bed material transport estimated from the virtual velocity of sediment this study evaluates the possibility of determining bed material transport using the virtual rate of travel of individual particles dimensions of the active layer of the streambed and porosity and density of streambed material magnetically tagged stones and scour indicators were employed in carnation creek british columbia to quantify transport rates observations cover flows up to 36 m3 s 1 0 081 transport rates ranging from 0 090 to 9 7 kg s 1 0 12 13 2 m3 h 1 display a relatively sensitive trend with maximum stream power as expected error analysis indicates that uncertainty in virtual velocity covers the majority of sample variance an evaluation of the two measurement techniques used to delineate active layer dimensions magnetically tagged stones and scour indicators indicates that they yield comparable depths widths and transport rates over the range of flows observed issues for further study are discussed 1998 john wiley sons ltd

sequence stratigraphy of the neoproterozoic infra krol formation and krol group lesser himalaya india a bstract a sequence stratigraphic study of terrigenous and carbonate rocks of the infra krol formation and krol group in the lesser himalaya fold and thrust belt of northern india was undertaken as part of a broader investigation of the significance of carbon isotope data in neoproterozoic successions eight regional stratigraphic discontinuities were traced over a distance of nearly 300 km and interpretations were anchored in a series of local studies involving the mapping of key beds and the measurement of closely spaced sections three of the regional surfaces are interpreted as sequence boundaries on the basis of 1 locally developed incised valleys 60 m deep 2 paleokarstic depressions with 50 m of mappable relief 3 subaerial dissolution and weathering products breccias and calcrete filling vertical fissures dikes cavities and shallow de pressions in underlying carbonate rocks and 4 small scale evidence for sub aerial exposure at an erosion surface the remaining five discontinuities are regional flooding surfaces identified on the basis of either facies changes with an abrupt upward deepening across the surface or transitions in facies stacking patterns typically from forestepping to backstepping a glacio eustatic origin is permitted although not required for the three sequence boundaries but no evidence has been found for marked lowering of sea level at other horizons a mismatch between the stratigraphic location of sequence boundaries and car bon isotope minima suggests that local diagenetic alteration or oceanographic phenomena unrelated to glaciation may be in part responsible for observed isotopic variation and that small ice sheets may have existed during apparently nonglacial times without producing either cap carbonates or negative carbon isotope excursions

particle path characteristics at the large gravel bed river danube results from a tracer study and numerical modelling a tracer study performed on a 3 km long reach of the danube river in austria is presented forty artificial stones of three different sizes intermediate b axis 25 mm 40 mm 70 mm were produced and a coded radio acoustic transmitter was implanted the measurement system had to be improved to be applicable to large rivers with water depths up to 12 m the positions of the stones were observed approximately once a week depending on hydrology over a period of at least one year by radio tracking from a boat including a 15 year flood event transport paths and velocities as well as the incipient motion of bedload transport could be monitored for the first time on a large gravel bed river the particle paths were found to be mostly bankline parallel even though the stones passed a 30 river bend the median of the transverse particle displacement was found to be 4 of the longitudinal displacement calculations considering both transverse slope and transverse flow velocities showed transverse transport to be 6 6 of the longitudinal transport indicating that marginal lateral transport is mainly influenced by morphology a three dimensional 3d numerical model using a stochastic particle tracing approach was validated with the data indicating that the observed positions are well reproduced by the model within the observation period 74 of all stones passed the reach with more than 1000 detections particle transport could be characterized by a mean travel velocity of about 10 m per day variable for the different grain sizes single tracer stones were transported up to 1000 m during a single flood event size selective behaviour could be shown and the incipient motion of the large 70 mm gravel was detected at lower discharges than predicted by commonly used uniform bedload transport formulae copyright 2012 john wiley sons ltd

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

cretaceous deformation in the western foothills of the sierra nevada california deformation of metamorphic rocks the tonalite of blue canyon several bodies of granite and granodiorite and the leucotonalite of ward mountain within an area of about 600 km 2 in the western foothills of the sierra nevada just south of the south end of the western metamorphic belt is attributed to emplacement of the leucotonalite in a nearly solid state the east flanks of two plutons of leucotonalite of ward mountain in the west central part of the deformed area dip gently beneath the area of deformed rocks whereas their west flanks are vertical or dip steeply east cata clastic planar and linear structures in the metamorphic rocks and in the tonalite of blue canyon form coherent and related patterns the planar structures generally strike parallel to contacts with the leucotonalite and dip outward between the two plutons of leucotonalite they form a synform lineations generally plunge outward from the leucotonalite but trend parallel to contacts within the synform heat and possibly volatiles that accompanied emplacement of the rising and westward moving mass of leucotonalite may have increased the susceptibility of the overlying rocks to attenuate normal to the planar structures and to stretch in the direction of the linear structures isotopic u pb and k ar determinations indicate that the age of the tonalite of blue canyon is about 114 m y and that the age of the leucotonalite of ward mountain coincides with the time of deformation at about 113 m y ago the isotopic age of the granodiorite of knowles which truncates cataclastic structures in the tonalite of blue canyon and the leucotonalite of ward mountain is 110 m y

