surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

microstratigraphy trilobite biostratinomy and depositional environment of the lower cambrian ruin wash lagerstatte pioche formation nevada abstract the uppermost 43 cm of dyeran strata at the ruin wash lagerstatte chief range lincoln county nevada contain nonmineralized invertebrates and exceptionally preserved articulated olenelloid trilobites however the environmental factors responsible for the preservation of olenelloids in this unusual state at ruin wash have received little study and are therefore poorly understood microstratigraphic analysis of this interval reveals that the strata comprised almost exclusively of clay sized particles and rather monotonous and featureless in outcrop were deposited as a series of thin event beds interpreted as tempestites the energy of deposition progressively waned then waxed through the interval and benthic redox conditions shifted concurrently biostratinomic data for more than 500 trilobite specimens encountered in the measured section reveal that the trilobite fauna was autochthonous although winnowed surfaces rich in bioclasts occurring at the base and top of the section indicate intervals of prolonged pre burial exposure time and or in situ reworking trilobite biostratinomy was strongly influenced by subtle environmental shifts the degree of disarticulation and sclerite fracturing correlate positively with event bed energy and inferred bottom water oxygen content these results demonstrate that 1 preservation of articulated trilobites is favoured near the distal limit of scouring associated with depositional events where rapid sedimentation occurs in the absence of substrate reworking and 2 differential taphonomic overprint on trilobite preservation can occur within a monofacial succession driven by subtle environmental change insufficient to leave a distinct lithological signature this highlights the need for careful microstratigraphic sedimentological and ichnological analysis prior to comparison of palaeobiological or palaeoecological parameters inferred from fossil assemblages even when the assemblages occur within the same lithofacies

rapid deposition of sand and gravel mixtures downstream of a negative step the role of matrix infilling and particle overpassing in the process of bar front accretion an experimental flow channel was used to investigate the rapid deposition of sand and gravel mixtures downstream of a negative step hydraulic processes give rise to the quasi simultaneous accumulation of openwork gravels matrix filled contact framework and dilated framework gravels the resultant structure is analogous to a bar front in gravel bed streams flow conditions were non uniform but steady in time whereas open and closed gravel fabrics are usually interpreted as representing deposition from unsteady flows for example a varying discharge regime consideration of the percentage of sand in the deposits indicated that in terms of packing the sediments may be considered as a simple binary mixture with partial framework dilation occurring with sand percentages in excess of c 32 despite dilation for sand percentages less than 50 structural stability of the foreset gravels was maintained so that the bar front exhibited a distinct brinkpoint and a planar slip face at the angle of initial yield which made an angular contact with the base of the flume for sand percentages in excess of 80 individual gravel clasts were completely supported by sand the original structural stability was lost so that the bar front eroded by reverse currents assumed a tangential contact with the flume base below the angle of initial yield the brinkpoint was rounded and indistinct in addition to altering the bar front slope increasing the quantity of sand in the bed sediments had a major influence on the dip of gravel particles on the foresets in all experimental runs a surface sand seal with openwork gravels beneath developed upstream of the brinkpoint the mechanics of sand seal formation require further investigation however an overpassing mechanism was noted to be very important in sorting gravel particles rolling over the brinkpoint a published mathematical model describing the overpassing mechanism was found to be appropriate to the present experimental observations

bar structure in an arid ephemeral stream abstract this study describes the structure of gravel bars in nahal zin an ephemeral stream in the negev desert the internal structure of the bars was examined along trenches and in shallow pits gravel sheets and unit bars form during transporting flow events in the main channel on intra bar channels and near bar heads unit bars are dominated by the go facies compound bars develop from accretion around and modification of unit bars compound bars are active under the current flow regime and the average depth of the fill layer is about 35 cm the structure of compound bars is dominated by gm massive containing large amounts of sand the second most common facies is clast supported openwork and well sorted sediments of the go pebbles facies bar formation and the development of the range of facies evident in the bars is controlled by sediment supply particularly the high volumes of sand sized sediment the passage of gravel sheets and bedforms during floods and the lateral and vertical instability of the channel repeated scour and fill events have produced a diverse arrangement of facies with numerous erosional contacts between depositional units lateral and downstream shifts in the pattern of scour and fill due to flow and antecedent conditions shape the channel morphology and bar internal structure ephemeral river bars differ from those of humid and proglacial rivers in terms of the dominant facies present the arrangement of the facies within the bars and the sedimentary structures developed within the depositional units and on the bar surface

