and bar top deposition and may be generated by bar tail accretion cross bar channel cutoff and subsequent fill or lateral accretion at the bar head bar top hollows occur in the upper part of the bar depositional sequence and may thus prove useful indicators for braid bar reconstruction in ancient sediments and should not be confused with channel scour

climatic variability during the last millennium in western iceland from lake sediment records the aim of this research was to create a decadal scale terrestrial quantitative palaeoclimate record for nw iceland from lake sediments for the last millennium geochemical stable isotope and chironomid reconstructions were obtained from a lake sequence constrained by tephra deposits on the snaefellsnes peninsula western iceland obtaining a quantitative record proved problematic but the qualitative chironomid record showed clear trends associated with past summer temperatures and the sedimentological records provided evidence for past changes in precipitation mediated through catchment soil in wash when the full range of chronological uncertainty is considered four clear phases of climatic conditions were identified 1 a relatively warm phase between ad 1020 and 1310 2 a relatively stable period between ad 1310 and 1510 cooler than the preceding period but still notably warmer than the second half of the millennium 3 a consistent reduction of temperatures between ad 1560 and 1810 with the coolest period between ad 1680 and 1810 and 4 ad 1840 2000 has temperatures mainly warmer than in the preceding two centuries with a rising trend and increased variability from c ad 1900 onwards the reconstructions show clearly that the first half of the millennium experienced warmer climatic conditions than the second half with a return to the warmer climate only occurring in the last c 100 years much of the variability of the chironomid record can be linked to changes in the north atlantic oscillation nao the reconstructions presented can track low frequency and long term trends effectively and consistently but high resolution and calibrated quantitative records remain more of a challenge not just in finding optimal sedimentary deposits but also in finding the most reliable proxy it is this that presents the real challenge for holocene climate reconstruction from this key area of the north atlantic