enigmatic origin of the largest known carbon isotope excursion in earth s history carbonate rocks from the middle ediacaran period in locations all over the globe record the largest excursion in carbon isotopic compositions in earth history this finding suggests a dramatic reorganization of earth s carbon cycle named the shuram excursion for its original discovery in the shuram formation oman the anomaly closely precedes impressive events in evolution including the rise of large metazoans and the origin of biomineralization in animals instead of a true record of the carbon cycle at the time of sedimentation the carbon isotope signature recorded in the shuram excursion could be caused by alteration following deposition of the carbonate sediments a scenario supported by several geochemical indicators however such secondary processes are intrinsically local which makes it difficult to explain the coincident occurrence of carbon isotope anomalies in numerous records around the globe both possibilities are intriguing if the shuram excursion preserves a genuine record of ancient seawater chemistry it reflects a perturbation to the carbon cycle that is stronger than any known perturbations of the modern earth if however it represents secondary alteration during burial of sediments then marine sediments must have been globally preconditioned in a unique way to allow ordinary and local processes to produce an extraordinary and widespread response

coarse sediment movement in the vicinity of a logjam in a neotropical gravel bed stream wood influences channel morphology by increasing channel roughness altering flow hydraulics and decreasing sediment transport in most fluvial systems where it is present in many locations the collection of wood into jams leads to even greater interruption of sediment transport by means of sediment impoundment and the creation of low velocity backwater flow zones we examined tracer clast movement near a wood jam in a neotropical gravel bed stream in order to evaluate the effect of wood mobility and piece transience on the ability of the jam to impede sediment transport we found that the jam had minimal influence on the passage of any individual clast with tracer clast mobilization and travel distance being best predicted by flow magnitude and grain size rather than location relative to the jam the rate of clast passage through the jam did not correlate with either the piece retention rate of the jam or with the density of the jam the jam did however temporarily trap a sediment wedge during a period when fluvially imported wood pieces blocked flow under a key wood piece diverting flow to a secondary flow path these results suggest that there is an upper bound on the flows in which wood is able to disrupt sediment transport and unlike for bedrock roughness elements this bound is frequently crossed at our study site

carbonate platform development in a paleoproterozoic extensional basin vempalle formation cuddapah basin india abstract sedimentological investigation of the late paleoproterozoic orosirian vempalle formation of the cuddapah basin dharwar craton india reveals three facies association that range from supratidal to deep subtidal sedimentary rocks of this succession are dominated by heterolithic carbonate mudstone intraformational carbonate conglomerate and a variety of columnar domal and stratiform microbialite facies deposition occurred in an extensional regime during development of a low gradient ramp where the distribution of microbialite facies is distinctly depth partitioned a gradual increase in synoptic relief of columnar stromatolites through the section and the upward transition from stratiform to columnar microbialites record a prolonged marine transgression with little or no influx of terrigenous detritus siliciclastic influx along the northeastern side of the shelf reflects the redistribution of topographic highs concomitant with large scale volcanic activity redistribution of topographic highs eventually led to progradation of peritidal facies and shutting down of the carbonate factory earthquake induced ground shaking and voluminous volcanism experienced by this platform point to the reactivation of a deep seated mantle plume that resulted in thermal doming of the dharwar crust prior to the onset of cuddapah deposition isotopic and elemental chemistry of a selection of vempalle formation carbonate rocks record elevated mn2 and fe2 concentrations and depleted carbon isotope values in inner ramp lagoonal facies relative to more open marine stromatolitic facies patterns of isotopic and elemental variation suggest the presence of geochemically distinct water masses either within the water column or within substrate pore fluids that resulted from a combination of globally low marine oxygenation and restricted oceanographic circulation in inner ramp environments these data suggest that even in the aftermath of early paleoproterozoic oxygenation that ocean chemistry was heterogeneous and strongly affected by local basin conditions

wildfire morphologic change and bed material transport at fishtrap creek british columbia abstract in 2003 a wildfire burned nearly two thirds of the fishtrap creek watershed including the forested floodplain annually repeated surveys of the stream channel combined with bed material tracer studies in 2006 and 2007 indicate that the channel has become unstable and that the bed material transport dynamics have changed since the fire using these data the morphologic changes have been quantified and event scale bed material transport rates have been estimated for four post fire freshets the immediate response of the channel during the 2005 and 2006 freshets was a progressive shift in channel morphology from a relatively featureless plane bed morphology devoid of significant sediment accumulations to a riffle pool morphology in which bars cover a significant proportion of the bed this transformation occurred in association with moderate bed material sediment transport rates and only minor bank erosion within the study reach extensive bank erosion occurred during the 2007 and 2008 freshets producing a dramatic change in channel morphology and increasing the local bed material transport rates by an order of magnitude post fire monitoring of streamflow and suspended sediment concentrations a surrogate for upstream sediment supply indicates that post fire increases are not detectable presented in eaton et al in press and our analysis demonstrates that major morphologic changes can occur following wildfire even when the common external drivers of stream discharge and sediment supply remain unchanged

tightening the siberian connection to western laurentia newly available geological and geophysical data tighten the proterozoic connection between the rifted margins of the northern siberian craton and western laurentia and permit a siberia laurentia australia troika with northern australia connected to the southern margin of the siberian craton the continental assembly is linked by a prominent 2 0 1 8 ga collisional belt and the ca 1 3 1 0 ga grenville orogen the reconstruction also aligns a 1 5 1 45 ga dike sill swarm that extends from the wyoming province through the belt purcell basin into the northern siberian craton separation of australia and siberia may have occurred by the early neoproterozoic but separation of siberia and laurentia may not have been completed until the early cambrian continental extension began along the zigzag siberia laurentia rift zone in the early mesoproterozoic rift related igneous and sedimentary assemblages dated at ca 1 5 1 38 and 1 2 to 1 0 ga correlate across the reconstructed siberia laurentia rift zone renewed rifting in the neoproterozoic and vendian culminated with seafloor spreading and thermal subsidence of the conjugate rift shoulders correlative archeocyathan reefs endemic olenellid trilobite fauna and exchange of detritus between the cratons imply that the rift may have remained relatively narrow until the atdabanian stage black sulfidic shales buried the archeocyathan reefs on the rapidly subsiding rift margins during the botomian sinsk event

