seismic and structural characterization of fluid escape pipes using 3d and partial stack seismic from the loyal field uk a multiphase and repeated intrusive mechanism acknowledgements we thank an anonymous reviewer for the several constructive comments the seismic interpretation and image processing was carried out in the seislab facility at the university of aberdeen sponsored by bg bp and chevron seismic imaging analysis was performed using geoteric ffa and analysis of seismic amplitudes was performed in petrel 2016 schlumberger we would like to thank the tuscany phd regional program and the erasmus exchange for funding the aberdeen permanence of one of us d m gazprom for supporting a j phd bp for the release of the loyal field seismic dataset utilized in this research paper and also n vanden beukel bp and m gorling bp and his colleagues for their assistance

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

hydrocarbon plumbing systems of salt minibasins offshore angola revealed by three dimensional seismic analysis analysis of three dimensional seismic data from the lower congo basin offshore angola reveals numerous fluid flow features in the miocene to holocene succession and the potential for large shielded traps underneath basinward overhanging salt structures the fluid flow evidence includes present day sea floor pockmarks clustered above salt structures pliocene pleistocene stacked paleopockmarks and miocene pockmark fields other fluid flow features include high amplitude cylindrical pipe structures 60 to 300 m 197 984 ft wide and 25 to 300 m 82 984 ft high within lower and middle miocene strata thick 150 m 492 ft high reflectivity zones within the pliocene succession associated with bottom simulating reflections and subvertical low amplitude chimneys originating from the deeper section 1 km 0 6 mi beneath the sea floor the miocene pockmark fields occur at a specific horizon suggesting a regional fluid expulsion event at ca 12 ma and the miocene fluid flow regime is interpreted to be dominated by thermogenic fluids supplied via carrier beds and leaking vertically above structural highs the pliocene pleistocene fluid flow regime was dominated by short distance vertical fluid migration and expulsion related to early stage diagenetic processes involving biogenic methane and pore water the present day fluid flow regime is inferred to be dominated by thermogenic fluids primarily controlled by kilometer scale salt flank controlled migration the study emphasizes the use of seismically imaged fluid flow features in hydrocarbon systems analysis by documenting the evolution of an overburden plumbing system through time involving several fluid types and flow regimes depending on the spatiotemporal availability of thermogenic and diagenetic fluids and the tectonostratigraphic occurrence of aquifers traps and seals

marginal fault systems of the northern carnarvon basin evidence for multiple palaeozoic extension events north west shelf australia abstract palaeozoic structures along the north west margin of australia have long been recognised as fundamental events responsible for the formation of the offshore basins that comprise this prolific hydrocarbon producing region however the tectonic setting in which this rifting occurred remains unclear detailed mapping of the geometry and tectono stratigraphy of permian and carboniferous structures of the inboard barrow dampier and beagle sub basins of the northern carnarvon basin is possible using regional scale interpretation of publicly available 2d and 3d seismic data through seismic interpretation and mapping we show two distinct orientations of structures that provide evidence for a poly phase rift history of the north west margin during the palaeozoic nne trending faults of the candace terrace barrow sub basin were initiated in the carboniferous or devonian but were underfilled resulting in erosion of the fault block crest and filling of the remnant rift related topography by conformable sequences of later permian and triassic sediments by contrast ne sw oriented faults of the mermaid nose dampier sub basin experienced a distinct phase of permian activity and are unconformably overlain by triassic sediments in the beagle sub basin both orientations of structures are present throughout the marginal fault systems of the northern carnarvon basin complex fault geometries and significant deformation of hanging wall strata are associated with reactivation of the eroded fault block crests and overprinting of faults during subsequent mesozoic extension this has implications for understanding the geodynamic evolution of a poly phase extensional continental margin

