structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

the integrated effect of condensation in numerical simulations of extratropical cyclogenesis abstract by combining traditional sensitivity studies with techniques that focus on the conservation and invertibility properties of ertel s potential vorticity pv we illustrate the effect of latent heating on the structure and evolution of three simulated extratropical cyclones the cases include one continental cyclone development 15 december 1987 which we examine extensively and two cyclones over the western atlantic ocean 6 january 1983 and 5 january 1985 of somewhat greater intensity which are diagnosed to assess the generality of our findings for the continental case each storm featured a weaker cyclonic low level circulation when latent heating was removed from the simulation but the magnitude of the effect varied greatly in all cases the difference in intensity was attributed to velocities associated with a positive condensation produced pv anomaly above the warm front the amplification of the surface thermal perturbations was not strongly altered in even the case most affected by

skolithos linearis haldeman 1840 at its early cambrian type locality chickies rock pennsylvania analysis and designation of a neotype abstract the trace fossil skolithos with its simple vertical to very slightly inclined tubular form is widely recognized and globally distributed in early cambrian to holocene strata representing deep sea to continental paleoenvironments the type species skolithos linearis was first described in 1840 by samuel s haldeman based on his observations of early cambrian quartzite at chickies rock a well known landmark on the east bank of the susquehanna river in pennsylvania the original description was meager no illustrations were published no holotype was established and no specimens directly associated with haldeman are known to exist today a neoholotype proposed by howell 1943 is invalid as it does not conform to requirements of the international code of zoological nomenclature as a result the iconic ichnogenus skolithos is inadequately characterized and some of the numerous ichnospecies that have subsequently been named are not unequivocally assignable to it in order to stabilize this important ichnogenus and to provide a basis for the taxonomic revision it urgently requires we have studied s linearis at its type locality our new material is described and illustrated here and we have designated a neotype accessioned by the u s national museum of natural history smithsonian institution the stratigraphy and regional geologic setting of chickies rock the sedimentology and environment of deposition of cross bedded quartzite with abundant s linearis constituting classic pipe rock and the structural deformation of this fabric are reviewed given the simple morphology of skolithos disparate organisms in several phyla have been proposed as its maker we concur in the general view that cambrian trace fossils assigned to s linearis were most probably made by burrowing phoronids or polychaete annelids the global abundance of largely monospecific pipe rock in analogous cambro ordovician settings is recognized as a characteristic feature of the ecology of shallow marine environments of that time the stage has now been set for a thorough re evaluation of all existing ichnospecies assigned and related to the ichnogenus skolithos

trace fossil evidence for restoration of marine ecosystems following the end permian mass extinction in the lower yangtze region south china abstract unlike the high abundance low diversity macrofaunas that characterize many early triassic benthic palaeocommunities ichnofossils were relatively common in the aftermath of the end permian mass extinction worldwide ichnofossils therefore are a good proxy for ecosystem recovery after the end permian biotic crisis this paper documents 14 ichnogenera and one problematic form from lower triassic successions exposed in the lower yangtze region south china post extinction ichnodiversity remained rather low throughout the griesbachian early smithian period and abruptly increased in the late smithian however several lines of evidence including extent of bioturbation burrow size trace fossil complexity and tiering levels indicate that diversification of ichnotaxa in the late smithian did not signal full marine ecosystem recovery from the permian triassic p tr mass extinction marine ichnocoenoses did not recover until the late spathian in south china the marginal sea provided hospitable habitats for tracemakers to proliferate in the aftermath of the end permian mass extinction

boundary layer friction in midlatitude cyclones results from an idealized three dimensional baroclinic life cycle model are interpreted in a potential vorticity pv framework to identify the physical mechanisms by which frictional processes acting in the atmospheric boundary layer modify and reduce the baroclinic development of a midlatitude storm considering a life cycle where the only non conservative process acting is boundary layer friction the rate of change of depth averaged pv within the boundary layer is governed by frictional generation of pv and the flux of pv into the free troposphere frictional generation of pv has two contributions ekman generation which is directly analogous to the well known ekman pumping mechanism for barotropic vortices and baroclinic generation which depends on the turning of the wind in the boundary layer and low level horizontal temperature gradients it is usually assumed at least implicitly that an ekman process of negative pv generation is the mechanism whereby friction reduces the strength and growth rates of baroclinic systems although there is evidence for this mechanism it is shown that baroclinic generation of pv dominates producing positive pv anomalies downstream of the low centre close to developing warm and cold fronts these pv anomalies are advected by the large scale warm conveyor belt flow upwards and polewards fluxed into the troposphere near the warm front and then advected westwards relative to the system the result is a thin band of positive pv in the lower troposphere above the surface low centre this pv is shown to be associated with a positive static stability anomaly which rossby edge wave theory suggests reduces the strength of the coupling between the upper and lower level pv anomalies thereby reducing the rate of baroclinic development this mechanism which is a result of the baroclinic dynamics in the frontal regions is in marked contrast with simple barotropic spin down ideas finally we note the implications of these frictionally generated pv anomalies for cyclone forecasting