calcification of cyanobacterial filaments girvanella and the origin of lower paleozoic lime mud the origin of lime mud in ancient shallow marine carbonate platforms is one of the most vexing mysteries in sedimentary geology possible sources previously suggested include the physical and biological disintegration of animal and algal bioclasts mineralizing pelagic organisms and spontaneous whitings from either abiotic precipitation or calcification of suspended picoplankton and organic matter the styles of occurrence of micrite walled tubes referred to girvanella in lower paleozoic limestones argue that occasional permineralization of mucilaginous sheaths of the benthic filamentous cyanobacteria precursor could have produced lime mud when the tubes fell apart estimated volumes are comparable to those calculated for the modern bahama platform the copious growth of cyanobacteria typical in shallow marine settings indicates that this mechanism could account for a considerable amount of lime mud especially in the early paleozoic

pleistocene sedimentary facies of the gran dolina archaeo paleoanthropological site sierra de atapuerca burgos spain abstract gran dolina is a cavity infill of the sierra de atapuerca containing three important early and middle pleistocene archaeo paleontological layers including hominid bones fauna and lithic remains due to the relevance of this site to understand human evolution in europe it is essential to define in detail the sedimentary processes and environments associated with the archaeological remains gran dolina has a 19 m thick sedimentary infill divided into 11 lithostratigraphic units in this work we describe the sedimentary facies of the early and middle pleistocene units and we update its stratigraphy for that purpose we have studied the stratigraphic excavation profiles available where we have combined field observations with laboratory sedimentary analysis sieving laser diffraction and image analysis to characterize the texture and structure of the sediments through these studies 19 sedimentary facies have been distinguished grouped as sediment gravity flow facies fluvial facies and autochthonous facies the facies associations indicate two main trends in the allochthonous sequence during the early pleistocene td4 td7 the cavity acted as a stream sink where channel and floodplain facies migrated along the sequence and were interbedded with lateral gravity sediment flows on the other hand the middle pleistocene sequence between td7 and td10 is dominated almost exclusively by gravity flows at least three main entrances have been inferred from input directions of the sediments which changed over time sediment characteristics have allowed us to preliminarily infer environmental conditions around the cavity

flow recession as a driver of the morpho texture of braided streams braiding has been widely studied in humid temperate climates though rarely in arid environments morpho texture of braided streams refers to the morphological textural organization in a braid cell stream section including bars anabranches and chutes that may strongly relate to different processes and hydrological regimes the objective of this study is to compare the morpho texture of braided streams governed by diverse flow recessions in different climates measurements were conducted in the wadis ze elim and rahaf southeast hyper arid israel in the mediterranean barranca de los pinos central spain and in humid temperate braided systems the la bleone river haute provence france and in the saisera and cimoliana torrents northeast italy terrestrial laser scanning was used to produce point clouds and high resolution digital elevation models of the braid cells wet braid cells in humid temperate environments were surveyed by a total station roughness and the upper tail of grain size distributions were derived from the scanned point clouds or from wolman sampling we found that anabranches are commonly finer grained than the bars in dryland systems and in semi arid sandy braided systems contrary to the humid temperate braided systems in both climates chutes are similar or coarser grained than the bars which they dissect in accordance with their steeper gradients due to the considerable bar anabranch relief the saisera s morpho texture is similar to that of the dryland braided channels despite the very humid temperate environment in which it is located due to its short lived ephemeral type hydrograph hydrograph shape specifically the duration of flow recession typical of a climate but not confined to it determines the morpho texture of braided streams and the textural differentiation between a depositional bar and the adjacent anabranches the morpho texture of chutes and bars results also from local erosional processes affected by local topography i e ungraded longitudinal profiles and is not solely determined by flow recession this new morpho textural model enables identifying primary depositional and erosional braiding processes copyright 2015 john wiley sons ltd

