north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

normal fault development during two phases of non coaxial extension an experimental study we use scaled experimental analog models to study the effect of a pre existing fault fabric on fault development during extension in our models a homogeneous layer of wet clay undergoes two noncoaxial phases of extension whose directions differ by up to 45 the normal faults that develop during the first phase create a pronounced fault fabric that influences normal fault development during the second phase in all models the pre existing faults are reactivated during the second phase of extension their sense of slip depends on the angle between the first and second phase extension directions specifically the component of dip slip relative to strike slip decreases as the angle between the first and second phase extension directions increases new normal faults also form during the second phase of extension in all models the number of new fault segments increases as the angle between the first and second phase extension directions increases the orientations of the new normal fault segments are both orthogonal and oblique to the second phase extension direction indicating that both the secondphase extension direction and the pre existing fault fabric control the orientation of new fault segments some of the new normal faults cut and offset the pre existing faults whereas others terminate against them producing complex fault patterns and interactions the modeling results explain fault interactions observed in the jeanne d arc rift basin of offshore newfoundland canada and the reactivation of abyssal hill normal faults at outer highs near subduction zones

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

early stage evolution of growth faults 3d seismic insights from the levant basin eastern mediterranean the geometry and kinematic evolution of small growth faults were analysed from a high resolution 3d seismic dataset located at the margins of the levant basin in the eastern mediterranean the 3d geometry segmentation history and throw distribution of one particular fault was reconstructed to evaluate and illustrate the changes in dimension and displacement distribution that occurred during the transition from purely blind propagation to propagation at the free surface the fault is considered to have grown by blind radial propagation of three main segments that hard linked prior to surface interaction the fault subsequently reached the seabed and continued to accrue displacement as a syn sedimentary fault most of the fault surface area formed during the blind propagation phase but most of the displacement was added during the syn sedimentary phase of the growth history with little increase in surface area the interaction of the fault with the free surface led to a change in the position of the point of maximum displacement as well as modifying the vertical throw distribution the amount of displacement added after this transition from blind fault to growth fault is discussed with respect to existing fault growth models

two stage rifting in the north viking graben area north sea inferences from a new three dimensional subsidence analysis abstract backstripping software from the ifp subtec was used to realize a three dimensional subsidence analysis of the norwegian part of the north viking graben for each considered epoch the software produces restored depth maps of the selected stratigraphic horizons as well as tectonic subsidence maps that allows in addition to classical subsidence curve analysis an overview of the spatial evolution of the studied basin the three dimensional data set consists of maps representing the present day geometry of the graben for this study these maps have been established on the basis of a new interpretation of available seismic lines taking into account new information on the time depth conversion and on the age of the different seismic markers data from wells give detailed information on lateral lithological variations sedimentological information and analysis of the geometry of the seismic markers have allowed palaeobathymetry and eroded thickness maps to be established and discussed with a reasonable confidence computed tectonic subsidence maps define three major events and allow discussion of their origin the lower jurassic thermal subsidence in relation to the previous triassic rifting event the jurassic rifting phase and the subsequent cretaceous post rift thermal subsidence and finally a rapid subsidence event at the beginning of the palaeocene thermal modelling provides theoretical subsidence curves the comparison with the observed curves allows testing of and discrimination between several hypotheses about two parameters the age of the first rifting event permo triassic and its relative amplitude with regard to the jurassic event the corresponding stretching factors were compared with the crustal stretching values observed along the nsdp1 seismic profile it appears that the first extensional phase is clearly triassic beginning about 240 ma and that it is characterized by higher stretching factors than the following jurassic phase the ability of different geological processes to produce both the palaeocene subsidence observed in the graben and the contemporaneous uplift of the basin margins is discussed the preferred interpretation involves buckling of the lithosphere in response to the onset of a compressional stress regime at the end of the cretaceous a simple method assuming uniform stretching is proposed for computing maps of stretching factors for both the jurassic and triassic events

