on the wave number spectrum of oceanic mesoscale variability observed by the seasat altimeter variations of sea surface height measured by the seasat altimeter in nearly repeat orbits during the last 24 days of the mission are used to compute the wave number spectrum of mesoscale variability in various parts of the oceans the instrument noise level 150 cm2 cycles km has limited the resulting oceanic spectrum to wavelengths longer than 100 km we found that the characteristics of the oceanic spectrum are dependent on the energy level of the mesoscale variability in the high energy areas close to major current systems most of the energy is contained at wavelengths longer than 250 km at wavelengths shorter than 250 km the spectrum basically follows a k 5 k is wave number dependence in the low energy areas remote from major current systems the spectrum follows a k 1 dependence at wave lengths from 100 to 1000 km based on the assumption of horizontal isotropy of mesoscale variability scalar wave number spectra of sea surface height and geostrophic kinetic energy are also presented dynamical implications of these spectra are discussed the effects of residual geoid and atmospheric water vapor on the computed oceanic spectra have been rigorously examined it was found that the general characteristics of the oceanic spectra were not significantly affected by them

the modification of chevron folds by simple shear examples from north cornwall and devon this contribution considers the effect of a horizontal simple shear deformation on an initially upright chevron fold pair using geometrical models the models utilize an initial fold geometry based on structures observed in the coastal sections of north cornwall and devon and consider various mechanisms by which the simple shear could be accommodated due to their different initial orientations the limbs of the chevron folds rotate at different rates during simple shear and this is accommodated by the modification of the fold structure possible modification structures include normal faulting in the opposite direction to the sense of shear on either the axial planes or the limbs of the folds and folding on the limb which dips in the same general direction as the sense of shear the results of the modelling can be used to interpret the structures observed in the studied sections it is shown that a southerly directed simple shear deformation acted in discrete zones resulting in the local modification of certain chevron folds this deformation is in the opposite direction to the main variscan movements in sw england nevertheless it is argued that the simple shear is an integral component of the main deformation and represents an analogous process to the mechanism of backthrusting present in most thrust belts

from swallow floats to argo the development of neutrally buoyant floats neutrally buoyant floats have been a vital tool in the exploration of the global ocean circulation and now provide a central element of the in situ ocean observing system through the argo project the paper traces the development of neutrally buoyant floats from their origins in the mid 1950s to the present day and highlights areas of ocean science to which floats made significant contributions

airborne expendable bathythermograph survey of the kuroshio extension and comparison with simultaneous altimeter measurements during the geosat exact repeat mission extensive airborne expendable bathythermograph axbt sections across the kuroshio extension during the geosat exact repeat mission erm were used to assess the ability of the geosat altimeter to monitor the locations of the kuroshio and its associated cold and warm core eddies the axbt sections in themselves provide detailed descriptions of the kuroshio extension to about 160 e these observations demonstrated that surface or near surface temperatures in this area may lead to incomplete and deceptive descriptions of the deeper thermal structure kuroshio eddy interactions in particular were not accurately portrayed by the near surface observations for this reason accurate mapping of the location of the kuroshio extension and of nearby eddies may not be practical from infrared ir imagery alone but requires augmentation from other measurement systems such as altimetry in the present analysis an estimate of the sea surface height was obtained from the altimeter ranges by time averaging sea surface heights in lieu of a geoid estimate sea surface height anomalies computed using the mean altimetric sea surface i e the geoid plus the temporal mean oceanographic signal can be significantly different from the actual oceanographic topography induced by mesoscale oceanographic features nevertheless it is shown that the positions of the kuroshio extension and of the stronger cold and warm core eddies associated with the kuroshio extension are easily located from these altimetric sea surface anomalies

comment on the bude formation sw england a three dimensional intra formational variscan imbricate stack by g e lloyd and n chinnery journal of structural geology 24 2002 1259 1280

discussion of an interpretation of the variscan structures of sw england discussion concernant un article publie dans le j geol soc london vol 139 4eme partie 1982 pp 533 541

transport mechanisms of sand in deep marine environments insights based on laboratory experiments reply first of all we would like to thank dr shanmugam for his interest in our study of transport mechanisms of sand in deep marine environments breien et al 2010 in order to answer the remarks of shanmugam we here provide some more details around the experiments and we specify the intention of the study the main objective of the experiments presented in our paper was to study transportation and depositional processes in sand rich slurries run in water and how these mechanisms respond to changing sand clay ratios we find some of the comments of shanmugam 2011 to be more concentrated on the bouma sequence and the properties of its divisions ta te than on the mechanism of sediment transport itself we do not claim to have produced a complete bouma sequence cf bouma 1962 walker 1965 middleton and hampton 1973 however we rather see that our experiments indicate that similar graded bed deposits may be produced by different transport mechanisms we show that dense laminar flows may transport sand through fluidization and incrementally produce sand deposits resembling deposits produced by turbulent turbidity currents thus we regard the process observed in the laboratory as only one out of several mechanisms to transport and deposit clean sand in submarine basins as part of a ph d program breien 2009 47 debris flow experiments were performed prepared with five different compositions of varying sand clay ratio 5 10 15 20 and 25 clay by weight content of water and coal

comparison data for seasat altimetry in the western north atlantic the radar altimeter flown on seasat in 1978 collected approximately 1000 orbits of high quality data 5 8 cm precision in the western north atlantic these data have been combined with a detailed gravimetric geoid in an attempt to produce profiles of dynamic topography in order to provide a basis for evaluation of these profiles available oceanographic observations in the gulf stream sargasso sea region have been compiled into a series of biweekly maps the data include xbt s satellite infrared imagery and selected trajectories of surface drifters and subsurface sofar floats the maps document the known locations of the gulf stream cyclonic and anticyclonic rings and mid ocean eddies during the period july october 1978

a synthetic geoid validation of geosat mesoscale dynamic topography in the gulf stream region a validation study is carried out for the geosat altimeter in the gulf stream meander and ring region a synthetic geoid containing the medium scales of interest for mesoscale research is constructed by subtracting an independent estimate of the oceanographic mean dynamic topography from the altimetric sea surface the oceanographic mean dynamic topography which is concurrent with the altimetric mean is derived from a year of real time nowcasts and forecasts gulfcast based on assimilating a composite data set into a dynamical model using the synthetic geoid absolute dynamic topography from geosat and gulfcast for a year and 4 months in 1988 and 1989 compare very well in signal shape and feature locations sixteen cases of comparison of dynamic heights derived from axbts along geosat tracks in 1987 are made with geosat absolute topography the rms difference is less than 10 cm thus the comparison of these two independent data sets validates the altimeter and the synthetic geoid within the noise and error levels of the system

seasat altimeter determination of ocean current variability radar altimeters of great precision roughly equal10 cm such as the one that flew on the seasat satellite are capable of measuring the small oceanic height variations associated with geostrophic ocean currents an experiment was concluded in the kuroshio current east of japan verifying this capability air expendable bathythermographs axbt s were dropped to coincide with the seasat subtract during flights on september 25 and october 5 and 13 1978 changes in surface dynamic height between flights were inferred from the axbt data they agreed generally to within 10 cm of height changes observed in the altimeter data

seasat altimeter observations of dynamic topography in the gulf stream region individual seasat altimeter profiles in the western north atlantic have been differenced with the best available geoid model to remove the gravitational component the resulting sea surface height profiles compare remarkably well with independent oceanographic observations the gulf stream is clearly apparent in each profile as a 1 to 2 m step and known positions of cyclonic and anticyclonic rings correspond with depressions and elevations respectively with amplitudes as large as 95 cm some of the most important altimeter data for analyzing the dynamic ocean signal were gathered during the last month of the mission when the same ground track was repeated every 3 days these data allow detailed examination of time varying ocean phenomena since the gravitational component is time invariant one set of collinear passes clearly shows a cyclonic ring as it moves out from underneath the spacecraft s track an event which was simultaneously observed with the aid of a satellite tracked surface buoy another striking feature seen in the altimeter data set is the apparent variability exhibited by the gulf stream on time scales of a few days surface transport indicated by the sea surface height difference across the stream varied by nearly 30 and over the entire 3 month period much larger fluctuations were observed suggesting significant changes in total mass transport altimetry may provide an effective means of determining the time and space scales associated with these variations

