sediment characteristics in the north branch of the yangtze estuary based on radioisotope tracers nuclide specific activity and sediment grain size were analyzed at locations along the north branch of the yangtze changjiang estuary the spatial distributions of various radioisotopes are presented along with the sources and applications of these nuclides for studies of the aquatic environment the specific activities of sediment radionuclides in the north branch increase toward the ocean indicating that the sediment is transported from the downstream side of the estuary into the north branch the 226ra 228ra ratio agrees well with the observed results and can be used to identify trends in erosion and accretion in the north branch

pyrite ooids in devonian black shales record intermittent sea level drop and shallow water conditions upper devonian black shales of the eastern united states contain in places unusual beds of pyrite ooids textural and geochemical studies show that these originated as chamositic iron ooids that were replaced by pyrite during early diagenesis pyrite mimics the laminated texture of the precursor grain yet inclusions of silicate minerals and instances of partial replacement reveal the secondary nature of the pyrite pyrite ooids occur above erosion surfaces that are considered sequence boundaries because of large lateral extent chamositic precursor ooids indicate an oxygenated water column and wave interaction with seafloor sediments at the time of their formation this scenario agrees with earlier work that stipulates that erosion surfaces in devonian black shales reflect lowering of sea level that allowed wave reworking and erosion of earlier deposited black shales pyrite ooid beds thus furnish direct evidence of significant sea level drops during the accumulation of upper devonian black shales in eastern north america

an improved method of sediment grain size trend analysis in the xiaoqinghe estuary southwestern laizhou bay china although deltas evolve with a regular cycle of growth and abandonment over centuries knowledge of these cycles and their effects is important given the fact that humans tend to locate near these areas this study examines sediment transport patterns in the xiaoqinghe estuary in southwestern laizhou bay china in order to identify the factors controlling the sedimentary environment in the estuary sediment samples collected from the bed of laizhou bay in 2007 were analyzed using the gao collins 2 d grain size pattern analysis method and two polymodal distribution functions the study identified three grain size subgroups 4 6 16 and 27 115 mu m and mapped the distribution of the relative percentage of the three components and the mean size distribution within each component the sediment transport trends for the three components were derived by a mathematical partitioning process generally the finest grains move from the local river mouths seaward in the north and south directions with a large anomaly suggesting input into the study area from the more distant huanghe river in the north in addition fine grained sediment is transported by marine hydrodynamic forces from the shallow sea areas toward the coast the medium sized grains move toward the river mouths settling over oyster beds and sandbars that create high turbulence zones while the fine silt grains move seaward in northerly and southerly directions the coarser grains tend to flow toward the coast brought in by seaward migration with some coarse material moving off the river mouths

impacts of relative sea level rise on the shoreface deposition shuidong bay south china the influence of relative sea level rise on shoreface deposition helps to elucidate changes in beach and nearshore geomorphology in response to different forcing factors in this study two sets of sediment samples one from 1982 and one from 2004 from the shuidong bay of south china were analyzed to determine the changes in shoreface depositions an eof empirical orthogonal function method was used to examine how these depositions changed based on the relative sea level rise the results show that shoreface sediments of shuidong bay are mainly composed of sand fine grained sediments are distributed in the lower shoreface offshore area and coarse grained sediments are mainly found in the upper shoreface nearshore area due to the altered hydrological forcing caused by relative sea level rise the sand fraction in sediments increased from 84 7 in 1982 to over 90 in 2004 and the clay and silt fractions decreased from 11 8 in 1982 to 5 6 in 2004 grain size parameters in sediments in 2004 became coarser slightly more well sorted less skewed and had lower kurtosis than those in 1982 in addition the shoreface deposition of shuidong in 1982 and 2004 is distinctly different a polarized mode was described by the first eigenfunctions and a homogenized mode was described by the second eigenfunctions the former means that the sediment components developed towards the two opposite poles undergoing both coarsening and refining processes the second mode indicates that the secondary variation in sediment components was mostly in the three intermediate grained sand components in the future the shuidong bay shoreface may be subjected to even further erosion because of increases in the energy of the environment resulting from rapid relative sea level rise

comparison of superdarn radar boundaries with dmsp particle precipitation boundaries 1 auroral boundary algorithms for superdarn ionospheric convection observations are introduced both the equatorward boundary of scatter ebs and the convection reversal boundary crb are found and compared with boundaries based on dmsp particle precipitation observations these comparisons provide an intercalibration between the two schemes and insight into the relationship between disparate phenomena the ebs is reliably poleward of the equatorward boundary of precipitation ebp at most local times but centers well on the equatorwardmost precipitation between 1600 and 2200 mlt when within 8 latitude of the radar station indicating a correspondence with the slerps slow long lived e region plasma structures of jayachandran near dawn the ebs coincides better with the structured unstructured boundary sub than the ebp as one might expect if the ionospheric irregularities responsible for this scatter were produced by the gradient drift instability the crb correlates well with the open closed boundary ocb as seen by dmsp there is however an equatorward offset of the crb relative to the ocb that varies from zero near noon to 1 near dawn and dusk and is largest near midnight this offset is consistent with a small viscous like interaction between the magnetosheath and the low latitude boundary layer resulting in a degree of antisunward flow on closed field lines the offset decreases under the influence of southward interplanetary magnetic field as one might expect if increased dayside merging interfered with this effect

grain size trends associated with net sediment transport patterns an example from the belgian continental shelf grain size trends in relation to net sediment transport pathways are examined using some commonly used grain size parameters the results of the trend analysis for 15 types of the trends are compared with a known net sediment transport pathways established on the basis of the sandbank hydro and sediment dynamics i e general water and sediment movement patterns and bedform asymmetry it is shown that 1 the results for grain size trends associated with a worsening in sorting along the transport pathways have little similarity to transport pathways 2 the results for grain size trends associated with an improvement in sorting along the transport pathways have relatively high degree of similarity to the identified pathways and 3 the residual pattern derived on the basis of a combined grain size trend used elsewhere gao and collins 1992 appears to be most similar and suitable for defining transport pathways

swell impact on reef sedimentary processes a case study of the la reunion fringing reef two surface sediment sampling campaigns were carried out in november and december 2003 before and after a strong swell event in the back reef area of a microtidal fringing reef on the western coast of la reunion indian ocean the spatial distributions of the mean grain size sorting and skewness parameters are determined and grain size trend analysis is performed to estimate the main sediment transport pathways in the reef the results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states under normal wave conditions there is a potential for onshore sediment transport from the reef flat to the back reef but this transport is episodic and occurs principally during high tide stages sediment transport trends revealed by the grain size trend analysis method show onshore and alongshore low energy transport processes that are in agreement with the hydrodynamic records the grain size trend analysis method also provides evidence of an offshore high energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef the impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport considering different combinations of the vector transport trends computed through the grain size trend analysis approach more realistic and pertinent results can be obtained by applying an exclusive or operation xor case on the vectors the main results presented here highlight a trend towards the accumulation of carbonate sands in the back reef area of the fringing reef these sediments can only be resuspended during extreme events such as storms or tropical cyclones

mud rich density driven flows along an early ordovician storm dominated shoreline implications for shallow marine facies models abstract dynamic physical and biological seafloor processes shape the three dimensional stratal architecture of modern and ancient mud dominated continental shelves when evaluating a mudstone unit as a potential source reservoir or seal it is imperative to understand the physical biological and chemical seafloor processes that control mudstone depositional fabric and diagenesis this study presents sedimentological ichnological and geochemical data of exceptionally preserved mudstone originating from hyperpycnal and possible combined flow deposits in the lower ordovician tremadocian beach formation bell island group newfoundland seven mudstone facies are described based on textural compositional and ichnological characteristics mudstone deposits interpreted to originate from hyperpycnal flows are well cemented exhibit high chlorite illite ratios and contain sharp grain size changes commonly forming beds with tripartite subdivisions deposits of wave enhanced sediment gravity flows are in contrast poorly cemented illitic mudstone these mudstone facies exhibit decimeter thick wave or combined flow structures within siltstone and very fine sandstone beds as well as laterally discontinuous nonbioturbated mudstone layers beds of this facies have abundant mudstone on mudstone and mudstone on sandstone erosional contacts low organic carbon loading from the nonvegetated early paleozoic hinterland combined with a high reworking frequency on a shallow marine wave dominated shelf is inferred to have resulted in high remineralization efficiency and low preservation potential of reactive organic carbon burial efficiency and bioavailability of organic matter are considered to be the critical variables controlling infaunal colonization and bioturbation in mud dominated open coastline paleoenvironments this work demonstrates that ancient fine grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal to distal facies relationships it is proposed that the spatial organization of fine grained sediment and facies architecture in such systems are controlled by 1 frequency of sediment supply events 2 direction of mud transport 3 diagenetic reactivity of minerals and bioavailable organic carbon and 4 residence time of mineral grains and organic matter close to the sediment water interface

geochemistry and sedimentology of shelf and upper slope sediments of the south central black sea abstract eighty five surface samples from oxic suboxic and anoxic sites of the south central black sea shelf consist predominantly of clayey silts and silty clays reflecting the moderate to high energy wave dominated hydrological regime grain size data and net sediment transport patterns suggest that the western part of this shelf is an area of east directed active sediment transport with the exception of localized nearshore zones the eastern shelf is by contrast an area of major sediment deposition the sediment transport vectors are correlated with patterns of surface water circulation and storm generated longshore currents the sources of the shelf sediments are indicated by the total concentrations of 30 major minor and trace elements in 59 surface samples factor analysis shows that 99 1 of the total variance can be explained by five factors factor 1 as cu cr fe pb and zn reflects anthropogenic pollution by the etibank copper mine factor 2 mainly total organic carbon and s is linked to anoxia redox as saline conditions factor 3 mainly al si represents aluminosilicates whereas factor 4 sand and silt abundance total carbonate ca and sr represents the carbonate component factor 5 fe mn p cr ni and v tracks primary detrital delivery with strong overprints by redox dependent biogeochemical reactions within the anoxic sediments and the oxic suboxic bottom waters the combined data suggest that the sediments on the south central black sea shelf were largely derived from the north anatolian mountains and supplied to the shoreline by a network of small rivers

