hydrocarbon generation migration alteration entrapment and mixing in the central and northern north sea abstract there is little doubt that sediments of upper jurassic to lowermost lower cretaceous age particularly those of the kimmeridge clay formation and its equivalents are the source of the vast bulk of the oil in the central and northern north sea this is true both of oil in conventional mesozoic plays and in tertiary clastic reservoirs the timing of oil generation and migration ranges from the late cretaceous through to the present the oil productivity of the kimmeridge clay formation in the central graben moray firth and south viking graben areas of the north sea is estimated to be in excess of 250 billion barrels of which about 25 is accounted for in accumulations discovered to date there is strong areal differentiation between oil trapped in mesozoic reservoirs as opposed to upper cretaceous chalk and tertiary reservoirs this paper is particularly concerned with hydrocarbons in tertiary reservoirs which have a wide range of compositions and appear to have complex accumulation and degradation histories migration to chalk and younger tertiary reservoirs occurs often through thick shale sequences the evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration mixing and degradation is proposed

temporal changes in fault strike to 90 and extension directions during multiple episodes of extension an example from eastern nevada in areas with prolonged extensional histories or multiple episodes of extension temporally distinct extensional fault systems including dip slip normal oblique slip and or strike slip faults may form these fault systems may be spatially distinct overlapped or completely superimposed and different fault systems may have different fault strikes and extension directions although fault strike is not a very sensitive indicator of principal stress directions changes through time in fault strike of as much as 90 exceed the uncertainty overprinted extensional fault systems of different ages with significantly different to 90 fault strikes and extension directions provide strong evidence of changes in the regional stress field with time tens of millions of years of extension occurred in the basin and range province of the united states and many temporally distinct fault sets formed through that time we document at least four extensional episodes and the fault kinematics of each where possible in the central hiko range eastern nevada the four cenozoic extensional events are prevolcanic synvolcanic postvolcanic miocene pliocene and postvolcanic pliocene quaternary the prevolcanic faults strike north south and are interpreted as footwall faults to the regional eocene oligocene snake stampede extensional system which caused approximately east west extension the synvolcanic faults are late oligocene miocene age and strike east west although they are rare and have minor offset they accommodated north south directed extension postvolcanic faults part of the timpahute lineament are approximately east west striking normal and northeast striking oblique slip faults they also accommodated approximately north south extension during miocene time the northeast striking left normal oblique slip fault set formed as new faults and records a change between north south and east west extension in miocene time later east west extension occurred along the pliocene to quaternary hiko fault zone these four overprinted extensional systems show two separate changes in normal fault strike of 90 from north south to east west and from east west back to north south consequently the extension direction similarly changed through time we suggest that causes for the changes in direction of upper crustal extension include a change from stresses created by 1 plate interactions which generated approximately east west extension to 2 mantle motions which generated approximately north south extension and 3 back again the extension related to mantle motions is associated with a band of volcanism that passed across the northern basin and range province moving generally from north to south during the protracted period of extension therefore a change from plate boundary or interaction derived stresses to mantle or volcanism related stresses and back again is possible

asymmetric tidal mixing due to the horizontal density gradient abstract stratification and turbulent mixing exhibit a flood ebb tidal asymmetry in estuaries and continental shelf regions affected by horizontal density gradients the authors use a large eddy simulation les model to investigate the penetration of a tidally driven bottom boundary layer into stratified water in the presence of a horizontal density gradient turbulence in the bottom boundary layer is driven by bottom stress during flood tides with low gradient ri and flux rf richardson numbers but by localized shear during ebb tides with ri and rf 0 2 in the upper half of the boundary layer if the water column is unstratified initially the les model reproduces periodic stratification associated with tidal straining the model results show that the energetics criterion based on the competition between tidal straining and tidal stirring provides a good prediction for the onset of periodic stratification but the tidally averaged horizontal richardson number rix has a threshold value of abou

correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

hydrocarbon evolution of the over mature sinian dengying reservoir of the neoproterozoic sichuan basin china insights from re os geochronology abstract rhenium osmium re os geochronology is a robust technique for constraining the accurate timing of hydrocarbon evolution but its effectiveness in over mature petroleum systems has not been well constrained here we conduct a case study in the neoproterozoic sichuan basin china i e the sinian dengying sequence 635 542 ma re os isotopic data from this highly mature hydrocarbon reservoir yield a re os isochron ages of 414 44 ma with an initial 187os 188os osi of 1 36 0 19 for bitumen and a 78 37 ma age with an osi of 3 21 0 17 for pyrobitumen coupled with thermal evolution of possible source rocks and fluid inclusion homogenization temperatures the 414 ma age marks the timing of oil generation and the 78 ma age indicates the timing of gas generation associated with the thermal cracking of oil and the formation of pyrobitumen in the reservoir a comparison of the osi of the 414 ma bitumen and that of possible source rocks at the time of bitumen formation reveal that it was primarily sourced from shale of the lower cambrian qiongzhusi formation the results of this study provide new insights to better understand the over mature oil gas system in the sinian sichuan basin and show that dengying formation reservoirs in the depocenter areas of the basin are potentially favorable for oil and gas exploration the results further highlight the utility of the re os geochronometer to constrain the accurate age and source of hydrocarbon evolution

residual circulation in shallow estuaries 1 highly stratified narrow estuaries long wave theory and simple turbulence closures have been used to show that three distinct types of circulation highly stratified weakly stratified and partially mixed arise in narrow shallow estuaries from the finite amplitude of the tide and the interaction of stratification with vertical mixing each type has a different dominant process causing the vertical exchange of salt and fresh water on the flood and each gives rise to a characteristic residual circulation the tidal circulation in highly stratified shallow estuaries described herein is the result of a finite amplitude internal motion driven by the barotropic tide shear instabilities at the interface are the major vertical exchange mechanism the residual circulation is caused primarily by ebb flood asymmetry in interface position and thickness a model based on our theoretical analysis shows that the interface thickness on flood is much less than the depth of flow up to a critical tidal amplitude at which the two layer flow is destroyed and correctly predicts the tidal amplitude of the neap spring transition in the columbia river estuary tidal frequency internal wave motion is not found in weakly stratified and partially mixed estuaries because of the reduced tidal shear shear instabilities are weak or absent and the residual circulation assumes a very different character as described in part 2

