morphology faunas and genesis of ordovician hardgrounds from southern ontario canada abstract we have used associations of different microfacies to define facies or microfacies associations which form reasonably well defined sequences which we infer from analogies with recent and ancient carbonate environments to have been deposited in a shelf environment characterized by small scale topographic differentiation into shoal slope and basinal environments shoal environments are characterized by typically cross bedded well sorted bioclastic sands with intershoal areas consisting of interbedded bioclastic sands and heavily bioturbated finer grained carbonates slope and basinal environments are typically represented by proximal and distal cycles respectively these we compare with deposits of carbonate ramp bypass channels and with the more thoroughly studied deep water clastic submarine fans many of the strong variations in environmental energy in these proximal and distal cycles can be attributed to migration of channels on the fans and the effect of funnelling of storm surges down the channels although hardground morphology and faunas are mostly related to local effects such as intensity of scouring time of exposure topographic differentiation of the surface and other factors differing hardground types tend to be found in different environments smooth and rolling hardgrounds occur in the deeper distal environments where the beds were subject to only slight scour and often limited exposure before renewed sedimentation hummocky and undercut hardgrounds are characteristic of the middle parts of proximal cycles where they developed marginally to the main bypass channel and in intershoal areas both these areas are sites of intermittent sedimentation and moderate turbulence where cemented beds may be exposed for some time in environments optimal for attached benthos these hardgrounds usually contain the most diverse hardground biotas pebbly and reworked hardgrounds occur in coarse basal units of proximal cycles which are interpreted as the grain flow fillings of the central parts of bypass channels though isolated examples occur in intershoal areas and in the higher parts of proximal channels these hardgrounds contain low diversity faunas reflecting the stresses imposed by intermittent or constant abrasion though some contain more diverse faunal assemblages formed after redeposition

late ordovician massive bedded thalassinoides ichnofacies along the palaeoequator of laurentia abstract massive bedded thalassinoides ichnofacies occurs pervasively in widely separated areas on the vast upper ordovician carbonate platforms along the palaeoequator of laurentia from the borglum river formation in north greenland through the red river formation and bighorn dolomite of the williston basin manitoba canada to wyoming usa to the ely springs dolomite and equivalent strata of the eastern great basin utah and nevada usa the late ordovician thalassinoides is characterised by complex three dimensional anastomosing or multi level galleries that are consistent in size pattern and density with preserved depth of 1 m or greater in addition to the similar thalassinoides burrows the ichnofacies across the palaeocontinent also contains typical taxa of the red river biota such as the soccer ball sized receptaculitid fisherites large shelled diverse and abundant nautiloids the distinctively planispiral gastropod maclurina as well as diverse tabulate and rugose corals the consistent characteristics of the red river biofacies and thalassinoides ichnofacies suggest a palaeogeographically homogeneous and temporally stable depositional environment along the palaeoequatorial belt of laurentia during the pre hirnatian late ordovician the thalassinoides ichnofacies marked the first phase of mega scale invasion of burrowers into relatively deep water platform and shelf environments by successively creating a well oxygenated deep burrow system for protection and deposit feeding such substrate tiering expansion constituted an important aspect of the great ordovician biodiversification event

lower triassic peritidal cyclic limestone an example of anachronistic carbonate facies from the great bank of guizhou nanpanjiang basin guizhou province south china abstract most shallow marine sections described from the lower triassic formed in mixed carbonate siliciclastic systems shallow marine limestones from an isolated carbonate platform the great bank of guizhou in the nanpanjiang basin south china provide a unique opportunity to examine a pure peritidal carbonate depositional system the platform had a low relief bank profile in the early triassic with oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and pelagics debris flow deposits and turbidites on gentle basin margin slopes interior strata are 265 m thick beginning in the lowermost triassic with renalcis biostromes followed by lime mudstone oolite and cyclic peritidal limestone the cyclic limestone is olenekian in age 164 m thick and contains up to 83 cycles parasequences parasequences are 0 2 7 4 m thick and typically shallow upward from subtidal oolite grainstone and skeletal packstone facies followed by renalcis reef mounds or biostromes and capped by intertidal flaser bedded ribbon rock the skeletal packstone and reef mounds contain a low diversity biota of cyanobacteria echinoderms bivalves gastropods lingulid brachiopods spirorbids and ostracodes ribbon rock contains alternating lime mud and fine peloidal packstone and grainstone laminae scour surfaces ripple cross lamination lime mud drapes and minor prism cracks parasequence stacking patterns exhibit gradual increase and decrease of parasequence thickness defining a third order sequence boundary and several 4th order parasequence sets that correlate between interior sections parasequence stacking patterns similar to those of lower palaeozoic green house sequences and different from ice house sequences the lower triassic platform interior parasequences represent an anachronistic facies in that they are strikingly similar to the common renalcis mound ribbon rock parasequences of the lower palaeozoic and different from other permo triassic parasequences e g capitan shelf parasequences or loferites facies similarities such as renalcis mounds and flaser bedded intertidal ribbon rock reflect anomalous oceanic conditions resulting in low biodiversity and low intensity of bioturbation after the end permian extinction similarities in parasequence stacking patterns reflect low amplitude high frequency sea level fluctuations resulting from green house conditions common to the early palaeozoic and early triassic

an optical technique for the measurement of longshore currents 1 we present an optical method optical current meter to measure the longshore component of nearshore surface currents by measuring the alongshore drift of persistent sea foam in the surf zone the method uses short time series of video data collected from an alongshore array of pixels these space time data are first fourier transformed to a frequency wave number spectrum and finally to a velocity spectrum a model of the velocity spectrum is fit to the observed spectrum to estimate the foam drift velocity confidence intervals and other measures of the input and output data quality are calculated field test comparisons were made against an in situ bidirectional electromagnetic current meter on the basis of 1 month of video data from the 1997 sandy duck field experiment the root mean square error between the two approaches was 0 10 m s linear regression analysis showed the gain between the two instruments to not be statistically different from one differences between the surface and interior measurements were compared to forcing mechanisms that may cause surface velocity shear velocity offsets and alongshore wind stress were well correlated for cases when waves and wind were not aligned to within 45 when wind and wave forced currents are reasonably separable calculated wind dependent surface current shear modeled as a surface boundary layer correlated well with the observed velocity offsets for observations of nonalignment between wind and waves this technique can be applied to study large scale coastal behavior

geomagnetic conjugate observation of nighttime medium scale and large scale traveling ionospheric disturbances front3 campaign 1 the third front f region radio and optical measurement of nighttime tid campaign was carried out during the new moon period of may june 2003 in order to investigate the geomagnetic conjugacy of medium scale and large scale traveling ionospheric disturbances mstids lstids at midlatitudes seven all sky airglow imagers were operated in japan and australia for almost all clear sky nights we observed mstids in the 630 nm airglow images with horizontal wavelengths of 100 400 km propagating southwestward in japan and northwestward in australia all of them show a one to one correspondence of wave structures between the northern and southern hemispheres indicating strong electrodynamic coupling between the two hemispheres through the geomagnetic field line we also found that airglow intensity variations with a timescale longer than that of mstids often show a good correlation between the two hemispheres on 28 may we succeeded in detecting an equatorward propagating lstid spatial scale 1000 km as airglow enhancements at the conjugate stations the airglow peak of the lstid in the northern hemisphere was 20 min earlier than that in the southern hemisphere indicating that the observed lstid is caused by a wave in the neutral atmosphere rather than by an electric field structure

identification of high latitude acoustic gravity wave sources using the goose bay hf radar observations of medium scale acoustic gravity waves using the goose bay hf radar are presented data were examined for the period of november and december 1991 and days that showed evidence of traveling ionospheric disturbances tids were selected for analysis tids were identified in the hf radar data by quasi periodic enhancements of the power in the ground scattered portion of the radar signal various parameters were determined from the data including the wave frequency the wavelength the propagation direction and the phase velocity it was found that multiple wave packets from multiple directions are often present simultaneously source times and locations were identified from data from 2 days december 5 and 6 1991 and these were compared with data from the greenland magnetometer chain the source times and locations were found to correspond to sudden magnetometer deflections indicating the correlation of gravity wave sources with the occurrence of ionospheric electrojet current surges finally the source times and locations were examined in local time and magnetic latitude and it was found that the sources were clustered in two locations near the magnetospheric cusp and near 1600 mlt at about 75 magnetic latitude