origin of overpressure and pore pressure prediction in the baram province brunei accurate pore pressure prediction is critical in hydrocarbon exploration and is especially important in the rapidly deposited tertiary baram delta province where all economic fields exhibit overpressures commonly of high magnitude and with narrow transition zones a pore pressure database was compiled using wireline formation interval tests drillstem tests and mud weights from 157 wells in 61 fields throughout brunei overpressures are observed in 54 fields both in the inner shelf deltaic sequences and in the underlying prodelta shales porosity vs vertical effective stress plots from 31 fields reveal that overpressures are primarily generated by disequilibrium compaction in the prodelta shales but have been generated by fluid expansion in the inner shelf deltaic sequences however the geology of brunei precludes overpressures in the inner shelf deltaics being generated by any conventional fluid expansion mechanism e g kerogen to gas maturation and we propose that these overpressures have been vertically transferred into reservoir units via faults from the prodelta shales sediments overpressured by disequilibrium compaction exhibit different physical properties to those overpressured by vertical transfer and hence different pore pressure prediction strategies need to be applied in the prodelta shales and inner shelf deltaic sequences sonic and density log data detect overpressures generated by disequilibrium compaction and pore pressures are accurately predicted using an eaton exponent of 3 0 sonic log data detect vertically transferred overpressures even in the absence of a porosity anomaly and pore pressures are reasonably predicted using an eaton exponent of 6 5

structure and evolution of hydrothermal vent complexes in the karoo basin south africa the karoo large igneous province formed at c 183 ma is characterized by the presence of voluminous basaltic intrusive complexes within the karoo basin extrusive lava sequences and hydrothermal vent complexes these last are pipe like structures up to several hundred metres in diameter piercing the horizontally stratified sediments of the basin detailed mapping of two sediment dominated hydrothermal vent complexes shows that they are composed of sediment breccias and sandstone the breccias cut and intrude tilted host rocks and are composed of mudstone and sandstone fragments with rare dolerite boulders sandstone clasts in the breccias are locally cemented by zeolite which represents the only hydrothermal mineral in the vent complexes our data document that the hydrothermal vent complexes were formed by one or a few phreatic events leading to the collapse of the surrounding sedimentary strata we propose a model in which hydrothermal vent complexes originate in contact metamorphic aureoles around sill intrusions heating and expansion of host rock pore fluids resulted in rapid pore pressure build up and phreatic eruptions the hydrothermal vent complexes represent conduits for gases and fluids produced in contact metamorphic aureoles slightly predating the onset of the main phase of flood volcanism

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

monsoon convection in the himalayan region as seen by the trmm precipitation radar three dimensional structure of summer monsoon convection in the himalayan region and its overall variability are examined by analyzing data from the tropical rainfall measuring mission trmm precipitation radar over the june september seasons of 2002 and 2003 statistics are compiled for both convective and stratiform components of the observed radar echoes deep intense convective echoes 40 dbz echo reaching heights 10 km occur primarily just upstream south of and over the lower elevations of the himalayan barrier especially in the northwestern concave indentation of the barrier the deep intense convective echoes are vertically erect consistent with the relatively weak environmental shear they sometimes extend above 17 km indicating that exceptionally strong updraughts loft graupel to high altitudes occasionally scattered isolated deep intense convective echoes occur over the tibetan plateau wide intense convective echoes 40 dbz echo 1000 km2 in horizontal dimension also occur preferentially just upstream of and over the lower elevations of the himalayas most frequently in the northwestern indentation of the barrier the wide intense echoes have an additional tendency to occur along the central portion of the himalayas and they seldom if ever occur over the tibetan plateau the wide intense echoes exhibit three mesoscale structures amorphous areas lines parallel to the mountain barrier and arc shaped squall lines perpendicular to and propagating parallel to the steep himalayan barrier the latter are rare generally weaker than those seen in other parts of the world and occur when a midlevel jet is aligned with the himalayan escarpment deep and wide intense convective echoes over the northwestern subcontinent tend to occur where the low level moist layer of monsoon air from the arabian sea meets dry downslope flow in a manner reminiscent of severe convection leeward of the rocky mountains in the central usa as the low level layer of moist air from the sea moves over the hot arid northwestern subcontinent it is capped by an elevated layer of dry air advected off the afghan or tibetan plateau the capped low level monsoonal airflow accumulates instability via surface heating until this instability is released by orographically induced lifting immediately adjacent to or directly over the foothills of the himalayas broad 50 000 km2 in area stratiform echoes occur in the eastern and central portions of the himalayan region in connection with bay of bengal depressions their centroids are most frequent just upstream of the himalayas in the region of the concave indentation of the barrier at the eastern end of the range the steep topography apparently enhances the formation and longevity of the broad stratiform echoes monsoonal depressions provide a moist maritime environment for the convection evidently allowing mesoscale systems to develop larger stratiform echoes than in the western himalayan region copyright 2007 royal meteorological society