lateral circulation in well mixed and stratified estuarine flows with curvature abstract a field experiment was conducted to examine stratified and unstratified curvature generated lateral circulation and momentum balances in an estuarine tidal channel conductivity temperature depth and current profiler data were collected vertically and laterally across the channel at a sharp bend over a fortnightly period to measure the terms of the lateral momentum budget well mixed conditions allow the development of classic two layer helical flow around a bend stratification strengthens curvature induced lateral circulation but the development of a lateral baroclinic pressure gradient opposes the resultant motions the spatial and temporal response of this baroclinic pressure gradient is different than centrifugal acceleration producing a three layer profile as the baroclinic term becomes stronger or as centrifugal acceleration disappears as the flow exits the bend two layer flow with the opposite direction from curvature occurs in both stratified and well mixed conditions downstre

petroleum source rock identification of united kingdom atlantic margin oil fields and the western canadian oil sands using platinum palladium osmium and rhenium implications for global petroleum systems this study demonstrates that petroleum and source rocks are enriched in pt and pd to the ppb level and that the 187os 188os composition coupled with the pt pd value permits the fingerprinting of petroleum to its source oils from the united kingdom atlantic margin sourced from the upper jurassic kimmeridge clay fm as well as source rock samples have been analysed for pt and pd when the pt pd value is compared with 187os 188os calculated at the time of oil generation osg the values from both the known source and the oils are similar demonstrating that they can be used as an oil to source fingerprinting tool this inorganic petroleum fingerprinting tool is particularly important in heavily biodegraded petroleum systems where traditional fingerprinting techniques e g biomarkers are severely hampered e g the world s largest oil sand deposit the west canadian oil sands wcos this has caused the source of the wcos to be hotly debated with no present day consensus between inputs from potential source units e g exshaw and gordondale fms 187os 188os and pt pd fingerprinting of the oil sands shows that the majority of the petroleum have similar 187os 188os and pt pd values supporting the hypothesis of one principal source analysis of the potential source rocks establishes that the principal source of the oil sands to be from the jurassic gordondale fm with a minor exshaw fm input thus the combination of previously pioneered re os petroleum geochronology with 187os 188os and pt pd values of petroleum permits both a temporal and spatial understanding of petroleum systems

evidence for reduced quartz cementation rates in oil filled sandstones when quartz rich sands are buried and heated pore space is gradually filled by precipitation of quartz cement from aqueous formation fluids here we examine whether the presence of oil in the pore space can retard or halt this loss of porosity by slowing or stopping quartz cementation the effect of oil fill on quartz cementation is examined by using the distribution of quartz cement in the brae formation deep water sandstone reservoir of the miller oil field north sea petrographic data demonstrate that sandstones from the oil zone have much less quartz cement and more porosity than sandstones from the water zone sandstones in both oil and water zones are compositionally and texturally identical and have been affected by a similar burial history kinetic modeling of the cementation process suggests that progressive oil charging has slowed quartz cement growth rates by at least two orders of magnitude halting it completely in the most extreme cases our data demonstrate that early oil charging in the crestal part of an anticline can preserve porosity in deeply buried sandstones this knowledge is especially relevant to porosity prediction for petroleum exploration in deeply buried sandstones

advection of the salt wedge and evolution of the internal flow structure in the rotterdam waterway an analysis of field measurements recorded over a tidal cycle in the rotterdam waterway is presented these measurements are the first to elucidate the processes influencing the along channel current structure and the excursion of the salt wedge in this estuary the salt wedge structure remained stable throughout the measuring period the velocity measurements indicate decoupling effects between the layers and that bed generated turbulence is confined below the pycnocline the barotropic m4 overtide structure is imposed at the mouth of the estuary and the generation of m4 overtides within the estuary is found to be relatively small internal tidal asymmetry does not make a significant contribution to the m4 velocity frequency band instead the combination of barotropic and baroclinic forcing in conjunction with the suppression of turbulence at the interface provides the main explanation for the time dependence and mean structure of the flow in the rotterdam waterway this gives rise to the observed differences in the length of the flood and ebb in the magnitudes of the flood and ebb velocities in the length of the slack water periods and in the timing of the onset of slack water at the surface and near the bed it results in the formation of distinct exchange flow profiles at the head of the salt wedge around slack water and the creation of maximal velocities at the pycnocline during flood advection governs the displacement and structure of the salt wedge since turbulent mixing is suppressed the tidal displacement of the salt wedge controls the height of the pycnocline above the bed at a particular site hence it controls the height to which bed generated turbulence can protrude into the water column consequently the authors find asymmetries in the structure of the internal flow turbulent mixing and bed stresses that are not related to classical internal tidal asymmetry

shear instability in a highly stratified estuary abstract shear instability is found to be the principal mechanism of vertical exchange within the pycnocline of a salt wedge estuary a field program involving high resolution velocity and density measurements as well as high frequency acoustic imagery allowed direct comparison of instantaneous richardson number distributions to the occurrence of shear instability the theoretical stability threshold of 0 25 is consistent with the measurements based on estimates of gradients that contain the mean as well as fluctuations due to internal waves an effective stability threshold based on mean gradients is found to be approximately one third reflecting a significant contribution of internal wave shear the integral effect of the mixing process is to homogenize the gradients of velocity and density producing linear profiles of these quantities across the pycnocline a turbulent prandtl number of unity is suggested by the vertical distributions of velocity and density during periods of active vertical mixin

the formation of a tidal intrusion front at the mouth of a macrotidal partially mixed estuary a field study of the dart estuary uk high resolution measurements of density and velocity were made before during and after the formation of a transient tidal intrusion front at the mouth of a narrow partially mixed estuary during spring tides detailed acoustic doppler current profiler adcp and density measurements throughout 1 km longitudinal transects at hourly intervals during spring tides indicated that the front formed when the barotropic inflow was sufficient to arrest the buoyant outflow from the estuary this has been shown to be driven by a constriction of the channel at the mouth and a depression in the seabed just landward of the mouth with these changes in topography shown to interact with the flow in a similar manner to theoretical two layer flow over the lee side of a sill a detailed analysis of the flow and stratification across the narrow frontal interface found a high degree of shear and mixing just prior to the plunge point which together with a hydraulic jump at the seabed depression eventually led to the destruction of the density interface and the total intrusion of seawater as the flooding tide strengthened there was no surface manifestation of this front during neap tides and further measurements have confirmed that the relatively weak barotropic flow at this time was not sufficient to overcome the stratification in a two layer regime an evaluation of the key frontal discriminators has confirmed the validity of their use in such an estuary