deep sea trace fossils of the oligocene miocene numidian formation northern tunisia abstract twenty two ichnogenera and thirty one ichnospecies have been recorded in the oligocene miocene numidian formation of northern tunisia heterolithic successions of thin bedded turbidite sandstones and interchannel mudstones contain the most diverse trace fossil assemblages thick to very thick bedded structureless sandstones and conglomerates representing the fill of channel complexes contain a low diversity trace fossil assemblage the ichnoassemblage in the lower part of the formation oligocene which includes paleodictyon isp scolicia strozzii spirorhaphe isp cosmorhaphe isp and halopoa isp can be ascribed to the paleodictyon ichnosubfacies of the nereites ichnofacies the ichnoassemblage in the upper part of the formation miocene aquitanian including diplocraterion cf habichi scolicia vertebralis and ophiomorpha isp is interpreted as the shallower part of the ophiomorpha rudis ichnosubfacies of the nereites ichnofacies the notable switch in ichnofauna between the oligocene and lower miocene reflects variation in environmental and depositional conditions the common occurrence of trace fossils of the ophiomorpha rudis ichnosubfacies and diplocraterion cf habichi in the early miocene indicates an increase in energy level greater environmental disturbance and probable shallowing this is also confirmed by a corresponding decrease in the abundance and diversity of benthic foraminifera the integration of ichnological sedimentological and microfossil contents has allowed the distinction of two quite distinct geographical depositional settings within the numidian formation the first domain includes the numidian succession of the tabarka cap negro cap serrat and bouhertma areas which are characterised by distal turbidites showing the paleodictyon ichnosubfacies that is compatible with a lower bathyal depth in the oligocene and an upper slope depositional environment during the early miocene the second domain includes the ne part of mogod mountain e g the ras el korane jebel gattous zoukar which exhibit more proximal characteristics compatible with a probable slope canyon interpretation the southern margin of the kroumirie balta and zouza areas and sejnene area shows a distal setting compared with the ras el korane and jebel gattous zoukar areas it is ascribed to a mid to upper slope depositional environment during the oligocene to early miocene

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

the ichnogenus rhizocorallium classification trace makers palaeoenvironments and evolution rhizocorallium is one of the oldest known trace fossils with wide distribution through the phanerozoic and all over the world originally introduced from the epicontinental triassic of central germany its high morphological lability gave reason for the subsequent erection of about twenty ichnospecies the study of newly collected material from the type area and many specimens from various collections permits the conclusion that rhizocorallium jenense and rhizocorallium commune are the only valid ichnospecies of rhizocorallium the type ichnospecies r jenense is a comparatively small inclined and heavily scratched firmground burrow with passive fill while r commune consists of extensive more or less horizontal burrows with occasionally scratched marginal tubes and an actively filled spreite between the tubes the faecal pellets coprulus oblongus are typically associated with r commune morphological variations of r commune are captured in ichnosubspecies and varieties of this ichnospecies and can aid a refined reconstruction of palaeoenvironments a review of more than 180 records from the literature reveals the common confusion of both ichnospecies which has consequences for the application of rhizocorallium in facies interpretations the end members of both ichnospecies may be linked by transitional forms which suggests the same kind of trace maker polychaetes are the most likely producers of marine rhizocorallium based on their long ranging occurrence morphological features appearance of faecal pellets associated soft body remains and modern analogues r commune occurs from early cambrian to holocene while r jenense just appears after the end permian mass extinction probably as a consequence of an adapted firmground burrowing lifestyle of its producer fluvial r jenense are probably produced by mayfly larvae in homology to marine polychaete burrows a consequent application of the newly established classification scheme allows for a more rigorous application of rhizocorallium in the reconstruction of palaeoenvironments thus palaeozoic and mesozoic r commune are restricted to the cruziana ichnofacies of shallow marine environments while in cenozoic time similar forms are also found in deep marine deposits r jenense on the other hand is a constituent of the widespread glossifungites ichnofacies and aside from continental environments occurs in peritidal to deep marine deposits several studies have demonstrated the value of rhizocorallium for interpreting sequence stratigraphical surfaces current directions and fluctuations in salinity and oxygen