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

morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region abstract flows in ephemeral channels in semiarid areas are only occasional and channel changes are episodic but the flash floods can be devastating and have major geomorphological impacts data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels for this purpose nine reaches of river channel in three catchments in se spain the nogalte torrealvilla and salada have been sites for measurement of flows and their effects over the period 1997 2012 the sites encompass a range of channel size channel morphology substrate vegetation and position within the catchments a major difference is between schist and marl bedrock areas peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events over the 16 year period an average of 0 5 flow events per year has been recorded at the schist sites and an average of one per year at the marl sites but occurrence has been highly variable from year to year threshold daily rainfall for channel flow is mostly 15 20 mm but higher rainfalls do not always produce flow one to two major floods have occurred in each of the catchments in the period including the extreme flood event of september 2012 in the nogalte catchment measured morphological changes have occurred between 2 and 10 times at the monitored sites the same size flow can have differing effects depending on the state of the system low flow can mobilise sediment without producing much morphological change the long term trajectory of the reaches and the sediment substrate has a major influence on response to events channel change is governed by threshold values of hydraulic conditions the measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in management

origin of cross stratal layering in fluvial conglomerates devonian malbaie formation gaspe quebec planar cross bedded conglomerates in proximal braid plain deposits of the devonian malbaie formation of eastem gaspe quebec display a distinctive cyclic layering of three facies conglomerate with sand matrix a matrix free conglomerate in which the voids are filled by spany white calcite cement c and coarse sandstone b the sequence was previously interpreted as abc but is here reinterpreted as acb b forms cross strataparallel layers facies a and c together make up the gravel layers with c passing down foreset into a across a matrix cement interface which dips at low angles in the same direction as the foreset the sequence results from migration of gravel sand bed forms across bar tops with deposition of gravel at bar margins as foresets and infiltration of sand into the gravel fabric from blackflow currents induced by flow separation at the foreset crests infiltration proceeds until the framework voids are plugged by granules and coarser sand grains after which sand and granules may continue to accumulate on the plugged surface to form a discrete layer occasional peaks on the matrix open framework interface record sites of more effective infiltration elongate peaks strike parallel or downdip possibly reflect organisation of the sand load into npples across the foreset at the time of its infiltration or they may reflect regular variation in grain size or packing and hence ingress potential of the framework partial sequences in which one or another of the layers is missing apparently result from variation in the efficiency of sand transport up the foreset coupled with variation in the efficacy and timing of framework plugging or variable sorting in bar top bed forms

the non layering of gravel streambeds under ephemeral flood regimes abstract the two layer format common to perennial streambeds in which a relatively coarse armour overlies a finer subarmour develops as a function of both the ingress and subsequent near surface winnowing of interstitial material and the selective non entrainment or slower transport velocity of coarse clasts ephemeral streams appear to lack such vertical layering or are characterized by weak layer development some of this may be due to the degree of mixing associated with the scour and fill process however continuous monitoring of bedload discharge in the nahal yatir in the northern negev desert reveals that sediment transport rates are extremely high so that the chance of armour layer development through selective non entrainment is much reduced indeed a comparison of the bedload and bed material size distributions confirms a high degree of similarity and hints at equal mobility regardless of clast size the monitoring programme also indicates that the bed becomes highly mobile at comparatively modest fluid shear so that practically all floods are associated with high transport rates consequently the winnowing that might be brought about by low transport rate events does not occur even within a single event winnowing is precluded by the rapid nature of flow recession that is so characteristic of flash floods the high degree of bed material mobility is attributable in part to the lack of strength that would otherwise be a corollary of armour development however it also highlights the divergent nature of the feedback loops that govern the relationship between flow and channel deposit in ephemeral and perennial systems

