the initiation of subduction by crustal extension at a continental margin summary we investigate how subduction may be triggered by continental crust extension at a continental margin the large topography contrast between continental and oceanic domains drives the spreading of continental crust over oceanic basement subduction requires the oceanic plate to get submerged in mantle so that negative buoyancy forces may take over and drive further descent this is promoted by two mechanisms loading by continental crust bends the oceanic plate downwards extension in the continental domain induces crustal thinning which acts to raise mantle above the oceanic plate in this model the width of the continental region undergoing extension is an important control parameter the main physical controls are illustrated by laboratory experiments and simple theory for elastic flexure coupled to viscous crustal spreading three governing dimensionless parameters are identified one involves the poorly constrained oceanic plate buoyancy we find that the oceanic plate can be thrust to depths larger than 40 km even if it is buoyant enabling metamorphic reactions and density increase in the oceanic crust another parameter is the ratio between the width of the continental extension region and the flexural parameter for the oceanic plate initiating subduction is easier if the continent thins over a short lateral distance or if the oceanic plate is strong the third important parameter is the ratio of oceanic plate thickness to initial continental crust thickness such that a weak plate and a thick crust do not favour subduction thus the change from a passive to an active margin depends on the local characteristics of the continental crust and is not determined solely by the age and properties of the oceanic lithosphere it is shown that the spreading of continental crust induces uplift of the margin as the adjacent seafloor subsides evidence for the emplacement of continental crust over oceanic basement at passive margins is reviewed

effect of early pliocene uplift on late pliocene cooling in the arctic atlantic gateway despite the undisputed role of the arctic ocean in the modern and pliocene climate system the arctic has only recently attracted public awareness that ongoing fundamental change in the arctic cryosphere could be a response to global warming clarification of the arctic s role in global climate during the pliocene is however largely hampered by equivocal stratigraphic constraints from a well dated pliocene sequence from the yermak plateau off nw spitsbergen we present sedimentological and geochemical data indicating that 4 million years ago terrigenous sediment supply and sources changed abruptly in response to a regional tectonic uplift event we argue that this event together with contemporary uplift and tilting along the northwestern european continental margin preconditioned the landmasses for glacial ice build up during intensification of the northern hemisphere glaciation inhg our data further suggest that the final deepening widening of the arctic atlantic gateway the fram strait between 6 5 and 5 ma gradually caused increased deep water mass exchange which in turn likely contributed to the intensification of the north atlantic thermohaline circulation coupled to the north atlantic warm pool as a regional moisture source declining atmospheric co2 levels and other feedback mechanisms during the pliocene the regional tectonic activities in the high northern latitudes caused decreased summer ablation and thus allowed the initial build up of glacial ice both in scandinavia and the sub aerially exposed svalbard barents sea culminating in the first large scale coastline shelf edge glaciations at 2 75 ma

opening of the fram strait gateway a review of plate tectonic constraints abstract we have revised the regional crustal structure oceanic age distribution and conjugate margin segmentation in and around the lena trough the oceanic part of the fram strait between the norwegian greenland sea and the eurasia basin arctic ocean the lena trough started to open after eurasia greenland relative plate motions changed from right lateral shear to oblique divergence at chron 13 times 33 3 ma earliest oligocene a new bouguer gravity map supported by existing seismic data and aeromagnetic profiles has been applied to interpret the continent ocean transition and the influence of eocene shear structures on the timing of breakup and initial seafloor spreading assuming that the onset of deep water exchange depended on the formation of a narrow oceanic corridor the gateway formed during early miocene times 20 15 ma however if the initial lena trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep water circulation the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around chron 5 times 9 8 ma late miocene paleoceanographic changes at odp site 909 northern hovgard ridge are consistent with both hypotheses of gateway formation we cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the lena trough the gravity seismic and magnetic observations question the prevailing hypotheses on the yermak plateau and the morris jesup rise as eocene oceanic plateaus and the hovgard ridge as a microcontinent

mafic intrusions east of svalbard imaged by active source seismic tomography a seismic refraction and reflection tomography experiment was performed across the igneous province east of svalbard which is a part of the cretaceous high arctic large igneous province seismic travel times from 12 ocean bottom seismometers hydrophones deployed along a 170 km line are inverted to produce smooth 2d images of the crustal p wave velocity and geometry of the acoustic basement and moho the inversion of travel times was complemented by forward elastic wave propagation modeling integration with onshore geology as well as multichannel seismic magnetic and gravity data have provide additional constraints used in the geological interpretation the seismic p wave velocity increases rapidly with depth starting with 3 km s at the sea floor and reaching 5 5 km s at the bottom of the upper sedimentary layer the thickness of this layer increases eastward from 2 km to 3 5 km on average the p wave velocity in the crystalline crust increases with depth from 5 5 km s to 6 8 km s the crustal thickness is typical for continental shelf regions 30 34 km finger shaped high velocity anomalies one reaching 12 and two of 4 6 velocity perturbation are obtained these velocity anomalies are concomitant with lower cretaceous basaltic lava flows and sills in the shallow sediments and elongated gravity and magnetic highs traced towards the northern barents sea passive continental margin we interpret the obtained velocity anomalies as signatures of dikes emplaced in the basement during breakup and subsequent spreading in the arctic amerasia basin

late cretaceous cenozoic intraplate contractional deformation at the norwegian continental shelf timing magnitude and regional implications abstract contractional structures large anticlines and synclines reverse faults and inverted centres of deposition of assumed late cretaceous cenozoic age are common in cretaceous tertiary basins of the northwestern european margin the similarities in style orientation and timing of these structures are striking the present detailed analysis of one anticline the ormen lange dome of the mid norwegian continental shelf indicates that the total contraction is moderate less than 2 3 and that the analysed anticline has been growing almost continuously since its initiation in eocene till present inversion in the barents sea started already in the late cretaceous this episode is suggested to be related to far field effects of active plate margin processes and transfer of stresses across the plate as a consequence of the sub hercynian and paleocene laramide event of the alpine orogeny the development of co axial structures was facilitated by stress focusing along pre existing high relief n s and ne sw trending fault complexes far field plate tectonic stresses originating mainly from the alpine orogeny seem to have been the most important cause of contractional deformation on the nw european shelf in addition ridge push from the north atlantic spreading may have contributed significantly particularly during the neogene