oblique rifting and sequential faulting in the jurassic development of the northern north sea abstract jurassic structural development of the northern north sea has characteristics of oblique rifting this is interpreted to result from an obliquity between jurassic nw se to wnw ese directed extension and a preexisting n s trending zone of deformation related to permo triassic rifting and thinning of the crust the zone of maximum jurassic extension i e the viking and sogn grabens defines a narrow 25 40 km depression which trends diagonally nne ssw across a broader 130 150 km permo triassic basin the jurassic rift zone consists of a system of ene chelon rift segments with changing symmetry along strike bounded by faults oblique to the overall graben envelope sequential jurassic fault development as well as the interference between n s and ne sw striking faults are explained within the context of oblique rifting the early late bajocian oxfordian rift stage was dominated by reactivation of n s striking major faults whereas a number of coeval but smaller faults have a ne sw orientation ne sw striking faults show increasing importance during the jurassic stretching phase and major faults defining this orientation accommodated most of the kimmeridgian volgian extension faults striking nesw are observed to cross cut earlier n s trending faults they interfere with n s trending faults to define faultblocks with rhombohedral shape and they are associated with partial collapse of crestal areas of n s oriented fault blocks to form structural terraces

cenozoic extension in coastal dhofar southern oman implications on the oblique rifting of the gulf of aden a detailed analysis of fault populations that affect the paleocene to early miocene sedimentary succession of southern dhofar allows the definition of a time sequence of paleostresses and the reconstruction of the rifting history of the eastern gulf of aden two distinct phases of n20j and n160j trending extensions took place during the deposition of the synrift dhofar group from late priabonian 35 ma to middle burdigalian 18 ma a period of tectonic instability preceded these events marked by normal and strike slip faulting as early as the mid eocene the two main directions of extension also recorded in southern yemen developed respectively oblique and normal to the n75e trend of the gulf of aden an anticlockwise succession of the two episodes from n20 to n160 only established in yemen accounts for the observed synrift fault pattern which is consistent with the type and geometry of faults predicted in analogue models of oblique rifting a latest phase of ns compression marked by strike slip faulting may represent a far echo of the arabia eurasia collision d 2002 elsevier science b v all rights reserved

fault superimposition and linkage resulting from stress changes during rifting examples from 3d seismic data phitsanulok basin thailand abstract the phitsanulok basin thailand provides examples of changing fault displacement patterns with time associated with faults of different orientations in the northern phitsanulok basin three main stress states have been identified associated with late oligocene recent fault development 1 late oligocene late miocene approximately e w extension n s shmax main rift stage 2 late miocene pliocene transtension to tranpression e w to ne sw shmax late rift stage and 3 pliocene recent very minor faulting e w extension n s shmax post rift stage syn rift faults tend to strike n s but also follow ne sw and nw se trends and are basement involved the late miocene deformation produced a distinctly different type of fault population from the main rift fault set characterized by numerous small displacement tens of metres faults striking predominantly ne sw most of these faults are convergent conjugate sets aligned in discrete zones and nucleated within the sedimentary basin reactivation of main rift faults trends during the late rift stage favoured strike directions between 350 and 50 the displacement characteristics of three large faults within the basin show variations depending upon fault orientation the low angle 23 30 dip western boundary fault 7 km throw displays little discernible difference in the distribution of displacement on fault zone during the different stress states other than increases and decreases in displacement amount smaller faults exhibit a more selective reactivation history than the western boundary fault and are more informative about fault response to a varying stress field activation of the oblique ne sw striking ntm 1 initially produced a fault divided into three segments splaying into n s trends stress reorientation during the late rift stage finally linked ne sw striking segments the partial linkage of the fault zone at the time of oil migration resulted in the southwestern part of the ntm 1 fault sealing hydrocarbon bearing reservoirs whilst late linkage areas along the northeastern part failed to seal hydrocarbons the n s striking pto 1 fault shows early isolated fault segments linkage during syn rift motion then a more patchy distribution of displacement late in the fault history perhaps due to non optimal orientation of the fault to the regional stress field when compared with the ntm 1 fault the fault characteristics described indicate that where strong pre existing fabrics are present and varying stress regimes have occurred fault population characteristics and evolution of fault displacement can depart considerably from extensional fault populations associated with a single phase of extension