petrography and temporal changes in petrofacies of deep marine ainsa jaca basin sandstone systems early and middle eocene spanish pyrenees a petrographic study of 157 samples from the early to middle eocene deep marine sandy systems ainsa jaca basin spanish pyrenees shows that each system has a characteristic petrofacies three main petrofacies are recognized petrofacies 1 sandstones comprise mainly siliciclastic grains 80 subordinate terrigenous carbonate grains and negligible intrabasinal grains petrofacies 2 hybrid arenites are characterized by significant amounts 10 of intrabasinal carbonate grains petrofacies 3 calcilithites contain relatively abundant 10 extrabasinal carbonate grains on the basis of these petrofacies a revised correlation of the sandy systems is proposed between the more proximal ainsa basin and the more distal jaca basin sediments now separated by the boltana anticline across which it is impossible to actually trace out individual beds or sandstone packages between both basins the arenite composition in the ainsa and jaca basins is interpreted as being controlled mainly by synsedimentary tectonic processes that led to changes in sediment sources during basin evolution

topographic controls on the development of contemporaneous but contrasting basin floor depositional architectures abstract sediment laden gravity driven flow deposits on the basin floor are typically considered to form either discrete lobes that stack compensationally or packages of laterally extensive beds commonly termed sheets these end member stacking patterns are documented in several basinfills however whether they can coexist in a single basin or there are intermediate or transitional stacking patterns is poorly understood an analysis of depositional architecture and stacking patterns along a 70 km dip oriented transect in the upper broto turbidite system jaca basin south central pyrenees spain which displays disparate stacking patterns in contemporaneous strata is presented proximal and medial deposits are characterized by discrete packages of clean sandstones with sharp bed tops which exhibit predictable lateral and longitudinal facies changes and are interpreted as lobes distal deposits comprise both relatively clean sandstones and hybrid beds that do not stack to form lobes instead localized relatively thick hybrid beds are inferred to have inhibited the development of lobes hybrid beds developed under flows which were deflected and entrained carbonate mud substrate off a carbonate slope that bounded the basin to the south evidence for this interpretation includes 1 divergent paleoflow indicators and hummock like features in individual beds 2 a decrease in hybrid bed thickness and abundance away from the lateral confining slope 3 a carbonate rich upper division not seen in more proximal turbidites the study demonstrates the co occurrence of different styles of basin floor stacking patterns in the same stratigraphic interval and suggests that characterization of deep water systems as either lobes or sheets is a false dichotomy

the charo arro canyon mouth sheet system south central pyrenees spain a structurally influenced zone of sediment dispersal abstract detailed field and photogeological mapping of the charo canyon and arro sandbody which can be traced directly into the canyon shows the relationships between shelf slope canyon and base of slope deposition the charo canyon is incised into slope and shelf facies of the castisent group 50 5 49 5 ma and was a sediment conduit for turbidity currents and their deposits during the upper part of the castisent group and the santa liestra group 49 5 44 ma the arro sandbody downslope from the charo canyon belongs to the upper part of the castisent group unlike the overlying santa liestra channel complex the arro sandbody shows few features typical of a channel fill deposit but is characterized by a base of slope facies association in front of the canyon mouth the key factors influencing the internal architecture of the arro sandbody were variations in slope angle and an increase in sediment supply both factors being largely controlled by mid castisent thrust activity this paper describes the composite fill of the charo canyon and investigates its relationship to the depositional setting of the downcanyon deposits

the fan that never was discussion of upper carboniferous fine grained turbiditic sandstone from southwest england a model for growth in an ancient delta fed subsea fan discussion and reply

tectonics of the bude formation north cornwall the recognition of northerly directed decollement the upper carboniferous bude formation of north cornwall and devon underwent deformation beginning shortly after its deposition which resulted in a complex geometry of folding and thrusting the deformation initially exploited slumped beds as decollement horizons and resulted in a significant northerly translation of thrust sheets the development of chevron folds for which the area is famous commenced at this stage but continued causing folding of thrust planes and cleavages during the deformation the dominant sense of thrust movement switched from a northerly to a southerly direction and this is interpreted as the effect of backthrusting associated with the northwards migration of the deformation front

patterns of folding within nappes and thrust sheets examples from the variscan of southwest england folding is a common response to deformation within nappes and thrust sheets and a wide variety of attitudes of folds can result two examples of patterns of variably oriented folds from southwest england are analysed in terms of thrust tectonics in northern cornwall the millook nappe contains a downward progression from upright to recumbent folding with a zone of oblique or sheath folds at its base these changes are related to an increasing simple shear component towards the base of the nappe in southwestern cornwall d1 and d2 deformations are related to the thrust emplacement of the lizard complex f1 folds in rocks below and to the north of the lizard complex have variable axial orientations alternating zones of folds trending normal and oblique to the transport direction have been mapped the oblique folds are interpreted as initiating in zones of differential movement within thrust sheets later d2 shear zones cut up section ahead of the advancing lizard complex in which case they result in refolding of f1 folds beneath the lizard complex these d2 shear zones cut down section extending but rarely refolding the d1 structures

observations of eddy fields in the northwest atlantic and northwest pacific by seasat altimeter data sea level variability related to the eddy field activity can be calculated from repeating tracks of altimetric data such as the seasat 3 day repeat data september 13 to october 10 1978 if we consider the eddy field in geostrophic balance the geostrophic relation gives the surface eddy velocities also an estimation of the eddy kinetic energy can be deduced under the assumption of quasi isotropy of the velocity variability this approach is used in the northwest atlantic and northwest pacific through the processing of seasat data high variability of sea surface topography up to 20 cm and high eddy kinetic energy 800 1600 cm sup 2 s sup 2 are detected in the vicinity of the gulf stream and the kuroshio power spectra of the observed sea level fluctuations give wavelengths ranging from 100 to 900 km for time scales between 3 and 25 days maps of sea surface topography variability and eddy kinetic energy are presented and discussed

seasat derived ocean surface topography comparison with coincident kuroshio hydrographic data during the seasat repeat orbit period a ctd and deep 1800 m xbt hydrographic experiment was conducted across the kuroshio to obtain cotemporaneous surface topography measurements for comparison with the altimeter derived surface height measurements the results showed that the altimeter could detect and measure the change in sea surface topography caused by movement of the kuroshio and the cold rings that were found in the hydrographic data after compensation for the small differences in the time of the measurements the altimeter measured changes in the surface topography that matched those measured by the hydrographic sections with an average difference of 9 6 cm for the 41 comparison points

the fan that never was upper carboniferous fine grained turbiditic sandstones from southwest england a model for growth in an ancient delta fed subsea fan discussion

the bude formation sw england a three dimensional intra formational variscan imbricate stack abstract the deformation of the upper carboniferous bude formation sw england is re interpreted in terms of a sedimentary multilayer sequence which represents a compromise between mechanically competent and mechanically incompetent behaviour the chevron folding that characterises the sandstone shale multilayer sequence is shown to be only a part of a more complex regional scale polyphase deformational history that developed at high structural levels in the late variscan orogeny the major tectonic features are thrust faults which are responsible for the imbrication of the original sedimentary pile six distinct thrust sheets are recognised in the 5 km coastal section studied northerly directed thrusts pre date chevron folding whilst structurally necessary southerly propagating back thrusts both pre and post date folding where they post date folding they impose a southerly shear onto the rocks leading to modification of existing folds the significance of these thrust structures has previously been ignored due to their tendency to develop parallel to bedding and to be overprinted by flexural slip features during chevron folding a model is presented that views the bude formation as a three dimensional intra formational imbricate stack which is at any single locality an instantaneous representation of an orogenic front propagating into its own foreland basin

a reappraisal of the facing confrontation in north cornwall fold or thrust dominated tectonics the problem of conflicting fold or thrust solutions to the interpretation of the structure of north cornwall is discussed via new detailed mapping of the coastal sections in addition to facing evidence shear criteria have been extensively applied in order to sustain new interpretations the facing confrontation at polzeath is confirmed but the high strain zone centred upon tintagel is ascribed to later superimposed northwards directed ductile shearing peak metamorphism was synchronous with this event subsequent northwards displacement became confined to discrete thrust planes dismembering the south facing structures which developed during an intermediate phase of backthrusting the major structures are thrust dominated though large recumbent folds were generated during the early ductile phases the facing confrontation is probably allochthonous having been carried northwards on a blind thrust it is suggested that the important rusey fault zone is the roof thrust to a triangle zone in which the lower grade rocks of the culm basin are uplifted over an underlying antiformal stack

