conodont palaeobiogeography and thermal maturation in the caledonides conodont elements are important in biostratigraphy in palaeoenvironmental and palaeobiogeographical analyses and in assessing the thermal history of lower palaeozoic strata throughout the caledonian belt the differentiation of ordovician conodont faunas into the north atlantic and north american midcontinent provinces is not closely comparable with the provincial patterns shown by other faunal groups and does not relate clearly to criteria for recognizing continental separation across the iapetus ocean some species associations adapted to cool normal marine waters were able to cross the ocean at the time of its presumed maximum extent the colours of conodont elements reflect the thermal history of strata and can be used in studies of low grade metamorphism in s wales for example metamorphic temperatures indicated by conodont colour are too high to he accounted for by simple burial beneath the known stratigraphical overburden under normal heat flow conditions elsewhere conodont colour trends also serve to constrain and test models of metamorphism that involve sedimentary burial in subsiding basins tectonic burial under nappes or the thermal effects of intrusions

non trionychid turtles from the paleocene of alberta canada turtle fossils of paleocene age have been recovered from four formations in alberta canada the upper paleocene part of the scollard formation the upper paleocene portion of the willow creek formation and the exclusively paleocene porcupine hills and paskapoo formations at least three non trionychid turtle taxa can be recognized definitely present are a generically indeterminate baenid the macrobaenid judithemys backmani and the chelydrid protochelydra zangerli the carapace of a juvenile chelydrid could be either a juvenile of p zangerli or a fourth distinct taxon the macrobaenid j backmani and the chelydrid p zangerli are the most abundant non trionychid turtles from the paleocene of alberta the turtles from the paleocene of alberta differ from those of comparable age in new mexico usa and other more southern localities in the north american western interior in i the presence of macrobaenids and chelydrids and ii the absence of kinosternoids these differences mirror those of the

variscan tectonics of central europe postaccretionary intraplate deformation of weak continental lithosphere the area occupied by the variscan belt of central europe forms part of gondwana derived microplates essentially avalonia and armorica that according to paleomagnetic data juxtaposed baltica and laurentia from the upper ordovician to the lower devonian the actual structure of this area is a puzzle of rather small fault bounded crustal blocks different in p t t histories which was created by later tectonic processes at around 360 to 320 ma according to a common view and by contrast to paleomagnetic data the structural record of fault bounded blocks is interpreted in terms of mid devonian to lower carboniferous amalgamation of narrow continental plates represented by the fault bounded blocks themselves however this is not supported in this article instead it will be shown that fault systems and fault bounded blocks were created by intraplate deformation of a weak domain of gondwana derived continental lithosphere significantly after its accretion deformation was partitioned into newly formed deep seated strike slip and kinematically connected reverse or normal detachment systems large translation magnitudes caused juxtaposition of crustal areas of variable thickness until they were emplaced along the fault systems the various categories of fault bounded complexes record different tectonic events category 1 metamorphic complexes represent deep seated parts of thickened crust some time before unroofing on the detachment systems between about 340 360 and 320 ma however the record of subduction and extreme crustal thickening during earlier stages of the collision history was erased to a high degree and is only preserved by mineral and structural relics strike slip and detachment systems propagated across and dismembered tectonic boundaries formed during these early events category 2 metamorphic complexes and the barrandian basin recording predominant pre late devonian metamorphic or stratigraphic events represent the brittle upper crustal parts during continuing metamorphism in the category 1 complexes weakly or unmetamorphosed lower paleozoic category 3 basins represent areas of thinned continental crust and record subsidence before and to some degree during activity of detachment systems the complex overall kinematic pattern of block bounding strike slip and detachment systems indicates compression and extension acting simultaneously this probably reflects the effects of continuing oblique plate convergence rotation and wsw extrusion of fault bounded blocks in addition to heating and extensional flow of previously thickened crustal areas

the lower middle ordovician palaeofield of scandinavia southern sweden revisited abstract we present a palaeomagnetic pole for the arenig llanvirn swedish orthoceras limestones based on a new analysis of some earlier reported palaeomagnetic data this new pole 18 n and 046 e differs from the original estimate of 30 n and 46 e the revised pole probably represents the most reliable ordovician pole from baltica although some uncertainties remain concerning the relative importance of diagenetic depositional controls on remanence acquisition based on the new pole from the swedish orthoceras limestone and recent palaeomagnetic results from the northern scandinavian caledonides it is now evident that baltica lay within southerly latitudes of between 30 and 60 s in cambro ordovician times subsequent anticlockwise rotation relative to eastern avalonia southern britain may indicate dextral shear across the tornquist suture prior to mid late ordovician amalgamation of eastern avalonia and baltica

palaeomagnetism of nw scotland syenites in relation to local and regional tectonics summary a detailed thermal demagnetization study has been carried out on a number of syenitic intrusions from north of the great glen fault in scotland multicomponent remanences of normal and reversed polarity have been recognized these define a series of palaeomagnetic poles from which an ordovician to silurian apparent polar wander path for northern scotland is deduced comparison of this apparent polar wander path with the established path for britain throws new light on the sequence of thrusting and magmatic activity in the nw highlands and precludes large scale 1500 km movement along the great glen fault later than the ordovician the data emphasize previously published discrepancies between the apparent polar wander paths of britain baltica and laurentia and are consistent with the suggestion that britain was among a set of intracratonic microplates which underwent complicated distinct movements throughout the caledonian orogeny

comment on palaeomagnetic results from volcanic rocks of the shelve inlier wales evidence for a wide late ordovician iapetus ocean in britain by c mccabe and j e t channell in a recent paper mccabe and channell 1 report a late ordovician palaeomagnetic pole from the shelve inlier wales and argue for a iapetus ocean of 30 degrees latitudinal width between laurentia and southern britain in late ordovician times they further suggest that southern britain lay in high latitudes adjacent to the northern margin of gondwana at this time unlike mccabe and channell we contend a primary llanvirn mid ordovician remanence age for the shelve volcanics additionally several important points regarding the palaeomagnetism of southern britain may have been overlooked by mccabe and channell in particular re examination of a previous palaeomagnetic study of the shelve inlier 2 reveals a dual polarity remanence which passes a fold test at 95 confidence and indicates temperature southerly palaeolatitudes of 32s 8