influence of fault reactivation during multiphase rifting the oseberg area northern north sea rift abstract multiphase rifts tend to produce fault populations that evolve by the formation of new faults and reactivation of earlier faults the resulting fault patterns tend to be complex and difficult to decipher in this work we use seismic reflection data to examine the evolution of a normal fault network in the oseberg fault block in the northern north sea rift system a rift system that experienced permian early triassic and middle jurassic early cretaceous rifting and exhibits n s nw se and ne sw oriented faults both n s and nw se striking faults were established during the permian early triassic rifting as indicated by triassic growth packages in their hanging walls in contrast the ne sw striking faults are younger as they show no evidence of permian early triassic growth and offset several n s and nw se striking faults structural analysis show that a new population of nw se striking faults formed in the lower middle jurassic inter rift period together with reactivation of n s striking permian early triassic faults indicating a ne sw inter rift extension direction during the middle jurassic early cretaceous rifting faults of all orientations n s nw se and ne sw were active however faults initiated during the middle jurassic early cretaceous rifting show mainly n s orientation indicating e w extension during this phase these observations suggest a reorientation of the stress field from e w during the permian early triassic rift phase to ne sw during inter rift fault growth and back to e w during the middle jurassic early cretaceous rift phase in the oseberg area hence the current study demonstrates that rift activity between established rift phases can locally develop faults with new orientations that add to the geometric and kinematic complexity of the final fault population

development of rift basins illustrated by the structural evolution of the oseberg feature block 30 6 offshore norway the mesozoic tilted fault block in norwegian north sea block 30 6 containing the giant oseberg oil and gas field is used to illustrate basin development during the jurassic and cretaceous there is seismic evidence for an early rifting phase in the northern viking graben on which the jurassic cretaceous rifting phase early bathonian to berriasian is overprinted the oseberg structure is representative of other fault blocks bordering the northern viking graben axis planar normal faults and listric faults which were restricted to the rifting phase dominate both fault types exhibit syn fault sedimentation listric faulting is recognized on seismic sections by the differential tilting reverse drag antithetic faulting and a wedge shaped syn rift reflector package the initiation of rifting is dated by baselap onto pre rift reflectors and cessation is dated by an unconformity beneath the generally onlapping post rift sediments steeply dipping planar normal faults often active along previously established fault zones played a significant part in the post rift development of the basin the last movement on planar normal faults in the oseberg fault scarp becomes younger away from the rift axis and this produced the complex fault scarp visible on many seismic lines the topography defined by the post rift unconformity is a composite surface which formed in response to subsidence processes it is not the result of orogenic events such as the kimmerian 9orogeny9 footwall uplift associated with planar normal faults caused local unconformities in complex fault scarps and on fault block crests

unconformities related to the jurassic cretaceous synrift post rift transition of the northern north sea in the jurassic cretaceous north sea basin the synrift sequence is separated from the post rift sequence by the base cretaceous or late cimmerian unconformity the unconformity covers almost the entire basin has a distinct character in seismic reflection data and wireline logs and hence is easily identified and correlated making it the most important marker horizon in the area the unconformity displays great local complexity in many localities and great variability on a regional scale from one locality to another thus the unconformity is classified as a nonconformity a disconformity and an angular unconformity we suggest that these variations basically reflect different structural position within the basin so that the short wavelength variation is dominated by local structural development e g the rotational history of a fault block whereas the long wavelength variation reflects basin scale tectonic thermal and isostatic processes the merging of this unconformity with younger erosional surfaces its complex configuration and polychronous character makes the general term base cretaceous unconformity inadequate thus the term northern north sea unconformity complex is used here

surface temperature measurements of active lava flows on kilauea volcano hawai i systematic hand held radiometer measurements of lava surface temperatures in active flows and tubes on kilauea volcano hawai i reveal complexities that cannot be resolved in remotely sensed data from aircraft or satellites using portable infrared minolta land cyclops radiometers we measured surface temperatures of flows at various distances from their sources and investigated cooling rates and the development of crust our measurements suggest that the upper surface of these lava flows can be split into a minimum of four thermal components core 1050 c visco elastic skin 750 900 c rigid solid crust 750 c and flow margins 175 c for the a a flows investigated a cool rigid crust characteristically developed in the central part of channels within 30 m of the source vent and incandescent lava was exposed in the marginal shear zones of channels this affects the heat loss and morphology of lava in active channels our investigations of temperature distributions on pahoehoe flow fields reveal temperature anomalies of up to 150 c above active tubes and tumuli