ancient fluid flow recorded by remarkably long buried pockmark trains observed in 3d seismic data exmouth plateau northern carnarvon basin abstract we present 3d seismic data from the exmouth plateau offshore northwest australia shows 275 paleo pockmarks of latest jurassic age organised into three linear nnw sse oriented pockmark trains the longest exceeding 72 km spatial statistics indicate a high probability that these linear pockmark arrangements are not random the trains are parallel to an array of linked normal faults with similar nnw sse strikes with pockmarks underlain by feeder pipes that nucleate along or close to the fault planes we interpret the faults to have intersected an overpressured unit and acted as a spatial control on the development of the feeder pipes and pockmarks our results reveal an important role of faults in controlling laterally extensive pockmark trains and highlight the value of 3d seismic data in identifying large scale ancient fluid flow within sedimentary basins

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

structure and evolution of baroclinic waves as inferred from regression analysis abstract the structure of transient disturbances with periods shorter than a week is documented an the basis of one point regression maps and longitude height sections derived from the national meteorological center nmc operational analyses for nine winter seasons the reference time series for the regression coefficients is highpass filtered normalized 500 mb height at a grid point in the pacific stormtrack the field variables that were regreesed on the reference time series were not filtered the regression statistics yield quantitative estimates of the amplitudes of the high frequency fluctuations in the geopotential height temperature wind ageostrophic wind vorticity divergence vertical velocity and outgoing longwave radiation fields the observed high frequency fluctuations exhibit a vertical and meridional structure suggestive of baroclinic waves evolving through the mature phase of their life cycle most of the results are in qualitative agreement with previous studies but the ageostrop

a natural gas hydrate system on the exmouth plateau nw shelf of australia sourced by thermogenic hydrocarbon leakage abstract the identification of natural gas hydrates and shallow free gas in sedimentary basins is critical for understanding the organic carbon cycle dynamics in the shallow geosphere as well as for geohazard studies related to the development of commercial hydrocarbon fields in this study we report for the first time the evidence for the potential occurrence of a natural gas hydrate system along the continental margin of australia on the exmouth plateau nw shelf by the use of high quality 3d seismic data calibrated by downhole data from odp and industry boreholes we interpret a series of shallow high amplitude anomalies including patchy bottom simulating reflections as the seismic expression of localised accumulations of free gas beneath the base of hydrate stability and overlying high saturation hydrates or authigenic carbonates the hydrate bearing reservoir is constituted by neogene and quaternary fine grained carbonate nannofossil and foraminifera rich oozes the patchy distribution of the shallow free gas and hydrate accumulations which reflects the geometry of deeper fault blocks is hypothesised to result from the leakage of thermogenic gas from deeper reservoirs the interpretation of a thermogenic origin for the hydrate forming gases is supported by 1 the existence in the study area of several thermogenic gas discoveries within late triassic reservoirs 2 seismic evidence of cross stratal and stratal pathways for migrating gases in the overburden 3 the presence of free gas accumulations at depths intermediate between the deep reservoirs and shallow gas hydrate systems and 4 geochemical and lithological evidence that the conditions which favour the generation of shallow microbial gas are not present in the area the acquisition of downhole log and sample data through the observed seismic amplitude anomalies is necessary to test the interpretations and hypotheses presented in this manuscript

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

the spatial and temporal distribution of pipe formation offshore namibia a group of nearly 400 pipe structures from the continental slope of northern namibia are analysed for their spatial and temporal distribution the pipes most likely formed as a result of highly focused fluid venting and understanding the factors controlling their distribution in space and time is key to their genesis we analysed their spatio temporal distribution using an arbitrary chronostratigraphic timescale from which it is concluded that the pipes did not form at the same time pipe formation is shown to be intermittent and persistent with 2 29 pipes forming in each of the 20 arbitrary time intervals that are considered to span the neogene period the spatial distribution of these pipes is clustered to dispersed spatial statistics conducted on the distribution of pipe formation timings have shown that two statistically significant groups of pipes exist within the population 1 in the north and west and 2 in the south with the former occurring prior to the latter locally pipe formation is sporadic with clusters and outliers occurring during the same time period a conceptual model is proposed whereby pipe formation in specific locations is the result of localised breaching of the seals for isolated pressure cells which are locally independent yet broadly controlled an inferred basinal fluid source is thought to determine the broader patterns of pipe formation and the focus of this fluid source shifts from north to south with time at a local scale multiple local factors interact producing a sporadic pipe formation distribution through a prolonged period of highly focused fluid migration once formed the pipes continued to focus fluids intermittently leading in some cases to later pockmark formation