deconvolving tectono climatic signals in deep marine siliciclastics eocene ainsa basin spanish pyrenees seesaw tectonics versus eustasy the eocene deep marine siliciclastic fill of the ainsa basin spanish pyrenees gives unprecedented temporal resolution of the causes and timing of coarse clastic sediment supply to a deep marine basin early eocene tectonic subsidence linked to pyrenean orogenesis created the ainsa basin with water depths of similar to 400 800 m above a foundered shallow marine mixed carbonate and clastic shelf the similar to 25 sandbodies or channelized submarine fans in the basin were controlled by the similar to 400 k y milankovitch frequency with modes at similar to 100 k y and similar to 41 k y possibly stacked similar to 23k y influencing bottom water conditions in the basin causing periodic stratification in the water column across a submarine sill at the western basin margin early boltana anticline intrabasinal tectonics defined and controlled the position of eight sandy systems and their constituent fans in a process of seesaw tectonics by 1 westward lateral offset stacking of sandy fans due to growth of the eastern side of the basin represented today by the mediano anticline and 2 eastward orogenward back stepping of the depositional axis of each sandy system due to phases of relative uplift of the boltana anticline during basin infill uplift of the boltana anticline led to increasing basin narrowing and depositional confinement unlike the earlier depositional systems the youngest deep marine system was fed from a more southern sediment source between the growth anticlines as was the overlying deltaic system all the older deep marine sandy systems were fed from southeast point sources from canyons and erosional lower slope channels eroding the growing mediano anticline the depositional style outlined in this paper might be common to other active margins where siliciclastic basins evolve between active thrusts

uncertainties in the mean ocean dynamic topography before the launch of the gravity field and steady state ocean circulation explorer goce 1 in anticipation of the future observations of the gravity mission gravity field and steady state ocean circulation explorer goce the present day accuracy of mean dynamic topography mdt is estimated from both observations and models a comparison of five observational estimates illustrates that rms differences in mdt vary from 4 2 to 10 5 cm after low pass filtering the fields with a hamming window with wavenumber n 120 corresponding to an effective resolution of 167 km rms differences in observational mdt reduce to 2 4 8 3 cm for n 15 1334 km differences in data sources geoid model in situ data are mostly visible in the small scale oceanic features while differences in processing filtering inverse modeling techniques are reflected at larger scales a comparison of seven different numerical ocean models demonstrates that model estimates differ mostly in western boundary currents and in the antarctic circumpolar current rms differences between modeled and observed mdt are at best 8 8 cm for n 120 and reduce to 6 4 cm for n 15 for models with data assimilation a minimal rms difference of 6 6 cm n 120 to 3 4 cm n 15 is obtained with respect to the observational mdts the reduction of differences between mdts with increasing filtering scales is smaller than expected while it is expected that goce will improve mdt estimates at small spatial scales improvement of mean sea surface estimates from satellite altimetry may be needed to improve mdt estimates at larger scales

dynamic topography estimates using geosat data and a gravimetric geoid in the gulf stream region summary a gravimetric geoid undulation on a 3 x 3 grid has been calculated in the gulf stream region 30 5 i 45 278 5 i 5 318 these undulations were calculated using two 360 potential coefficient models land ship and altimeter derived gravity anomalies and bathymetric data least squares collocation and fast fourier transform procedures were used with various data selection and gridding procedures results from five different undulation computations are described with comparisons made with synthetic geoid undulations along geosut tracks in the region the standard deviation of the undulation differences was f14cm when a cubic polynomial was used to model long wavelength errors a point verification of the geoid undulation at the laser tracking station on bermuda was also made with a discrepancy ground truth minus model undulation of 40 cm within the predicted standard deviation the gravimetric geoid undulation was used to compute dynamic topography along geosat tracks for comparison with existing estimates based on hydrographic data in the gulf stream region the agreement between these two estimates is on the order of f15 cm although the discrepancies can reach 60 cm the larger differences are usually associated with a location on a track that passes near a seamount where the gravity data may be inadequate to represent the high frequency variations in the geoid undulations this effect will be represented in the undulation standard deviations that have been calculated using the least squares collocation procedure the average accuracy is fl6cm with the range from f14 to f48cm the dynamic height derived from the gravimetric undulations and altimeter data has been used to calculate characteristics of the gulf stream width velocity centre location height profile using an implied velocity model for the set the results are compared with previous estimates with generally good agreement however the maximum velocities and the jump function are approximately 30 per cent larger than previous studies that used an average of altimeter tracks to define the geoid undulation the dynamic topography was calculated for the entire region using a mean sea surface based on geos 3 seasat and geosat data the results are compared with two hydrographic estimates due to martel wunsch and letraon mercier the agreement is at the f25cm level with the best correlation coefficient reaching 0 72 with the martel wunsch model

dynamics of the slope water off new england and its influence on the gulf stream as inferred from satellite ir data abstract the movements of warm core rings and the gulf stream front were studied in the new england slope water region by using both satellite ir data and available in situ sea surface temperature data it is found that 1 the rotating speed of the rings exhibits a marked seasonal variation with the maximum speed occurring in the winter and the minimum in the late fall 2 the surface area of the rings increases monotonically with time and 3 the gulf stream front at the north wall migrates seasonally and attains its northernmost position in the late fall based on these findings we calculated the horizontal eddy viscosity for the rings as 4 10 8 cm 2 5 furthermore by comparing the seasonal variations of the rotational velocity of the rings and the total mass transport of the gulf stream we suggest that the seasonal variation of the slope water hydrography through local air sea interactions could play an important role in the dynamics of the gulf stream system

architecture of the tectonically influenced sobrarbe deltaic complex in the ainsa basin northern spain abstract the syn tectonic sobrarbe deltaic complex eocene of the ainsa basin spanish pyrenees is confined by lateral thrust ramps and influenced by intra basinal growth anticlines six facies associations have been distinguished within the deltaic complex i slope marls and turbidite sandstones ii distal delta front silty and bioturbated sandstones iii proximal delta front and delta plain deposits tidal inlet tidal flat mouth bar bay distributary channel and floodplain environments iv biogenic deposits at flooding surfaces v collapse zone sediments and vi nummulite dominated shallow marine carbonates the deltaic complex comprises four composite sequences which each contain a number of minor sequences of the genetic maximum flooding surface bounded type regressive unconformities and their correlative surfaces separate the composite sequences cs and each cs can be divided into lowstand transgressive and highstand components at the base the comaron cs is a wnw prograding deltaic complex containing six minor sequences characterized by basinward stepping sandstone wedges separated by transgressive mudstones double regressive unconformities are often associated with these sandstone wedges proximally in the basin growth of the intra basinal arcusa anticline caused gentle folding of the comaron cs and syn growth strata at the base of the overlying las gorgas cs contain a prominent forced regressive sandstone wedge the las gorgas sandbody and display thinning of bedsets onto the crest of the anticline moreover it can be demonstrated that relative sea level rise took place in the growth synclines at the same time as a fall in relative sea level occurred on the growth anticlines the tectonic deformation caused a shift in the direction of deltaic progradation towards the north northwest as demonstrated by the well developed clinoforms in the highstand sequence set of the las gorgas cs a second phase of tectonic activity this time triggering large scale collapse of the delta front occurred at the transition between the las gorgas and barranco el solano cs tilting of the basin floor led to the development of coeval transgressive and regressive strata separated by a fulcrum line of zero net vertical movement of the shoreline in the post tilt phase reduced sediment supply and accelerated subsidence led to widespread transgression and a change from clastic to carbonate dominated sedimentation this phase was terminated by a gradual increase in sediment supply causing progradation of a mixed clastic carbonate system dominated by large nummulite banks and bioturbated shoreface marls and sandstones finally a pronounced fall in relative sea level associated with the transition to the buil cs triggered slope instabilities and eventually established fluvial conditions all over the study area with the exception of the anticline crests the relatively high rate of tectonic subsidence in the study area suppressed relative sea level falls resulting in development of discontinuous lowstand strata and bounding surfaces the segmented nature of many regressive unconformities may be related to incremental growth of thrust related structures and each segment is separated from neighbouring segments by gaps of limited vertical and lateral displacement precursors of progressive unconformities are seen in the upper proximal part of the comaron cs by downdip fanning and updip convergence of minor sequences these differentially tilted stratal units provide reliable indicators of syn sedimentary tectonism