growth and linkage of a segmented normal fault zone the late jurassic murchison statfjord north fault northern north sea abstract the structure of the 25 km long northeastern portion of the murchison statfjord north fault zone and adjacent syn rift stratigraphy are integrated to reconstruct the temporal and spatial evolution during c 30 5 myr of late jurassic north sea rifting based on a structural analysis d d data alone approximately 14 precursor fault strands are identified incorporation of stratigraphic data shows that only six of these strands were important in controlling stratal architecture and distribution three main stages in the evolution of the fault zone are recorded in the syn rift stratigraphy and are biostratigraphically constrained these are 1 following initiation of rifting six isolated fault strands developed each 9 km long fault segments separated by a 2 km wide relay ramp that controlled the stratigraphy for at least the following c 10 5 myr and 3 the two fault segments hard linked forming a single continuous fault trace during the final c 7 myr of rifting the results of this study reveal the necessity to adopt an integrated structural and stratigraphic approach when reconstructing the evolution of normal fault zones the results may also help to further constrain models of fault evolution

fault interactions and reactivation within a normal fault network at milne point alaska a normal fault network from milne point alaska is investigated focusing on characterizing geometry displacement strain and different fault interactions the network constrained from three dimensional seismic reflection data comprises two generations of faults cenozoic north northeast trending faults and jurassic west northwest trending faults which highly compartmentalize upper triassic to lower cretaceous reservoirs the west northwest trending faults are influenced by a similarly oriented underlying structural grain this influence is characterized by increases in throw on several faults strain localization reorientation of faults and an increase in linkage maturity reconstructing fault plane geometries and mapping spatial variations in throw identified key characteristic features in their interactions and reactivation of pre existing structures faults are divided into isolated abutting and splaying faults isolated faults exhibit a range of displacement profiles depending on the degree of restriction at fault tips fault splays accommodate step like decreases in throw along larger main faults with a throw maximum at the intersection with the main fault throw profiles of abutting faults are divided into two groups early stage abutting faults with throw minima at both the isolated and abutting tips and developed abutting faults with throw maxima near the abutting tip developed abutting faults accumulate throw after initial abutment locally reactivating and transferring throw onto the pre existing fault two abutting faults can link kinematically by reactivating a segment of the pre existing fault forming a trailing fault the motion sense of the trailing fault can be synthetic or antithetic to the reactivated pre existing fault producing increases or decreases in the throw of the pre existing fault respectively

how do the properties of a pre existing normal fault population influence fault development during a subsequent phase of extension abstract we use scaled experimental analog models to investigate how the properties of a population of pre existing normal faults influence fault development during a subsequent phase of extension in the models a homogeneous layer of wet clay undergoes two phases of extension whose extension directions differ by 45 to vary the properties of the first phase fault population we vary the magnitude of the first phase extension as the magnitude of the first phase extension increases the number average and maximum length and average and maximum displacement of the first phase normal faults increase for a poorly developed first phase fault population new normal faults which strike perpendicular to the second phase extension direction form during the second phase for a well developed first phase fault population many first phase normal faults are reactivated as oblique slip faults during the second phase new normal faults also form these second phase normal faults are shorter and have displacement maxima adjacent to the reactivated first phase faults they are less likely to cut the pre existing first phase faults than second phase normal faults that form in models with a less developed first phase fault population in all models pre existing faults serve as nucleation sites for new faults in models with a well developed first phase fault population the pre existing faults also act as obstacles to the propagation of the second phase normal faults fault geometries in the models vary considerably parallel zig zag or intersecting fault geometries develop depending on whether the first phase fault population is poorly moderately or well developed respectively

the structural evolution of the northern viking graben and its bearing upon extensional modes of basin formation recent advances in the understanding of rift basin formation coupled with the increasing public availability of seismic and well data across the northern viking graben 60 61 n have enabled a detailed analysis of its development two rifting episodes can be recognized late permian early triassic and bathonian ryazanian major regional unconformities thought to be primarily tectonic rather than eustatic in origin separate and subdivide the rifting episodes the earlier episode involved extension about a n s axis ensuing triassic mid jurassic thermal subsidence was accommodated on steep faults during the later episode a new ne sw fault trend was superimposed on pre existing patterns major block rotation marking active rifting ceased at the end of the ryazanian during the second post rift episode there was a progressive migration of active faulting towards the basin margins and as a result a widening with time of the area undergoing subsidence asymmetric subsidence of the central part of the basin was hinged at the western margin of the horda platform and accommodated to the nw on major faults within the tampen spur factors for the second rifting episode were calculated both by relating subsidence to extension and by measuring observed extension values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases but are greater for the latter phase subsidence patterns are similar for both rifting and thermal subsidence episodes so that there is vertical stacking of relatively thick sequences in the axis of the northern viking graben these factors preclude the application of models involving uniform and non uniform stretching and also preclude oblique extension depth dependent stretching is preferred

land offshore tectonic links in western norway and the northern north sea aeromagnetic and marine gravity data sets for the northern north sea and western norway have been interpreted in terms of land to offshore tectonic links the data allow identification of linking structures both in crystalline basement and overlying sedimentary rocks and consequently facilitate a more comprehensive interpretation of regional structural features and trends with the help of bathymetric data in the inshore region major fault structures can be traced between western norway and the offshore region west of the oygarden fault zone in this way spatial and chronological links have been established between tectonic events recognized on land and the development of the north sea basin an interpretation of basement geology is proposed for the region between western norway and the uer terrace this is complemented with a depth to top crystalline basement map covering the north sea basin between the uer terrace and the east shetland basin two regional nw se lineaments were recognized offshore western norway and given the names marflo lineament and troll lineament the marflo lineament is interpreted to be a caledonian or older zone of weakness that accommodated development of a 20 30 km offset in the jurassic viking graben axis the lineament can be traced into the north atlantic where it parallels oceanic fracture zones and transform faults the troll lineament relates to a deep geological discontinuity crossing the uer and lomre terraces a grouping of earthquake epicentres along part of the lineament suggests that the discontinuity is tectonically active

spatio temporal evolution of strain accumulation derived from multi scale observations of late jurassic rifting in the northern north sea a critical test of models for lithospheric extension abstract we integrate observations of lithospheric extension over a wide range of spatial and temporal scales within the northern north sea basin and critically review the extent to which existing theories of lithospheric deformation can account for these observations data obtained through a prolonged period of hydrocarbon exploration and production has yielded a dense and diverse data set over the entire viking graben and its flanking platform areas these data show how syn rift accommodation within the basin varied in space and time with sub kilometer scale spatial resolution and a temporal resolution of 2 3 myr regional interpretations of 2d seismic reflection refraction and gravity data for this area have also been published and provide an image of total basin wide stretching for the entire crust these image data are combined with published strain rate inversion results obtained from tectonic subsidence patterns to constrain the spatio temporal evolution of strain accumulation throughout the lithosphere during the 40 myr 170 130 ma period of late jurassic extension across this basin for the first 25 30 myr strain localisation dominated basin development with strain rates at the eventual rift axis increasing while strain rates over the flanking areas declined as strain rates across the whole basin were consistently very low 16 s l thermally induced strength loss cannot explain this phenomenon the strain localisation is manifest in the near surface by a systematic migration of fault activity the pattern and timing of this migration are inconsistent with flexural bending stresses exerting an underlying control especially when estimates of flexural rigidity for this area are considered the best explanation for what is observed in this time period is a coupling between near surface strain localisation driven by brittle or plastic failure and the evolving thermal structure of the lithosphere we demonstrate this process using a continuum mechanics model for normal fault growth that incorporates the strain rate dependence of frictional strength observed in laboratory studies during the final 10 myr of basin formation strain accumulation was focused within the axis and strain rates declined rapidly replacement of weak crust by stronger mantle material plus crustal buoyancy forces can adequately explain this decline

an early mid miocene strike parallel shelfal trough and possible karstification in the northern carnarvon basin northwest australia abstract as part of a study to investigate relative sea level history from the tertiary north west shelf of australia we describe a seismically imaged stratigraphic architectural element not previously associated with prograding carbonate clinoforms a strike oriented trough on an early mid miocene sequence boundary this trough located on a shallowly dipping carbonate ramp is recognized on both 2 d and 3 d seismic data by truncation reflector interruption and amplitude variations it is composed of three individual segments each up to 500 m wide and 60 m deep with variable cross sections their combined length orthogonal to the progradation direction is 8 km the trough occurs where there is a slight basinward increase in dip and a facies change on the ramp from sand sized calcarenite to clay sized calcilutite it has both a cross cutting and sub parallel relationship with underlying paleogene faults reactivated within a mesozoic basin forming trend the trough does not conform to known drainage patterns or contour current incisions mapped in similar environments elsewhere we propose that this seismically mapped trough is karst topography that developed as a result of preferential dissolution focused by heterogeneities within the exposed carbonate ramp stable isotope analyses conducted on bulk carbonate samples 2 km updip suggest a mixed marine to slightly meteoric origin for associated porewaters furthermore the sequence boundary on which the trough is developed is contemporaneous with recognized subaerial exposure surfaces to the northeast and southwest the presence of such a karst feature indicates a minimum fall in relative sea level at this location of 80 160 m during the early mid miocene

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

structural styles and depositional architecture in the triassic of the ninian and alwyn north fields implications for basin development and prospectivity in the northern north sea abstract interpretation of well calibrated three dimensional seismic volumes sedimentological analysis and electrical well log correlations from the ninian and alwyn north fields challenge the long held view that mid late jurassic extensional faults in the east shetland basin represent a simple reactivation of older triassic fault systems restoration for the effects of the younger predominantly eastward dipping mid late jurassic structures clearly demonstrates that triassic precursors had a steep westerly dip in contrast to the eastern flank of the viking graben e g troll and oseberg areas where the west dipping triassic structures are reutilised in the mid late jurassic those of the east shetland basin have largely been dissected and rotated during the later event those west dipping faults that did see later movement appear to have simply acted as minor antithetic structures to the throughgoing east dipping ones the triassic normal fault patterns actively controlled sediment thicknesses and facies distribution within the lunde and teist formations in the basin use of seismic stratigraphic surfaces calibrated by biostratigraphy and chemostratigraphic markers provides strong evidence that the triassic depocentres are spatially offset from their mid late jurassic counterparts the combination of structural stratigraphic and sedimentary effects reveal the existence of an emergent deeper triassic play opportunity in footwall locations to the mid late jurassic normal faults which has the potential to extend the life of what is otherwise mature acreage

four dimensional analysis of the sembo relay system offshore angola implications for fault growth in salt detached settings subsurface mapping of several relay ramps from a raft related fault array in the lower congo basin offshore angola reveals a full spectrum of fault linkage styles a comprehensive three dimensional geometric and kinematic appraisal of a more complex relay system within the fault array the sembo relay system srs highlights differences with current structural models of relay ramp genesis evolution and breaching the srs is a rearward upper ramp breached relay system with a maximum fault overlap and spacing of 9500 and 3600 m 31 000 and 11 800 ft respectively this system is characterized by a structural geometry that becomes increasingly complex with depth as the relay system is gradually assimilated into the structural architecture of a separate and structurally deeper fault system a detailed kinematic appraisal of the srs indicates that the throw patterns on the frontal and rearward segments are intrinsically different throw backstripping reveals different initiation ages for the rearward and frontal segments of about 5 5 and 2 5 ma respectively mutual overlap is estimated to first occur about 2 5 ma at the 5 0 ma structural level with fault linkage and ramp breaching occurring subsequently the srs therefore represents a complex amalgamation of faults that have each developed independently at different times the genesis and evolution of the srs have been governed through time by both salt withdrawal and associated fault detachment histories in conjunction with increased congo fan progradation and sedimentation rates and phases of tectonic tilting of the underlying salt detachment surface

geometrically coherent continuous deformation in the volume surrounding a seismically imaged normal fault array abstract we calculated an apparent dip attribute which was used to ascertain the spatial distribution of fault related continuous deformation the vertical component of displacement calculated from the continuous deformation acts to fill in missing displacement in the fault throw profile this result shows that apparently complex 3d patterns of continuous strain in the volumes surrounding the fault array developed as part of a single geometrically coherent fault array however if this component of continuous deformation was not added to the throw profile the fault array could have been misinterpreted as a series of isolated fault segments with coincidental overlaps this technique permits the analysis of continuous deformation structures which are up to an order of magnitude smaller than previously described in the study area these structures are interpreted as small fault propagation folds forming in a shale dominated cover sequence the fault propagation folds above the upper tip line of the mapped fault array bifurcate upwards from the fault surface into three coherent lobes and resemble secondary fault segments the near constant along strike length of the region of continuous deformation throughout the syn rift sequence implies that the length of the fault array was established at an early stage in its growth prior to the establishment of a seismically visible fault surface

fault growth and interactions in a multiphase rift fault network horda platform norwegian north sea abstract physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non colinear normal fault sets furthermore multiphase rifts will display a greater frequency and range of styles of fault interactions than single phase rifts although these physical models have yielded useful information on the evolution of fault networks in map view the true 3d geometry of the faults and associated interactions are poorly understood here we use an integrated 3d seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern horda platform northern north sea in particular we aim to i determine the range of styles of fault interaction that occur between non colinear faults ii examine the typical geometries and throw patterns associated with each of these different styles and iii highlight the differences between single phase and multiphase rift fault networks our study focuses on a ca 350 km 2 region around the 60 km long n s striking tusse fault a normal fault system that was active in the permian triassic and again in the late jurassic to early cretaceous the tusse fault is one of a series of large 1500 m throw n s striking faults forming part of the northern horda platform fault network which includes numerous smaller 2 10 km long lower throw nd stage nw se striking faults grew interacted and linked with the n s striking tusse fault documenting a range of interaction styles including mechanical and kinematic isolation abutment retardation and reactivated relays our results demonstrate that i isolated and abutting interactions are the most common fault interaction styles in the northern horda platform ii pre existing faults can act as sites of nucleation for 2 nd stage faults or may form mechanical barriers to propagation iii the throw distribution on reactivated 1 st stage faults will be modified in a predictable manner if they are intersected or influenced by 2 nd stage faults iv sites of fault linkage and relay breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd stage faults and v the development of fault intersections is a dynamic process involving the gradual transition from one style to another

evolution of the oseberg fault block in context of the northern north sea structural framework abstract the central segment 60 20 61 n of the northern north sea 170 km in width demonstrates contrasting basin geometries related to permo triassic and jurassic rift episodes in the oseberg area representing a part of this segment major faults of two generations dip in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin ca 20 km in width is underlain by a wider ca 35 km w tilted permo triassic half graben the early jurassic thickness distribution was governed by a westerly palaeotilt mild extensional tectonics influenced early jurassic rhaetian aalenian deposition whereas the middle late jurassic main rift episode is expressed by an accelerated fault related subsidence from the late bajocian during the middle late jurassic the oseberg area evolved through a series of high frequency rift phases characterized by rotational tilt events separated by periods during which extension was less severe this allows the subdivision of the jurassic stretching episode into distinct rift phases 4 6 myrs which involved smaller scale units corresponding to rotational tilt events 1 2 myrs the large scale pattern of middle late jurassic syn rift infill is overall one of upwards fining reflecting a deepening trend as the rift evolved syn rotational sediment architecture related to a single rift phase shows systematic variations from a threefold shallow marine sandstone mudstone sandstone motif tarbert fm through a twofold shallow marine sandstone mudstone motif heather fm to a twofold deep marine conglomerate sandstone mudstone motif draupne fm the vertical stacking of these syn rotational packages reflects an inability of sediment supply to keep pace with the rift related subsidence and the temporal evolution from a sediment balanced through a sediment underfilled to a sediment starved rift basin