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

alternative interpretations for microstructure patches in the thermocline abstract two interpretations of microstructure patches measured in the main thermocline of the north pacific by gregg 1980 are questioned he concludes that the observed microstructure is not fossil temperature turbulence and that the observed cox numbers imply vertical diffusivities by turbulent mixing which am about 10 2 times smaller than canonical values of order 10 4 m2 s 1 the first conclusion that the micro structure is not fossil depends on an unnecessary assumption that in order to be fossil the microstructure must not be moving actually fossil turbulence microstructure must always have internal wave and laminar restratification motions the second conclusion depends on the first the pattern of thorpe displacement scales for the patches containing zero temperature gradients implies they were produced by turbulence with vertical scales as large as several meters however the large distances separating the zero gradient points implies that the microstructure is fossil at all scales at the ti

turbulence and entrainment in a buoyant surface plume in winter tidal outflow from the leschenault estuary forms a buoyant sheared stratified plume in koombana bay on each outgoing tide the turbulence in the plume and the local entrainment into the plume are examined based on measurements collected in an intensive field program coherency measurements between horizontally separated sensors are used to examine the anisotropy of the turbulence the effects of viscosity and buoyancy on the turbulence are studied using an activity diagram which is also an indicator of the mixing efficiency and total mixing the osborne cox model is tested and found to be valid in the plume

density and velocity fine structure enhancement in oceanic eddies advection diffusion models of the oceanic thermocline require a global ocean mean vertical eddy diffusivity of about 1 cm2 s 1 however maximum values estimated from microstructure measurements at mid gyre locations are generally smaller and occasionally 1 2 orders of magnitude less depending on the particular assumptions made by individual analysts mesoscale features are high kinetic energy sources which may fuel vertical mixing mechanisms on fine structure scales resulting in local enhancements of eddy diffusivity above the canonical value of 1 cm2 s 1 the effects of one such mechanism the kelvin helmholtz instability are assessed for a gulf stream ring and a mid thermocline eddy the necessary richardson numbers are computed from yvette profiles obtained in these features and are accurate to within about 10 for ri 1 and more accurate at the critical value ri 0 25 a plausible extension of the miles howard theorem for a nonparallel shear flow is formulated for a two dimensional perturbation the shear appropriate for this richardson number calculation is well approximated by the total shear for slowly depth varying direction as is the case for the vast majority of the data upper and lower bounds on the vertical scale for the richardson number calculation are set by the shear spectra and the ozmidov scale median richardson number was lower toward the center of the eddy because of a large decrease in brunt vaisala frequency n2 and was depressed on the fringes by high shear lower median ri is also found at the center of the ring as a result of low n2 lower bounds on vertical eddy diffusivity are estimated based on the assumptions of a simple mixing length model and of complete mixing of each region where ri is less than 0 25 the spatial distribution of this quantity within the eddy and the ring mirrors that of median ri values range from az 1 1 cm2 s 1 near the center of the eddy and 0 90 cm2 s 1 near the center of the ring to zero in regions outside of the features where no ri less than 0 25 were observed

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

inter well scale natural fracture geometry and permeability variations in low deformation carbonate rocks regional natural fracture networks often show variations on a scale below that captured by seismic reflection data this variability is not considered in most reservoir models but likely impacts uncertainties in permeability we quantify this uncertainty using a database of 13 000 fractures in nine outcrops digitised in the carbonate jandaira formation potiguar basin brazil distance between outcrops is on average 11 km with a minimum of 300 m which is comparable to the distance between wells in naturally fractured reservoirs in between outcrops significant variations exist in orientation intensity length and topology using discrete fracture matrix flow models we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity based analyses such as percolation probabilities particularly when the matrix is permeable the permeability variations associated with subseismic scale fracture variability are not captured in conventional stochastic models but can be captured using deterministic outcrop models with flow through discrete fractures the deterministic models provide a permeability range associated with subseismic fracture variability that can be assigned to grid cells of fractured reservoir flow models as an alternative to assuming constant permeability in the absence of subseismic scale deformation

on the structure and dynamical features of intrusive layering in the eurasian basin in the arctic ocean 1 numerous conductivity temperature depth data obtained in the arctic basins are analyzed to describe structural features of intrusive layering special attention is paid to large intrusions vertical scale of 40 100 m observed in upper intermediate and deep layers depth ranges of 150 200 200 600 and 600 1000 m respectively the analysis of the intrusions is accompanied by descriptions of the frontal zones where the layering was observed based on observations detailed estimates of frontal zone parameters are presented vertical profiles of temperature and salinity are found to have a well defined sawtooth or cog shape displaying a sequence of relatively thick weak gradient layers where temperature and salinity are decreasing with depth interleaved with relatively thin high gradient sublayers where temperature and salinity are increasing with depth some hypotheses about causes responsible for cog structure existence are discussed intrusions with high amplitude anomalies in the vertical profiles of temperature and salinity are shown to be present at baroclinic fronts based on models of interleaving and data analysis the apparent vertical and lateral diffusivity in the frontal zones of the upper and deep ocean layers are estimated and the slope of unstable modes relative to the isopycnals is examined at the baroclinic front in the situation when both temperature and salinity are stably stratified