the combined effects of gulf stream induced baroclinicity and upper level vorticity on u s east coast extratropical cyclogenesis abstract the atlantic surface cyclone intensification index ascii is a forecast index that quantifies the strength of low level baroclinicity in the coastal region of the carolinas it is based on the gradient between the coldest 24 h average air temperature at cape hatteras and wilmington north carolina and the temperature at the western boundary of the gulf stream the resulting prestorm baroclinic index psbi is used to forecast the probability that a cyclone in the domain will exhibit rapid cyclogenesis the initial ascii study covered the years 1982 90 this dataset was recently expanded to cover the years 1991 2002 which doubled the number of cyclone events in the sample these additional data provide similar position and slope of the linear regression fits to the previous values and explain as much as 30 of the variance in cyclone deepening rate despite operational value the neglect of upper tropospheric forcing as a predictor in the original ascii formulation precludes explanation of a l

a new ambystomatid salamander dicamptodon antiquus n sp from the paleocene of alberta canada the discovery of a skull and partial postcranial skeleton of dicamptodon from northern alberta is the earliest certain record of the subfamily dicamptodontinae the specimen comes from late paleocene lake sediments which also contain the remains of fish and plants the close resemblance of the specimen to larvae or neotenes of extant dicamptodon shows that this family exhibits the common trend of extreme conservatism known from other salamanders the specimen is found in association with floral assemblages confirming nussbaum s hypothesis of the origin of the genus in northwestern north america

palaeogeographic significance of mid silurian palaeomagnetic results from southern britain major revision of the apparent polar wander path for eastern avalonia summary wenlock c 430 ma lavas from the east mendips inlier southern briain are characterized by either single component magnetizations type 1 or a more complex system of three magnetization components type 2 during stepwise thermal demagnetization the type of demagnetization behaviour is related to changes in magnetic petrology within the lava pile the lower and intermediate unblocking temperature components of type 2 represent magnetic overprints of tertiary recent and hercynian mid carboniferous origin respectively the primary nature of the high unblocking temperature magnetization component types 1 and 2 dec 095 c inc 24 ag5 8 8 is demonstrated by positive agglomerate tests conversely an overlying upper old red sandstone sequence did not provide primary magnetizations the magnetic signature is governed by syn tectonic hercynian remagnetizations the primary silurian data demonstrate that the east mendips inlier experienced considerable clockwise rotation probably of the order of 80 prior to partial remagnetization during hercynian deformation and folding the silurian palaeopole vgp 13 n 271 e dp dm 5 9 cannot therefore be used for apparent polar wander path construction nevertheless the palaeolatitude estimate 13 f 5s suggests that southern britain eastern avalonia was at comparable mid silurian latitudes to baltica and northern britain 10 20 s both the iapetus ocean and tornquist sea therefore which separated southern britain from laurentia and baltica respectively in ordovician times were closed by wenlock time as ordovician and silurian palaeomagnetic data from baltica and eastern avalonia now record a comparable northwards translation from high southerly to near equatorial latitudes during this time we postulate pre wenlock collision of these blocks to form balonia baltica eastern avalonia a new apparent polar wander path for eastern avalonia constructed on the basis of this palaeogeographic model is presented

a practical suggestion regarding the use of scandinavian and russian palaeomagnetic data to determine the palaeo position of baltica in ordovician time abstract there is a discrepancy between ordovician palaeomagnetic pole positions from the russian plate and from scandinavia however it is clear from faunal and tectonic evidence that the two regions were parts of a single continent through palaeozoic time data from both regions are few in number and some are controversial in nature therefore it is suggested that the palaeomagnetic discrepancy merely reflects the incomplete nature of the palaeomagnetic dataset for baltica it is notable that palaeolatitudes for baltica derived from the scandinavian dataset are confirmed by other lines of geological evidence it is therefore concluded that the scandinavian dataset offers the most reliable palaeomagnetic controls on the lower palaeozoic drift history of baltica placing it in mid southerly latitudes in early ordovician time rotated clockwise through at least 50 relative to its present orientation

the lower palaeozoic apparent polar wander path for baltica palaeomagnetic data from silurian limestones of gotland sweden summary well dated and undeformed silurian lower wenlock limestones from gotland southern sweden yield two stable remanence components following detailed thermal and alternating field demagnetization studies 1 a low blocking temperature coercivity magnetization termed l delineated below 250dc 10mt is oriented parallel to the present earth s field dec 001 inc 67 n 4 sites a95 16d 2 a higher blocking temperature coercivity magnetization termed h unblocked between 250 400dc 10 35mt has a nne declination and shallow negative inclination dec 025 inc 19 n 5 sites a95 5d this h component direction compares favourably with a previous result from gotland based upon blanket cleaning given a lack of evidence for subsequent geological heating conodont alteration index 1 1 5 or pervasive palaeomagnetic overprinting the h palaeopole is regarded as reliable and primary early diagenetic in origin 19ds 352de dp dm 3 5 the only other well constrained mid silurian pole from baltica that from the ringerike sandstone of the oslo district is in excellent agreement with the gotland data these combined poles resolve previous problems regarding the shape and time calibration of silurian apparent polar wander relative to baltica

radar backscatter across the gulf stream sea surface temperature front ku band backscatter responses to frontal sea surface temperature sst changes are studied and applications of a high resolution scatterometer to remote sensing of an sst front are suggested ocean backscatter signatures were measured with an airborne ku band scatterometer across the gulf stream sst front during the surface wave dynamics experiment oceanic and atmospheric parameters were measured by buoys by the scanning radar altimeter and by the advanced very high resolution radiometer and the surface current fields analyzed by the fleet numerical meteorology and oceanography center were obtained vertical polarization backscatter difference across the sst front with an sst difference of 9 spl deg c is more than 5 db in several flight lines large horizontal polarization backscatter changes are also observed across the sst front with an sst difference approximately one half of that in the vertical polarization backscatter case corresponding wind speed differences cannot account for the large backscatter changes in view of seasat a satellite scatterometer sass geophysical model functions depending only on neutral wind velocity for both polarizations upwind backscatter on the cold side is smaller than or close to crosswind backscatter on the warm side for incidence angles larger than 20 spl deg and smaller than 60 spl deg this suggests that the sst front can be detected with backscatter measured by a spaceborne radar at a fixed azimuth angle even if wind directions are different over the cold and warm sides