mud deposition and diagenesis within an early palaeozoic clinothem power steps formation newfoundland canada the early ordovician 385 ma power steps formation newfoundland canada exposes a well preserved mudstone dominated clinothem that serves as an excellent archive for understanding how mud has been produced transported and converted into mudstone prior to the evolution of globally widespread deep soil horizons sedimentological analysis of four sandstone and five mudstone facies along the ochre cove clinothem reveal that mud and sand were delivered by unidirectional currents and experienced episodic reworking by storm waves petrographic examination and x ray diffraction from described mudstone facies reveal significant variability in the distribution of illite versus chlorite between the lower and upper part of the ochre cove clinothem this research highlights that in the present day clay mineral fraction illite is often detrital whereas chlorite originated via the alteration of silt sized highly unstable mafic volcanoclastic grains throughout all sedimentologic facies albeit in different proportions these mafic lithic grains were diagenetically altered via in situ weathering before significant compaction occurred resulting in the precipitation of significant volumes of pore bridging silica and iron rich chlorite cement compositional diagenetic and textural attributes across the ochre cove mud clinothem vary as a function of starting composition hydrodynamic sorting and grain density given that a significant proportion of clay minerals has been generated via in situ transformation of a mafic non stable precursor assemblage we recommend future studies to incorporate detailed petrographic description along with x ray diffraction analyses when aiming to employ trends in whole rock clay mineral data as a proxy in provenance and palaeoclimate studies of very old pre devonian mudstones and sandstones

residual sediment transport paths on a tidal sand bank a comparison between the modified mclaren model and bedform analysis abstract in order to evaluate the validity of the modified mclaren model for sand transport on a tidal sand bank 42 grab samples taken from the northern part of the kwintebank were decalcified sieved and analyzed for statistical parameters the areal distribution of mean grain size standard deviation and skewness were defined and used to determine the residual transport directions the grain size trends taken into consideration were that the sediment becomes finer better sorted and more negatively skewed along the transport pathways f b and the sediment becomes coarser better sorted and more positively skewed along the transport pathways c b these were compared with the transport paths inferred from bedform asymmetries obtained by side scan sonar records there were major differences between the sediment transport paths resulting from the two techniques when the f b trend and small dune asymmetries are compared only 5 out of 24 cases showed agreement 30 whereas in 9 cases the trends were 180 30 different there was even less agreement between the c b trend and the asymmetry of the small dunes only 1 out of 24 cases agreed 30 and almost half of the cases were 90 30 different the sediment transport directions deduced from the morphological analysis of the large dunes all point in the direction of the peak flood current the large dunes seem to be more suitable indicators of the sediment transport paths than the small ones however they conflict with the vectors resulting from the f b trend only one out of 20 cases agrees 30 while in 13 cases the vectors are 180 30 different and in three cases 90 30 neither do the transport directions from the c b trend agree with those deduced from the large dunes only one case agrees 30 while in four out of 20 cases the vectors point in opposite directions in four cases the vectors are 90 30 different the asymmetric cross section of the sand bank suggests sediment transport in a northwest direction it does not seem probable however that sediment transport occurs by migration of the whole sand bank the transport directions inferred from the bank morphology are quite different from the f b trend in 12 out of 42 cases the vectors agree 30 in four cases the vectors point in opposite directions and in 15 cases they are 90 30 different there is slightly more agreement between the c b trend and the transport directions deduced from the sand bank 16 out of 42 cases agree 30 in nine cases the vectors point in opposite directions and three cases are 90 30 different from this study it seems that the residual sediment transport directions can best be deduced from the morphological characteristics of the large dunes the departures between the results of the sediment trend analysis according to the modified mclaren model and the morphology of the subaqueous bedforms are partly explained by the location of the study area near the edge of the sand bank probably better results of the sediment trend analysis would be obtained if samples over the whole length of the sand bank were analyzed and compared perhaps a smaller spacing between the samples would improve the results as well and maybe the samples should not have been decalcified possibly the different transport patterns are attributed to different sediment transport processes which makes a comparison virtually impossible

net sediment transport patterns over the bohai strait based on grain size trend analysis grain size trend analysis indicates two distinct characteristics of sediment transport in bohai strait eastward transport dominates the western area and along the coast of the shangdong peninsula this result supports the previous work which indicated that the yellow river sediments are transported from the bohai sea to the yellow sea through the south channel of bohai strait and dispersed into the southern yellow sea along the coast of shangdong peninsula in the central eastern bohai strait net deposition is taking place as indicated by the convergence of the grain size trends this result is consistent with current circulation pattern on bohai strait and the interpretation of strata disclosed by seismic reflection profile this study supports the use of grain size trend analysis for large scale areas on the continental shelf

a new dmsp magnetometer and auroral boundary data set and estimates of field aligned currents in dynamic auroral boundary coordinates we have developed a method for reprocessing the multidecadal multispacecraft defense meteorological satellite program special sensor magnetometer dmsp ssm data set and have applied it to 15 spacecraft years of data dmsp flight 16 18 2010 2014 this level 2 data set improves on other available ssm data sets with recalculated spacecraft locations and magnetic perturbations artifact signal removal representations of the observations in geomagnetic coordinates and in situ auroral boundaries spacecraft locations have been recalculated using ground tracking information magnetic perturbations measured field minus modeled main field are recomputed the updated locations ensure the appropriate model field is used we characterize and remove a slow varying signal in the magnetic field measurements this signal is a combination of ring current and measurement artifacts a final artifact remains after processing step discontinuities in the baseline caused by activation deactivation of spacecraft electronics using coincident data from the dmsp precipitating electrons and ions instrument ssj4 5 we detect the in situ auroral boundaries with an improvement to the redmon et al 2010 algorithm we embed the location of the aurora and an accompanying figure of merit in the level 2 ssm data product finally we demonstrate the potential of this new data set by estimating field aligned current fac density using the minimum variance analysis technique the fac estimates are then expressed in dynamic auroral boundary coordinates using the ssj derived boundaries demonstrating a dawn dusk asymmetry in average fac location relative to the equatorward edge of the aurora the new ssm data set is now available in several public repositories

response of the ionospheric convection reversal boundary at high latitudes to changes in the interplanetary magnetic field in this paper we present a systematic study of the location of the convection reversal boundary for southward interplanetary magnetic field by using defense meteorological satellite program dmsp f13 and f15 spacecraft measurements during local summer seasons from 2000 to 2007 for both hemispheres all the convection reversal boundaries are identified pass bypass by locating the highest latitude location where the plasma flow shows a large scale two cell pattern and reverses direction from sunward to antisunward the location of the convection reversal boundaries are placed into 10 different categories based on by and the magnitude of southward bz observations suggest that 1 the location of the boundary is well organized by the magnitude of bz being at lower latitudes for stronger negative bz and also organized by the polarity of by moving toward the dawnside duskside when by changes from negative to positive in the northern southern hemisphere 2 the average latitudinal movement of the boundary associated with by changes is comparable to the average movement of the boundary with bz changes 3 an initial reconfiguration of the boundary near local noon is redistributed around the dawnside or duskside dependent on the direction of by and 4 the boundary has a general spiral shape which varies depending on bz and by

application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas abstract in this paper we apply the gao and collins procedure of grain size trend analysis for the first time in an intertidal sedimentary system our purpose is to evaluate a reliable method to determine residual transport directions in intertidal environments where sediment movement is not well understood residual transport patterns can be determined by grain size trend analysis if the following criteria are applied 1 a single sediment transport unit must be precisely defined and investigated 2 the thickness of sampling has to be chosen in order to investigate the most recent sedimentary event and 3 a regular mesh grid is sampled to avoid bias in the calculation of grain size trends the gao and collins method was undertaken simultaneously with a topographic survey and a tracer experiment during consecutive meteorological conditions of fair weather and a storm event the topographic changes observed between these two situations and the directions of sediment movement deduced from tracer tracking are coherent with the residual transport pattern calculated from the grain size trend analysis the method was tested on a ridge and runnel system which corresponds to the intertidal part of a macrotidal beach called la salie beach located along the southwest french coast in a high wave energy environment this study permits us to recognize two different residual transport patterns for this intertidal ridge and runnel system one for fair weather and a second for storm conditions during fair weather specific sites are subject to sand accretion while during storm conditions these sand stocks are subsequently spread out over the whole area and remain partly on the beach

the habberley formation youngest tremadoc in the welsh borderlands the habberley formation overlies the shineton shale formation in the shelve inlier shropshire and includes the youngest tremadoc strata known from the welsh basin it probably represents deposition during the interval cut out by the sub arenig unconformity in north wales and removed by the sub caradoc unconformity in the wrekin district there is no angular unconformity between tremadoc and arenig in the shelve inlier the habberley formation is likely to correlate in part with the hunnebergian stage of scandinavia it was deposited probably in a largely stagnant basin and records a shallowing upwards sequence prior to the arenig transgression of the stiperstones quartzite a sparse trilobite fauna proves the presence of the angelina sedg vickii biozone and a succeeding interval is characterized by asaphellus cf graffi the trilobites are briefly described they include the first undistorted material of angelina sedgwvickii the brachiopod lingulella bella walcott hitherto known only from eastern newfoundland is described by a w a rushton

sediment dynamic processes of the yuehu inlet system shandong peninsula china in order to investigate the sediment dynamic behavior of the yuehu a small inlet system characterized by abundant sediment supply and rapid sediment infilling measurements and sampling were undertaken to obtain data sets of tidal water levels current velocities suspended sediment concentrations grain size parameters deposition rates and organic carbon contents sediment budget and the time velocity asymmetry patterns of the inlet system were analyzed the results show that the deposition rates are relatively high within the tidal basin the total sediment flux cannot be balanced by the input from the open sea the aerosol and biological production rather the material from land which has been intensified by agricultural activities over the past several decades represents a major component for the balance thus the denudation rate must be reduced to protect the yuehu as a natural reserve furthermore it is found from the present study that the yuehu inlet system exhibits all of the four time velocity asymmetry patterns with varied frequencies of occurrence compared with the two asymmetry patterns identified for larger inlet systems such phenomena are partly due to the adjustment of entrance channel geometry this behavior may be representative of the small tidal inlets at their late stage of morphological evolution and therefore may be utilized to prolong the lifespan of small inlet systems c 2003 elsevier ltd all rights reserved