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

substrate control of benthos in a middle cambrian near shore epeiric palaeoenvironmental setting late middle cambrian mail change limestone a thin b30 m lime mudstone unit of the epeiric middle and late cambrian georgina basin australia is unusually rich in epifaunal linguliform brachiopods especially acrotretids it is the only unit of this abundantly fossiliferous cambrian basinal succession where the representation of this group is more prolific than that of trilobites the diminutive size of acrotretids generally less than 3 mm in shell diameter in the case of common taxa from the mail change limestone raises questions of how an epizoic lifestyle was achieved on muddy substrates facies analysis indicates that lime mud substrates associated with deposition of the mail change limestone included microbial firm ground which developed in upper shoreface settings and ephemeral evaporate horizons of supratidal or high intertidal association during the shallow water phases of repeating parasequence cycles lime muds of shoreface association are brachiopod rich suggesting that firm ground substrates were favoured attachment sites for populations of anchoring epizoic acrotretids the conical shell form typical of this group evolved in part to minimize current drag reducing stress on pedicle attachment and in part to induce turbulence at the shell gape to facilitate feeding the high incidence of undamaged acrotretid valves representing a spectrum of growth stages obtained from the mail change limestone suggests that failure of pedicle attachment was a major contributor to mortality in this group firm ground was also characterised by ubiquitous fine scale planolites like open burrows which housed substantial populations of wormlike suspension feeders polychaetes which also took advantage of firm ground substrates near shore substrates were also host to suspension feeding lingulella and protospongia and a deposit feeder responsible for thalassinoides ichnofossils substrates associated with deposition of the mail change limestone were unfavorable to colonization by vagile seafloor feeding ptychopariid trilobites which are poorly represented in the unit in contrast agnostid trilobites of nektonic habit were less limited by trophic opportunities and are more commonly represented diverse agnostids ranged into very shallow marine shoreface environments represented by the mail change limestone the association of abundant epifaunal linguliforms and infaunal suspension feeders with firm ground suggests that substrate stability strongly influenced the nature and biomass of middle cambrian sessile benthos evolutionary strategies among sessile benthos to take full advantage of shallow marine level bottom environments were not realised until the ordovician biodiversity event

scour fill and burial depth of coarse material in gravel bed streams scour fill and burial depths of coarse particles were examined in two ephemeral streams using magnetically tagged particles and scour chains the burial depth varied within a bedform and from one bedform to another the maximum burial depth was recorded in bars but differences in the mean burial depth in the pools bar and thalweg were insignificant mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg more than eighty per cent of the tagged particles which were located on or close to the bed surface moved in each event although previously buried particles were moved by flood events others which were initially exposed remained stationary on the surface or were buried in situ the data indicate that the mean burial depth was intermediate between the mean depths of scour and fill deeply buried particles probably reflect the development of scour holes during flood flows aggradation and degradation changed the recorded burial depth relative to the local bed surface of stationary tracer particles these observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge

characteristics of gravel bars in ephemeral streams abstract bars are major sediment storage places within channels and much is known about their character from proglacial and temperate regions little is know however about bar characteristics from ephemeral streams this study describes the morphology and composition of simple and compound gravel bars in nahal zin israel an ephemeral desert stream a hierarchy of microscale mesoscale and macroscale structures and bed forms was identified in nahal zin that is similar to the hierarchy described for perennial streams while the hierarchy is similar between arid and perennial streams bar composition patterns are distinct compound bars and unit bars in humid areas are known to have armored surfaces composed of structured gravels whereas the bar surfaces of both unit bars and compound bars in nahal zin were found to lack surface structures and to contain a large amount of sand in ephemeral streams both accreted and dissected compound bars do not display any downstream fining in contrast downstream fining along bars in humid areas is well documented the flashy nature of floods high sediment supply high sediment transport rates and large amount of sand associated with the bars are likely reasons the surfaces were not armored in nahal zin erosion and accretion dominate the bar edges and accretion alone dominates the platform part of the bars in summary sediments in ephemeral streams of the nahal zin type are well mixed unsorted and unlikely to leave a well defined stratigraphic record these characteristics are distinct from their counterparts in proglacial and temperate regions and may be useful when investigating paleoenvironmental conditions

diagenetic nonevaporative origin for gypsum paleoenvironmental interpretations commonly cite the occurrence of gypsum associated with nonfossiliferous redbeds as evidence for arid conditions and high evaporation rates such interpretations ignore the common occurrence of gypsum in gossan on weathered black shale surfaces and especially in pleistocene glacial deposits glaciolacustrine deltaic sequences in ohio contain abundant large gypsum crystals that formed diagenetically as a result of oxidation of sulfides by calcium rich oxidizing ground water crystals display two forms related to the host sediment euhedral tabular crystals occur in pliable prodelta mud whereas bladed dovetail gypsum sand crystals occur in grain supported delta front sand the diagenetic non evaporative model could explain the formation of gypsum in numerous sedimentary sequences dune tidal flat beach lagoon reef lagoon deltaic and barrier bar lagoon massive extensive sulfate accumulations probably formed under arid conditions however the nonevaporative diagenetic model should be considered in the interpretation of scattered gypsum crystals and thin gypsum crusts