provenance of the pre devonian sediments of england and wales sm nd isotopic evidence nd values and clast petrography of the longmyndian sediments of shropshire indicate a provenance dominated by juvenile high nd t uriconian volcanic sources but with an increasing detrital contribution from older low nd t metamorphic sources up section by contrast most lower palaeozoic strata of england and wales have low nd t values typical of sediments derived from long established continental crust the sm nd isotopic evidence suggests that avalonia received sediment from an adjacent large continent in the cambrian to lower ordovician and in the silurian ordovician and silurian volcanicity supplied juvenile detritus only during and shortly after active volcanism

oceans island arcs and olistostromes the use of fossils in distinguishing sutures terranes and environments around the iapetus ocean the shallow water benthos of cratonic areas distinguish different continents and the closure of the iapetus ocean during the ordovician and silurian can be monitored by the faunas which crossed the ocean at different geological times brachiopod and trilobite distributions carry different palaeobiological evidence than for example contemporary conodont provinces which probably reflected a combination of temperature differences and water depths the celtic 9province9 is reviewed and it is concluded that each of the island faunas should be treated separately since many have links with adjacent continents rather than together as a province in newfoundland faunas help to locate the site of the main iapetus closure at the reach fault although a substantial island arc in the notre dame bay area accreted on to america in early caradoc times in the late ordovician and early silurian of newfoundland fossils assist in the dating of quite local fault controlled marginal basins some of which include large olistostromes undisturbed assemblages of brachiopods in life position give indications of the depth of water in some basins

airborne scatterometer detection of winds and sea surface roughness changes across the gulf stream front abstract this article investigates the scatterometer radar cross section distributions and wind stress spatial variability across a sea surface temperature sst front under different wind directions and synoptic scale atmospheric forcings shipboard meteorological measurements in concert with airborne k u band 14 0 ghz rotating scatterometer data show evidence of mesoscale circulation near the front during low ambient winds 4 m s blowing from the cold side of the sst front to the warm side the mesoscale signature is characterized by a 25 35 counterclockwise shift in the wind direction and a maximum of 4 9 db increase in the backscattering cross section across the front the mesoscale circulation is reduced when the wind direction reverses and the ambient wind flow increases to 13 6 m s the maximum cross section change across the front is reduced to 3 6 db the azimuthal characteristics of the scatterometer data are compared with the predictions of two scatterometer model functions according to the models the anisotropy of the short waves is inversely related to the wind speed such that the short wave directional spreads tend to broaden as the wind speed increases the scatterometer data however show greater short wave anisotropy at the higher wind speeds this measured difference could be caused by current velocity changes or by longwave directional changes across the front

a three dimensional numerical investigation of a carolina coastal front and the gulf stream rainband abstract a three dimensional mesoscale planetary boundary layer pbl numerical model is used to investigate mesoscale circulations over the carolina coastal and gulf stream baroclinic zones idealized ambient onshore and offshore flows are investigated which represent the synoptic conditions during the intensive observation period 2 iop 2 of the 1986 genesis of atlantic lows experiment gale for the easterly onshore flow a confluence zone appears west of the gulf stream in response to the effect of the oceanic baroclinicity the confluence zone is nearly parallel to the coastline and the sst isotherms with northeasterly southwesterly flow to the west east a shallow coastal front forms below 2 km as the cyclonic shear of the ageostrophic flow becomes strong quasi stationary rainbands are produced by cumulus convection along the coastal front the northern part of the front and the rainbands later encroach inland as the cold air intensity over ground weakens due to onshore warm air advection

emergence of subaqueous depositional environments in advance of a major ignimbrite eruption capel curig volcanic formation ordovician north wales an example of regional volcanotectonic uplift abstract the garth tuff of the ordovician capel curig volcanic formation comprises a laterally extensive sheet of largely welded rhyolitic ash flow tuff that can be traced from a proximal subaerial to a distal marine environment six facies associations are recognized within subjacent sedimentary successions facies are interpreted as deposits of stream dominated alluvial fans ephemeral streams braidplain lower delta plain delta front and shallow marine environments the development of a large scale coarsening and or shallowing upward sequence reflects the amount of differential tectonic uplift between fault bound highlands and depositional basin there is no evidence for volcanicity associated with sedimentation uplift resulted in aggradation and progradation of fan and braidplain deltas a basinward shift in the loci of dominant sedimentation and a 15 km advance in the position of the pre eruption coastline associated tilting of fault blocks influenced the position of fluvial systems on braidplain with channel belts localizing along one margin in the area of greatest subsidence the spatial correlation between pre emplacement geography and location of probable vent for garth tuff implicates upward and or lateral migration of the magma as the most likely mechanism driving these tectonic changes

lower palaeozoic and precambrian igneous rocks from eastern england and their bearing on late ordovician closure of the tornquist sea constraints from u pb and nd isotopes the u pb isotope ages and nd isotope characteristics of asuite of igneous rocks from the basement of eastern england show that ordovician calc alkaline igneous rocks are tectonically interleaved with late precambrian volcanic rocks distinct from precambrian rocks exposed in southern britain new u pb ages for the north creake tuff zircon 449 13 ma moorby microgranite zircon 457 20 ma and the nuneaton lamprophyre zircon and baddeleyite 442 3 ma confirm the presence ofan ordovician magmatic arc tectonically interleaved precambrian volcanic rocks within this arc are verified by new u pb zircon ages for tuffs at glinton 612 21 ma and orton 616 6 ma initial end values for these basement rocks range from 4 to 6 consistent with generation of both c 615 ma and c 450 ma groups of rocksin continental arc settings the u pb and sm nd isotope data support arguments for an ordovician fold thrust belt extending from england to belgium and that the ordovician calc alkaline rocks formed in response to subductionof tornquist sea oceanic crust beneath avalonia

