seismic images of continental lithosphere seismic reflection profiles in usa and west germany over thirty years ago showed strong reflections from the lower crust but technical advances through the 1970s were needed for the method to image the continental lithosphere the british institutions reflection profiling syndicate birps found advantage in working offshore and has obtained over 12 000 km of profiles around britain during the past decade giving the densest regional coverage anywhere reflections are observed from strata in sedimentary basins from low angle faults that can be followed from surface to mid crust from a laterally variable reflective zone in the lower crust from the moho and from fault like features in the upper mantle there is evidence around britain that faults bounding sedimentary basins are older structures which have been reactivated it is argued that lower crustal reflectivity around britain is mainly due to anastomosing ductile shears which accommodate extension in the lower crust commensurate with extension in the upper crust by faulting and block rotation there is also evidence of reflections preserved from older orogenic features so that reflections interpreted as extensional ductile shears in the lower crust may also derive from older features that have been reactivated most reflections in the lower crust arise from rocks that have been highly strained evidence of lateral variability in the reflective character of the moho suggests that the moho has been actively involved in the structural evolution of the lithosphere upper mantle reflections are interpreted as shear zones which transfer crustal deformation through the lithosphere

calcretes at sequence boundaries in upper carboniferous cyclothems of the sydney basin atlantic canada abstract nodular and associated groundwater calcretes in coal bearing cyclothems of the sydney basin mark the boundary between underlying marginal marine and overlying alluvial deposits they are inferred to represent lowstand surfaces sequence boundaries the host sediments include both sand siltstones and palustrine limestones microfabrics of calcretes with detrital hosts show evidence of replacement displacement and shrinkage alpha fabrics suggesting that the calcretes formed under relatively arid conditions in contrast microfabrics of nodular calcretes with limestone hosts exhibit predominantly beta fabrics with root induced brecciation and subordinate shrinkage fabrics the calcretes and host limestones are inferred to have formed in topographic lows thick alluvial sediments with red calcic vertisols overlie the calcretes and formed within the transgressive systems tract under conditions of abundant sediment supply coals and associated hydromorphic palaeosols lie near the transgressive maximum and in the highstand systems tract the presence of calcareous palaeosols on lowstand surfaces suggests that the lowstands were times of relative climatic aridity

changes in physical properties of a reservoir sandstone as a function of burial depth the etive formation northern north sea abstract rock physical properties like velocity and bulk density change as a response to compaction processes in sedimentary basins in this study it is shown that the velocity and density in a well defined lithology the shallow marine etive formation from the northern north sea increase with depth as a function of mechanical compaction and quartz cementation physical properties from well logs combined with experimental compaction and petrographic analysis of core samples shows that mechanical compaction is the dominant process at shallow depth while quartz cementation dominates as temperatures are increased during burial at shallow depths

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

western pacific warm pool region sensitivity to convective triggering byboundary layer thermals in the nogaps atmospheric gcm the sensitivity of the atmospheric general circulation model of the navy operational global atmospheric prediction system to a parameterization of convective triggering by atmospheric boundary layer thermals is investigated the study focuses on the western pacific warm pool region and examines the results of seasonal integrations of the model for the winter of 1987 88 a parameterization for thermal triggering of deep convection is presented that is based on a classification of the unstable boundary layer surface based deep convection is allowed only for boundary layer regimes associated with the presence of thermals the regime classification is expressed in terms of a richardson number that reflects the relative significance of buoyancy and shear in the boundary layer by constraining deep convection to conditions consistent with the occurrence of thermals high buoyancy to shear ratios there is a significant decrease in precipitation over the southern portion of the northeast trade wind zone in the tropical pacific and along the itcz this decrease in precipitation allows for an increased flux of moisture into the region south of the equator corresponding to the warmest portion of the pacific warm pool improvements in the simulated distribution of precipitation precipitable water and low level winds in the tropical pacific are demonstrated over the western pacific the transition from free convective conditions associated with thermals to forced convective conditions is found to be primarily due to variations in mixed layer wind speed low level winds thus play the major role in regulating the ability of thermals to initiate deep convection the lack of coupling with the ocean in these simulations may possibly produce a distorted picture in this regard

quantitative radiometric and biostratigraphic calibration of the pennsylvanian early permian cisuralian time scale and pan euramerican chronostratigraphic correlation a quantitative biostratigraphic and radiometric calibration is presented for the pennsylvanian through early permian global time scale based upon high precision isotope dilution thermal ionization mass spectrometer id tims u pb zircon ages for interstratified ash beds in the parastratotype sections of the southern urals of russia twenty four ash bed ages in three outer ramp and basinal sections of the pre uralian foredeep bracket the biotic definitions of global stages and regional substages from the base of the upper pennsylvanian kasimovian stage to the base of the lower permian artinskian stage four additional ash bed ages in two sections of the eastern slope of the urals constrain the global bashkirian and serpukhovian stages quantitative stratigraphic methods conop9 are applied to a compilation of over 2000 bioevents in 22 stratigraphic sections supplemented by our dated volcanic horizons to refine the pennsylvanian early permian global time scale significant shifts in the duration of several stages are demonstrated ranging from one to six million years compared with prior estimates the unprecedented density of radiometric calibration points for the pennsylvanian permian transition provides a high resolution 0 1 ma global chronostratigraphic standard for testing and improving biostratigraphic correlations across euramerica we integrate radiometric ages biostratigraphic correlation and cyclostratigraphic tuning of major cyclothems to the long period 404 ka eccentricity cycle to elucidate the tempo magnitude and forcing of eustatic changes and cyclothemic deposition associated with the waxing and waning of gondwanan ice sheets and establish a pan euramerican chronostratigraphic framework for most of pennsylvanian and early permian time

calcrete palaeosols from the lower carboniferous llanelly formation south wales abstract three calcrete bearing palaeosol units are described from the lower carboniferous llanelly formation in south wales and are named the tyle r bont pedocomplex the cwm dyar pedoderm and the llanelly pedocomplex these units were formed on semi arid to arid floodplains and are associated with sheet flood stream flood and meandering channel deposits three major processes operated during pedogenesis calcification pedoturbation and solution pedoturbation resulted in the formation of brecciated horizons pseudo anticlinal and prismatic structures and a predominance of disorthic nodules the soils developed in smectite rich clays under a seasonally arid climate resulting in strong argillipedoturbation