cambrian chronostratigraphy current state and future plans abstract important steps have been made by the international subcommission on cambrian stratigraphy iscs toward global chronostratigraphic subdivision of the cambrian the consensus of opinion is that the system should be subdivided into four series representing subequal spans of time the lower two series will correspond approximately to the traditional lower cambrian the third series will correspond approximately to the traditional middle cambrian and the fourth series corresponds approximately to the traditional upper cambrian the fourth series called the furongian series was ratified by the international commission on stratigraphy ics and the international union of geological sciences iugs in 2003 selection of horizons representing evolutionary events that can be correlated on a global scale and which can be used as stage or series boundaries is much more difficult for the lower two series intervals of the cambrian than it is for the upper two series intervals of the cambrian the most practical concept for subdividing the system into stages involves the establishment of two stages each for the first and second series and the establishment of three stages each for the third and fourth series the lowermost stage of the furongian called the paibian stage has been ratified by the ics and the iugs

morphotextural characterization of dryland braided channels braided streams have been extensively studied in humid environments or in flumes that simulate them dryland rivers have bare catchments rapid recession hydrographs and unarmored beds resulting in high bed load discharges our objective was to characterize the morphotexture of the morphological elements bar anabranches chutes and confluences in a dryland braided system morphological elements measured in wadis ze elim rahaf and roded located in southeast israel were scanned using terrestrial laser scanning from which digital elevation models were generated roughness was evaluated from the standard deviation of detrended surfaces or from wolman sampled surface texture armoring of the bar and the adjacent anabranch was also evaluated scour chains were deployed in confluences to measure scour and fill during flow events dryland anabranches were finer grained and less armored than the adjacent bars bed load deposited as midchannel bars or on top of existing bars and thus associated with the depositional braiding process was enriched by the coarser fractions while the remaining bed load was deposited in the anabranches during the rapid flow recession chutes associated with erosional braiding processes were formed as topographic features with high local gradients enabling winnowing of fines deposited immediately downstream or transported further away scour chains inserted in the confluence zones demonstrated the formation and obliteration of a scour hole during a flow event the terrestrial laser scanning based digital elevation models and roughness analyses suggest that the hydrological regime of ephemeral channels with short lived recessions is responsible for the morphotextural setting of braid systems in arid environments

observations of desert flood bores flood bores have been measured in desert stream floods the bores were steep and small pebbles were observed to be pushed ahead bore velocity changed downstream and was controlled by local channel geometry in narrow reaches the bore advanced at rates twice those of wide reaches mean bore velocity was about 50 per cent of that of mean flow at peak flood discharge the surfaces of shallow bores were covered by air foams this was not the case in deeper faster examples

experiments on the effect of hydrograph characteristics on vertical grain sorting in gravel bed rivers 1 desert ephemeral gravel bed streams typically have bed surfaces that are relatively unarmored compared to the substrate below while gravel bed streams in humid and snowmelt areas typically have well armored surfaces the degree of armoring can be characterized in terms of an armor ratio defined as the ratio of the surface median size to the substrate median size a set of field data shows desert ephemeral gravel bed streams with armor ratios ranging from 0 5 to 2 4 and with an average value of 1 2 the armor ratio of snowmelt fed gravel bed streams in the same set ranges from 2 to 7 with an average value of 3 4 the reason for this difference is sought in terms of differing hydrological characteristics and sediment supply regimes thirteen experiments were conducted to study the formation of armoring under a range of hydrological conditions the experiments have two limiting cases a relatively flat hydrograph that represents conditions produced by continuous snowmelt and a sharply peaked hydrograph that represents conditions associated with flash floods all constant hydrograph experiments developed a well armored structured surface while short asymmetrical hydrographs did not result in substantial vertical sorting all symmetrical hydrographs show some degree of sorting and the sorting tended to become more pronounced with longer duration sediment supply appears to be a first order control on bed surface armoring while the shape of the hydrograph plays a secondary role