a statistical scaling model for fracture network geometry with validation on a multiscale mapping of a joint network hornelen basin norway 1 fracture patterns are characterized by a complex geometry which involves a large length distribution and nonhomogeneous density distributions here we address the issue of the modeling of this complex geometry over scales through a first order model providing the characterization of the number of fractures of a given length and at a given scale we propose that the simplest model is a power law in both space and fracture length with three main parameters the exponent a of a power law length distribution the fractal dimension d which fixes the scale dependence of the number of fractures and the fracture density we verify the applicability of this model on seven fracture patterns mapped from the metric scale up to almost the kilometric scale in the hornelen basin the model efficiently describes fracture network properties at all scales with a single set of parameters for the hornelen fracture networks we found a simple relationship between basic exponents a d 1 implying that the fracture network is self similar through this analysis we present different methodological developments for deriving the basic exponents a and d and for verifying the consistency of the model overall the main methodological development is about the normalization of the measurements made from different scales of observation finally we discuss both the limitations and the uses of such a model for analyzing the hydraulic and mechanical properties of fracture networks

is interleaving in the agulhas current driven by near inertial velocity perturbations abstract recent observations taken at a number of latitudes in the agulhas current reveal that the water mass structure on either side of its dynamical core is distinctly different moreover interleaving of these distinct water masses is observed at over 80 of the stations occupied in the current particularly within the subsurface density layer between tropical surface water and subtropical surface water masses and within the intermediate layer between the antarctic intermediate water and red sea water masses direct velocity measurements allow for a comparison between the characteristic vertical length scales of the agulhas intrusions and those of velocity perturbations found throughout the current it is found that the interleaving scales match those of the velocity perturbations which are manifest as high wavenumber vertical shear layers and are identified as near inertial oscillations furthermore the properties of the intrusions indicate that double diffusion is not an important process in thei

fractal geometries of vein systems and the variation of scalingrelationships with mechanism abstract investigation of vein geometries has identified empirical relationships which allow extrapolation of outcrop scale observation to larger scales measurements of vein shapes and aspect ratios in a number of different environments demonstrate that veins follow similar empirical scaling laws to those of faults geometries of veins are easier to characterise accurately than faults because their thickness is related to the variation in displacement from zero at their tips to a maximum at their thickest point vein sizes obey the empirical relationship l kta where l length in mm t thickness in mm 20 1 this suggests that veins amplify initially by inflation and subsequently by elongation

double diffusive interleaving due to horizontal gradients in this paper we present a linear stability analysis for an unbounded vertically stratified fluid which has compensating horizontal temperature and salinity gradients so there is no horizontal density gradient we obtain the most unstable perturbation for given linear horizontal and vertical gradients and calculate the growth rates the vertical lengthscale of the intrusion and the slope of the intrusion to the horizontal we show that the system is most unstable to two dimensional disturbances and that except for a small region in which the temperature stratification is unstable and the salinity stratification is stable the most unstable disturbance is non oscillatory we also obtain a solution to the fully nonlinear equations and calculate the fluxes of heat and salt the nonlinear solution shows that alternating interfaces of salt finger and diffusive interfaces will eventually appear on the intrusion when the vertical stratifications are both stable

oligocene to lower pliocene deposits of the norwegian continental shelf norwegian sea svalbard denmark and their relation to the uplift of fennoscandia a synthesis abstract this study provides the results of the first integrated study of oligocene pliocene basins around norway within the study area three main depocentres have been identified where sandy sediments accumulated throughout the oligocene to early pliocene period the depocentre in the norwegian danish basin received sediments from the southern scandes mountains with a general progradation from north to south during the studied period the depocentre in the basinal areas of the uk and norwegian sectors of the north sea north of 58 n received sediments from the scotland shetland area because of the sedimentary infilling there was a gradual shallowing of the northern north sea basin in the oligocene and miocene a smaller depocentre is identified offshore northern nordland between ranafjorden approximately 66 n and vesteralen approximately 68 n where the northern scandes mountains were the source of the oligocene to early pliocene sediments in other local depocentres along the west coast of norway sandy sedimentation occurred in only parts of the period shifts in local depocentres are indicative of changes in the paleogeography in the source areas in the barents sea and south to approximately 68 n the oligocene to early pliocene section is eroded except for distal fine grained and biogenic deposits along the western margin and on the oceanic crust this margin was undergoing deformation in a strike slip regime until the eocene oligocene transition the early oligocene sediments dated in the vestbakken volcanic province and the forlandssundet basin represent the termination of this strike slip regime the change in the plate tectonic regime at the eocene oligocene transition affected mainly the northern part of the study area and was followed by a quiet tectonic period until the middle miocene when large compressional dome and basin structures were formed in the norwegian sea the middle miocene event is correlated with a relative fall in sea level in the main depocentres in the north sea formation of a large delta in the viking graben frigg area and uplift of the north and south scandes domes in the norwegian danish basin the sorgenfrei tornquist zone was reactivated in the early miocene possibly causing a shift in the deltaic progradation towards the east a late pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2 7 ma when the scandes mountains were strongly eroded and became a major source of sediments for the norwegian shelf whilst the frigg delta prograded farther to the northeast

mixing 3d mapping and lagrangian evolution of a thermohaline intrusion abstract observations of the three dimensional structure and evolution of a thermohaline intrusion in a wide deep fjord are presented in an intensive two ship study centered on an acoustically tracked neutrally buoyant float a cold fresh low oxygen tongue of water moving southward at about 0 03 m s 1 out of possession sound washington was observed the feature lay across isopycnal surfaces in a 50 80 m depth range the large scale structures of temperature salinity velocity dissolved oxygen and chlorophyll were mapped with a towed depth cycling instrument from one ship while the other ship measured turbulence close to the float with loosely tethered microstructure profilers observations from both ships were expressed in a float relative lagrangian reference frame minimizing advection effects a float deployed at the tongue s leading edge warmed 0 2 c in 24 h which the authors argue resulted from mixing diapycnal heat fluxes inferred from microstructure were 1 2 orders of magnitude too sm