isotopic records of brachiopod shells from the russian platform evidence for the onset of mid carboniferous glaciation we performed isotopic analyses of carboniferous brachiopod shells from the russian platform to examine global and regional environmental change along the western and eastern margins of laurussia during the formation of pangea and specifically to examine the isotopic evidence for the onset of mid carboniferous glaciation shell preservation was evaluated from shell microstructure cathodoluminescence trace element content and isotopic comparison with matrix material most interior nonluminescent nl prismatic shell appears to be chemically well preserved as indicated by low to undetectable si al fe and mn contents with minor exception nl shell 13c and 18o values are higher than those of corresponding cements and matrix the 13c record for the russian platform clearly shows a 3 increase from 2 4 0 7 to 5 5 0 6 in the serpukhovian or early bashkirian this shift was first reported by popp et al popp b n anderson t f sandberg p a 1986 brachiopods as indicators of original isotopic compositions in some paleozoic limestones geol soc am bull 97 1262 1269 but had not been documented for a single region widespread occurrence of high 13c values in the late carboniferous support the interpretation of popp et al with regard to this shift as a record of increased burial of organic carbon north american sections show a mid carboniferous 13c shift of only 1 5 we hypothesize that the reduced 13c shift reflects enhanced upwelling on the epicontinental seas of north america after the closing of the seaway between laurussia and gondwana the 18o record for the russian platform shows a 1 8 increase in the mid carboniferous correlative with increased occurrence of glacial sediments and a drop in sea level as a first approximation ice volume calculations suggest that 0 7 of the mid carboniferous 18o shift is due to changes in seawater 18o and 1 1 is due to 5 c cooling concurrent positive 13c and 18o shifts provide evidence for a relationship between mid carboniferous glaciation and burial of organic carbon presumably through changes in atmospheric co2 levels

isotopic fingerprints of milankovitch cycles in pennsylvanian carbonate platform top deposits the valdorria record northern spain sedimentary cyclic sequences deposited during the late palaeozoic ice age are widespread glacio eustatic control of the cyclic patterns is commonly accepted and the durations of the cyclothems generally match the short and long eccentricity milankovitch orbital parameters nevertheless geochemical fingerprints of orbital parameters are poorly documented in deep time sedimentary records here we report on well exposed bashkirian cyclothems of c 123 ka and c 400 ka durations from the valdorria platform the shorter term cyclothems can be grouped into longer term composite sequences that are consistent with generally accepted durations of c 125 ka and c 400 ka for milankovitch eccentricity cycles the stratigraphic pattern is mirrored by the isotope geochemical signals which show distinct recurring trends these trends are confirmed by statistical tests whereas intrinsic factors and or subaerial exposure related to sea level lowstands might have truncated cycle patterns in tectonically stable basins rapid subsidence of the valdorria platform s foreland basin appears to have contributed to a faithful recording of cyclothems of different orders the patterns and biostratigraphic constraint revealed in this study demonstrate the power of orbital forcing in imprinting sedimentary and geochemical signals in the rock record

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

modelled palaeo temperature on voring offshore mid norway the effect of the lower crustal body abstract the voring area offshore mid norway has a complex geological history has experienced several extensional phases and was significantly influenced by the break up of the north atlantic we have modelled a cross section over the voring basin aiming to 1 reconstruct the basin evolution in a realistic way and 2 to investigate the heat flow and temperature history in the basin for the modelling we used the following tectonic events the opening of the basin during the permo triassic an event during the middle to late cretaceous and an event in the late cretaceous paleocene the theoretical effects of the lithospheric stretching are depending on the palaeo water depths of the area we present a prediction of the palaeo water depth and a sensitivity analysis of the influence of the palaeo water depth on the estimated beta factors in the area a lower crustal high velocity body found in the area is often interpreted as magmatic underplating related to the break up of the norwegian sea we show the temperature history calculated by models that were run with and without assumption of underplating by a magmatic body emplaced during the early tertiary the observed vitrinite reflectance in the voring area is best explained by numerical calculations of the vitrinite reflectance without a magmatic underplating our conclusion is that the lower crustal body is not related to magmatic underplating or to significant sill intrusions the body may consist of older mafic rocks or a mixture of old continental crust and mafic intrusions

physical and chemical stratigraphy suggest small or absent glacioeustatic variation during formation of the paradox basin cyclothems the paradox basin cyclothems previously have been interpreted as milankovitch style glacial interglacial cycles from the late paleozoic ice age but an unambiguous test for a glacioeustatic origin has not been conducted a high resolution coupled chemical and physical stratigraphic analysis of two outcrop sections and three core segments provides new evidence that supports either minor sea level change of several meters or an autocyclic mechanism for parasequence formation high amplitude sea level change is ruled out by the scale of thin top negative isotopic meteoric diagenesis trends associated with parasequence tops and subaerial exposure fabrics isotopic gradients from shelf light to basin heavy indicate that parasequences are deposited diachronously with isotopes of more distal sections recording increased basin restriction these results support the idea that the late pennsylvanian was a prolonged period of relatively static eustasy agreeing with recent studies in the western usa the methods provide a new set of tools and context for extracting environmental information from cyclic upward shallowing carbonate parasequences