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

proximal braidplain deposits in the middle devonian malbaie formation of eastern gaspe quebec canada the middle devonian malbaie formation of eastern gaspe canada comprises sharply alternating conglomerate and sandstone units their petrography suggests derivation from the same source but palaeocurrents indicate different dispersal systems for the sand and gravel the principal conglomerate facies is horizontally stratified with well developed imbrication characteristic of deposition on a high energy proximal braidplain minor cross stratified conglomerate shows well defined size sorting attributed to avalanching down foresets and sorting within minor bedforms on bar tops the sandstone units mainly comprise erosion surfaces overlain by mudstone intraclasts alternating with lineated low angle to horizontally stratified sandstone or trough cross stratified sandstone the sandstone units were deposited on a proximal braidplain with highly variable discharge but the absence of calcrete indicates that dry periods were not prolonged the malbaie is the coarsest uppermost formation of a devonian clastic wedge formed during the acadian orogeny the uniformity of facies association and palaeocurrents particularly in conglomerate units indicates derivation from a broad upwarp to the south this implies that the acadian uplands resulted from straight compression in contrast to the localized uplifts formed by strike slip faulting during the carboniferous

an opportunity to connect the morphodynamics of alternate bars with their sedimentary products field investigations that help clarify local sedimentary processes involved in the migration of alternate bars as a consequence of flood events are lacking a simple approach combining scour chains stratigraphy and frequent bathymetric surveys is proposed to connect the dynamics of free migrating alternate bars present in disconnected channels of large sandy gravelly rivers with their sedimentary products and vice versa the results show that the spatial distribution of bars before a flood partly governs the scour and fill processes and that the sediment transport rates vary significantly on a single cross section this can be due to preferential axes of the migration of the bars determined by their location on the cross section the bank direction and the discharge the approach allows the reconstruction of local sedimentary processes involved in alternate bar migration by combining maximum scour depths reached during a flood with frequent channel bed topography surveys and post flood stratigraphy it is also possible to distinguish deposited and preserved sediments compared with sediments by passed during the flood copyright 2011 john wiley sons ltd

sequence stratigraphy cyclic facies and lagerstatten in the middle cambrian wheeler and marjum formations great basin utah abstract recurrent taphofacies including conservation lagerstatten are identified within a spectrum of facies in fourth order sequences in the middle cambrian wheeler and marjum formations of the drum mountains and house range west central utah these sequences are 3 20 m thick and commence with sharply based compact oncolitic oolitic or pelletal pack and grainstones with sharply defined corroded and mineralized upper contacts that record drowning discontinuities and early transgressive systems tracts tsts overlying intervals of calcareous shale and thin bedded wacke to packstones with abundant disarticulated polymerid and agnostoid trilobites represent late tsts these are commonly followed by lavender gray mudstones rich in sponge spicules and comminuted fossil debris that reflect condensed maximum flooding zones the overlying early highstand hst intervals of black fissile shales are typically barren except for indistinct circular carbonized algae but in rare instances include soft bodied animal remains a combination of lower dysoxic anoxic conditions with a fluctuating oxycline and relatively rapid episodic influx of fine grained detrital sediment favored repeated burial and preservation of abundant organic detritus and rarely soft bodied animals interbedded dark gray shales include abundant articulated agnostoid trilobites and diminutive polymerids e g jenkinsonia overlying platy calcareous bedding planes covered with articulated bodies and molts of the polymerid elrathia indicate rapid blanketing of undisturbed seafloors by calcareous mud layers these beds grade upward successively into interbedded sparsely fossiliferous platy to flaggy shale and thin pale gray weathering calcisiltites and burrow mottled to nodular limestones recording late hst to falling stage fsst carbonate shedding thin calcisiltites include fossil debris and articulated larger polymerid trilobites and the eocrinoid gogia preserved by obrutionary deposits the repeated recurrence of these patterns provides the rudiments of a predictive model that not only explains the differing modes of preservation but may also aid in prospecting for new lagerstatten