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

coping between crises early triassic early jurassic bivalve diversity dynamics abstract the triassic is bounded by two of the most severe biotic crises but nevertheless this time was for bivalves both a recovery and a diversification period and a moment to fully exploit some of their evolutionary novelties just how and when this was achieved is analyzed in this paper which covers induan to sinemurian bivalve diversity based on a newly compiled database taxonomic diversity and ecospace dynamics are examined separately diversity and evolutionary rates were assessed extinction selectivity was tested using a resampling algorithm and cohort analysis was used to study extinction patterns during the early triassic most bivalve genera were survivors from the permian and they were mainly cosmopolitan epifaunal and semi infaunal endobyssate taxa reclined epifaunal and semi infaunal bivalves increased in diversity during the triassic but from norian on their diversity declined and they were strongly affected by the t j crisis although the triassic jurassic extinction strongly impacted bivalve taxonomic diversity it had little impact on bivalve ecologic diversity not a single bivalve life strategy was eliminated at the end of the triassic the present study does not support previous conclusions that infaunal bivalves suffered greater extinction than epifaunal ones during the t j extinction not all life strategies were equally affected by the extinction event being the deep infaunal burrowers positively selected bivalves with major energetic requirements seem to have been more affected with negative selectivity on fast shallow burrowers the ecologic diversity changes of bivalves during the late triassic and several adaptations of durophagous predators reflect the effects of increasing predation pressure and support a late triassic origin of the mesozoic marine revolution

universal time variation of high latitude thermospheric disturbance wind in response to a substorm the temporal and spatial variation in thermospheric winds are studied at 400 km altitude in response to substorms that start at different universal time ut using a global ionosphere and thermosphere model the substorm induced disturbance winds at high latitudes are mainly in the poleward westward and upward directions in the dusk sector and in the equatorward westward and upward directions in the nighttime the daytime perturbation is due to ion drag driven by variations in interplanetary magnetic field imf bz whereas the nighttime perturbation is due to both the bz and hemispheric power input the nightside disturbed winds respond somewhat later than the dayside owing to low background ion density ion drag is the dominant driving force in the daytime for both meridional and zonal disturbed winds whereas joule heating is the dominant factor for the vertical winds the nighttime meridional and zonal winds are driven by a combination of ion drag joule heating and heating of the auroral belt whereas the vertical winds are mainly caused by auroral belt heating the viscous force acts to resist the ion drag whereas the coriolis force is negligible the disturbed winds exhibit large variations with ut during equinox and local winter conditions with more solar illumination stronger disturbed winds can be generated weak or even opposite variations with ut in the disturbed winds are found in local summer which is due to a smaller ut variation of the daytime ion density and a larger contribution from auroral heating than from ion drag

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

microwave radar cross sections and doppler velocities measured in the surf zone 1 the relationship between microwave imaging radar measurements of fluid velocities in the surf zone and shoaling breaking and broken waves is studied with field observations normalized radar cross section nrcs and doppler velocity are estimated from microwave measurements at near grazing angles and in situ fluid velocities are measured with acoustic doppler velocimeters advs joint histograms of radar cross section and doppler velocity cluster into identifiable distributions the nrcs values from pixels with large nrcs and high doppler velocities 2 m s decrease with decreasing bore height to the shoreline similar to scattering from a cylinder with decreasing radius the doppler velocities associated with these regions in the histograms agree well with theoretical wave phase velocities radar and adv measurements of fluid velocities between bore crests have similarly shaped energy density spectra for frequencies above about 0 1 hz but energy levels from the radar are an order of magnitude higher than those of the adv data instantaneous interbore doppler velocities are correlated with adv measured fluid velocities but are offset by 0 8 m s this offset may be due to bragg wave phase velocities wind drift range and azimuth sidelobes the finite spatial resolution of the radar and differences between mean flows measured at the surface with radar and flows measured below the surface with advs shoaling and breaking waves measured through radar grating lobes significantly affect both the doppler velocities near the edges of the images and the scattering from the rear faces of waves causing large doppler velocities to be observed in these regions

super medium scale traveling ionospheric disturbance observed at midlatitude during the geomagnetic storm on 10 november 2004 1 medium scale traveling ionospheric disturbances mstids whose peak to peak amplitude was larger than 20 tecu 1016el m2 were observed at midlatitude during the geomagnetic storm on 10 november 2004 this amplitude was more than 10 times larger than that of the average mstid high resolution data of the gps earth observation network geonet clarified the characteristic of the total electron content tec disturbances over japan on 10 november 2004 the disturbances started around 1000 ut in the central part of japan the maximum of tec temporal change was 7 2 tecu in 30 s the disturbances had several wave fronts which extended from northwest to southeast and propagated from northeast to southwest tec data around japan revealed that the disturbances were mainly observed from 18 n s to 34 n s of the geomagnetic latitude in the both hemispheres since those characteristics were similar to those of mstids in spite of the unusual large amplitude the mstids are referred as super mstids in this paper tec variations of the super mstids were also observed at 460 km altitude by the grace satellite the ion density fluctuations of the super mstids were observed in situ by the champ and dmsp f15 satellites which flew at 360 km and 850 km respectively it is found that the plasma density variations of the super mstids occurred mainly above 360 km altitude the characteristics that distinguish the event from plasma bubbles are its successive wave fronts constant northwest southeast direction along which the wave fronts stretched and late local time of the occurrence it is found that the uplift of the ionosphere around sunset excited the super mstids at midlatitudes the uplift was attributed to the strong eastward electric field during the geomagnetic storm

evolutionary palaeoecology of early epifaunal echinoderms response to increasing bioturbation levels during the cambrian radiation abstract increasing bioturbation depth and intensity during the cambrian radiation created a transition in dominant subtidal soft substrates from firm proterozoic style soft substrates without a well developed mixed layer to soupier phanerozoic style soft substrates with a well developed mixed layer microbial mats were also relegated to settings with inhibited metazoan activity but made resurgences during later ecological crises previous work suggests that this substrate change strongly influenced the evolution of cambrian benthic suspension feeding echinoderms in order to test this previous work and reveal longer term evolutionary patterns the substrate adaptations of 93 genera in the three classes of benthic suspension feeding echinoderms with definitive cambrian origins edrioasteroids eocrinoids and helicoplacoids were examined throughout their fossil records this examination reveals that genera adapted to typical proterozoic style soft substrates were taxonomically dominant during and were almost entirely restricted to the early and middle cambrian thereafter from the late cambrian through the carboniferous genera adapted to typical phanerozoic style soft substrates were taxonomically dominant this trend supports previous studies and defines a fundamental evolutionary shift in echinoderm substrate interactions in response to increased mixed layer development during the cambrian radiation a notable exception to this trend is the late devonian edrioasteroid cooperidiscus which is morphologically convergent with the early and middle cambrian sediment attaching edrioasteroid stromatocystites this convergence is likely the result of cooperidiscus adapting as a sediment attacher to typical proterozoic style soft substrates that developed during or shortly after the late devonian mass extinction this study indicates for the first time that adaptation to non actualistic substrates during ecological crises can result in morphological convergence with forms adapted to similar substrates common during the cambrian radiation

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

beach wizard nearshore bathymetry estimation through assimilation of model computations and remote observations article i nfo a data model assimilation method called beach wizard is presented with which the nearshore subtidal bathymetry can be accurately estimated based on video derived observations of wave roller dissipation and variation of the intertidal shoreline and or radar derived observations of wave celerity using many consecutive images these observed properties are compared with numerical model results and through a simple optimal least squares estimator approach the estimated bathymetry is adjusted gradually for each image in order to improve the fit between model output and observations the key advantages of the technique are that it is based on multiple sources of information i e different remote sensors and or data products depends on only a few free parameters to which the model results are insensitive and shows good skill herein the technique is applied to a synthetic case and two sets of field data from sites at duck nc usa and egmond the netherlands the method which may be extended with observations of other properties from other sources than the three described in this paper can deliver coastal state information i e simultaneous updates of bathymetry waves and currents with high temporal and spatial resolution and can be used in conjunction with or instead of in situ measured data