seal failure assessment of a major gas field via integration of seal properties and leakage phenomena we present a seismic and well based interpretation of a large leakage zone above the scarborough gas field exmouth plateau north west shelf of australia this leakage zone well imaged on three dimensional seismic data extends over a region of 100 km2 39 mi2 encompassing both the crest and flanks of the anticlinal trap and is termed here as distributed crestal leakage the present day gas water contact is 85 m 278 ft and the spillpoint is 110 m 328 ft below the crest implying that the trap is underfilled at present the leakage zone comprises more than 500 pockmarks at the present day seabed with no crosscutting or cannibalization suggesting that they formed in a short interval of time these are underlain by sediment remobilization features and amplitude anomalies consistent with a relatively high flux leakage of gas from the underlying cretaceous deep water sand rich reservoir by analyzing the geometrical relationship between the leakage zone the top seal properties and the gas water contact we conclude that the mode of leakage in this specific setting is not the result of gradual addition of gas charge but is instead consistent with a sudden increase of aquifer overpressure we suggest two alternative models for seal failure in this case study a conservative model consistent with a modest but rapid increase in aquifer overpressure leading to membrane seal failure and a model dominated by high aquifer overpressure leading to leakage through hydraulically dilated faults and fractures

3d seismic classification of fluid escape pipes in the western exmouth plateau north west shelf of australia fluid escape pipes are vertical pathways of focused flow venting from a variety of deep overpressure sources these geological features are typical of many sedimentary basins including proven petroliferous provinces worldwide such as the north sea and the exmouth plateau in the northern carnarvon basin northwest australia high quality three dimensional 3d seismic reflection data from the western exmouth plateau revealed the occurrence of exceptionally well imaged fluid escape pipes affecting the jurassic strata and the triassic mungaroo formation a key reservoir unit in the basin a total of 171 fluid escape pipes including blowout seepage and hydrothermal pipes were mapped and their geomorphic characteristics were analysed in the study area these features form prominent vertical columns up to 4 5 km long disrupting continuous reflections of the triassic to jurassic section numerous fluid escape pipes terminate with paleo pockmarks affecting at the upper jurassic syn extension strata providing evidence for pipe genesis during the early stages of the late jurassic rifting in the exmouth plateau fluid escape pipes were found rooting from different stratigraphic levels suggesting multiple fluid sources within the triassic sediments several fluid flow structures nucleated along or nearby rift related fault planes within the mungaroo formation providing further evidence of rifting as a main triggering factor of important fluid flow in the basin in the study area the presence of fluid escape pipes represents a significant risk for the preservation of potential hydrocarbons accumulations as when these features form vertical fluid venting breaches through stratigraphy compromising the integrity of seal units this seems supported by the lack of significant discoveries within the area covered by seismic survey analysed in this research

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

seepage in vietnam onshore and offshore examples abstract hydrocarbon seepages in vietnam are generally linked to migration from tertiary source rocks and seeps are present both onshore and offshore residual oil can be observed at outcrop in breached traps within tertiary sections and in exhumed buried hill traps in pre tertiary rocks in the onshore hanoi basin there is active oil seepage on the western margin of the offshore phu khanh basin through fractured granites that outcrop at the basin margin there are examples of onshore gas seepages in southern vietnam these are predominantly non hydrocarbon mantle derived gases sometimes mixed with biogenic methane and are seeping via hot springs from fractured mezosoic igneous rocks in active fault zones offshore in the nam con son basin sonar seismic data and sea bed cores show a variety of seepage features including shallow gas anomalies mounds and pockmarks on the sea bed and gas effects in the water column sometimes visible on sonar records however sea bed seepage features are not particularly common and have a low preservation potential in the area due to powerful sea bed currents aircraft surveys of the sea surface have revealed several oil slicks that could be related to active oil seepages in the nam con son basin seepage appears to be occurring in vietnam at two fundamentally different rates background seepages flow at low rates typically tens to thousands of cubic feet per day of gas and up to tens of barrels per day of oil these seeps flow episodically for extended periods of months or years and leading to the formation of sea bed mounds higher flow rate eruptive seepages may have formed some of the pockmarks and have a far shorter duration probably only a few hours or days with flow rates of millions of cubic feet per day of gas and any associated liquids

