the relationship of weddell polynya and open ocean deep convection to the southern hemisphere westerlies abstractthe weddell polynya of the mid 1970s is simulated in an energy balance model ebm sea ice ocean coupled general circulation model gcm with an abrupt 20 increase in the intensity of southern hemisphere sh westerlies this small upshift of applied wind stress is viewed as a stand in for the stronger zonal winds that developed in the mid 1970s following a long interval of relatively weak zonal winds between 1954 and 1972 following the strengthening of the westerlies in this model the cyclonic weddell gyre intensifies raising relatively warm weddell sea deep water to the surface the raised warm water then melts sea ice or prevents it from forming to produce the weddell polynya within the polynya large heat loss to the air causes surface water to become cold and sink to the bottom via open ocean deep convection thus the underlying layers cool down the warm water supply to the surface eventually stops and the polynya cannot be maintained anymore during the 100 yr long model simulation

explaining the weddell polynya a large ocean eddy shed at maud rise satellite observations have shown the occasional occurrence of a large opening in the sea ice cover of the weddell sea antarctica a phenomenon known as the weddell polynya the transient appearance position size and shape of the polynya is explained here by a mechanism by which modest variations in the large scale oceanic flow past the maud rise seamount cause a horizontal cyclonic eddy to be shed from its northeast flank the shed eddy transmits a divergent ekman stress into the sea ice leading to a crescent shaped opening in the pack atmospheric thermodynamical interaction further enhances the opening by inducing oceanic convection a sea ice ocean computer model simulation vividly demonstrates how this mechanism fully accounts for the characteristics that mark weddell polynya events

the connection between the southern annular mode and a feature based perspective on southern hemisphere midlatitude winter variability abstractthis article provides a reconciling perspective on the two main but contradictory interpretations of the southern annular mode sam sam was originally thought to characterize meridional

high resolution fault displacement mapping from three dimensional seismic data evidence for dip linkage during fault growth abstract detailed mapping using high resolution three dimensional seismic data has revealed a number of sub horizontal anomalies in the distribution of vertical displacement throw on the planes of growth faults in the gulf of mexico recognition of these anomalies is highly sensitive to the interval at which the fault displacements are sampled because they represent local decreases in throw which are confined to small discrete parts of the fault planes the distribution of the anomalies is inconsistent with model displacement fields of quasi elliptical concentric contours and is therefore incompatible with models of fault growth by uniform slip distribution and radial tip line propagation an alternative model is proposed whereby the evolution of a fault plane is established by the propagation and linkage of precursor fault segments in the dip direction dip linkage overlap and linkage of fault tips in the dip direction results in relay structures that are sub parallel to fault strike and therefore displacement minima that are sub horizontal on normal and thrust faults however since they are orthogonal to the main slip direction on the fault these structures have a low preservation potential and are therefore unlikely to be well resolved on cross sectional seismic profiles

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

the significance of normal faults in the exploration and production of north sea hydrocarbons abstract the mesozoic geological history of the northern north sea was dominated by extensional faulting in addition to forming the most important hydrocarbon traps such faults can be shown to exert a significant degree of control over the distribution of mature source rocks and the deposition and erosion of reservoir rocks as exploration and production have progressed the importance of small normal faults has been increasingly recognized although they do not totally offset reservoir formations such small faults may provide lateral seals thus disrupting hydrocarbon migration routes forming subtle traps and causing technical problems during production by unanticipated compartmentalization of fields consequently as the commercial size of fields is reduced by improving production technology and the north sea matures as a hydrocarbon province a thorough understanding of the origins and characteristics of normal faults as well as a command of the increasingly sophisticated techniques for analysing the behaviour of these faults will be vital to successful exploration programmes

geodynamic and hydrodynamic evolution of the broad fourteens basin the netherlands in relation to its petroleum systems abstract data analysis in combination with 2d basin modelling is used to study the hydrogeologic and hydrodynamic response of the basin fill of the broad fourteens basin to its geodynamic evolution and the significance of this response for the evolution of the petroleum systems in the basin data analysis resulted in the identification of the major mechanical processes involved in overpressure and fluid flow evolution in the basin sedimentary loading and unloading tectonic compression and extension topography of the groundwater table and provided a timeframework for the important permeability alterations in the basin and the distinct phases of fluid flow observed present day diagenetic features and fracture characteristics in the basin indicate permeability alterations and paleo fluid flow during distinct periods of tectonic activity in the basin e g during late jurassic rifting and late cretaceous inversion the basin boundary fault zones were repeatedly reactivated during the periods of tectonic activity the 2d basin modelling included sedimentary loading and unloading topography of the water table and petroleum generation as pressure and fluid flow influencing mechanisms in addition the influence of time dependent permeability of fault zones on the overpressure history and the evolution of petroleum systems was modelled and evaluated the favoured modelling scenario including a time dependent permeability of faults shows that syn rift and post rift sedimentation in combination with gas generation induced overpressured conditions in restricted parts of the basin that is mainly in the deeper low permeable carboniferous shales and zechstein evaporites the calculated pre inversion overpressured conditions disappear during subsequent inversion of the basin predicted present day pressures in the reservoir horizons are near hydrostatic and reasonably in accordance with observed pressures the favoured scenario also explains the known location of oil fields and the location and saturation characteristics of the gas occurrences the model results further show that the difference in timing of oil charging of the p9 and q1 lower cretaceous reservoirs explains the observed differences in geochemical composition of the accumulated oils the biodegraded and water washed nature of the late cretaceous charged q1 oil reservoir is consistent with the concentrated topography induced groundwater flow through lower cretaceous reservoir units during the late cretaceous inversion period late charging of the lower cretaceous oil reservoir in the p9 area explains the non biodegraded character of the accumulated oils in general this paper shows the importance of using data analysis to obtain an a priori characterization of the basin geofluid evolution and shows that paleohydrodynamic conditions and time dependent permeability of the hydrogeological framework have influenced significantly the petroleum systems in the basin

seismotectonics of madagascar abstract instrumental seismic activity in madagascar over a 16 years period as well as the largest earthquakes experienced over the last century are studied using seismic signal recordings and the archives of the antananarivo geophysical observatory institut et observatoire de geophysique d antananarivo earthquakes occur in most of the island the known focal mechanisms indicate a general e w extension consistent with the stretching currently observed in the mozambique channel and on the eastern edge of the african continent seismic areas cover the main pliocene quaternary tectonic formations other events are located near pan african tectonics structures preferentially reactivated within the precambrian basement complex a regional origin of stresses cannot explain completely the spatial distribution of all the earthquakes in the central highlands of madagascar an other possible stress origin can be a thermal bulge on which the main pliocene quaternary tectonic and volcanic structures of this region are situated the current tectonic phase of extension seems to correspond to an early stage of reactivation madagascar could be part of the e w extension zone associated with diffuse seismicity affecting east africa south of the equator