paleoecology of pelmatozoan attachment structures from a hardground surface in the middle silurian massie formation southeastern indiana abstract the contact between the basal limestone and overlying mudstone interval of the massie formation silurian wenlock sheinwoodian represents a major flooding surface that is well exposed at the new point stone quarry at napoleon southeastern indiana at this locality this surface is a locally microbiohermal hardground encrusted by numerous attachment structures of both crinoids and blastozoan echinoderms the distribution of attachment structure morphologies is nonrandom with respect to variations in substrate properties and microtopographic relief discoidal structures and thecal attachments predominantly representing diploporites are concentrated on fine grained winnowed crests of the undulatory surface reflecting the stability of this substratum complex root like and runner type structures attributable to long stemmed crinoids and rhombiferans dominate the coarser muddier poorly sorted hardground troughs reflecting the need for greater surface area in more unstable rubbly areas microbioherms are densely encrusted by thickened radix systems belonging to long stemmed pelmatozoans the cause of thickening is unclear but may represent a pathologic response to some biotic interaction or investment by encrusting taxa in crustose holdfasts in order to prevent dislodgement this study supports previous interpretations of pelmatozoan attachment paleoecology wherein solid permanent discoids preferentially encrusted stable homogenous substrata whereas more complex structures were needed to occupy more heterogeneous and presumably less stable substrata thus the hardground studied here highlights the strong influence of substrate variations in influencing paleoecological dynamics in topographically complex carbonate settings possibly leading to locally increased alpha diversity and development of biofacies not typically encountered in certain normal marine environments

ediacaran epifaunal tiering epifaunal tiering the subdivision of vertical space within a community is a fundamental attribute of phanerozoic suspension feeding communities this paper documents tiering including the presence of meter tall organisms in neoproterozoic ediacaran communities ediacaran tiering was studied from three exceptionally preserved deep water communities at mistaken point newfoundland which contain in situ census populations of hundreds to thousands of organisms tiering consists of overlapping populations of dominant organisms and is characterized by gradational rather than abrupt tier boundaries at least three tiers are apparent a lower level 0 8 cm above the seafloor an intermediate level between 8 22 cm above the seafloor and an upper level that extends as high as 120 cm tier boundaries are relatively consistent between communities but the constituent organisms in each level are variable suggesting that some ediacaran taxa could fill different tiers interchangeably development of a tiered epifaunal structure is consistent with suspension feeding or absorbing dissolved nutrients directly from seawater despite the common occurrence of tall organisms all communities share a similar population structure in which biomass is concentrated in the basal 10 cm above the seafloor comparison with shallow water ediacaran localities suggests that the observed tiering structure is typical of ediacaran communities ediacaran tierers also show the fundamental subdivision between organisms and or colonies that fed along their entire length and those that developed a specialized feeding apparatus implying that the features of phanerozoic tiered skeletal ecosystems were first initiated in soft bodied communities in the late neoproterozoic

beyond black shales the sedimentary and stable isotope records of oceanic anoxic events in a dominantly oxic basin silurian appalachian basin usa abstract episodes of instability in the global climato oceanic system have become the hallmark of the silurian period these events are marked by six large positive carbon isotope excursions associated with major extinctions the widespread environmental consequences of these perturbations of the global carbon cycle remain poorly documented a high resolution chronostratigraphic reconstruction of the appalachian foreland basin afb provides a framework to evaluate environmental signatures of two of these carbon isotope excursions valgu and ireviken events telychian sheinwoodian at a regional scale integration of published biostratigraphic range data mapping of sequence stratigraphic surfaces and facies and generation of high resolution carbon isotope profiles for several transects provides precise correlation of the basin stratigraphy yielding a high resolution temporal framework this chronostratigraphic reconstruction of the afb highlights the importance of time specific facies tsf during these intervals for instance packages of red green and gray marine rocks separately occupied discrete time intervals cutting across local facies belts indicative of shallow to deep marine environments similarly widespread iron mineralization occurred during discreet time slices as bathtub rings rimming the margins of the basin changes from one time specific facies to the next are coincident with changes in carbon isotope values indicating a genetic link between fractionation of the global carbon reservoir and redox changes from generally oxic to anoxic oceanic conditions in parts of the afb the basal part of the study interval was deposited during the valgu event this first event begins with an unconformity marking global lowstand this fall in sea level was coincident with rising carbon isotope values as recorded in adjacent basins a slight sea level rise and flooding of the subaerial unconformity occurred near the peak in carbon isotope values oxidized iron minerals were deposited in a zone that extended from the lower shoreface into the basin center pinching out into shallower parts of the basin thin pyrite phosphorite glauconite layers associated with black shales in the basin center were deposited over these ferruginous strata as the event ended and carbon isotope values shifted negatively to a more stable baseline temperatures warmed sea level reached a silurian high and oxic conditions associated with very low rates of organic carbon oc burial were established these conditions were relatively stable for nearly four million years this long period of stasis was punctuated by the ireviken event which displays a strikingly similar progression of tsf patterns yet more intense and longer lived than the preceding valgu event with the first positive shift in carbon isotopes at the onset of the ireviken event the basin redox system changed from largely oxidizing to reducing coincident with a rapid drop in sea level and an abrupt reappearance of iron mineralization on the basin margins the sea level fall associated with the shift to peak values of the carbon isotope excursion is marked by the progradation of a significant body of sand well out into the basin during this sea level drop conditions in the basin center became highly reducing and periodically sulfidic widespread ironstones and ankeritic carbonates were deposited isochronously rimming the shallow basin margins where they alternated with light gray pyritic shales indicating fluctuating redox conditions a large negative carbon isotope excursion of 3 is coincident with a shift from regression to transgression suggesting glacial melting via methane release continued deposition of ironstones through this time interval suggests a primary link to shallow marine redox processes rather than large scale transgression or regression of the shoreline the ironstones are overlain by gray to black pyritic shales deposited across all environments revealing a final stage of redox progression into sustained sulfidic conditions as peak values of the carbon isotope excursion returned to a high stable baseline near 4 the similar expression of tsfs within the afb of these two global events demonstrates that fractionation of the global atmospheric and oceanic carbon reservoirs had a predictable cascading impact on shallow sea floor environments the associated redox processes reveal the dynamic regional interactions of a shallow oxic epicontinental water mass with a broader anoxic oceanic water mass providing valuable insight into the origin of some of the largest extinctions in the silurian period

statistical study of nighttime medium scale traveling ionospheric disturbances using midlatitude airglow images 1 we have investigated statistical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at two stations rikubetsu 43 5 n 34 8 mlat and shigaraki 34 9 n 25 4 mlat in japan for 1998 2000 near the solar maximum period most of the observed mstids propagate southwestward in the images the typical wavelength velocity period and amplitude are 100 300 km 50 100 m s 0 5 1 5 h and 5 15 respectively seasonal variations in these parameters are not clear the occurrence rate has a major peak 50 60 in summer that appears 2 months earlier at lower latitudes and a minor peak in winter similar occurrence characteristics are obtained from midlatitude spread f signatures using multipoint ionosonde data in japan though the coincidence of the spread f and the mstids in airglow images is only 10 15

cbathy a robust algorithm for estimating nearshore bathymetry 1 a three part algorithm is described and tested to provide robust bathymetry maps based solely on long time series observations of surface wave motions the first phase consists of frequency dependent characterization of the wave field in which dominant frequencies are estimated by fourier transform while corresponding wave numbers are derived from spatial gradients in cross spectral phase over analysis tiles that can be small allowing high spatial resolution coherent spatial structures at each frequency are extracted by frequency dependent empirical orthogonal function eof in phase two depths are found that best fit weighted sets of frequency wave number pairs these are subsequently smoothed in time in phase 3 using a kalman filter that fills gaps in coverage and objectively averages new estimates of variable quality with prior estimates objective confidence intervals are returned tests at duck nc using 16 surveys collected over 2 years showed a bias and root mean square rms error of 0 19 and 0 51 m respectively but were largest near the offshore limits of analysis roughly 500 m from the camera and near the steep shoreline where analysis tiles mix information from waves swash and static dry sand performance was excellent for small waves but degraded somewhat with increasing wave height sand bars and their small scale alongshore variability were well resolved a single ground truth survey from a dissipative low sloping beach agate beach or showed similar errors over a region that extended several kilometers from the camera and reached depths of 14 m vector wave number estimates can also be incorporated into data assimilation models of nearshore dynamics