large scale convection patterns observed by dmsp the authors present a comprehensive compilation of the average distribution of the electrostatic potential across the high latitude ionosphere the averages are compiled from potentials along the satellite path calculated from thermal ion drift data from instrumentation on the defense meterological satellite program dmsp flights 8 and 9 satellites data were collected from the dmsp f8 satellite during the period september 1987 to december 1990 and from the dmsp f9 satellite during the period march 1988 to december 1990 the potential distributions are separated by geomagnetic position season and orientation of the interplanetary magnetic field imf and then averages of the distributions are calculated the average potential distributions clearly show the displacement of polar cap convection contours to the dusk or dawk flanks under the influence of the imf b sub y component the cross cap potential decreases as imf b sub z changes from southward to northward the average distributions indicate that the development of more than two convection cells for northward imf is either uncommon or nonexistent for imf b sub z 0 and b sub z vert bar b sub y vert bar a distorted pattern is observed in the average potential distribution not a four cell pattern as some previous studies suggest it should be for allmore orientations of the imf the convection reversal boundary at the poleward edge of the auroral zone is observed in the average distributions to be a rotational boundary it is not a shear boundary as suggested by some previous investigations on average the harang discontinuity convection reversal in the auroral zone near midnight is observed to exist weakly or not at all when examining individual passes a strong eastward flow is present sometimes in the region of the harang discontinuity especially on the poleward boundary but not at all times as implied by the heppner maynard model 39 refs 9 figs 2 tabs less

potential gain and loss of sand by some sand banks in the southern bight of the north sea abstract a detailed echo sounding and side scan sonar survey has shown that sand banks in the southern bight of the north sea have rounded heads in the approximate upstream direction and tapered tails in the approximate downstream direction of net regional sand transport thus the plan view of sand banks can be used as an indicator of the approximate direction of net sand transport sand wave aprons occur in front of the heads and downstream of the tails of the sand banks the asymmetry of the sand waves implies that sand is being added to sand wave aprons at the heads and to the upstream flanks of these sand banks but is shed from the downstream sand wave aprons there is no evidence for a closed sand circulation on the banks

seasonal dependence of high latitude electric fields the seasonal dependence of the high latitude electric field was investigated using sondrestrom incoherent scatter radar data average e times b drifts were derived from 5 years of measurements centered around solar minimum the electrostatic potentials that best fit the observed average electric field were calculated it was found that the large scale convection pattern significantly changes with season this change involves the overall shape of the convection pattern as well as the electric field intensity and thus the total dawn dusk potential across the polar cap the cross polar cap potential drop is largest in fall followed by winter spring and summer the small difference found between the summer and winter cross polar cap potential can be attributed to differing field aligned potential drops in view of the well known relationship between field aligned currents and parallel potential drop this is consistent with the observations that birkeland currents are larger in the summer than in winter changes in the overall shape of the convection pattern are consistent with the simple notion that the whole pattern is shifted toward the nightside as well as to a lesser extent toward the dawnside in summer as compared to winter this assumption is based on the following observed effects 1 themore rotation of the overall convection pattern toward earlier local times with respect to the noon midnight direction is maximum for summer on the dayside 2 on the nightside the harang discontinuity is typically located within the radar field of view lambda 67 to 82 in the winter averaged patterns but it is equatorward of the field of view in summer 3 the line that joins the dawn and dusk potential maxima is shifted toward the midnight sector in summer as compared to winter by about 5 degree 4 in the dawn cell the latitude of the convection reversal is the lowest during summer in the dusk cell the latitude of the reversal is the lowest during winter less

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

a new methodology for the development of high latitude ionospheric climatologies and empirical models many empirical models and climatologies of high latitude ionospheric processes such as convection have been developed over the last 40 years one common feature in the development of these models is that measurements from different times are combined and averaged on fixed coordinate grids this methodology ignores the reality that high latitude ionospheric features are organized relative to the location of the ionospheric footprint of the boundary between open and closed geomagnetic field lines ocb this boundary is in continual motion and the polar cap that it encloses is continually expanding and contracting in response to changes in the rates of magnetic reconnection at the earth s magnetopause and in the magnetotail as a consequence models that are developed by combining and averaging data in fixed coordinate grids heavily smooth the variations that occur near the boundary location here we propose that the development of future models should consider the location of the ocb in order to more accurately model the variations in this region we present a methodology which involves identifying the ocb from spacecraft auroral images and then organizing measurements in a grid where the bins are placed relative to the ocb location we demonstrate the plausibility of this methodology using ionospheric vorticity measurements made by the super dual auroral radar network radars and ocb measurements from the image spacecraft fuv auroral imagers this demonstration shows that this new methodology results in sharpening and clarifying features of climatological maps near the ocb location we discuss the potential impact of this methodology on space weather applications

an investigation of the characteristics of the convection reversal boundary under southward interplanetary magnetic field 1 the characteristics of the convection reversal boundary crb as determined from super dual auroral radar network superdarn observations of convection are examined and modeled convection patterns were calculated for all intervals within the 11 year period 2000 2010 when the interplanetary magnetic field met a restrictive set of criteria when there were sufficient observations the crb was determined and binned as a function of latitude and magnetic local time there were over 90 000 determinations of the crb included in the study distributions of crb locations were formed for each hour of magnetic local time the distributions varied in average latitude and in variance with the lowest latitude and broadest widths occurring near midnight the distributions were skewed toward high latitudes on the dayside and toward low latitudes on the night side the crb was modeled as a linear sum of terms dependent on the interplanetary magnetic field the solar wind and the symh indices finally the dynamic behavior of the boundary is discussed and modeled in an attempt to reproduce the observed distributions

grain size trends used to assess the effective discharge for floodplain sedimentation river waal the netherlands abstract the importance of floods of different magnitude on floodplain sedimentation can be estimated from sedimentation measurements carried out during a series of floods however because these measurements represent sediment accumulation during the entire flood they cannot be used to estimate the importance of individual flood stages on sediment deposition in this study the importance of different flood stages on floodplain sedimentation was assessed from analysis of spatial variations in grain size distributions which are indicative of sediment transport directions as a secondary objective the applicability of grain size trend analysis to fine grained floodplain sediments was tested the grain size trend analyses were carried out in a geographical information system and applied to sediment deposited on an embanked floodplain section along the river waal in the netherlands during a large flood in december 1993 because flow patterns at the studied floodplain section vary with flood stage comparison of the identified sediment transport pathways with computed flow patterns indicates at which discharge most sediment is deposited the results indicate that large discharges with a recurrence time of more than two years are most effective in depositing suspended sediment on floodplain areas enclosed by a minor river dike on floodplain sections that directly border the main channel moderate discharges with a recurrence time of about one year seem to be more efficient contrary to the results of floodplain sedimentation models low but increasing discharges with a recurrence time of less than one year and during which only low lying areas near residual channels are inundated appear important for deposition of suspended sediment in these low lying areas this observation is confirmed by measurements of spatial concentration gradients and by floodplain sedimentation measurements comparison of the trends with additional information on sediment transport directions indicates that trends in which sediment becomes finer better sorted and more negatively skewed when measured in units are most suitable for defining transport pathways on river floodplains trends may however deviate up to 90 from true transport directions flocculation does not seem to have any negative effects on the applicability of grain size trend analysis

first middle ordovician biota from southern new brunswick stratigraphic and tectonic implications for the evolution of the avalon continent a limestone boulder in the triassic lepreau formation near saint john new brunswick has yielded the first diverse marine fauna from the sub caradoc ordovician of the western avalon continent this fauna includes the first arenig conodonts recovered from avalon and represents an unexposed interval in southern new brunswick association of the conodonts drepanoistodus and baltoniodus and the trilobites neseuretus nileus and stapeleyella emphasizes the faunal dissimilarity of avalon and laurentia through the late middle ordovician extension of the ranges of neseuretus cf neseuretus parvifrons and stapeleyella from britain into new brunswick further emphasizes that eastern and western avalon were confluent parts of a unified insular avalon continent that originated in the latest precambrian this fauna correlates with the lower amorphognathus lenodus variabilis zone kundan stage of baltica and the terminal arenig upper middle ordovician lower darriwilian stage of avalonian britain available evidence suggests that an arenig cover sequence with local shallow water hematitic iron ore quartz arenite and rare limestone extended across the avalonian marginal and inner platforms from eastern newfoundland to the boston massachusetts region this western avalonian arenig shows the greatest similarity with the arenig of the welsh borderlands phosphatic fossils from the boulder have a thermal alteration index much lower than that of nearby lower paleozoic outcrops and suggest derivation of the boulder from a weakly heated avalonian succession brought into the bay of fundy region by post ordovician transcurrent faulting

impact of the vertical dynamics on the thermosphere at low and middle latitudes gitm simulations in this study the influences of the electric fields at low and middle latitudes on the ionosphere and thermosphere are investigated by using the non hydrostatic global ionosphere and thermosphere model gitm the equatorial ionization anomaly eia and the equatorial thermosphere anomaly eta are well reproduced in the simulation when the electric fields are included the term analysis of the continuity equation of the neutral mass density shows that the daytime upward vertical wind near the geomagnetic equator tends to increase the local neutral mass density at 400 km altitude while the divergence in the meridional wind associated with the meridional ion drag force tends to transport the neutral mass density away from the geomagnetic equator which might contribute to the formation of the eta trough the vertical dynamics is modulated by the vertical forces including ion drag force and pressure gradient force acting on the neutrals and the changing vertical dynamics can also feedback to vertical ion drag and pressure gradient forces particularly near the geomagnetic equator the daytime vertical ion drag force near the geomagnetic equator is generally upward while the daytime vertical pressure gradient force near the geomagnetic equator is reduced at most times after adding in the electric fields at low and middle latitudes meanwhile the sudden introduction of the electric fields at low and middle latitudes induces an acoustic wave