new zircon ages for precambrian granites gneisses and granulites from central and southern madagascar significance for correlations in east gondwana institiif fiir geozuissenschnffen universitiit mainz 55099 mainz gevniany 2depnrtnienf of geology university of leicesfer leiccsfev le 1 7r h uk 3mnx plnnck lnsfitzit fiiv clzeniie postjnclz 3060 55020 mcriiiz geuniany 4depf of applzed geology ciirfin university of t c c z j i o o pevflz wa 6001 airstvaliii 5dc ppnrfeniei f des sciences nnfirreiles uiiiversitt de toliavn tolinrn mndngascav

paleostresses of the groningen area the netherlands results of a seismic based structural reconstruction article i nfo we describe a novel workflow to reconstruct paleostresses in the subsurface where the traditional outcrop based method that uses fault slip measurements is not possible we use 3d seismic data and structural restoration to determine fault surfaces and slip vectors these data are then used as input for paleostress reconstruction algorithms the study area of ca 750 km 2 is situated in the groningen block the netherlands excellent quality 3d seismic data were used to interpret 11 horizons and approximately 80 faults between the tertiary and the top rotliegend indicators of fault slip direction are fault undulations sedimentary structures offset by faults and shapes of horizon cut outs these indicators were used as a basis of 3d restoration of the interpreted horizons a stepwise restoration approach was chosen that removed younger deformation to obtain slip vectors for older deformation events in a following work step numeric dynamic analysis nda was used to calculate paleostress tensors for the middle and lower tertiary upper cretaceous and upper rotliegend sequences the results presented in this paper are consistent with existing paleostress interpretations for nw europe however in contrast to previous studies they are derived from a subsurface volume where paleostress information was lacking until now issues that need further study include the effect of the size of the study area on the assumptions of a homogenous stress field and an analysis of the ambiguity of the interpretation of fault slip indicators on 3d seismic data

structural and tectonic setting of the permo triassic basins of northwest europe abstract the permo triassic basins of nw europe formed by i late orogenic spreading of the variscan mountain belt eventually leading to ocean floor formation in the mid atlantic ii continental rifting propagating south from the arctic and iii thermal subsidence following carboniferous volcanic activity in the north sea spreading values in the northernmost north sea west of shetland and west and southwest of britain are relatively high but the sediments are dominantly continental the permo triassic rifting affected lithosphere thickened during caledonian and variscan orogenesis however subsidence associated with the arctic rifting together with global sea level changes allowed marine incursions into the north sea producing the large zechstein salt basins interference of the different basin formation mechanisms led to a complex three dimensional fault pattern and multidirectional extension across britain and the north sea this fault pattern formed the basic framework for subsequent jurassic and cretaceous basin formation

the effect of increased fresh water from antarctic ice shelves on future trends in antarctic sea ice observations show that in contrast to the arctic the area of antarctic sea ice has increased since 1979 a potential driver of this significant increase relates to the mass loss of the antarctic ice sheet subsurface ocean warming causes basal ice shelf melt freshening the surface waters around antarctica which leads to increases in sea ice cover with climate warming ongoing future mass loss rates are projected to accelerate which has the potential to affect future antarctic sea ice trends here we investigate to what extent future sea ice trends are influenced by projected increases in antarctic freshwater flux due to subsurface melt using a state of the art global climate model ec earth in standardized climate model intercomparison project phase 5 cmip5 climate change simulations virtually all cmip5 models disregard ocean ice sheet interactions and project strongly retreating antarctic sea ice applying various freshwater flux scenarios we find that the additional fresh water significantly offsets the decline in sea ice area and is even able to reverse the trend in the strongest freshwater forcing scenario that can reasonably be expected especially in austral winter the model also simulates decreasing sea surface temperatures ssts with the sst trends exhibiting strong regional variations that largely correspond to regional sea ice trends

gold occurrences in madagascar south india and sri lanka significance of a possible pan african event abstract gold occurs in various quantities mainly in the central and southern parts of sri lanka although gold is recovered mainly from river sediments at present it has been mined in the past also from a concordant quartz reef in central sri lanka and from other types of sediments such as marshy beds surrounding dykes of ultramafic composition in southern sri lanka the sedimentary gold has been interpreted as being derived from the mineralizations of the latest deformational features such as ductile and brittle shears and fractures consisting of quartz veins minor pegmatites and sulphide mineralizations mainly of pyrite pyrrhotite and chalcopyrite the mineralization of gold is exclusively in the highland complex rocks of sri lanka which represent archaean late proterozoic metamorphic complexes in madagascar gold is present in the precambrian basement rocks consisting of some greenstone belts and metasediments as a diffused mineral in the rocks concordant quartz reefs and more recent discordant quartz veins the concordant quartz veins and diffused gold are related to both archaean and proterozoic rock associations and the discordant veins which have been identified as permo triassic are found mainly in the north within the contact zone of proterozoic rocks and the phanerozoic cover gold is also recovered form ancient and recent alluvial accumulations and lateritic earth the mineralization of vein deposits is mainly gold quartz and gold sulphide associations the sulphides being galena chalcopyrite and pyrite in south india gold occurs in archaean metamorphic units comprising of granite greenstone complexes in the kolar classic gold field and in granulite terranes in more southerly occurrences such as the historic wynad fields in both cases gold occurs in gold quartz veins which occupy fissures and shears within the archaean metavolcanics gold also occurs in the attapadi area of kerala both in sediments and in primary epigenetic gold deposits which are hosted by precambrian amphibolites and granitic gneisses the attapadi lode veins are predominantly structurally controlled and are closely associated with the proterozoic bhavani shear zone gold is recovered both from the primary and placer deposits and the primary deposits contain gold quartz veins gold quartz carbonate veins and gold quartz sulphide veins the sulphide minerals are mainly galena pyrite chalcopyrite and arsenopyrite the rocks in the southern madagascar southern india and sri lanka belong to granulite terranes that have peak metamorphic imprints and tectonic development during the pan african the emplacement of gold mineralization mainly in madagascar and south india can be correlated in the archaean the gold deposition in the later deformational structures with concordant and discordant gold bearing veins can be correlated also with those in sri lanka as a pan african mineralizing event it is also evident that co2 rich fluids from a deep seated source has continued from archaean and were still active during the proterozoic being responsible for the pan african event of gold deposition particularly in the younger structures in these countries

preconditioning and formation of maud rise polynyas in a high resolution earth system model abstractopen ocean polynyas oops in the southern ocean are ice free areas within the winter ice pack that are associated with deep convection potentially contributing to the formation of antarct