low magnesian calcite marine cement in middle ordovician hardgrounds from kirkfield ontario abstract middle ordovician trentonian biosparites from the bobcaygeon and verulam formations near lake simcoe ontario exhibit numerous features demonstrating lithification near the sediment water interface these include planar erosion surfaces which truncate shells and intraclasts undercut hummocks on upper surfaces vertical borings which cross cut fossil debris and early cement and a diverse fauna of encrusting organisms which grew attached to lithified surfaces a marine origin for early cement is indicated by the development of hardgrounds within a transgressire regionally onlapping sequence the occurrence of dozens of such units within normal marine sediments and a lack of features recording early oxidation and or partial dissolution during exposure to meteoric water marine cement from four of these units examined in thin section by sem and by cathodoluminescence consists of clear zoned syntaxial overgrowths on echinoderm debris and equant spar on trilobite bryozoan and brachiopod fragments as such this cement 1 is morphologically identical to meteoric phreatic low magnesian calcite cement from calcitized pleistocene sequences 2 is interpreted as having been precipitated as low magnesian calcite 3 is anomalous in habit and inferred composition in comparison with holocene marine cement and 4 demonstrates that generalizations which relate cement morphology and composition to environmental water chemistry in modern diagenetic systems may not be valid when applied to more ancient carbonate sequences

phanerozoic shallow water diversity driven by changes in sea level shallow water 50 m marine diversity curves for the phanerozoic based on area changes due to sea level variation and continental movements are presented it is shown that a change in the degree of endemism can alter diversity more than the effect of sea level change or change in the number of faunal provinces the pattern produced for a constant degree of endemism shows some rapid but not periodic falls in diversity these occur in the middle cambrian at the end of the ordovician devonian permian cretaceous and eocene and in the messinian there is no recurring single cause for these falls

macroevolutionary transition in crinoids following the late ordovician extinction event ordovician to early silurian abstract the end katian late ordovician crinoid mass extinction triggered the change from the early to the middle paleozoic crinoid evolutionary faunas cefs this was a change from diplobathrid camerate disparid hybocrinid dominated faunas to faunas dominated by monobathrid camerate cladid and flexible crinoids all clades suffered extinctions at the end katian event but diplobathrid camerates disparids and hybocrinids suffered higher rates of extinction the primary amount of diversification occurred in clades that would become dominant during the silurian however the formation of the characteristic middle paleozoic cef was protracted beyond the late ordovician extinction event monobathrid camerates and flexibles diversified through the llandovery but both dendrocrinid and cyathocrinid cladids did not diversify until later monobathrid camerate genera and families diversified the flexible diversification was largely at the genus level cyathocrine diversification was largely among families and dendrocrinids did not diversify significantly until after the llandovery overall disparity decreased during the end katian extinction by reducing the disparity within each clade disparity remained fairly constant during the hirnantian but increased significantly during the llandovery by both increasing disparity within clades and expanding the morphospace of the disparids due to the radiation of families with new morphologies north america was the biogeographic center of origination for the families that survived to become dominant silurian clades

assimilated observations of thermospheric winds the aurora and ionospheric currents over alaska we present simultaneous measurements of thermospheric winds auroral emissions and ionospheric currents over alaska obtained from four separate instruments thermospheric f region wind maps were recorded by an all sky imaging fabry perot spectrometer located at poker flat and observing at 630 0 nm auroral images at 557 7 nm were obtained from the low resolution visible imager on board the polar satellite white light all sky auroral images were recorded by ground based all sky cameras located in alaska at poker flat 65 07 n 212 34 e and at kaktovik 70 06 n 217 24 e finally the east west component of the ionospheric f region plasma convection was inferred using the alaskan meridian chain of magnetometers montage images of these four data sets are presented projected onto a geographic map of the alaskan region we examine a 10 hour period during the alaskan local nighttime of february 10 1997 these montages illustrate a close relationship between spatial structures occurring in the aurora in the ionospheric plasma convection and in the f region wind field latitudinal shear of the geomagnetic zonal wind often observed in the premidnight time sector was seen to be associated with both the equatorward and poleward boundaries of the discrete aurora we focus particularly on a period commencing just after 0900 ut when a strong shear in the zonal wind was observed to sweep southward across alaska after magnetic midnight the wind field was dominated by the emergence of the cross polar jet from the polar cap this overwhelmed any wind features associated with local auroral processes

traveling ionospheric disturbances observed in the oi 630 nm nightglow images over japan by using a multipoint imager network during the front campaign pilot observations using a network of five all sky imagers asis were conducted during the new moon period of may 19 22 1998 as part of the f region radio and optical measurement of nighttime tid front campaign the network observation enabled us to track propagation of medium scale traveling ionospheric disturbances tids in the oi 630 nm nightglow over a distance of more than 2500 km the tids were observed every night during the campaign period but occurrence was limited from evening to midnight they have horizontal wavelengths of 200 600 km travel a horizontal distance of more than 1000 km and last for more than three hours in every case the tids moved southwestward with a velocity of 83 137 m s using dual site tid images the altitude of the tid structures in the 630 nm nightglow was calculated to be 260 km which corresponds to the bottom side of the mid latitude ionospheric f layer

trace fossil model for reconstructing oxygenation histories of ancient marine bottom waters application to upper cretaceous niobrara formation colorado abstract trends of decreasing trace fossil diversity burrow size and penetration depth with diminishing oxygen availability in contemporary marine settings have been incorporated with the concept of trace fossil tiering to develop a model for reconstructing the oxygenation history of ancient basin bottom waters more sensitive than traditionally employed criteria the model permits detailed evaluation of relative degree of oxygenation through the recognition of oxygen related ichnocoenosis ori units or units of strata deposited under similar levels of bottom water oxygenation when employed in detailed vertical sequence analyses the model may also be used to construct interpreted oxygenation curves that reflect rates and magnitudes of temporal change in redox conditions the utility of the model is demonstrated by its application to rhythmically bedded calcareous strata of the niobrara formation upper cretaceous exposed in colorado non laminated strata of the niobrara are characterized by four recurring trace fossil suites referred to as the 1 chondrites 2 zoophycos teichichnus 3 planolites and 4 thalassinoides assemblages on the basis of trends in trace fossil diversity burrow diameter and penetration depth these assemblages are recognized as oxygen related ichnocoenoses interpreted oxygenation curves for the basal fort hays member reflect high magnitude redox cycles characterized by rapid deoxygenation events followed by gradual reoxygenation phases curves for the overlying smoky hill member reflect an overall lower degree of oxygenation with more irregular lower magnitude redox fluctuations significant correlation between interpreted levels of paleooxygenation and organic carbon content illustrate the model s potential for evaluating the distribution of organic rich fine grained strata co interpretation of these variables with carbonate content supports the premise that deposition was controlled by paleoceanographic perturbations modulated by milankovitch like climatic cycles comparison with traditionally emphasized macroinvertebrate body fossil criteria clearly demonstrates the greater utility of the trace fossil approach for evaluating paleo oxygenation

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

tiering in suspension feeding communities on soft substrata throughout the phanerozoic tiering of benthic marine suspension feeding communities on soft substrata has varied throughout the phanerozoic epifaunal tiering was most developed during the middle and late paleozoic and the triassic to jurassic with large scale reductions in tiering occurring during the permian triassic extinctions and after the jurassic infaunal tiering reached its highest level of organization after the paleozoic

settling strategy of stalked echinoderms from the kaili biota middle cambrian guizhou province south china abstract a total of 124 articulated echinoderms including sinoeocrinus lui n 30 s globus n 92 one indeterminate gogiid and one indeterminate edrioasteroid from the kaili formation middle cambrian eastern guizhou china was examined among them 73 of gogiid echinoderms are preserved attached to skeletal substrates suitable skeletal substrates for gogiid holdfasts in the kaili biota are organophosphatic brachiopods large trilobite fragments including cranidia free cheeks thoracic segments and pygidia hyoliths and scenella shells the high frequency of s globus attached to organophosphatic brachiopods is due to the high richness of organophosphatic brachiopods rather than a host specific association in the kaili biota however the possible discrimination against attachment to small trilobites such as pagetia requires further investigation based on 11 hand samples echinoderm population density epd varies from 0 3 to 4 5 echinoderms per 50 grind points 0 06 to 0 96 echinoderms per cm 2 depending on the percent coverage of skeletal debris crowding effect is evident when epd is approximately 0 32 echinoderms per cm 2 and the skeletal coverage is less than 20