a study of the kuroshio s seasonal variabilities using an altimetric gravimetric geoid and topex poseidon altimeter data the first year of topex poseidon t p altimeter data were used to study the seasonal variabilities of the kuroshio current the intercomparison between the t p and gauge sea levels at selected tide gauge stations around taiwan shows that the two have a correlation of about 0 9 at the immediate vicinity of the deep ocean and both show an annual cycle with an amplitude of 15 cm a 3 3 geoid for the western pacific was constructed by least squares collocation using gravity anomalies and sea surface gradients derived from seasat geosat ers 1 and t p altimetry to account for the oceanographic signal in the altimeter data we derived a covariance function for the gradients of the sea surface topography sst based on a global averaging concept and a spherical harmonic expansion of the levitus sst to degree 50 the accuracy of the geoid ranges from 5 to 40 cm the sst values derived from the geoid and the data along t p s descending tracks were fitted to the hyperbolic functions in a two step procedure to find the kuroshio s seasonal axes and the parameters that describe its characteristics the mean variabilities in the kuroshio s path maximum velocity baroclinic transport and width are 22 km 19 cm 8 sv and 27 km respectively the averaged percentage variability of all quantities is 25 all the variabilities are relatively large near the northeast coast of taiwan and the starting point of the kuroshio extension the large scale circulations over the western pacific were obtained by median filtering the sst at the 1334 km spatial scale the pacific s subtropical gyre is clearly visible and it shows different features over the four seasons and its kinetic energy shows possible correlations with the determined parameters over the south china sea a warm ring with a radius of 300 400 km and a center at 15 n 113 e was detected in the spring and summer

calibration of the cryosat 2 interferometer and measurement of across track ocean slope this paper describes the calibration of the cryosat 2 interferometer whose principal purpose is to accurately measure the height of the antarctic and greenland ice sheets a sequence of cryosat 2 data acquisitions over the tropical and midlatitude oceans were obtained between june and september 2010 from the siral a and redundant siral b radars operating in their sarin mode during a sequence of satellite rolls between 0 6 and 0 4 using the arrival angle of the echo relative to the interferometer baseline the attitude of the satellite determined by the star trackers and estimates of the ocean surface across track slope from the egm08 geoid we determined the errors in the interferometer estimate of surface slope as functions of the roll angle and ocean surface waveheight these were found to be in close agreement with the theoretical description the scale factor of the interferometric measurement of angle was determined to be 0 973 0 002 we estimate the accuracy of the across track slope measurement of the interferometer by applying this scale factor to the measured phase in applying this scale factor to the measurements the across track slope of the marine geoid was obtained with an accuracy of 26 rad at 10 km and 10 rad at 1000 km we conclude that the instrument performance considerably exceeds that needed for the accurate determination of height over the sloping surfaces of the continental ice sheets the results also demonstrate that cryosat 2 provides the first observations of the instantaneous vector gradient of the ocean surface and that the normal incidence interferometric configuration has a greater potential for the measurement of the ocean across track slope than has been previously recognized

collinear track altimetry in the gulf of mexico from seasat measurements models and surface truth abstract from 17 september to 10 october 1978 seasat made collinear passes over the gulf of mexico altimeter data for eight three day repeat passes over the eastern gulf were examined using an arc segment fitting technique to determine the mesoscale temporal variability of the sea surface the pattern of sea height variability was then compared with sea height data generated by a numerical model of the gulf hurlburt and thompson 1980 from the simulation of a complete cycle of loop current intrusion and shedding of an anticyclonic eddy the model data was found to match that from the seasat altimeter when an anticyclonic eddy separated from the loop current and the loop began to repenetrate into the eastern gulf analysis of sparse ground truth data from ship of opportunity xbt s satellite infrared imagery of the loop current boundary and synthetic aperture radar sar imagery also from seasat tend to confirm the circulation patterns deduced from the altimeter data and the numerical model author

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

filling the north european early middle eocene ypresian lutetian boundary gap insights from the pyrenean continental to deep marine record abstract the early middle eocene ypresian lutetian transition is represented by a hiatus in many north european sections including those in which the classic stratotypes were originally defined however the global stratotype section and point of the lutetian stage which is still pending definition should be placed at a globally correlatable event included within that unrepresented interval the pyrenean eocene outcrops display sedimentary successions that offer the rare opportunity to analyse the ypresian lutetian boundary interval in almost continuous sections and in very different settings seven reference stratigraphic sections were selected on the basis of their quality and correlated by means of biomagnetostratigraphic data this correlation framework casts light on the sequence of chronostratigraphic events that characterize the ypresian lutetian boundary interval which may prove useful in defining the main correlation criterion of the base of the lutetian all of the pyrenean sections show a similar sedimentary evolution despite being up to 350 km apart from each other containing deposits of different origins intrabasinal carbonate sediments siliciclastic sediments sourced from the iberian plate and terrigenous sediments sourced from the uplifting pyrenees and despite having been accumulated in different sedimentary environments from continental to deep marine and in different geodynamic settings piggy back basin foreland basin and cratonic margin this common evolution can be readily interpreted in terms of a sea level driven depositional sequence whose lowstand and transgressive systems tracts are included within the ypresian lutetian boundary interval the pyrenean ypresian lutetian depositional sequence can reasonably be correlated with depositional sequences from classic north european areas shedding light on the palaeoenvironmental history which in those areas has not been recorded furthermore these depositional sequences may possibly correlate with others from the antarctic ocean and from new jersey as well as with oceanic temperature variations suggesting that they might be the result of climatically driven glacioeustatic sea level changes should this hypothesis prove correct it would confirm previous suggestions that the onset of antarctic glaciations needs to be backshifted to the late ypresian at least

absolute measurement by satellite altimetry of dynamic topography of the pacific ocean satellites are the only foreseeable possibility for obtaining observations of the ocean circulation on the basin and global scales required to understand it such observations are essential for an understanding of the role of the ocean in various important problems for example climate the 3 month seasat mission1 has demonstrated2 3 that altimetry is capable of providing global observations of oceanic variability we show here that the data from this short sub optimum mission are also adequate for a determination of the absolute sea surface topography of the ocean on large scales a much more difficult4 and even more valuable measurement an absolute determination of the subtropical gyre of the north pacific ocean has been obtained we believe this to be the first direct measurement showing the existence of such a feature that does not depend on conventional hydrography and a series of assumptions

the bude formation lower westphalian sw england siliciclastic shelf sedimentation in a large equatorial lake the 1300 m thick turbiditic bude formation was deposited in a lake lake bude but disagreement persists over whether the environment was a deltaic or deep water fan the tectonic setting of the lake was the northern flank of a northerly advancing variscan foreland basin close to the westphalian palaeo equator palaeocurrents indicate sediment sourcing from all quadrants except the south there is a dm m scale cyclicity whereby sandstone bodies comprising amalgamated event beds alternate with mudstone intervals containing non amalgamated event beds the ideal cycle is a symmetrical coarsening up fining up cycle consisting of three facies i 2 and 3 arranged in 12321 order facies 3 in the middle of the cycle is an amalgamated sandstone body up to 10 m thick which interfingers laterally with thin cm mudstone layers the sandstone body comprises amalgamated beds of very fine sandstone which are largely massive and up to 0 4 m thick channels are absent except for scours up to 0 2 m deep which truncate the interfingering mudstone layers sandstone bodies are inferred to be tongue shaped in three dimensions facies 1 and 2 completing the 12321 cycle are respectively dark grey fine and light grey coarse varved mudstone containing thin 0 4 m sandstone event beds fossils and burrows indicate that facies 1 and 2 were deposited respectively in brackish rarely marine and fresh water hence the ideal cycle 12321 reflects an upward decrease then increase in salinity brackish fresh brackish this is attributed to the lake sill being periodically overtopped by the sea due to glacio euitatic sea level oscillations the resulting oscillations in lake depth produced the coarsening up fining up regressivetransgressive cyclicity the central sandstone body representing the regressive maximum event beds are interpreted as river fed turbidites deposited during catastrophic storm floods combinedflow ripples and other wave influenced structures occur in event beds throughout the ideal cycle suggesting deposition of the entire bude formation above storm wave base the proposed environment is a shelf of continental shelf dimensions but lacustrine instead of marine sandstone bodies are interpreted to be river connected tongues or lobes the absence of cycles containing nearshore or emergent facies is attributed to i the lake sill preventing the water level from falling below sill level thereby insulating the lake floor from eustatically forced emergence and ii relatively distal deposition beyond the reach of shoreline progradations the lack of palaeoflow from the south is attributed to a now eroded deep water trough lying to the south in front of the northerly advancing orogen some facies 2 laminated mudstone beds grade laterally into massive and or contorted beds interpreted as in situ seismites facies 4 consistent with an active foreland basin setting development of seismites was possibly facilitated by gas bubbles and or weak cohesion in the fresh water bottom mud the late quaternary black sea with its broad northwestern shelf is probably a good physiographical analogue of lake bude and was likewise fresh at times