cretaceous tertiary inversion history of the dampier sub basin northwest australia insights from quantitative basin modelling abstract seismic sequence analysis has been combined with a kinematic and flexural model for the deformation of the lithosphere to define the history distribution and magnitude of inversion within the dampier sub basin northwest australia during the cretaceous and tertiary inversion tends to be focused along the trend of pre existing border fault systems and or internal to the basin across the roll over anticlines of collapsed hangingwall blocks the spatial distribution of inversion varied with different faults involved in the inversion process at different times whereas cretaceous inversion concentrated along major boundary faults of the northeast southwest oriented rankin madeleine and rosemary legendre trends the locus of miocene inversion was located adjacent to the northwest limits of the rosemary legendre trend total shortening of the lithosphere during the santonian and tertiary was modelled to be 2 6 and 0 16 km respectively with northeast southwest trends being preferentially reactivated the amplitudes of inversion structures range from 1000 m over the eastern rankin trend to hundreds of metres for inversion structures comprising the rosemary legendre trend although responsible for the development of relatively subtle features inversion has critically controlled the major structures for trapping hydrocarbons within the dampier sub basin

the coupled release of ree and pb to the soil labile pool with time by weathering of accessory phases wind river mountains wy abstract rare earth element ree distributions and pb isotope compositions were explored in soils varying in age from ca 0 4 to 300 ka developed on moraines in the wind river mountains wyoming soil extracts 0 6 m hcl were used to examine the soil labile pool while the major element distribution in soil profiles was used to determine the extent of weathering at different soil depths the results show that the chondrite normalized ree patterns of the deepest bulk soil within each profile reflects the composition of the moraine till except for the oldest soil up to ca 12 ka the soil extract fraction is enriched in light ree indicating early release of light ree to the soil labile pool while that of the two oldest soils are relatively enriched in heavy ree in the soil extracts the la sm ratio normalized to the deepest soil la d sm d decreases systematically with soil age similarly the eu anomaly in the deepest soil from each profile eu d eu d decreases slightly with soil age in the three young soils however eu d eu d increases with soil age in the older soils the systematic trends of these two ratios indicate the depletion of light ree in young soils and the enrichment of eu and heavy ree in the older soils based on the pb isotope ratios the relative contribution of pb to the soil labile pool via mineral weathering of u or th rich phases was assessed for the different stages of weathering the whole soil profile 208 pb 204 pb ratio was found to decrease with soil age and with la d sm d whereas it increased with the eu d eu d ratio in each horizon pb isotope ratios 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratio generally decrease with soil age in order to overcome possible effects from parent material heterogeneity the amount of radiogenic pb as compared to the whole soil composition was calculated and this was found to decrease systematically with soil age

seismic morphologic and scale variabilities of subsurface pipes and vent complexes in a magma rich margin subsurface pipes related to fluid flow are observed in seismic reflection data as vertical to sub vertical features of low amplitude reflections linking chaotic reflections at the base root zones of volcanic constructs to their summits which can comprise craters mounds or eye shaped vents to date uncertainties remain regarding the linear correlation and scaling relationship between pipes and their overlying vent structures using 3d seismic reflection data from a magma rich basin the vigrid syncline in the voring basin offshore norway this study provides a seismic morphometric and statistical description of forty 40 pipes and their associated structures these pipes include conical bifurcated fault controlled and columnar types which are a consequence of the intrusion of two mappable magmatic sills of early eocene age the heights av 1098 m widths av 1740 m and slenderness ratios i e the heights widths of the pipes av 0 6 show low to moderate correlation coefficients with vent parameters such as height av 258 m area av 2 3 km2 and ellipticity av 1 5 the morpho statistical analyses provided here show that pipe formation mechanisms are mutually exclusive and that vent geometries are not particularly systematic in nature