blocking and frontogenesis by two dimensional terrain in baroclinic flow part i numerical experiments the shallow atmospheric fronts that develop in the early winter along the east coast of north america have been attributed in various modeling and observational studies to the land sea contrasts in both surface heating and friction however typical synoptic conditions are such that these coastal fronts could also be a type of upstream influence by the appalachian mountain chain generalized models have suggested that relatively cold air can become trapped on the windward side of a mountain range during episodes of warm advection without a local contribution from differential surface fluxes such a process was proposed decades ago in a study of observations along the coast of norway could coastal frontogenesis be primarily a consequence of a mountain circulation acting on the large scale temperature gradient a two dimensional terrain following numerical model is used to find conditions under which orography may be sufficient to cause blocking and upstream frontogenesis in a baroclinic environment the idealized basic flow is taken to have constant vertical shear parallel to a topographic ridge and a constant perpendicular wind that advects warm or cold temperatures toward the ridge land sea contrasts are omitted in the observed cases the mountain is narrow in the sense that the rossby number is large this by itself increases the barrier effect but the experiments show that large scale warm advection is still crucial for blocking for realistic choices of ambient static stability and baroclinicity the flow can be blocked by a range like the northern appalachians if the undisturbed incident wind speed is around 10 m s21 cold advection weakens the barrier effect the long term behavior of the front in strongly blocked cases is described and compared to observations because of the background rotation and large scale temperature advection blocked solutions cannot become steady in the assumed environment however the interface between blocked and unblocked fluid can settle into a balanced configuration in some cases a simple argument suggests that in the absence of dissipation the frontal slope should be similar to that of the ambient absolute momentum surfaces

sedimentological evidence for a limited separation between armorica and gondwana during the early ordovician the vast extent of sedimentation deposits making up the gres armoricain and its equivalents over the north gondwanan domain is used in this study to test the hypothesis of continuity between the armorica and gondwana plates during the early ordovician the distribution of continental and marine environments the large volume of transported elastic material and the consistent current directions all indicate that the source of sediment supply on the north gondwanan margin was to the south of the sahara although there were local signs of incipient rifting between the two plates armorica was not yet detached from gondwana by arenigian time

sm nd garnet age for the ordovician borrowdale volcanic group english lake district garnets separated from andesites and dacites of the calc alkaline borrowdale volcanic group are highly enriched in heavy rare earth elements hree relative to their host rocks d gt yb from 9 in andesite to 37 in dacite sm nd ratios and d gt lree show a wide range probably resulting from small quantities of an ree rich impurity in the separates the four garnet host rock pairs analysed yield sm nd ages identical within analytical error of a weighted mean of 457 4 ma the borrowdale group overlies upper llanvirn sediments and is unconformably overlain by mid caradoc the age of 457 ma is considered to be the best estimate available for the age of the llandeilo as the samples analysed are from the lower part of the group the age suggests that a lower palaeozoic timescale intermediate between those of gale et al 1979 and mckerrow et al 1980 might be the most appropriate

paleomagnetic results from volcanic rocks of the shelve inlier wales evidence for a wide late ordovician iapetus ocean in britain abstract in order to shed light on the early paleozoic paleogeography of iapetus bordering continents samples for paleomagnetic study were collected from middle ordovician llanvirn volcanic rocks of the shelve inlier welsh borderland the folding within the inlier is constrained to late ordovician ashgill time thus offering a fold test with tight age brackets after stepwise thermal demagnetization a pre folding characteristic magnetization component was isolated from 95 specimens the mean of 11 site mean directions for the characteristic magnetization gives d i 116 4 67 9 k 89 4 95 4 9 and the paleomagnetic pole lies at 26 6 n 36 1 e p 6 9 m 8 2 the fold test is positive at the 99 confidence level indicating that the magnetization was acquired during the middle or late ordovician we infer from geological considerations that this magnetization is not a primary thermoremanence but was acquired during late ordovician time as a result of a thermochemical disturbance of that age our results indicate that southern britain was near 51 south latitude during the later ordovician since middle to late ordovician paleolatitudes for gondwana and laurentia are well determined our result can be used to test various scenarios for the closure of iapetus we conclude that 1 the iapetus ocean in britain still had a latitudinal width of some 30 at this time thus rendering a postulated ordovician closure unlikely 2 southern britain avalon and hercynian europe all occupied high latitudes during the later ordovician consistent with a paleoposition near the northern margin of gondwana and 3 the acadian orogeny in britain and north america could have been the result of the collision of gondwana and laurentia during early devonian time

a note on the age and pyroxene chemistry of the igneous rocks of the shelve inlier welsh borderland geological survey electron microprobe analyses of clinopyroxenes and isotopic age determinations have revealed that the intrusive dolerites and basic intermediate lavas of the shelve ordovician inlier are part of a co magmatic suite which show transitional affinities between tholeiites and alkali basalts the ages of most of the intrusives are shown to be mid ordovician

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

on the predominant nonlinear response of the extratropical atmosphere to meridional shifts of the gulf stream abstractthe north atlantic atmospheric circulation response to the meridional shifts of the gulf stream gs path is examined using a large ensemble of high resolution hemispheric scale weather research and forecasting model simulations the model is forced with a broad range of wintertime sea surface temperature sst anomalies derived from a lag regression on a gs index the primary result of the model experiments supported in part by an independent analysis of a reanalysis dataset is that the large scale quasi steady north atlantic circulation response is remarkably nonlinear about the sign and amplitude of the sst anomaly chosen over a wide range of gs shift scenarios the nonlinear response prevails over the weak linear response and resembles the negative north atlantic oscillation nao the leading intrinsic mode of variability in the model and the observations further analysis of the associated dynamics reveals that the nonlinear responses are accompanied by the shift of the north atlantic eddy

numerical simulation of a mesolow over a gulf stream filament a three dimensional mesoscale numerical model is used to investigate mesoscale circulation over a gulf stream filament two numerical experiments are performed with different initial uniform ambient wind speeds u 0 1 m s 1 3 5 m s 1 and 7 m s 1 for a typical winter day it is found that for both low and moderate winds a closed mesoscale circulation forms over the gulf stream filament when the gulf stream filament was removed the model did not predict a mesoscale circulation the modeled circulation over the filament is in agreement with the observations suggesting that the atmospheric circulations over the filaments may be an important mechanism in the u s east coast cyclogenesis