a new age model for the middle eocene deep marine ainsa basin spanish pyrenees abstract the middle eocene ainsa basin spanish pyrenees comprises 4 km of deep marine sedimentary rocks belonging to the hecho group despite extensive study of these exemplary deep marine clastic successions there has been no comprehensive chronostratigraphic framework that provides primary ages for the submarine fan and related deposits here we present a new composite basin stratigraphy based upon biostratigraphic analyses of the upper hecho group submarine fan and interfan deposits calcareous nannofossil data suggest that deposition of the gerbe through to guaso systems occurred during biozones np14 16 42 6 and 48 9 ma based on our age model additional biostratigraphic ages from the lower hecho group suggest that the entire hecho group no older than biozone np13 51 ma the improved chronostratigraphic control enables correlations between submarine canyons and submarine fans of the ainsa and jaca basins to be assessed our new age model provides a means of comparison of stratigraphic events with regional sections allowing a better understanding of the lateral and temporal evolution of these depositional systems from source to sink

mesoscale ocean eddy measurements by multibeam altimetry a multibeam microwave radar altimeter concept is numerically simulated to evaluate its capability to remotely sense mesoscale oceanographic features and eddies in particular the study tests the sensitivity of the sensor to variations of systematic and environmental parameters including sensor attitude angle sensor position and system errors a novel concept of computing eddy vorticity from the multibeam data is explored application of this concept to the detection of simulated ocean eddies in the presence of tracker noise gives excellent results the technique is shown to be simple and accurate the minimum size of the eddy detectable by the multibeam altimeter is presented for a given performance characteristic of the radar

upper palaeozoic successions and nappe structures in north cornwall for many years the geology of north cornwall has been interpreted in terms of a south facing overfold model which predicts a major confrontation at padstow with the north facing structures of south cornwall new evidence indicates the existence of contrasting successions separated by flat lying thrusts in upward succession the port isaac tredorn and boscastle nappes are identified the first appears to have been emplaced by gravity sliding in late visean times followed by the tredorn and boscastle nappes in the early namurian strata represented in the inverted limb of the port isaac nappe not previously distinguished are described as the jacket9s point slate formation throughout the nappe pile there is consistent evidence of north facing and northward transport for distances measured in tens of kilometres not more than 3 km of south facing strata may now exist at the padstow confrontation and this feature is unlikely to be of great regional significance the allochthon extends northwards to the rusey fault zone where the autochthon was locally backfolded over the allochthon in late westphalian times this appears to be the only significant confrontation of facing directions in north cornwall

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

sand body orientation palaeoslope analysis and basin fill implications in the westphalian a c of great britain channel orientation and palaeoflow analyses across the british westphalian carboniferous coalfields show that three main inflow directions dominated the palaeogeography from the mid langsettian to the mid bolsovian in eastern scotland and ne england flow was mainly from the n and ne in the pennine basin of north central england flow was mainly from the w and nw whilst in south wales main flow from the sw was compatible with a westerly system that also branched to give the northerly inflows recorded in the culm basin of southwest england the depositional area included discrete tectonic depocentres notably the pennine basin which was traversed directly and tangentially by major channel belts these basins were essentially incidental to the main channel pathways but sand body characteristics vary according to basin location a new depositional model for the post rift pennine basin is proposed relating sand concentrations and connectivities to the depositional and tectonic setting the description of dominant sw to ne flow across south wales through much of the langsettian and duckmantian in contrast to the centripetal inflows previously proposed implies some similar channel depocentre relationships to those described here for the pennine basin

morphology and geometry of duplexes formed during flexural slip folding abstract bedding parallel slip on the limbs of chevron style folds during flexural slip folding results occasionally in the formation of small scale duplexes the duplexes described here from upper carboniferous turbidites in sw england generally range in thickness from 0 3 to 30 cm and are up to 2 4 m long they have smooth nearly flat roofs and both the internal thrusts and the slickenfibres on them are commonly oblique to the mean transport direction as indicated by slickenfibres on the floor and roof thrusts the morphology of the duplexes suggests that they developed between active floor and roof thrusts and they show a characteristic lack of hangingwall anticlines on the link thrusts their shear sense always corresponds to that required by flexural slip and the total bedding parallel displacement across each is commensurate with that predicted by the flexural slip model all thrust surfaces in the duplexes are marked by quartz fibre veins a feature which distinguishes them from soft sediment and other pre folding duplexes and carry slickenfibres whose mean orientation and complex variations in slip direction on different fibre sheets on the same slip surface are identical to those on flexural slip movement horizons from the same fold limb the duplexes form either as a result of resistance to thrust propagation by local facies or bed thickness changes or develop as transfer structures between the tips of movement horizons propagating along adjacent slip surfaces late stage duplexes develop from imbricated fibre veins and also form on slip surfaces oblique to the axial planes of major folds

the tourmaline bearing granite pluton of bodmin cornwall uk magnetic fabric study and regional inference the magnetic fabrics and microstructures of the variscan granite pluton of bodmin cornwall have been studied its low susceptibility magnitude consistent with its lack of magnetite comes from biotite and tourmaline as the magneto crystalline behaviour of tourmaline is inverse compared with that of the phyllosilicates the magnetic fabric was remeasured after heating the specimens to enhance the biotite magnetic signal by the growth of mimetic magnetite the roughly similar magnetic fabrics before and after heating demonstrate that the effect of tourmaline is not important as long as the tourmaline content does not exceed that of the phyllosilicates regionally this study reveals a well defined nnw trend of the magnetic lineations with opposite plunges on each side of a separation line crossing the pluton centre this pattern very similar to that documented in the nearby carnmenellis pluton is ascribed to unroofing during emplacement it agrees with the late to post magmatic nw stretch that characterizes the devonian to carboniferous formations located to the north of this region the thrust and fold structure of which is attributed to southward compression we conclude that syntectonic emplacement may have characterized the whole cornubian batholith at the very end of the variscan orogeny in cornwall

orbital forcing as principal driver for fine grained deep marine siliciclastic sedimentation middle eocene ainsa basin spanish pyrenees abstract the relative importance of climate tectonics and or autocyclicity in driving deposition of laminated deep marine fine grained siliciclastic sediments in tectonically active basins remains controversial consequently the recognition of milankovitch periodicities in such successions remains poorly documented this study evaluates the cyclostratigraphy and its likely drivers in the middle eocene ainsa basin spanish pyrenees a basin that is known to have been associated with major syndepositional tectonics this basin was infilled by a thick succession of siliciclastic sediments characterised by an alternation of coarse grained sandbodies interpreted as submarine fans and finer grained packages of interfan fan lateral margin and channel levee overbank sediments this study presents time series analysis of outcrop spectral gamma ray and cumulative sandstone turbidite abundance data from eight fine grained essentially interfan sections located between coarse grained sandbodies submarine fans the 1 4 km of cumulative stratigraphy studied show that milankovitch cyclicity can be recognised throughout the entire stratigraphic evolution of the ainsa basin even though the basin was tectonically active and suggest that the accumulation of the interfan deposits was orbitally controlled orbital parameters most likely paced the cyclic delivery of the fine grained sediments mainly by river and delta supplied turbidity currents from the non marine and shallow marine tremp basin immediately to the east sediment accumulation rates determined from spectral analysis show a gradual decrease throughout the deep marine stratigraphy from 57 to 24 cm kyr this study shows that orbitally induced climate change acted as a principal driver on deep marine terrigenous sediment accumulation within a tectonically active basin high frequency climate variability therefore should be considered when studying controls on siliciclastic sedimentation in tectonically active regions