facies geometry and growth phases of the valdorria carbonate platform pennsylvanian northern spain the 14 km wide valdorria outcrop pennsylvanian northern spain is one of the few examples of entirely exposed flat topped and high relief carbonate platforms reported in the fossil rock record laterally and vertically traceable stratal patterns expose three phases of growth phase i is a 430 m thick platform to slope succession that prograded over 6 km and is dated as early bashkirian akavasian askynbashian phase ii aggraded and prograded exhibiting 180 m thickness of cyclical platform top deposits dated as late bashkirian asatauian phase iii is a mound shape structure that developed over the platform top of phase ii as a new phase of platform nucleation it is 535 m thick and 2 km wide and dated as late bashkirian asatauian transition interval the observed changes of growth styles during platform evolution from a prograding to an aggrading prograding system and a rapid aggradational phase are inferred to be controlled by flexural subsidence in the active cantabrian foreland basin at the variscan orogenic front the metre scale shallowing upward cycles of the platform top are most probably due to glacioeustasy as evidenced by well recorded subaerial exposure surfaces superimposed on subtidal deposits and by a stratal pattern recurrent in a short interval of about 160 kyr observations of outcropping bashkirian cyclothems in an isolated carbonate system devoid of siliciclastic input are relevant for a better understanding of the impact of high frequency sea level fluctuations on the carbonate factory moreover progradation of the platform margin during phase i reaches a rate of 2500 m myr and 1810 m myr during phase ii rates that are high when compared to other pennsylvanian examples the aggradation rate of 447 m myr calculated for late bashkirian transition interval phases i and ii uncorrected for compaction missing beats and erosion is uncommonly high in comparison to coeval pennsylvanian examples the platform exhibits a self nourishing prograding microbial boundstone dominated slope thus the slope shedding model applies well to valdorria however phase ii recorded eustatic variations able to inhibit the slope microbial boundstone factory during low sea level stands this is marked by common slope red stained breccias synchronous to platform top subaerial exposure phases contrarily periods of relative high sea level and rapid subsidence in phase iii registered a greater development of cemented microbial boundstone these observed partly opposing relationships of sea level stands shedding modes and slope architecture provide an improvement of the currently used slope shedding model the overall architecture of the valdorria outcrop compares well with that of other contemporaneous platforms such as sierra del cuera and bolshoi karatau valdorria shares the high relief and flat topped steep slopes cyclothemic patterns and occurrence of karst features with the pricaspian basin platforms tengiz karachaganak and kashagan with minor variations in facies distribution of the internal platform furthermore the continuous seismic scale outcrop of valdorria together with its isolated setting and asymmetrical growth makes it an additional good candidate for potential subsurface analogues of hydrocarbon bearing systems

sequence stratigraphy and onlap history of the donets basin ukraine insight into carboniferous icehouse dynamics abstract the degree to which permo carboniferous cyclothemic successions archive evidence for long term variations in ice volume during the late paleozoic ice age is insufficiently resolved here we develop the sequence stratigraphy and onlap offlap history for a 33 my interval of the carboniferous using the u pb calibrated succession of the donets basin ukraine in order to assess the relationship between sea level high latitude changes in glacial extent and climate integrated subsurface and outcrop data permit meter scale correlation of 242 biostratigraphically constrained limestones and coals and in turn individual cyclothems across 250 km of the donets basin rapid uniform subsidence and basinwide continuity of marker beds indicate pennsylvanian deposition under relatively stable tectonic conditions three scales of sequences avg durations of 140 ky 480 ky and 1 6 my are recognized on the basis of stratigraphic stacking patterns and basinwide architecture of marine to terrestrial facies assemblages the hierarchy of sequences and the geographic and stratigraphic positions of shifts in base level sensitive facies across the donets ramp permit the construction of an onlap offlap history at a sub 400 ky scale major sea level lowstands occur across the mid carboniferous boundary and during the early moscovian these lowstands coincide with glacial maxima inferred from high latitude glacigenic deposits the middle to late pennsylvanian is characterized by a stepwise onlap culminating in an earliest gzhelian highstand suggesting contraction of carboniferous ice sheets prior to the initiation of early permian glaciation the stratigraphic position of climate sensitive facies within individual donets cyclothems indicates a turnover from seasonal sub humid or semi arid climate to everwet conditions during the late lowstand and maximum ice sheet accumulation comparison of the stratigraphic and aerial distribution of coals and evaporites in the donets basin with the onlap offlap history further indicates everwet conditions during lowstands and inferred glacial maxima and drier climate during onlap and inferred ice sheet contraction at the intermediate 0 8 to 1 6 my and long 106 yr time scales taken together the relationship between inferred climate and glacioeustasy suggests a likely teleconnection between high latitude ice sheet behavior and low latitude atmospheric dynamics

evidence for extensional shear zones in the mantle offshore britain and their implications for the extension of the continental lithosphere deep seismic profiles recorded in the seas around the british isles have revealed bands of seismic reflections in the uppermost mantle on the basis of their appearance geophysical characteristics and association with major crustal faults these features are best interpreted as mantle shear zones furthermore in the north sea the mantle reflectors appear to follow an extensional trend and when interpreted as extensional shear zones help explain the regional stratigraphy of the overlying basin the crosscutting relationships between mantle reflections to the west of scotland and a major strike slip fault the great glen fault ggf suggest that the mantle structure postdates the ggf and hence is probably related to subsequent extension furthermore kinematic analysis of lithospheric deformation to the north of scotland is consistent with the structure observed on the seismic data if the flannan mantle reflection is an extensional shear zone reconstruction of the lithosphere prior to permian extension restores the flannan to the edge of the rockall trough a rift probably initiated in the carboniferous thus the flannan fault may have developed during carboniferous rifting it is concluded that most of the mantle reflections are some form of extensional shear zone in the mantle and the role of such structures during lithospheric extension is considered

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

lithospheric stretching and north sea jurassic clastic sourcelands uniform lithospheric stretching cannot explain three important aspects of north sea basin evolution namely 1 the rapid growth of middle jurassic uplands from which were liberated major fluvial deltaic clastic wedges now forming the main hydrocarbon reservoirs 2 the occurrence of basin centre upwarp and basaltic volcanism and 3 widespread and significant 1 km subsidence outside the area of demonstrable crustal thinning i present here the suggestion that a combination of nonuniform stretching and lithospheric flexuring accounts for these fine tuning effects of the uniform stretching model with magnitudes close to those demanded by independent geological evidence