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

shallow plumbing systems inferred from spatial analysis of pockmark arrays abstract this study describes and analyses an extraordinary array of pockmarks at the modern seabed of the lower congo basin offshore angola in order to understand the fluid migration routes and shallow plumbing system of the area the 3d seismic visualization of feeding conduits pipes allowed the identification of the source interval for the fluids expelled during pockmark formation spatial statistics are used to show the relationship between the underlying polarised polygonal fault ppfs patterns and seabed pockmarks distributions our results show ppfs control the linear arrangement of pockmarks and feeder pipes along fault strike but faults do not act as conduits spatial statistics also revealed pockmark occurrence is not considered to be random especially at short distances to nearest neighbours

1000 m long gas blow out pipes abstract this study presents seismic observation of pipe anomalies from offshore nigeria outcrops of blow out pipes from rhodes greece and geophysical modelling of an acoustic pipe the studies give insight into how pipes form their internal structure the seismic image and geophysical artefacts related to the pipes over one hundred seafloor craters 100 m 700 m wide and up to 30 m deep have been observed on the seafloor offshore nigeria they are underlain by interpreted cones and seismic pipe anomalies that can be traced down to reservoir zones at 1000 m 1300 m below the seafloor the seismic pipe anomalies are 50 m 150 m wide and almost vertical they are interpreted as up scaled pipes found in outcrops on rhodes greece the outcrops show pipe related structures at three levels lowest the reservoir rock contains metre sized cavities which are filled with a mixture of clay derived from the overlying cap rock in the middle several circular to oval structures in plane view of pipes are observed in the lowest part of the cap rock highest 15 m into the clay cap rock strongly sheared country rock forms circular structures with a core of structureless clay based on outcrop observation on rhodes we constructed an acoustic model of a 50 m wide and 1000 m long pipe seismic modelling proves that such pipes would be expressed in seismic data that they are similar to the seismic pipe anomalies offshore nigeria but this study also revealed that prominent intra pipe reflections are artefacts a formation model for the pipes is suggested high fluid overpressure in the reservoir generated hydro fractures from the reservoir to seafloor where a mixture of gas and fluid flowed at high speed to form pipes cones and seafloor craters after hours to weeks of gas and fluid flow through the pipe the pore pressure in the reservoir dropped and the blow out terminated muddy slurry fell back and plugged the cavity in the reservoir and the pipe

geometric and depositional responses of carbonate build ups to miocene sea level and regional tectonics offshore northwest australia abstract the geometric and depositional responses of isolated carbonate build ups to miocene sea level change and regional tectonics are investigated using 3d seismic and borehole data from the browse basin north west australia combined with outcrop information from the cariatiz reef southeast spain the interpreted seismic volume documents five 5 miocene sequence boundaries and five 5 main seismic facies seismic attribute analyses proved to be a highly effective tool for interpreting carbonate facies but when compared with outcrop information from southeast spain attribute data are limited to features larger than 16 4 m vertically and 18 75 m horizontally estimations of reservoir potential are thus significantly underestimated when only based on the interpretation of seismic data as a corollary of the structural analysis in this work growth patterns suggest messinian structural partitioning across the browse basin with deformation associated with plate collision focused on preferentially oriented faults i e only influencing carbonate build up evolution at a local scale

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

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

time variation of 500 mb height fluctuations with long intermediate and short time scales as deduced from lag correlation statistics abstract the time variation of northern hemisphere wintertime 500 mb height fluctuations with short intermediate and long time scales is investigated using lag correlation patterns derived from time filtered data fluctuations with short 2 5 6 day periods time scales propagate eastward at a rate consistent with the notion of a steering level around 700 mb which supports an interpretation in terms of baroclinic waves the mobile teleconnection patterns associated with the intermediate 10 30 day periods time scales exhibit a pattern of time variation suggestive a rossby wave dispersion with a predominance of southward dispersion from middle latitudes into the tropics the geographically fixed teleconnection patterns characteristic of the longer time scales do not show a well defined pattern of time variation but their horizontal structure resembles that of the fastest growing normal mode associated with barotropic instability of the climatological mean wintertime flow