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

application of the wigner ville distribution to temperature gradient microstructure a new technique to study small scale variations the wigner ville distribution a new tool in the time frequency analysis of signals is applied to temperature gradient microstructure records in particular the wigner ville distribution is used to compute the local instantaneous and maximum frequencies of the signal as a function of depth and these frequencies are then related to the dissipation of turbulent kinetic energy the method is applied to two temperature gradient microstructure records from the wellington reservoir it is shown that a high resolution estimate of the dissipation is obtained that provides insight into the patchiness the wavenumber content and the reynolds froude number variability of the integral scales of motion in a strongly stratified water column

sensitivity to long term climate change of subpermafrost groundwater systems in svalbard deep subpermafrost aquifers are highly climate dependent with the permafrost as an aquitard preventing groundwater recharge and discharge a study from the high arctic island of spitsbergen svalbard shows that during a glacial to interglacial phase both the permafrost and the glacier regime will respond to climatic changes and a glacier fed groundwater flow system will vary accordingly a full glaciation results in the melting of permafrost and groundwater can flow through pores and fracture systems in the rocks and sediments below the temperate zones of glaciers these groundwater flow systems will mainly be localized to fjords and valleys and form low lying terrestrial springs when the relative sea level drops during deglaciation due to glacio isostatic rise during an interglaciation permafrost develops and thickens and the groundwater recharge and discharge areas will thereby be gradually reduced to a minimum reached at the warmest part of an interglaciation an already frozen spring system cannot reopen before the permafrost melts only groundwater springs related to permanently warm based glacial ice will persist into the next glaciation during a new glaciation flow systems that terminated during the previous interglaciation may become revitalized if overridden by warm based ice causing permafrost thawing

double diffusive interleaving part i linear stability analysis abstract quasi horizontal interleaving between water masses is frequently observed in the frontal regions between different water masses where there are significant compensating isopycnal gradients of temperature and salinity it is believed that these intrusions are driven by double diffusive convection which transports salt heat and density across sharp quasi horizontal interfaces i e across regions of large vertical property gradients stern and other investigators have parameterized the vertical flux of salt in these intrusions by an eddy diffusivity multiplied by the vertical gradient of salinity whereas laboratory experiments show that sharp interfaces tend to occur by double diffusive convection and that the vertical fluxes of properties depend on the property contrasts across the interfaces in this paper it is assumed that the vertical fluxes of double diffusive convection are proportional to the salinity contrast across the sharp interfaces that occur between the quasi horizontal intrusio

late cenozoic uplift and volcanism on spitsbergen caused by mantle convection regional tectonic uplift heat flow measurements and p t estimates on upper mantle xenoliths associated with neogene volcanic rocks indicate a strongly thinned 50 km thick lithosphere beneath svalbard 650 km north of scandinavia data on neogene volcanic rocks and xenoliths indicate an 50 c temperature anomaly in the underlying asthenosphere together with volatile rich conditions in the upper mantle the svalbard uplift is one of several cenozoic epeirogenic uplifts along the margins of the north atlantic boundary processes occurring where hot spot influenced asthenosphere abuts cold deep continental lithosphere seem to be likely explanations for the uplifts

cenozoic margin development and erosion of the barents sea core evidence from southwest of bjornoya abstract five stratigraphic boreholes at the western barents sea margin reveal an evolution from a palaeocene normal shelf setting to a complex late cenozoic offshore marginal marine system influenced by mass flows and finally a glacially influenced shelf environment palaeocene epeiric sea sedimentation was sourced by erosion at the stappen high earliest eocene extension associated with volcanism was followed by rapid subsidence of the vestbakken volcanic province which became filled by sediments from an uplifted stappen high by the middle eocene siliciclastic shelf sediments were deposited and the infill had reached a balance with subsidence tectonic movements at this time may have caused local uplift which restricted the ventilation of local basins west of the stappen high but marine conditions existed in the area until early oligocene times when subaerial exposure was caused by tectonic uplift and probably also a fall in eustatic sea level pronounced oligocene and pliocene unconformities reflect major events of uplift and erosion at the margin and abundant fossil reworking indicates erosion of the uplifted cretaceous and tertiary strata the oligocene erosion had its associated depocentre to the south and west of the study area and was less important regionally than the pliocene pleistocene phase the pliocene uplift first led to local erosion along the margin subsequent subsidence may initially have had a thermal component this was followed by extensive downwarping under the load of largescale deposition sourced by regional erosion in the barents shelf region an eocene volcanic phase was probably related to the initiation of seafloor spreading isotopically dated volcaniclastic intervals in one of the cores give evidence of a late pliocene volcanic phase this event was associated with local tectonic movements which may be part of a regional uplift in the western northwestern part of the barents sea glaciations caused by the neogene climatic deterioration became enhanced by uplift and this led to extensive regional glacial erosion the main depocentre was offset to the south by ice flow curving around the uplifted area

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

lineament domain of regional strike slip corridor insight from the neogene transtensional de geer transform fault in nw spitsbergen lineaments on regional scale images represent controversial features in tectonic studies published models explain the presence of the lineament domains in most geodynamic environments as resulting from the enhanced erosion along strikes normal to the upper crustal regional extension despite their success in many tectonic frameworks these models fail to explain the existing lineament domains in the regional strike slip corridors that separate regional blocks including the transform faults the present paper investigates the lineament distribution in such environments and specifically presents the results from a study along the shear corridor of the de geer transform fault in the north atlantic responsible for the separation and drifting away between northern greenland and the svalbard archipelago since oligocene times the study spans from satellite image analysis and outcrop scale investigations to a more regional analysis on a digital bathymetric model of the north atlantic arctic ocean lineaments were automatically detected in the spectral band 8 0 52 0 9 m of a landsat 7 image 15 m pixel resolution a total of 320 image lineaments were extracted from both the regional and the local scale investigations and statistically analyzed results from the multi scalar lineament analyses revealed the existence of a main n s lineament domain regionally persistent from the de geer corridor to the western margin of northern spitsbergen where it relates to the youngest post oligocene tectonics observed onshore this is confirmed by field observations showing that the n s faults represent the youngest brittle deformation system and systematically cut the deformations associated with the building of the tertiary west spitsbergen fold and thrust belt the n s lineament domain is the result of the activity of a larger regional scale tectonic feature nw se oriented and responsible for the localized extension within its deformation corridor the de geer transform fault a model is presented that involves the presence of a thin upper crust with brittle behavior lying above a deeper crustal layer characterized by a more ductile deformation the lower layer suffers more diffuse homogeneous strain this strain is transmitted to the upper brittle layer forming clusters of enhanced fracturing zones aligned following the induced stress trajectories lineaments develop along these weaker fractured zones preferentially etched by erosional processes and align perpendicular to the least horizontal compression sigma3 which in turn forms an angle to the shear kinematics in the western part of spitsbergen this angle is smaller than 45 due to the transtensional tectonic regime the proposed model for lineament domain origin in strike slip environments well integrates the existing models in literature and could be applied to other similar geodynamic contests