palaeomagnetism of the ordovician moulin de chateaupanne formation vendee western france summary a palaeomagnetic study of the moulin de chateaupanne formation reveals two characteristic components of magnetization the first one isolated by thermal treatment at intermediate temperatures is strongly resistant to chemical leaching its direction d 217 i 25 ag5 5 5 and the corresponding pole position lat 21 s long 320 e are typical of the hercynian overprints in the armorican massif the second component carried by fine grained haematite presents a steep downward direction d 228 i 81 ag5 6 pole position lat 34 n long 343 e already recognized in other ordovician rock units from the same area it is resistant to high temperature demagnetization treatment and is believed to be of chemical origin as assessed by a conglomerate test a mutual consistency test with the nearby thouars massif suggests that the tilt of the formation has a sedimentary origin and that the thouars massif has not suffered significant tilt during the hercynian orogenic events

a train based case study of stratiform convective transition within a warm conveyor belt abstractclouds are both produced by and interact with the mesoscale and synoptic scale structure of extratropical cyclones etcs in ways that are still not well understood cloud scale radiative and latent heating modifies the thermal environment leading to a response in the dynamics that can in turn feed back on cloud distribution and microphysical properties key to the structure of etcs is the warm conveyor belt wcb the poleward ascending airstream that produces the bulk of the clouds and precipitation this paper examines a long lived wcb that persisted over the western north atlantic ocean in nearly the same location for several days during this time the storm was sampled multiple times by nasa s a train satellite constellation and a clear transition from stratiform to convective clouds was observed examination of coincident temperature and water vapor data reveals destabilization of the thermodynamic profile after the cyclone reached maturity cloudsat radar reflectivity from two sequential

a palaeomagnetic study of the builth wells llandrindod wells ordovician inlier wales palaeogeographic and structural implications summary discrepancies exist in the southern british ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes although previous palaeomagnetic investigations from the builth inlier have delineated a three component remanence structure doubts have been raised concerning i the magnetization age of the supposed primary component p ii the structural setting of the sampling area llanelwedd quarry within a zone of strike slip deformation and iii whether detailed step wise demagnetization has fully separated the various magnetization components in addressing these problems we present new palaeomagnetic results as follows i a positive palaeomagnetic conglomerate test establishing a pre late llanvirn age for component p ii an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike slip tectonism are minor within the builth sampling area and iii evidence that component p is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35 s to be representative for the builth inlier we also present evidence for local syn volcanic deformation within llanvirn volcanics and for intrusion related deformation of llanvirn shales when the revised llanvirn pole from the inlier 3 s 4 e is combined with other data from southern britain in a statistical spline analysis a mean palaeolatitude of 44 5 s is calculated for builth in llanvirn times a palaeoreconstruction for 468 474 ma c mid llanvirn is presented utilizing this analysis

baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications torsvlk t h smethurst m a van der voo r trench a abrahamsen n and halvorsen e 1992 baltlca a synopsis of vendlan permmn palaeomagnetic data and their palaeotectonlc implications earth sci rev 33 133 152 in light of recent additions to the palaeozoic palaeo magnetlc data base particularly for the ordovlclan era a revised apparent polar wander apw path for baltica has been constructed following a rigorous synthesis of all late precambrlan perm lan data the apw path is characterized by two prominent loops firstly a late precambrlan camb rlan loop probably relating to a rifting event and secondly a younger loop relating to a mid silurian scandlan colhsion event these features imply major change in plate tectonic reconfiguratlon baltlca probably represented an individual continental unit m early palaeozoic times and was positioned m high southerly latitudes in an inverted geographic orientation in such a reconstruction baltlca was separated from the northern margin of gondwana by the tornqulst sea and from laurentla by the iapetus ocean the tornqulst zone is thus interpreted as a passive or dextral transform margin during the early palaeozoic while undergoing counter clockwise rotations up to 1 6 ma baltica drifted northward through most ol the palaeozoic except for a short period of southerly movement in late silurian early devonian times after colhslon with laurentla rapid movements in latitude up to 9 cm yr are noted m late precambrlan earl y palaeozoic times and slgmficant decrease in velocities throughout palaeozoic time probably reflect the progressive amalgamation of a larger continent by early devonian euramerlca and permian pangea times the tornqulst sea had a principal component of palaeo east west orientation hence it is difficult to be precise in the timing of when micro continents such as eastern avalonla and the european masslfs ultimately collided along the southwestern margin of baltica these micro continents are considered to have been peripheral to gondwana m high southerly latitudes during the early ordovlclan eastern avalonla clearly had rifted off gondwana by llanvlrn llanded o times and may have collided with baltlca during late ordovlclan times although the present available sdunan palaeomagnetlc data from eastern avalonia may suggest colhslon in late silurian times across the lapetus facing margin of baltica laurentla was s tuated in equatorml to southerly latitudes during most of the lower palaeozoic these continents collided in mid silurian times l e a first collision between southwestern norway and greenland scotla nd which gave rise to the early scandlan orogeny 425 ma in southwestern norway possible followed by a later but less dramatic scandlan event in northern norway at around 410 ma since baltlca was geographically reverted m early palaeozoic times the colhsional margin could not have been a margin that once rifted off laurentm as assumed in a number of plate tectonic models

the ordovician history of the iapetus ocean in britain new palaeomagnetic constraints new late tremadoc early arenig palaeomagnetic results from sw wales imply that s britain part of eastern avalonia occupied a southerly latitude of c 60 s in early ordovician times when combined with scottish ordoviaan palaneomagnetic data which indicate a 15 s latitude the results indicate that the british sector of the iapetus ocean reached n latitudinal width of c 5000 km in tremadoc arenig times which was reduced to c 3000 km by llanvirn llandeilo mid ordovician times the new data resolve two previous controversies in palaeozoic palaeogeography first the high southerly palaeolatitude links avdonia to gondwana marginal to w africa thus reconciling codlicting reconstructions based upon either palaeomagnetic or faunal facies evidence alone second reliable llanvim palaeomagnetic data imply that avlonia had rifted northwards by arenig time whereas armorica remained proximal to northern africa throughout the ordovician the combined data therefore establish that avdonia and armorica formed separate micro continents when rifting from gondwana

the palaeogeographic position of the lake district in the early ordovician the early ordovician was a time of maximum continental separation and hence a time when faunal evidence can be used to assess palaeogeography in a critical way we summarize the known trilobite occurrences 18 genera from the arenig llanvirn of the lake district and record some genera for the first time maps of the distribution of some of these forms are given all genera except cyclopyge were confined to the gondwana continent at the time and some are known from many localities and two species are widespread in england wales france iberia and bohemia the fauna is entirely distinct from those of scandinavia and north america all the palaeontological evidence points to the lake district being adjacent to ordovician gondwana in the earlier ordovician it is not reasonable to suggest that the iapetus ocean lay to the south of the lake district as did allen 1987