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

contraction and extension in northern borneo driven by subduction rollback abstract during the paleogene the proto south china sea was subducted beneath northern borneo subduction ended with early miocene collision of the dangerous grounds reed bank north palawan block and the sabah cagayan arc much of northern borneo then became emergent forming the top crocker unconformity later in the early miocene subsidence resumed it is proposed that northward subduction of the celebes sea initiated formation of the sulu sea backarc basin followed by subduction rollback to the se this formed a volcanic arc which emerged briefly above sea level and collapsed in the middle miocene as rollback continued the sulu arc was active during middle and late miocene between sabah and the philippines rollback drove extension in northern borneo and palawan accompanied by elevation of mountains crustal melting and deformation offshore there were two important extensional episodes the first at about 16 ma is marked by the deep regional unconformity and the second at about 10 ma produced the shallow regional unconformity both episodes caused exhumation of deep crust probably on low angle detachments and were followed by granite magmatism the nw borneo palawan trough and offshore sabah fold and thrust belt are often interpreted as features resulting from collision regional compression or subduction however there is no seismicity dipping slab or volcanicity indicating subduction nor obvious causes of compression the trough developed after the middle miocene and is not the position of the paleogene trench nor the site of neogene subduction inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough the trough is interpreted as a flexural response to gravity driven deformation of the sediment wedge caused by uplift on land that resulted from extension with a contribution of deep crustal flow

mechanism of thin skinned detachment in the amazon fan assessing the importance of fluid overpressure and hydrocarbon generation abstract since about 10 ma a wedge of clastic sediment up to 10 km in thickness has accumulated near the mouth of the amazon river forming the amazon fan thin skinned extensional and contractional structures root into a common basal detachment hundreds of kilometers long extensional faults have formed landward of the prograding delta slope and contractional folds and faults have formed seaward of it by plan view restoration we show that extension and contraction balance we therefore infer that slope instability has provided the driving force for thin skinned deformation on seismic data the detachment appears as a sharp surface within late cretaceous strata however there is no evidence at that level for soft layers such as evaporites or muds abnormal fluid pressure provides a more reasonable mechanism for the detachment at depths of several thousand meters deep wells have encountered fluid overpressures amongst the possible causes of abnormal fluid pressures are compaction and hydrocarbon generation although compaction may have contributed to fluid overpressures encountered in wells we argue that hydrocarbon generation provides the best explanation for detachment in cretaceous rocks which were old and lithified when it occurred in particular the broadly triangular area of detachment coincides with an inferred pod of cenomanian turonian source rock which is interpreted to have been in the gas window during detached deformation we have developed new techniques of sandbox modelling to investigate the geometries of fault patterns produced by fluid flow through porous media for the amazon fan we have been able to reproduce the structural pattern on the assumption that fluid overpressures existed over a broadly triangular area beneath the detachment

heat flow and thermal maturity modelling in the northern carnarvon basin north west shelf australia abstract the northern carnarvon basin is located at the southern end of the north west shelf of australia it was developed by rifting during the jurassic earliest cretaceous heat flow and thermal maturity in seven wells from three sub basins rankin platform and exmouth plateau of the northern carnarvon basin were modelled using basinmod 1d program multiple thermal maturity parameters were used to constrain the influence of anomalously low vitrinite reflectance those t max data with reliable quality can be applied to correlate with vitrinite reflectance establish thermal maturity and calibrate the modelled results the modelled results indicated that the measured maturity data in some wells were consistent with the rift heat flow model jarvis mckenzie associated with the jurassic rift and the earliest cretaceous seafloor spreading events the maximum values of heat flow were in the range from 67 mw m 2 jurabi 1 to 105 mw m 2 bowers 1 in the exmouth and barrow sub basins on the exmouth plateau the maximum values of heat flow were modelled to be 72 mw m 2 in the jupiter 1 well and 78 mw m 2 in the investigator 1 well these maximum values were modelled to occur during syn rift phase which were 29 88 and 33 37 greater than their current heat flow values in the sub basins and on the exmouth plateau respectively this study suggests that maturity indicators are less diagnostic of rifting thermal histories if the maximum thermal effect is associated with cretaceous and cainozoic burial in this basin

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago