resurgent strike slip duplex development along the hitra snasa and verran faults more trondelag fault zone central norway abstract lineament analysis of the ene wsw verran and hitra snasa faults of the long lived more trondelag fault zone mtfz has revealed the presence of a complex array of anastomosing faults and fractures this has the geometric configuration of a major dextral strike slip fault zone and compares well with characteristic patterns of braided wrench faulting e g the san andreas fault system of california the fault array recognized in conjunction with the verran fault is clearly post caledonian and is considered to define a dextral strike slip duplex system associated with the parallel hitra snasa fault are riedel like structures which tend to point to an earlier component of sinistral movement rock products present along the hitra snasa fault and its secondary faults comprise mylonites hydrothermally altered rocks and small scale recrystallized breccias along the main verran fault evidence of late polyphasal deformation is seen in several discrete episodes of brecciation hydrothermal alteration and locally pervasive prehnite and stilbite veining the fault structures occurring along the hitra snasa and verran faults are thought to have originated as a sinistral fault system of late devonian age especially for the hitra snasa lineament subsequently strike slip movement reversed in sense and shifted locus towards the verran fault system during the late jurassic or early cretaceous during this strike slip reversal some earlier fractures related to the sinistral system were rejuvenated within the stress field of the evolving dextral duplex system strike slip displacements of a similar age are known from fault complexes on the norwegian continental shelf and in the northern north sea the regional picture indicates that the mtfz was almost certainly linked to the fault systems of northern scotland prior to the opening of the viking graben

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

cenozoic and late mesozoic stratigraphy and subsidence history of the norwegian margin the stratigraphy of the passive continental margin off norway is mapped utilizing both deep sea drilling project dsdp data at five sites on the outer margin and multichannel seismic mcs data collected by lamont doherty geological observatory distinct units in the acoustic stratigraphy are tied to biostratigraphic and lithostratigraphic units in the drill data and mapped throughout most of the margin stratigraphy of the pre lower eocene section not encountered in drilling is inferred from depositional patterns and correlation with the continental shelf sequences the stratigraphy of which has been developed independently from detailed surveys the margin can be divided into three physiographic provinces two broad shelf and slope regions separated by the jan mayen fracture zone and the steep narrow shelf and slope off the lofoten islands each experienced a separate cenozoic subsidence history the voring plateau is partly underlain by oceanic crust it subsided nearly 1 000 m less than expected from thermal contraction but it did so following the development of a relatively deep water environment in the paleocene north of the voring plateau the margin may have subsided a few hundred metres more than thermal studies had predicted there is no evidence for a phase of extensional deformation associated with the inception of spreading the youngest faulted level occurs at the late jurassic level preceding sea floor spreading by nearly 100 ma and deformation in the cretaceous section is characterized by large uplift structures that may be of halokinetic origin the physiographic provinces as well as the cenozoic subsidence patterns along the margin appear to be related to the style and extent of mesozoic basin development and tectonics along the margin

forced folding and basement detached normal faulting in the haltenbanken area offshore norway triassic evaporites affected the structural development of the haltenbanken area of offshore norway during the late jurassic and early cretaceous by mechanically isolating triassic and younger strata from older strata and basement many folds in the haltenbanken area are forced folds above basement involved normal faults forced folds formed at least in part because triassic evaporites behaved ductilely decoupling overlying strata from underlying faulted strata and basement seismic data show that these forced folds are asymmetric flexures that affect lower cretaceous jurassic and triassic strata strata beneath the traiassic evaporites are faulted some forced folds die out along strike into and are cut by basement involved normal faults folding predominated above salt swells where decoupling was enhanced whereas faulting occurred on the flanks of salt swells where salt thicknesses were reduced and decoupling was less effective many normal faults in the haltenbanken area are basement detached and flatten within the triassic evaporites seismic data show that rollover anticlines and antithetic normal faults affect lower cretaceous jurassic and triassic strata within the hanging walls of these basement detached normal faults strata beneath the evaporites are not affected by this deformation some basement detached normal faults may be secondary structures associated with forced folding others especially thosemore with large displacements may have formed in response to gravity sliding less