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

arenig biostratigraphy and correlation in the welsh basin recent work on the arenig series in the welsh basin is reviewed it is now known to be far more complete and richly fossiliferous than has been supposed three regional stages moridunain whitlandian and fennian and seven trilobite based biozones have been defined outstanding problems are highlighted among which remains the definition of a stratotype for a base for the series for which there appears to be only one feasible candidate in this area in the shelve inlier

survey of a gulf stream frontal filament an assortment of data is used to map and characterize a gulf stream filament during 21 25 april 1980 a filament was captured as it moved through an array of moored current meters on the northeast florida continental shelf current and temperature time series along with satellite vhrr and aircraft art are used to reconstruct the event the event is found to consist of an anticyclonically rotating warm tongue inshore of a cold dome the rotational scheme of the current in the warm tongue is opposite to previous hypotheses upwelling occurs in both the cold dome region and below the warm tongue

structural analysis of the adjacent acadian and variscan fold belts in belgium and northern france from geophysical and geological evidence abstract two palaeozoic fold belts are juxtaposed in belgium and northern france the northern belt of the brabant massif traditionally considered a part of the european caledonides was folded during the acadian orogeny in the early devonian although it is largely concealed gravity and magnetic maps give a general picture of the existing structures a curved gravity trend is interpreted as an arc shaped succession of granitic batholiths structures north and south of this arc are completely different the northern subdomain containing magnetic lower cambrian metasediments shows multiple thrust faults towards the south over the granites whereas the southern subdomain without magnetic rocks is moulded around the granitic core the southern variscan belt is characterized in general by thrusting with a north nw and ne vergence during the variscan orogeny the brabant massif acted as an obstacle to the general transport of the ardennes massif to the n nw the oblique convergence with the brabant massif caused differential displacement towards the northwest the western areas having travelled farther as seen from a pattern of wnw oriented strike slip faults

cambrian ordovician paleogeography of baltica recent paleomagnetic data and existing paleontological evidence show that baltica occupied temperate southern latitudes during cambrian and early ordovician time but was inverted with reference to its present orientation hence the currently opposed margins of the baltic and laurentian shield were not conterminous in the early paleozoic laurentian and baltic late precambrian rifting episodes may therefore have occurred along unrelated continental margins closure of the tornquist sea was accompanied by the counterclockwise rotation of baltica relative to avalonia in early to middle ordovician time this rotation initiated in late cambrian early ordovician time was coeval with the finnmarkian orogeny in the northern scandinavian caledonides

dynamical analyses of marine atmospheric boundary layer structure near the gulf stream oceanic front the effects of the sea surface temperature s s t front at the edge of the gulf stream on the marine atmospheric boundary layer mabl are investigated using a numerical model to study the modification effects of an oceanic front on the mabl structure the situation simulated is flow from over cold shelf water to over the warm water of the gulf stream the initial temperature and humidity profiles of the air are specified to be near neutral over the cold water and are therefore typical of undisturbed conditions the differential in s s t across the oceanic front creates a horizontal variation in the surface perturbation pressure and the stability the surface perturbation pressure and turbulent fluxes modulate the flow and produce horizontal variations in horizontal wind components with associated vertical motions a thermally direct cell is produced as a result of the s s t difference across the front the isotherms slope upward towards the warm water entrainment of inversion layer air and upward vertical motion over the warm water cause the mabl to be deeper there a layer of cloud forms over warm water and is associated with mixed layer deepening rather than lowering of the condensation level turbulent fluxes in the mabl show considerable spatial variation surface stress is much larger over the front and over the warm water than over the cold water this is mostly caused by wind speed changes associated with the front changes in the drag coefficient due to changes in surface roughness and stability are much less important mean budgets for temperature and total water indicate that there is a balance between horizontal advection and turbulent flux divergence the u momentum budget shows that once the geostrophic balance terms are subtracted the balance is mainly between the pressure gradient force associated with the induced temperature field and turbulent friction with horizontal advection and the coriolis force acting on the geostrophic departure playing minor roles the v momentum budget shows a balance between horizontal advection coriolis force and friction although there are few data for comparison the results are in qualitative agreement with observations in the area this study shows that the s s t front at the gulf stream edge produces marked local changes in the nearby atmospheric surface layer

the palaeogeographic evolution of southern britain during early palaeozoic times a reconciliation of palaeomagnetic and biogeographic evidence abstract palaeomagnetic biogeographic and palaeoclimatic evidence together suggest that in the early ordovician southern britain lay off the west african margin of gondwana at around 60 s the combination of these disciplines reduces latitude uncertainties to around 5 to 10 degrees rifting of avalonia from gondwana was followed during most of the ordovician by northward drift as avalonia and baltica converged with subduction of tornquist sea crust both continents had similar moderate northward drift rates 3 6 cm yr so their convergence probably had a considerable longitudinal component silurian and early devonian data indicate that northward drift of avalonia and baltica continued after their collision and that southern britain reached a latitude of around 20 s by c 400 ma

a reassessment of the early ordovician celtic brachiopod province in the early ordovician laurentia baltica and gondwana each had endemic shallow water cratonic faunas dominated by trilobites and brachiopods as well as some more widespread faunas around the continental margins the latter include the toquima table head faunas around laurentia and the 9celtic9 brachiopod faunas which form the main topic of this paper the celtic faunas were thought to have been distributed along and offshore of only the gondwana side of the iapetus ocean however fresh analysis of the celtic occurrences reveals a wider distribution of these brachiopods ranging from a substantial volcanic island arc the bronson hill tetagouche lushs bight island arc close to laurentia to sites firmly attributable to avalonia and possibly also baltica thus unlike most contemporary trilobite faunas these brachiopods which are not a homogeneous fauna had wider latitudinal tolerance than previously supposed and the term 9celtic province can be abandoned