high resolution mapping of tec perturbations with the gsi gps network over japan two dimensional total electron content tec perturbations over japan are mapped with the geographical survey institute gsi gps network geonet gps earth observation network its spatial resolution is 0 15 latitude 0 15 longitude and temporal resolution is 30 seconds two dimensional tec observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances tids in the nighttime mid latitude ionosphere on july 03 1997 a preliminary result of the tec perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail coordinated observations with other ionospheric observation techniques such as incoherent scatter is radars airglow imagers and ionosondes are needed to clarify the vertical structure of the ionosphere

bathymetry correction using an adjoint component of a coupled nearshore wave circulation model tests with synthetic velocity data 1 the impact of assimilation of wave averaged flow velocities on the bathymetric correction is studied in tests with synthetic model generated data using tangent linear and adjoint components of a one way coupled nearshore wave circulation model weakly and strongly nonlinear regimes are considered featuring energetic unsteady along beach flows responding to time independent wave averaged forcing due to breaking waves it is found that assimilation of time averaged velocities on a regular grid mimicking an array of remotely sensed data provides sensible corrections to bathymetry even though the wave data are not assimilated flow velocity assimilation utilizes adjoint components of both the circulation and wave models the representer formalism allows separating contributions of these two components to the bathymetric correction in a test case considered involving a beach with an alongshore varying bar the adjoint wave model contribution was mainly to determine the cross shore position of the bar crest the adjoint circulation model provided an additional contribution mostly adding to alongshore variability in the shape of the bar the array mode analysis reveals that there are very few modes that can be effectively corrected given the assumed data error level bathymetry perturbations associated with these modes are a mixture of near coast intensified modes as well as modes extending their influence to deep water along the background wave characteristics additional tests show the utility of different observational arrays in providing the bathymetric correction

response of the marine infauna to triassic jurassic environmental change ichnological data from southern england abstract the trace fossil record through the triassic jurassic boundary interval is examined at three sites in central and southern england st audrie s bay somerset pinhay bay devon and long itchington warwickshire the lower pre planorbis beds of the blue lias formation record low ichnotaxonomic diversity low bioturbation intensity small burrow diameters and an absence of deep tier bioturbation the stepwise reappearance of ichnotaxa following this interval is similar at the three sites suggesting similar rates of recovery in the benthic marine ecosystem and highlighting the potential contribution of these trace fossils to stratigraphic correlation mass extinction in the late triassic is increasingly linked to the emplacement of the central atlantic magmatic province camp timing of the onset of camp volcanism in the uk is currently imperfectly known but potentially occurred within either the westbury formation or the lilstock formation if the onset of camp was within the lilstock formation the modestly diverse trace fossil assemblage of the langport member of the lilstock formation suggests that emplacement of camp had little lasting effect on the marine benthos in central and southern england the decline in benthic activity recorded in the pre planorbis beds appears to be unrelated to the onset of camp and any associated environmental change it is more likely related to an episode of marine anoxia an episode of marine anoxia also provides a suitable causal mechanism for the reduction of infaunal tiering

multievent analysis of oscillatory motion of medium scale traveling ionospheric disturbances observed by a 630 nm airglow imager over tromso

unusual preservation of the trace fossil conostichus in middle silurian carbonate facies of indiana usa the long ranging plug shaped ichnofossil conostichus attributed to solitary polypoid cnidarians is most commonly described in the paleozoic from fine grained siliciclastic sediments with few de

taphonomy of diploporite echinodermata holdfasts from a silurian hardground southeastern indiana united states palaeoecologic and stratigraphic significance a microbioherm bearing hardground within the middle silurian wenlock massie formation near napoleon southeastern indiana united states is encrusted by the attachment structures of numerous pelmatozoan echinoderms among the most common of these holdfasts are multi plated discoidal structures representing the thecal attachments of diploporite cystoids this large population of holdfasts permits the first detailed taphonomic and palaeoecologic study of hardground diploporite attachments allowing for increased morphological understanding of these rarely studied structures and facilitating identification of holdfasts in deposits where they might have been overlooked or misidentified the biostratinomic sequence commences with detachment of thecae followed by weathering of isolated discoidal holdfasts to bring out radiating canal structures and plate sutures eventually leading to removal of the interior floor to expose the underlying substrate continued exposure can result in separation of component holdfast plates though cementation to the substrate prevents scattering of plates diagenetic precipitation of pyrite occurred after burial the large size of crystals suggests late diagenesis perhaps seeded by early diagenetic pyrite crystallites produced by decay of ligamentary tissue extrinsic taphonomic factors include overgrowth of holdfasts by laminar stenolaemate bryozoans and other echinoderm attachment structures diploporite holdfasts are not bored and are absent on microbioherms taphonomic data indicate the time averaged nature of this hardground and its diploporite assemblage and permit prediction of similar occurrences at major flooding surfaces

component concept for the study of the paleocommunities with an example from the early carboniferous of southern indiana u s a abstract predominantly suspension feeding faunas of three contemporaneous laterally contignous early carboniferous early mississippian facies are studied from exposures in southern indiana u s a each major taxonomic group is examined for the primary limiting factors controlling its distribution the paleoecology of the entire fauna is more easily evaluated from a component viewpoint five components are recognized with important limiting factors listed for each component as follows 1 organisms that lived at the sediment water interface which are influenced by sediment mobility and grain size including brachiopods bryozoans etc 2 organisms controlled by prevalent energy conditions such as crinoids 3 organisms controlled by turbidity such as sponges 4 commensal parasitic or predaceous organisms that are dependent upon the distribution of other organisms and 5 nektonic and planktonic organisms whose distribution and abundance are not only controlled by their original biological distribution but also by the depositional rate including fish and conodonts the distributions of different community components are independent however community integrity within a component is maintained from place to place at any time within a paleogeographic province

tidal data inversion interpolation and inference initial efforts in applying inverse methods to studies of ocean tides have focused on making the best use of a small number of observations to map tidal fields in a large area as such inversion can be viewed as an objective analysis scheme which uses a dynamically appropriate spatial covariance derived from the shallow water equations to interpolate and smooth a sparse data set data from recent altimetry missions are not sparsely distributed relative to tidal wavelengths in the open ocean apparently reducing the need for complicated dynamically based interpolation schemes altimetric data sets are also quite large making application of rigorous inversion methods to global tidal modeling a challenging computational problem we describe here a new iterative solution scheme which allows us for the first time to fit the full set of topex poseidon cross over differences the resulting solution tpxo 3 fits validation tide gauges significantly better than previous inverse solutions tpxo 3 also reduces residual cross over variances relative to other recent inverse and empirical solutions particularly in shallow water where improvements are dramatic with the new solution approach very significant improvements in global tidal models should be possible in shallow areas and in the vicinity of complex bathymetry where high accuracy tidal modeling remains a challenging problem with the recent improvements in the definition of tidal elevations in the open ocean it should now also be possible to resolve some long unanswered questions about tidal energetics and dynamics inverse methods provide a natural framework for addressing these issues and making inferences about tidal dynamics in particular by bringing data and dynamics together in a single solution we can rigorously test the consistency of the two we present results of global and local inversions which suggest that over elongated bathymetric features oriented perpendicular to tidal flows energy dissipation in the open ocean is significantly enhanced presumably due to conversion of barotropic tidal motions into baroclinic modes for the m2 tide our preliminary results suggest that perhaps as much as 0 5 tw of energy is dissipated in this manner however due to the simplified linear dynamics and limited spatial resolution used for our inversion there are significant uncertainties associated with these results a more careful application of inverse methods to make more rigorous inferences about tidal energetics including use of more reasonable prior dynamics and the highest possible spatial resolution should allow for closure of the tidal energy budget within the next few years

data assimilation and bathymetric inversion in a two dimensional horizontal surf zone model 1 a methodology is described for assimilating observations in a steady state two dimensional horizontal 2 dh model of nearshore hydrodynamics waves and currents using an ensemble based statistical estimator in this application we treat bathymetry as a model parameter which is subject to a specified prior uncertainty the statistical estimator uses state augmentation to produce posterior inverse updated estimates of bathymetry wave height and currents as well as their posterior uncertainties a case study is presented using data from a 2 d array of in situ sensors on a natural beach duck nc the prior bathymetry is obtained by interpolation from recent bathymetric surveys however the resulting prior circulation is not in agreement with measurements after assimilating data significant wave height and alongshore current the accuracy of modeled fields is improved and this is quantified by comparing with observations both assimilated and unassimilated hence for the present data 2 dh bathymetric uncertainty is an important source of error in the model and can be quantified and corrected using data assimilation here the bathymetric uncertainty is ascribed to inadequate temporal sampling bathymetric surveys were conducted on a daily basis but bathymetric change occurred on hourly timescales during storms such that hydrodynamic model skill was significantly degraded further tests are performed to analyze the model sensitivities used in the assimilation and to determine the influence of different observation types and sampling schemes