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

a potential vorticity based study of the role of diabatic heating and friction in a numerically simulated baroclinic cyclone abstract a particularly intense case of western atlantic baroclinic cyclogenesis was investigated in this study specifically the roles of latent heat of condensation and surface friction were examined from the potential vorticity or pv thinking perspective the methodology used for this study involves three key components 1 a full physics mesoscale model which provides a continuous and dynamically consistent dataset and provides full user control over physical processes 2 a partitioned pv integration which temporally integrates the accumulation of pv due to various physical processes in the model s eulerian framework and 3 the piecewise inversion method of davis and emanuel which calculates the balanced wind and mass field associated with particular pv anomalies potential vorticity features obtained through the partitioned integration technique were inverted to yield their direct contributions to the total circulation in addition sensitivity studies were carried out to determine the overal

the role of trace fossil ichnofabric analysis in the development of depositional models for the upper jurassic fulmar formation of the kittiwake field quadrant 21 ukcs

a lagrangian based analysis of extratropical cyclones ii a detailed case study a detailed case study analysis is undertaken of the occurrence of significant coherent ensembles of trajectories cets that accompany atlantic cyclogenesis the approach is based upon the lagrangian based analysis scheme introduced in part i the analysis reveals the existence of several distinct moist ascending and dry descending cets two types of moist ascending cets associated with strong condensational processes ascend from the boundary layer of the warm sector either in the close vicinity of the cyclone centre or in the trailing cold frontal region the latter is the main contributor to the precipitation along the cold front during the early phase of the development another type of moist cets distinguished by maximum water vapour flux travels at low levels through the warm sector and ascends to mid tropospheric levels in the warm frontal region where it produces strong precipitation around the time of maximum storm intensity cets with an upper level origin are linked to the classical dry intrusion different cets correspond to strong descent of upper level tropospheric air that penetrated to the lower troposphere the movement of stratospheric air toward the centre of the maturing cyclone and an event of stratosphere to troposphere exchange upstream of the upper level trough two different visualizations of time sequences of the moist ascending cets indicate that they represent well defined flexible tubes or airstreams that exist over a time period comparable with the duration of the main cyclone intensification they provide a translating flexible but coherent river bed for the quasi continuous ascent of moist boundary layer air to the upper troposphere these tubes are akin to the concept of warm conveyor belts and the present analysis method objectively diagnoses their geometrical and physical characteristics and potential vorticity pattern some consideration is also given to the relationship of cets and tropospheric rivers and to possible shortcomings of the approach

hydrocarbon seep carbonates of a miocene forearc east coast basin north island new zealand an ancient hydrocarbon seep province of 14 isolated authigenic carbonate deposits has been identified in fine grained deep marine siliciclastic strata of the miocene east coast basin north island new zealand these forearc sediments have been uplifted and complexly deformed into accretionary ridges adjacent to the still active hikurangi convergent margin older active and passive margin strata mid cretaceous to oligocene in age underlie the neogene sequence and contain oil and gas prone source rocks older mesozoic meta sedimentary rocks constitute the backstop against which the current phase of subduction related sedimentation has accumulated 24 ma present the seep carbonates up to 10 m thick 200 m across archive methane signatures in their depleted carbon isotopes to 13c 51 7 pdb and contain chemosynthesis based paleocommunities e g worm tubes bathymodioline mussels and vesicomyid lucinid and thyasirid bivalves typical of other cenozoic and modern seeps northern and southern sites are geographically separated and exhibit distinct lithological and faunal differences structural settings are variable seep associated lithologies also are varied and suggest carbonate development in sub seafloor seafloor and physically reworked diapiric expansion gas explosion gravity slide or debris flow settings similar to italian apennine seep deposits of overlapping ages peculiar attributes of the new zealand miocene seep deposits are several including digitate thrombolites of clotted microbial micrite encased in thick isopachous horizons and botryoids of aragonite seep plumbing features are also well exposed at some sites displaying probable gas explosion breccias filled with aragonite tubular concretions fluid conduits and carbonate cemented thin sandstone beds and burrows within otherwise impermeable mudstones a few seeps were large enough to develop talus debris piles on their flanks which were populated by lucinid bivalves and terebratulid brachiopods firmgrounds and hardgrounds were common as evidenced by trace fossil associations or caryophyllid coral thickets atop some seep carbonate deposits thus the new zealand examples show strong evidence of formation in sediments at or just beneath the seafloor but some were clearly exhumed by erosion to sustain later non seep epifaunal and boring paleocommunities