interaction of the antarctic circumpolar current with bottom topography an investigation using satellite altimetry theoretical studies on the interaction of a zonal current with a zonal ridge an isolated bump and a meridional ridge compare favorably with hydrographic observations within the eastward flowing antarctic circumpolar current where it flows over similar topographic features however the existing hydrographic data are insufficient for examining the temporal stability and kinematic behavior of the resulting mesoscale structures in this study some of these transient features have been compared with patterns in sea surface variability derived from collinear satellite altimetric data when these features occurred near the crossing point of two satellite ground traces it was possible to characterize their length scales dynamic height relief and translational and surface geostrophic velocities

sampling strategies and model assimilation of altimetric data for ocean monitoring and prediction numerical forecasts using simulated altimeter data are generated in order to examine the assimilation of altimeter derived sea surface heights into numerical ocean circulation models a one layer reduced gravity primitive equation circulation model of the gulf of mexico is utilized the gulf of mexico is chosen because of its amenability to modeling and the ability of low vertical mode models to reproduce many of the observed dynamical features of gulf circulation the simulated data are obtained by flying a hypothetical altimeter over the model ocean and sampling the model sea surface in a manner similar to a real altimeter the data are used to examine spatial sampling requirements for accurate resolution of oceanic eddies and in forecast mode the assimilation of asynoptic altimeter data into numerical models results indicate that for a stationary circular eddy approximately two tracks either ascending or descending across the eddy are sufficient to ensure adequate spatial resolution an irregularly shaped eddy may require three or four tracks in addition the study reveals that if the track spacing is sufficient to resolve the height field of an eddy the along track geostrophic velocity component is determined with equivalent accuracy to that of the cross track component simulated gulf of mexico circulation forecasts suggest that the numerical model can effectively assimilate asynoptic altimeter measurements optimum sampling strategies for a single beam altimeter and intermittent updating of the nowcast forecast are examined

the gulf stream front a comparison between seasat altimeter observations and theory in a recent paper by cheney and marsh 1981 seasat altimeter data were used to derive quantitative information on sea surface height anomalies across the gulf stream in another recent paper by kao 1980 the dynamics of the gulf stream front was investigated and a similarity solution was obtained the model gives a universal shape of the sea surface height rise and the width of that anomaly across the gulf stream in this paper we present a quantitative comparison between the model and six gulf stream altimeter profiles representing a broad range of conditions the remarkable closeness of fit is mutually reinforcing to both the model and to the role of satellite altimetry in ocean dynamics comparisons of the data with the well known theories of stommel 1966 and charney 1955 are also made and implications of these comparisons are explored

ocean mesoscale variability from repeat tracks of geos 3 altimeter data the geos 3 satellite altimeter observed numerous sea surface profiles along nearly repeated tracks in the western north atlantic during its 3 5 year lifetime enabling observation of the variation of sea surface topography along these tracks analysis of 14 north going and 13 south going sets of repeated tracks has yielded the variability of the surface at a resolution of 1 from 25 to 41 n latitude and from 60 to 80 w longitude the observed rms variation of surface topography ranges from about 8 cm in the sargasso sea to a maximum of 48 cm in the gulf stream meander region in agreement with known mesoscale energetics of this region

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

the confrontation of structural styles and the evolution of a foreland basin in central sw england detailed mapping of the rocks to the north and south of plymouth reveals a sedimentary sequence deformed by a series of folds and thrusts two structural zones exist each with a different style of deformation in the lower to upper devonian rocks of the southern zone slip vectors vergence and facing of d1 folds indicate that the transport direction is to the north west an associated first phase cleavage dips to the south east the northern zone of upper devonian and lower carboniferous strata extends into central devon and east cornwall and the geometry and facing of the early folds in these rocks indicate a transport direction to the south or south east d1 folds generally verge north but are downward facing towards the south a flat lying penetrative slaty cleavage occurs in the mudrocks and also indicates southward facing generally the carboniferous rocks in this area are inverted the two structural zones confront each other at an e w trending line which passes through cargreen 8 km north of plymouth here the deformation is more intense as the cleavage common to the southern zone overprints that of the northern zone resulting in the formation of d2 folds the confrontation is interpreted as a northerly dipping backthrust produced by large scale underthrusting it is proposed that the northward advancing variscan thrust belt progressively underthrust the carboniferous foreland basin flysch deposits which became inverted and backthrust towards the south

models of strain variation in nappes and thrust sheets a review abstract strain within nappes and thrust sheets can be modelled using simple boundary conditions an original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust deformation gradient tensors are determined for the models and solutions found for the principal strains a two dimensional model considers heterogeneous simple shear combined with a stretch in the direction of shear simple shear zones arise as a special case where 1 recumbent fold nappes characteristic of gravitational collapse can be modelled with 1 and thrust sheets with layer parallel shortening and folding with differential transport of nappes gives rise to additional wrench type shears solutions for the principal strains in this type of model are found and used to interpret side wall ramps and steep zones parallel to nappe movements by including a stretch in the transport direction these differential transport models produce prolate strains 1 and oblate strains finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history these predict possible crenulation of early thrust fabrics at ramps

life history of a cyclonic ring detached from the kuroshio extension as seen by the geosat altimeter the sea surface dynamic topography ssdt sea surface height relative to the geoid is approximately estimated by combining the temporal fluctuation of ssdt determined from altimetry data with the climatological mean ssdt calculated from hydrographic data this approximated ssdt or composite ssdt is obtained in the area southeast of japan for the first year 1986 1987 of the geosat exact repeat mission variations in the kuroshio current system are well described by the composite ssdt in particular a complete life history of a cyclonic ring is observed for the first time in this region namely westward propagation of a southward meander of the kuroshio extension its pinching off to form a cyclonic ring the ring s westward movement its coalescence with the kuroshio and its eastward advection all available hydrographic data and cloud free satellite infrared images support the existence of this series of phenomena

preliminary estimates of gulf stream characteristics from topex data and a precise gravimetric geoid topex sea surface height data has been used with a gravimetric geoid to calculate sea surface topography across the gulf stream this topography was initially computed for nine tracks seven descending and two ascending on cycles 21 to 29 due to inaccurate geoid undulations on one track results for eight tracks are reported in the paper the sea surface topography estimates were used to calculate parameters that describe gulf stream characteristics from two models of the gulf stream one model was based on a gaussian representation of the velocity while the other was a hyperbolic representation of velocity or the sea surface topography the parameters of the gaussian velocity model fit were a width parameter a maximum velocity value and the location of the maximum velocity the parameters of the hyperbolic sea surface topography model were the width the height jump position and the sea surface topography at the center of the stream both models were used for the eight tracks and nine cycles studied comparisons were made between the width parameters the maximum velocities and the height jumps for one track d04 near 36 n 73 w the average width parameter was 69 15 km based on the gaussian velocity fitting and 75 14 km based on the hyperbolic sea surface topography fit with a 10 km smoothing function along the same track the average maximum velocity was 164 30 cm s using the velocity fit and 163 37 cm s with the hyperbolic sea surface topography fit some of the parameter estimates were found to be highly 0 9 correlated when the hyperbolic sea surface topography fit was carried out but such correlations were reduced for either the gaussian velocity fits or the hyperbolic velocity model fit a comparison of the parameters derived from 1 year of topex data showed good agreement with values derived by kelly 1991 using 2 5 years of geosat data near 38 n 66 w longitude width 78 22 km this paper 82 25 km kelly height jump 115 28 cm 123 19 cm maximum velocity 171 59 cm s 1 179 46 cm s 1 the accuracy of the geoid undulations used in the calculations was of the order of 16 cm with the accuracy of a geoid undulation difference equal to 15 cm over a 100 km line in areas with good terrestrial data coverage the north edge of the gulf stream was studied with topex data from cycles 1 to 37 the north edge was located at the position corresponding to the half width of the gulf stream north of the center of the stream along each track with all parameters estimated from the gaussian velocity fit procedure the location of the north edge along one track generally agreed with the location defined by national oceanic and atmospheric administration national ocean survey noaa nos maps based on advanced very high resolution radiometer avhrr data and with a north wall location provided by cornillon at 2 day intervals the results for this topex track showed the north edge at the highest 37 8 n latitude in october november 1992 falling to the lowest 36 9 n latitude in february march 1993 after which the stream moves north a second track 550 km to the east of the first track showed consistent agreement with the cornillon data for the edge location when such data were available in one case with the noaa data there was a 77 km discrepancy between the topex and noaa estimates of the north edge analysis of the sea surface topography suggested the noaa avhrr location may be inaccurate at this one location and time this paper demonstrates that our knowledge of geoid undulations and undulation differences in a portion of the gulf stream region is sufficiently accurate to determine characteristics of the jet when used with topex altimeter data the method used here has not been shown to be more accurate than methods that average altimeter data to form a reference surface used in analysis to obtain the gulf stream characteristics however the results in the paper show the geoid approach may be used in areas where lack of current meandering reduces the accuracy of the average surface procedure