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

nature and timing of late mississippian to mid pennsylvanian glacio eustatic sea level changes of the pennine basin uk the pennine basin of northern england contains a comparatively complete serpukhovian moscovian succession characterized by high resolution ammonoid zonation and cyclic paralic sedimentation two new isotope dilution thermal ionization mass spectrometry zircon ages from a bentonite deposited during the arnsbergian mid serpukhovian regional substage and tonstein of earliest bolsovian early moscovian regional substage have been determined the weighted mean 206 pb 238 u ages of 328 34 0 55 and 314 37 0 53 ma total uncertainty respectively require modification of the time scale for the western europe regional chronostratigraphy the areal extent of acme ammonoid facies is used as a proxy for the magnitude of 47 discrete flooding events incised valleys major sequence boundaries are used as a proxy for the magnitude of sea level falls the frequency of these events in the light of the new radiometric dating indicates the following 1 there is temporal coincidence between major glaciations in gondwana and phases of increased frequency of sequence boundaries in the pennine basin 2 high amplitude flooding surfaces have an average frequency of c 400 ka 3 average cycle durations during the pendleian early arnsbergian and chokierian bolsovian of c 111 and c 150 ka respectively reflect short duration eccentricities 4 multiple flooding surfaces with the same ammonoid assemblages may equate with sub 100 ka precession or obliquity frequencies supplementary material u pb method description and data procedure for the calculation of the areal extent of marine bands and tables showing a full listing of biostratigraphical data used in the study are available at www geolsoc org uk sup18505

cenozoic sequence stratigraphy of the central and northern north sea basin tectonic development sediment distribution and provenance areas the cenozoic succession in the central and northern north sea has been investigated to establish a regional sequence stratigraphic framework changes in sediment distribution indicate a complex pattern of regional vertical movements along older palaeozoic and mesozoic structures in cenozoic times these vertical movements mainly related to tectonic processes along the continental margin to the north and north west were responsible for the generation and removal of provenance areas for sediments delivered to the north sea basin through cenozoic time during the early through middle palaeogene sediments were mainly sourced from areas in the west and from the atlantic margin in the north uplift in the northern north sea in the late eocene was in the earliest oligocene followed by marked basin subsidence and tectonic uplift of southern norway a similar pattern of tectonic movements resulted in subaerial exposure of the northern north sea in the early miocene followed by significant tectonic subsidence in the basin and along the atlantic margin in late miocene pliocene times at the same time southern norway was uplifted and became a major sediment source after the miocene pliocene subsidence uplift events glacial processes in southern norway and fluvial processes in a large drainage area east and south east of the north sea were responsible for the main sediment influx to the north sea the cenozoic depositional sequences in the north sea developed in close interaction with regional tectonic movements and changes in provenance areas tectonic movements in north west europe overprinted global sea level changes so that the generation of depositional sequences and sequence boundaries apparently occurred independently of the rate of eustatic sea level change

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

the moho boundary above upper mantle peridotites or lower crustal eclogites a global review and new interpretations for passive margins abstract we have performed a global study of 2d crustal scale wide angle profiles across passive margins with regard to local elevations in the moho which could possibly be interpreted as indicative of lower crustal eclogites a total of 16 candidates have been found mainly in the north atlantic and around australia these cases make up c 6 only of the total profile length studied confirming the interpretation of the moho generally representing the top of the mantle the interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the barents sea off mid norway in the newfoundland appalachians and in the yilgarn craton western australia it is also possible that there is a genetic link between the formation of caledonian eclogites and the jan mayen fracture zone which is the only major fracture zone in the north atlantic several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain such as coastlines and shelf edges indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture interpreting the moho beneath the bedout high on the northwest shelf of australia as the top of a body of lower crustal eclogites may imply that the northern termination of the lambert shelf represents a paleo suture zone and that the western termination of the broome platform acted as a major transfer zone the significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history subsidence and hydrocarbon maturation modelling

lithosphere rheology and sedimentary basins introduction the dynamics of sedimentary basins is re flected in the wide range of observational scales inside sedimentary basins the advent of high qu ality data sets have significantly improved the resolution of the record of near surface tectonic processes crustal thinning mechanical and thermal sub sidence sediment filling are involved in exten sional basin evolution and controlled by complex interactions between ductile and brittle modes of deformation of the whole lithosphere the rate of loading extension and sediment filling and the thermal evolution are among the most important controlling parameters these nonlinear interac tions do possess a memory of the evolution his tory and loading quantitative understanding of basin subsidence and the offlap onlap strati graphic patterns of a specific basin obviously benefits from progress in understanding the geo dynamical context horvlth 1993 this issue in compressional settings foreland basins re sult from the flexural lithospheric response to loading most of the models proposed so far have considered the lithosphere as a rheological unit and have been based on classical elastic and viscoelastic plate theory the wavelength and am plitude of the flexural response is not an intrinsic property of the lithosphere but result from the history of the competitive interactions between rate of loading and rate of viscous dissipation thermally activated a clear physical description of this flexural mode has not yet been proposed even though some recent results on the mecha nisms of uplift shoulder formation during rifting evolution may be considered bassi 1991 chery et al 1992 the geodynamical context of those basins is complex and the relationship between the transition of extensional and compressional domains is a topic of vigorous research current models for extensional and compressional basins are strongly based on a bulk rheological descrip tion of the whole lithosphere and on a kinematic description of the deformation mechanisms sawyer 1985 houseman and england 1986 quinlan et al 1993 this issue the basin record does reveal to some extend the memory of the deformation history starting from the construction of the internal structure of the basins i e from the processes leading to the formation of rocks sedimentation diagenesis compaction including possible buildup of fluid overpressures and the pattern of the large de formations by faulting or folding to enhance the understanding of the formation and evolution of sedimentary basins it is important to fully address the physical mechanisms operating at different scale in the continental lithosphere for example faulting forms a most important expression at least at the surface of large scale deformation in the basins how those basins are related to the faulting process and the fault interactions is an unsolved question pull apart basins are certainly

syn rift evolution and resulting play models in the snorre h area northern north sea abstract an upper jurassic wedge shaped syn rift succession comprising the heather and draupne formations is present in the hangingwall trough of the snorre fault block the succession is bounded to the west by the statfjord east fault whereas it onlaps the snorre fault block to the east it consists of a two fold coarsening upward sequence from shale to sandstone of shallow marine shoreline origin active fault block rotation and subsidence in the snorre h area commenced in the mid bathonian and lasted through the ryazanian the heather formation was deposited during the early rift stage mid bathonian early oxfordian 3 cumulative tilt whereas the draupne formation late oxfordian ryazanian 9 cumulative tilt accumulated during the main and late rift stages the lower part of the heather formation was likely deposited across a submerged tilted fault block terrain with a predominant extra basinal sediment supply deposition of the upper heather formation however was governed by gradually emerging footwall islands albeit yet without significant local erosion as a result of increased fault block rotation during deposition of the draupne formation shale sequences i ii late early oxfordian early mid volgian footwall islands became firmly established providing a predominant local sediment source to the snorre h sub basin clay and silt were supplied from erosion of the heather formation on the snorre h hangingwall with subordinate input of sand from the statfjord east footwall subsequent deposition of the draupne formation sequences iii v late mid volgian ryazanian was governed by significant relief on the footwall islands causing deep erosion into the brent group on the snorre h hangingwall dip slope and leading to progradation of the upper draupne sandstone shoreline complex across the snorre h area deposition of the draupne formation and temporal shoreline position were likely partly controlled by northwards fault tip propagation of the statfjord east fault various syn rift play models and depositional reservoir facies are present within the snorre h hangingwall basin they include dip slope shallow marine shoreline sands basin floor gravity transported sands and likely footwall talus sands enveloped in organic rich shales of the draupne formation the distribution of reservoir facies is intimately linked to exposure and erosion of the middle jurassic brent group below the syn rift unconformity