characteristics of nighttime medium scale traveling ionospheric disturbances observed over alaska 1 we focused on propagating wave like structures which frequently appeared in the o i 630 0 nm airglow images obtained by an all sky imager installed at poker flat research range 65 1 n 147 4 w magnetic latitude 65 6 in alaska these events are classified as medium scale traveling ionospheric disturbances mstids on the basis of the wavelength and propagating speed the unique points of our observation are 1 the two dimensional structures of mstids in the subauroral region are revealed 2 the horizontal direction of the electric field can be estimated from the motion of the evening co rotating patch ecp aurora appearing simultaneously and 3 neutral winds are simultaneously observed by a fabry perot spectrometer statistical study of these mstid events from november 2001 to april 2002 indicates the following characteristics the mstids were observed almost every evening and sometimes in the morning but were not observed at midnight typical propagating speed direction and wavelength of the wave phenomena were about 135 m s southwestward and about 250 km respectively when the mstids appeared northward neutral winds and westward plasma drifts were dominant this indicates that the perkins instability does not contribute to the development of mstids in the alaska region the vertical wavelength analysis using the dispersion relation of gravity waves with the observed wave parameters and background winds suggests that the observed mstids over alaska are the atmospheric gravity waves agws as a case study temporal variation of an mstid event on 21 december 2001 is shown results of a ray tracing analysis of this event suggest that the agws come from the equatorward edge of the auroral oval

a lost world archaic crinoid dominated assemblages on an antarctic seamount abstract the previously unsurveyed admiralty 67 s 171 e and scott island 67 22 s 179 55 e seamounts to the north of the ross sea were explored using cameras and physical sampling gear during the new zealand ipy caml research voyage tan0802 in february 2008 a striking assemblage dominated by stalked crinoids and brachiopods was found at 580 600 m depths on isolated knolls at the northwest and southeast extremities of admiralty seamount the seabed at these sites was littered with crinoid ossicles and crinoid stalk bases were conspicuous on exposed rocks suggesting that these assemblages have persisted for a considerable period of time the crinoid sites were limited to the isolated knolls but large areas of the flanks of the main seamount were covered by dense populations of suspension feeding ophiuroids these assemblages are more similar in structure to those preserved in fossil strata from the palaeocene and late eocene than to any extant assemblages yet described from the antarctic in comparisons with faunal assemblages on scott island seamount the abundance of stalked crinoids was strongly inversely correlated with the abundance of echinoid asteroid and lithodid crab predators and both asteroids and echinoids were photographed feeding on crinoids these observations are consistent with the prevailing hypotheses that crinoid and ophiuroid dominated assemblages which were widespread in the palaeocene were displaced by the radiation of mobile predators and that conditions in isolated habitats in the southern ocean may have acted as refugia allowing the persistence of archaic benthic assemblages

rise of echinoderms in the paleozoic evolutionary fauna significance of paleoenvironmental controls echinoderms were a major enduring component of paleozoic marine faunas beginning with the rapid diversification of crinoids and other classes in the early ordovician this diversification was triggered by increased availability of habitable areas accompanying sea level rise and changed sedimentation styles newly collected early ordovician echinoderms facilitate determination in detail of life modes and important adaptations during this transition interval substrate consistency and stability were crucial spatial limiting factors that resulted in heterogeneous distribution patterns for echinoderm classes crinoids were overwhelmingly large food groove suspension feeders with relatively open filtration fans attached by small discs to hard ground surfaces in shallow water they were preadapted for this life mode rhombiferans were mobile small food groove suspension feeders they lived on soft substrates at various depths several important crinoid clades underwent a second phase of diversification during the middle ordovician by developing holdfasts adapted to soft substrates and densely pinnulate arms with small food grooves leading to dominance of this class among paleozoic echinoderms our findings are in basic agreement with the overall onshore diversification pattern of most paleozoic benthic invertebrates but we argue for an extrinsic environmental control substrate availability for the observed echinoderm distribution

on the role of thermospheric winds and sporadic e layers in the formation and evolution of electrified mstids in geomagnetic conjugate regions

variational assimilation of satellite observations in a coastal ocean model off oregon 1 satellite along track sea surface height ssh and multisatellite sea surface temperature sst maps are assimilated in a coastal ocean circulation model off oregon the study period is june october 2005 featuring intensive separation of the coastal upwelling jets in the eddy dominated coastal transition zone ctz the data assimilation da system combines the nonlinear regional ocean modeling system roms and the advanced variational regional ocean representer analyzer avrora tangent linear and adjoint codes developed by our group the variational representer da method is implemented in a series of 6 day time windows with initial conditions corrected at the beginning of each window to avoid the problem of matching the model and observed ssh mean levels the observed ssh slope has been assimilated location timing and intensity of jets and eddies in the ctz are constrained to improve accuracy of nonlinear model analyses and forecasts in the case assimilating ssh alone the geometry of the sst front is improved ssh assimilation results in the cross shore transport more uniformly distributed along the coast than in the free run model an outer front is identified in the da analyses at a distance of 200 km from the coast a strong subsurface horizontal temperature gradient across this front influences the depth of the thermocline in an area between the front and the continental slope the da correction term is comparable in magnitude to dominant terms in the volume integrated heat equation the time averaged da correction term in the volume integrated heat balance is closer to 0 in the combined ssh sst assimilation case than in the case assimilating ssh alone

taphonomy of cystoids echinodermata diploporita from the napoleon quarry of southeastern indiana usa the lower silurian massie formation as an atypical lagerstatte abstract diploporites like most pelmatozoan echinoderms are characterized by complex multi element skeletons prone to complete disarticulation if left exposed for extended periods of time consequently preservation of abundant articulated diploporite thecae is rare and generally restricted to environments where rapid burial events could catastrophically entomb individuals one such environment is represented by the lower portion of the wenlock age massie formation at the new point stone quarry near napoleon southeastern indiana which we recognize as a konservat lagerstatte yet taphonomic evidence does not support live burial diploporites holocystites spp are dominantly preserved as intact thecae without any portions of brachioles and with damage plate shifting and plate loss plate jumbling on one side post mortem encrustation is common but epibionts are typically present on the well preserved sides of thecae geopetal sediment fill of thecae shows that the well preserved side commonly faced upward following burial this taphonomic state is paradoxical as burial of live diploporites would have resulted in preservation of complete individuals with no encrusters and only compaction induced damage rapid burial of diploporites following a short interval of exposure would have resulted in preservation similar to observed patterns but with encrusters and geopetal infills indicating that the poorly preserved side faced up and burial after extended exposure would have resulted in thorough disarticulation of thecae rather a variable and in some cases complex taphonomic history is suggested for diploporites from the napoleon quarry with at least some individuals having experienced one or more brief episodes of exhumation prior to final burial early diagenetic cementation of initial theca filling sediment is the most likely mechanism for keeping thecae intact during subsequent exposure

geobiology and palaeogenomics abstract geobiology is centered on interactions of the biosphere with the atmosphere hydrosphere and lithosphere in deep time geobiology has focused on critical intervals of change for earth and its biota such geobiological studies include data from palaeobiology geochemistry and sedimentary geology within an interdisciplinary framework palaeogenomics has a variety of research agendas and one of them is to understand the genes involved in key changes in the evolutionary history of life and when those genes and their interactions first evolved the combination of geobiology and palaeogenomic studies is a powerful approach which leads to a more fundamental understanding of how earth and life have changed through time for example linking palaeogenomic studies of biomineralization genes in modern organisms and when they first evolved in the cambrian with geobiological studies of the impact this had on the production of carbonate sedimentary facies such as encrinites and the development of the neritan ocean provides a unique perspective on how genes have shaped formation of the sedimentary record another component of the cambrian explosion the evolution of vertical bioturbation at the start of the cambrian has had significant effects on biogeochemical cycling and sediment production and provides an inviting target for future genomic studies the remaining phanerozoic includes a broad variety of evolutionary innovations which within a joint geobiological and palaeogenomic context can also be profitably studied in pelagic environments the genomic changes leading to evolution of the calcium carbonate biomineralized skeletons of coccolithophores contributed to the widespread deposition of carbonate sediment in deep settings and development in the mesozoic of the cretan ocean on land linking palaeogenomic studies of the genes that led to the palaeozoic evolution of lignin and their associated geobiological effects such as deposition of coal provide another example of the effects of genes upon development of the sedimentary record such work will ultimately provide a history of genomic change and the environmental factors that influenced it as well as how genomic change influenced environments

