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

brunt vaisala frequency and rossby radii in the south atlantic abstract brunt vaisala frequency profiles have been calculated in the south atlantic and neighboring regions on a 5 5 grid between 30 n and 70 s 70 w and 70 e using the annual mean temperature and salinity profiles computed by levitus from data available from the national oceanographic data center nodc these brunt vaisala frequency profiles are used in the computation of the first and second internal rossby deformation radii the external rossby radius is computed for reference these results compare very well with those of emery et at for the equatorial atlantic very small values of the radii are evidenced in the extreme south less than 10 km in the antarctic circumpolar current for the first internal mode high vertical variability in brunt vaisala frequency profiles is also observed at the center of the subtropical gyre this behavior is probably due to the lack of deep data in this region

tertiary uplift and inversion history in the north celtic sea basin and its influence on source rock maturity abstract tertiary uplift and basin inversion have been widely recognized in the area of the north celtic sea basin offshore ireland but the magnitude and timing of the various events have not been well documented an understanding of these events is important because recent basin history generally has a major influence on hydrocarbon source rock maturity levels a multi disciplinary approach was used to investigate the timing and nature of uplift in the north celtic sea basin involving seismic data interpretation well log correlation vitrinite reflectance measurement apatite fission track analysis and a cretaceous chalk group isopach and velocity study both regional uplift and compressive inversion can be interpreted to have occurred based on missing geological section compressive reactivation of earlier normal faults and basin centred uplift two tertiary erosion events are recognized a regional uplift in the palaeocene and compressive inversion characterized by basin doming and fault reversal probably associated with an oligo miocene phase of the alpine orogeny separating these was a period of basinal deposition in the eocene to oligocene a map of the magnitude of erosion generated as a result of the two events shows that the amount of uplift is quite variable in the northeast part of the basin where the later event was most severe uplift was as much as 1100 m reconstruction of the basin geometry before inversion together with thermal modelling at selected well locations suggests that upper jurassic source rocks reached maturity for oil generation only in the central portion of the basin whereas lower jurassic source rocks entered the gas window in much of the basin prior to tertiary uplift

the post variscan thermal and denudational history of ireland the thermal and denudational history of ireland is evaluated using an extensive new apatite fission track aft dataset derived from surface samples modelled thermal histories are used to construct maps of denudation for a number of time slices from triassic time to 10 ma using a time dependent palaeogeotherm the maps illustrate the spatial variability of denudation and subsidence within each time slice the patterns of denudation are complex showing considerable variability at the length scale of 101 102 km with especially high denudation rates found over known igneous centres such as the mournes of county down based on the onshore aft data alone there is no definitive signature of an irish sea dome extending significantly across ireland in early tertiary time the cumulative amount of denudation during tertiary time varies depending on the aft annealing model used but is generally in the region between 1 and 2 km and without clear spatial trends high amounts of denudation have been mapped over the tertiary intrusions in county down reflecting their unroofing since emplacement in paleocene time the cumulative denudation from triassic time to 10 ma shows relatively low amounts of denudation 2 km in the irish midlands and the extreme ne of the island consistent with the observation that mesozoic tertiary sediments and igneous products are preserved in the ulster basin the western flank of ireland and the region between dublin and county down show high cumulative amounts of denudation 4 km the latter being consistent with the high amounts of denudation interpreted for the irish sea region this denudation pattern explains in part the outcrop of precambrian and lower palaeozoic rocks in these areas the spatial integration of the denudation over the entire landmass gives the average denudation rate and the sediment discharge from ireland as a function of time average denudation rates are moderately high in triassic time falling to low values in cretaceous time and increasing substantially in tertiary time however the total volumetric discharge of sediment in tertiary time is an order of magnitude smaller than the preserved solid volume of tertiary sediment in the basins offshore western ireland

evidence for cenozoic tectonic deformation in se ireland and near offshore 1 an integrated study of topography bathymetry high resolution aeromagnetic data and structural observations demonstrates significant cenozoic fault activity in se ireland tectonically generated knickpoints and reddened fault breccias along topographic escarpments that are underlain by greywacke bedrock and trend oblique to the regional caledonian strike provide evidence for fault displacement near offshore faults with similar geometry produce present day bathymetric scarps and localized tectonic topography in the inverted kish bank basin the integration of offshore high resolution aeromagnetic data and structural interpretation of the kish bank basin provides evidence for dextral transtension on nnw trending faults and sinistral transpression on ene trending faults bounding a lower paleozoic to carboniferous basement block these faults correlate onshore with previously recognized caledonian faults producing topographic offsets and surface uplift to the north offshore structures can be traced onshore and cut exposures of the caledonian leinster granite structural analysis of these outcrops indicates post variscan deformation a major fault on the nw margin of the batholith cuts a major erosion surface developed on carboniferous carbonate rocks and nonmarine miocene deposits are preserved above this surface fault kinematics provide evidence of two paleostress systems 1 nw se 1 subvertical 2 and ne sw 3 followed by 2 a clockwise swing of 1 to nnw sse timing of deformation in both stress systems is probably post oligocene age the mechanism driving this deformation is likely ridge push much is already known about cenozoic tectonics and exhumation from offshore basins this study shows that onshore ireland has also been affected by significant tectonic activity and exhumation during the cenozoic

mapping climatological seasonal variations of surface currents in the tropical atlantic using ship drifts the seasonal variability of current velocities in the tropical atlantic was studied by grouping ship drift velocity observations into 2 5 boxes and calculating monthly mean velocity values these values were used to calculate and map the annual mean velocity the seasonal variation about the mean the annual and semiannual harmonics and the first two empirical orthogonal functions eofs the seasonal variation is primarily zonal in the equatorial band and in the north equatorial countercurrent necc and primarily alongshore near the coast of south america maxima of seasonal variation of 23 cm s are centered in the necc near 6 n 42 5 w and in the gulf of guinea near 2 n 7 5 w most 80 of the variance in the necc and along the western boundary of the area studied has an annual period most of the variance along the equator in the mid atlantic has a semiannual period over the whole region 49 of the seasonal variance is explained by the annual harmonic and 69 is explained by a combination of the annual and semiannual harmonics the second eof contains 29 of the variance of the data set and shows a simultaneous speeding slowing of the major equatorial currents the south equatorial current sec the north brazil current the necc and the guinea current along their principal axes of variation with a concurrent slowing speeding of the guyana current and the brazil current the pattern of variation resembles a large equatorial gyre centered along 4 n that flows clockwise from may to september and counterclockwise most of the rest of the year the first eof accounts for 35 of the variance and shows a simultaneous speeding slowing of eastward velocity from 5 s to 10 n except in the western sec the western end of the north brazil current and the guinea current the out of phase fluctuations apparent in the western sec near the equator are explained by the slowing and reversal of the south equatorial current near 2 n 40 w between april and june this slowing of the sec is associated with the start up of the necc which accelerates eastward in may june and july and flows eastward across the atlantic from july through december the sec divides seasonally near the eastern tip of brazil where residual alongshore velocities are northward for half the year peaking during may and june and southward for the other half of the year a second division can be seen north of the amazon where the north brazil current continues up the coast into the guyana current during the first half of the year but partially retroflects into the necc during the last half of the year a fast eastward flow in the necc coincides with below average velocities in the guyana current and above average velocities in the western sections of the north brazil current and the sec north of the equator