geological setting and controls on the development of graphite sillimanite and phosphate mineralization within the jiamusi massif an exotic fragment of gondwanaland located in north eastern china abstract china is the world s biggest producer and exporter of graphite and also possesses the world s largest reserves of crystalline graphite one of the main production areas is in northeastern china around jixi in heilongjiang province where graphite sillimanite and phosphate form in original sedimentary horizons within the mashan group the mashan group is composed of khondalitic metasediments and tectonically interleaved orthogneisses all metamorphosed to granulite facies the peak conditions have been calculated at 800 850 c at 5 3 6 2 kb and the p t t path defines a tight clockwise loop involving simultaneous decrease in temperature and pressure falling to 410 490 c at less than 3 kb this metamorphic event is interpreted as resulting from continent continent collision with emplacement of mantle derived mafic magma and possible delamination at the base of the crust metamorphism has been precisely dated at 500 ma using u pb zircon shrimp techniques it appears likely that this terrane formed part of an originally more extensive orogenic belt of late pan african age rocks of similar age are recorded from east antarctica western australia india and sri lanka suggesting that the mashan group was most likely juxtaposed with these areas within gondwanaland the mechanism by which the mashan group arrived at its present position between the siberian and north china cratons is poorly constrained but it appears likely that along with the north china south china and tarim blocks it underwent a northward drift from an initial location off northern australia to finally dock with the siberian craton in the late permian to late jurassic

observed interaction between pacific sea ice and the western pacific pattern on intraseasonal time scales the relationship between north pacific sea ice and the western pacific wp pattern is examined using wintertime observational data between 1978 and 2008 weekly averaged data are chosen to capture the characteristically short time scale of the wp a clear relationship is found between the wp and sea ice concentrations in the bering sea where the positive polarity of the wp is accompanied by increasing sea ice concentrations and the negative wp by decreasing sea ice concentrations sea ice concentrations in the sea of okhotsk however are shown to be largely insensitive to the strength of the wp feedback of bering sea sea ice concentrations onto the wp is tested by fitting weekly averaged observations to a vector autoregressive var model results from the var model indicate that feedback of bering sea sea ice onto the wp plays a significant role in the dynamics of the wp and that this feedback is positive that is wp induced changes in bering sea sea ice concentrations help sustain existing wp conditions thereby lengthening the time scale of variability of the wp

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

provenance and tectonic significance of the palaeoproterozoic metasedimentary successions of central and northern madagascar abstract new detrital zircon u pb age data obtained from various quartzite units of three spatially separated supracrustal packages in central and northern madagascar show that these units were deposited between 1 8 and 0 8 ga and have similar aged provenances the distribution of detrital zircon ages indicates an overwhelming contribution of sources with ages between 2 5 and 1 8 ga possible source rocks with an age of 2 5 ga are present in abundance in the crustal segments antananarivo antongil and masora domains either side of a purported neoproterozoic suture betsimisaraka suture zone recently possible source rocks for the 1 8 ga age peak have been recognised in southern madagascar all three supracrustal successions as well as the archaean blocks onto which they were emplaced are intruded by mid neoproterozoic magmatic suites placing a minimum age on their deposition the similarities in detrital pattern maximum and minimum age of deposition in the three successions lend some support to a model in which all of madagascar s archaean blocks form a coherent crustal entity the greater dharwar craton rather than an amalgamate of disparate crustal blocks brought together only during neoproterozoic convergence however potential source terranes exist outside madagascar and on either side of the neoproterozoic sutures so that a model including a neoproterozoic suture in madagascar cannot be dispelled outright

a possible link between the weddell polynya and the southern annular mode abstract shortly after the advent of the first imaging passive microwave sensor on board a research satellite an anomalous climate feature was observed within the weddell sea during the years 1974 1976 a 250 103 km2 area within the seasonal sea ice cover was virtually free of winter sea ice this feature the weddell polynya was created as sea ice formation was inhibited by ocean convection that injected relatively warm deep water into the surface layer though smaller less persistent polynyas associated with topographically induced upwelling at maud rise frequently form in the area there has not been a reoccurrence of the weddell polynya since 1976 archived observations of the surface layer salinity within the weddell gyre suggest that the weddell polynya may have been induced by a prolonged period of negative southern annular mode sam during negative sam the weddell sea experiences colder and drier atmospheric conditions making for a saltier surface layer with reduced pycnocline stability t

the physics of gas chimney and pockmark formation with implications for assessment of seafloor hazards and gas sequestration pockmarks form where fluids discharge through seafloor sediments rapidly enough to make them quick and are common where gas is present in near seafloor sediments this paper investigates how gas might lead to pockmark formation the process is envisioned as follows a capillary seal traps gas beneath a fine grained sediment layer or layers perhaps layers whose pores have been reduced in size by hydrate crystallization gas accumulates until its pressure is sufficient for gas to invade the seal the seal then fails completely a unique aspect of capillary seals releasing a large fraction of the accumulated gas into an upward propagating gas chimney which displaces water like a piston as it rises near the seafloor the water flow causes the sediments to become quick i e liquefied in the sense that grain to grain contact is lost and the grains are suspended dynamically by the upward flow the quickened sediment is removed by ocean bottom currents and a pockmark is formed equations that approximately describe this gas piston water drive show that deformation of the sediments above the chimney and water flow fast enough to quicken the sediments begins when the gas chimney reaches half way from the base of its source gas pocket to the seafloor for uniform near surface sediment permeability this is a buoyancy control not a permeability control the rate the gas chimney grows depends on sediment permeability and the ratio of the depth below seafloor of the top of the gas pocket to the thickness of the gas pocket at the time of seal failure plausible estimates of these parameters suggest gas chimneys at blake ridge could reach the seafloor in less than a decade or more than a century depending mainly on the permeability of the deforming near surface sediments since these become quick before gas is expelled gas venting will not provide a useful warning of the seafloor instabilities that are related to pockmark formation however detecting gas chimney growth might be a useful risk predictor any area underlain by a gas chimney that extends half way or more to the surface should be avoided c 2009 elsevier ltd all rights reserved

discovery of ring faults associated with salt withdrawal basins early cretaceous age in the east texas basin abstract the jurassic louann salt in the east texas basin has played a dominant role in influencing the structural and depositional history of the basin particularly during the jurassic and cretaceous periods salt tectonics is closely associated with sandstone distribution depositional facies and reef growth and consequently with petroleum traps in the basin salt withdrawal basins developed during the early cretaceous in response to salt movement and dissolution processes are characterized by the presence of an expanded section of lower cretaceous marine and deltaic sedimentary rocks recognition of fault sets associated with the evolution of these salt withdrawal basins has gone undetected until the recent coherence cubetm processing of a non proprietary 3 d seismic survey conducted by schlumberger in the la rue dome fairway field area henderson county texas images from coherence cube processing aptly exhibit extraordinary sets of concentric ring faults that comprise the periphery of two salt withdrawal basins the fairway oil field is located at the junction of these two sets of ring faults the structural style of these high angle ring faults creates a multitude of possible fault traps in a previously unattractive structural setting early cretaceous age of the ring faults establishes that these faults are a significant element in evaluating petroleum migration patterns and traps in the basin the discovery of early cretaceous ring faults in the east texas basin by coherence cube processing brings new perspectives to development and exploration drilling in this mature petroleum province