aspects of basin inversion in southern britain the wessex basin of southern england a permian to cretaceous extensional basin can be structurally divided into a set of constituent asymmetrical graben bounded by major e w trending zones of en echelon syn depositional normal faults the graben were inverted in late cretaceous and tertiary times by compressive stresses oriented roughly north south inversion structures fall into two related categories regional upwarps overlie earlier graben depocentres and were formed by bulk shortening of the graben fill superimposed upon and geographically delimiting the regional upwarps are roughly east west trending linear zones of en echelon inversion structures these coincide with the earlier graben bounding faults and typically have the form of monoclinal or periclinal flexures each underlain by a partially reversed normal fault the linear reverse fault monocline inversion structures were a relatively inefficient method of basin shortening because upper crustal faults in the region steepen upward markedly reversal of these faults under compression resulted in a shortening discrepancy at shallow depths locally particularly in south dorset this was overcome by bucklefolding and low angle reverse faulting which increased the amount of shortening attainable across the linear inversion structures elsewhere however the shortening discrepancy was accommodated by bulk shortening and regional upwarp of the graben sedimentary fill this occurred preferentially in those graben containing young poorly lithified and therefore weak sediments thus the early cretaceous depocentres of the weald and channel basins were strongly upwarped with axial uplifts of over 1000 m conversely graben having older more lithified sequences suffered little regional upwarp shortening primarily by fault reversal along the linear inversion structures the amount of crustal shortening which accompanied inversion was considerably less than the earlier crustal extension

indication of transpressional tectonics in the gullfaks oil field northern north sea abstract new seismic data have provided important insights into the tectonic evolution of the gullfaks area and the northern north sea extensional tectonics which predominate in the north sea basin were accompanied by subordinate compressional deformation in the gullfaks field involving the formation of thrust and reverse faults and compressional folds the local compression is interpreted as a product of dextral strike slip movement along the ne sw trend of the tampen spur in late jurassic to early cretaceous times in a regional context the strike slip movement may be related to dextral strike slip movements along the more trondelag fault zone further to the northeast

1300 m high rising bubbles from mud volcanoes at 2080m in the black sea hydroacoustic characteristics and temporal variability a mud volcano area in the deep waters 2000 m of the black sea was studied by hydroacoustic measurements during several cruises between january 2002 and june 2004 gas bubbles in the water column give strong backscatter signals and thus can be detected even in great water depths by echosounders as the 38 khz ek500 scientific split beam system that was used during the surveys because of their shape in echograms and to differentiate against geochemical plumes and real upwelling bubble water plumes we call these hydroacoustic manifestations of bubbles in the water column flares digital recording and processing of the data allows a 3d visualization and data comparison over the entire observation period without artefacts caused by changing system settings during our surveys we discovered bubble release from three separate mud volcanoes dvurechenskiy dmv vodianitskiy vmv and the nameless seep site nss in about 2080 m water depth simultaneously bubble release was observed between 9 june 2003 and 5 june 2004 the most frequently surveyed dmv was found to be inactive during very intensive studies in january 2002 the first activity was observed on 27 june 2002 which finally ceased between 5 and 15 june 2004 after a period of continuously decreasing activity this observed 2 yr bubble release period at a mud volcano may give an indication for the duration of active periods the absence of short term variations within days or hours may indicate that the bubble release from the observed mud volcanoes does not undergo rapid changes the recorded echograms show that bubbles rise about 1300 m high through the water column to a final water depth of about 770 m which is 75 m below the phase boundary of pure methane hydrate in the black sea with a release depth from 2068 m and a detected rise height of 1300 m the flare at vmv is among the deepest and highest reported so far and gives evidence of highly extended bubble life times up to 108 min in deep marine environments to better understand how a methane bubble gas analyses of the pore water and gas hydrate gave 99 4 methane can rise so high without dissolving we applied a recently developed bubble dissolution model that takes into account a decreased mass transfer due to an immediately formed gas hydrate rim using the hydroacoustically determined bubble rising speeds 19 22 cm s at the bottom 12 14 cm s at the flare top and the relation between the rising speed of dirty gas hydrate rimmed bubbles and the bubble size we could validate that a gas hydrate rimmed bubble with a diameter of 9 mm could survive the 1300 m rise through the water column before it is finally dissolved a diameter of about 9 mm is reasonable for bubbles released at seep sites and the coincidence between the observed bubble rising speed and the model approach of a 9 mm bubble supports the assumption of gas hydrate rimmed bubbles