thermochronological constraints to late cenozoic exhumation of the barents sea shelf abstract the cenozoic evolution of the barents sea has been widely debated for its implications on hydrocarbon exploration in this paper we provide the first for the area apatite u th he thermochronology data on early middle jurassic and early cretaceous sandstone reservoir samples obtained from three wells located on the western part of the barents shelf a large range of grain ages have been detected ranging from 1 58 to 50 65 ma these thermochronological data initially integrated with vitrinite reflectance measurements to properly constrain the burial history evolution have been modelled on the basis of estimated maximum temperature in order to evaluate the cooling path to present day temperatures outputs from modelling indicate that 1 the amount of net uplift and denudation is in the order of 1000 m and 2 the last important phase of exhumation occurred during late miocene early pliocene time therefore challenging the prevailing idea of substantial uplift linked to the observed shelf progradation along the margin as a result of the plio pleistocene glaciations the timing of the distinct exhumation event documented here may be instead attributed to different mechanisms these may include basin inversion widespread on the nw european margin that is probably related to local changes in the north atlantic spreading vector while other mechanisms may include thermal and lithospheric scale anomalies observed at the northwestern corner of the barents svalbard shelf

crustal structure of northwestern svalbard and the adjacent yermak plateau evidence for oligocene detachment tectonics and non volcanic breakup summary in 1999 new seismic refraction data were collected off northwestern svalbard and the adjacent yermak plateau a 260 km long profile provides detailed velocity information for the northeastern edge of the eurasian continent and the adjacent yermak plateau north of forlandsundet graben the depth of the moho varies between 23 and 28 km and remains at this depth to the northern edge of the profile at 81 n the crustal lithology off western svalbard can be related to the basement province west of the raudfjorden fault zone off the northern shoreline of svalbard the structure of the tertiary danskoya basin is mapped below this a late silurian early devonian basin with seismic velocities between 5 1 and 5 8 km s 1 and a thickness of up to 8 km is present a palaeozoic sequence of up to 6 km thickness is expected below the tertiary cover north of the danskoya basin an earlier suggestion that oligocene rift processes affected the southern yermak plateau is confirmed a detachment structure is situated below the palaeozoic basin below danskoya basin which is probably a consequence of simple shear tectonics the middle crust exhibits low seismic velocities above the detachment fault the lowermost crust beneath is slightly contaminated by mantle derived melts which is deduced by the slightly elevated velocities of the lowermost crust these melts can be attributed to decompressive melting caused by modest uplift of the moho during stretching the velocity depth model provides no evidence for large magmatic activity which implies a non volcanic rifted margin history this leads to the assumption that the proposed yermak hotspot during the breakup of svalbard from northern greenland did not exist

meso cenozoic morphotectonic evolution of southern norway neogene domal uplift inferred from apatite fission track thermochronology apatite fission track aft thermochronology of precambrian and paleozoic basement samples from southern norway reveals a post paleozoic exhumation history related to offshore mesozoic and cenozoic extensional basin development the data indicate two major phases of rapid exhumation a first mesozoic phase started in the triassic 220 ma in the east and south of the study area and migrated to the west where jurassic 160 ma ages of exhumation predominate a second event is indicated by thermal history modeling of aft ages and track length distributions it is inferred to be neogene in age initiated at about 30 ma and it produced a domal pattern of aft isochrons which follow present day topographic elevation youngest aft ages 100 ma are encountered at sealevel in the inner fjords near the areas of highest topography ages increase radially outward to the mountain peaks and the coastlines forward modeling of age elevation patterns suggests that mesozoic geothermal gradients were 10 15 c km higher than the present value of 20 c km during the triassic and jurassic a total of 1 3 3 5 km of overburden was removed from the study area assuming a 30 c km geothermal gradient for that period we attribute this to rift margin erosion as a result of erosional base level lowering and flank uplift as evidenced by thick continental clastic sequences deposited in triassic jurassic half grabens in the north sea basins we propose that 1 5 2 5 km of neogene exhumation were a result of late stage domal uplift this is supported by basinward dipping pre neogene strata in the basins surrounding southern norway and the infill of a 1 to 2 km thick neogene sediment wedge containing various internal unconformities domal uplift probably started in the late oligocene may have been amplified in the pliocene and was overprinted by plio pleistocene glacial erosion maximum neogene tectonic uplift is estimated at approximately 1 1 5 km radially decreasing outward to a value 500 m near the shoreline neogene domal uplift is coincident with oligocene and pliocene plate reorganizations in the north atlantic similar neogene domes are found around the norwegian greenland sea i e svalbard and the barents sea northern norway east greenland suggesting a regional tectonic cause the onset of neogene uplift postdates major volcanism and continental breakup by 25 m y and predates plio pleistocene glaciations its origin is possibly a combination of induced mantle convection resulting in thermal erosion of the lithosphere and the operation of intraplate stresses