all sky imaging observations of conjugate medium scale traveling ionospheric disturbances in the american sector 1 all sky imaging systems at arecibo puerto rico 18 3 n 66 7 w 28 mag lat and mercedes argentina 34 6 s 59 4 w 24 6 mag lat are used to study ionospheric conjugate processes at lower midlatitudes for the first time in the american sector the simultaneous occurrence in both hemispheres of medium scale traveling ionospheric disturbances has been observed the first year of observations yielded 43 nights 40 with simultaneous occurrence of airglow bands supporting information from gps receivers indicate the presence of vertical total electron content variations that correlate with the airglow structures observed with the imagers weak phase fluctuations have been measured indicating that these structures do not produce severe large scale ionospheric irregularities

large scale imaging of high latitude convection with super dual auroral radar network hf radar observations the hf radars of the super dual auroral radar network superdarn provide measurements of the e b drift of ionospheric plasma over extended regions of the high latitude ionosphere with the recent augmentation of the northern hemisphere component to six radars a sizable fraction of the entire convection zone approximately one third can be imaged nearly instantaneously 2 min to date the two dimensional convection velocity has been mapped by combining line of sight velocity measurements obtained from pairs of radars within common volume areas we describe a new method of deriving large scale convection maps based on all the available velocity data the measurements are used to determine a solution for the distribution of electrostatic potential expressed as a series expansion in spherical harmonics the addition of data from a statistical model constrains the solution in regions of no data coverage for low order expansions the results provide a gross characterization of the global convection we discuss the processing of the radar velocity data the factors that condition the fitting and the reliability of the results we present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field imf in the case of a sudden polarity change from northward to southward imf the convection is seen to reconfigure globally on very short 6 min timescales

trace fossil tiering in flysch sediments examples from the guipuzcoan flysch cretaceous paleogene northern spain abstract distribution of trace fossils in flysch sediments is in great part conditioned by tiering that is the vertical partitioning of trace producing organisms below the sediment water interface ichnologic studies in the guipuzcoan flysch upper albian lower eocene northern spain show that tiering in flysch sediments is strongly controlled by sediment character mode and rate of deposition and degree of oxygenation of pore waters depending on the mode of deposition trace fossil tiering in flysch developed and was preserved in two radically different styles 1 in event layers chiefly turbidites tiering is preserved without secondary distortion owing to synchronous colonization and the lack of vertical ascent through time vertical tiering structure depends primarily on sediment composition sequence and thicknesses of structural divisions and oxygen profile variations in tiering are interpreted to reflect the particular oxygen tolerances penetration potentials and nutritional requirements of tracemakers 2 in background sediments hemipelagites and pelagites tiering resulted from successive colonizations that were influenced by background sedimentation rates sediment composition and oxygen levels of pore waters tiering of actively or passively filled burrows is reflected by complex ichnofabrics and the superposition of different tiers by ascension tiering structure was frozen upon deposition of superjacent event layers the original tiering of graphoglyptids open burrows may be reconstructed from their cross cutting relationships on turbidite soles these contrasting styles of tiering development are characteristic of flysch and other sediments composed of alternating event and background deposits

sequences cycles and basin dynamics in the silurian of the appalachian foreland basin abstract field stratigraphic analysis of the early and medial silurian strata of ontario new york and pennsylvania permits recognition of six major sequences reflecting 3rd order cycles in the niagaran llandoverian ludlovian of new york and adjacent regions these sequences correspond approximately to the medina lower clinton middle clinton upper clinton two sequences and lockport groups each is bounded by widespread unconformities produced by the interplay of eustatic sea level drop and local tectonic uplift in general erosional sequence boundaries and transgressive surfaces are merged with no record of the lowstand wedge each sequence is subdivisible into two to five sub sequences that are marked by sharp though generally non erosional basal discontinuities investigation of the clinton and lockport groups corroborates earlier suggestions that carbonate and siliciclassic tongues extended basinward from opposite margins synchronously in response to sea level drops analysis of the thickness and basinward extent of the progradational tongues reveals the existence of multi scale sedimentary cycles sequences and component sub sequences are correlative basinwide and are synchronous within the resolution of bio and event stratigraphy major drops in relative sea level are represented by the sequence bounding discontinutiies these surfaces are overlain by siliciclastic wedges near terrigenous source areas or winnowed carbonate pack and grainstones on the tectonically passive margin overlying highstand deposits typically shales calcareous mudstones and limestones are separated from lowstand or transgressive deposits by thin condensed intervals commonly marked by phosphatic or glauconitic material and or surfaces of maximum sediment starvation the relative highstand deposits of sequences and sub sequences are developed in relatively deep water facies and are at most slightly progradational hence most sequences and sub sequences are sharply bounded roughly upward deepening to slightly shallowing successions of strata in turn sub sequences are further divisible into widespread minor parasequences and parasequence sets probably corresponding to 6th and 5th order cycles respectively the smaller scale units 0 2 5 mthick commonly display an upward shallowing motif the nested relationship of these cycles supports the hierarchical model of transgressive regressive allocycles proposed by busch and rollins 1984 niagaran cycles discussed herein are equivalent to third fourth and fifth order cycles and are traceable circumbasinally depocenters of successive sequences and sub sequences display a pattern of eastward westward eastward basin axis migration through the silurian during early llandoverian the taconic queenston deltaic complex began to subside and the basin axis depocenter and eastern shoreline shifted eastward approximately 200 km over a 6 million year period as the basin axis migrated eastward the western basin ramp forebulge was repeatedly upwarded and eroded resulting in the generation of regionally angular unconformities at the bases of sequences ii iv and vi the pattern of unconformity greatest to the west suggests rise of the algonquin arch concomitant with eastward basin axis migration during the late llandoverian to early wenlockian the algonquin arch subsided slightly concurrently with a reversal in direction of basin axis migration during deposition of upper clinton and lockport vernon strata sequences v vi the basin axis shifted approximately 300 km back to the west eastward migration of the basin axis corresponds with a time of tectonic quiescence and probable thrust load relaxation the abrupt reversal of migration in the late llandoverian may be a signal of renewed thrusting in the hinterland at the onset of the salinic disturbance

effects of wave current interaction on shear instabilities of longshore currents 1 we examine the effects of wave current interaction on the dynamics of instabilities of the surf zone longshore current we utilize coupled models for the simulation of the incident waves and the wave induced nearshore circulation the coupling between the models occurs through radiation stress gradient terms accounting for the generation of nearshore circulation and through wave current interaction terms leading to the modification of the wave field by the generated circulation field simulations are carried out with a realistic barred beach configuration and obliquely incident waves for two frictional regimes the results show that the shear instabilities of the longshore current have a significantly altered finite amplitude behavior when wave current interaction effects are included for beaches with relatively high frictional damping the primary effects are a reduction of the offshore extent of the motions and a delay of the onset of instabilities in addition the energy content of the motions within two surf zone widths is reduced the propagation speed increases and tendency to form offshore directed jets is reduced the horizontal mixing induced by the instabilities is also reduced when wavecurrent interaction is considered leading to a larger peak mean longshore current and a larger offshore current shear these effects appear to be primarily linked to a feedback mechanism whereby the incident wave field gains energy at locations of offshore directed currents for more energetic shear instability fields that occur when frictional damping is small this feedback affects the propagation speed and energy content of the instabilities near and onshore of the current peak only minimally however the offshore extent of the motions and the tendency to shed vortices offshore are still reduced a reduction in the mixing due to the instabilities is evident offshore of the current peak hence the mean longshore current profile is only affected offshore of the current peak the inclusion of wave current interaction significantly affects the shear instability signature observed in the shoreline runup for either frictional regime these results indicate that the energy content and frequency extent of the shoreline response is increased markedly due to the wavecurrent interaction process this effect appears to be related to variations in the forcing of the circulation that arise due to the refraction of the incident waves around offshore directed features of the circulation index terms 4255 oceanography general numerical modeling 4512 oceanography physical currents 4546 oceanography physical nearshore processes