measurements of dynamic topography during synop utilizing a geosat synthetic geoid dynamic topography estimates were obtained for the gulf stream region employing a previously derived synthetic geoid and geosat radar altimeter measurements ascending tracks passed through the central and eastern arrays of the synoptic ocean prediction experiment by utilizing the geoid estimate instead of the mean altimetric signal the axis position and velocity can be computed a time series of the dynamic height profiles crossing the gulf stream and a table of the positions of the axis of the stream along two tracks are given time series of the maximum velocity perpendicular to the ground track were computed for both arrays it was found that there was a seasonal cycle in this time series with a maximum in november

variscan facies and structure in central sw england the character and distribution of middle devonian to upper carboniferous facies in central sw england is described these may be interpreted in terms of the simple model of a shelf extending from a continent to the north across most of sw england in earliest devonian times within it a major e w trending basin developed during the middle devonian possibly as a half graben structure with an active northern hinge on this shelf in mid and late devonian times argillite successions accumulated to the north and a carbonate complex on the now starved platform to the south of the basin in the early carboniferous basinal conditions extended northwards over the shelf but to the south at first flysch and then paralic sediments with a southern origin were ponded against the carbonate complex flysch penetrated through and across the platform into the intra shelf basin this flysch prograded northward to cover the whole area by early late carboniferous times the western part of the main basin suffered structural inversion in late visean times and semiconsolidated sediments spread northward across its margin the eastern extension of the basin was not deformed until the late namurian at which time successions were folded and disrupted into nappe structures showing northward transport the most far travelled nappes are represented at the highest structural levels the stratigraphy of the coastal section of n cornwall which has been used to devise a structural model involving a major autochthonous south facing overfold is reassessed the nappe structures and successions recognized inland are identified on the coast and the overfold model is disproved the whole of central sw england forms part of southerly derived thrust and nappe terrane

southern ocean mean monthly waves and surface winds for winter 1978 by seasat radar altimeter data acquired by the seasat radar altimeter during the 3 month satellite lifetime are analyzed in a study of the sea state of the southern hemisphere oceans the lifetime of the seasat satellite july 7 to october 10 1978 corresponds to the antarctic winter mean monthly maps of wind speed significant wave height and swell have been generated from the altimeter measurements along the satellite tracks these maps delineate spatial and temporal differences of these parameters in the atlantic indian and pacific oceans several features of the southern ocean wind and wave fields agree with conventional descriptions for example the principle zonal wind regimes established by the southeast trades and westerlies are clearly evident in the monthly averages significant wave height and swell also exhibit minima near the doldrums at low latitudes with steady increases southward to the latitudes of the westerlies however superimposed on these general patterns is significant variability with horizontal scales as small as 1000 km the maps also document a gradual migration of the region of absolute maximum wind and wave from the atlantic eastward to the indian ocean and finally into the pacific

variscan very low grade metamorphism in southwest england a diastathermal and thrust related origin abstract regional metamorphism in the external variscides of southwest england varied from diagenetic level to greenschist facies there is a fundamental difference in the metamorphic character between the northern and southern regions of the area in the north m1 metamorphism is of a sedimentary burial character associated with high heat flow whilst to the south it is related to tectonic burial during thrust thickening processes with lower geothermal gradients this pattern appears to be related to the character of basin development and its subsequent tectonic evolution the northern region has features that accord with a diastathermal extensional origin for the very low grade metamorphism whilst in the southern region the very low grade metamorphism is linked to thrusting as a consequence of variscan compression the tintagel high strain zone presents an anomaly in this regional pattern where an m2 metamorphic phase is attributed to localized d2 thrust stacking along the southern margin of the culm basin there is no extensive overprint of the regional metamorphic pattern by the contact aureoles surrounding the granite plutons of the region however there is a noticeable coincidence between the areas of regional epizone grade and the extent of the geophysically defined subsurface limit of the granite batholith excluding the north devon area this link is attributed largely to the late stage structural up doming of the higher grade areas over the roof of the batholith

seasat altimeter height calibration the seasat altimeter has been calibrated for height bias using four overflight passes of bermuda that were supported by the bermuda laser the altimeter data was corrected for tides by using recorded tide gage data for propagation effects by using meteorological data taken around the time of each pass for acceleration lag and for sea state bias including both surface effects and instrumental effects altimeter data for each of the four passes was smoothed and extrapolated across the island interpolation between passes then produced an equivalent altimeter measurement to the geoid at the laser site so that the altimeter bias could be estimated without the use of a geoid model the estimated height bias was 0 0 0 07 m

the padstow confrontation north cornwall a reappraisal the gravel caverns section new polzeath north cornwall shows clear evidence of multiphase deformation tight f1 folds with axial planar s1 slaty cleavage are reported for the first time these are deformed by north verging f2 folds with a south dipping spaced cleavage the fold and fabric relationships are inconsistent with the widely accepted model of structural confrontation previously described for the region this model is reassessed

upper carboniferous fine grained turbiditic sandstones from southwest england a model for growth in an ancient delta fed subsea fan abstract the upper carboniferous crackington and bude formations of southwest england comprise laminated black mudstones gray siltstones thin medium and thick bedded sandstones and contorted silty sandstones the thick bedded sandstones only occur in the bude formation which overlies the crackington the sandstones were deposited predominantly by turbidity currents in a relatively shallow basin they are unusual for two reasons 1 sediment coarser than fine sand is entirely absent 2 unlike many previously described ancient subsea fan deposits organized bundles of sandstones displaying asymmetric upward thickening or upward thinning sequences are no more common than symmetric sequences and both types of organized bundles are much less common than disorganized nonsequential bundle particularly in the bude formation sediment was supplied directly from a delta to the north by resedimentation of delta front sands and slumping of upper pro delta muds and silts to form a lower pro delta turbidite fan fan growth is not readily explained by current models for single sourced tripartite subsea fans displaying radial growth it developed instead a bipartite growth pattern which was strongly influenced in its upper part by external variables including grain size distributary channel switching and other deltaic processes active tectonism within the basin and possibly sea level fluctuations the fan grew by down slope construction of independent levee channel complexes each of which headed in the upper pro delta and even possibly the delta front slumping and mobilization of argillaceous facies resulted in the random occurrence of contorted beds in all parts of the fan regionally extensive mudstones known as key shales within the fan deposits probably reflect large scal upslope delta lobe abandonment the crati and ebro fans of the mediterranean sea would appear to be good modern analogs for the crackington bude fan system

late carboniferous tectonic subsidence in south wales implications for variscan basin evolution and tectonic history in sw britain detailed stratigraphic data have been used to backstrip seven sections from the carboniferous south wales coal basin resulting tectonic subsidence curves for the interval 319 305 ma namurian westphalian d are convex up indicating increasing subsidence rate with time with rates between 130 and 250 m ma 1 suggesting a foreland basin setting forward modelling of subsidence due to flexural loading in front of a propagating orogenic wedge shows that an orogenic load migrating in a north northeasterly direction across sw england between 319 and 305 ma could have generated the backstripped subsidence patterns sensitivity tests show that while many of the forward model parameters are poorly constrained and the model results non unique backstripped subsidence patterns allow reasonable constraint on the different model cases so that model predictions can be treated as one possibility in a limited range the predicted load evolution is consistent with current knowledge of tectonic and stratigraphic features of sw england these results suggest that subsidence in other late carboniferous uk basins may also have been influenced by flexure due to a propagating orogenic load

altimetry ship gravimetry and the general circulation of the north atlantic gravity accelerations estimated from satellite altimetric mean sea surfaces seasat and geos 3 are compared to ship gravity measurements ship gravity are closer to an estimate based on least squares collocation orbit perturbations altimetry and terrestrial gravity than to an estimate based on fourier transforms orbit perturbations and altimetry only both altimetric estimates yield a smoothed picture of the geostrophic component of sea surface currents in the north atlantic when gravity acceleration data from only nine cruises are subtracted from the altimetric gravity

on determining the large scale ocean circulation from satellite altimetry to determine the surface geostrophic currents which are proportional to the slope of the dynamic topography from satellite altimetry one needs an accurate and independent estimate of the geoid currently these estimates are given in terms of spherical harmonics while the high degree terms short wavelengths are either uncertain or completely unknown the low degree terms long wavelengths are reasonably accurate furthermore in terms of spherical harmonics most of the dynamic topography s power is contained in the low degree terms if the dynamic topography is treated as the signal and the geoid uncertainty as the noise the signal to noise ratio is the highest for these low degree terms therefore a spherical harmonic expansion of the difference between the altimeter derived mean sea surface and the geoid estimate should reveal the large scale circulation of the ocean surface layer when one examines the low degree terms methods based on this principle are proposed and partially demonstrated over the pacific ocean using the mean sea surface derived from the seasat altimeter and the goddard earth model 9 earth gravity model the preliminary results show a well defined clockwise gyre in the north pacific and a much less well defined counterclockwise gyre in the south pacific when the dynamic topography so obtained is compared to wyrtki s 1975 dynamic topography derived from hydrographic data the agreement is within the limit of geoid uncertainties and satellite orbital errors to fully determine the three dimensional ocean circulation one still needs hydrography the three dimensional density distribution of the ocean a method is presented for the determination of the ocean circulation and the improvement of the geoid in the combined problem of geodesy hydrography and satellite altimetry

3d mechanical stratigraphy of a deformed multi layer linking sedimentary architecture and strain partitioning abstract stratigraphic influence on structural style and strain distribution in deformed sedimentary sequences is well established in models of 2d mechanical stratigraphy in this study we attempt to refine existing models of stratigraphic structure interaction by examining outcrop scale 3d variations in sedimentary architecture and the effects on subsequent deformation at monkstone point pembrokeshire sw wales digital mapping and virtual scanline data from a high resolution virtual outcrop have been combined with field observations sedimentary logs and thin section analysis results show that significant variation in strain partitioning is controlled by changes at a scale of tens of metres in sedimentary architecture within upper carboniferous fluvio deltaic deposits coupled vs uncoupled deformation of the sequence is defined by the composition and lateral continuity of mechanical units and unit interfaces where the sedimentary sequence is characterized by gradational changes in composition and grain size we find that deformation structures are best characterized by patterns of distributed strain in contrast distinct compositional changes vertically and in laterally equivalent deposits results in highly partitioned deformation and strain the mechanical stratigraphy of the study area is inherently 3d in nature due to lateral and vertical compositional variability consideration should be given to 3d variations in mechanical stratigraphy such as those outlined here when predicting subsurface deformation in multi layers

the branching of the gulf stream southeast of the grand banks during march april 1987 101 hydrographic stations were occupied on three sections spanning a triangle between the azores faial the southern tip of the grand banks of newfoundland and bermuda information on the near surface processes in the interior of the triangle were obtained from 32 satellite tracked buoys deployed during the cruise and a composite infrared image based on cloud free noaa 9 data during april 1987 the data were combined to analyze the eddy field and the branching of the gulf stream into the north atlantic current and the azores current calculations of mass transports through the legs of the triangle gave a total of 46 sv supplied by the gulf stream 31 sv of which left the area as the north atlantic current and westwind drift north of the azores the remaining 14 sv continued towards east southeast as the azores current and southern recirculation additional conductivity temperature depth stations from a cruise in april 1986 into the same area allowed also study of the large scale circulation within that triangle in deeper layers the azores current appears as a baroclinic stream which reaches down to approximately 1000 m intensive mixing was observed at the continental slope of newfoundland between water of the labrador current and the gulf stream mixed water owing to cabbeling and consecutive convective mixing this water penetrates down to 2000 m depth and creates horizontal density gradients to the surrounding gulf stream water which intensifies the north atlantic current this process is considered to be an important energy source for this current

the geoid edin2000 and mean sea surface topography around the british isles summary this paper describes a new rationale for computing a gravimetric geoid and reports that the resulting geoid model edin2000 is now good enough to resolve previously contradictory estimates for mean sea surface topography msst around great britain for at least 30 yr it has been known that msst derived from tide gauges levelling and oceanography were mutually inconsistent and differed by an order of magnitude when combined with an altimetric mean sea surface edin2000 is also able to map realistic msst over the northwest european shelf and identify and quantify mean currents flowing in the deep ocean parallel to the shelf edge when compared with 11 gps referenced tide gauges on the british mainland our estimate of msst has a standard deviation of only 0 03 m and its variation with latitude is not significantly different from zero for these sites long distance levelling errors are larger than geoid errors we identify a systematic jump by 0 24 0 05 m in the levelled transfer of ordnance datum newlyn affecting all sites in great britain to the north of latitude 53 n even after this correction the variability of levelling remains larger than that of the geoid and gps implying a more complex structure to the levelling error than a simple step away from coasts we find that the best way to validate marine gravity data is their ability to predict msst with low local variability when combined with altimetric mean sea level there is a large reduction in msst variability when marine gravity data are subjected to an anti aliased adjustment of the mismatch where ship tracks cross we also report two msst model comparisons from a shelf seas and a deep ocean model both of high resolution there is quantitative and qualitative agreement between our geoid derived msst and the model predictions indicating significant improvements compared with earlier geoid models we also show that with the improved accuracy of geoid based msst it will become necessary to validate models and observations at matching epochs

the evolution of the hercynides of central sw england towards the end of lower carboniferous times sedimentation accompanied by widespread igneous activity proceeded in a tectonically active unstable and constricted basinal zone visean flysch and olistostromic sequences were generated in front of an advancing deformation front which caused erosion of submarine rises and heralded the beginning of the hercynian orogeny in this region between dartmoor and bodmin moor upper devonian basin and rise facies sediments were thrust northwards over both upper devonian and lower carboniferous northern equivalents which were themselves incorporated onto the allochthon the tectonic deformation history began in the late visean and early namurian with the gravity sliding dl of the bulk of the lower carboniferous northwards to form the greystone nappe subsequently the main thrusting event d2 from late lower namurian times onwards led to the successive overthrusting and emplacement of the heathfield petherwin and tredorn nappes towards the end of the namurian and in the westphalian the intrusion of the granite batholith caused the fold belt to tighten which resulted in the formation of numerous low angle normal faults d3 offsetting earlier thrusts to the n overall the regime is one of very thin skinned thrust and nappe tectonics with the allochthon probably not exceeding 1 km in thickness

palaeostress and strain estimates from boudinage structure and their bearing on the evolution of a major variscan fold thrust complex in southwest england abstract this paper develops a mesoscopic approach to palaeostress estimation based on applying a new fibre loading type theory to boudinage structure the theory implies that if boudinage develops by a sequential fracture and separation process the distribution of boudin aspect ratios should be controlled by a critical ratio below which the tensile stress cannot exceed the tensile fracture strength of the boudinaged layer simulations based on distributions of tensile fracture strength and elastic moduli derived from published experimental work allow a distribution of boudin aspect ratios to be predicted this compares very favourably with the observed aspect ratio distribution of quartzite boudins within lower carboniferous slates at the southern margin of the culm synclinorium southwest england hence the new theory can be used to derive an estimate of the elastically supported differential stress in the slates at the time of boudinage development an associated palaeostrain analysis is also performed using a new strain reversal method the boudinage occurs just below the base of a major fold thrust complex essentially a large overfold of namurian and westphalian rocks emplaced at the end of the carboniferous over devonian and lower carboniferous slates with thin quartzites and limestones we interpret the boudinage in the quartzite layers as a gravitational spreading response to the superincumbent overfold the thin limestones however show no competence contrast with the surrounding slates and we have therefore used a limestone flow law to estimate the rate of vertical shortening beneath the overfold using our boudinage strain value we then estimate that the overfold took between 0 75 and 1 5 ma to evolve probably during the stephanian