hydrocarbon seep carbonates associated with mesozoic environmental perturbations example from the lower bajocian of morocco abstract in the lower bajocian of the jebel bou kendill section central high atlas mountain three peculiar levels of authigenic carbonates are observed within the carbonate poor agoudim iii member morphological sedimentological and geochemical evidences indicate that the two upper levels have been deposited at a hydrocarbon seep site whereas the lowermost level likely underlines the zone where hydrocarbon fluids were generated the first seep carbonate level is made of mineralized burrows that have acted as fluid conduits leading to a conspicuous cap carbonate bed on top of which several chimneys and chemoherm structures are embedded hence this carbonate bed is a fossilized sea floor carbonate crust the second seep carbonate level is made of chemoherm structures buttressed against the first carbonate beds of the agoudim iv member they were probably formed within the sedimentary column close to the sea floor similar seep carbonates are observed regionally within the agoudim iii member in the highly subsiding central high atlas troughs a relationship between these seep carbonates occurrence and the late early bajocian global environmental perturbation can be deduced as this latter has led to the deposition of a relatively organic matter rich sedimentary sequence in these troughs via seawater eutrophication the decomposition by bacterial activity of this organic matter aided by rapid burial rates has led to the generation of alkaline rich fluids promoting the precipitation of the seep carbonates a similar relationship between transient environmental perturbations and seep carbonates occurrence is observed in numerous mesozoic examples and can be explained by the fact that hydrocarbon seeps are supply limited systems transient deviation from the mesozoic greenhouse climate norm either toward hothouse or coldhouse climates favours the deposition of organic rich sediments or transient methane storage respectively hence increasing the likelihood for the formation of hydrocarbon seepage

geological imprint of methane seepage on the seabed and biota of the convergent hikurangi margin new zealand box core and grab carbonate results abstract short box cores to 30 cm bsf and seafloor carbonate grab samples were acquired at mapped hydrocarbon seep sites 600 1200 m water depths during the 2007 rv sonne so191 cruise on the hikurangi margin offshore eastern north island new zealand to evaluate the influence of methane seepage on sedimentologic biotic mineralogic and stable isotopic attributes of seabed sediments sedimentary horizons in the box cores consist of siliciclastic silts and sands shell beds and nodular microcrystalline aragonite bands up to 15 cm thick the megafauna is dominated by infaunal to semi infaunal chemosymbiotic bivalves calyptogena lucinoma and acharax as well as associated worms and carnivorous and grazing gastropods burrows in silts some occupied by worms or juvenile acharax mainly have simple morphologies more typical of high energy nearshore settings than deep sea environments while a few are large and sparsely branched with wall scratch marks inferred to be of decapod crustacean origin the box core silts and nodular carbonate samples vary in toc content from 0 2 to 0 9 wt carbonate content from 4 to 78 and 13 c and 18 o values from 50 3 to 0 6 pdb and 0 77 to 3 2 pdb respectively low carbonate content silt samples have the most enriched 13 c values implying a seawater source for their pore water bicarbonate negative 13 c and positive 18 o values typify the nodular microcrystalline aragonite bands indicating formation during microbially mediated sulphate dependent anaerobic oxidation of methane aom in a cold near seafloor environment as is also supported by lipid biomarker data a clear isotopic mixing trend of decreasing 13 c and increasing 18 o and carbonate content in the fine seafloor grab carbonate samples show greater textural variability and are divided into two types fresh appearing grey to white blocks yield similar mineralogic isotopic and biomarker signatures to the nodular carbonate bands in the cores a largely seep related epifauna affiliated with these grab samples include chemosymbiotic bathymodiolin mussels siboglinid tube worms methanotrophic suberitid sponges and grazing limpets which in places are entombed within the carbonate by contrast some dark reddish to brown iron stained microcrystalline dolomitic slabs and tubular concretions support abundant non seep epifaunal encrusters from the surrounding deep sea indicative of long exposure on the seafloor distinct stable isotopic signatures of these exhumed dolostones 13 c c 20 pdb 18 o up to 7 pdb suggest derivation from an oxidised methane pool and pore fluid freshening by gas hydrate dissociation or from mobilized burial fluids that have undergone clay mineral dehydration