quantification of tertiary erosion in the inner moray firth using sonic velocity data from the chalk and the kimmeridge clay abstract sonic velocities for the chalk and kimmeridge clay were analysed to determine the importance and magnitude of tertiary erosion for 26 wells in the inner moray firth apparent erosion height above maximum burial depth was derived by the displacement along the depth axis of a given velocity depth trend from the normal undisturbed trend the similarity in apparent erosion results derived from the cretaceous chalk and late jurassic kimmeridge clay successions of the inner moray firth suggests that burial beyond present depths caused the observed overcompaction rather than any sedimentological and or diagenetic process resultant apparent erosion estimates are variable across the inner moray firth such values reach approximately 1 km in the western part of the basin and decrease progressively to zero in the eastern inner moray firth however the actual magnitude of erosion equal to the sum of apparent erosion and post erosional tertiary burial was approximately 1 km throughout the whole inner moray firth area indicating that early tertiary erosion was regional and not simply restricted to the inverted basin margins however a well defined mechanism sufficient to have generated the regional event is still sought

isotopic evidence for the age and origin of pitchstones and felsites isle of eigg nw scotland an 8 point whole rock and mineral rb sr isochron for the sgurr of eigg yields an age of 52 1 1 0 ma 2 this is the youngest accurate date yet reported for igneous activity in the british tertiary province and indicates that sub acid rocks of the small isles represent one of the latest episodes of hebridean magmatism pb isotope compositions of these rocks yield an apparent age of 2660 75 ma 2 interpreted as a mixing line between lewisian torridonian and mantle derived pb and indicating the presence of lewisian basement under eigg pb sr and nd isotopic evidence points to contamination of basaltic differentiates and granulite facies lewisian melts by torridonian sandstone but precludes significant involvement of amphibolite facies lewisian which may have been largely removed by erosion before deposition of the torridonian sediments in the small isles

seasonal variability from a model of the tropical atlantic ocean abstract a numerical model incorporating a single baroclinic mode and realistic coastline geometry is used to analyze the linear dynamic response to estimates of the seasonal wind field over the tropical atlantic ocean the forced periodic response consists of a spatially dependent combination of a locally forced response kelvin waves rossby waves and multiple wave reflections the seasonal displacements of the model pycnocline are compared with observed dynamic height annual and semiannual fluctuations dominate the seasonal signal throughout the basin in general the distribution of amplitude and phase are similar for annual changes in dynamic height and pycnocline depth major features of the seasonal response are reproduced e g east west changes in pycnocline depth about a nodal point at the equator the seasonal pycnocline movement along the northern and southern coast of the guinea gulf and a significant changes of phase in the ocean variability north and south of the itcz the relative impo

the seasat altimeter data and its accuracy assessment the seasat satellite launched on june 27 1978 carried a radar altimeter designed to measure the altitude of the satellite above the ocean surface the surface wave height and the ocean surface backscatter coefficient from which wind speed can be inferred postlaunch engineering assessment indicated that the seasat altimeter met the performance specification for 10 cm precision noise in the altitude measurements however to determine the accuracy of this measurement as well as the accuracy of the wave height and wind speed measurements a significant calibration validation and model development effort was required this summary describes the instrument atmospheric and geophysical effects which influence the radar altimeter measurement accuracies and the attendant correction models adopted for the altimeter geophysical data record also summarized are the activities of the seasat altimeter precision orbit determination experiment team directed towards the validation and improvement of these models as well as the investigations required to assess the accuracy of the altimeter measurement and the computed satellite altitude ephemeris finally an accuracy assessment is made for the various altimeter measurement corrections which are included on the altimeter geophysical data record

seasonal response of the sea surface to the wind in the equatorial atlantic from february 1983 through september 1984 18 inverted echo sounder deployments yielded time series from 10 locations as part of the seasonal response of the equatorial atlantic sequal program using historical and in situ data the sounders travel time data are interpreted as dynamic height 0 relative to 500 dbar and then related to representations of the synoptic wind field the seasonal variations of the zonal pressure gradient along the equator and the height of the dynamic ridge along 3 n relative to the equator and 9 n are described the pressure gradient between 10 w and 34 w has a minimum each april and a maximum each july its value ranges between 1 4 not significantly different from zero and 8 3 10 5 dyn g 1 during the observational period the zonal pressure gradient is correlated with zonal wind stress from an in situ wind sensor at midfetch and a 10 day lag time is indicated the north equatorial countercurrent trough attains a maximum in the late boreal summer and fall and a minimum in the spring it ranges from 39 to 8 dyn cm deep at 38 5 w and from 18 to 1 dyn cm at 28 w a two layer model calculation using monthly mean winds derived by servain et al 1986 for the appropriate time period generally reproduces the observed seasonal variation along the two meridians and the large zonal variation between them tracking the individual terms month by month illustrates the rate of the sverdrup adjustment to the local wind stress with surface elevation rising as fast as 10 cm per month

eddy energy of the northwest atlantic and gulf of mexico determined from geos 3 altimetry from may 1975 to october 1978 the geos 3 satellite altimeter made numerous repeated observations of sea surface topography in the northwest atlantic and gulf of mexico by comparing members of about 1000 collinear pairs of altimeter profiles we have determined mesoscale sea height variability and eddy kinetic energy in these ocean regions our results agree qualitatively with estimates made from traditional oceanographic surveys but significant quantitative differences exist in certain areas especially in the gulf stream between florida and cape hatteras where the altimetric results show less variability the reason for this appears to be due to differences in spatial sampling historical oceanographic measurements are relatively sparse and must be aggregrated into small geographic boxes to compute variability statistics results therefore represent a combination of temporal and spatial variability in contrast repeated satellite altimeter tracks provide point measurements of changes of sea height and slope this enables determination of temporal variability alone a quantity more representative of eddy energy it is important to make this distinction between space and time because in regions of strong horizontal gradient such as the gulf stream spatial variability can exceed the temporal component in mid ocean where spatial variability is negligible altimetric and oceanographic results are in excellent agreement