early cenozoic crust at the norwegian continental margin and the conjugate jan mayen ridge multichannel seismic profiles at the voring plateau margin off norway and the northern jan mayen ridge have provided a framework for the early tertiary evolutionary history of these areas which were adjacent prior to the opening of the norwegian sea we propose that their paleogene evolution is quite similar and that the two acoustic basement reflectors ee and jo were formed in the early eocene by extrusion of flow basalts from the time of opening to about anomaly 23 time oceanic seafloor was generated by icelandic type spreading during that time the central jan mayen fracture was the main transform the seaward dipping reflector sequences are flow basalts generated by the icelandic spreading the existence of less well developed dipping sequences seaward of the primary ones probably reflects that these regions submerged later because of higher initial elevation during the early eocene subaerial spreading episode which is related to the north atlantic volcanic province basalt flows also covered the adjacent thinned and heavily intruded continental crust it is proposed that the continent ocean boundary is located just landward of anomaly 24b a short distance seaward of the voring plateau escarpment reflector k is only recognized landward of this boundary in a region of transitional crust the escarpment experienced syndepositional faulting and the most elevated parts of the voring marginal high did not subside below shallow water depths before oligocene miocene time we suggest that the voring margin and the jan mayen ridge represent volcanic passive margins the evolution of this margin type may relate to initial uplift due to rifting in previously thinned crust

basin structure on the norwegian margin from analysis of digitally recorded sonobuoys during r v robert d conrad cruise 21 a large number of sonobuoys were recorded in the voring more and adjacent basins at the margin off norway the digital sonobuoy data have been transformed into the domain of intercept time tau and ray parameter p and inverted by the tau sum method to obtain better definition of the near seafloor velocities using also the precritical energy a move out correction has been applied to the tau p data conventional analyses of the x t data were also performed in general the various types of analyses complement each other and should be used interactively together with forward modeling to obtain the optimal velocity depth function the sonobuoy results have outlined in a regional sense the pre cenozoic sedimentary basin at the margin this basin attains a maximum sediment thickness of 8 10 km of which only the upper half is defined by seismic reflection profiling at the outer margin the marginal escarpments form major discontinuities in the lateral velocity distribution the survey has proven that sonobuoy profiles recorded during standard seismic reflection profiling in major marginal basins may provide important new information particularly about the deeper parts of the basins that is not directly available from the reflection profiles

natural marine seepage blowout contribution to atmospheric methane the release of methane sequestered within deep sea methane hydrates is postulated as a mechanism for abrupt climate change however whether emitted seabed methane reaches the atmosphere is debatable we observed methane emissions for a blowout from a shallow 22 m hydrocarbon seep the emission from the blowout was determined from atmospheric plume measurements simulations suggest a 1 1 gas loss to dissolution compared to 10 loss for a typical low flux bubble plume transfer to the atmosphere primarily was enhanced by the rapid upwelling flows induced by the massive discharge this mechanism could allow methane suddenly released from deeper 250 m waters to contribute significantly to atmospheric methane budgets copyright 2006 by the american geophysical union

post cretaceous uplift events on the voring continental margin the early tertiary voring margin off central norway records several distinct uplift events that have strongly influenced the deposition and composition of cenozoic sediments and may be linked with climatic change the events constitute two types uplift as a precursor to the opening of the norwegian greenland sea and subsequent intraplate deformation the late cretaceous paleocene dynamic uplift associated with the formation of the volcanic voring margin created a main western source area for the paleogene voring basin sediments the fennoscandian epeirogenic uplift which probably began in the late oligocene and continued through the pliocene was followed by glacial rebound deep erosion of the landmass left a huge late neogene sedimentary wedge along the margin and differential loading caused regional intrabasinal arching and local diapirism

dimensions of the late cretaceous paleocene northeast atlantic rift derived from cenozoic subsidence abstract the distribution of cenozoic subsidence across northeast atlantic volcanic margins have been evaluated to define the width of the rift zone and magnitude of extensional deformation the subsidence profiles are corrected for the effects of lower crustal magmatic bodies emplaced during continental break up the dimensions of the bodies have been derived from the crustal velocity structure the width of the late cretaceous paleocene northeast atlantic rift zone was more than 300 km and the lithospheric extension factor increases gradually towards the line of continental separation a large number of high quality seismic reflection data tied to scientific and commercial wells reveals that the initiation of extensional deformation preceded continental separation by 18 m y on the voring margin off norway these results show that the northeast atlantic volcanic margins commonly considered as typical volcanic margins indeed have similar dimensions as non volcanic margins and as continental rifts thus these margins contrast significantly with previously suggested evolutionary models based on narrow rift zones and formation during rapid lithospheric failure the wide rift is compatible with volume of igneous rocks observed along these margins and with a thermal anomaly similar to that associated with production of northeast atlantic oceanic lithosphere

mesozoic sedimentary rocks in edoyfjorden and beitstadfjorden central norway implications for the structural history of the more trondelag fault zone abstract a seismic reflection profiling survey has indicated the existence of downfaulted mesozoic sequences in edoyfjorden south of smola trondheimsleia and in beitstadfjorden these rocks are preserved in halfgrabens within the more trondelag fault zone mtfz which is interpreted as an important structural element in central norway the mtfz probably originated in the palaeozoic and at least two phases of reactivation can be recognized in the mesozoic sequences