internal structure and depositional environment of late carboniferous mounds from the san emiliano formation carmenes syncline cantabrian mountains northern spain well exposed mounds are common in limestone of the late carboniferous san emiliano formation cantabrian mountains northern spain they occur as obvious primary topographic features careful study of the mound intervals and surrounding strata revealed the internal structures of mounds and the factors controlling their growth the substrate 2 3 m of the mounds consists of greyish to reddish bedded oolitic and oncolithic packstone and grainstone crinoids fragments of the alga epimastopora and rarely bryozoans are present ooids and oncoids indicate a wave dominated high energy environment presence of quartz indicates the influence of terrigenous siliciclastic input mound intervals 6 12 m thick are characterized by skeletal microbial boundstone donezellid algae agglutinated worm tubes and calcisponges are the dominant fossils smaller foraminifers gastropods and brachiopods are also present a peloidal clotted matrix is characteristic and accounts for more than 30 of the mound volume intraframe pores are mainly filled by peloidal sediment and early marine cement intermound strata are approximately one third as thick as time equivalent mounds mound fossils algae agglutinated worm tubes and sponges are uncommon however intermound strata are generally more diverse than the mounds containing fusulinids smaller foraminifers bryozoans gastropods crinoids and bioclasts some of these fossils have micritic envelopes bedded packstone and grainstone 3 6 m thick with siliciclastic debris rugose corals and chaetetid sponges characterize the capping facies coated grains and small ooids are uncommon this facies indicates shallowing to a higher energy environment and or a higher input of siliciclastics inhibiting mound growth mounds are interpreted to have accreted in a quiet environment below wave base this position is comparable to the depositional environment inferred for many late paleozoic mounds described elsewhere e g from texas and new mexico canadian archipelago and carnic alps in austria mound relief is explained by 1 accumulation of peloidal clotted sediments limited to boundstone and probably related to microbial activities 2 widespread marine cementation within this area and 3 low export of mound fossils to intermound areas the position of the mounds within the sequence and their initiation size and termination seem to be mainly controlled by sea level fluctuations and siliciclastic input d 2001 elsevier science b v all rights reserved

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

bed clusters in humid perennial and mediterranean ephemeral gravel bed streams the effect of clast size and bed material sorting summary a short review of the literature on particle clusters on gravel river beds reveals investigations of both process and form dominated by the intensive study approach using a restricted geographical sample or evidence from flumes an alternative presented here is extensive sampling from three climatic zones several channels in each and at multiple transects at each site it uses insights provided by a more intensively studied base station wittenberg l newson m d 2005 particle clusters in gravel bed rivers an experimental morphological approach to bed material transport and stability concepts earth surface processes and landforms 30 11 1351 1368 transect surveys were completed in each selected reach to establish flow depth bed material size and bed structure a total of more than 5000 sample points reveals the vital presence of bed material of 100 mm d50 for all sub types of clusters to occur thereafter cluster frequency relates directly to the d90 with an improving correlation at d90 256 mm a better integration of data from the diverse hydrological hydraulic regimes can be achieved by correlating cluster frequency with a sorting index for bed material further analysis of hydrological and hydraulic data for all sites is required to develop a dynamic explanation

δ34s of lower carboniferous anhydrite cumbria and its implications for barite mineralization in the northern pennines recent hydrocarbon exploration in the solway basin has revealed the existence of lower carboniferous paralic sediments which contain numerous discrete anhydrite beds anhydrite s isotope ratios from the easton 1 well are compared with new isotopic data from barite mineralization that occurs along the faulted southern margin of the northumberland solway basin and published data from the northern pennine orefield similarities betw een the 34 s of anhydrite and barites from major mines at haydon bridge and the alston district of the northern pennine orefield supports a lower carboniferous marine sulphate source for mineralization at these sites identification of extensive evaporite deposits hi the solway basin resolves several longstanding problems associated with mineralization hi the northern pennines including the source of barite sulphate and the origin of hypersaline mineralizing fluids in an earlier investigation of the s isotope geochemistry of carboniferous hosted barite mineralization in and around the alston district of thenothern pennine orefield npo fig 1a solomon et al 1971 drew attention to the similarity between the 34 s of lower carboniferous marine sulphate and the sulphur isotopic composition of barite deposits a model for barite mineralization was proposed in which deep circulating bacl 2 brines mixed with shallow et al 1971 is consistent with aspects of barite mineralization more recent studies of the evolution of pore fluid geochemistry in sedimentary basins land 1987 hanor 1994a b argue against a marine connate origin for the sulphate component