three dimensional gravity and magnetic modelling of the irish sector of the ne atlantic margin abstract a new 3d lithospheric model has been constructed using high resolution gravity data from the irish national seabed survey the sedimentary component of the model incorporated density variations due to laterally varying overcompaction associated with cenozoic denudation after optimisation based on gravity inversion regional crustal thickness variations were defined which are in reasonable agreement with the results of wide angle seismic experiments high crustal extension factors 5 characterise the deeper parts of the rockall and porcupine basins and in places the model indicates extreme stretching 10 beneath these basins this could be because of instability in the gravity inversion although other recent investigations have independently suggested similarly high extension factors in contrast the hatton basin is characterised by an apparent extension factor of about 2 the modelling resolves a pattern of ne to nne trending local mesozoic basins on the margins of the rockall trough helping to delineate structures that were previously only sparsely sampled by seismic surveys it appears possible that rifts with similar trends underlie the volcanic rocks which obscure the deeper parts of the hatton basin the linear trends of the basins to the south and east of ireland are interpreted to have been inherited from a basement fabric that was initially established during the late precambrian assembly of this basement and subsequently subjected to caledonian and variscan reactivation magnetic modelling indicates that the variations in the thickness of the crystalline crust predicted by the gravity models can explain the regional magnetic anomaly patterns over the rockall and porcupine basins but that significant additional magnetic material probably igneous rocks of both palaeogene and cretaceous ages is required to explain the anomalies in the hatton basin region the magnetic signature of the rockall basin is distinctly different to that over the basement of similar apparent thickness formed during mid cretaceous c34n opening of the ocean basin to the south this is an impediment to hypotheses that invoke mid cretaceous sea floor spreading rather than intracontinental rifting to explain the development of the basin the exception is in the extreme south of the basin where the volcanism associated with the barra volcanic ridges combined with indications of relatively strong lithosphere could be evidence of incipient ocean opening

observing large scale temporal variability of ocean currents by satellite altimetry with application to the antarctic circumpolar current a new method is developed for studying large scale temporal variability of ocean currents from satellite altimetric sea level measurements at intersections crossovers of ascending and descending orbit ground tracks using this method sea level time series can be constructed from crossover sea level differences in small sample areas where altimetric crossovers are clustered the method is applied to seasat altimeter data to study the temporal evolution of the antarctic circumpolar current acc over the 3 month seasat mission july october 1978 the results reveal a generally eastward acceleration of the acc around the southern ocean with meridional disturbances which appear to be associated with bottom topographic features this is the first direct observational evidence for large scale coherence in the temporal variability of the acc it demonstrates the great potential of satellite altimetry for synoptic observation of temporal variability of the world ocean circulation

sea level time series in the equatorial pacific from satellite altimetry geosat a navy satellite launched in march 1985 will provide the first long term global altimeter data set these observations will enable construction of monthly sea level maps of the equatorial pacific much like those presently derived from island tide gauges but with greatly improved spatial resolution and coverage during the first half of the geosat mission the satellite ground track will not repeat requiring time series analyses to be based on altimetric height differences at crossover points we have used the 3 month seasat data set in the equatorial pacific to test the feasibility and accuracy of this procedure crossover differences were sorted into diamond shaped areas with zonal and meridional dimensions of 200 and 400 km respectively the sea level time series in each of these areas was then determined using objective analysis these computations show agreement within 5 cm between altimeter and island tide gauge observations on time scales greater than 1 month using this technique we propose to construct monthly maps of sea level variability in the equatorial pacific for the duration of the geosat mission approximately 3 years

the tertiary lavas and sediments of northwest rhum inner hebrides several small outliers of tertiary lavas and sediments rest with strong unconformity on a buried landscape eroded from torridonian sediments and tertiary granophyre erosion continued during the period of sediment and lava accumulation four formations are recognized these are in order of increasing age the orval formation hawaiite and basaltic hawaiite lavas the guirdil formation icelandite lavas interbedded conglomerates the upper fionchra formation tholeiitic basaltic andesite lavas hyaloclastite deposits basal conglomerate and the lower fionchra formation alkali and transitional basalt basaltic hawaiite and hawaiite lava flows basal conglomerate each is separated by an erosional interval clasts in the conglomerates reveal a history of erosion of a terrain exposing gneisses torridonian sediments igneous rocks derived from the rhum tertiary central complex including allivalites and tertiary lavas of local origin but also including in the oldest conglomerates tholeiitic basalts not now preserved on or near rhum prior to and during lava and sediment accumulation erosion on rhum had cut down to a level similar to that of the present day although not to the extent that high grade thermally altered rocks which are a marked feature of the central complex were being eroded in any quantity a sequence of east west trending valleys possibly initiated on the line of the earlier main ring fault drained the area of the central complex which then as now must have been high ground small lakes occasionally formed in the valleys allowing the accumulation of fine grained sediment with plant remains and promoting the formation of hyaloclastite deposits when buried by later flows no source for any of the lava formations is preserved on rhum they are thought to have come from feeders north of rhum possibly near canna and to have ponded against the hills and valleys near and in the central complex the oldest tholeiitic lavas not now found in situ were followed by alkali and transitional flows compositionally similar to the skye main lava series but characteristically feldsparphyric the most mafic also contain phenocrysts of magnesian olivine with included cr al rich spinels and aluminous spinel both the early alkalic transitional basalts and the youngest hawaiites and basaltic hawaiites equilibrated at pressures apart from a few n s to nw se trending basalt dykes the lava formations represent the youngest tertiary igneous event on rhum

poorly crystalline components in aggregates from soils under different land use and parent material abstract fe and al compounds of low degree of crystallinity are important components for the development and conservation of soil structure in many soils in this work the influence of parent material and land use on the abundance of poorly crystalline forms of fe and al was studied in six macroaggregate fractions from 28 soils the soils selected are developed on two geological materials with very different composition granites or amphibolites and under two land uses shrubland or agricultural poorly crystalline fe and al were extracted with oxalic acid ammonium oxalate inorganic and organic forms and with pyrophosphate organic forms soils developed on amphibolite were richer in organic matter and poorly crystalline fe and al compounds than soils developed on granite agricultural soils were impoverished in organic carbon and organic complexed al with respect to shrubland soils and enriched in inorganic poorly crystalline forms of fe the differences related to land use were more evident in the amphibolite soils aggregate stability assessed by water dispersible clay quantification decreased in agricultural soils with respect to shrubland soils in particular for those developed on amphibolite this reduction of aggregate stability in agricultural soils is likely due to a combination of several processes loss of organic matter higher ph and an overall loss of poorly crystalline fe and al compounds in particular al organic matter complexes

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

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

observing the seasonal variability in the tropical atlantic from altimetry the tropical atlantic circulation is dominated by a strong wind driven seasonal cycle which is here described by means of the sea level heights measured by geos 3 and seasat altimeters seasat worked for just 3 months and geos 3 yielded an inhomogeneous space time coverage during its 3 5 years of operation to remedy this coverage shortfall all geos 3 and seasat data were merged together on a monthly basis without regard to year thereby ignoring the weak interannual perturbations of the tropical atlantic in this way a complete time series was produced for 1 year along each profile altirnetric heights were referenced to a global mean sea surface and then filtered to remove high and low frequency noise the residual heights were objectively analyzed to produce monthly maps of sea level anomaly between 10 s and 20 n these maps show a large annual signal in the western side of the basin between the equator and 10 n where the north equatorial countercurrent and south equatorial current are predominant the signal has an amplitude of 8 cm from a minimum in april may to a maximum in october november in the east the signal is weaker and depicts a semiannual cycle these results have been compared to similar maps obtained from historical hydrographic data merle and arnault 1985 the two sets of maps are in good agreement especially north of the equator where the largest seasonal variability occurs the major difference comes from underestimation of the altimetric signal amplitude due to the strong filtering and uneven distribution of the data

p and s wave velocities of consolidated sediments from a seafloor seismic survey in the north celtic sea basin offshore ireland a geophysical survey was conducted over a hydrocarbon prospect in the north celtic sea basin using a small array of ocean bottom seismographs obss the purpose of this study was to determine the ratio of p compressional to s shear wave velocity of consolidated sedimentary rocks in order to constrain possible subsurface variations in pore fluid content the ratio of vp and vs is known to be particularly sensitive to lithology porosity and pore fluid content making it a useful parameter for evaluating hydrocarbon prospects obss offer a relatively cheap and time effective means of acquiring multi component data compared with ocean bottom cables in this contribution we demonstrate the ability of an obs survey comprising three pairs of two obss spaced at 1 6 km to recover lateral variations in the vp vs ratio a key requirement of this type of study is that s waves will be generated by mode conversions in the subsurface since they cannot be generated in nor travel through fluids in this survey the contrast in physical properties of the hard seabed of the north celtic sea basin provided a means of generating converted s waves two dimensional ray tracing and forward modeling was used to create both vp and vs models along a profile crossing the blackrock prospect in the north celtic sea basin these models comprise four layers and extend to a maximum depth of 1 1 km the observed northward decrease in the vp vs ratio at depths of 500 1000 m below the seafloor in the study area is interpreted to represent lateral variation in the amount of gas present in the pore space of upper cretaceous chalks and shales overlying the prospective reservoir

in situ wind measurements and the ocean response in the equatorial atlantic during the programme francais ocean et climat dans l atlantique equatorial and seasonal response of the atlantic ocean experiment in situ wind measurements collected as part of the programme francais ocean et climat dans l atlantique equatorial focal seasonal response of the equatorial atlantic sequal experiment 1983 1984 in the western and eastern parts of the equatorial atlantic basin are described they were obtained from meteorological stations placed saint peter peter and saint paul rocks spp 1 n 29 w and at the top of a surface buoy moored in the gulf of guinea 0 n 4 w from the wind observations the wind stress was inferred and results are compared with climatology the wind stress time series show the abrupt increase of the winds during the spring that at spp reaches a value as high as 0 35 dyn cm2 in 2 weeks for both observed years the 11 day running mean time series shows that the onset of the zonal component of the wind stress occurs at spp on april 10 1983 and on may 17 1984 and in the gulf of guinea gg on april 5 1983 and april 10 1984 the monthly mean observations show an interannual variability both in the time of the onset and in the strength of the trade winds at spp and gg the total wind stress increases 1 month earlier than climatology in 1983 but at the same time as climatology in 1984 at spp the zonal component of the wind stress also intensifies 1 month earlier than climatology in 1983 but 1 month later in 1984 the equatorial temperature records at 28 w and 4 w show that the depth of the 20 c isotherm on a seasonal time scale decreases during the relaxation period of the trade winds boreal winter in 1983 1984 this occurred in december 1983 at 28 w and in march 1984 at 4 w after the onset of the local trade winds the thermocline continues to move upward during 1 month at 28 w and during 3 months at 4 w thereafter the thermocline deepens at both locations at the surface the temperature decreases when the trade winds intensify and remains low as long as the trade winds are blowing the seasonal variations of the temperature both at the surface and below the surface at 28 w and 4 w are interpreted in the light of the results of a nonlinear multilevel model in the cases of a sudden increase and a sudden relaxation of the trade winds

the forced annual reversal of the atlantic north equatorial countercurrent abstract we analyze the variability of the thermal structure associated with the atlantic north equatorial countercurrent necc and its relation to the seasonally varying winds the analysis performed allows us to establish the period of time and the region where the necc reverses direction west of 25 w the depth of the thermocline in the southern side of the necc 4 to 7 n annually oscillates 180 out of phase to the oscillations on the northern side 7 to 10 n east of 25 w the thermocline rises and falls nearly in phase across the countercurrent if the flow can be uniquely presumed from the thermal structure the necc disappears during the boreal spring in the western basin the reversal of phase from north to south over one part of the ocean but no the other is shown to be mirrored in the annual variation of the curl of the stress induced at the surface by the winds in order to quantify this result the different terms of the vorticity equation are calculated from the data we conclude that t

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

the tectonic evolution of the north celtic sea and cardigan bay basins with special reference to basin inversion abstract the morphology and structural evolution of the north celtic sea basin ncsb and cardigan bay basin cbb are in large part controlled by reactivation of basement features of caledonian and possibly variscan origin from earliest triassic until maastrichtian times sedimentation was almost continuous initially in a rapidly subsiding rift system and finally in a progressive passive sag phase at the onset of the alpine orogeny both basins experienced spectacular inversion along readily identifiable axes the inversion takes the form of a compressive reactivation and reversal of the pre existing growth faults and a broad regional upwarping of the cretaceous depocentre the amount of inversion varies depending on the location within the basin but values in excess of 1000 m are possible by utilising regional seismic data the timing of inversion can be estimated as occurring between maastrichtian and eocene times which correlates with the so called laramide pulse of the alpine orogeny

palaeomagnetism and radiometric dating of the british tertiary igneous province muck and eigg summary the lavas dykes and other intrusive bodies of muck and eigg have been sampled for palaeomagnetic purposes all the bodies are reversely magnetized except for four dykes of muck which are normally magnetized the lavas show variations of direction of magnetism believed to be a record of secular variation the radiometric dates support the geological evidence that the lavas of eigg and muck predate parts of the rhum central igneous complex the lavas of rhum and canna and some of those of skye the combined evidence shows that most of the activity took place during an r n r n sequence between 63 and 58 ma the younger r n sequence is the same as the first part of the r n r sequence found in mull but the sgurr pitchstone of eigg and parts of the eastern redhills of skye belong to later reversed intervals and correspond to chron 26r and chron 26 the igneous activity occurred over a 10 myr period from about 63 ma and can probably be associated with chrons 27r to 23r of the harland et al time scale

effects of lime and gypsum on clay dispersion and infiltration in samples of a brazilian oxisol samples of the surface layer of an acid oxisol were treated with various amounts of caco3 lime or with caso4 gypsum and incubated in the laboratory to study possible effects on clay dispersion and infiltration the treatments consisted of incorporation of gypsum and lime or superficial application of lime infiltration rates were determined with a rainfall simulator and clay dispersion by measuring clay concentration in runoff effects of treatments with lime or gypsum were similar in some respects but different in others incorporating lime increased clay dispersion and reduced infiltration rates significantly incorporating gypsum in contrast increased clay dispersion and reduced infiltration slightly as compared with the control highly significant correlations were found between ph and both clay dispersion and infiltration rates as well as between clay dispersion and infiltration rates the relationship between increased clay dispersion and lower infiltration rates was linear application of lime to surfaces of soil samples reduced clay dispersion less than did incorporation covering the samples with wheat straw reduced clay dispersion and maintained high infiltration rates on the whole effects from additions of gypsum were more favorable than those of lime the more favorable results suggest further tests through field trials

hydrocarbon prospectivity in the irish sea area insights from recent exploration of the central irish sea peel and solway basins abstract compared with the prolific success of the triassic play in the east irish sea basin eisb the lack of hydrocarbon discovery in neighbouring permo triassic basins of the irish sea has been an enigma however recent exploration of the peel solway and central irish sea basins has provided new insights into the geology of these basins and the controls upon hydrocarbon prospectivity in the irish sea area regional seismic interpretation suggests that 12 of the 15 exploration wells drilled in the basins adjacent to the eisb tested valid structural closures at top triassic reservoir level re evaluation of the irish sea petroleum system reveals that although effective reservoirs occur in the lower middle triassic ormskirk sandstone formation and evaporites in the middle upper triassic mercia mudstone group provide a regional top seal the major factor controlling hydrocarbon prospectivity is the limited presence of effective source rocks in the underlying carboniferous section a further control upon prospectivity is the timing of hydrocarbon migration from those areas where carboniferous source rocks were deposited and preserved the namurian basinal marine oil and gas prone shales which form the principal source of hydrocarbons for the triassic play in the eisb are restricted to an east west fairway extending from the eisb into the kish bank basin rocks of this age are absent from the peel and solway basins as a result of variscan uplift and erosion however palaeogeographical reconstructions based on well and outcrop data suggest that even if preserved the depositional environment was not conductive to the formation of marine oil and gas prone source rocks well and seismic data suggest that rocks of namurian age were not deposited in the central irish sea area which remained high during much of dinantian and namurian time potential source rock development in the central irish sea area is therefore limited to the westphalian section which is organically lean and dominated by intertinitic kerogens potential hydrocarbon traps in the central irish sea peel and solway basins formed largely as a result of early cretaceous tectonism and were subsequently modified by fault reactivation during tertiary uplift phases trap formation appears to postdate the most likely timing of hydrocarbon charge which this study suggests would have occurred in late triassic and jurassic time hydrocarbon entrapment in the eisb may have been favoured by limited early cretaceous uplift coupled with renewed hydrocarbon generation and re migration during early tertiary time it is concluded that the remaining prospectivity of the triassic play in the irish sea area is likely to be restricted to the proven play fairway within the eisb

the north equatorial countercurrent observed during the programme francais ocean climat dans l atlantique equatorial experiment in the atlantic ocean july 1982 to august 1984 observations from programme francais ocean climat dans l atlantique equatorial focal cruises in 1982 and 1984 have confirmed that in the central atlantic ocean the north equatorial countercurrent necc has a well defined seasonal regime with a very reduced flux during spring the main core of the necc always lies between 4 n and 6 n focal observations have also shown that a long term change of necc may occur and contribute to the development of an el nino type event in the eastern atlantic ocean

effect of granite crystal grain size on soil properties and pedogenic processes along a lithosequence this study generated new insight into the effect of bedrock grain sizes on pedogenesis under identical topographic and climatic environment the physico chemical and mineralogical properties of two adjacent typic dystrochrepts usda 1999 respectively developed from fine and coarse textured granites were compared this research study was performed in the morvan mountains france analysis of the two underlying bedrocks revealed similar chemical and mineralogical properties with the crystal grain size being the only parameter which differed in these soils bedrock played the key role in the particle size fraction distribution the main factor controlling water retention in the soils weathering reactions of clay minerals were more marked in the fine textured granite soil in this soil both clay mineral swelling and mica transformation into expansible phyllosilicates were greater compared to the coarse textured granite soil in the clay fraction of the fine textured granite soil there were smaller amounts of low crystallised fe and al minerals with higher carbon content in the topsoil as compared to the coarse granite soil the exchangeable cation analysis of the fine textured granite soil revealed a higher proportion of base saturation and a smaller proportion of altit than in coarse textured granite soil which could be explained by preferential leaching of al cations the decrease in exchangeable al the higher swelling of the smectitic layer and the smaller proportion of fe and al oxy hydroxides could be explained by the complexing acid conditions which increased mineral weathering and al leaching the higher water retention increased the time of contact between minerals and the soil solution and the higher carbon content in the topsoil could have enhanced the complexing acid conditions resume d auteur

assimilation of altimeter eddy fields in a limited area quasi geostrophic model abstract techniques for the synoptic analysis vertical inference dynamical adjustment and forecast of altimetric and deeper in situ data are presented as a first step towards the design of continuous assimilation schemes in limited area oceanic domains a year long time series of streamfunction maps denoted mark 2 drawn in the polymode area of the western north atlantic is used as a benchmark for various tests and simulations an original projection extension scheme using empirical modes of density and or pressure anomalies is used to obtain a first guess of the three dimensional structure of the currents starting from surface topography only in the mark 2 domain this technique works well since the first empirical mode is surface intensified and largely dominant an alternative approach is to incorporate deeper data e g float trajectories below the main thermocline the first guess currents are specified as initial and boundary condition of the harvard 6 level quasi geostrophic open ocean mode

near surface current and temperature variability observed in the equatorial atlantic from drifting buoys we examine data from 23 surface drifters which were deployed between june 1983 and july 1984 at 4 w 1 5 4 s the drifters were equipped with a window shade drogue centered at 15 m depth and in most cases a 117 m long thermistor chain drift data indicate a westward south equatorial current with typical speeds of about 20 cm s 1 south of the equator maximum westward flow of 30 40 cm s 1 occurred in june through september of 1983 and 1984 consistent with climatology near zero westward flow which was significantly weaker than was expected from climatology by about 20 cm s 1 occurred from february to april 1984 this probably represents real interannual variability and may be related to the fact that the equatorial atlantic was warmer than usual in the spring and summer of 1984 energetic variations on time scales of o 1 month and less and space scales of o 100 km and less are ubiquitous in the drift and temperature data kinetic energy levels associated with these variations south of the equator are typically 100 cm2 s 2 with slightly higher values in boreal summer energy levels north of the equator are about 500 cm2 s 2 on the basis of data available only during the boreal summer and fall the sources of this energy include inertia gravity waves instabilities of the general circulation and other phenomena for which there is no simple explanation

a study of the hydrocarbon distribution and lower cretaceous greensand prospectivity in blocks 48 15 48 17 48 18 and 48 19 north celtic sea basin

response of the equatorial atlantic ocean to the 1983 1984 wind from the programme francais ocean et climat dans l atlantique equatorial cruise data set variations of the zonal pressure gradient zpg and the equatorial undercurrent euc are described in the equatorial atlantic ocean between 34 30 w and 6 30 e as observed during eight pairs of programme francais ocean et climate dans l atlantique equatorial cruises between october 1982 and august 1984 in 1982 and 1983 the annual cycle of weak trades early in the year followed by comparatively strong and sustained trades were relatively normal in the boreal winter of 1984 the extent of the collapse of the trade winds was exceptional and consequences were observed in the upper layers of the ocean along the equator the 20 c isotherm depth representative of the thermocline depth was unusually deep along the equator in the gulf of guinea a near zero value of the zpg was observed from the greenwich meridian westward an eastward surface current separated from the euc by a layer of reduced velocity was observed over much the same fetch west of 10 w the maximum velocity of the euc showed very little seasonal variation usually between 70 and 80 cm s 1 except in the boreal fall of 1983 when it exceeded 100 cm s 1 during this period in both 1983 and 1984 the euc transport at 23 w reached 25 106 m3 s 1 or twice its annual average which derived not only from the increase in speed but also for a deepening of the current to below 100 m it was also the season when the zpg was strongest and has a similar amplitude at both the surface and 50 dbar relative to 500 dbar the seasonal variations of the euc in the gulf of guinea were even more pronounced during the boreal summer and fall the current weakened while the local zpg reversed direction compared to the west the stronger penetration of the euc into the gulf occurred in the alternate seasons when there was no local reversal in the eastward acting zpg force the large changes in the oceanic and atmospheric circulation during the 1983 1984 period are hypothesized to be related to the suppression of the coastal period are hypothesized to be related to the suppression of the coastal benguela upwelling along the namibia coast this atlantic equivalent to el nino occurred 1 year after the exceptionally strong event in the pacific

40ar 39ar step heating ages of the tertiary igneous rocks of mull scotland twenty one samples from throughout the mull tertiary igneous succession were dated of these eight gave a satisfactory age plateau and the dates show a systematic decrease throughout the succession extrusion of the lavas began c 60 ma ago contemporaneous with the bulk of activity in the british tertiary igneous province igneous activity continued until c 57 ma probably the lavas were extruded during the reversely magnetized chron 26r development of the central igneous complex continued into the normal chron 26 while the late dykes were intruded during 25r if this is so then according to the polarity timescale of harland et al 1982 the duration of igneous activity lies between 0 7 and 4 7 ma consistent with the dates the usefulness of the age plateau selection criteria of lanphere dalrymple 1978 is supported by the results

a fluid inclusion study of cement and vein minerals from the celtic sea basins offshore ireland abstract fluid inclusion petrography and microthermometry have been carried out on jurassic sandstone cements quartz calcite and dolomite and later fracture filling calcite quartz veins from the north celtic sea and the fastnet basins fluid inclusions in the sandstone cements are small 1 8 m monophase liquid only or liquid rich two phase liquid vapour aqueous inclusions all display irregular to elliptical morphologies the two phase aqueous inclusions homogenise to the liquid phase between 60 122 c and have salinities ranging from 7 0 16 0 wt nacl equivalent indicating precipitation of the cements by moderate salinity waters in contrast the veins host both aqueous and petroleum inclusions the aqueous inclusions are liquid rich two phase liquid vapour inclusions 2 30 m long that are typically primary and show irregular and negative crystal shape morphologies their homogenisation temperatures to liquid range from 50 145 c and salinities from 6 20 wt nacl equivalent indicating broadly similar salinities coupled with a wider range of minimum trapping temperatures to those recorded from the cements yellow brown two phase liquid vapour petroleum inclusions are hosted by vein calcite from several wells in the central north celtic sea basin some of these inclusions appear to be primary and all are spatially associated with the aqueous inclusions the two phase liquid vapour petroleum inclusions homogenise mostly to the liquid between 50 130 c petroleum inclusions in the vein calcites indicate that petroleum was transported via fractures at a late stage through the jurassic and cretaceous strata of the celtic sea basins and apparently not through the sandstone matrix

effects of two century land use changes on soil iron crystallinity and accumulation in southeastern piedmont region usa abstract to evaluate effects of land use changes on iron fe crystallinity in mineral soil this study quantified labile short range ordered and relatively crystalline iron pools in upper mineral soils of old hardwood forests cultivated agricultural fields and old field pine forests a common trajectory of land use history in the upland of the southern piedmont usa particularly in comparable old field pine forest but with varying erosion histories we indexed their surface mineral soil iron crystallinity and compared iron cycling accretion in forest floor and mineral soil horizons in a variety of different forest ecosystems our results indicate that i comparable sites with three land uses showed a significantly higher iron crystallinity in cultivated soil than soils supporting old hardwoods or in formerly cultivated soils that have supported 50 years of pine forest regeneration ii five selected pine forest soils showed increasing iron crystallinity with elevated erosion and iii iron accretion in organic and surface mineral soils horizons are ubiquitous across a variety of forests with a higher accretion in non needle materials than needles given the continued soil erosion and more technologically intensive plowing across the piedmont region we attribute that agriculture activities accelerate loss of organic complexed fe in the surface soil and resulted in the crystalline iron oxide at depth exposed to surface also large organic input during forest regrowth for decades reestablished the reactivity and significant accretion of iron oxides in soil profiles suggesting major influence of biological activities in mediating the transformation of soil iron oxides and carbon compounds particularly in organic soil horizon this study suggests that land use changes agriculture and reforestation play a profound role in transforming the iron crystallinity and its interaction with organic matter decomposition in biologically active soil and litter layers it remains unclear how biological activities via animal or microbes in these layers have driven the iron biogeochemical transformation and redistribution in terrestrial forest ecosystems

chalk porosity and tertiary uplift western approaches trough sw uk and nw french continental shelves porosities have been derived from sonic logs for the cenomanian maastrichtian chalk of 22 hydrocarbon exploration wells in the western approaches trough although the burial depth of the chalk studied ranges from 40 1500 m below sea bed porosities are all within the range 0 45 the most deeply buried chalk sequences exhibit close to normal porosity depth relations for offshore chalks abnormally low porosities in the remainder of the wells result from burial at greater depth than that presently observed low porosities were preserved during tertiary alpine related uplift of the area for a given well the magnitude of uplift not reversed by subsequent subsidence apparent uplift equals the displacement of its porosity depth relation from the normal relation along the depth axis apparent uplift in the western approaches trough ranges from 0 1 3 km in the western approaches trough chalk porosity data provide evidence of more widespread tertiary uplift than do seismic reflection records alpine related compression and uplift fault bounded basin inversion is apparent only on seismic records in the southern part of the trough brittany and south west channel basins whereas chalk porosity data suggest regional uplift occurred throughout the trough and adjacent highs chalk porosity data were also used to quantify tertiary uplift in the cleethorpes l well of the east midlands shelf the resultant value of 1 1km is considerably greater than that previously derived from shale sonic velocities approximately 0 3 km and slightly less than that based on apatite fission track analysis 1 3 1 7 km

comparison of topex poseidon altimetry and in situ sea level data at sao tome island gulf of guinea in situ sea level data from a shallow pressure tide gauge mean depth 3 21 m at sao tome island gulf of guinea and altimeter data from topex poseidon t p were analyzed and compared the texas model a t p derived tide model is used for the tidal correction of altimeter data sea level anomaly time series from both data sets were low pass filtered by using a gaussian recurrent interpolation scheme suppressing high frequency fluctuations of periods much less than 2 months according to the 1992 1993 sao tome tide gauge data a clear seasonal signal was observed both in 1992 and in 1993 presenting two sea level maxima in february and october and two minima in june and december these sea level variations are consistent with the known seasonal mean sea level cycle of the area most of which can be explained by steric sea level changes due to the seasonal cycle of upper 500 m water column properties in the gulf of guinea on the basis of the 60 day low passed tide gauge time series significant year to year variations were observed as well with a 6 3 cm sea level difference in february 8 1 cm in 1992 versus 1 8 cm in 1993 and a 4 4 cm difference in october 4 6 cm in 1992 versus 9 0 cm in 1993 minimum sea levels occurring just prior to the upwelling season july august were almost the same for both years 9 to 10 cm but lasted much longer in 1992 2 months than in 1993 2 weeks during the 15 month period of concomitant observations from october 1992 to december 1993 these seasonal and year to year sea level variations are remarkably well reproduced by the t p sea level time series with an rms difference of 2 2 cm and a correlation coefficient of 0 88 this result in the equatorial atlantic is consistent with other intercomparisons in the pacific and indian oceans this excellent recovery of the oceanic signal is undoubtedly the result of unprecedented high precision of t p measurements and the reliable t p derived tide model that is used in the present study

radial orbit error reduction and mean sea surface computation from the geosat altimeter data using the altimeter data from the geosat exact repeat mission we have produced yearly averaged mean profiles and a global mean sea surface the radial error of each 6 day orbital arc computed with the gem t2 geopotential was first estimated by calculating the amplitude and phase of the nine dominant frequencies of the difference between the altimetric profiles and the mean sea surface obtained when adding the permanent sea surface topography computed from the levitus climatological atlas to the gem t2 geoid we show that this operation is little affected by the choice of the geoid or by its formal error the resulting correction has been subtracted from each individual arc yearly mean profiles were then obtained by averaging the corrected altimetric data of each repeat cycle on a yearly basis their noise level is 1 to 2 cm and their resolution is 20 km but the differences of the altimetric heights at crossovers of ascending and descending tracks are still 30 cm nns the latter can be reduced to 7 cm rms by a crossover analysis in addition to the mean values standard deviations were computed at each point of the repeat cycle this yearly along track variability is of the order of 10 cm rms and is dominated by the ocean mesoscale variability a global yearly mean sea surface has been derived by bilinear interpolation its resolution ranges approximately from 160 km to 80 km depending on the latitude it is shown to be much less noisy than those deduced from geos 3 and seasat data

tropical atlantic sea level variability from geosat 1985 1989 geosat altimeter data between april 1985 and september 1989 are analyzed in the tropical atlantic ocean first improvements due to the use of new corrections and orbit computations are found to be effective especially in the gulf of guinea where part of the previously missing signal is recovered then the variability of the ocean is examined using empirical orthogonal functions eofs only three eofs are needed to describe 80 of the seasonal variance the first one describes the meridional tilting of the tropical atlantic along the mean location of the intertropical convergence zone with an annual period the second describes a mass redistribution due to the equatorial upwelling peaking in june july the third function presents a clear semiannual signal looking at interannual variability the first eof reveals a mass redistribution between the equatorial region 10 n to 10 s and the northern and southern ones 10 n to 30 n 10 s to 30 s in the equatorial region the upper layer volume increases from about 1 5 to 1 5 x 1014 m3 between 1987 and 1989 occurring 1 year after the pacific el nino this phenomenon recalls the 1984 anomaly observed during the programme francais occan et climat en atlantique tropicavseasonal equatorial atlantic experiments

inversion and exhumation of the st george s channel basin offshore wales uk the western uk basins of the irish sea have provided one of the best natural laboratories for investigating the causes and consequences of intracratonic uplift and erosion exhumation to date the emphasis has been on igneous underplating as the chief process driving their exhumation in this paper we demonstrate that tectonic inversion the shortening of formerly extensional basins and reactivation of their constituent faults dominated the exhumation of the st george9s channel basin offshore wales based on mapping of an extensive 2d seismic grid evidence is presented for at least two major inversion episodes in the late cretaceous and the neogene plus minor shortening during the eocene inversion was distinctly noncoaxial especially during the neogene when coeval transpression and transtension was focused at discrete bends and stepovers on the basin bounding st george9s bala and northwest flank faults that the principal mechanism driving these uplift episodes was inversion as opposed to igneous underplating is corroborated by analysis of thermal history data apatite fission track and vitrinite reflectance they reveal late cretaceous and neogene geothermal gradients that were comparable with that at the present day i e no significant increase in basal heat flow sonic velocity profiles logged in hydrocarbon boreholes constrain the minimum thickness of the eroded section which varies between c 1000 m in the centre and c 2240 m at the margins of the basin given the strength of evidence for tectonic inversion in the st george9s channel basin our favoured model invokes superimposition of the effects of inversion and igneous underplating to account for the complex exhumation history of the st george9s channel basin in particular and the western uk basins in general

sea slope changes associated with westward propagating equatorial temperature fluctuations at five locations in the eastern equatorial pacific between 113 w and 130 w both sea height and temperature fluctuations were observed during the repeated ground track phase of the seasat mission a fluctuation of 1 6 0 6 cm deg latitude in the smoothed sea slope between 2 n and 4 n is associated with the passage of two temperature disturbances the corresponding sea height fluctuation of 1 0 0 9 cm is not statistically significant the sea slope estimate together with kinematic assumptions about velocities provides an approximate evaluation of the principal contributions to the meridional momentum balance in the propagating wave

mineralogical variability in weathering microsystems of a granitic outcrop of galicia spain summary several products of weathering have been studied in a granitic outcrop in galicia n w spain spain alteration took place under a humid temperate climate the various materials and the microsystems in which they occur are 1 fissures containing gibbsite and or 1 1 sheet silicates of varying degrees of crystallinity 2 fissures containing 2 1 sheet silicates of beidellite type 3 encrustations of siliceous material showing varying degrees of structural order with or without organic matter and 4 encrustations of non crystalline matter composed chiefly of al p and si the results demonstrate the importance of considering the different microsystems which contribute to the formation of secondary products in a given weathering system

a hot spot model for early tertiary volcanism in the n atlantic s u m m a r y the initial stages of rifting of the n atlantic were accompanied by massive extrusion of volcanic rocks and the accretion to the lower crust of even greater volumes of igneous rock emplacement of the bulk of the igneous rocks along the 2000 km long continental rift occurred in as little as 2 3 my the pattern and timing of magmatic activity can be explained by partial melting of anomalously hot asthenosphere as it welled up to fill the space left by the stretched and thinned continental lithosphere asthenosphere temperatures were elevated regionally by 100 150 over a 2000 km diameter region by the mushroom shaped head of hot material fed by a mantle plume which at present is centred beneath iceland

geological and geophysical evidence for a mafic igneous origin of the porcupine arch offshore ireland sedimentary basins west of ireland contain a number of deep seismic structures that have been variously interpreted as fault blocks serpentinite extrusions or igneous complexes the porcupine arch pa is a deep level 11 km domal 50 km wide seismic feature associated with a prominent free air gravity anomaly high and high p wave velocities detailed seismic mapping of igneous sill complexes in the porcupine basin suggests a possible connection with the pa the sills form a thick 5 km interconnected network extending from the pa into the flanking post rift cretaceous stratigraphy suggesting that the pa may be the top of a large ultra mafic intrusion that fed the sills an intrusive origin for the pa is in agreement with geophysical modelling gravity and v p the seismic character of the porcupine arch structure and the primitive bulk composition of the porcupine sills and is consistent with documented regional cenozoic uplift in the basin with the development of shallow water and the occurrence of paleocene eocene deltaic depositional systems similar mafic ultramafic intrusive complexes have been documented elsewhere on the northeastern atlantic margin including the rockall trough these findings emphasize that higher heat flow in the early cenozoic may have prevailed over the northern part of the porcupine basin

the british tertiary igneous province palaeomagnetism and ages of dykes lundy island bristol channel summary of 66 dykes collected 52 gave stable directions 44 reversed 4 normal and 4 intermediate the mean direction of magnetization was n3 6 e 62 7 down equivalent to a pole position of 82 6 on 155 0 e this is significantly different from the present pole and displays right handed farsidedness the bulk at least of the dykes fall within the apparent span 45 54 my yet they display approximately the same small proportion of normal dykes as do the older dyke swarms of the province which were formed during a different polarity period or periods

further studies on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds upper ocean temperature data obtained during the seasonal response of the equatorial atlantic experiment and the francais ocean et climat dans l atlantique equatorial program are used to describe the variations of the thermocline observed along the equator from february 1983 to september 1984 in response to rapid seasonal changes in zonal wind stress the thermocline underwent sequences of upwelling followed by downwelling or conversely depending upon whether the winds were intensifying or relaxing these sequences increased systematically in magnitude and duration to the east both the sequential behavior and its zonal inhomogeneity represent departures from the slowly varying and in phase climatological description of the annual thermocline response an analytical reduced gravity equatorial long wave model forced by zonal wind stress distributions representative of the variations observed along the equator was employed to reconcile the differences between the 1983 1984 synoptic measurements and the climatologically averaged description qualitative agreements between the model results and the data were found for many salient features of the annual cycle including the zonal pressure gradient calculated by finite difference the features in the model arise as interference patterns between directly forced and reflected kelvin and long rossby waves that are generated with each change in the wind stress the manner in which the wind stress changes from year to year is therefore crucial to the equatorial ocean s response

iron oxide coatings on sand grains from the atlantic coastal plain high resolution transmission electron microscopy characterization nanoscale characterization of so called iron oxide coatings on aquifer sands is vital for understanding the fate and transport of naturally occurring and anthropogenic chemical species these coatings which typically have a strong reddish color are commonly assumed to consist primarily of iron oxides and oxyhydroxides this work shows that the yellowish red to strong brown coatings on sediments from an atlantic coastal plain aquifer in virginia are predominantly a mixture of si and al rich nanophases of variable crystallinity with interspersed smectite and agglomerates of goethite nanoparticles clusters of bacterial cells diatom fossils sponge spicules and other trace minerals are also observed

polarity stratigraphy and duration of the tertiary igneous activity of mull scotland previous work left unresolved whether the tertiary igneous activity had spanned a magnetic polarity succession r n r n r or if overprinting had occurred only r n r new work is reported that demonstrates that thermal overprinting has occurred in a narrow zone c 600 m wide bordering the outermost major intrusions of centre 2 criteria for the recognition of overprinting are examined the polarity sequence is now believed to be r n r in conjunction with radiometric dates which show that activity occurred from c 60 ma to c 57 ma our data show that the sequence corresponds to chrons 26r 26 25r of the polarity time scale of harland et al 1982 or 25r 25 and 24r of breggren et al 1985 upper and lower limits to the duration of the activity are respectively 4 67 ma and 0 67 ma or 4 07 ma and 0 60 ma a duration of about 3 5 ma is thought probable the magnetic evidence supports the view that the loch scridain sills correspond to the early acid and intermediate cone sheets of centre 1

colloidal stability in some tropical soils of southeastern nigeria as affected by iron and aluminium oxides abstract the stability of microaggregates in soils as opposed to its dispersion is a very important soil phenomenon that checks degradation arising from unguided tillage and soil erosion ten soils from southeastern nigeria were sampled from their typical a and b horizons for the study the aim was to identify the extent of colloidal stability of the soils and the forms of fe and al oxides in the soils contributing to their stability the soils are mostly ultisols and inceptisols formed on sandstones and shale parent materials the soils are low in soil basic cations including the soil organic carbon soc the major clay mineral is kaolinite while the soil is acid in reaction the various forms of soil fe and al oxides are high with the total forms of fe and al being most dominant and dithionite extracted fe and al oxalate extracted fe and al pyrophosphate extracted fe and al the water dispersible clay and silt wdc and wdsi which are index of dispersion in most soils are low to medium thus reflecting in the low to medium dispersion ratio dr the clay flocculation index cfi and aggregated silt clay asc were moderate to high implying the high potential stability of the soils soil organic carbon did not seem to be contributing much to the stability of the microaggregates while oxalate and pyrophosphate extractable fe feox fep and to some extent total al alt were among the different forms of oxides that act as aggregating agents we propose here that rather than soc acting as a disaggregating agent in the soils it might have acted in association with these oxides in a linkage or bridge such as c p om c to ensure stability of the soils

observation of long equatorial waves in the pacific ocean by seasat altimetry abstract synoptic maps of the mesoscale dynamic topography in a band between 7 5 n and 7 5 s in the pacific ocean are drawn from seasat altimeter data they show a set of eddies 600 km in diameter and 15 20 cm in amplitude moving westward with a velocity of about 40 km day 1 along 4 5 n their occurrence is consistent with the surface temperature front undulations observed by legeckis south of the equator the signal is less coherent but a significant degree of symmetry with the north is evidenced the dynamics of the wave system might also present some degree of nonlinearity as some water seems to be carried along with the wave