the low latitude boundary layer and the boundary plasma sheet at low altitude prenoon precipitation regions and convection reversal boundaries the dayside zone of soft precipitation can be divided into four distinct types of plasma regimes each corresponding to the respective magnetospheric source region the cusp the mantle the low latitude boundary layer llbl and the dayside extension of the bps based on a detailed spectral study including comparisons with nonsimultaneous isee 1 satellite llbl data we identify regions of llbl type plasma in the dmsp data set and compare these plasma boundaries with convection reversal boundaries crbs as determined by either sondrestrom or the drift meter instrument on board the dmsp f9 spacecraft the nine cases considered are all in the prenoon local time sector we find that in eight of the nine cases the crb occurs within the llbl as expected generally near to but not coincident with the equatorward edge of the llbl type plasma in our sample set chosen for cases with latitudinally wide easily identifiable llbl signatures the average latitudinal width was 1 85 magnetic latitude the crb defined as the onset of steady antisunward convection occurred about 30 of this width beyond the equatorward onset of llbl type particles the most equatorward portion of the region with llbl type plasma usually had near zero or erratic convection and may correspond to the stagnation region reported from isee observations the potential drop observed across the low altitude llbl is roughly estimated to be typically 5 kev a summary is given on how the various high altitude sources can be identified when plasma regions are observed at low altitude in the dayside auroral oval

influence of mixtures of grain size populations on the parametric and modal characteristics of coastal sands herault mediterranean sea france abstract grain size distributions in lower beach and nearshore sands of a segment of the coast of the golfe du lion france were analyzed by a parametric method and by modal analysis the results have been considered both in a spatial framework delineating geographically distinct sedimentary compartments and cells and in a morphodynamic framework separating the dynamic components of the shoreline berm collision zone inner bar outer bar lower shoreface modal statistics indicate that a mixture of three dominant components end members contributes to the grain size distribution gsd of the sediments fine sand sedimentary type i modal value 0 195 mm i 0 35 medium and coarse sand st ii modal value 0 680 mm i 0 8 and very coarse sand and gravel st iii i modal value 2 3 mm i 1 5 quasi log normal one component gsds form a minority group and mixtures produce various apparently unimodal sands and bimodal sediments a large variation of grain size indices results from mixing a simulation of mixing of log normal populations close to the end members shows the great sensitivity of parameters sorting skewness and kurtosis to small changes in the compositional formula of the mixture the procedure followed supplies a good preliminary tool enabling rapid identification and localization of the main sand sources on a regional scale these components derive from potential sources available in the region well known from previous studies st i originates from the river rhone and provides the textural base for most of the sediments st ii and iii form a local component originating either from fluvial input aude orb and herault rivers or from the nearshore reworking of ancient quaternary sediments and late holocene beachrocks each st takes on local aspects in relation to the morphological environment but the regional scale of the study was too large to precisely reflect the local morphodynamic regime a significant change in the st i sorting of bar sands is however observed probably due to the net offshore migration reported for the bar system

application of image based granulometry to siliceous and calcareous estuarine and marine sediments abstract grain size analysis has long been used as a descriptor of transport and depositional processes this paper presents the possibility of using image based granulometries not yet widely used in the earth sciences to characterize granulometric composition of unconsolidated estuarine and marine sediments to test the method conventional sediment analysis of siliceous and calcareous sediments are compared to image based analysis of sediments obtained along the ore estuary northern sweden and the adriatic sea croatia and italy these grains have different textural characteristics composition roundness and specific surface area granulometric parameters are calculated using both a graphical method and the mathematical method of moments grains have been imaged using a microscope and mathematical granulometries have been applied to the digital data image based granulometric moment descriptors are compared with sieve coulter counter derived moments although it is not claimed that digital imaging should be the only method used in sedimentology the results show the potential of applying digital electronic imaging to granulometric analysis of sediments in this way sampling for granulometric analysis and sieving processes combined with coulter counter analysis of fraction

pattern of sediment transport in a microtidal river mouth using geostatistical sediment trend analysis abstract we perform a grain size trend analysis gsta to investigate sediment transport mechanisms in the grand rhone microtidal mouth during various hydroclimatic conditions the objective is to determine the efficiency of this method to explain the directions of residual transport pattern and mode of distribution of the fluvial sediment input in an environment that is very difficult to equip with instrumentation during extreme events the known biases of this sedimentological approach are reduced by using enriched geostatistical processing and choosing periods of sampling subject to unequivocal hydrodynamic forcings the modeling results and grain size distributions of surface sediments clearly show three vector fields during periods of low river discharge the first vector field corresponds to an upstream zone under fluvial influence the second field is characteristic of a mixing zone confined inside the river mouth and marked by heterogeneous sedimentation this sector is interpreted as the confrontation zone between alluvial and marine dynamics farther offshore the vectors are oriented towards the river and at counter slope in deeper zones the vectors reflect the sediment transport generated by wave refraction at the top of the mouth bar at the delta front bathymetry from 5 m to 20 m the vectors are interpreted as representing a lag deposit the periods of medium and extreme floods are associated with storms the marine dynamic regime generates a longshore drift current which brings sediments onto the mouth bar during medium flood events only the inner part of the mouth bar is highly influenced by the river during extreme flood events the river influences both the eastern part of the mouth and the wave regime in the central part consequently the gsta method shows that even during flood events the river solid discharge is not transferred towards the adjoining upper shoreface in the context of a wave dominated delta the distribution of surface sedimentation in a microtidal mouth remains controlled mainly by the swell even in periods of flood when the intensity of river dynamics is exacerbated finally all these results are similar to the known hydro sedimentological behaviours of the rhone river mouth nevertheless gsta results seem not self sufficient to explain all the processes but this method proposes an alternative approach to traditional methods used to measure bed load sediment transfer during extreme events

downdrift coarsening of beach foreshore sediments at tidal inlets an example from the coast of new jersey analysis of grain size statistics of upper foreshore sediments on sand beaches at two tidal inlets in new jersey u s a reveals that sediments are coarser at beaches flanking the inlets than updrift although sediments become finer downdrift at the broad regional scale the local reversal of the regional trend in size grading is attributed to 1 the offshore diversion of the finer sands along the surf zone on the ebb tidal delta and 2 the removal of the finer sands from the inlet flank beach caused by low wave energy conditions at low stages of the tide and by deflation sediments thus become coarser at inlet beaches as a result of alterations in the interaction of waves with the beach and as a result of aeolian processes not solely as a result of increased tidal current velocities as previously reported the distance along the new jersey barrier islands over which inlet processes are likely to affect changes in sediment size updrift averages less than 1100 m but the impacts of inlets on the sedimentary record can be extended greater distances as a result of inlet migration

trace fossils and the aftermath of the permo triassic mass extinction evidence from northern italy abstract the duration of early triassic anoxia in the carbonate ramp settings of the werfen formation dolomites northern italy has been constrained using ichnofabric and sedimentological data this includes fine lamination and abundant pyrite framboids commonly reworked into lags by storm events the anoxic event spanned the entire griesbachian stage and extended from deep waters into extraordinarily shallow water settings evidence for oxygen deficiency can be found in mid and inner ramp facies the extent and duration of this event may at least partially explain the magnitude of the permo triassic mass extinction normal benthic conditions returned rapidly in the dienerian stage and pervasively bioturbated distal ramp facies testify to the ventilation of the deeper water areas of the region in post griesbachian times a post mass extinction radiation is not particularly well displayed in either trace fossil or body fossil diversity compilations from the dolomites moderate low levels of trace fossil diversity are maintained throughout the post griesbachian werfen formation whilst the body fossil data shows a moderate increase from the mid smithian stage there is thus a curious lag period spanning the dienerian to mid smithian when environmental conditions were apparently normal but the marine fauna failed to show any recovery

a dynamical model of high latitude convection derived from superdarn plasma drift measurements 1 a discrete set of climatological patterns of high latitude ionospheric convection are derived using line of sight plasma drift data from the super dual auroral radar network superdarn the patterns are derived independently for the northern hemisphere and southern hemisphere and for varying solar wind interplanetary magnetic field imf and dipole tilt angle conditions by interpolating between discrete patterns a dynamical model of convection is obtained which can uniquely specify the high latitude electrostatic potential distribution for a wide range of solar wind imf and dipole tilt parameter values accounting for solar wind velocity dependencies in convection leads to better resolving the large scale convection pattern as compared to previous statistical models based on superdarn data it is shown that the mesoscale features of the climatological model compare favorably to the features seen in instantaneous patterns of convection observed with superdarn comparison of the model to other statistical or empirical models derived from ground and space based measurements shows good agreement with most models

sedimentology and oceanography of early ordovician ironstone bell island newfoundland ferruginous seawater and upwelling in the rheic ocean abstract the bell island and wabana groups together comprise a ca 150 m thick succession of interbedded clastic and chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin of the rheic ocean lithofacies stacking patterns indicate that deposition occurred during a marine transgression with superimposed small scale sea level fluctuations producing at least six parasequences parasequences containing ironstone are 10 to 20 m thick and composed of hummocky cross stratified sandstone interbedded with organic rich mudstone and phosphatic fe silicate bearing siltstone which is overlain by hematitic granular ironstone capped by an erosive flooding surface this lithofacies association is interpreted to record the deposition of upwelling related ironstone on a storm dominated shelf the close relationship between fe silicates and phosphorite typical of upwelling systems suggests that fe was delivered from deep anoxic nutrient rich seawater that also stimulated high surface productivities the result was the precipitation of authigenic sedimentary apatite in anoxic organic rich sediments that accumulated near the upwelling front the gradual advection of fe rich waters away from the upwelling front initiated precipitation of fe silicate coated grains and cements in suboxic pore waters iron pumped into shallower environments through advection and fe redox cycling is interpreted to have precipitated fe oxyhydr oxide grains in sediment of the oxygenated middle shelf these coated grains were subsequently concentrated by fairweather and storm currents on the shoreface to create granular economic fe deposits we challenge conventional models of paleozoic ironstone deposition that rely on a continental source of fe by proposing a hydrothermal source that supplied fe2 to the shelf through upwelling it also highlights the potential connection between the delivery of anoxic ferruginous seawater to the margins of the rheic ocean and the early ordovician extinctions that punctuated the beginning of the great ordovician biodiversification event