distance of movement of coarse particles in gravel bed streams distributions of distance of bedload particle movement were examined in two gravel bed streams using several hundred magnetically tagged cobbles and pebbles the compound poisson model of einstein hubbell sayre and a simple gamma function model were compared with observed distributions of moved particles and of all particles both models fit the data reasonably well for small mean displacements but notable misfits occurred in an event with large mean displacement when mean particle travel distance approaches the scale of bar spacing trapping in the bars interrupts particle progress and the dispersion process the data remain very noisy so definitive discrimination of suitable models will require trials with more than 103 particles

influence of bed patchiness slope grain hiding and form drag on gravel mobilization in very steep streams steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers despite their importance key unknowns remain perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low gradient rivers to address this knowledge gap we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment patch development in five small drainage areas of 0 04 2 km 2 and steep slopes of 5 37 tributaries of elder creek california united states we found that channel beds organized into size sorted sediment patches which displayed active fluvial transport of gravel annually consistent year to year patch median grain sizes partial transport of bed material and significantly higher values of critical shields stress for incipient sediment motion compared to that observed for lower gradient rivers the high critical shields stresses up to 0 5 for the median grain size agree within a factor of 3 to theoretical predictions which account for slope dependent hydraulics grain hiding and sediment patches for grains of approximately the same size as the roughness length scale slope dependent hydraulics and bed patchiness are the dominant controls on critical shields stress values while grain hiding is important for grains larger or smaller than the roughness length scale form drag exists in our monitored tributaries but has a smaller influence than the above effects our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows

response of a gravel bed river to dam closure insights from sediment transport processes and channel morphodynamics this work deals with the impacts of dams on large gravel bed rivers in terms of altering coarse transport regimes and the relationship with river morphodynamics using data collected by a tracer based monitoring program carried out in a 4 km long study sector of the parma river italy located downstream from a relatively recently established dam we applied a virtual velocity approach to estimate the coarse bed material load at four river cross sections monitoring and calculation results provided new insights into the impacts of the dam on streambed material mobility and the sediment regime over the 17 month calculation period a longitudinal gradient of effects was observed along the study sector sections located closer to the dam are characterized by more evident impacts due to deficits in coarse sediment input from upstream sediment mobility here is strongly altered especially in the highly armored main channel and the overall bed material load is extremely low a partial recovery of sediment dynamics was observed at the sections located further from the dam where estimates indicate higher sediment yield the observed longitudinal trend in the coarse sediment transport regime matches the morphology as the river shifts downstream from a sinuous configuration with alternate bars to a wandering one the novel insights into alteration of coarse sediment dynamics and the relationship with river morphodynamics are potentially applicable to many other fluvial contexts affected by similar impoundments

integrated ediacaran chronostratigraphy wernecke mountains northwestern canada abstract terminal neoproterozoic ediacaran ca 600 543 ma strata of the upper part of the windermere supergroup are well exposed in the mackenzie mountains and the wernecke mountains of northwestern canada windermere strata in the mackenzie mountains contain an exceptional ediacaran biostratigraphic and isotopic c and sr record while the sequence stratigraphic record is subtle throughout this predominantly deep water succession coeval strata in the wernecke mountains can be correlated with the succession in the mackenzie mountains on a formational level in contrast to the deep water setting of the mackenzies succession the werneckes succession preserves a predominantly shallow water succession amenable to detailed sequence stratigraphy integrated lithostratigraphy chemostratigraphy biostratigraphy and sedimentology partitions the wernecke mountains succession into five depositional sequences and constrains correlation with strata in the mackenzie mountains the siliciclastic and carbonate sediments deposited along the margin of the proto pacific ocean record accumulation in continental slope neritic and terrestrial paleoenvironments distinctive temporal chemostratigraphic and biostratigraphic attributes allow these strata to be correlated with other ediacaran successions worldwide integrating sequence stratigraphy with these attributes is a robust yet under utilized correlation tool and is a step toward erecting a more detailed working neoproterozoic chronostratigraphy

microbialite sediment interactions on the slope of the campbellrand carbonate platform neoarchean south africa abstract microbialite resedimented dolostone cycles form a prominent part of slope facies for the 2 6 2 5 ga campbellrand carbonate platform transvaal supergroup south africa microbialites are typically transitional between four end members 1 cuspate microbialites 2 plumose microbialites 3 stratiform domal and columnar microbialites and 4 incipient microbialites resedimented facies include 1 dolarenites 2 massive to laminated dolostones 3 dolomite laminites and 4 lumpy dolostones with roll up structures on a cm and dm scale microbial and resedimented facies are arranged into symmetric or asymmetric microbialite cycles with resedimented facies commonly grading upward into microbialite facies cycles are transitional between a microbialite dominated end member with almost no evidence for clastic carbonate sedimentation and a sediment dominated end member where microbialite relief is strongly subdued and resedimented carbonate makes up most of the cycle thickness the microbialite dominated cycles are remarkably uniform on the platform slope systematic variation in cycle architecture leads to dm scale stacked microbialite cycles which in turn form the main building blocks of m thick microbial units on the scale of decameter thick sequences microbial units pass upwards to progressively thicker units dominated by resedimented slope carbonates microbialite cycles show a distinct inverse relationship between the development of microbial structures and the abundance of detrital carbonate sediment in cycles thus cyclicity is interpreted as primarily controlled by variations in sediment influx on the largest scales sediment influx may be controlled by sediment export off the platform margin and upper slope which was influenced by sea level change due to the deep depositional environment and stratigraphic distribution of cycles dm scale cycles are interpreted as primarily controlled by allocyclic processes

size and distance of travel of unconstrained clasts on a streambed we have examined the relation between the mean distance of movement during individual flood events and the mean particle size of unconstrained clasts in gravel bed rivers distance of movement was scaled using the mean distance of movement of the median size group of the surface material size was scaled using the median b axis diameter of the subsurface material the scaled data are fitted with a nonlinear function clasts larger than the median of surface material exhibit a steep decline of mobility with an upper limit for mobility near di d50sub 10 smaller materials exhibit a less sensitive relation we suppose that trapping of small clasts affects their travel distance these results indicate that the movement of free surface stones is size preferred a subordinate analysis of free constrained and buried particles reveals that bed surface structure acts to reduce differential movement

redox dependent distribution of early macro organisms evidence from the terminal ediacaran khatyspyt formation in arctic siberia abstract the ediacaran period witnessed the first appearance of macroscopic animal life in earth s history however the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain in part due to the dearth of integrated paleobiological and chemostratigraphic datasets in this study a comprehensive geochemical analysis was conducted on the fossiliferous khatyspyt formation in arctic siberia in order to gain insights into the ediacaran paleoenvironments this study was designed to specifically address the relationship between paleoredox conditions and ediacaran fossil occurrences in the khatyspyt formation our data reveal a dramatic shift in pyrite sulfur isotope compositions 34 s pyrite from ca 20 to ca 55 and this shift is intriguingly associated with the first occurrence of ediacara type macrofossils at the studied section suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms based on multiple lines of sedimentological and geochemical evidence we propose that the development of oceanic euxinia which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal ediacaran period may have locally prohibited the colonization of ediacara type organisms and resulted in low 34 s pyrite values in the lower khatyspyt formation in the middle and upper khatyspyt formation progressive secular transition from euxinic to non euxinic and more habitable conditions may have allowed for the colonization of ediacara type and other macro organisms

coarse sediment transport in a bedrock channel with complex bed topography 1 independent lithologic and structural controls in fluvial bedrock systems interact with coarse sediment transport processes to play a key role in bedrock incision processes such as abrasion during a 3 year study on the ocoee river in the blue ridge province of the southern appalachians usa we used painted tracer clasts to measure coarse sediment transport dynamics and address whether different scales of morphologic variability in bedrock channels lead to coarse sediment transport processes that differ from alluvial channels at the reach scale folded metasedimentary units are exposed in the channel bed and appear as linear bedrock ribs that vary in amplitude and orientation to flow under similar flow conditions for which size dependent transport has been observed in alluvial channels dimensionless shields stress within 1 5 2 0 times the dimensionless critical shear stress transport distance was a significant function of grain size where bedrock ribs were longitudinal to flow reach 1 and reach 2 however transport distance was not size dependent where bedrock ribs were oblique to flow reach 3 at different intrareach scales the variables characterizing the local bedrock topography and sediment architecture were the best predictors of transport distance in all three reaches therefore bed load transport processes may be influenced by bed forms in bedrock streams bedrock ribs but at potentially smaller scales than bed forms in alluvial channels the strong influence of bedrock ribs on coarse sediment transport suggested that coarse sediment transport processes are controlled by different factors in bedrock channels only when bedrock ribs cross the channel at a high angle to the flow

fluvial erosion transport equation of landscape evolution models revisited we present a mesoscale erosion deposition model which differs from previous landscape evolution models equations by taking explicitly into account a mass balance equation for the streamflow the geological and hydrological complexity is lumped into two basic fluxes erosion and deposition and two averaged parameters unit width discharge q and stream slope s the model couples the dynamics of streamflow and topography through a sediment transport length function x q which is the average travel distance of a particle in the flow before being trapped on topography this property reflects a time lag between erosion and deposition which allows the streamflow not to be instantaneously at capacity the so called x q model may reduce either to transport limited or to detachment limited erosion modes depending on x but it also may not we show in particular how it does or does not for steady state topographies long term evolution and high frequency base level perturbations apart from the unit width discharge and the settling velocity the x q function depends on a dimensionless number encompassing the way sediment is transported within the streamflow using models of concentration profile through the water column we show the dependency of this dimensionless coefficient on the rouse number we discuss how consistent the x q model framework is with bed load scaling expressions and einstein s conception of sediment motion

thresholds of erosion and sediment movement in bedrock channels abstract this study examines the erosive resistance of the discontinuous loose joint blocks of various sizes that comprise the bed material of the etobicoke creek an incised bedrock channel found in an urbanized setting within the city of toronto ontario canada in order to accomplish this both field and laboratory experiments were conducted on the bed material found in this channel the field work involved repeated detailed surveying of the channel bed and estimations of distances of movement of various clasts during many sediment transport events we found that rates of erosion and or deposition can be significant during the snowmelt spring events and that there was a greater loss of bed material over the study reach than was gained in several spots with bed lowering 0 10 m in some locations the field work also showed that the distances moved by the rock clasts scaled directly with shear stresses observed during rain events and that average distances of transport tend to be short the frequency distributions of distance of transport scaled with particle size is log normally distributed flume experiments demonstrated that the clasts offered different levels of resistance to movement depending on their orientation the platy nature of the rock fragments clast orientation and their imbrication significantly affect the threshold of erosion the results have significant implications for the understanding of bedrock rivers from a management perspective especially in the case of those rivers experiencing the effects of urban development in their drainage basins

biostratigraphy of the vendian cambrian sukharikha river section northwestern siberian platform the sukharikha river section contains more than 800 m of fossiliferous vendian and lower cambrian carbonate rock deposited in ramp shelf and slope environments a diverse fauna of small shelly fossils calcibionts brachiopods trilobites and archaeocyaths has allowed us to develop a multi taxa biostratigraphic framework for this section a dearth of distinctive fossils low in the sukharikha formation prevents us from determining the position of the vendian cambrian boundary abundant small shelly fossils and archaeocyaths in the uppermost sukharikha formation and low in the krasnoporog formation provide ample biostratigraphic control near the base of the tommotian stage but the nemakit daldynian tommotian boundary as defined at ulakhan sulugur on the aldan river is temporally ambiguous for this reason there is no precise definition of this boundary in the sukharikha river section we have provisionally placed the base of the tommotian stage at the first occurrence of nochoroicyathus sunnaginicus

revised neoproterozoic and terreneuvian stratigraphy of the lena anabar basin and north western slope of the olenek uplift siberian platform abstract the early to mid neoproterozoic pre glacial sedimentary succession of the lena anabar basin northeast siberian platform records protracted faulting and subsidence possibly as part of the widespread continental rifting and the break up of rodinia there is a significant stratigraphic unconformity separating the pre glacial neoproterozoic strata and the overlying upper ediacaran succession in the lena anabar basin with the terreneuvian strata most likely to be deposited in a foreland of the central taimyr accretionary belt the cryogenian sensu strictum i e younger than 720 ma and lower ediacaran deposits are missing in the area in this study we assess the palaeontological content of the precambrian and terreneuvian strata of the lena anabar basin and the adjacent north western slope of the olenek uplift and revise the chronostratigraphy of the region with special emphasis to biostratigraphic index taxa for the pre glacial neoproterozoic section we establish the new tukulan kulady taimylyr formations and redefine the khastakh formation we also refine the ediacaran and terreneuvian stratigraphy by formalising the maastakh khatyspyt and turkut formations of the khorbusuonka group whereas the kessyusa formation is raised to group rank and subdivided into the syhargalakh oppokun mattaia and chuskuna formations the proposed stratigraphic correlation scheme is based upon depositional unity and is consistent both lithologically and biostratigraphically providing a robust framework for future stratigraphic sedimentological and palaeobiological studies

carbonate hosted avalon type fossils in arctic siberia avalon type fossils are crucial to understanding the origin of phanerozoic ecosystems but their usual occurrence in volcaniclastic and siliciclastic facies greatly limits their paleobiological resolution the unique carbonate hosted assemblage of the khatyspyt formation on the olenek uplift of north central siberia promises a much enhanced anatomical and paleo ecological view of these enigmatic organisms avalon type fossils are preserved by authigenic carbonate cementation in intervals of finely laminated nodular limestones khatyspyt type taphonomic window interbedded silicified calcareous mudstones yield diverse carbonaceous compressions occasionally with taphonomic phantoms of avalon type taxa miaohe type taphonomic window styles of moldic preservation do not appear to be taxon selective and therefore cannot alone be responsible for the morphological distinctiveness of ediacaran macrofossils and the profound disparity in the taxonomic composition between fossil assemblages on the other hand the exclusion of avalon type fossils from carbonaceous compressions miaohe type preservational window is a real taphonomic signal that provides an important constraint on the properties of certain ediacaran tissues

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

the relation between particle path length distributions and channel morphology in gravel bed streams a synthesis abstract the path length downstream displacement over a given time period of individual bed particles in gravel bed rivers is central to morphological methods for measuring bed load transport rate and is also fundamental to understanding the bed load transport process and the development of channel morphology previous studies of particle movement using tracers report predominantly strongly positively skewed frequency distributions of path length with modes close to the point of entrainment however gravel bed rivers often have regularly spaced erosion scour pools and deposition channel bars sites that are several channel widths apart and it is reasonable to expect that particle path length would reflect this morphological scale at least during flows large enough to create and modify the morphology here we synthesize and re analyze results from published bed load tracing experiments in gravel bed rivers to identify the variety of possible path length distributions for differing channel morphology channel dimensions bed particle size and particle mobility i e flow magnitude and to look for occurrences of path length coinciding with the length scale of the morphology the results show that path length distributions may be positively skewed symmetrical and uni bi or multi modal and may include modes that coincide with known or expected pool bar spacing primary path length modes equivalent to possible pool bar spacing are more probable at higher non dimensional bed shear stress from which it is inferred that both particle mobility and channel morphology exert an influence on particle path lengths and that particle movement is unlikely to be stochastic except at relatively low particle mobility existing data are inadequate for more than a preliminary analysis of this problem consequently there is a need for new data collected explicitly and systematically to confirm these preliminary results isolate the effect of the several variables that influence the characteristics of path length frequency distributions and identify the conditions under which path length coincides with the length scale of the dominant morphology