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

oil source rock correlation in the north viking graben abstract based on evaluation of geochemical properties of nearly 100 oils from the north viking graben we have identified three hydrocarbon populations one population is derived from marine shales of the draupne fm one from marine shales of the heather fm that are rich in land plant detritus and one from a mixture of the two while the draupne fm is the dominant source rock the heather fm lower callovian is an important source on the northern horda platform furthermore on the northern horda platform heather fm shales play a major role in controlling migration oil from the draupne fm migrates only into upper jurassic reservoirs as no large titled fault blocks permit juxtaposition of draupne fm and brent gp sands and the heather fm shales are thick and extensive oil from the heather fm migrates into both upper and middle jurassic reservoirs variations in properties of the hydrocarbons in the north viking graben petroleum system are due to a complex interplay of organic source maturity migration pressure distribution and biodegradation integration of geochemical and geological data on a regional scale has enhanced our ability to evaluate prospects in this important hydrocarbon system

re os geochronology for the nist rm 8505 crude oil the importance of analytical protocol and uncertainty abstract the national institute of science and technology nist research material rm 8505 is a venezuelan crude oil certified for its vanadium concentration it has recently been proposed as a matrix matched standard for interlaboratory comparison of re os isotopic analyses while serving as a benchmark for petroleum based re os method development here the nist rm 8505 oil is characterized using a multi solvent asphaltene precipitation permitting interlaboratory re os data comparison and evaluation of techniques used to derive re os isochron ages we present a detailed discussion of analytical blank sources critical evaluation of analytical uncertainties method improvements and data corrections additionally we provide a comprehensive discussion on the effect of data population size and analytical uncertainty on isochron statistics and the robustness of isochron ages in addition to nist rm 8505 2 43 0 15 ng g re 30 0 0 7 pg g os we provide the first re os data for nist srm 1634c 1 73 0 01 ng g re 32 5 0 8 pg g os and enviromat scp science 39 1 pg g re 1 01 0 02 pg g os two other commercially available hydrocarbon trace metal standards the application of several asphaltene asph precipitations using different n alkane solvents pentane heptane and decane for the nist rm 8505 significantly improved the spread of data in the 187re 188os 187os 188os space multi solvent asphaltene precipitations yield an asphaltene only model 1 isochron 75 24 ma and the maltene crude oil asphaltene triplets yield a more precise model 1 isochron age of 78 5 2 3 ma with a 187os 188osinitial of 0 877 0 021 our age is considerably older compared to a previously reported model 1 age of 62 7 5 7 ma based on c7 asph crude oil malt triplets liu and selby 2017 and considerably younger than the model 1 age of 98 4 9 5 ma based on asph separates liu et al 2019 the analytical reasons leading to these age differences are discussed in this paper the geological context for the nist 8505 oil is unknown therefore we use trace metal data ni v fe mo etc to derive plausible constraints for the origin of this oil the nist 8505 oil shows trace metal data similar to published data for oils from the urdaneta district the la paz mara and lagunillas oil fields and source rocks of the la luna formation in the maracaibo basin venezuela in this geological context our 79 ma age for the nist 8505 oil implies a late cretaceous early hydrocarbon generation event from older upper cretaceous source rocks and overlaps with the youngest age of potential source rocks in the maracaibo basin however the age of large scale oil generation in the maracaibo basin is significantly younger lasting from the oligocene to the pliocene

re os geochronology and os isotope fingerprinting of petroleum sourced from a type i lacustrine kerogen insights from the natural green river petroleum system in the uinta basin and hydrous pyrolysis experiments abstract rhenium osmium re os geochronology of marine petroleum systems has allowed the determination of the depositional age of source rocks as well as the timing of petroleum generation in addition os isotopes have been applied as a fingerprinting tool to correlate oil to its source unit to date only classic marine petroleum systems have been studied here we present re os geochronology and os isotope fingerprinting of different petroleum phases oils tar sands and gilsonite derived from the lacustrine green river petroleum system in the uinta basin usa in addition we use an experimental approach hydrous pyrolysis experiments to compare to the re os data of naturally generated petroleum in order to further understand the mechanisms of re and os transfer to petroleum the re os geochronology of petroleum from the lacustrine green river petroleum system 19 14 ma all petroleum phases broadly agrees with previous petroleum generation basin models 25 ma suggesting that re os geochronology of variable petroleum phases derived from lacustrine type i kerogen has similar systematics to type ii kerogen e g selby and creaser 2005a selby and creaser 2005b finlay et al 2010 however the large uncertainties over 100 in some cases produced for the petroleum re os geochronology are a result of multiple generation events occurring through a 3000 m thick source unit that creates a mixture of initial os isotope compositions in the produced petroleum phases the 187os 188os values for the petroleum and source rocks at the time of oil generation vary from 1 4 to 1 9 with the mode at 1 6 oil to source correlation using os isotopes is consistent with previous correlation studies in the green river petroleum system and illustrates the potential utility of os isotopes to characterize the spatial variations within a petroleum system hydrous pyrolysis experiments on the green river formation source rocks show that re and os transfer are mimicking the natural system this transfer from source to bitumen to oil does not affect source rock re os systematics or os isotopic compositions this confirms that os isotope compositions are transferred intact from source to petroleum during petroleum generation and can be used as a powerful correlation tool these experiments further confirm that re os systematics in source rocks are not adversely affected by petroleum maturation overall this study illustrates that the re os petroleum geochronometer and os isotope fingerprinting tools can be used on a wide range of petroleum types sourced from variable kerogen types