inversion of the broad fourteens basin offshore netherlands a small scale model investigation abstract the southern north sea exhibits spectacular examples of graben inversion which have been extensively documented by oil industry exploration the broad fourteens basin which is located at the southern limit of the southern permian salt basin displays numerous structural patterns of positive inversion which are related to the inversion which are related to the presence and thickness of zechstein salts in the northern part of the broad fourteens basin the zechstein salt is rather thick 500 m allowing decollement of the mesozoic series during both extension and compression salt is missing to the southern part of this graben and both mesozoic series and palaeozoic basement display similar patterns of deformatiqn the mechanical significance of inversion patterns was investigated through laboratory experiments on brittleductile models models were built with sand and silicone putty that represent respectively the frictional behaviour of the mesozoic cover as well as the palaeozoic basement and the viscous behaviour of a decollement layer mainly composed of zechstein salts which is intercalated between them the models were scaled to fit natural configurations observed in the broad fourteens basin all small scale experiments were carried out in two steps 1 graben formation with synkinematic sedimentation and 2 compression at various angles of obliquity to the graben experimental results show that the structures generated by or reactivated during inversion are strongly dependent on a the strength of the decollement layer which is a function of the layer thickness and of the displacement velocity applied at the model boundaries and b the strength of the sedimentary overburden which is a function only of its thickness for a given lithology reactivation of normal faults occurs when the angle between the compression and the direction of the normal faults is smaller than 45 the ductile layer which can be a source for diapirs during extension plays during compression an important ro1e in the thrusting of the graben fill onto the adjacent platforms

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

geochemistry of pelitic and psammopelitic precambrian metasediments from southwestern sri lanka implications for two contrasting source terrains and tectonic settings most of the pelitic and psammopelitic metasediments of southwestern sri lanka are compositionally transitional between shales and greywackes and are of two isotopically distinct types metasediments of the northern part have nd model ages of 1 5 ga and belong to the relatively younger nd model age province of wanni complex wc model ages of two southerly located samples are 2 8 ga being compatible with those of the highland complex hc in accordance with mostly mesoproterozoic to late archaean crustal residence ages cr ni la th and ree data also suggest that the sources of these metasediments are plagioclase fractionated post archaean upper crustal material crustal differentiation of source terrains corresponding to the hc and the wc probably occurred at distinctly different time intervals significant differences exist between the major and trace element chemistry of the metapelites from the wc north and the hc south suggesting derivation from two different source terrains metasediments of the south are slightlymmore siliceous low in sc and v and highly enriched in lree 220 ppm their sources have been chemically evolved felsic igneous rocks and or recycled sediments relatively high v sc feo mgo tio2 and slightly low sio2 in the rocks of the wc indicate contribution of more basic sources cia chemical index of alteration estimates and comparative alkali alkaline earth element patterns suggest relatively fresh source material the o isotope data indicate that the pre metamorphic isotope signatures are preserved and the clay component of the original sediments mainly consisted of illite typifying continental weathering conditions sediments of the south hc were probably deposited in a passive continental margin continental rift environment while those of the northern part wc were probably formed at an andean type active continental margin the two units were tectonically juxtaposed prior to pan african granulite metamorphism

southern ocean sector centennial climate variability and recent decadal trends abstractevidence is presented for the notion that some contribution to the recent decadal trends observed in the southern hemisphere including the lack of a strong southern ocean surface warming may have originated from longer term internal centennial variability originating in the southern ocean the existence of such centennial variability is supported by the instrumental sea surface temperatures ssts a multimillennial reconstruction of tasmanian summer temperatures from tree rings and a millennial control integration of the kiel climate model kcm the model variability was previously shown to be linked to changes in weddell sea deep convection during phases of deep convection the surface southern ocean warms the abyssal southern ocean cools antarctic sea ice extent retreats and the low level atmospheric circulation over the southern ocean weakens after the halt of deep convection the surface southern ocean cools the abyssal southern ocean warms antarctic sea ice expands and the low leve

bulls eye pockmarks and polygonal faulting in the lower congo basin relative timing and implications for fluid expulsion during shallow burial abstract this study describes a new type of pockmark association from the lower congo basin offshore west africa consisting of up to 8 stacked paleopockmarks separated by intervals of drape and onlap fill the stacked paleopockmarks occur within the depocentres of polygonally faulted plio pleistocene sediments and are distributed evenly in the downslope parts of two salt mini basins the majority of the stacked pockmarks initiated synchronously in the late pliocene 3 ma with a subordinate initiation phase in the mid pliocene 4 ma the primary agents in pockmark formation are interpreted to be pore water expelled during early stage compaction together with biogenic methane bottom simulating reflections bsrs associated with free gas overlain by gas hydrates are currently found in the area it is speculated that biogenic methane accumulated within and below a clathrate cap which was repeatedly breached forming pockmarks at discrete horizons separated by intervals of draping sedimentation the mid and late pliocene pockmark initiations appear to coincide with sea level falls following periods of relatively stable highstand conditions several subsequent pockmark horizons may similarly correlate with subsequent sea level falls during the late pliocene and early pleistocene the stacked paleopockmarks are completely surrounded by polygonal faults and consistently occur within polygonal fault cells that crosscut the succession containing the stacked pockmarks early stage compaction and dewatering of the pliocene sediments thus preceded polygonal faulting providing a constraint on the conditions leading to polygonal faulting of the fine grained host sediments the relationship documented here is interpreted as due to the presence of a hydrate cap in the plio pleistocene mini basins which may have retarded the normal compaction processes and facilitated pockmark formation by allowing the build up of gas hydrate and free gas in the basin centres the relative timing and spatial relationships implies that fluids expelled due to polygonal faulting were not implicated in pockmark formation in this area

antarctic offshore polynyas linked to southern hemisphere climate anomalies offshore antarctic polynyas large openings in the winter sea ice cover are thought to be maintained by a rapid ventilation of deep ocean heat through convective mixing these rare phenomena may alter abyssal properties and circulation yet their formation mechanisms are not well understood here we demonstrate that concurrent upper ocean preconditioning and meteorological perturbations are responsible for the appearance of polynyas in the weddell sea region of the southern ocean autonomous profiling float observations collected in 2016 and 2017 during the largest polynyas to form near the maud rise seamount since 1976 reveal that the polynyas were initiated and modulated by the passage of severe storms and that intense heat loss drove deep overturning within them wind driven upwelling of record strength weakened haline stratification in the upper ocean thus favouring destabilization in 2016 and 2017 we show that previous weddell polynyas probably developed under similarly anomalous conditions which are associated with a mode of southern hemisphere climate variability that is predicted to strengthen as a result of anthropogenic climate change measurements collected during recent polynya events in the southern ocean reveal that these sea ice openings formed as a result of weakened stratification and severe storms and were sustained by deep overturning