carbonate deposition and hydrocarbon reservoir development at the precambrian cambrian boundary the ara group in south oman abstract the ediacaran early cambrian ara group in the south oman salt basin consists of six evaporite carbonate cycles a0 a1 to a6 that record tectono eustatic sea level changes the a4 cycle developed at the precambrian cambrian boundary 542 ma it forms a single depositional sequence with evaporites deposited in a lowstand systems tract lst overlying carbonates represent an open marine shallowing upward ramp succession that developed in transgressive tst and highstand systems tracts hst the low energy carbonate ramp occupied a relatively protected site between a large shelf and an exposed paleogeographical high the tst facies include sulfates evaporite carbonate laminites and organic rich carbonate laminites that record initial flooding deepening of the basin and establishment of an outer ramp depositional environment carbonate sediment flux was low and the environment was partly subject to cyclically elevated salinity subsequent hst facies comprise mostly fine grained clastic carbonates and stromatolites that formed in middle and inner ramp settings these facies show evidence of shoaling and establishment of a carbonate factory that probably operated over most of the middle and inner ramp sediment was redistributed in suspension by muddy turbidity currents muddy debris flows storm and shallow water currents during the late hst carbonate facies were affected by elevated salinity and recorded the gradual transition to the overlying lst evaporite unit a combination of strong tectonic subsidence and transient flooding caused significant shallow water evaporite deposition to occur not only down dip but also on top of the former carbonate platform where several hundreds of meters of evaporites accumulated the transgressive carbonate laminites are the main reservoir facies and thus represent a relatively unusual reservoir unit the presence of organic material and the relative scarcity of carbonate mud influenced diagenesis and reservoir properties distribution of organic material and carbonate mud can be linked to specific environmental conditions low physical and biogenic disturbance of sediment and stratified water mass and the sequence stratigraphic position low flux of fine grained carbonate during tst in contrast diagenetic evaporite formation has largely degraded reservoir quality in porous shallow water facies near the top of the a4c

size selective entrainment of bed load in gravel bed streams entrainment of mixed size gravel bed material was studied in nine reaches of three high power streams in scotland and norway paired measurements of at a point shear stress estimated from velocity profiles and bed load transport by hand held sampler were made they extended to very high values 400 n m 2 3 5 kg m x s x analyses of maximum bed load diameter mean bed load diameter transport rates of individual size fractions and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size despite strong relative size effects precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates size selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to be significant

using passive integrated transponder pit tags to investigate sediment transport in gravel bed rivers abstract in gravel bed rivers measuring the displacement of individual grains by fluid flow is essential in order to understand sediment transport processes and to investigate changes in channel morphology we present preliminary results of a new technique that traces pebble movements by inserting 23 mm passive integrated transponders pit into individual clasts because each pit has its own signal identification this technique is ideal for tracking the individual movements of episodically transported particles in gravel bed rivers two hundred and four tagged particles were inserted into a 130 m long reach of a gravel bed river with a 2 slope and a bed material with a d50 of 70 mm the b axis size of the tagged particles ranged from 40 mm to 250 mm recovery percentages after two competent floods were 96 and 87 clearly demonstrating the effectiveness of this new technique buried particles can be recovered at a depth of 0 25 m pit tags are also suited for long term studies over several years

new carbon isotope stratigraphy of the ediacaran cambrian boundary interval from sw china implications for global correlation the yangtze platform preserves relatively thick carbonate successions and excellent fossil records across the ediacaran cambrian boundary interval the intensely studied meishucun section in east yunnan was one of the global stratotype section candidates for the precambrian cambrian boundary however depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified the laolin section located in ne yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the precambrian cambrian boundary however the stratigraphic framework and correlations were controversial we studied and systematically sampled the laolin section and present here new carbon isotope data for this section the laolin section consists of in ascending order the baiyanshao dolostone of the dengying formation the daibu siliceous dolostone zhongyicun dolomitic phosphorite lower dahai dolostone and upper dahai limestone of the zhujiaqing formation and the black siltstone of the shiyantou formation our data reveal a large negative 13 c excursion 7 2 l1 in the daibu member which matches the previously published data for the laolin section and a large positive excursion 3 5 l4 in the dahai member which was not shown in the published data the excursion l1 correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in siberia and mongolia similar magnitude excursions are also known from morocco and oman for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 ma thus confirming a global biogeochemical event near the ediacaran cambrian boundary our data also indicate that deposition was more continuous at the laolin section compared with the meishucun section where there are no records of a comparable negative excursion near the ediacaran cambrian boundary nor any comparable positive excursion in the dahai member therefore the laolin section has proven potential to be a supplementary global stratotype section for the ediacaran cambrian boundary on the yangtze platform

detrital zircon age and biostratigraphic and chemostratigraphic constraints on the ediacaran cambrian transitional interval in the irkutsk cis sayans uplift southwestern siberian platform