lateral interaction between metamorphic core complexes and less extended tilt block domains the alpujarras strike slip transfer fault zone betics se spain abstract the alpujarras area in southeastern spain exhibits one of the scant documented examples of extension related strike slip faults bordering core complexes in the world faults of the alpujarras fault zone define a regional scale complex ene striking transfer zone that marks the boundary among the sierra nevada elongated dome a highly extended constricted core complex and a less extended domain formed by large scale tilt blocks detailed mapping and structural analysis show that the alpujarras fault zone is an integral part of the wsw directed normal fault systems that thinned the betic hinterland during the middle miocene to recent time fault patterns and palaeostress analysis both indicate that dextral movement along the strike slip faults was induced by a local stress field with a sub horizontal e w to ese wnw trending maximum principal stress axis which is synchronous with the regional stress field driving the normal fault systems palaeostress analysis also indicates subsequent variations in the stress field with a sub horizontal nw se to n s trending maximum principal stress axis thus producing both the tectonic inversion of the northern fault of the alpujarras system and shortening of the unloaded extensional detachment footwall a simplified kinematic model for the tectonic evolution of the alpujarras area from the middle miocene to recent emphasizes the kinematic coupling of normal faults and strike slip transfer zones in the extensional process

re os geochronology and fingerprinting of united kingdom atlantic margin oil temporal implications for regional petroleum systems we demonstrate that the re os system can be used to understand the temporal evolution of a petroleum system as well as aid in the identification of source units traditional geochemical methods high performance liquid chromatography carbon isotope gas chromatography and biomarker analysis indicate that the main source of 18 oils analyzed for re os geochronology from the united kingdom atlantic margin clair schiehallion cuillin and foinaven fields is late jurassic marine shales this is supported by the os isotopic composition 187 os 188 os of the late jurassic source 0 9 2 4 at the timing of oil generation being similar to that of the oil 68 ma 0 92 1 12 indicating that the re os system can potentially be used to fingerprint the source of an oil the re os data for the 18 oils yield an age 68 13 ma that agrees with both the relative basin models and absolute ar ar geochronology timing of oil generation indicating that that re os oil geochronology records oil generation events

vertical axis rotations in the las vegas valley shear zone southern nevada paleomagnetic constraints on kinematics and dynamics of block rotations paleomagnetic study of vertical axis rotations at 23 localities along the right lateral las vegas valley shear zone lvvsz in southern nevada indicates that clockwise rotations generally increase with proximity to the lvvsz reaching 100 at the closest localities rates of rotation determined at four localities range from l m y to 12 m y the maximum characteristic size of rotating blocks is 2 4 km considerably smaller than the dimensions of the zone of deformation associated with the shear zone 100 km in length 15 km in half width thus the deformation does not accord with kinematic models of block rotations that assume uniform rotations within domains having dimensions of the order of the width of the deforming zone instead the deformation appears to be quasi continuous when considered on a scale of 10 km we suggest that it is consistent with the deformation of a highly plastic layer of upper crustal material mechanically decoupled from deeper parts of the crust and that the across strike distribution of rotations is controlled by the rheological properties of the upper crust the length of the shear zone and the total amount of offset across the shear zone

osmium isotopes in hydrothermal fluids from the juan de fuca ridge we present os data for axial high temperature and off axial low temperature hydrothermal solutions from the juan de fuca ridge the high temperature h s bearing axial fluids have unradiogenic os isotopes pointing to a nearly complete domination of osmium isotopes from the basalts during hydrothermal circulation the ridge axis fluids typically do not show large enrichment in osmium concentration over seawater although one high temperature fluid has an os concentration enhanced by a factor of 4 above seawater it appears that the os concentration of high temperature hydrothermal fluids is typically buffered at roughly the seawater concentration we suggest that subseafloor precipitation of pyrite from the high temperature hydrothermal fluids controls the osmium transportation the axial hydrothermal activity does not supply significant amounts of unradiogenic osmium to the deep oceans in contrast a low temperature off axis fluid is enriched in non radiogenic osmium over seawater by a factor of 9 showing much less precipitation of osmium at low temperature because a large fraction of the cooling of oceanic lithosphere occurs on ridge flanks os from low temperature ridge flank hydrothermal circulation may be a significant contributor to the balance of os in the oceans a detailed balance between os contributions from dissolution of cosmic dust and hydrothermal fluids is still not possible the low temperature hydrothermal sample gives os os 0 110 0 001 this extremely unradiogenic osmium can only come from a source that underwent depletion of re over 2 6 ga ago assuming no contamination during sample collection this result suggests that the convecting upper mantle contains ancient depleted material that imparted unradiogenic osmium to intruding basaltic melts

modeling influence of stratification on lateral circulation in a stratified estuary abstract the dynamics of lateral circulation in the passaic river estuary is examined in this modeling study the pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining during highly stratified ebb tides the lateral circulation exhibits a vertical two cell structure strong stratification suppresses vertical mixing in the deep channel whereas the shoal above the halocline remains relatively well mixed as a result in the upper layer the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg this density gradient drives a circulation with surface currents directed toward the shoal and the currents at the base of the pycnocline are directed toward the thalweg in the lower layer the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide a lateral baroclinic pressure gradient is a dominant dri

measurements of tidal flow around a headland with a shipboard acoustic doppler current profiler a shipboard acoustic doppler current profiler adcp and moored current meters were used to obtain detailed measurements of the spatial structure of the tidal flow around a headland in vineyard sound massachusetts where tidal currents typically range from 50 to 70 cm s 1 eight shipboard surveys were conducted each of which followed one of five trapezoidal tracks in the vicinity of the headland completing 11 12 circuits in the course of the tidal cycle 12 4 hours the measurements from the adcp compare favorably with moored velocity measurements at two locations rms deviations of 3 cm s 1 but the comparison showed more scatter at two other sites rms deviations of 7 cm s 1 the adcp measurements from separate cruises were merged to form a composite spatial representation of the tidal and residual currents providing resolution of the spatial structure of the flow around the headland at scales from several hundred meters to 10 km the semidiurnal tidal flow is relatively uniform in space roughly following the bathymetry around the headland while a residual current field consists of counterrotating eddies on either side of the headland with spatial scales of 5 8 km and velocities as high as 25 cm s 1 the instantaneous current field indicates the formation of transient eddies on the downstream side of the headland during flood and ebb with clear evidence of flow separation near the tip of the headland