long term study of medium scale traveling ionospheric disturbances using o i 630 nm all sky imaging and ionosonde over brazilian low latitudes 1 in this paper we report a long term study of medium scale traveling ionospheric disturbance mstid occurrence using all sky images of o i 630 nm airglow emission our study is based on a 10 5 year data series in which 5 5 years compound a new data set the images were obtained by an all sky imager installed at cachoeira paulista 22 7 s 45 w 15 s magnetic latitude our results show the greatest occurrence of mstids during solar minimum and a minor occurrence rate during descending and ascending solar activity periods during solar maximum we have not detected mstid signatures on all sky images all detected events have occurred during geomagnetically quiet conditions simultaneous measurements using both all sky images and ionograms obtained at the same site show the occurrence of spread f and a sharp rise in the ionospheric f layer at the same time as dark bands are optically registered over the zenith it is possible that for certain weaker events the ionosonde may resolve bands that are not sufficiently raised to cause darkening of the all sky images in order to investigate this possibility we have conducted a study using only ionograms for a 1 year period march 2000 february 2001 during solar maximum when we have not seen any mstid events in the all sky images as we conjectured mstids also occur during solar maximum and the risings of the ionospheric f layer are not able to disturb the airglow layer during such events

alongshore currents over variable beach topography the nonlinear dynamics of unstable alongshore currents in the nearshore surf zone over variable barred beach topography are studied using numerical experiments these experiments extend the recent studies of allen et al 1996 and slinn et al 1998 which utilized alongshore uniform beach topographies by including sinusoidal alongshore variation to shore parallel sandbars the model involves finite difference solutions to the nonlinear shallow water equations for forced dissipative initial value problems and employs periodic boundary conditions in the alongshore direction effects of dissipation are modeled by linear bottom friction forcing for the alongshore currents is provided by gradients in the radiation stress which are specified using linear theory and the dissipation function for breaking waves formulated by thornton and guza 1983 distinct flows develop depending on the amplitude and wavelength of the topographic variability and the dimensionless parameter q the ratio of an advective to a frictional timescale for q greater than a critical value qc the flows are linearly stable for q qc q 0 the flow can be unstable for small values of q the effect of increasing is to stabilize or regularize the flows and to cause the mean flow to approximately follow contours of constant depth equilibrated shear waves develop that propagate along the mean current path at phase speeds and wavelengths that are close to predictions for the most unstable mode from linear theory applied to alongshore averaged conditions at intermediate values of q unsteady vortices form and exhibit nonlinear interactions as they propagate along the mean current path occasionally merging pairing or being shed seaward of the sandbar eddies preferentially form in the mean current when approaching alongshore troughs of the sandbar and break free from the mean current when approaching alongshore crests of the sandbar at the largest values of q examined the resulting flow fields resemble a turbulent shear flow and are less strongly influenced by the alongshore variability in topography as the amplitude of the alongshore topographic variability increases alongshore wavenumber frequency spectra of the across shore velocity show a corresponding increase in energy at both higher alongshore wavenumbers and over a broader frequency range with significant energy at wavenumbers of topographic variability and harmonics across shore fluxes of mass and momentum generally increase with increasing topographic amplitude and increasing q time and space lagged correlations of the across shore velocity show that correlation length scales decrease as topographic perturbation amplitudes increase terms from the vorticity equation show that the alongshore variation of the radiation stresses and the value of q are of importance to the flow behavior hybrid experiments separating effects of spatially variable forcing and the dynamic influence of topography on time averaged currents show that the effects are generally comparable with the relative importance of each effect a function of q the results show that topographic variability has a significant influence on nearshore circulation

complete biotic and sedimentary records of the permian triassic transition from meishan section south china ecologically assessing mass extinction and its aftermath abstract the meishan section south china is the global stratotype section and point gssp for the permian triassic boundary ptb and is also well known for the best record demonstrating the permian triassic mass extinction ptme all over the world this section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest phanerozoic biocrisis of life on earth many important scenarios interpreting the great dying have been proposed on the basis of data from meishan nevertheless debates on biotic extinction patterns and possible killers still continue this paper reviews all fossil and sedimentary records from the permo triassic p tr transition based on previously published data and our newly obtained data from meishan and assesses ecologically the ptme and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis eight updated conodont zones clarkina yini clarkina meishanensis hindeodus changxingensis clarkina taylorae hindeodus parvus isarcicella staeschei isarcicella isarcica and clarkina planata zones are proposed for the ptb beds at meishan major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between bed 24e 5 and bed 24e 6 suggesting an extinction horizon in a thin stratigraphic interval the irregular surface in the middle of bed 27 is re interpreted as a firmground of glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface both fossil fragment contents and ichnodiversity underwent dramatic declines in beds 25 26a coinciding with metazoan mass extinction fossil fragment content ichnodiversity and all ichnofabric proxies including burrow size tiering level bioturbation level indicate that the p tr ecologic crisis comprises two discrete stages coinciding with the first and second phases of the ptme in meishan ecologic crisis lagged behind biodiversity decline during the ptme pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest changhsingian became euxinic in beds 25 26a turned dysoxic in bed 27 then varied from euxinic to anoxic through most of the griesbachian the 9 c increase in seawater surface temperature from bed 24e to bed 27 at meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in beds 25 26a but had little effect on all ecologic proxies both metazoans and infauna seem not to have been affected by the pre extinction anoxic euxinic condition the anoxic event associated with the ptme may have occurred in a much shorter period than previously thought and is only recorded in beds 25 26a at meishan fossil fragment contents ichnofaunas ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in bed 27 the early griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower yinkeng formation in which the ichnofauna is characterized by small simple horizontal burrows of planolites and metazoan faunas are characterized by low diversity high abundance opportunist dominated communities the rapid increase of 9 c in sea surface temperature and a short anoxia or acidification coincided with the first pulse biocrisis while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second pulse ptme marine ecosystems started to recover coupled with environmental amelioration in the late griesbachian

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

medium scale traveling ionospheric disturbances detected with dense and wide tec maps over north america 1 nighttime and daytime medium scale traveling ionospheric disturbances mstids are detected with dense and wide detrended total electron content tec maps over north america using multiple gps receiver networks the tec maps cover a wide region of 60 130 w and 24 54 n 30 65 n in geomagnetic latitude and have a spatial resolution of 1 05 1 05 in latitude and longitude 0 15 0 15 with 7 7 pixel smoothing and a temporal resolution of 30 seconds the tec maps reveal for the first time that the nighttime mstids propagate southwestward with 200 500 km wavelengths over north america and have wavefronts longer than 2 000 km we also observe that daytime mstids with 300 1 000 km wavelengths propagate southeastward until mid afternoon and southwestward in the late afternoon in the mid to late afternoon these mstids propagating in the different directions are superimposed the tec maps can be a new powerful tool to investigate the mstids

aftermath of the permian triassic mass extinction event paleoecology of lower triassic carbonates in the western usa paleoecologic study of invertebrate faunas from three successive early triassic seaways reveals that biotic recovery from the end permian mass extinction event was slow and that full recovery did not occur until after the early triassic simple cosmopolitan opportunistic generalists and low diversity low complexity paleocommunities were characteristic of the entire early triassic in the western usa an increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late early triassic spathian to the almost exclusively molluscan faunas of the earlier early triassic nammalian potential disaster forms the inarticulate brachiopod lingula and the paper pecten claraia dominated the earliest early triassic faunas griesbachian and even occurred in the late early triassic normal marine stromatolites comparison with data on faunas from the permian and triassic suggests that even the most diverse early triassic faunas in the spathian were rather low in guild diversity and species richness these characteristics of genera and paleocommunities in the early triassic may be typical of mass extinction aftermaths

nighttime medium scale traveling ionospheric disturbances at low geomagnetic latitudes 1 nighttime medium scale traveling ionospheric disturbances mstids are a commonly observed structure in the middle latitude ionosphere during the months surrounding the solstices and low solar flux conditions mstids consist of one or more narrow bands exhibiting uplift in f region electron density which are elongated from northwest to southeast in the northern hemisphere and southwest to northeast in the southern hemisphere these electrified structures propagate westward and toward the equator in a direction perpendicular to their long dimension previously this type of mstid was not thought to occur at magnetic latitudes equatorward of the equatorial anomalies or approximately 15 geomagnetic latitude here we present observational evidence from a field aligned narrowfield imaging system of mstids existing very close to the magnetic equator we discuss the implications of this observation in terms of the development and propagation of mstids