a new auroral boundary determination algorithm based on observations from timed guvi and dmsp ssusi an automatic auroral boundary determination algorithm is proposed in this study based on the partial auroral oval images from the global ultraviolet imager guvi aboard the thermosphere ionosphere mesosphere energetics and dynamics satellite and the special sensor ultraviolet spectrographic imager ssusi aboard the defense meteorological satellite program dmsp f16 this algorithm based on the fuzzy local information c means clustering segmentation can be used to extract the auroral oval poleward and equatorward boundaries from merged images with filled gaps from both guvi and ssusi both extracted poleward and equatorward boundary locations are used to fit the global shape of the auroral oval with a off center quasi elliptical fitting technique comparison of the extracted auroral oval boundaries with those identified from the dmsp ssj observations demonstrates that this new proposed algorithm can reliably be used to construct the global configuration of auroral ovals under different geomagnetic activities at different local times the statistical errors of magnetic latitudes of the fitted auroral oval boundaries were generally less than 3 at 2 sigma and indicate that the the fitted boundaries agree better with b2e and b5e than b1e and b6 boundaries this proposed algorithm provides us with a useful tool to extract the global shape and position of the auroral oval from the partial auroral images

assessment of the non hydrostatic effect on the upper atmosphere using a general circulation model gcm 1 under hydrostatic equilibrium a typical assumption used in global thermosphere ionosphere models the pressure gradient in the vertical direction is exactly balanced by the gravity force using the non hydrostatic global ionosphere thermosphere model gitm which solves the complete vertical momentum equation the primary characteristics of non hydrostatic effects on the upper atmosphere are investigated our results show that after a sudden intense enhancement of high latitude joule heating the vertical pressure gradient force can locally be 25 larger than the gravity force resulting in a significant disturbance away from hydrostatic equilibrium this disturbance is transported from the lower altitude source region to high altitudes through an acoustic wave which has beensimulated inaglobal circulation model forthefirst time due to the conservation of perturbation energy the magnitude of the vertical wind perturbation increases with altitude andreaches 150 250 m sat300 430 kmduringthe disturbance the upward neutral wind lifts the atmosphere and raises the neutral density at high altitudes by more than 100 these large vertical winds are not typically reproduced by hydrostatic models of the thermosphere and ionosphere our results give an explanation of the cause of such strong vertical winds reported in many observations citation deng y a d richmond a j ridley and h l liu 2008 assessment of the non hydrostatic effect on the upper atmosphere using a general circulation model gcm geophys res lett 35 l01104 doi 10 1029 2007gl032182

palaeozoic oolitic ironstones on the north american craton abstract more than 40 mostly minor palaeozoic oolitic ironstones oi accumulated on low latitude cratonic north america almost entirely in usa a few middle cambrian oi among the oldest anywhere were deposited on the western cratonic shelf of usa widely scattered late cambrian ones developed on the southwestern southeastern and northeastern flanks of the transcontinental arch middle ordovician oi were deposited on the cratonic interior and on the southern and southeastern cratonic margins in latest ordovician time neda oi spread across north central usa east of the arch and south of the laurentian upland minor ones developed in the southern part of the taconian foreland basin after major orogeny early and middle silurian clinton oi flourished throughout the foreland basin in eastern usa producing the largest oi deposit on the north american craton minor early late silurian oi accumulated in the central part of the basin middle and late devonian oi in the acadian foreland basin in northeastern cratonic usa developed progressively westward of the encroaching catskill delta an isolated middle devonian one accumulated in southwestern cratonic usa and latest devonian ones in north central usa east of the arch during this palaeozoic episode sites of oi deposition shifted eastward across the craton most of the oi were deposited during a hiatus in normal sedimentation accumulating in the upper part of shoaling upward sequences some early palaeozoic ones occur in glauconitic siliciclastic carbonate facies and contain mostly spherical hematitic ooids these suggest derivation from iron rich soils developed on glauconitic deposits oi in wholly siliciclastic facies containing distorted chamositic ooids with cores of mud peloids were common in later palaeozoic time these oi like many other phanerozoic ones suggest a synsedimentary to early diagenetic origin

electrostatic potential drop across the ionospheric signature of the low latitude boundary layer 1 a study of the behavior of the ionospheric signature of the low latitude boundary layer is conducted from signatures of the precipitating electrons and the ionospheric convection velocity observations are made under southward interplanetary magnetic field imf conditions in a highly dynamic environment where temporal changes produce large excursions in the location of both the convection reversal boundary and the poleward edge of the particle precipitation associated with the outer edge of the low latitude boundary layer we describe the latitudinal width of the boundary layer as the displacement between these boundaries and the bulk plasma flow as the potential difference across the region on either side of local noon the boundary layer has a latitudinal width of about one degree widening to about two degrees near dawn and dusk the potential drop across the boundary layer increases toward local noon and accounts for no more than 30 of the total potential across the polar cap while the boundary layer is physically wider on the duskside than on the dawnside the average potential across the dawnside boundary layer is larger than that across the duskside layer the resulting electric field across the dawnside layer is approximately twice that found in the duskside layer we also find a higher level of variability in the boundary layer width and potential on the dawnside than on the duskside that may be related to higher levels of turbulence and wave activity associated with the orientation of the imf with respect to the bow shock

tidal asymmetry and residual circulation over linear sandbanks and their implication on sediment transport a process oriented numerical study received 12 january 2007 revised 24 july 2007 accepted 17 september 2007 published 22 december 2007 1 a series of process oriented numerical simulations is carried out in order to evaluate the relative role of locally generated residual flow and overtides on net sediment transport over linear sandbanks the idealized bathymetry and forcing are similar to those present in the norfolk sandbanks north sea the importance of bottom drag parameterization and bank orientation with respect to the ambient flow is examined in terms of residual flow and overtide generation and subsequent sediment transport implications are discussed the results show that although the magnitudes of residual flow and overtides are sensitive to bottom roughness parameterization and bank orientation the magnitude of the generated residual flow is always larger than that of the locally generated overtides also net sediment transport is always dominated by the nonlinear interaction of the residual flow and the semidiurnal tidal currents although cross bank sediment transport can occur even in the absence of a cross shore residual flow on the other hand net sediment divergence convergence increases as the bottom drag decreases and as bank orientation increases the sediment erosion deposition is not symmetric about the crest of the bank suggesting that originally symmetric banks would have the tendency to become asymmetric

behavior of grain size characteristics on reflective and dissipative foreshores broken bay australia abstract beach morphology wave current dynamics or sediment attributes such as grain size changes and sorting processes intrinsically characterize each other the extreme cases of the morphological spectrum include reflective beaches which are steep and devoid of inshore topographic expression or surf zone circulation and dissipative beaches which are flat and have inshore barred topography with attendant longshore currents and rips for a study of four beaches in broken bay australia representing these morphological extremes four facts become obvious first reflective beaches have rapid variaiton in foreshore grain size alongshore mean settling velocity changes greater than 0 3 log10 cm sec km grain size changes greater than 0 2 mm km whereas dissipative beaches have weak r variation mean settling velocity changes approximate 0 1 log10 cm sec km grain size changes less than 0 1 mm km second the pattern on reflective foreshores remains fixed over time whereas the pattern on dissipative foreshores varies to the point that size gradients can reverse direction within one year third this temporal variation reflects the directional width of the incoming wave spectra and not changes in the level of wave power reflective beaches have waves approaching almost shore normal because of the nullification of deep water variation by wave refraction or by the sheltering effects of headlands wave approach on dissipative beaches varies daily and the beach planform and sediment must respond over time to this variation fourth grain size changes fit one of two postulates the energy postulate states that grain size and sorting increase along a foreshore as energy increases the drift postulate states that grain size increases downdrift the energy postulate is more appropriate on reflective beaches whereas the drift postulate accounts for the difference in the magnitude of grain size changes alongshore between reflective and dissipative beaches on reflective foreshores coarse material is naturally concentration at the base of the swash zone because of gravity effects or shear sorting in backwash larger grains here move faster alongshore than finer ones near the top of the foreshore because longshore currents at the base of the swash are stronger than the zigzag motion of swash drift further up the beach face this drift sorti g produces strong longshore size gradings on the foreshore this effect is negated on dissipative beaches by swash bore transport of coarse grains upslope by dilution with inshore sediment that has undergone preferential movement of fines alongshore in suspension and by locally reversed longshore currents near rips

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

an interpretation of trends in grain size measures abstract the mean grain size sorting and skewness of a sedimentary deposit are dependent on the sediment grain size distribution of its source and the sedimentary processes of i winnowing erosion ii selective deposition of the grain size distribution in transport and iii total deposition of the sediment in transport if a source sediment undergoes erosion and the resultant sediment in transport is deposited completely the deposit must be finer better sorted and more negatively skewed than the source this trend is referred to as case i the lag remaining after erosion on the other hand must be coarser better sorted and more positively skewed case ii if sediment in transport undergoes selective deposition the resultant deposit can either be finer case iiia or coarser cas iiib than the source but the sorting will be better and the skew more positive although exceptions to these trends may occur they suggest that comparison of one sediment must be made with another for the proper identification of the sedimentary process and therefore it is not possible for a single grain size distribution to identify the depositional environment the trends also suggest that the skewness of a grain size distribution has been widely misinterpreted and implies neither the truncation of one of the tails nor the mixing of more than one mode rather a skewed sediment is the natural result of the sedimentary process in a system of related environments these trends can be used to identify both the probable source and the probable deposit and by inference the net sediment transport paths among sedimentary deposits such an analysis provides a rapid understanding of the sedimentary processes identifies patterns of erosion and accretion and may suggest transport processes