a new palaeocene genus and species of percopsiform teleostei paracanthopterygii from the paskapoo formation smoky tower alberta a new genus and species of teleostean fish lateopisciculus turrifumosus fossil taxon from the palaeocene paskapoo formation at smoky tower alberta is described this new species is classified in the family percopsidae paracanthopterygii percopsiformes based on the presence of a dorsal process on the maxilla the presence of this fish extends the earliest known age of this family from the eocene amphiplaga and erismatopterus fossil taxa to the late palaeocene the fossil assemblage at the smoky tower locality includes pike esocidae an osteoglossomorph and two salamanders as well as the new species of percopsid the site was likely an oxbow lake or shallow swamp a mass death event is indicated by the multiple species and size and age class distribution of the specimens

introduction to the special issue commemorating the 30th anniversary of the royal tyrrell museum of palaeontology with a summary of the museum s early history and its research contributions located just west of drumheller in southern alberta canada the royal tyrrell museum of palaeontology rtmp is nestled among outcrops of the upper cretaceous horseshoe canyon formation exposed along the red deer river valley fig 1 since it officially opened on 25 september 19851 the museum has become one of alberta s must see tourist attractions a significant contributor to the local economy and earned an international reputation for the quality of its palaeontological collections and the research conducted by its scientists the rtmp is unique within canada in being the only government supported museum dedicated to palaeontology and it is one of the few such institutions in the world fig 1 the royal tyrrell museum of palaeontology a front of museum and main entrance circa 2010 looking westwards and with horizontal beds of the upper cretaceous horseshoe canyon formation exposed in the walls of the red deer river valley in the distance b aerial photograph oblique angle and looking to the north northeast the museum sits on top of the number 7 coal seam sensu gibson 1977 and at the base of the horsethief member of the horseshoe canyon formation d a eberth pers comm 2015 that stratigraphic position correlates with an age of about 71 5 ma i e late campanian and lies within the upper part of the edmontosaurus regalis pachyrhinosaurus canadensis dinosaur assemblage zone see eberth et al 2013 fig 6 c the iconic running theropod logo that until recently graced the exterior of the museum below a life sized tyrannosaurid sculpture by brian cooley one of many such sculptures by cooley that have been featured at the museum since its opening in 1985 and with the education wing opened in 2003 as the atco tyrrell learning centre in the background d the cretaceous alberta life sized diorama opened in 2007 an example of a rtmp exhibit that relies heavily on discoveries and interpretations by museum researchers in this case work done in the albertosaurus bonebed and at other localities throughout the horseshoe canyon formation all photographs courtesy of the royal tyrrell museum of palaeontology this special issue of the canadian journal of earth sciences presents a collection of papers commemorating the rtmp s 30th or pearl anniversary our rationale for doing a 30th anniversary volume was two fold first it is an opportunity to showcase the breadth of research conducted by current and former museum scientists as well as by some colleagues having a history of collaboration with the rtmp the 13 invited papers included in this volume are a mix of review and original research papers all thematically focused on the geology and palaeontology of alberta to varying degrees each contribution is the result of work supported by the rtmp and relies on specimens housed in the museum s collections second the 30th anniversary is an opportunity to reflect on the rtmp s history and its research program as is typical for most institutions the rtmp has done little to formally document its own history this year likely will be the last major milestone for which the original generation of museum staff are still working and available to share their recollections about the museum fieldwork and research already deaths and departures have winnowed away part of the original

a numerical investigation of the gulf stream and its meanders in response to cold air outbreaks the three dimensional princeton ocean model is used to examine the modification of the gulf stream and its meanders by cold air outbreaks two types of gulf stream meanders are found in the model meanders on the shoreward side of the gulf stream are baroclinically unstable they are affected little by the atmospheric forcing because their energy source is stored at the permanent thermocline well below the influence of the surface forcing meanders on the seaward side of the stream are both barotropically and baroclinically unstable the energy feeding these meanders is stored at the surface front separating the gulf stream and the sargasso sea which is greatly reduced in case of cold air outbreaks thus meanders there reduce strength and also seem to slow their downstream propagation due to the southward ekman flow heat budget calculations suggest two almost separable processes the oceanic heat released to the atmosphere during these severe cooling episodes comes almost exclusively from the upper water column transport of heat by meanders from the gulf stream to the shelf though it is large does not disrupt the principal balance it is balanced nicely with the net heat transport in the downstream direction

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

spatial patterns and intensity of the surface storm tracks in cmip5 models abstractto improve the understanding of storm tracks and western boundary current wbc interactions surface storm tracks in 12 cmip5 models are examined against era interim all models capture an equatorward displacement toward the wbcs in the locations of the surface storm tracks maxima relative to those at 850 hpa an estimated storm track metric is developed to analyze the location of the surface storm track it shows that the equatorward shift is influenced by both the lower tropospheric instability and the baroclinicity basin scale spatial correlations between models and era interim for the storm tracks near surface stability sst gradient and baroclinicity are calculated to test the ability of the gcms match reanalysis an intermodel comparison of the spatial correlations suggests that differences relative to era interim in the position of the storm track aloft have the strongest influence on differences in the surface storm track position however in the north atlantic biases in the surf

superimposed recent permo carboniferous and ordovician palaeomagnetic remanence in the builth volcanic series wales the builth volcanic series of llanvirnian age in llanelwedd quarries mid wales carries three components of natural remanent magnetisation component p regarded as primary is a thermochemical remanence directed at d 181 7 i 54 5 95 4 4 relative to bedding component s is a secondary component with in situ d 178 7 i 6 7 95 5 4 and is believed to be a low temperature chemical remanence crm of permo carboniferous age component r is directed close to the present geomagnetic field and is believed to be a recent viscous remanence vrm the results are of interest for three reasons first they are an unusually good example of multi component nrm analysis the three components being so clearly discriminated by thermal demagnetisation because they have almost completely separate blocking temperature ranges second they provide evidence of a permo carboniferous event possibly a mild thermal or hydrothermal pulse promoting crm acquisition some 40 km north of the hercynian orogenic front third they illustrate very clearly the importance of detailed demagnetisation this work revises the pole position for these rocks by 10 and removes an obstacle to the palaeomagnetic recognition of the 1000 km wide iapetus ocean cutting britain in ordovician time