oxygen carbon and strontium isotope records of ediacaran carbonates in central iberia spain carbon oxygen and strontium isotope ratios were determined in the uppermost neoproterozoic carbonate rocks at pastores sw salamanca central iberia the low 18o v smow values 15 19 indicate an alteration of the whole stratigraphic series however the alteration process does not seem to have affected most of the 13c and 87sr 86sr data these data reveal that only one particular level of the carbonate section shows simultaneous relative increases in mn sr and 87sr 86sr ratios decreases in the 18o and 13c values and covariations between 87sr 86sr and the other parameters despite this most of the carbonate section lacks these covariations and its 13c 4 6 to 0 5 and 87sr 86sr 0 70845 0 70853 ratios probably reflect the seawater isotopic features at the time of sedimentation the data for c and sr isotopes at the pastores carbonate section and the presence of cloudina in platform carbonates together with an overlying major sub cambrian unconformity following a relative sea level fall are features comparable to those frequently shown by proterozoic cambrian boundary series across the world thus our results consistently support the notion that the carbonates at pastores are equivalent to other carbonates deposited close to the ediacaran cambrian boundary

integrated chronostratigraphy of the vendian system of siberia implications for a global stratigraphy integrated 13 c chemostratigraphy and sequence stratigraphy are developed for a succession of vendian strata nokhtuisk section on the southern margin of the siberian platform the carbonates exhibit secular variations in 13 c and at least three major depositional sequences that encompass the last c 20 million years

chemostratigraphic and sequence stratigraphic constraints on vendian cambrian basin dynamics northeast siberian craton delta 13 chemostratigraphic and sequence stratigraphic data from terminal vendian and earliest cambrian strata of northeast siberia are used to constrain the history of regional basin development these boundary strata consist of 300 to 500 m of latest vendian age carbonate ramp deposits and 100 m of nemakit daldyn age siliciclastic shelf deposits the two successions are separated by a regional paleokarst unconformity six delta 13 c chemostratigraphic profiles of the carbonates exhibit patterns of secular variation similar to those in coeval strata with allowances for local diagenetic and tectonic effects isotopic profiles are used to recognize time lines chemo chrons within individual depositional sequences and to illustrate the geometry of stratigraphie units and variation in subsidence and stratigraphie completeness across the basin the vendian khorbosuonka group and correlative deposits are divided into 3 depositional sequences that record sedimentation from ca 555 to 543 ma in a ge

salts in southern yakutian kimberlites and the problem of primary alkali kimberlite melts abstract alkali carbonates sodalite gypsum anhydrite halite and sylvite are present in the groundmass and matrix of many kimberlites in the southern part of the yakutian kimberlite province the kimberlites were emplaced through 2 km thick evaporite bearing carbonate sediments saturated with brines in the global context southern yakutian kimberlites are unprecedented in the amount of the crustal carbonate and evaporite material included in the pipes as evidenced by the bulk major element chemistry and isotopic compositions of sr c o cl and s we present geological and hydrogeological data on country rocks and kimberlites of the udachnaya mir and international naya pipes the secondary crustal origin of na k cl and s rich minerals is supported by the following 1 a regional correlation between the geology and hydrogeology of the local country rocks and the kimberlite mineralogy in particular the difference between southern and northern yakutian kimberlites 2 a restriction of halite or gypsum mineralization in the mir and international naya pipes to depths where pipes intersect country rock strata with similar mineralogy 3 the localization of the highest abundances of na k cl s bearing minerals in the udachnaya east kimberlite at a depth interval that correlates across three magmatic phases of kimberlites and coincides with the roof of the halite bearing country rock and an aquifer carrying anomalously na rich brines 4 the presence of evaporite xenoliths and veins of halite gypsum and carbonate cutting through the kimberlite and xenoliths 5 a secondary origin of halite and alkali carbonates as observed in their textural relationships to serpentine and other groundmass minerals 6 the geochemical and isotopic evidence for crustal contamination addition of crustal salts to kimberlite melt began prior to the volcanic fragmentation as a result of preferential melting and assimilation of evaporite xenoliths and may have continued in situ after the pipe emplacement via reactions with external saline fluids the hybrid alkali s and cl rich compositions of residual melts and fluids were trapped in secondary inclusions in olivine the crustal origin of salts in the udachnaya east kimberlite demonstrated here is incompatible with a model of alkali rich primary kimberlite melt it is significantly more ca na b and s rich than the deep seated mantle k and ba rich fluid inclusions in fibrous diamonds our analysis suggests that the udachnaya east kimberlite is not exceptional and uniquely fresh but rather typical of the other crust contaminated southern yakutian kimberlites

molar tooth structures in calcareous nodules early neoproterozoic burovaya formation turukhansk region siberia abstract molar tooth structures are abundant in large 1 2 m diameter carbonate nodules within fine grained subtidal carbonates of the early neoproterozoic lower upper riphean burovaya formation along the sukhaya tunguska river turukhansk uplift northwestern siberia although molar tooth structures are regionally abundant in this unit here they occur only within the nodules stable isotopic compositions of molar tooth filling dolomicrospar cements and of thinly bedded dolomicrite within and surrounding the nodules are indistinguishable from one another the carbon isotopic compositions mean 13c 2 8 pdb 0 4 reflect mean average oceanic surface water composition during their formation the light oxygen isotopic compositions mean 18o 6 4 pdb 2 2 are generally similar to those of other little altered meso to neoproterozoic limestones and dolostones these molar tooth structures have no features that would support a tectonic origin they more likely formed through bacterial processes carbonate cement filling of these voids occurred soon after their formation but the mechanism responsible for this carbonate precipitation is currently uncertain local restriction of molar tooth structures to early diagenetic nodules suggests that penecontemporaneous lithification was required for the formation or at least preservation of these widespread mesoproterozoic to neoproterozoic features