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

the early paleozoic development of bioturbation evolutionary and geobiological consequences abstract bioturbation the physical and chemical mixing of sediments by burrowing animals is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean wide biogeochemical cycling well mixed sediments have long been assumed to appear at the precambrian cambrian boundary with the first occurrence of the index fossil and three dimensional burrow treptichnus pedum however field based analyses synthesizing ichnological stratigraphic sedimentological and taphonomic data collected from lower paleozoic successions worldwide indicate that sediment mixing in marine shelf environments remained limited until at least the late silurian 120 million years after the precambrian cambrian transition in spite of early advances in complex modes of infaunalization mixed layer development had a much more gradual trajectory and did not occur in step with the first appearance of three dimensional burrows the delayed appearance of modern style intensities of sediment reworking postdating both the cambrian explosion and the great ordovician biodiversification event may be due to the late stage radiation of mobile infaunal deposit feeders biological bulldozers the organisms which are in modern marine settings the most efficient bioturbators the protracted development of the sediment mixed layer holds important implications for contemporaneous biogeochemical cycling and oxygenation of the ocean atmosphere system the delayed development of intensive sediment mixing may have also mediated exceptional preservation of both fossilized soft tissues and shallow tier trace fossils and may therefore have contributed to the anomalous preponderance of konservat lagerstatten and exceptionally preserved shallow tier trace fossils and bioglyphs characteristic of the lower paleozoic stratigraphic record

sediment sorting at the sand motor at storm and annual time scales bed sediment composition with a focus on the median grain size d50 was investigated at a large scale nourishment the sand motor at the dutch coast 21 5 million m3 sand considerable alongshore heterogeneity of the bed composition d50 was observed as the sand motor evolved over time with 1 coarsening of the exposed part of the sand motor 90 to 150 m and 2 a depositional area with relatively fine material 50 m finer just north and south of the sand motor the alongshore heterogeneity of the measured d50 values was most evident outside the surfzone i e seaward of msl 4 m coarsening of the bed after construction of the sand motor was attributed to hydrodynamic sorting processes because the alongshore heterogeneity of the d50 showed a similar spatial pattern as the mean bed shear stresses the observed alongshore heterogeneity of the d50 and correlation of d50 with modelled mean bed shear stresses suggest that preferential erosion of the finer sand fractions has taken place the selective transport of finer sand fractions results in a coarser top layer of the bed at the sand motor the preferential transport is most dominant during mild and moderate conditions when hydrodynamic forcing conditions are close to the critical bed shear stresses for transport the measurements also show the impact of a storm which consists of a 40 m finer d50 of the offshore bed composition in front of the sand motor i e where a considerably coarser bed was in place additionally storms may generate a temporary zone with fine bed material at the toe of the deposition profile this means that the coarsening of the bed is reduced by storms as a result of the mobilization of both coarse and fine sediment and mixing of the bed with the relatively finer substrate

microbial mats implicated in the generation of intrastratal shrinkage synaeresis cracks intrastratal shrinkage often termed synaeresis cracks are commonly employed as diagnostic environmental indicators for ancient salinity stressed transitional fluvial marine or marginal marine depositional environments despite their abundance and use in facies interpretations the mechanism of synaeresis crack formation remains controversial and widely accepted explanations for their formation have hitherto been lacking sedimentological ichnological petrographic and geochemical study of shallow marine mudstone beds from the ordovician beach formation of bell island newfoundland has revealed that crack development cf synaeresis cracks on the upper surface of mudstone beds is correlated with specific organic geochemical and sedimentological parameters contorted sinuous sand filled cracks are common at contacts between unbioturbated mudstone and overlying sandstone beds cracks are absent in highly bioturbated mudstone and are considered to pre date firmground assemblages of trace fossils that include planolites and trichophycus the tops of cracked mudstone beds contain up to 2 1 wt total organic carbon relative to underlying mudstone beds that contain around 0 5 wt total organic carbon high resolution carbon isotope analyses reveal low 13corg values 27 6 on bed tops compared with sandy intervals lacking cracks 24 4 to 24 9 cracked mudstone facies show evidence for microbial matgrounds including microbially induced sedimentary structures on bedding planes and carbonaceous laminae and tubular carbonaceous microfossils in thin section non cracked mudstone lacks evidence for development of microbial mats microbial mat development is proposed as an important prerequisite for intrastratal shrinkage crack formation both microbial mats and intrastratal shrinkage cracks have broad palaeoenvironmental distributions in the precambrian and early phanerozoic in later phanerozoic strata matgrounds are restricted to depositional environments that are inhospitable to burrowing and surface grazing macrofauna unless evidence of synaeresis i e contraction of clay mineral lattices in response to salinity change can be independently demonstrated the general term intrastratal shrinkage crack is proposed to describe sinuous and tapering cracks in mudstone beds

marcasite in black shales a mineral proxy for oxygenated bottom waters and intermittent oxidation of carbonaceous muds abstract black shales in the geologic record have long been considered to reflect deposition under anoxic or even euxinic conditions although bottom water anoxia favors deposition of black shales certain biological indicators such as benthic fossils and bioturbation suggest that bottom water conditions may not have been as persistently anoxic as commonly presumed examination of twelve marine carbonaceous shale bearing units ranging in age from middle proterozoic to cretaceous suggests that in addition to paleontological clues early diagenetic marcasite formed in uncompacted surficial sediments is a reliable indicator of oxygen bearing bottom waters marcasite requires low ph values to form and oxidation of already existing sedimentary pyrite provides a plausible chemical scenario to achieve that condition in the studied examples degraded pyrite framboids and corrosion features on pyrite grains indicate partial pyrite destruction in surface sediments and suggest that intermittent reoxidation of earlier formed iron sulfides may indeed have generated the low ph values required for marcasite formation thus observations of textures spatially associated with secondary marcasite growth are consistent with a scenario whereby oxygen in overlying sea water drove downward migration of oxidation fronts pervasive marcasite in black shales from a wide range of occurrences suggests multiple reoxygenation events during the deposition of these shale units and calls for more dynamic ocean circulation than previously assumed the latter consideration may for example prove important for those instances where a black shale is associated with an oceanic anoxic event oae because these are commonly presumed to have been deposited under fully anoxic conditions

transport of riverine sediment from different outlets in the pearl river estuary during the wet season abstract riverine sediment is important for the development of river deltas and for carrying both nutrients and contaminants into estuaries and coasts previous studies of sediment transport have focused on single sourced estuaries and paid less attention to multi sourced estuaries estuaries with multiple river discharge sources in this study we used the coupled ocean atmosphere wave sediment transport coawst modeling system to study the sediment transport in the pearl river estuary pre where riverine sediments come from four different outlets during a typical wet season 2007 about 6 8 million tons of riverine sediments were discharged into the pre most of which were trapped in shoals during neap tides while about 11 8 by mass was transported out of the estuary during spring tides the proportions of the multi sourced sediments trapped in the pre or escaping from the estuary depended on the morphology of the estuary and the location of the outlets in relation to the estuarine morphology the distributions of different riverine sediments were mostly independent in neap tides but overlapped more in spring tides the seaward sediment transport was dominated by river freshwater discharge in the upper estuary and by tidal forcing in the lower channels while tides and winds controlled the sediment transport in the lower shoals this study aids our understanding of sediment transport processes in multi sourced estuaries and has implications for coastal environmental management

modelling of bed sediment composition changes at the lower shoreface of the sand motor abstract large perturbations in the coastline such as the sand motor nourishment 21 million m3 at the holland coast can initiate considerable spatial and temporal changes in the median grain size d 50 of the sea bed on the lower shoreface the relevance of hydrodynamic conditions for the development of the heterogeneity in d 50 at large scale nourishments was assessed with a numerical model delft3d which required a validation against 2 5 years of d 50 measurements a good representation of the observed spatial pattern of d 50 was obtained independent of a 2dh or 3d approach and initial condition for the d 50 of the bed five sediment size fractions and a multi layer administration of the bed composition were used the extent and magnitude of the coarsening of the bed is related to the velocity of the horizontal tide while a far less pronounced coarsening takes place during energetic conditions i e h m 0 3 m differential suspension behaviour between the size fractions which are all mobilized at the bed causes a preferential transport of fine sediment in alongshore direction away from the sand motor at the lower shoreface i e seaward of msl 6 m storm conditions may induce a partial removal of the coarse top layer due to mobilization of all of the size fractions and mixing with the relatively fine substrate material simulations also show that transport of the fine sand fraction extents to much deeper water than for the medium and coarse sand fractions models with multiple sediment fractions are therefore required for the assessment of environmental impacts of large scale coastal structures or land reclamation s and sediment transport on the lower shoreface

the use of grain size trend analysis in macrotidal areas with breakwaters implications of settling velocity and spatial sampling density abstract in a macrotidal environment with offshore breakwaters elmer west sussex a new approach for the identification of the sediment transport pathways with grain size trend analysis gsta was undertaken using statistical parameters mean sorting and skewness directly derived from settling velocities distributions the same samples were analysed with sieving quarter and half phi resolution and gsta was performed again in order to directly compare the resultant sediment transport directions derived with the two analytical techniques furthermore both regular and irregular sampling distributions were used to recalculate gsta hydrodynamic data were collected in different locations around the breakwaters and net sediment transport directions were calculated in order to assess the accuracy of the sediment transport pathway directions derived with the different analytical techniques the accuracy of settling velocity in determining the statistical parameters of the grain size distribution is identified especially for the fine medium sand sediments settling velocities produced better results than the sieving the quarter phi resolution producing the poorer results in comparison with the coarser half phi resolution the results for the different spatial sampling strategies are found to depend upon the number of samples utilised that shows that the accuracy of the gsta is based upon the ability of representing adequately the spatial distribution of the sediment parameters

statistical patterns of high latitude convection obtained from goose bay hf radar observations we have derived patterns that describe the statistical interplanetary magnetic field imf dependencies of ionospheric convection in the high latitude region of the northern hemisphere the observations of plasma motion were made with the hf coherent backscatter radar located at goose bay labrador over the period september 1987 to june 1993 the area covered by the measurements extended poleward of 65 to a working limit of about 85 distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics the patterns are the first derived from direct ground based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies rich and hairston 1994 weimer 1995 we show the dependence of the convection on imf angle in the gsm y z plane for three intervals of imf magnitude in this plane except for predominantly northward imf the convection is primarily two cell the dusk cell is larger in terms of both spatial extent and potential variation the effect of imf by is apparent in the global shaping of the cells and the orientation of the overall pattern in mlt for by by the dusk dawn cell is more round crescent shaped and the pattern more rotated toward earlier mlts the by effect on the nightside convection is pronounced and is hemispherically antisymmetric like the well known day side by effect for imf increasingly northward the convection trajectories on the dayside become increasingly distorted evolving through a three cell to a four cell circulation the additional cells appear on either side of the noon meridian and result in sunward flow the overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with weimer 1995 there are significant differences with the statistical patterns derived from magnetometer measurements which tend to show domination by the dawn rather than the dusk cell