multi centennial variability controlled by southern ocean convection in the kiel climate model a quasi oscillatory multi centennial mode of open ocean deep convection in the atlantic sector of the southern ocean in the kiel climate model is described the quasi periodic occurrence of the deep convection causes variations in regional and global surface air temperature southern hemisphere sea ice coverage southern ocean and north atlantic sea surface height the antarctic circumpolar current and the atlantic meridional overturning circulation amoc the deep convection is stimulated by a strong built up of heat at mid depth when the heat reservoir is virtually depleted a coincidental strong freshening event at the sea surface shuts down the convection the heat originates from relatively warm deep water formed in the north atlantic the several decades lasting recharge process of the heat reservoir depends on the amoc and the weddell gyre and sets a minimum delay for the deep convection to recur while the strength of the amoc increases the weddell gyre weakens during the non convective regime convection onset and shutdown also depend on the stochastic occurrence of favorable sea surface conditions which contributes to the multi centennial period of the phenomenon the shutdown triggers a century long deviation in amoc strength caused by significant reductions in bottom water formation and surface salinity in the southern ocean s atlantic sector additional numerical experimentation reveals that sea ice has an important effect on the frequency of occurrence and intensity of the deep convection further we find intriguing similarities to the weddell polynya observed during the 1970s

3d seismic analysis of circular evaporite dissolution structures eastern mediterranean buried circular collapse structures above a tabular evaporitic body are recorded by recently acquired 3d seismic data on the levant basin and continental margin offshore israel eastern mediterranean the structures formed during the pliocene as buried messinian late miocene evaporites underwent extensive dissolution in a submarine deep water setting three dimensional seismic analysis is used to describe the detailed morphology of the structures and the associated overburden allowing the reconstruction of their origin and development it is proposed that evaporite dissolution led to the collapse of the weakly lithified overburden and this deformed with a series of concentric extensional faults from the structural analysis of the overburden the estimated maximum duration of the dissolution event is 0 75 1 ma the mechanism proposed for the creation of the circular collapse structures is subjacent dissolution of the more soluble evaporites in the messinian evaporites as a result of focused vertical fluid flow at the base of the evaporitic series rapid release of overpressured fluids as for example during an earthquake is thought to have initiated the focused fluid flow which impinged on the evaporitic seal to the point where dissolution occurred creating the localized circular collapse structures in the overburden

fluid flow during early compartmentalisation of rafts a north sea analogue for divergent continental margins high quality 3d seismic data tied to eighteen 18 boreholes are used to investigate the styles of faulting and associated fluid flow features in triassic early jurassic rafts of the broad fourteens basin southern north sea the study area is presented as an analogue for continental margins experiencing early stage gravitational gliding i e prior to complete separation and downslope translation of individual rafts in such a setting and for present day stress conditions fault slip data indicate that chasms and faults separating rafts in the broad fourteens basin comprise structures subject to dip slip and strike slip reactivation chasms and faults sub parallel to these latter chasms comprise the most significant bypass areas for fluid sourced from pre salt strata faults sub parallel to the main chasms show limited propagation into early cretaceous and cenozoic strata draping the rafts a character further stressed by the depth of occurrence of fluid pipes and dim spots this is an important observation and leads us to postulate that faults formed during early stage rafting control fluid flow in regions where gravitational gliding is limited such as west and equatorial africa southeast brazil and parts of the gulf of mexico

geological controls on focused fluid flow associated with seafloor seeps in the lower congo basin a synthesis of backscatter imagery coupled with a large 3d seismic dataset in the lower congo basin lcb reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth with the exception of one region of anomalous backscatter positive relief mounds all inferred seep sites occur in negative relief pockmarks the extensive 3d seismic dataset in the lcb offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems and in general to reconstruct the relationship between tectonics and fluid flow in continental margins the fluid seeps in the lcb are associated with morphologically stratigraphically or tectonically controlled focused fluid flow the integration of the geophysical datasets backscatter imagery coupled to 3d seismic clearly indicates that fluid seeps are not randomly distributed but their seabed organization reflects 1 the location of the underlying structure reservoir or trap where the fluids are coming from 2 the geometry and morphology of the reservoir trap and 3 the discontinuities in the sedimentary column along which fluids have migrated in the lcb seafloor pockmarks are always associated with underlying tectonic structures fault zones salt diapirs polygonal faults or buried sedimentary bodies turbiditic channels erosional surfaces whereas they never occur above sub horizontal parallel stratified fine grained sediments even if triggering processes can not be clearly defined here we propose a model of seafloor fluid seep organization which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from this qualitative 3d model provides insight into the geohydrologic processes of continental margins

integrating 3 d seismic data field analogs and mechanical models in the analysis of segmented normal faults in the wytch farm oil field southern england united kingdom we propose a methodology for the analysis of normal fault geometries in three dimensional 3 d seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault controlled oil fields limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization detailed seismic data analyses that incorporate principles of normal fault mechanics however can reveal evidence of fault segmentation we integrate seismic attribute analyses outcrop analog observations and numerical models of fault slip and displacement fields to augment the use of 3 d seismic data for fault interpretation we applied these techniques to the wytch farm oil field in southern england resulting in the recognition of significant lateral and to a lesser extent vertical segmentation of reservoir scale faults slip maxima on fault surfaces indicate two unambiguous segment nucleation depths controlled by the lithological heterogeneity of the faulted section faults initiated preferentially in brittle sandstone and limestone units subsequent growth and linkage of segments predominantly in the lateral direction resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima reservoir compartmentalization is greatest at the level of prevalent segment linkages which corresponds at wytch farm with the predominant hydrocarbon producing unit the sherwood sandstone at relatively shallower depths fault segments are younger and less evolved resulting in a greater degree of segmentation with intact relay zones

implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults abstract reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults concentric faults both or neither explanations for this variation are offered based on integration of fault kinematics published studies and seismic examples strata around diapirs can be divided into three structural domains with characteristic fault styles 1 roof zone between the present day depositional surface and crest of a buried inactive diapir this zone is characterised by doming radial faults and occasionally conic graben doming is usually caused by differential compaction and increases with depth 2 a steeply dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius recording near surface diapir growth in poorly lithified sediments these contain early gravity slumps and late concentric extensional faults regional layer bound polygonal fault systems form radial faults within approximately one diapir radius the only significant radial faulting mechanism below the roof zone 3 diapir root zone of strata whose structural architecture records the diapirs initiating mechanism typically rim synclines or graben that detach on the salt source layer concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata these models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging for instance below overhanging salt

physical modeling of structures formed by salt withdrawal implications for deformation caused by salt dissolution by creating 15 physical models we investigated deformation above subsiding tabular salt salt walls and salt stocks dry quartz sand simulated a brittle sedimentary roof above viscous silicone representing salt the modeled diapiric walls had linear planforms and rectangular semicircular triangular or leaning cross sectional shapes the stock was cylindrical in models where the source layer or allochthonous salt sheet was initially tabular a gentle flat bottomed syncline bounded by monoclinal flexures formed above a linear zone where the silicone was locally removed above all subsiding diapirs the deformed roof was bounded by an inner zone of steep convex upward reverse faults and an outer zone of normal faults above subsiding diapiric walls extensional and contractional zones were balanced above the subsiding salt stock conical concentric fault zones comprised inner reverse faults and outer normal faults sediments were added both before prekinematic and during synkinematic salt withdrawal in entirely prekinematic roofs reverse fault zones and normal fault zones both widened with time reverse faults propagated upward from the corners of the withdrawing diapirs new reverse faults formed in the footwalls of reverse faults each nearer the center of the deepening roof trough conversely new normal faults formed successively outward from the sagging trough synkinematic deposition retarded faulting but the pattern of inner reverse and outer normal faults was repeated however reverse faults formed successively outward whereas normal faults formed inward new conceptual models suggest that salt dissolution forms similar structures to those physically modeled for salt withdrawal the appropriate physical models resemble natural dissolution structures above tabular salt extension alone above diapirs is not caused merely by salt withdrawal or dissolution but by regional extension or active diapirism

southern ocean bottom water characteristics in cmip5 models 1 southern ocean deep water properties and formation processes in climate models are indicative of their capability to simulate future climate heat and carbon uptake and sea level rise southern ocean temperature and density averaged over 1986 2005 from 15 cmip5 coupled model intercomparison project phase 5 climate models are compared with an observed climatology focusing on bottom water bottom properties are reasonably accurate for half the models ten models create dense water on the antarctic shelf but it mixes with lighter water and is not exported as bottom water as in reality instead most models create deep water by open ocean deep convection a process occurring rarely in reality models with extensive deep convection are those with strong seasonality in sea ice optimum bottom properties occur in models with deep convection in the weddell and ross gyres bottom water formation processes are poorly represented in ocean models and are a key challenge for improving climate predictions

recent antarctic sea ice trends in the context of southern ocean surface climate variations since 1950 this study compares the distribution of surface climate trends over the southern ocean in austral summer between 1979 2011 and 1950 1978 using a wide variety of data sets including uninterpolated gridded marine archives land station data reanalysis and satellite products apart from the antarctic peninsula and adjacent regions sea surface temperatures and surface air temperatures decreased during 1979 2011 consistent with the expansion of antarctic sea ice in contrast the southern ocean and coastal antarctica warmed during 1950 1978 sea level pressure slp and zonal wind trends provide additional evidence for a sign reversal between the two periods with cooling warming accompanied by stronger weaker westerlies and lower higher slp at polar latitudes in the early late period such physically consistent trends across a range of independently measured parameters provide robust evidence for multidecadal climate variability over the southern ocean and place the recent antarctic sea ice trends into a broader context

structural evolution of inverted basins in the dutch offshore abstract the structural evolution of the dutch central north sea graben and the fault bounded broad fourteens basin is discussed graben formation started during the early triassic and culminated in strong differential subsidence during the late jurassic early cretaceous narrow fault bounded grabens and troughs and broad intervening highs were formed as a result of crustal distension and associated transtensional deformations the thickness of the late jurassic to early cretaceous fill of these basins may have exceeded 3000 m concurrent with the filling of these basins the bordering highs became deeply truncated during the late cretaceous and early tertiary compressive stresses resulted in inversion of these basins whereby movements along their bounding normal faults were reversed giving rise locally to overthrusting as for instance in the broad fourteens and west netherlands basins the timing of these compressional deformations has been palaeontologically dated and coincides with major orogenic events in the alps

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

seismic characteristics of fluid escape pipes in sedimentary basins implications for pipe genesis abstract fluid escape pipes were first documented from 3d seismic data over a decade ago and have subsequently been identified in many petroliferous basins worldwide they are characterized on seismic data by vertical to sub vertical zones of reduced reflection continuity that have a columnar geometry in three dimensions the upper terminations of these pipes commonly coincide with pockmarks or palaeo pockmarks signifying a close connection of pipe formation with a high flux fluid expulsion process dimensions range from tens to hundreds of metres in diameter and hundreds to over a thousand metres in height and the slenderness ratio defined as height diameter ranges from 0 8 to over 20 pipes are frequently associated with sub vertical clustering of amplitude anomalies on seismic data related either to the presence of free gas or to cementation linked to the passage of hydrocarbons three mechanisms have been suggested to explain pipe genesis 1 hydraulic fracturing 2 erosional fluidisation and 3 capillary invasion we suggest a further two possible mechanisms in the form of localised collapse by volume loss and synsedimentary flow localisation we review all five mechanisms and conclude that it is unlikely that a single mechanism applies but that combinations of these processes may all occur in particular contexts fluid escape pipes may be far more widespread that currently appreciated and they may play a critical role in secondary hydrocarbon migration and in providing leakage pathways for trapped hydrocarbons through overlying seals

synthesis of salt tectonics in the southern north sea uk abstract a structural model encompassing the southern north sea basin west of the central graben has been developed this model consists of a rift system affecting the post salt section around the basin margin and a large area of detached compressional buckle folds within the basin this pattern is initially a response to gravity sliding of the post salt section on the salt within the basin during the late triassic to late jurassic a close relationship between the location and trend of the peripheral graben system and basement structures in the pre salt is noted pre jurassic extension across the peripheral graben systems was balanced by the sum of fault heaves at the pre salt rotliegend level and shortening across salt cored buckle folds in the post salt section salt pillows and swells passively infilled the cores of these gravity induced buckle folds cretaceous and tertiary inversion involved basin tilt and renewed movement on basin bounding basement faults notably reverse movements did not propagate from basement structures up into the peripheral graben systems the post salt sedimentary section experienced gravity spreading in response to inversion related uplift resulting in syn inversion extensional faulting in the sole pit high where the mesozoic section was thickest this extension combined with a loss of fault heave in the pre salt section was balanced by amplification of salt cored buckle folds in the centre of the basin in the context of the model described here salt pillows represent passive infill of thin skinned compressional buckle folds which later amplified during thick skinned basement shortening crestal collapse of such folds occurs via normal faulting accompanied by reactive diapirism such reactive diapirs establish conduits through which salt may leak leading to pillow deflation and ultimately conduit preservation as a salt wall flanked by rim synclines in areas where the buckle folds were emergent the salt structures described here are related to cover folds and faults which in turn reflect episodes of basin extension tilting and inversion hence individual salt structures can be said to be only remotely connected with regional intraplate stresses

the tectonic evolution of the southern dutch north sea during the palaeogene basin inversion in distinct pulses abstract in this paper we discuss the response of a sedimentary basin to compressional reactivation of extensional faults in distinct pulses the inversion of the broad fourteens basin in the southern dutch north sea is used as a case study the first pulse of inversion occurred during the late mesozoic as a result of the sub hercynean phase a second pulse occurred during the mid palaeocene laramide phase a final inversion pulse occurred around the eocene oligocene boundary coinciding with the pyrenean tectonic event we reconstructed the stratigraphic and structural development of the area during the palaeogene in detail basic data are two 2d seismic surveys supported by 74 geophysical wireline logs on which newly constructed depth and thickness maps are based the reconstruction is aided by a quantitative subsidence analysis cessation of compression resulted in relaxation and tensional reactivation of faults caused differential subsidence inheritance of geological structures is a key element in the tectonic activity in the broad fourteens basin during the palaeogene tectonic movement during the palaeogene was always accommodated by reactivation of palaeozoic mesozoic faults the intensity of inversion in the southern north sea basin during the pyrenean phase appears much larger than previously noticed moreover the area affected by the inversion is much wider than during previous phases minor differences in the direction of the local stress field between the tectonic phases and by the deposition of a thick sedimentary succession during the periods of tectonic quiescence between the inversion phases can account for this

reservoir leakage along concentric faults in the southern north sea implications for the deployment of ccs and eor techniques high quality 3d seismic and borehole data in the broad fourteens basin southern north sea is used to investigate newly recognised concentric faults formed in salt withdrawal basins flanking reactivated salt structures throw depth and throw distance plots were used to understand the growth histories of individual faults as a result three families of concentric faults are identified a intra seal faults within a salt withdrawal basin b faults connecting the seal and the reservoir on the crest of an inverted anticline c raft bounding faults propagating into reservoir units they have moved obliquely and show normal throws even though they formed during a period of regional compression faults in the salt withdrawal basin and on the inverted anticline are highly segmented increasing the chances of compartmentalisation or localised fluid flow through fault linkages slip tendency analysis was carried out on the distinct fault families to compare the likelihood of slip along a fault at different pore fluid pressures and within different lithologies our results show that sections of the faults are optimally oriented with regards to maximum horizontal stresses hmax increasing the slip tendency the identified faults cut through a variety of lithologies allowing different values of pore fluid pressures to build up before faults reactivate within the vlieland sandstones pore fluid pressures of 30 mpa are not sufficient to reactivate pre existing faults whereas in the deeper posidonia shales faults might reactivate at pore fluid pressures of 25 mpa fluid flow features preferentially occur near fault segments close to failure heterogeneity in slip tendency along concentric faults and high degrees of fault segmentation present serious hazards when injecting co2 into the subsurface this study stresses the importance of high quality 3d seismic data and the need to evaluate individual fault systems when investigating potential reservoirs for carbon capture and storage and enhanced oil recovery

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

the role of oscillating southern hemisphere westerly winds southern ocean coastal and open ocean polynyas abstractan oscillation in intensity of the southern hemisphere westerly winds is a major characteristic of the southern annular mode its impact upon the sea ice ocean interactions in the weddell and ross seas is investigated by a sea ice ocean general circulation model coupled to an energy balance model for three temporal scales and two amplitudes of intensity we find that the oscillating wind forcing over the southern ocean plays a significant role both in regulating coastal polynyas along the antarctic margins and in triggering open ocean polynyas the formation of coastal polynya in the western weddell and ross seas is enhanced with the intensifying winds resulting in an increase in the salt flux into the ocean via sea ice formation under intensifying winds an instantaneous spin up within the weddell and ross sea cyclonic gyres causes the warm deep water to upwell triggering open ocean polynyas with accompanying deep ocean convection in contrast to coastal polynyas open ocean polynyas in the we

fluid migration and fluid seepage in the connemara field porcupine basin interpreted from industrial 3d seismic and well data combined with high resolution site survey data this study documents the suite of processes associated with source to seafloor fluid migration in the connemara field area on the basis of 3d seismic data well logs 2d high resolution seismic profiles subbottom profiles short cores and sidescan sonar data the combination of datasets yields details about fluid migration pathways in the deep subsurface in the unlithified shallow subsurface and about the distribution of fluid and gas seeps pockmarks at the sea floor the connemara field area is characterized by vertical fluid migration pathways seismic chimneys or gas chimneys that extend from the top of the jurassic sequence cross cutting the entire cretaceous sequence to the upper tertiary deposits over a vertical distance of up to 1 5 km their localization is mainly structurally controlled to the crest of tilted fault blocks along the main hydrocarbon migration pathways these chimneys are important conduits for focused vertical fluid gas flow from the deep to the shallow subsurface however gas seeps pockmarks at the sea floor are almost randomly distributed which indicates a change from focused to diffuse fluid gas migration in shallow unconsolidated sediment where the vertical chimneys reach up to unlithified eocene to miocene sands widespread deformation interpreted as fluidization occurs around the main conduit this deformation affects about 32 of the entire unconsolidated tertiary section late eocene miocene a plio pleistocene glaciomarine drift with up to five horizons with iceberg ploughmarks seals the tertiary sands in the near surface sediments it is observed that gas accumulation occurs preferentially at iceberg ploughmarks it is inferred that lateral migration at five levels of randomly oriented ploughmarks dispersed gas over larger areas and caused random pockmark distribution at the sea floor independent from the underlying focused migration pathways this study demonstrates that fluid flow migration changes from structurally controlled focused flow in the deep consolidated subsurface to diffuse flow controlled by sediment variability in the shallow subsurface this result is relevant to a better understanding of the distribution of seepage induced features at the seafloor related to focused hydrocarbon migration pathways known from industry data and fluid flow modeling

juxtaposition of india and madagascar a perspective abstract proterozoic terrains in south india and madagascar provide important clues in understanding the gondwanaland tectonics especially the assembly of this mega continent during the pan african period the archaean terrains in both madagascar and india are characterized by n s trending greenstone belts occurring within gneissose granitic rocks in the northern part extensive development of k rich granitic rocks of ca 2 5 ga is also characteristic in both areas such a broad age zonation of younger dharwar ca 2 6 3 0 ga in the north and the older sargur ca 3 0 3 4 ga in the south as in south india remains to be identified in future studies from madagascar the occurrence of greenschist facies rocks in the northeastern part and higher grade rocks in most of other parts in the north central terrain of madagascar is comparable with the general tendency of increasing metamorphic grade from northwestern to southern areas ranging from greenschist to granulite facies in south india the proterozoic crystalline rocks in both continents show pronounced lithological similarity with the wide occurrence of graphite bearing khondalite in association with charnockitic rocks while the archaean proterozoic boundary is well defined in southern india by the palghat cauvery or the kkpt shear zones as recently identified this boundary is ill defined in madagascar due to extensive pan african overprinting as well as the development of the proterozoic cover sequence the itremo group there is also a possible general correlation between the mesoproterozoic cover sequences in madagascar and india such as between the itremo group of west central madagascar and the kaladgi and cuddapah sequences of south india the pan african granulite facies metamorphism of ca 0 5 ga extensively developed in both india and madagascar is generally comparable in intensity and extent p t conditions and p t t paths also appear comparable with the general range of ca 700 1000 c and 6 9 kb and near isothermal decompressional paths a type granite plutons and alkaline rocks including anorthosites and mafic plutonic rocks of ca 500 800 ma develop in both terrains provide strong basis for the correlation of both terrains and define a pan african igneous province within east gondwanaland major shear zones in both continents are expected to play a critical role in the correlation albeit are still poorly constrained detailed elucidation of the tectonic history of the shear zones and the timing of various events along the shear zones would provide important constraints on the correlation of the two continental fragments

high resolution 3d seismic data indicate focussed fluid migration pathways above polygonal fault systems of the mid norwegian margin seismic attribute analysis and interpretation of high resolution 3d and 2d seismic data reveal focussed fluid flow processes through the gas hydrate stability zone ghsz at the northern flank of the giant storegga slide diffusive fluid migration predominantly starts from a widespread polygonal fault system in fine grained sediments of the miocene kai formation the overlying 600 700 m thick plio pleistocene naust formation shows spatially related soft sediment deformation and overlying fluid conduits a low relief antiform structure connects to an overlying 250 m high 300 m wide and 3 km elongated columnar zone where seismic signatures suggest self enhanced permeability i e natural hydraulic fracturing push down effects create an elongated depression caused by increased gas accumulations where a cluster of vertical cylindrical acoustic pipe structures originates these pipe clusters pierce the ghsz and indicate focussed fluid flow pathways originating from potentially overpressured sediments high seismic reflection amplitudes at the seafloor above the pipe structures may indicate pockmarks with authigenic carbonates and or gas hydrates the observed objects and seismic features presented are not stand alone indicators for fluid flow but a joint perspective illustrates that they are vertically tied together providing new insights to the effects of focussed fluid flow

evidence for prograde metamorphic evolution of sri lankan pelitic granulites and implications for the development of continental crust petrological evidence for prograde metamorphic evolution is obtained for pelitic granulites of the newly defined highland complex in sri lanka it includes the occurrences of relict kyanite quartz staurolite corundum kyanite hercynite kyanite and sapphirine kyanite spinel within garnet in the sillimanite quartz rich rocks of special interest is the mineralogy of khondalites graphitic garnet sillimanite k feldspar quartz gneisses the matrix of which is free of hydrous minerals indicating that dehydration reactions have been completed in this kind of rocks however relict hydrous minerals such as al ti rich more than 58 wt al2o3 and more than 1 wt tio2 staurolite and extremely ti rich up to 9 8 wt tio2 biotine occur as inclusions within garnet the local relict mineral assemblages within garnet in khondalites indicate the following continuous staurolite breakdown reactions which may have progressed as temperature increased and pressure decreased staurolite quartz kyanite garnet h2o staurolite corundum kyanite garnet h2o staurolite kyanite hercynite garnet h2o staurolite sillimanite hercynite garnet h2o some of these dehydration reactions are inferred to have also taken place in other widespread pelitic granulites of the highland complex moreover garnet in the highland complex pelitic granulites occasionally preserves growth zoning though modified slightly to extensively by post growth volume diffusion based on the evidence a clockwise prograde p t path of evolution is inferredfor meta sedimentary granulites belonging to the highland complex on the other hand no evidence for prograde metamorphism has so far been obtained in lower grade rocks of the wanni complex to the northwest of the highland complex such a difference between these complexes may be the first petrological feature which supports the new geotectonic division of the sri lankan basement rocks based virtually on the distinctly different neodymium model ages it suggests that these two complexes were amalgamated during the very last part of prograde metamorphism of the highland complex rocks that is during decompression and heating probably by the lower crustal lateral flow after tectonic overthickening and delamination the clockwise prograde p t t path followed by the meta sedimentary granulites of the highland complex is in marked contrast with the near isobaric cooling path for meta igneous granulites suggested by some authors it is proposed that both types of p t t paths albeit for different rock types are possible and resulted from diverse deep crustal processes such as underplating of continental crust by sediments and magmas or near convergent plate boundaries

causal interactions between southern ocean polynyas and high latitude atmosphere ocean variability abstractweddell sea open ocean polynyas have been observed to occasionally release heat from the deep ocean to the atmosphere indicating that their sporadic appearances may be an important feature

salt dissolution and salt related deformation of the forth approaches basin uk north sea abstract this paper addresses the potential role of regional scale salt dissolution as a mechanism responsible for salt related deformation this analysis is based on an investigation of the late permian to triassic succession of the forth approaches basin on the nw margin of the north permian basin and makes use of a regional 2d seismic grid tied to five key exploration wells this basin is ideal for this study because it consists of a deformed central region with a ne sw trending axis and an undeformed periphery which provides a template and key datums for reconstruction of the adjacent zone of deformation structural styles in this zone include simple salt cored anticlines salt walls salt diapirs detachment faults and unusually for the north sea intra zechstein salt cored folds pre triassic detailed mapping was carried out in uk block 26 10 and this shows that the dominant structural trend is ne sw suggesting that basement tilting influenced structural development the stratal geometry of the numerous triassic mini basins is used to constrain the way in which accommodation space in the mini basins was created by depletion of mobile salt the spatial pattern of salt depletion can be accounted for by two contrasting mechanisms or some combination thereof 1 deformation through downbuilding during a phase of regional subsidence or 2 flow induced by regional salt dissolution volumetric arguments necessary to discriminate between these two mechanisms are inconclusive due to later deformation of the top zechstein datum selective preservation of z3 and z4 cycles of the zechstein over large parts of the block 26 10 study area suggests that much of the salt depletion process preferentially removed z2 halite this observation is compatible with a process of subjacent dissolution possibly resulting from low salinity groundwater circulating in the pre zechstein aquifers

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

orebody geometry in lode gold deposits from zimbabwe implications for fluid flow deformation and mineralization the geometry of some orebodies can be described simply and accurately by three orthogonal axes u v w the ratios between these axes can be expressed as a parameter j u v 1 v w 1 and represented by a graph of u v plotted against v w analogous to the treatment of strain ellipsoids the orientations of orebodies can be plotted simply on projections using the uvw axes measurements of ore bodies from two examples of lode gold deposits from the zimbabwe craton show that most of these orebodies are oblate however orebodies can have significant u v ratios implying a component of pipe like fluid flow during mineralization pipe flow is demonstrated to be orders of magnitude more conductive than flow in planar veins and faults there are significant variations in orebody geometry between deposits and within different sections of a single deposit w values appear to be influenced by host rock more permeable rocks have higher w a negative trend of j value with orebody volume indicates that orebodies do not evolve in a self similar way but tend to more oblate shapes with increasing volume

southern ocean warming delayed by circumpolar upwelling and equatorward transport unlike the arctic the southern ocean has shown little warming an analysis of observations and numerical simulations suggests that southern ocean warming patterns are shaped by meridional overturning more than surface heating