the effect of periodic stratification on floc size distribution and its tidal and vertical variability geum estuary south korea abstract to understand the spatiotemporal variability in the floc size distribution the factors controlling floc size and the timing of flocculation with sediment flux in the periodically stratified geum estuary korea simultaneous measurements of current salinity suspended sediment concentration ssc and floc size distributions were analyzed and floc size was compared with stratification turbulence ssc and sediment flux salinity measurements indicated that the water column was stratified during ebb and well mixed during flood consistent with the process of strain induced periodic stratification coincident with periodic stratification was an ebb flood asymmetry in floc size where coarser multimodal and variable distributions occurred during the stratified ebb whereas finer unimodal and relatively constant distributions occurred during the well mixed flood vertically flocs coarsened downward during the stratified ebb and were vertically homogenous during the well mixed flood the ebb flood asymmetry in floc size was due to the ebb flood asymmetry in stratification and turbulence furthermore while floc size decreased with turbulence the ssc increased with turbulence as a consequence large flocs occurred with relatively small ebb directed fluxes whereas small flocs occurred with relatively large flood directed fluxes overall these observations indicate that the variability of the floc size distribution in periodically stratified estuaries is different than in well mixed estuaries and that ebb directed fluxes may be more flocculated than flood directed fluxes in these systems

two stage gold mineralization of the axi epithermal au deposit western tianshan nw china evidence from re os dating s isotope and trace elements of pyrite the axi gold deposit is one of the largest epithermal deposits in northwestern china and is characterized by multistage generations of pyrite associated with gold mineralization genetic models for superjacent epithermal au and porphyry cu systems involve either contemporaneous or episodic mineralization implying different metal sources and ore forming events nine pyrite separates from disseminated ores associated with pyrite sericite quartz alteration in the axi deposit yield a re os isochron age of 350 10 ma mswd 5 1 initial 187os 188os ios 0 20 0 11 this age likely reflects a mixed contribution of two subtypes of disseminated pyrite py1 based on zoned pyrite crystals the isochron age of 353 6 ma mswd 1 6 ios 0 107 0 021 n 6 excluding samples with pyrite cores overlaps previous ages for andesite from the dahalajunshan formation ca 356 ma indicating that the early mineralization event occurred shortly after the formation of host rocks ca 353 ma pyrite from disseminated ores shows little variation of sulfur isotopic compositions 2 9 to 4 0 and has high cu co ni and v contents which favors a magmatic hydrothermal origin pyrite grains from gray quartz veins yield a younger re os isochron age of 332 8 ma mswd 0 22 n 4 vein hosted pyrite shows characteristics of a mantle derived magma source ios 0 171 0 024 34s 0 10 3 10 which result from the intrusion driven convective hydrothermal circulation accompanying fluid exsolution and metal remobilization from basement and wallrocks our data demonstrate that the axi gold deposit was formed during two temporally separated hydrothermal events this model of ore formation may apply to other epithermal porphyry deposits within the axi tawuerbieke district disseminated au and porphyry style au cu mineralization occurred shortly after magmatic activity 356 353 ma whereas epithermal style au mineralization occurred at ca 332 ma

evidence for an active shear zone in southern nevada linking the wasatch fault to the eastern california shear zone previous studies have shown that 5 of the pacifi c north america relative plate motion is accommodated in the eastern part of the great basin western united states near the wasatch fault zone and other nearby faults deformation is currently concentrated within a narrow zone of extension coincident with the eastern margin of the northern basin and range farther south the pattern of active deformation implied by faulting and seismicity is more enigmatic to assess how present day strain is accommodated farther south and how this relates to the regional kinematics we analyze data from continuous global positioning system gps stations and model the strain rate tensor fi eld using the horizontal gps velocities and earthquake focal mechanisms the results indicate an 100 km wide zone of 3 3 mm yr extension at 40 5 n that broadens southward from the wasatch fault zone to a width of 400 km at 36 n this broadening involves at least one zone of localized extension in northwestern arizona that encroaches into the southwestern plateau and an eastnortheast trending sinistral shear zone the pahranagat shear zone through southern nevada this shear zone may accommodate as much as 1 8 mm yr and is a key feature that enables westward transfer of extension thereby providing a kinematic connection between the wasatch fault zone and the eastern california shear zone

deformation pattern around the conjoining strike slip fault systems in the basin and range southeast nevada the role of strike slip faulting in basin formation and inversion within the extensional regime of the basin and range strike slip faults create a regional pattern of opposing sense of fault systems the relationship between these faults and other deformational features nearby is enigmatic this paper addresses a diverse assemblage of contractional and extensional structures reflecting local uplift and subsidence respectively at the junction of two large neogene strike slip faults in southeastern nevada the right lateral las vegas valley shear zone and the left lateral bitter spring valley fault of the lake mead fault system first a middle miocene lacustrine carbonate basin the bitter ridge lovell wash carbonate basin formed north of the strike slip faults second the lacustrine basin inverted locally while sediments accumulated south of the strike slip faults third the study area was deformed by north northeast trending high angle oblique faults with normal and left slip components the results both from field observations and numerical modeling of the intersecting strike slip faults show that the las vegas valley shear zone and the bitter spring valley fault may have produced the basin in the north and its intense contractional deformation as well as the southward shift of deposition during the inversion event we conclude that conjoining strike slip fault systems can promote localized vertical tectonics and lead to basin formation and uplift right next to each other subsequent inversion of the earlier basinal deposits however requires a reversal in the sense of slip across the las vegas valley shear zone and a change in the regional stress system