radio frequency identification rfid technology applied to the definition of underwater and subaerial coarse sediment movement abstract in this paper radio frequency identification technology has been applied to track both underwater and subaerial displacement of pebbles along an artificial coarse beach at marina di pisa italy several preliminary laboratory tests have been performed to adapt the rfid technique for underwater use which has been the primary impediment to this promising approach to the study of coarse sediment transport and movement tests showed the reliability of low frequencies for this kind of work since they enable good signal transmission and reception through water passive abs plastic transponders were inserted into about 100 pebbles and released onto the beach in march 2009 a core 125 reader was chosen as the operating antenna to continuously transmit low frequency 125 khz signals an acoustic signal toned whenever a pebble was detected while the unambiguous identification code of the pebble is shown immediately on the screen of a laptop connected to the reader the positions of the pebbles were recorded with a total station after two months may 2009 74 marked pebbles were retrieved 77 of the total the positions of the retrieved pebbles were also recorded with the total station thus allowing calculation of the coarse sediment transport tendency about 60 of the recovered pebbles 44 out of 74 were found on the upper shoreface the analysis of the marked pebble trajectories revealed a divergent transport movement in the northernmost sector of the beach this movement was probably triggered by an irregularity of the submerged breakwater fronting the shoreline the southern sector is characterised by chaotic pathways related to the formation and evolution of beach cusps this outcome highlights and confirms the importance of a complete definition of the beach system with no separation between the underwater and the subaerial portion of the shore when it comes to sediment transport and movement this successful application of rfid technology to the underwater environment provides a chance to broaden understanding of a topic in need of further study

lithostratigraphy of the cambrian lower ordovician bell island and wabana groups of bell little bell and kellys islands conception bay eastern newfoundland the upper cambrian arenigian succession of bell little bell and kellys islands conception bay eastern newfoundland consists of at least 1500 m of interbedded micaceous sandstones siltstones shales and ironstones the succession has previously been formally subdivided into only two groups namely a lowermost bell island group and an overlying wabana group the existing lithostratigraphic nomenclature below group level has to date only been informally proposed and is therefore herein formally revised the lowermost bell island group comprises from base to top the kellys island little bell island beach redmans ochre cove and dominion formations of these the ochre cove and dominion formations are newly proposed and the beach formation is considerably revised from its historical usage the beach formation contains two newly proposed members the mcgraw and eastern head members both of which in previous nomenclature were informally referred to as beds the disconformably overlying wabana

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

deriving transport pathways in a sediment trend analysis sta abstract sediment trend analysis sta is a technique that enables patterns of net sediment transport to be determined by relative changes in grain size distributions of all naturally occurring sediments in addition sta can determine the dynamic behaviour of bottom sediments with respect to erosion accretion or dynamic equilibrium the data requirements for sta are the full grain size distributions taken from sediment grab samples collected at a regular spacing over a particular area of interest two types of methods are presently used in the derivation of the transport pathways a line by line approach in which transport pathways are determined by searching for sample sequences in which the distributions change in a statistically acceptable manner and various vector approaches in which each sample is compared to neighbouring sites from which a vector sum is calculated the basic assumption for sta is that the processes that cause sediment transport will affect the statistics of sediment distributions in a predictable way in reality this type of analysis is complicated through the inclusion of a number of uncertainties or noise the goal of sta is to extract the information the transport pathways from the noisy signal the grain size distributions an approach that is made difficult because neither the nature of the information nor the noise is known because of this obtaining results by simply applying its theory in a black box approach may provide poor solutions the line by line approach to sta draws from communications theory to achieve a solution in some communications systems the information from many sources is combined into one signal the resulting signal is from a statistical viewpoint nothing but noise the extraction of specific information assumes that information is indeed present and determines if that assumption is consistent with the received signal for sta the procedure is to assume a transport direction over an area comprising many sample sites from this assumption the predicted sediment trends are compared with the pathways determined by the actual samples the assumed transport direction is repeatedly modified until the best fit is achieved vector techniques may be very helpful to provide insights and guidance to the line by line approach however the approach is ultimately necessary to finalize a credible solution as well as providing important further information on the dynamic behaviour of the sediments and to delineate specific sediment transport environments

residual transport model in correlation with sedimentary dynamics over an elongate tidal sandbar in the gironde estuary southwestern france abstract this study qualitatively describes by a multidisciplinary approach hydrodynamic and residual sediment transport over a sandbar in a macrotidal environment the sandbar is elongated and attached to a headland that is located in the gironde estuary southwestern france bathymetric surveys side scan sonar sonograms grain size trends of surficial sediment and 2dh numerical simulations of current patterns were used to define a conceptual model for the dynamics of this sandbar the sandbar is oriented anticlockwise with respect to the main flow the channel oriented bar face is ebb dominated whereas the opposite face is flood dominated resulting in a clockwise residual transport the line of sediment flux convergence corresponds to the crest of the bar the residual flow over the bar appears to originate from the regional estuarine flow the dominant process responsible for the maintenance of the sandbar seems to be the depth averaged main tidal flow rather than secondary circulation due to headlands or the interaction between the tidal flow and the seabed to generalize this regional conceptual model a qualitative comparison is made with the theories of sandbar dynamics due to tidal currents pingree and maddock 1979 zimmerman 1981 huthnance 1982 and others the seabed stability approach developed by huthnance 1982 seems to be the most reliable theory to explain the saint georges bank dynamics even though many natural factors are not taken into account

the role of wave reworking on the architecture of storm sandstone facies bell island group lower ordovician eastern newfoundland stacked shallow marine cycles in the lower ordovician bell island group of bell island newfoundland show upward thickening and upward coarsening sequences which were deposited on a storm affected shelf in the beach formation each cycle has a facies sequence comprised from base to top of dark grey mudstones light grey mudstones tabular sandstones and mudstones lenticular sandstones and mudstones and thick bedded lenticular sandstones reflecting a progressive increase of wave orbital velocities at the sediment surface the mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents the lenticular sandstones in the succeeding facies are wave reworked sands commonly lying in erosional hollows and having erosional tops and internal hummocky cross stratification planar lamination is relatively uncommon and sole marks are mainly absent in this facies oscillatory currents were dominant and accumulated sand in patches generally 10 30 m in diameter the facies formed on the inner shelf where the oscillatory currents generated by storm waves had powerful erosional effects and also determined the depositional bedforms mud partings and second order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds this interpretation has important implications for attempts to estimate event frequency by counting sandstone beds within a sequence and for estimates of sand budgets during storm events the thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings in the overlying redmans formation the process of amalgamation progressed even further so that nearly all the mud partings were removed resulting in the formation of thick bedded tabular sandstones sequence stratigraphic analysis of the cyclical sequence suggests that the cycles were eustatically controlled the rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb there is a gradational but rapid facies transition from the tabular to the lenticular sandstone facies which is interpreted as occurring at the inflexion point on the falling limb the thick bedded facies of the beach formation and the thick bedded tabular facies of the redmans formation represent periods of maximum sea level fall the stacked cycles in the beach formation are interpreted as an aggradational high frequency sequence or parasequence set bounded at the top by a sequence boundary and succeeded by the three aggradational parasequences of the redmans formation the recognition of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies

the grain size characterisation of coastal sand from the somme estuary to belgium sediment sorting processes and mixing in a tide and storm dominated setting abstract sand rich holocene to modern clastic deposits in the eastern english channel and the southern north sea coasts of france and belgium occur extensively as nearshore sand bank estuarine tidal flat aeolian dune and beach sub environments sand samples n 665 collected from these deposits suggest the presence of three different populations a largely dominant 83 medium to fine quartz sand population b and finer 14 and coarser grained 4 populations respectively c and a the distribution of these populations among the four sub environments reflects tide and storm dominated sorting and transport processes and a variable degree of mixing these populations are derived from a mixture of very fine to very coarse grained fluvial outwash and paraglacial sediments deposited on the beds of the eastern english channel and southern north sea during the late pleistocene lowstand the nearshore sand bank environment which also corresponds to the main offshore source area of the coastal deposits exhibits population heterogeneity reflecting the variability of hydrodynamic conditions and sediment sorting in this zone the nearshore topography of tidal ridges banks and troughs in these tidal seas leads to variable bed and tide and storm induced shear stress conditions these conditions only allow for the mobilisation and onshore transport of some of the finer fractions populations b and c leaving an offshore mixture of these finer populations with coarser less mobilisable sediments population a once in the coastal zone these two finer populations undergo further hydrodynamic sorting and segregation variably sorted very fine sands to silts population c are trapped in the low energy estuarine tidal flat sub environment while the highly homogeneous population b is further sorted in aeolian dune and beach sub environments this sorting occurs via a coastal sand transport pathway linking the somme estuary mouth to the southern north sea bight where tidal range and wave energy decrease relative to the english channel since this sand transport pathway enables longshore transport of hydrodynamically sorted medium to fine sand derived directly from the immediate nearshore zone it has further contributed to a net flux of this sand population from the eastern english channel sea bed to the southern north sea

crowded rosselia ichnofabric in the early devonian of brazil an example of strategic behavior abstract the occurrence of crowded rosselia ichnofabric in early devonian deposits of transition beds western gondwana parana basin southern brazil and the paleobiology and paleoecology of its potential tracemakers are discussed in this paper crowded rosselia ichnofabric has been recorded chiefly in cenozoic storm beds associated with high sedimentation rates on the inner shelf and is usually interpreted as resulting from opportunistic behavior of terebellid polychaetes rosselia is a common ichnotaxon in the archetypical cruziana ichnofacies developed preferentially in fair weather deposits formed in inner shelf settings during storm surges however this endobenthic community is strongly affected decimating those that are unable to escape new records presented herein reinforce the conclusion that short term colonization represented by crowded rosselia ichnofabric occurs essentially in erosive storm deposits of high sedimentation rates rather than being opportunistic the crowded rosselia ichnofabric appears to be the result of a strategic behavior developed by stress tolerant terebellid polychaetes in inner shelf zones during or just after storm surges this strategic behavior appeared during the early paleozoic and was adopted by terebellids from their earliest appearance