a revised palaeozoic apparent polar wander path for southern britain eastern avalonia summary a revised apparent polar wander path apwp is presented for palaeozoic southern britain the new path based on a structural reinterpretation of existing data combined with new data from wales differs significantly from previous estimates in the following ways 1 the 1 ocus of the ordovician path segment is extended by approximately 25 degrees of arc 2 revised time calibration of the apwp suggests more ordovician apw than previously calculated and 3 the new path implies middle ordovician separation across the british sector of iapetus to be greater than previous palaeomagnetic estimates based on apwp analyses c 3300 km northern britain c 133 southern britain c 45s

warm water pathways transports and transformations in the northwestern north atlantic and their modification by cold air outbreaks 1 this paper presents a numerical study of the warm water pathways transports and water mass transformation in the newfoundland basin region and an investigation of the rectification effects of a series of cold air outbreaks caos on the above processes an initial mean state simulation was compared with observations and showed good agreement then repeated cao events were explicitly included in the surface fluxes and illustrated the following rectification effects the thermal regime of the entire baroclinic layer was impacted as the thermocline deepened and the temperature anomaly was noticeable down to 500 m different mechanisms were responsible for the propagation of the temperature anomaly at different stages during the onset of the cao vertical diffusion propagated the temperature anomaly downward near the surface then vertical advection further propagated the anomaly downward between cao events to about 500 m depth with caos the north atlantic current carried more warm water and its pathway in the northwest corner shifted towards the southeast the volume averaged mean and eddy kinetic energy increased by 30 and 20 respectively and the water mass transformation rate in the newfoundland basin was doubled the gulf stream carried more heat but heat transport to the eastern basin decreased owing to the increase in heat release to the atmosphere

reply to comment of a trench and t h torsvik on paleomagnetic results from volcanic rocks of the shelve inlier wales evidence for a wide late ordovician iapetus ocean in britain

summary of fossil vertebrate taxa named by richard c fox with an annotated list of taxa named between 1962 and 2012 and new photographs for non mammalian therapsid and mammalian holotypes erected between 1968 and 1994 beginning in 1962 and extending to the present richard c fox and colleagues have named 87 species of fossil vertebrates 1 fish 4 amphibians 2 choristoderes 12 lizards 1 crocodile 1 dinosaur 2 pelycosaurs 2 non mammalian therapsids and 62 mammals and numerous new supraspecific taxa virtually all of these species continue to be accepted although the higher level assignments of several have been altered the vast majority of the named species were founded on specimens collected during the mid 1960s to early 2000s by field parties under fox s direction from the late cretaceous late santonian to late maastrichtian and paleocene of alberta and saskatchewan canada and that are housed at the university of alberta laboratory for vertebrate paleontology here we present i an annotated list of all fossil vertebrate species named by richard fox between 1962 and 2012 ii updated information on the stratigraphic nomenclature and age estimates for the eight localities in alberta that yielded ho

the effect of gulf stream induced baroclinicity on u s east coast winter cyclones abstract midlatitude cyclones develop off the carolinas during winters and move north producing gale force winds ice and heavy snow it is believed that boundary layer and air sea interaction processes are very important during the development stages of these east coast storms the marine boundary layer mbl off the mid atlantic coastline is highly baroclinic due to the proximity of the gulf stream just offshore typical horizontal distances between the wilmington coastline and the western edge of the gulf stream vary between 90 and 250 km annually and this distance can deviate by over 30 km within a single week while similar weekly gulf stream position standard deviations also exist at cape hatteras the average annual distance to the gulf stream frontal zone is much smaller off cape hatteras normally ranging between 30 and 100 km this research investigates the low level baroclinic conditions present prior to observed storm events the examination of nine years of data on the gulf stream position

the influence of coastal shape on winter mesoscale air sea interaction abstract in the case of cold air outbreaks the combination of the coastal shape and the sea surface temperature sst pattern is shown to have a profound effect in establishing a low level mesoscale atmospheric circulation as a result of differential heating due to both variations in overwater path length and the sst a convergence or divergence line then forms along a line exactly downwind of the major bend in the coastline this is consistent with the structure of the cloud patterns seen in a high resolution landsat picture of the cloud streets the major features are also simulated well with a boundary layer model the dominant convergence line is marked by notably larger clouds to its cast the convective roll clouds grow downstream in accord with the deepening of the boundary layer to its west i e coastal side near the convergence line where the induced pressure field forces a strong westerly component in the boundary layer the wind shear across the inversion gives rise to kelvin helmholtz w

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

marine boundary layer structure and circulation in the region of offshore redevelopment of a cyclone during gale abstract marine boundary layer structure and circulation is documented for the 24 february 1986 case of offshore redevelopment of a cyclone during the genesis of atlantic lows experiment gale intensive observing period iop 9 mesoscale and satellite information emphasize that the onshore cyclone is not well organized as it moves offshore to the cold shelf waters with redevelopment occurring later over the gulf stream region within hours of redevelopment low level aircraft data were obtained in the region vertical aircraft profiles down by the national center for atmospheric research ncar king air in the vicinity of redevelopment over the gulf stream as well as the midshelf front region and cold shelf waters reveal two distinct boundary layers over the gulf stream region approximately 50 km south southwest of the redeveloping cyclone the near neutral marine boundary layer h l 6 6 capped by layered stratocumulus is characterized by a low cloud base 360 m relatively thick stratocumulus c

the significance of isotopic dates from the english lake district for the ordovician saurian time scale the lower palaeozoic time scale is discussed in the light of a new date for the threlkeld microgranite and a reassessment of other published dates from the lake district which suggest ages of c 410 ma for the base of the devonian c 421 ma for the ashgill c 429 ma for the late caradoc c 439 ma for the early llandeilo and c 468 ma for the early llanvirn