comprehensive evolution of a petroleum system in absolute time the example of brynhild norwegian north sea abstract petroleum systems are inherently complex comprising multiple components and processes which variably interact in space and time to form petroleum accumulations improved understanding of these complex systems requires a holistic approach of integrating diverse geological geophysical and organic and inorganic geochemical data here we present an applied and comprehensive re os geochronological and geochemical study on the brynhild petroleum system from the norwegian north sea essential components of this system include shale source rocks of the mandal and farsund formations reservoir sandstones of the ula formation and their bitumen extracts and produced brynhild crude oil rock eval trace metal and re os data reveal the excellent oil generation potential of the shaley source rocks high contents of organic matter containing large amounts of type i kerogens and constrain their depositional conditions anoxic bottom waters in a high productivity regime driven by enhanced supply of land derived nutrients seven re os shale ages between 146 and 134 ma are consistent with existing volgian ryazanian age estimates and constrain the initial 187os 188os of the shales to 0 52 in the lowermost farsund formation and 0 75 in the uppermost mandal formation solvent extracted reservoir rocks of the ula formation contain insoluble organic matter with type iii type iv kerogens likely supplied by erosion of older a precise 179 ma re os age with unrealistically low initial 187os 188os coal bearing sediments or organic rich shales the brynhild crude oil has relatively low 187os 188os and a generation age of 44 ma based on an asphaltene only re os isochron maltenes from the brynhild crude oil are isotopically affected by interaction with organic rich source rocks that represent the seal for the brynhild oil field compared with the crude oil bitumen from ula formation sandstones have contrasting re os properties high 187os 188os ratios and young generation ages between 8 and 0 ma based on asphaltene bitumen maltene re os triplets asphaltene only re os regressions and re os model ages for components with extremely high 187re 188os the 44 ma and 8 0 ma re os ages agree well with regional burial models that indicate oil generation from 44 ma to present day a genetic link between crude oil and bitumen is indicated by their similar alkane patterns v and ni contents and v ni and pristane phytane ratios modeling of 187os 188os for individual organic components through time shows that shales of the mandal formation developed 187os 188os ratios that match those of the crude oil and bitumen at 44 ma and 8 ma respectively and therefore confirm the source for both hydrocarbon phases we suggest that bitumen formed during in reservoir mixing of a 44 ma old early mature asphaltene poor oil brynhild crude oil with an 8 ma old asphaltene rich oil

temporal and spatial variability of vertical salt flux in a highly stratified estuary 1 the temporal and spatial variability of vertical salt flux in the fraser river estuary british columbia was investigated observationally using several different direct and indirect indicators of buoyancy flux data were collected from the estuary using shipboard instrumentation primarily an acoustic doppler current profiler and a towed conductivity temperature depth unit direct estimates of buoyancy flux were made from along channel control volume analyses and from measurements of overturn scales the spatial and temporal evolution of the salt wedge structure through a tidal cycle was evaluated using the results of these buoyancy flux calculations as well as gradient richardson number froude number and stratification profiles observations indicate that buoyancy flux is driven primarily by interfacial stress and not bottom stress as is common in many estuaries vertical salt flux as opposed to seaward advection of high salinity fluid was found to be the dominant mechanism responsible for removal of salt from the estuarine channel during each daily tidal cycle buoyancy flux was highly variable in time and space however with vertical salt flux during ebb tides on the order of 2 to 3 times greater than that estimated during floods this is due to an increase in the vertical shear of horizontal velocity and a sharp increase in stratification which was observed during early ebb enhanced mixing was observed spatially within a region dominated by a channel constriction in which the channel narrows by approximately 25

the long term fate of co2 in the subsurface natural analogues for co2 storage abstract co 2 is a common gas in geological systems so that planned storage of co 2 in the subsurface may do no more than mimic nature natural co 2 has a wide number of sources that can be at least partly identified by carbon stable isotope geochemistry three pairs of case studies with different reservoir characteristics and co 2 contents have been examined to assess the natural impact of adding co 2 to geological systems carbonate minerals partially dissolve when co 2 is added simply because the co 2 dissolves in water and forms an acidic solution therefore carbonate minerals in the subsurface are not capable of sequestering secondary co 2 the addition of co 2 to a pure quartz sandstone or a sandstone in which the supply of reactive aluminosilicate minerals has been exhausted by excess natural co 2 addition will have no consequences the co 2 will simply saturate the water and then build up as a separate gas phase the addition of co 2 to carbonate cemented sandstone without reactive aluminosilicate minerals will induce a degree of carbonate mineral dissolution but no solid phase sequestration of the added co 2 when co 2 is naturally added to sandstones it will induce combined aluminosilicate dissolution and carbonate cementation if the aluminosilicate minerals contain calcium or magnesium or possibly iron examination of a co 2 filled porous sandstone with abundant reactive aluminosilicate minerals that received a huge co 2 charge about 8000 to 100 000 years ago reveals minimal evidence of solid phase sequestration of the added co 2 this indicates that either dissolution of reactive aluminosilicates or precipitation of carbonate minerals is relatively slow it is very likely that the slow dissolution of reactive aluminosilicates is the rate limiting step solid phase sequestration of co 2 occurs only when reactive aluminosilicates are present in a rock and when the system has had many tens to hundreds of thousands of years to equilibrate the two critical aspects of the behaviour of co 2 when injected into the subsurface are 1 that the rock must contain reactive ca and mg aluminosilicates and 2 that reaction to produce carbonate minerals is extremely slow on a human timescale the reactive minerals include anorthite zeolite smectite and other fe and mg clay minerals such minerals are absent from clean sandstones and limestones but are present in dirty standstones lithic arenites which are mineralogically immature and some mudstones the analysis of geological analogues shows that injection of co 2 into carbonate bearing rocks that do not contain reactive minerals will induce dissolution of the carbonate whether it is a matrix cement rock fragment fault seal or part of a top sealing mudstone