seismic stratigraphic subdivision of the triassic succession in the central north sea integrating seismic reflection and well data the triassic sedimentary succession in the central north sea has been investigated to establish a broader understanding of the triassic period from the combined interpretation of seismic reflection data and well data the triassic succession has been subdivided into four seismic units where unit boundaries are characterized by regional seismic amplitude anomalies reflecting changes in gross sedimentary facies or rock properties a successful correlation between sedimentary facies interpreted within the well sections and distinct seismic reflection patterns allowed a thorough mapping of the gross palaeoenvironment throughout the triassic the method presented of subdividing a continental sedimentary succession into seismic units should be applicable elsewhere in other basins the main source area during the triassic was scandinavia to the north and sediment transportation was mainly along north south and ne sw trending lineaments which are at present located onshore southern norway and in the asta graben and the varnes graben offshore an uplifted skagerrak graben area acted as source area in the early and early middle triassic with sediment dispersal to the south and sw high relief existed for a longer period in western scandinavia than in eastern scandinavia which supports an asymmetric shape of the scandinavian mountains during the triassic accommodation space in the early triassic was mainly controlled by the relief inherited from a late carboniferous permian rift phase although thermally induced regional subsidence continued in the middle and late triassic creation of local accommodation space was mainly limited to halokinesis including redistribution and withdrawal of salt from the subsurface the upper triassic succession is eroded across the western and central parts of the study area although the upper triassic unit is preserved in synforms adjacent to salt structures in the western part of the study area dry playa conditions prevailed during the early triassic although fluvial systems supplied long transported sandy detritus southeastwards in the late early triassic more sandy detritus was transported into the sedimentary basin in the middle and late triassic concurrently with a gradually wetter climate supplementary material uninterpreted seismic sections are available at www geolsoc org uk sup18726

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

high precision u pb zircon age calibration of the global carboniferous time scale and milankovitch band cyclicity in the donets basin eastern ukraine 1 high precision id tims u pb zircon ages for 12 interstratified tuffs and tonsteins are used to radiometrically calibrate the detailed lithostratigraphic cyclostratigraphic and biostratigraphic framework of the carboniferous donets basin of eastern europe chemical abrasion of zircons use of the internationally calibrated earthtime mixed u pb isotope dilution tracer and improved mass spectrometry guided by detailed error analysis have resulted in an age resolution of 0 05 or 100 ka for these carboniferous volcanics this precision allows the resolution of time in the milankovitch band and confirms the long standing hypothesis that individual high frequency pennsylvanian cyclothems and bundles of cyclothems into fourth order sequences are the eustatic response to orbital eccentricity 100 and 400 ka forcing tuning of the fourth order sequences in the donets basin to the long period eccentricity cycle results in a continuous age model for the middle to late pennsylvanian moscovian kasimovian ghzelian strata of the basin and their record of biological and climatic changes through the latter portion of the late paleozoic ice age detailed fusulinid and conodont zonations allow the export of this age model to sections throughout euramerica additional ages for mississippian strata provide among the first robust radiometric calibration points within this subperiod and result in variable lowering of the base ages of its constituent stages compared to recent global time scale compilations

crustal stretching in the scandinavian caledonides as revealed by deep seismic data the normalization of overthickened orogenic crust after a continent continent collision typically involves several different processes including erosion plate divergence gravity driven collapse of the orogenic wedge and viscous flow of the lower crust as a contribution to this discussion we here utilize reprocessed deep seismic data to image the scandinavian part of the major caledonian continent continent collision zone where we identify a double set of extensional shear zones one in the upper to middle crust hardangerfjord shear zone and a major oppositely dipping moho offsetting shear zone in the lower crust and upper mantle the latter shear zone may have a true displacement close to 50 km and appears to offset the moho vertically by 10 km extending downward beyond the 50 km depth limit of the seismic data while the upper structure offsets the basal caledonian thrust the moho shear zone is more difficult to date however they are kinematically consistent and located at the transition zone between thick and thin skinned post collisional tectonics and we suggest that they may represent a crustal pinch or zipper like structure that separated viscously flowing caledonian lower crust from cooler rigid basement representative for the rest of the baltic shield later extension created the north sea rift but the general rift axis and the associated riftrelated thinning developed in a narrower zone that runs oblique to the devonian trend hence the two generations of extension and thinning can be distinguished at the crustal scale

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

crustal thinning and nature of extension in the northern north sea from deep seismic reflection profiling a regional network of deep seismic reflection profiles recorded in the northern north sea has been used to map mesozoic and cenozoic basin thickness and crustal thickness in the viking graben and adjacent platform areas depth to the reflection moho varies from about 20 km in parts of the viking graben to about 32 km beneath the shetlands and the norwegian margin the shallowing of the reflection moho beneath the viking graben implies crustal stretching factors for mesozoic extension greater than 2 in the center of the north sea basin the axis of crustal thinning is located directly beneath the viking graben the axis of the sedimentary basin steeply dipping basin bounding faults are imaged in the upper crust and several dipping reflectors are observed in the upper mantle but no continuous reflective feature extending from the sedimentary basin to beneath the moho is observed on any of the deep profiles thus these data do not support the existence of lithosphere penetrating low angle detachments zones of simple shear as the cause of extension in the northern north sea some of the mantle reflectors dip to the west and some to the east suggesting that simple shear if it occurs in the upper mantle is not of uniform sense rather these data suggest a complex depth dependent pattern of brittle extensional deformation in the upper crust pervasive ductile extension bulk pure shear in the lower crust which is decoupled from deformation in the mantle and extension accommodated by discrete dipping shear zones in the lithospheric mantle