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

stable isotope geochemistry of the lower cambrian sekwi formation northwest territories canada implications for ocean chemistry and secular curve generation abstract three curves delineating 13 c variations across the early cambrian sekwi formation carbonate ramp mackenzie mountains northwest territories canada are incorporated into a biostratigraphic and sequence stratigraphic framework that provides a higher resolution temporal and spatial framework for the sekwi formation the three 13 c curves were correlated across a range of depositional environments from tidal flat to deep subtidal on the sekwi carbonate ramp eight 13 c cycles in the curves a h were correlated across the basin complimenting the sequence stratigraphic framework the most complete 13 c curve from the sekwi formation correlates well with a composite early cambrian 13 c curve from the siberian platform however the differing magnitude and absolute timing of some of the correlative isotopic excursions records the influence of regional tectonism sea level changes and diagenesis on the sekwi ramp additionally the sekwi formation 13 c curve has more high frequency variations than the siberian curve due in part to the higher sample density used to construct the sekwi curve the early middle cambrian boundary was not sampled in this study but a large negative isotopic excursion in the very latest early cambrian coincides with a regional drowning that may be correlative throughout western laurentia but recognizing this event globally is problematic

determining fluvial sediment virtual velocity on the mojave river using k feldspar irsl initial assessment abstract the mojave river of southern california was chosen as a field site to investigate the applicability of luminescence dating to sediment transport rate problems grains in the active channel of the river are expected to show signs of partial bleaching and this makes it difficult to determine time since deposition accurately a modification of the multiple elevated temperature post ir irsl metpirir procedure buylaert et al 2009 li and li 2011 was used for k feldspar grains 175 200 m at temperature increments of 50 95 140 185 and 230 c in order to provide more information about relative signal bleaching among samples the measurements show an exponential decrease in equivalent dose de with distance down the mojave river higher temperature pirir signals are bleached more slowly than lower temperature ones buylaert et al 2009 the de for samples at 50 c is roughly constant along the river these results suggest cyclical bleaching and burial as grains are transported downriver and higher energy deeper traps are vacated the pattern of de values for the mojave river can be used to constrain the sediment transport rate for this river by building a model of growth and bleach for each temperature increment a bleaching experiment was run with multiple aliquot samples for direct sunlight exposure times of 0 10 30 300 1000 3000 10 000 and 30 000 s the met pirir procedure was applied at each temperature increment for each exposure time aliquot and the results for all exposure times were fit to the general order kinetics equation using a non linear regression the bleaching parameters were used in conjunction with the sar growth curves to build a model of partial bleaching of grains during transport that is fitted with a 2 test to the pirir data from the mojave river this model is not a unique solution but can be used to assess the likelihood of various sediment transport regimes

carbonate platform growth and cyclicity at a terminal proterozoic passive margin infra krol formation and krol group lesser himalaya india the infra krol formation and overlying krol group constitute a thick 2 km carbonate rich succession of terminal proterozoic age that crops out in a series of doubly plunging synclines in the lesser himalaya of northern india the rocks include 18 carbonate and siliciclastic facies which are grouped into eight facies associations 1 deep subtidal 2 shallow subtidal 3 sand shoal 4 peritidal carbonate complex 5 lagoonal 6 peritidal siliciclastic carbonate 7 incised valley fill and 8 karstic fill the stromatolite rich peritidal complex appears to have occupied a location seaward of a broad lagoon an arrangement reminiscent of many phanerozoic and proterozoic platforms growth of this complex was accretionary to progradational in response to changes in siliciclastic influx from the south eastern side of the lagoon metre scale cycles tend to be laterally discontinuous and are interpreted as mainly autogenic variations in the number of both sets of cycles and component metre scale cycles across the platform may result from differential subsidence of the interpreted passive margin apparently non cyclic intervals with shallow water features may indicate facies migration that was limited compared with the dimensions of facies belts correlation of these facies associations in a sequence stratigraphic framework suggests that the infra krol formation and krol group represent a north to north westfacing platform with a morphology that evolved from a siliciclastic ramp to carbonate ramp to peritidal rimmed shelf and finally to open shelf this interpretation differs significantly from the published scheme of a basin centred on the lesser himalaya with virtually the entire infra krol krol succession representing sedimentation in a persistent tidal flat environment this study provides a detailed neoproterozoic depositional history of northern india from rift basin to passive margin and predicts that genetically related neoproterozoic deposits if they are present in the high himalaya are composed mainly of slope basinal facies characterized by fine grained siliciclastic and detrital carbonate rocks lithologically different from those of the lesser himalaya

virtual velocity of tracers in a gravel bed river using size based competence duration virtual velocity vi of river gravels is commonly used to determine sediment transport rates and gravel dispersion dynamics virtual velocity is calculated from tracer gravel step length data as the distance travelled divided by the duration of competence however no allowance is usually made for differences in competence duration according to grain size in this investigation vi of gravel tracer clasts for the river rede northumberland uk is calculated using a method that takes into consideration an approximation of size based competence duration although scaled transport distance data compared favourably to past studies it was the comparatively smaller clasts that tended to have lower vi in comparison to coarser clasts because of their longer competence duration contrasting with previously published research the key findings of the study serve as proof of concept and should be adopted in future studies that focus upon vi estimation

carbon isotope stratigraphy of the precambrian cambrian sukharikha river section northwestern siberian platform a high resolution carbon isotope profile through the uppermost neoproterozoic lower cambrian part of the sukharikha section at the northwestern margin of the siberian platform shows prominent secul