cretaceous tectonics off mid norway implications for the rockall and faeroe shetland troughs between 62 and 68 n on the norwegian continental margin the hypothesis of a cretaceous or permian ocean extending northwards from the rockall trough can be tested with data from commercial reflection seismic profiles two major mesozoic basin systems occur the helgeland basin is a late triassic and early jurassic depocentre with a thin upper jurassic and cretaceous cover except in two late cretaceous sub basins the more lnner voring basin system is a middle to late cretaceous depocentre in which the pre cretaceous section is deeply buried and rarely seen on seismic profiles the two basin systems are separated by a complex zone of faulted 9marginal highs9 active in jurassic times and reactivated during cretaceous times pre cenomanian lavas or sills are interpreted within the more basin and a pre cretaceous block faulted sequence can be identified across the inner voring basin except in a narrow axial zone these features suggest the presence of an extremely narrow zone of oceanic crust of cretaceous age fault patterns confirm a major tectonic episode of mid cretaceous age the geology off mid norway supports a mid cretaceous age for sea floor spreading in the rockall trough but suggests that the generated oceanic crust narrowed northwards and that plate motion was partially accommodated by dextral transcurrent faulting reconstruction of jurassic tectonic trends in nw europe must allow for subsequent cretaceous distortion

fate of rising methane bubbles in stratified waters how much methane reaches the atmosphere there is growing concern about the transfer of methane originating from water bodies to the atmosphere methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport this work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere the bubble model predicts the evolving bubble size gas composition and rise distance and is suitable for almost all aquatic environments the model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep oxic saline water with excellent results methane bubbles from within the hydrate stability zone typically below 500 m water depth in the ocean are believed to form an outer hydrate rim to explain the subsequent slow dissolution a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone the calibrated model explains the impressively tall flares 1300 m observed in the hydrate stability zone of the black sea this study suggests that only a small amount of methane reaches the surface at active seep sites in the black sea and this only from very shallow water areas 100 m clearly the black sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere although substantial amounts of methane may reach the surface in shallow lakes and reservoirs

model simulations of tsunamis generated by the storegga slides abstract a mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of water waves generated by the submarine storegga slides on the norwegian continental slope the equations are solved numerically by a finite difference technique computations of wave amplification effects reveal run up heights for the second storegga slide between 3 and 5 m in exposed areas along the eastern coast of greenland iceland and scotland and the western coast of norway the calculated run up heights agree remarkably well with possible tsunami wave heights deduced from geological evidences along the eastern coast of scotland the generated wave heights are strongly dependent on the acceleration of the slide the effects of shear stress at the interface between the water and the slide body has turned out to be important

evidence for a thick oceanic crust adjacent to the norwegian margin the oceanic crust created during this first few million years of accretion in the norwegian greenland sea lies at an unusually shallow depth for its age has a smooth upper surface and in many places the results of multichannel seismic reflection profiling reveal that its upper layers comprise a remarkable sequence of arcuate seaward dipping reflectors these have been attributed to lava flows generated during a brief period of subaerial seafloor spreading we describe the results of inversions of digitally recorded sonobuoy measurements and two ship expanded spread profiles collected over the oceanic crust adjacent to the norwegian passive margin we find that the crust of the deep lofoten basin is indistinguishable from normal oceanic crust in thickness and structure closer to the margin we observe up to a four times expansion in thickness of layers with velocities equal to those of oceanic layer 2 while the layer 3 region retains approximately the same thickness the area over which the seaward dipping reflectors can be observed on reflection profiles corresponds to the region of greatest expansion in layer 2 thickness in the very oldest crust immediately adjacent to an escarpment that probably marks the continent ocean boundary we see evidence for a low velocity zone overlying an indistinct reflector that may mark the dyke lava interface in the thick crust comparing the structure of the thick crust to that of eastern iceland we find a strong resemblance especially in the expansion in thickness of material with layer 2 velocities these results support the suggestion that during the earliest stages of spreading extrusive volcanism at the ridge crest was unusually voluminous building a thick pile of lavas erupted from a subaerial spreading center

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

structure of the more basin mid norway continental margin abstract in the more basin offshore mid norway the basis of the cretaceous sequence reaches depths of more than 5000 m the basin is limited on its eastern margin by a system of extensional faults which probably were initiated in the triassic and which were active periodically throughout the aptian the internal basin floor is divided into subbasins by structural highs which are rotated fault blocks presumably rooted in the basement the main structuring of the basin started in late triassic and was followed by accelerating subsidence in the early cretaceous subsidence was interrupted by a mild phase of inversion in the latest cretaceous and a more pronounced inversional phase in the eocene miocene the latter developed folds with wavelengths in the order of kilometers and local low angle reverse faults and the inversion of depocenters

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

tectonic development of the mid norway continental margin abstract the area reviewed covers the mid norway continental margin between latitudes 62 n and 68 n main structural elements as defined at the base cretaceous level are the trondelag platform underlying the inner shelf the more and voring basins located beneath the outer shelf and slope and the more platform and the outer voring plateau forming a base of slope trend of highs sediments contained in the mid norway basin range in age from late palaeozoic to cenozoic the basement was consolidated during the caledonian orogenic cycle devonian and early carboniferous wrench movements along the axis of the arctic north atlantic caledonides are thought to have preceded the namurian onset of crustal extension rifting processes were intermittently active for some 270 my until crustal separation between greenland and fennoscandia was achieved during the early eocene during the evolution of the norwegian greenland sea rift system a stepwise concentration of tectonic activities to its axial zone the area of subsequent continental separation is observed during the late palaeozoic to mid jurassic a broad zone was affected by tensional faulting during the late jurassic and cretaceous the trondelag platform was little affected by faulting whilst major rift systems in the more and voring basins subsided rapidly and their shoulders became concomitantly upwarped during the latest cretaceous and early palaeogene terminal rifting phase only the western more and voring basins were affected by intrusive and extrusive igneous activity following the early eocene crustal separation and the onset of sea floor spreading in the norwegian greenland sea the voring segment of the mid norway marginal basin subsided less rapidly than the more segment during the early and mid tertiary minor compressional deformations affected the voring basin and to a lesser degree the more basin tensional forces dominated the late palaeozoic to early cenozoic evolution of the mid norway basin and effected strain mainly in the area where the crust was weakened by the previous lateral displacements the lithosphere thinned progressively and the effects of the passively upwelling hot asthenospheric material became more pronounced massive dyke invasion of the thinned crust preceded its rupture

double plume integral models for near field mixing in multiphase plumes we present a generalized integral model for multiphase plumes in stratified ambient conditions based on the double plume approach where the plume is composed of a rising multiphase core plume surrounded by a counterflowing outer ring plume of dense fluid the generalized model captures as limiting cases the current approaches in the literature including two fluid and mixed fluid equations continuous and discrete detrainment dispersed phase mass transfer and two models for entrainment in the counterflow region these modeling approaches are compared and validated against both laboratory and field scale data in unstratified conditions all model formulations perform equally well in stratification entrainment in the counterflow region is best represented by correlation to the inner plume velocity instead of the difference between the inner and outer plume velocities the vertical distribution of the exchange between the inner and outer plumes in the models differs from that measured in the prototype due to enhanced entrainment at the detrainment zone and forced entrainment from the collapsing intrusion layer nonetheless the models predict well the length scales and volume fluxes at the detrainment zone and intrusion layer applications are demonstrated for reservoir air bubble plumes the mass transfer and near field mixing in the double plume integral model prove sufficiently accurate to predict the depth of maximum plume rise both the locations of total dissolution of the bubbles and the maximum height of the decelerating plume and the volume flux dissolved constituent mass flux and trap height of the intrusion

an automated approach for extracting barrier island morphology from digital elevation models abstract the response and recovery of a barrier island to extreme storms depends on the elevation of the dune base and crest both of which can vary considerably alongshore and through time quantifying the response to and recovery from storms requires that we can first identify and differentiate the dune s from the beach and back barrier which in turn depends on accurate identification and delineation of the dune toe crest and heel the purpose of this paper is to introduce a multi scale automated approach for extracting beach dune dune toe dune crest and dune heel and barrier island morphology the automated approach introduced here extracts the shoreline and back barrier shoreline based on elevation thresholds and extracts the dune toe dune crest and dune heel based on the average relative relief rr across multiple spatial scales of analysis the multi scale automated rr approach to extracting dune toe dune crest and dune heel based upon relative relief is more objective than traditional approaches because every pixel is analyzed across multiple computational scales and the identification of features is based on the calculated rr values the rr approach out performed contemporary approaches and represents a fast objective means to define important beach and dune features for predicting barrier island response to storms the rr method also does not require that the dune toe crest or heel are spatially continuous which is important because dune morphology is likely naturally variable alongshore