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

late palaeozoic mesozoic tectonostratigraphic development of the eastern faroe shetland basin new insights from high resolution 3d seismic and well data abstract the faroe shetland basin fsb belongs to the sedimentary basins that encompass outer parts of the ne atlantic continental margin the fsb contains several kilometres thick cenozoic and cretaceous strata which overlie poorly understood pre cretaceous strata regional high resolution 3d seismic reflection data used in this study covers the eastern half of the basin generally devoid of thick basaltic successions the pre cretaceous successions are preserved as erosional remnants of originally more extensive deposits throughout the fsb devono carboniferous and permo triassic rifting probably took place in the fsb but the magnitude and regional extent of each phase is less constrained than in the neighbouring inner hebrides shetland rift basins major rifting took place in jurassic times and generated a fault controlled marine basin during the apto albian and cenomanian distributed extension occurred throughout the fsb suggesting wide rift mode of extension the subsequent campanian maastrichtian extensional phase on the contrary was localized in the flett sub basin controlled by the westray and corona faults along its western margin and oppositely dipping faults along the eastern basin margin the fault controlled cretaceous deposition in the fsb is a distinct feature that is documented in the basins along the mid norwegian margin but rarely recorded in other large cretaceous basins along the ne atlantic margin in the fsb late cretaceous faults frequently reactivated earlier structures suggesting that a structural inheritance played an important role in basin development the existence of permo triassic evaporites is postulated to explain geometries of jurassic and lower cretaceous strata and fault patterns in the foula sub basin a partial mantle serpentinization during early cretaceous times proposed for other outer basins along the ne atlantic margin is unlikely to have occurred in the fsb

heterogeneous stretching simple shear and basin development abstract the models of basin development which involve either homogeneous stretching of the whole lithosphere or displacement on a lithospheric scale shear zone are but two end members of a range of possible extensional models the homogeneous extension model thins the lower lithosphere beneath the thinned upper crust and superimposes a thermal subsidence basin on the earlier fault bounded basin the shear zone model offsets the zone of lower lithospheric stretching and thermal subsidence it is more likely that the zones of upper and lower lithospheric stretching will be heterogeneous and patchy but will often overlap in plan view this will produce localised uplift and subsequent thermal subsidence within the faulted basin and may explain many of the anomalies between the various stretching estimates made using different structural stratigraphic and geophysical techniques the model which combines heterogeneous lithospheric stretching and associated simple shear may explain 1 variations in dip of the major detachment zones in the large basins 2 variations in types of strain on or beneath the detachment zones 3 regional uplift of part of a basin to erode the earlier fault blocks and 4 the development of volcanism in basins with only low values of upper crustal extension the zone of stretched lower crust and lithospheric mantle may lie beneath the centre of the zone of upper crustal stretching or to one side it may be linked to the upper crustal zone by faults which dip consistently in one direction or by extensional systems which change their dominant dip direction with depth pulling out the mid crust as one or more wedges possible examples are discussed from the basin and range province and northwest european continental shelf

how preexisting weaknesses control the style of continental breakup continental breakup is a highly variable process differences occur in the relative timing and extent of volcanism uplift and graben formation as well as in the mode and amount of continental extension before breakup we propose a model which reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends continental lithosphere is viewed as a composite material composed of two strong layers one in the upper mantle and one in the middle crust finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust this leads to early melt segregation and volcanism margin uplift during the late stages of the extension process and relatively narrow symmetrical extended margins in contrast failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle this produces initial graben formation cooling in the lower crust and upper mantle and broad asymmetrical extended margins volcanism only occurs late in the process failure at laterally offset weaknesses within both strong layers leads to a deformation pattern dominated simple shear thus differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup

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

periodicity of mesoscale phanerozoic sedimentary cycles and the role of milankovitch orbital modulation data on more than 200 mesoscale sedimentary cycles indicate that phanerozoic cycle periods are randomly distributed with respect to the four major milankovitch orbital parameters except late mississippian through late pennsylvanian cycles which show positive clustering about the 413 000 yr eccentricity period cycle periods calculated from average thicknesses and accumulation rates are strongly dependent on the former correlation coefficient 0 802 but relatively independent of the latter correlation coefficient 0 360 hence calculated period is largely a function of average cycle thickness and milankovitch range periods will be preferentially calculated for cycles with average thicknesses between 1 m and 20 m regardless of actual causes of cyclicity for individual cyclic sequences arguments for milankovitch control based solely on average period are unfounded comparison of short term holocene sedimentation rates and long term phanerozoic accumulation rates for cyclic peritidal and delta

numerical simulation of rifting in the northern viking graben the mutual effect of modelling parameters numerous basin modelling studies have been performed on the viking graben in the northern north sea during the past decades in order to understand the driving mechanisms for basin evolution and palaeo temperature estimations in such modelling it is important to include lithospheric flexure the values derived for the lithospheric strength by these studies vary considerably i e up to a factor of 30 in this study which is based on new interpretation of a regional transect we show that both the estimated value of the effective elastic thickness and the derived b profile are dependent on the assumed value of the depth of necking the use of models that implicitly set the level of necking at a depth of 0 km generally leads to an underestimation of the lithospheric strength and an overestimation of the thinning factors in the northern viking graben a necking depth at intermediate crustal levels gives results comparable to the observations extension by faulting is modelled to be a significant factor in conclusion rifting in the northern viking graben can be explained with various models of effective elastic thicknesses eet varying from 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking it is also shown that the development of the basin during the post rift phase cannot be explained by pure shear simple shear extension two mechanisms are proposed here to explain the post rift subsidence pattern namely intra plate stress and phase boundary migration the two extreme models for eet mentioned above 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking give very different responses to compressional stress the latter gives basically no response for realistic intra plate stress d 2004 elsevier b v all rights reserved

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

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

latest caledonian to present tectonomorphological development of southern norway abstract the regional resultant stress field of the northeastern north atlantic has shifted significantly throughout the phanerozoic in fennoscandian parts of the caledonian orogen mountain building which was characterized by nw se contraction reference to present north was followed by a collapse with transport both parallel and transverse to the mountain chain the late palaeozoic mesozoic saw several stages of e w to nw se extension varying in time and position local episodes of inversion are traceable in some cases particularly in connection with deep seated and long lived zones of weakness the cenozoic has to a larger degree been affected by compression including folding and basin inversion again some of the more pronounced effects of local inversion are related to pre existing fault systems neogene uplift of the western mountainous area in scandinavia can be unravelled by potential field study aft data and reflection seismic sections assuming that the region is close to isostatic equilibrium the uplifted areas must be supported at depth by substantial volumes of low density material within the crust or the mantle close to the crust mantle interface or close to the lithosphere asthenosphere interfaces a series of nw se oriented cross sections representing successive stages of development from the late caledonian to present were prepared and used to analyse the tectonomorphological development as related to the shifting stress configurations three stages are inferred stage 1 devonian late permian denudation of the caledonian mountain chain during the latest stage of closing of the iapetus ocean in early to mid devonian times the caledonian mountain chain reached its maximum elevation of perhaps as much as 8 9 km including the foreland basins to the east the average topographic gradient of the eastern flank may have been in the order of 1 3 the denudation of the caledonian mountains continued into the permian and by the end of the permian the mountain system was more or less obliterated with a gradient of the eastern flank probably continued to fall to less than 0 1 stage 2 triassic late cretaceous tectono thermal uplift of central south norway uplift of central south norway was rejuvenated in triassic times and continued throughout the jurassic and early cretaceous the gradient of the eastern flank increased to a maximum of approximately 0 15 and master structural elements like the laerdal gjende olestol fault complex again played important roles in the development stage 3 tertiary present renewed tectono thermal activity and post glacial rebound a second phase of post caledonian tectono thermal uplift of south central norway started in oligocene time again increasing the gradient of the eastern flank of south norway around 0 2

subaerial exposure and deposition of shallowing upward sequences evidence from stable isotopes of purbeckian peritidal carbonates basal cretaceous swiss and french jura mountains purbeckian lowermost cretaceous peritidal carbonates are characterized by open marine lagoonal intertidal and lacustrine facies arranged in milankovitch type shallowing upward sequences shallowing upward sequences typically consist of 2 6 individual beds the sequences may be i complete ii incomplete or ii pedogenetically overprinted reflecting the duration of subaerial exposure and or the extent of erosion and pedogenetic modification at the cycle tops the stable isotopic composition of the peritidal micrites reveals homogenous 6 o values attributed to diagenetic stabilization in a meteoric water buffered system carbon isotopes show three distinctly different carbon isotope patterns dependent on the completeness of the shallowing upward sequences complete shallowing upward sequences consist of l6 individual carbonate beds the carbon isotope values show a facies dependent pattern open marine carbonate muds record enriched 6i3c values of 0 28 while lagoonal 0 82 intertidal 2 46 10 and lacustrine micrites 2 96 are increasingly depleted this distinct pattern is explained by carbonate mud deposition in environments of differing salinity and marine influence incomplete sequences 2 5 carbonate beds are characterized by depleted 6 c values below subaerial exposure surfaces that become progressively enriched in c with increasing depth pedogenetically overprinted sequences 1 3 carbonate beds show strong i3c depletion throughout the sequence with little variation in the carbon isotopic composition the depleted values 4 51 10 of the pedogenetically altered micrites suggest that modification during subaerial exposure was associated with equilibration with meteoric solutions enriched in isotopically light soil gas coz the duration of subaerial exposure is the most crucial factor determining the extent of pedogenetic alterations the completeness of the shallowing upward sequences and the carbon isotope pattern the recorded patterns clearly illustrate that micrites have a good potential for the preservation of their primary carbon isotopic composition if the duration of subaerial exposure is rather brief otherwise the recorded carbon isotope patterns may support sequence stratigraphic analysis by providing a refinement of the time stratigraphic interpretation

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

architecture of shoreface to deep water systems in segmented rift systems evidence from the southern margin of the sogn graben northern north sea the spatial distribution of syn rift deposits and temporal evolution of sandy gravity flows in the context of rift segmentation are poorly constrained based on conventional core description well log analysis and 3d seismic interpretation this study focuses on the upper jurassic successions in the southern margin of the sogn graben northern north sea thirteen facies associations are classified in order to discuss the architecture of shoreface gravity driven submarine fans and basin plain deposits on the scale of centimeters to meters in the eastern part of the study area gamma ray log stacking patterns suggest that northeast southwest oriented shoreface successions underwent progradational to retrogradational deposition during the oxfordian age lithological description of conventional cores indicates that large submarine fan system formed by debris flow dominated channels and turbidity flow dominated lobe complexes covers a broad 22 20 km depositional area the entry of regional drainages and the location of sandy gravity flow deposits were controlled by first order rift segmentation whereas the route of submarine canyon feeder system and the orientation of submarine fan lobes were determined by second order rift segmentation thus both first order and second order rift segmentation should be considered when determining the sedimentary facies and depositional architecture of sandy gravity flow deposits in individual rift segments

automated thermotectonostratigraphic basin reconstruction viking graben case study we present a generic algorithm for automating sedimentary basin reconstruction automation is achieved through the coupling of a two dimensional thermotectonostratigraphic forward model to an inverse scheme that updates the model parameters until the input stratigraphy is fitted to a desired accuracy the forward model solves for lithospheric thinning flexural isostasy sediment deposition and transient heat flow the inverse model updates the crustal and mantle thinning factors and paleowater depth both models combined allow for automated forward modeling of the structural and thermal evolution of extensional sedimentary basins the potential and robustness of this method is demonstrated through a reconstruction case study of the northern viking graben in the north sea this reconstruction fits present stratigraphy borehole temperatures vitrinite reflectance data and paleowater depth the predictive power of the model is illustrated through the successful identification of possible targets along the transect where the principal source rocks are in the oil and gas windows these locations coincide well with known oil and gas occurrences the key benefits of the presented algorithm are as follows 1 only standard input data are required 2 crustal and mantle thinning factors and paleowater depth are automatically computed and 3 sedimentary basin reconstruction is greatly facilitated and can thus be more easily integrated into basin analysis and exploration risk assessment

quantitative analysis of triassic extension in the northern viking graben it has been recognized for over a decade that large displacement pre jurassic faults are present in the northern viking graben part of the north sea rift these faults define a series of major fault blocks below the more obvious jurassic rift basin we attempt here to quantify the amount of extension associated with this older rift event which is probably of early triassic age quantitative modelling of the triassic rift and the succeeding period of thermal subsidence has been undertaken using a combination of flexural backstripping and flexural cantilever forward modelling these techniques suggest that triassic extension across the horda platform norwegian sector reached c 40 s 1 4 the consequences of this extension were deposition of a thick 3 km triassic upper jurassic syn rift and post rift sequence prior to renewed but minor extension in the late jurassic earliest cretaceous the thickness of the viking group reservoirs in the troll area appears to have been almost entirely controlled by sediment loading during post triassic thermal subsidence jurassic extension on the horda platform was in the uk sector of the viking graben triassic structures are less obvious than those below the horda platform because of jurassic overprinting they are however still present average triassic extension across the east shetland basin was c 15 comparable with the magnitude of jurassic extension in the same area we believe that the tern eider and cormorant fault blocks with proven shallow basement comprised a large eroded horst during the early triassic uplifted in the footwalls of major faults flanking the magnus and statfjord half graben during the triassic the magnus half graben was contiguous with the unst basin now situated in the western footwall of the younger jurassic basin the presence of the unst basin suggests that triassic extension occurred across the area that is now the northern shetland platform continuing into the west shetland area although the more obvious structures in the viking graben are jurassic in age the earlier triassic event was equally as important in controlling the structural and stratigraphic history of the basin

extensional geometry of the mid norwegian margin before early tertiary continental breakup abstract interpretation of reflection seismic data integrated with existing crustal models provide an interpretation of the deeply buried mesozoic extensional geometry of the voring and more margins in the norwegian sea whereas late paleozoic to triassic basins are limited by high angle normal faults with nw and se dips the late jurassic early cretaceous voring and more basins are characterised by low angle normal faults that dip towards the nw between the voring and more basins at the se end of the jan mayen fracture zone a synthetic transfer zone is interpreted geometrical models based on basin and fault geometries show that the rift system detached near the upper crust lower crust transition in the study area this rift system accommodated between 110 and 140 km of post early jurassic extension according to the geometry of the present day pre cretaceous upper crust a simple geometrical forward model suggests that a substantial part of this stretching occurred during the late cretaceous paleocene thinning the central and nw segments of the late jurassic early cretaceous rift

fault distribution in the precambrian basement of south norway abstract mapping of the structural pattern by remote sensing methods landsat spot aerial photography potential field data and field study of selected structural elements shows that the cratonic basement of south norway is strongly affected by a regular lineament pattern that encompasses fault swarms of different orientation age style attitude and frequency albeit counting numerous fault and fracture populations the faults are not evenly distributed and n s to nne ssw nnw sse and ne se ene wsw systems are spatially dominant n s to nnw sse structures can be traced underneath the caledonian nappes to the western gneiss region in western and central south norway emphasizing their ancient roots dyke swarms of different ages are found within most of these zones also the ostfold oslo trondheim and the mandal molde lineament zones coincide with trends of sveconorwegian post collision granites we conclude that the n s trend includes the most ancient structural elements and that the trend can be traced back to the proterozoic svecofennian and sveconorwegian orogenic events some of the faults may have been active in neoproterozoic times as marginal faults of rift basins at the western margin of baltica remnants of such fault activity have survived in the cores of many of the faults belonging to this system the ancient systems of lineaments were passively overridden by the caledonian fold and thrust system and remained mostly but note entirely inactive throughout the sub cambrian peneplanation and the caledonian orogenic collapse in the silurian devonian the system was reactivated in extension from carboniferous times particularly in the permian with the formation of the oslo rift and parts of it remain active to the present albeit by decreasing extension and fault activity

palaeomagnetic dating of fault rocks evidence for permian and mesozoic movements and brittle deformation along the extensional dalsfjord fault western norway summary palaeomagnetic and structural studies of the dalsfjord nappe western norway show that the basal ow angle detachment dalsfjord fault is a long lived fault zone and that the most important phase of faulting was of devonian extension probably nucleated on an earlier silurian scandian thrust fault rocks produced during subsequent movements indicate that the dalsfjord fault underwent periods of brittle low angle extensional reactivation during the permian 250 260 ma and upper jurassic lower cretaceous c 150 ma corresponding with stages of major extensional movements on the continental shelf palaeomagnetic studies may be of great importance for dating faults and major movement stages in long lived fault systems the particular importance of the results is that they show that low angle normal faults can operate in a brittle upper crustal regime

structural analysis of the smeaheia fault block a potential co2 storage site northern horda platform north sea abstract smeaheia a prominent fault block located on the horda platform northern north sea is identified as a potential subsurface co2 storage site we utilise the gn1101 3d seismic survey to generate a high resolution subsurface geomodel to inform the structural style and evolution of the fault block to investigate geological controls on proposed co2 storage and provide a geometric framework as a basis for future analyses two basement involved first order north south trending fault systems the vette fault zone vfz and the oygarden fault complex ofc bound the 15 km wide fault block the vfz bifurcates down section where it is hard linked with two separate basement structures a phenomenon we term as dual rooted apart from activity during the permo triassic rift phase 1 and the late jurassic early cretaceous rift phase 2 we present evidence that rifting in this part of the north sea continued into the late cretaceous with minor reactivation in the palaeocene eocene two segments of the vfz interacted and linked at a relay ramp during rift phase 2 second order thin skinned faults show basement affinity and developed during rift phase 2 in two distinct pulses a population of polygonal faults intersects the overburden and developed during the eocene to middle miocene we have revised the areal extent of two structural closures that define the smeaheia fault block alpha vfz footwall and beta ofc hanging wall which consist of upper jurassic viking group target formations simplified cross fault juxtaposition analysis of the vfz and second order intra block faults are presented and inform pressure communication pathways between the smeaheia and tusse fault block as well as reservoir integrity and compartmentalisation the geomodel further identifies important geological controls on co2 storage in the fault block including a thinning caprock above the alpha structure and identification of hard linkage between deep tectonic faults and shallow polygonal faults