hybrid event beds dominated by transitional flow facies character distribution and significance in the maastrichtian springar formation north west voring basin norwegian sea hybrid event beds comprising clay poor and clay rich sandstone are abundant in maastrichtian aged sandstones of the springar formation in the north west voring basin norwegian sea this study focuses on an interval informally referred to as the lower sandstone which has been penetrated in five wells that are distributed along a 140 km downstream transect systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings although individual beds were not correlated the lower sandstone shows an overall reduction of total thickness bed amalgamation sand to mud ratio and grain size in distal wells turbidites dominated by clay poor sandstone are at their most common in relatively proximal wells whereas hybrid event beds are at their most common in distal wells hybrid event beds typically comprise a basal clay poor sandstone non stratified or stratified overlain by banded sandstone with clay rich non stratified sandstone at the bed top the dominant type of clay poor sandstone at the base of these beds varies spatially non stratified sandstone is thickest and most common proximally whereas stratified sandstones become dominant in distal wells stratified and banded sandstone record progressive deposition of the hybrid event bed thus the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer this layer changed from non cohesive at the front through a region of transitional behaviour fluctuating non cohesive and cohesive flow to cohesive behaviour at the rear further spatial variation in the dominant type of clay poor sandstone at the bed base suggests that the front of the flow remained non cohesive and evolved from high concentration and turbulence suppressed to increasingly turbulent flow this is thought to occur in response to deposition and declining sediment fall out this research may be applicable to other hybrid event bed prone systems and emphasises the dynamic nature of hybrid flows this article is protected by copyright all rights reserved

dual sensor obc technology before the invention and successful implementation of the towed streamer in the late 1940s the ocean bottom cable obc method and variations thereof represented our only means for acquiring seismic data in marine areas the marine streamer facilitated more rapid acquisition of 2 d data its widespread adoption relegated obc to shallow waters where streamers could not be towed

horizontal potential vorticity dipoles on the convective storm scale the structure and dynamics of potential vorticity pv anomalies generated by convective storms is investigated both theoretically and in a numerical model case study linear theory suggests that if the storm induced heating is on a sufficiently small scale relative to the rossby radius of deformation and the environment contains moderate vertical wind shear of order 1 m s 1 km 1 then the dominant mode of a diabatically generated pv anomaly is a horizontally oriented dipole the horizontal dipoles are typically of 10 pvu compared with the 1 pvu vertical dipoles that have been studied extensively throughout the literature furthermore the horizontal pv dipoles are realized almost entirely as relative vorticity anomalies on a time scale of the order of tens of minutes after the heating has been turned on the analysis of horizontal pv dipoles offers a new perspective on the vorticity dynamics of individual convective cells implying that moist processes play a role in the maintenance of vertical vorticity in the convective storm environment copyright 2009 royal meteorological society

the statfjord 3 d 4 c obc survey this paper presents initial processing and interpretation of 3 d multicomponent seismic data acquired over parts of statfjord field in the last quarter of 1997 statfjord field in the tampen spur area straddling the british norwegian border in the northern portion of the viking graben covers about 500 km2 and has estimated oil reserves of 674 106 m3 production started in 1979 the reservoir units are jurassic sandstones of the brent group dunlin group and statfjord formation

the dichotomous structure of the warm conveyor belt the warm conveyor belt wcb of an extratropical cyclone generally splits into two branches one branch wcb1 turns anticyclonically into the downstream upper level tropospheric ridge while the second branch wcb2 wraps cyclonically around the cyclone centre here the wcb split in a typical north atlantic cold season cyclone is analysed using two numerical models the met office unified model and the cosmo model the wcb flow is defined using off line trajectory analysis the two models represent the wcb split consistently the split occurs early in the evolution of the wcb with wcb1 experiencing maximum ascent at lower latitudes and with higher moisture content than wcb2 wcb1 ascends abruptly along the cold front where the resolved ascent rates are greatest and there is also line convection in contrast wcb2 remains at lower levels for longer before undergoing saturated large scale ascent over the system s warm front the greater moisture in wcb1 inflow results in greater net potential temperature change from latent heat release which determines the final isentropic level of each branch wcb1 also exhibits lower outflow potential vorticity values than wcb2 complementary diagnostics in the two models are utilised to study the influence of individual diabatic processes on the wcb total diabatic heating rates along the wcb branches are comparable in the two models with microphysical processes in the large scale cloud schemes being the major contributor to this heating however the different convective parametrization schemes used by the models cause significantly different contributions to the total heating these results have implications for studies on the influence of the wcb outflow in rossby wave evolution and breaking key aspects are the net potential temperature change and the isentropic level of the outflow which together will influence the relative mass going into each wcb branch and the associated negative pv anomalies at the tropopause level flow