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

sand transport under the combined influence of waves and tidal currents an assessment of available formulae abstract various formulae are used to predict the transport of sand under the combined influence of waves and currents these approaches include the use of the unidirectional formulae of einstein 1950 frijlink 1952 yalin 1963 engelund and hansen 1967 sternberg 1972 ackers and white 1973 and gadd et al 1978 modified for the presence of waves in accordance with the techniques described by bijker 1967 and swart 1976 and those of bagnold 1963 madsen and grant 1976 and vincent et al 1981 predicted rates are compared with measurements based upon fluorescent sand tracer studies in an area of high tidal current and wave energy northern bristol channel u k in general predicted rates are lower than those measured and only the formulae of madsen and grant 1976 and the modified formula of sternberg 1972 appear to provide realistic estimates of transport under wave and tidally induced currents in comparison with the field measurements

sediment transport patterns inferred from grain size trends and trace metal dispersion near the santa rosalia mining district gulf of california abstract the transport of continental materials of natural and or anthropic origin as well as their dispersion and final deposition in marine environments can be inferred from the analysis of the textural tendencies of sediments the exploitation of copper ore since the 19th century in the santa rosalia mining district has caused the accumulation of potentially toxic elements ptes in sediments off the western coast of the gulf of california however after several decades of mining little is known about the mobilization and final destination of these ptes in the present work the net sedimentary transport and dispersion of cu and zn is inferred in front of the mining district of santa rosalia at the western margin of the gulf of california net sedimentary transport is dominantly towards the southeast with a change towards the east of the port of santa rosalia the spatial distribution of cu and zn showed the same pattern as the net sediment transport which suggests that the dispersion of ptes is controlled by the textural tendencies of the sediments and their transport corroborated by hydrodynamic models of the marine currents at the western margin of the gulf of california

sediment transport patterns determined from grain size parameters overview and state of the art abstract grain size trends have been applied in many diverse sedimentary environments to determine sediment transport paths generally coinciding with information from tracer studies current measurements and the orientation of sedimentary structures the different methods proposed to date are critically analysed and compared with reference to recent field studies it is concluded that the two dimensional methods produce comparable results and may in fact complement each other in spite of the advances several problems still exist which include the sampling method and density the choice of trend types the relative weight of grain size parameters and the interpretation of results these are discussed together with possible solutions

influence of trace metals in recent benthic foraminifera distribution in the pearl river estuary this work analyzed the distribution of trace metals and benthic foraminifera in the pearl river estuary and studied the influence of environmental parameters i e trace metals organic matter and sediment grain size on the total living plus dead benthic foraminiferal assemblages the results indicate that the distribution patterns of co cr cu ni pb and zn are strongly related to the behavior of the sedimentary clay fraction kaolinite and illite and are dispersed with sedimentary material whereas ba sr v and zr follow different trends the study area is moderately to severely polluted with co cr cu ni pb and zn and maximum values were found in the upstream and on the western side of the estuary where the lowest levels of h s fisher alpha index and number of species are situated analyses of species abundance and community diversity as well as the subsequent canonical redundancy analysis were conducted to reveal the relationship between the foraminifera data and environmental parameters two assemblages were established by cluster analysis and were distributed in relation to bathymetry the distribution of foraminiferal assemblages was mainly determined by cu zn and pb while sand may exert an influence on particular species ammonia tepida haplophragmoides canariensis and elphidium nakanokawaense are tolerant to the metal enrichment while the abundances of the other species decline and are prejudiced this study indicates that benthic foraminifera can be used as a bio indicator of trace metal pollutants in the pearl river estuary and the results promote a better understanding of the response of benthic foraminifera to human induced pollution in estuaries c 2014 elsevier b v all rights reserved

a geophysical interpretation of the geology of conception bay newfoundland geophysical data from conception bay and the adjacent peninsulas of the avalon peninsula newfoundland are presented and quantitatively interpreted using two dimensional models to interpret the geology beneath the bay the portion of the bay underlain by mafic volcanic rocks is determined and the maximum extent of the cambro ordovician rocks containing the wabana hematite deposit is delineated all gravity and magnetic anomalies in the area are explained in terms of density and magnetic susceptibility variations confined to the upper 12 km of the crust the geophysical models indicate that mafic volcanics underlie a significant portion of the study area and are more extensive than indicated by the surface outcrop on land the models also indicate significant vertical movement on the topsail fault and on the extension of a fault passing out into the bay near holyrood the cambro ordovician sediments are confined to the southern portion of the block bounded by these faults the geophysical data are unable t

role of metalliferous mudstones and detrital shales in the localization genesis and paleoenvironment of volcanogenic massive sulphide deposits of the tally pond volcanic belt central newfoundland canada the cambrian tally pond volcanic belt in central newfoundland contains numerous volcanogenic massive sulphide vms deposits and prospects associated with exhalative metalliferous mudstones deposits in the belt are bimodal felsic vms deposits that are both base metal bearing e g duck pond boundary and base metal and precious metal bearing lemarchant at the lemarchant deposit metalliferous mudstones are stratigraphically and genetically associated with mineralization in the remainder of the tally pond belt detrital shales occur predominantly in the northeastern part of the belt mostly as unrelated mid ordovician structural blocks in the upper sections of the cambrian volcanic stratigraphy but locally also are intercalated with metalliferous mudstones their relationships to massive sulphides are less obvious with many spatially but not necessarily genetically related to mineralization upper cambrian to lower ordovician black shales from bell island which represent pelagic sedimentation not associated with hydrothermal activity and volcanism are compared with the tally pond belt mudstones and shales exhalative mudstones like those at lemarchant have elevated fe al and base metal values and have shale normalized negative ce and positive eu anomalies indicative of deposition from high temperature 250 c hydrothermal fluids within an oxygenated water column mudstones and shales sampled from other tally pond prospects have more variable signatures ranging from hydrothermal to nonhydrothermal black shales no positive eu anomalies flat rare earth element patterns low fe al and base metal contents to those that have mixed signatures accordingly mudstones from areas with a lemarchant like hydrothermal and vent proximal character are more attractive exploration targets than mudstones and shales with predominantly detrital signatures

cambrian successions of the meguma terrane nova scotia and harlech dome north wales dispersed fragments of a peri gondwanan basin abstract the meguma terrane of nova scotia and the harlech dome of north wales preserve similar sedimentary successions of cambrian age both successions comprise a thick succession of early cambrian sandstone turbidites overlain by early to middle cambrian alternating mud rich and sand rich units in which manganese is concentrated in two stratigraphic intervals above these both successions comprise anoxic organic rich turbidites shallowing upward into paler more bioturbated tremadocian mudstone with rhabdinopora within the limited constraints of the available biostratigraphic and geochronological data major changes in environment occurred synchronously in the two successions both successions show much greater similarity to each other than to adjacent successions on avalonia9 a detrital zircon analysis from the rhinog formation low in the harlech dome succession reveals distinct clusters of ages around 537 ma and 2 0 2 1 ga a close similarity to analyses from the meguma terrane suggests proximity between the two terranes on the margin of gondwana during the cambrian period we suggest the term megumia for the palaeogeographical domain that included the two successions which was dispersed during subsequent appalachian and caledonian movements these observations suggest that megumia may have separated terranes previously regarded as parts of avalonia supplementary material u pb detrital zircon analytical data are available at http www geolsoc org uk sup18431

empirical high latitude electric field models electric field measurements from the dynamics explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn dusk ogo 6 measurements j p heppner 1977 the analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones paralleling the previous analysis the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the y component of the interplanetary magnetic field the objective which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns is met by deriving one pattern model bc for the northern hemisphere with a y interplanetary magnetic field imf and southern hemisphere with a y imf and two patterns models a and de for the northern hemisphere with a y imf and southern hemisphere with a y imf the most significant large scale revisions of the ogo 6 models are 1 on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the imf y component 2 on the nightside where a westward flow region poleward from the harang discontinuity appears under model bc conditions and 3 magnetic local time shifts in the positions of the convection cell foci the modeling above was followed by a detailed examination of cases where the imf z component was clearly positive northward neglecting the seasonally dependent cases where irregularities obscure pattern recognition the observations range from reasonable agreement with the new bc and de models to cases where different characteristics appeared primarily at dayside high latitudes the analysis of these differences for strong bz conditions using passes through different mlt zones led to finding that the deviations from both the bc and de models could be modeled by extending the evening cell foci toward and beyond noon with a deformation that roughly resembles a rotational twist of the extended evening cell the morning cell accommodation to the model bc deformation produces a narrow tongue of eastward convection near 75 invariant latitude on the dayside the model de deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 mlt sector in both cases the deformations of the two cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern thus the nightside dilemmas that plague three and four cell models designed to explain sunward convection in polar regions under bz conditions do not appear

sand waves and sediment transport around the end of a tidal sand bank two detailed surveys have been made of the north western end of the haisborough sand off the norfolk coast using echosounder 3 5 khz reflection profiler and side scan sonar asymmetrical sand waves indicate north westerly sand movement on the southern side and south easterly sand movement on the steeper northern side of the bank secondary superimposed megaripples which are probably better indicators of sediment movement give evidence of a cross bank component between the north westerly and south easterly facing sand waves on the tip of the bank there is a zone of symmetrical sand waves these are usually taken to indicate zero net transport but in this case the oblique orientation of megaripples in their troughs indicates transport parallel to the sand wave crests this suggests the route by which sand travels around the end of the bank to form a roughly closed circulation sediment textural parameters support the notion that sand is winnowed from the foot of the bank on both sides and is transported to the middle with an overall net transport from the south to the north analysis of charts dating back to 1886 shows that the bank is stable within the error limits of position fixing though that could allow more than 0 25 km shift to the north east in 100 years to pass undetected a box model is drawn up for the estimated sediment fluxes around the end of the bank and implications for residence times and circulation rates are drawn from it