analysis and 3d inversion of magnetotelluric crooked profile data from central svalbard for geothermal application abstract broadband 0 001 1000 s magnetotelluric mt data along a crooked profile collected to investigate the geothermal potential on spitsbergen could not be fully explained by two dimensional 2d models hence we interpret the data with three dimensional 3d inversion herein to better accommodate 3d features and nearby off profile resistivity structures the full mt impedance tensor data together with the tipper were inverted as a model control a detailed bathymetry is systematically incorporated in the inversion our results from testing different inversion settings emphasised that appropriately choosing and tuning the starting model data error floor and the model regularization together are crucial to obtain optimum benefit from mt field data through the 3d inversion we reproduced out of quadrant impedance components and obtained an overall satisfactory data fit rms 1 05 the final 3d resistivity model displays a complex geology of the near surface region 2 km conductive anomaly confirming the regional nature of the fault the fault zone is positioned between two uplifted basement blocks 1000 m of presumably pre devonian caledonian metamorphic rocks and the fault may have been responsible for deformation in the overlying paleozoic mesozoic unit upper crustal conductive anomalies

message in a stainless steel bottle thrown into deep geological time abstract in the 60th year after the placing of the corner stone under the polish polar station at hornsund ppsh spitsbergen svalbard norway a new capsule has been laid down in the vicinity of the ppsh it is made of stainless steel and includes five stainless steel containers each carrying a message on different themes in our lives the message is written in the language of objects each of them speaking for itself the capsule with containers has been buried in a 4 2 m deep hole drilled for scientific purposes the host rocks for the capsule are the precambrian gneisses representing the basement of the polar archipelago we estimate that the capsule now some 6 m a s l will appear again on the surface after ca 0 5 ma due to the combined effect of uplift and erosion we also believe that it will be found and the message understood contrary to other messages sent by mankind into space

intrusions what drives them abstract the driving mechanism for the observed interleaving of water masses is generally assumed to be double diffusive mixing however some observations of intrusions have been made in regions where the mean stratification is stable to double diffusive mixing it has been hypothesized that a finite amplitude disturbance must occur to produce regions where the stratification allows double diffusive mixing or that an instability due to differences in the molecular diffusivity of salinity and temperature produces the desired stratification for double diffusive mixing to start there is also the possibility of a differential vertical flux of salt and heat due to incomplete mixing by turbulence the basis of this idea is described in this paper growth rates vertical scales and cross frontal slopes of intrusions predicted by this process are compared to those predicted by double diffusive mixing

intrusions in double diffusively stable arctic waters evidence for differential mixing abstract intrusions like those observed in double diffusively stable regions of the arctic ocean can grow from uniform ambient temperature and salinity gradients if diapycnal mixing of these two components differs assuming this to be the driving mechanism the observed 40 60 m intrusion heights constrain the turbulent diffusivity for heat to be less than about 0 01 cm2 s 1 and the salt to heat turbulent diffusivity ratio to be greater than about 0 6 if the diffusivities are constant observations indicate that the intrusions slope across isopycnals in a sense that is consistent with such a scenario although the along intrusion density ratio is greater than that predicted by linear theory for the fastest growing intrusions numerical solutions for growing intrusions resemble observed temperature and salinity profiles

the erosional and uplift history of ne atlantic passive margins constraints on a passing plume new apatite fission track analyses from nw britain indicate that a maximum of 2 5 km of erosion has occurred there during the cenozoic similar to values for se greenland and the east greenland coast north of scoresby sund the erosion may have been facilitated by magmatic underplating during break up however at kangerdlugssuaq east greenland 4 6 km of erosion is measured since 45 ma lower mid eocene marine sedimentary rocks overlying the lavas on the blosseville coast indicate that magmatic underplating on the central greenland coast substantially post dated flood volcanism and break up behaviour not predicted by simple plume rift models subsidence reconstructions of the hebrides shelf and the east and west greenland coasts show that rapid dynamic uplift was effectively synchronous at 63 ma and preceded volcanism by c 400 m is compatible with a mantle temperature anomaly of c 100 c these data suggest very rapid lateral flow of the impacting iceland plume head the predicted crossing of the plume by the east greenland coast in the mid late eocene would account for post rift magmatic underplating and dynamic support on the greenland but not the european side of the north atlantic basin

the diffusive regime of double diffusive convection the diffusive regime of double diffusive convection is discussed with a particular focus on unresolved issues that are holding up the development of large scale parameterizations some of these issues such as interfacial transports and layer interface interactions may be studied in isolation laboratory work should help with these however we must also face more difficult matters that relate to oceanic phenomena that are not represented easily in the laboratory these lie beneath some fundamental questions about how double diffusive structures are formed in the ocean and how they evolve in the competitive ocean environment

pliocene exhumation and landscape evolution of central north island new zealand the role of the upper mantle 1 mudstone porosity analyses show that over 2 km of exhumation has occurred in central north island new zealand since 5 ma this combined with a coeval surface uplift of 500 m indicates a maximum 2 5 km of rock uplift in central north island the magnitude and wavelength 400 km of the rock uplift is similar to some topographic doming observed in continental areas associated with mantle upwelling yet central north island is recognized as a region of back arc extension marine terraces 100 150 km from the center of maximum exhumation show uplift rates of 0 2 0 3 mm yr 1 consistent with about 1 km of exhumation if averaged over 4 5 myr which compares well with mudstone porosity analyses seismic attenuation and slow pn velocities indicate that a thermal anomaly in the upper mantle is the source of this rock uplift the rock uplift may be explained by the replacement of a 100 km thick mantle lid by asthenosphere with a density 66 kg m 3 less than the lid about half this density contrast can be explained by thermal expansion and the rest is ascribed to partial melts in the upper mantle southward migration for the locus of maximum rock uplift is consistent with the zone of maximum incision erosion being 50 km south of the southernmost volcano such a migration is in keeping with other geological markers of volcanic and thermal phenomena and further strengthens the link of landscape evolution at active continental margins with processes in the mantle