investigating complex isochron data using mixture models the isochron technique for dating geological events is widely used in many fields of isotope geochemistry however data sets can be complex and many samples may not behave as closed systems resulting in excess scatter around a regression line in certain data sets however excess scatter may result when geological samples are partially reset or when samples are comprised of multiple components recording different geological processes separated in time and or initial isotope composition here we introduce a new approach for investigating evidence of such multicomponent mixtures within isochron space we provide a mathematical framework to resolve the number of mixture components without requiring any prior knowledge of this number crucially the model reports the proportion of each individual sample that belongs to each mixture component allowing the user to return to the samples and independently test model outputs with other techniques it is important to distinguish accurate and meaningful ages and initial daughter isotope compositions from the meaningless values that are caused by mismatch between geological processes and the models that we use to describe them first we demonstrate our new model on a synthetic data set to show that it can successfully separate distinct isochrons in a complex mixture we further validate our approach with a previously published data set using the 187re 187os system in bitumen and 147sm 144nd system in magmatic rocks we identify discrete components in these data sets and using complementary geological observations discuss the implications of treating these scattered data as recording multiple geological processes

growing faults in the lab insights into the scale dependence of the fault zone evolution process analog sandbox experiments are a widely used method to investigate tectonic processes that cannot be resolved from natural data alone such as strain localization and the formation of fault zones despite this it is still unclear to which extent the dynamics of strain localization and fault zone formation seen in sandbox experiments can be extrapolated to a natural prototype of paramount importance for dynamic similarity is the proper scaling of the work required to create the fault system wprop using analog sandbox experiments of strike slip deformation we show wprop to scale approximately with the square of the fault system length l which is consistent with the theory of fault growth in nature through quantitative measurements of both wprop and strain distribution we are able to show that wprop is mainly spent on diffuse deformation prior to localization which we therefore regard as analogous to distributed deformation on small scale faults below seismic resolution in natural fault networks finally we compare our data to estimates of the work consumed by natural fault zones to verify that analog sandbox experiments scale properly with respect to energy i e that they scale truly dynamically

long term performance of a mudrock seal in natural co2 storage the ability of mudrock seals to prevent co 2 leakage is a major concern for geological storage of anthropogenic co 2 the long term performance of a mudrock seal which provides a natural analogue in the north sea miller oil fi eld has been evaluated this mudrock seal is immediately above a natural co 2 rich reservoir the paper reports the stable isotopes of carbon from carbonate minerals in the mudrock that have precipitated in contact with co 2 during 4 km of burial a well defi ned linear trend of upward decreasing 13 c traces the progressive penetration of free phase co 2 causing dissolution and reprecipitation of carbonate minerals the co 2 was emplaced ca 70 80 ma and has only penetrated 12 m vertically in this case the infi ltration rate is estimated as 9 8 10 7 g cm 2 yr 1

a holistic model for the origin of orogenic gold deposits and its implications for exploration the term orogenic gold deposits has been widely accepted but there has been continuing debate on their genesis early syn sedimentary or syn volcanic models and hydrothermal meteoric fluid models are now invalid magmatic hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships the most plausible models involve metamorphic fluids but the source of these fluids is equivocal intra basin sources within deeper segments of the hosting supracrustal successions the underlying continental crust subducted oceanic lithosphere with its overlying sediment wedge and metasomatized lithosphere are all potential sources several features of precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic fluid source these include the presence of hypozonal deposits in amphibolite facies domains their anomalous multiple sulfur isotopic compositions and problems of derivation of gold related elements from devolatilization of dominant basalts in the sequences the phanerozoic deposits are largely described as hosted in greenschist facies domains consistent with supracrustal devolatilization models a notable exception is the jiaodong gold deposits of china where ca 120 ma gold deposits are hosted in precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization other deposits in china are comparable to those in the massif central and elsewhere in france in that they are hosted in amphibolite facies domains or clearly post date regional metamorphic events imposed on hosting supracrustal sequences if all orogenic gold deposits have a common genesis the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold bearing sulfide rich sedimentary package or the associated metasomatized mantle wedge with co2 released during decarbonation and s and ore related elements released from transformation of pyrite to pyrrhotite at about 500 c although this model satisfies all geological geochronological isotopic and geochemical constraints and is consistent with limited computer based modeling of fluid release from subduction zones the precise mechanisms of fluid flux are model driven and remain uncertain from an exploration viewpoint the model re emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction related orogenic belts and importance of continental scale lithosphere tapping fault and shear zones to focus large volumes of auriferous fluid it confirms the importance of the consistent spacing between world class deposits broadly equivalent to the depth of the moho as derived from empirical observations

recent developments in the study of ocean turbulence abstract this review describes the changes in the understanding of turbulence and mixing in the upper layers of the ocean the abyssal ocean and in continental shelf seas that have come in the past 25 years largely through advances in instruments and methodology

reply to the comment by wu et al 2016 on behavior of re and os during contact between an aqueous solution and oil consequences for the application of the re os geochronometer to petroleum geochim cosmochim acta 158 2015 1 21 abstract we reply here to the questions raised by wu et al concerning the results published by mahdaoui et al 2015 this paper describes experiments in which aqueous solutions containing reo 4 and oscl 6 2 were brought in contact with natural oils at various ranges of concentration time and temperature the main observation is that the transfer of re and os to oils is very efficient under all experimental conditions wu et al argue that thermodynamic equilibrium was not achieved in these experiments as apparent partition coefficients are inconsistent they conclude that the experiments were flawed by possible leaking of reactors and that the conclusions by mahdaoui et al 2015 were not justified in the following reply we explain that mahdaoui et al 2015 never claimed that thermodynamic equilibrium was achieved any calculations or considerations in this context are therefore meaningless we recall the objectives of our publication which were to experimentally test the behavior of reo 4 and oscl 6 two plausible chemical forms of re and os in deep aquifers of petroleum systems in aqueous solution oil systems to our knowledge these are the first experiments of their kind the parameters that could influence the precision and reproducibility of our results were discussed in detail in mahdaoui et al 2015 the essential point is that all 60 of the experiments provide evidence of substantial transfer of re and os from water to oil in contrast to what was mistakenly understood by wu et al the paper does not challenge the use of re os to date geological events affecting petroleum instead by providing a mechanism that might allow os isotopic homogenization on a basin wide scale a critical step missing from most current models it offers a possible explanation of how re os geochronology in oils could potentially work more generally our study suggests that transfer of re and os from waters to oil may be an important phenomenon that should not be overlooked