depositional character and preservation potential of coarse grained sediments deposited by flood events in hyper arid braided channels in the rift valley arava israel abstract four coarse grained braided channels undergoing rapid deposition in the hyper arid arava rift valley have been studied to determine the dynamics of strata deposition by monitored flood events and to ascertain the sedimentologic character of these event deposits the systems span granule sand to sandy gravel bed material having longitudinal bars with simultaneously increasing grains size slope and bed relief scour and fill were monitored along cross sections using scour chains and repeat surveys while event strata fill were described with reference to sediment calibre type of support grading thickness and location unlike many previous investigations of gravel sedimentology the source of information for this study involves not only stratigraphic description but also observation of the concomitant dynamics of the channel bed as expressed by the extent of event deposition the texture of the deposited sediment generally coarsens in sympathy with the surface bed texture of the studied channels the thickness of event deposited sediments increases as the magnitude of flow events increases the stratigraphic record is characterized by 1 sub parallel stratification 2 no grading 3 clast supported gravel infilled with sand granule matrices and 4 rapid sedimentation rates this character is hypothesized to mirror the elevated bedload fluxes in this hyper arid fluvial setting lacking densely vegetated banks the proximal braidplain of this arid environment often contains no extensive fine textured floodplain successions the depth of fill as well as the extent of strata obliteration increase with flood magnitude explaining the increased preservation potential of event strata with increase in flood magnitude it also explains why most event strata including large ones are only partially preserved

unit bar architecture in a highly variable fluvial discharge regime examples from the burdekin river australia unit bars are relatively large bedforms that develop in rivers over a wide range of climatic regimes unit bars formed within the highly variable discharge burdekin river in queensland australia were examined over three field campaigns between 2015 and 2017 these bars had complex internal structures dominated by co sets of cross stratified and planar stratified sets the cross stratified sets tended to down climb the development of complex internal structures was primarily a result of three processes i superimposed bedforms reworking the unit bar avalanche face ii variable discharge triggering reactivation surfaces and iii changes in bar growth direction induced by stage change internal structures varied along the length and across the width of unit bars for the former down climbing cross stratified sets tended to pass into single planar cross stratified deposits at the downstream end of emergent bars such variation related to changes in fluvial conditions whilst bars were active a hierarchy of six categories of fluvial unsteadiness is proposed with these discussed in relation to their effects on unit bar and dune internal structure across deposit variation was caused by changes in superimposed bedform and bar character along bar crests such changes related to the three dimensionality of the channel and bar geometry when bars were active variation in internal structure is likely to be more pronounced in unit bar deposits than in smaller bedform for example dune deposits formed in the same river this is because smaller bedforms are more easily washed out or modified by changing discharge conditions and their smaller dimensions restrict the variation in flow conditions that occur over their width in regimes where unit bar deposits are well preserved their architectural variability is a potential aid to their identification this complex architecture also allows greater resolution in interpreting the conditions before and during bar initiation and development

formation and evacuation of a large gravel bar deposited during a major flood in a mediterranean ephemeral stream nahal me arot nw israel abstract an unusual 240 mm rainstorm and a consequent major flood peak discharge 110 m 3 s 1 with an estimated recurrence interval of about 50 years occurred on dec 31 1998 in nahal me arot an ungauged 25 km 2 coastal ephemeral stream in mt carmel nw israel the flood caused morphological modifications along the channel including intensive stripping of the channel bed and floodplain along several segments and deposition of large gravel bars downstream of these segments one of such segments served as a study reach composed of a massive 1270 m 3 coarse 200 m long gravel bar formed downstream of a segment 150 m long that was deeply scoured the study reach was carefully mapped cross sections and driftwood lines allowed the calculation of the hydraulic parameters and peak flow using the slope area method the bar s sedimentological characteristics such as surface and substrate texture and stratigraphy were studied in detail using a survey of 15 pits the initial recovery of the channel started when dense low shrub vegetation re stabilized along the affected reaches a year later two smaller floods 3 and 4 years later evacuated and reworked the sediment until it lost most of its volume the study suggests that the flood s large impact and disturbance was local short lived and the channel almost returned to its pre flood state within about 4 years