cenozoic erosion and the preglacial uplift of the svalbard barents sea region abstract the creation of the huge fans observed in the western barents sea margin can only be explained by assuming extremely high glacial erosion rates in the barents sea area glacial processes capable of producing such high erosion rates have been proposed but require the largest part of the preglacial barents sea to be subaerial to investigate the validity of these proposals we have attempted to reconstruct the western preglacial barents sea our approach was to combine erosion maps based on prepublished data into a single mean valued erosion map covering the whole western barents sea and consequently use it together with a simple airy isostatic model to obtain a first rough estimate of the preglacial topography and bathymetry of the western barents sea margin the mean valued erosion map presented herein is in good volumetric agreement with the sediments deposited in the western barents sea margin areas and as a direct consequence of the averaging procedures employed in its construction we can safely assume that it is the most reliable erosion map based on the available information by comparing the preglacial sequences with the glacial sequences in the fans we have concluded that 1 2 to 2 3 of the total cenozoic erosion was glacial in origin and therefore a rough reconstruction of the preglacial relief of the western barents sea could be obtained the results show a subaerial preglacial barents sea thus during interglacials and interstadials the area may have been partly glaciated and intensively eroded up to 1 mm y while during relatively brief periods of peak glaciation with grounded ice extending to the shelf edge sediments have been evacuated and deposited at the margins at high rates the interplay between erosion and uplift represents a typical chicken and egg problem initial uplift is followed by intensive glacial erosion compensated by isostatic uplift which in turn leads to the maintenance of an elevated and glaciated terrain the information we have on the initial tectonic uplift suggests that the most likely mechanism to cause an uplift of the dimensions and magnitude of the one observed in the barents sea is a thermal mechanism

the scaling of hydraulic conductivity in rock fracture zones beyond the scale of a few meters fracture traces as viewed on aerial photographs represent fracture zones thus for bulk fractured rock permeability the hydraulic properties of fracture zones are important here observations on joint zones in sandstones from western norway are used to build a quantitative model relating joint zone length and effective hydraulic conductivity using simple rules for hydraulic conductors in series and parallel applied to joint zone geometry the effective hydraulic aperture the aperture of a single parallel walled channel that conducts the same flow is estimated for 72 joint zones of known length a power law relation between trace length l and effective hydraulic aperture be with an effective exponent of around 0 27 is found which may extend to km scales this exponent contrasts with values of 0 5 to 2 0 reported for veins

the late mesozoic and cenozoic evolution of the sorvestsnaget basin a tectonostratigraphic mirror for regional events along the southwestern barents sea margin abstract seismic interpretation and mapping of the sorvestsnaget basin at the southwestern barents sea margin has revealed a complex basin history related to large scale plate tectonic movements in the norwegian greenland sea area the pre cenozoic evolution of the sorvestsnaget basin is poorly understood due to lack of well data and poor seismic data quality regional pre cenozoic geologic models that includes the sorvestsnaget basin should await more and better data prior to break up and sea floor spreading in the norwegian greenland sea late cretaceous and palaeocene shear movements along the senja fracture zone led to structuring and possibly elevation of the southern part of the basin as sea floor spreading took place and propagated northwards along the senja fracture zone the western areas of the basin were uplifted and eroded two large and two smaller intrabasinal features in the southern sorvestsnaget basin are characterised by a low values on the gravimetric anomaly maps b surrounding synforms and c little response on magnetic anomaly maps the features have been interpreted as salt structures the tertiary evolution of intrabasinal salt structures seems to have been governed by extensional faulting and subsidence of the margin during the late palaeocene and eocene periods the oligocene and miocene periods were characterised by local and regional uplift of the sorvestsnaget basin respectively during these periods the area in particular the western part of the basin was subjected to transpressional compressional forces which can be tentatively correlated to contemporaneous large scale plate reorganisations and variations of sea floor spreading rates in the norwegian greenland sea the oligocene and miocene transpressional compressional events influenced the salt structures and is here suggested to be partially responsible for the complex expression of the largest salt structures the late neogene and pleistocene periods are represented by a thick westward prograding wedge indicating subsiden3e with coinciding high sediment input to and minor adjustment of the salt structures in the sorvestsnaget basin

evidence for post early eocene tectonic activity in southeastern ireland the role played by cenozoic deformation in denudation and landscape development in ireland has historically been difficult to assess because of the lack of widespread pre glacial cenozoic deposits onshore here we combine analysis of apatite fission track data and geomorphic observations to place constraints on the timing kinematics and magnitude of onshore deformation in southeastern ireland relationships between apatite fission track central age and elevation for samples from the wicklow and blackstairs mountains and tullow lowland suggest that these rocks record an exhumed apatite partial annealing zone which after cooling was dismembered by differential vertical displacements of up to several hundred metres we use inverted models of sample thermal history to show that samples across the region experienced very similar thermal histories up to and including a cooling event in late paleocene or early eocene time this effectively rules out strongly spatially heterogeneous denudation and implies that differential rock uplift occurred in post early eocene time the central age elevation relationships define at least three spatial domains with internally consistent apatite fission track data separated by known faults or topographic escarpments geomorphic analysis of these structures shows that patterns of catchment incision and sinuosity as well as the presence of antecedent drainage are best explained by differential vertical displacements at or near the domain boundaries the kinematics and magnitudes of these displacements are consistent with those implied by the apatite fission track results and are compatible with other examples of known cenozoic deformation from ireland and the adjacent continental margin

oceanic thermohaline intrusions observations intrusions are commonly observed in the upper deep and coastal oceans and are closely linked to lateral fluxes of heat salt and momentum this is a review of observations of intrusions and the results of comparisons of properties such as scale slopes microstructure activity and fluxes with theoretical models a summary of estimates of lateral heat fluxes indicates a wide range of lateral diffusivities we conclude by noting that our present knowledge is insufficient to predict the structure length scales and lateral fluxes of thermohaline intrusions with confidence and list a number of unresolved questions suggestions are made for compilation of existing data into a database for exploratory analysis and testing of theoretical hypotheses an outline is given of a potential collaborative field experiment using ctd fluorescent dye and microstructure observations