the exaerobic zone a new oxygen deficient marine biofacies classical biofacies models1 2 for reconstructing palaeoenvironments of strata deposited in oxygen deficient marine settings define three principal facies aerobic 1 0 ml 1 1 o2 dysaerobic 1 0 to 0 1 ml 1 1 o2 and anaerobic 0 1 ml 1 1 o2 zones these models have postulated a decrease in organism size and degree of calcification as well as a drastic reduction in the relative percentage of fauna possessing calcified skeletons as the dysaerobic anaerobic boundary is approached through use of evidence independent of that provided by body fossils we demonstrate here that in portions of the monterey formation miocene california the bivalve anadara montereyana occurs in situ almost exclusively in strata deposited at the dysaerobic anaerobic boundary the occurrence of fossils of large well calcified benthic macroinvertebrates at this redox boundary contradicts classical biofacies models1 2 and there fore provides the basis for definition of a new oxygen related biofacies the exaerobic zone the exaerobic zone concept when adjusted for differences in basin configuration and palaeoceano graphic conditions provides a potentially useful model for explain ing occurrences of shelly benthic fossils within laminated organic rich strata of other phanerozoic marine sequences

vertical open burrows in deep sea sediments 2 m in length previous studies of the mixed layer in deep sea sediments suggest a maximum burrowing depth of about 10 30 cm ref 1 however we now report that two recently obtained cores from the north east atlantic s126 2 and s126 4 display open burrows to a depth of 214 cm within a distal pelagic turbidite an organic lining in one of the burrows indicates a modern origin many of the burrows are less than 0 5 mm across and are only visible on fractured surfaces their effects on sediment mixing are probably minimal but they provide a network of open vertical channels which considerably increases the permeability this is of crucial importance to studies involving pore water movement such as those associated with the radioactive waste disposal project the effect of the burrows changes the calculated permeability from the equivalent of a clay to that of a coarse sand the delicate structure of the burrows may result in their closure during handling thus requiring their effect on pore water fluxes to be studied in situ

a sedimentological process based approach to depositional reservoir quality of deep marine sandstones an example from the springar formation northwestern voring basin norwegian sea reservoir properties of deep marine sandstones deposited by various sediment gravity flow types in the northwestern voring basin norwegian sea are characterized using detailed sedimentological and petrographic analyses the sandstones are quartz arenites and subarkoses having similar mineralogical compositions a low degree of diagenetic modification and low to moderate volumes of quartz cement up to 6 however significant textural variability is observed for the various sandstone types which were subdivided based upon their interpreted processes of deposition in the studied wells there is a predominance of turbidites deposited by high density turbidity currents hdts and a range of hybrid event beds hebs hdts are coarser grained and contain less detrital clay than the various hebs in addition the dominant grain size of hebs decreases down the depositional profile whilst the content of detrital clay increases porosities of the various bed types span the same interval but overall the hdts and proximal hebs have a higher proportion of samples with porosities higher than 20 compared to distal hebs permeabilities in contrast are significantly different with the hdts having permeabilities approximately two orders of magnitude higher than clay rich hebs a comparison of the observed variability in composition and textural parameters with porosity and permeability indicates that sedimentological flow processes control the depositional reservoir quality of deep marine sandstones understanding these processes therefore enhances our ability to predict distribution of reservoir quality in deep marine systems

the structure and evolution of a continental winter cyclone part i frontal structure and the occlusion process the frontal structure and occlusion process in a cyclone of moderate intensity that affected the central united states in january 1995 is examined the deep warm frontal zone associated with this cyclone had a lateral extension to the southwest of the sea level pressure minimum that although characterized by cold air advection near the surface had many of the characteristics of a warm front aloft in fact this feature had a structure similar to the so called bent back fronts previously documented only in association with explosively deepening maritime cyclones the development of a warm occluded structure was investigated with the aid of a numerical simulation of the event performed using the university of wisconsin nonhydrostatic modeling system the development of the warm occluded structure was asynchronous in the vertical occurring first at midtropospheric levels and later near the surface in contrast to the classical occlusion process near the surface the warm occluded front was formed as the warm front was overtaken by the frontogenetically inactive portion of the historical coldfrontal zone at midtropospheric levels the warm occluded structure formed as a result of the cold frontal zone approaching and subsequently ascending the warm frontal zone in accord with a component of the classical occlusion mechanism the observed asynchronous evolution of the occluded structure is proposed to result from the vertical variation in vortex strength associated with the upper level potential vorticity pv anomaly that controls the cyclogenesis it is suggested that the occlusion process begins aloft where the associated vortex strength is greatest and gradually penetrates downward toward the surface during the cyclone life cycle additionally a characteristic treble clef shape to the upper level pv anomaly is shown to be a sufficient condition for asserting the presence of a warm occluded structure in the underlying troposphere

the beast burrowed the fluid followed crustacean burrows as methane conduits abstract an extensive pockmark field with associated methane seep carbonates has recently been reported from the late albian lower cretaceous ubidepea mudstone of the black flysch group in the basque country northern spain but the exact pathways of the migrating methane rich fluids remained elusive here we provide petrographic stable carbon and oxygen isotope evidence that abundant crustacean burrows in the surrounding mudstone preserved as the trace fossil thalassinoides and the seep carbonates themselves have acted as long lasting fluid conduits in this system the thalassinoides infill generations show a diagenetic parasequence often starting with a distinctive lining followed by one to several phases of cementing of the burrow walls and burrow infills and finally late diagenetic sparry calcite that filled the remaining open cavities and conduits the micrite cementing the burrow walls shows negative 13 c values similar to those reported from the seep carbonates indicating that methane oxidation was involved in their precipitation rather than or in addition to the oxidation of other organic matter even the late diagenetic sparry calcite shows 13 c values as low as 30 4 versus pdb providing evidence that these burrows served as fluid conduits for an extended period of time our study supports the growing body of evidence that crustacean burrows play an important role in channeling seeping fluids in such systems we anticipate that this phenomenon is much more widespread than currently appreciated especially in examples where other types of fluid conduits are absent

a comparison of streamer and obc seismic data at beryl alpha field u k north sea compressional p wave ocean bottom cable obc seismic data from the beryl alpha field in the u k north sea provide a superior image of the subsurface compared to heritage streamer seismic data to determine the reason for the superiority of obc data the results of a detailed comparison of these obc and streamer data sets are compared the streamer and obc data sets are reprocessed using a strategy that attempts to isolate the roles of processing fold azimuth pz combination and hydrophone and geophone data have on the improved obc image the vertical component of the geophone obc z provides the major contribution to the improved obc image the imaged obc z datacontain fewer multiples and have a higher signal to noise ratio than the streamer the obc data have a lower level of multiple contamination because of the contribution from the obc z component together with an effective suppression of receiver side water column reverberations as a result of the combination of the obc hydrophone and geophon

seismic stratigraphic analysis of the middle jurassic krossfjord and fensfjord formations troll oil and gas field northern north sea abstract the syn rift middle jurassic krossfjord and fensfjord formations troll field northern north sea contain a complex distribution of wave and tide dominated deltaic shoreline and shelf depositional environments of varying reservoir potential uncertainty exists in depositional models used to explain the spatial and temporal distribution of these depositional environments and the absence of coeval coastal plain deposits to date the proposed influence of growing rift related structures on stratigraphic architectures and sedimentation patterns in the units has been poorly defined in this study 3d seismic data are integrated with core biostratigraphic and wireline log data to produce a consistent geological interpretation for the formations seismic analysis has identified nine parasequences containing nne ssw striking delta scale clinoforms that prograded westwards over much of the field quantitative analysis highlights an increase in height and dip of clinoforms from proximal to distal locations coincident with an increase in grain size clinoform geometry is sigmoidal with well developed topsets that based on core data lack subaerial deposits these geometrical and sedimentological characteristics suggest that a subaqueous delta depositional system deposited the krossfjord and fensfjord formations in the troll field in the northeast of the field clinoforms exhibit highly variable strike and oblique cross sectional geometries which suggest that sediment was supplied from here and then redistributed through southward directed wave and longshore current activity rift related faulting is recognised to have occurred in the western part of the troll field only during deposition of the youngest fensfjord formation parasequence thus challenging the notion that these units are syn rift seismically imaged clinoforms in the under explored area south of the troll field prograded southward and are interpreted to represent coeval formation of a southward prograding spit that developed landward of the subaqueous delta platform present in the troll field the interpreted long lived subaqueous delta in the troll field constitutes a novel type of shallow marine reservoir

the place of tubular concretions in hydrocarbon cold seep systems late miocene urenui formation taranaki basin new zealand the late miocene urenui formation cropping out on the eastern margin of taranaki basin currently new zealand s only commercially exploited hydrocarbon basin is dominated by siliciclastic slope mudstone 5 carbonate that locally includes a variety of tubular concretions 50 85 carbonate dominated by commonly large pipe and bulbous varieties as much as 0 5 to more than 10 m 1 6 to 33 ft long and 5 to 70 cm 2 to 28 in across these concretions formed from the precipitation of fine grained calcite or dolomite cement within siliciclastic mud in the shallow subsurface likely 100 m burial most support a central conduit that may be empty or filled with sediment or multiple generations of post shallow burial carbonate cements depleted 13c values of the concretionary calcite cements 40 to 25 pdb indicate that their carbon was sourced from oxidized methane in contrast enriched 13c values of the concretionary dolomite cements 10 to 11 pdb indicate that their carbon was derived from methanogenic co2 and or extensive methane oxidation the range of 18o values for the concretionary cement types 2 to 5 pdb supports precipitation from fluids both depleted and enriched with respect to new zealand miocene marine waters which are suggested to reflect episodes of gas hydrate formation and dissociation respectively the tubular carbonate concretions are interpreted to mark the subsea floor pathways of focused methane infused upward fluid escape and as such they represent a part of the shallow subsurface plumbing system of a cold seep system developed on the continental margin bounding the taranaki basin in the late miocene this margin has been strongly influenced by periodic movements along the major taranaki fault thrust system which coincidentally directly underlies the urenui concretion occurrences and was probably the most likely avenue for active fluid migration within the hydrocarbon seep system the tubular concretions experienced periodic intervals of exhumation and burial caused by margin failure because of greater slope instability from injected fluids and resulted in conglomeratic channel fill deposits within the urenui formation that include mass transported tubular concretions

the enigmatic trace fossil tisoa de serres 1840 abstract a new attempt is made to shed light on the enigmatic trace fossil tisoa that was introduced from the lower jurassic of france about 180 years ago morphological variability and diagenetic overprint were the reasons for the erection of numerous ichnotaxa now regarded as synonymous with tisoa tisoa is an ichnogenus of the arenicolitidae and comprises simple vertical to horizontal narrow u shaped burrows with paired tubes and a very high length width ratio two ichnospecies are distinguished t siphonalis the type ichnospecies occurs in firmground and has a sharply defined burrow margin and passive fill glossifungites ichnofacies while t habichi comb nov occurs in softground and has an irregular outline and active or passive fill skolithos ichnofacies tisoa is known worldwide from the lower ordovician and occurs in a wide range of marine environments from paralic settings to the deep sea based on 67 evaluated records from the literature tisoa and bathichnus reach a length of up to 9 m and thus are the deepest invertebrate burrows recorded so far tisoa is often associated with major stratigraphical surfaces such as omission and erosion surfaces t siphonalis commonly occurs in organic rich and oxygen poor substrate and in association with cold seep deposits there the extremely long burrows acted as venting conduits which led to the precipitation of minerals in form of concretions and obliteration of the enclosed burrow t habichi is known from sandy well oxygenated substrates polychaetes bristle worms are good candidates for producing tisoa partly being able to employ chemosynthetic symbiosis to gain nutrition and able to burrow to extraordinary depths this review aims to raise awareness of tisoa which is more common than previously anticipated and to utilize its presence in palaeoenvironmental reconstructions it demonstrates once again the importance of a solid ichnotaxonomical evaluation as basis for further interpretations

deep burrowing in the early palaeozoic deep sea examples from the cambrian early ordovician meguma group of nova scotia enigmatic and heterogeneously deformed burrows are described from the cambrian early ordovician meguma group of nova scotia because of their morphological variability and the absence of previously defined morphotypes the burrows are unnamed yet do provide a cautionary note to the naming of trace fossils even at the ichnogeneric level by ichnologists the traces record the activity of unknown and mobile deposit feeding organisms that inhabited interchannel or levee areas immediately adjacent to and up to 5 m laterally from a 2 m deep channel developed on a deep sea mid outer submarine fan complex many of the vertically to subvertically oriented systems penetrate up to 40 cm suggesting that existing models on the depth of early palaeozoic benthic boundary layers obtained from shelf environments must be utilized with caution