evolution of a mediterranean salt lens scalar properties abstract the evolution of a mediterranean salt lens meddy over a two year period is examined several nondimensional numbers can be used to describe the overall decay in the structure of the moddy two rossby numbers one using the central relative vorticity and another using the radius and velocity of the azimuthal velocity maximum did not change over the two year period however the burger number n2h2 f2l2 increased as the meddy decayed another burger number the ratio of total kinetic energy to total available potential energy decreased from 1 1 to 0 6 over a one year period the rates at which the meddy lost salt and heat are consistent with estimates of horizontal fluxes by intrusions a horizontal diffusivity of o 5 m2 s 1 is needed if this flux by intrusions is parameterized by an eddy coefficient simple models of the evolution of an isolated eddy by horizontal and vertical mixing of mass and momentum are examined these simple attempts to explain the evolution of the meddy suggest more c

differential mixing by breaking internal waves 1 diapycnal mixing occurs at spatial scales which are unresolved in numerical models of the ocean thus it is essential to understand small scale mixing processes properly in order to parameterize their fluxes in numerical models especially those used in climate studies in the ocean diapycnal mixing is actually a process of mixing two variables heat or temperature and salt or salinity which both contribute to the density of ocean water presently numerical ocean models parameterize the unresolved diapycnal fluxes as an eddy diffusivity times a mean property gradient normal to the isopycnals most models also use the same eddy diffusivities for heat and salt mixing in the ocean interior is due mainly to breaking internal waves in this paper vertical fluxes and diffusivities of two tracers with different molecular diffusivities were obtained for a wide range of breaking internal wave activity in the laboratory

episodic cenozoic tectonism and the development of the nw european passive continental margin the north atlantic margins are archetypally passive yet they have experienced post rift vertical movements of up to kilometre scale the cenozoic history of such movements along the nw european margin from ireland to mid norway is examined by integrating published analyses of uplift and subsidence with higher resolution tectono stratigraphic indicators of relative movements including results from the stratagem project three episodes of epeirogenic movement are identified in the early mid and late cenozoic distinct from at least one phase of compressive tectonism two forms of epeirogenic movement are recognised referred to as tilting coeval subsidence and uplift rotations 1 over distances of 100s of kilometres and sagging strongly differential subsidence rotations up to 4 over distances 100 km each epeirogenic episode involved relatively rapid 10 ma km scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity bounded stratigraphic units early cenozoic tilting late paleocene to early eocene c 60 50 ma caused the basinward progradation of shelf slope wedges from elongate uplifts along the inner continental margin and from offshore highs mid cenozoic sagging late eocene to early oligocene c 35 25 ma ended wedge progradation and caused the onset of contourite deposition in deep water basins late cenozoic tilting early pliocene to present 4 0 5 ma again caused the basinward progradation of shelf slope wedges from uplifts along the inner margin including broad dome like features and from offshore highs the early mid and late cenozoic epeirogenic episodes coincided with atlantic plate reorganisations but the observed km scale tectonic movements are too large to be accounted for as flexural deflections due to intra plate stress variations mantle lithosphere interactions are implied but the succession of epeirogenic episodes of differing form are difficult to reconcile with the various syn to post rift mechanisms of permanent and or transient movements proposed in the hypothetical context of a plume beneath iceland the epeirogenic movements can be explained as dynamic topographic responses to changing forms of small scale convective flow in the upper mantle tilting as coeval upwelling and downwelling above an edge driven convection cell sagging as a loss of dynamic support above a former upwelling the inferred cenozoic succession of epeirogenic tilting sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening a process that may also be the underlying cause of plate reorganisations the postulated episodes of flow reorganisation in the ne atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin as well as on other atlantic type passive margins

timing and mechanisms of north atlantic cenozoic uplift evidence for mantle upwelling postrift domal uplift patterns are a distinct feauture of northern north atlantic margins on the basis of apatite fission track data offshore seismic stratigraphy geomorphology gravity and seismic tomography we argue that southern norway is characterized by predominantly neogene domal uplift currently available data suggest similar processes for other uplifted regions such as spitsbergen northern norway the british isles aad parts of east greenland

modelling late cenozoic isostatic elevation changes in storfjorden nw barents sea an indication of varying erosional regimes abstract storfjorden fan off nw barents sea contains 116 103 km3 of sediments which are interpreted to have been derived from a drainage area measuring 69 103 km2 during the last ca 2 3 m y published isopach maps of the storfjorden deposits have been used in a numerical model to simulate late cenozoic isostatic elevation changes in the storfjorden drainage area the volume estimates in the depositional area for various time intervals together with the corrected density estimates for the eroded sediments indicate that 1100 m of sediments have been eroded from the drainage area during the past ca 2 3 m y the results of isostatic modelling show three distinct topographic phases during this time a subaerial phase 2 3 1 4 ma a transition phase 1 4 0 8 ma and a submarine phase 0 8 ma present in addition sediment yield values from the drainage area during various intervals have been calculated highest sediment yield values are obtained for the subaerial phase while those for the submerged phase are the lowest the age estimates are somewhat uncertain but based on the modelling results together with the estimates of sediment yield it is suggested that the changes in elevation and sediment yield values can be linked to the documented late cenozoic paleoclimatic shifts along the western svalbard barents sea margin the doubling of sediment yield in the 1 6 1 4 ma time from the preceding 2 3 1 6 ma interval despite lower topography is related to major ice expansion under a subaerial scenario the lowest yield values during the past 0 8 m y despite repeated glacial advances are attributed to submergence of the area below sea level such that periods of erosion were limited to peak glacials with negligible erosion during the intervening interstadials and interglacials