tidal and river discharge forcing upon water and sediment circulation at a rock bound estuary guadiana estuary portugal the relative impacts of tidal neap spring and river discharge including a flood event forcing upon water and sediment circulation have been examined at the rock bound guadiana estuary near bed and vertical profiles of current salinity turbidity plus surface suspended sediment concentrations ssc at some stations only were collected at the lower and central upper estuary during tidal and fortnightly cycles in addition vertical salinity and turbidity profiles were collected around high and low water along the estuary tidal asymmetry produced faster currents on the ebb than on the flood especially at the mouth this pattern of seaward current dominance was enhanced with increasing river flow due to horizontal advection that was confined within the narrow estuarine channel the freshwater inputs and at a degree less the tidal range controlled the vertical mixing and stratification importance well mixed spring and partially stratified neap conditions alternated during periods of low river flows with significant intratidal variations induced by tidal straining especially at the partially stratified estuary highly stratified conditions developed with increasing river discharge intratidal variability in the pycnocline depth and thickness resulted from current shear during the ebb a salt wedge with tidal motion was observed at the lower estuary during the flood event depending on the intensity of turbulent mixing the residual water circulation was dominantly controlled either by tidal asymmetry or gravitational circulation the ssc was governed by cyclical local processes resuspension deposition mixing advection driven by the neap spring fluctuations in tidal current velocities more intratidal variability in stratification indicated the significance of tidal pumping at the partially and highly stratified estuary the estuary turbidity maximum etm was enhanced with increasing current velocities and displaced downstream during periods of high river discharge during the flood event the etm was expelled out of the estuary and the ssc along the estuary was controlled by the sediment load from the drainage basin under these highly variable river flow conditions our observations suggest that sand is exported to the nearshore over the long term years

origin and migration of hydrocarbon gases and carbon dioxide bekes basin southeastern hungary the bekes basin is a sub basin within the pannonian basin containing about 7000 m of post cretaceous sedimentary rocks natural gases are produced from reservoirs precambrian to tertiary in age located on structural highs around the margins of the basin gas composition and stable carbon isotopic data indicate that most of the flammable gases were derived from humic kerogen contained in source rocks located in the deep basin the depth of gas generation and vertical migration distances were estimated using quantitative source rock maturity carbon isotope relationships for methane compared to known neogene source rock maturity depth relationships in the basin these calculations indicate that as much as 3500 m of vertical migration has occured in some cases isotopically heavy 7 0 co2 is the predominant species present in some shallow reservoirs located on basin margin structural highs and has probably been derived via long distance vertical and lateral migration from thermal decompositon of carbonate minerals in mesozoic and older rocks in the deepest parts of the basin a few shallow reservoirs 2000m contain isotopically light 50 to 60 0 methane with only minor amounts of c2 homologs 3 v v this methane is probably mostly microbial in origin above normal pressures occuring at depths greater than 1800 m are believed to be the principal driving force for lateral and vertical gas migration these pressures are caused in part by active hydrocarbon generation undercompaction and thermal decomposition of carbonates

crustal inhomogeneities in the northern north sea from potential field modeling inherited structure and serpentinites abstract a new crustal model for the northern north sea was developed by gravity and magnetic modeling along the deep seismic line nsdp84 1 utilizing vertical gradients allowed distinguishing between shallow and deep crustal sources the upper crust is characterized by low magnetic susceptibilities and low densities which is typical for felsic rocks a new finding was that the deep crust below the western viking graben and the east shetland basin is the source of high magnetic anomalies combined with low gravity anomalies which was interpreted to represent rocks with very high magnetic susceptibilities and low to intermediate densities such rock parameters may indicate serpentinites but intermediate intrusives or a combination of both is also possible honoring the string of three near equidistant magnetic maxima which follow the trend of the nne ssw striking east shetland basin in the map plane it is suggested that this area is part of an island arc of the iapetus ocean which has been assembled during the collision between laurentia and baltica in late silurian times partly serpentinized peridotites and intermediate intrusives will relate in such a model to slab dehydration of the subducting oceanic plate below the island arc these inherited or synorogenic serpentinites are expected to persist in the geothermal regime of the caledonian orogeny to a depth of at least 50 km increased heat flow by later rift phases will have caused metamorphism of the remaining serpentinites to meta peridotites at depth below the present day moho fluid release related to dehydration of the serpentinites may have triggered further serpentinization of the inherited partly serpentinized rocks at shallower depth an alternative origin for the suggested serpentinites valid only for the area under the western part of the viking graben may be synrift serpentinization due to the heavy faulting during the jurassic rift phase

direct radiometric dating of hydrocarbon deposits using rhenium osmium isotopes rhenium osmium re os data from migrated hydrocarbons establish the timing of petroleum emplacement for the giant oil sand deposits of alberta canada at 112 5 3 million years ago this date does not support models that invoke oil generation and migration for these deposits in the late cretaceous most re os data from a variety of deposits within the giant hydrocarbon system show similar characteristics supporting the notion of a single source for these hydrocarbons the re os data disqualify cretaceous rocks as the primary hydrocarbon source but suggest an origin from older source rocks this approach should be applicable to dating oil deposits worldwide

evaluation of bitumen as a 187re 187os geochronometer for hydrocarbon maturation and migration a test case from the polaris mvt deposit canada abstract re os analyses of bitumen from the polaris mississippi valley type zn pb deposit demonstrate the potential utility of the re os system for establishing the absolute timing of hydrocarbon migration and generation the polaris deposit is hosted by carbonate rocks of the upper ordovician thumb mountain formation and sulphide mineralization during late devonian time is constrained by a rb sr sphalerite date of 366 15 ma and a paleomagnetic date bitumen occurs in open space fillings and coatings and is interpreted to have formed during the main and late stages of sulphide mineralization samples of bitumen were taken from a variety of locations from the main deposit at polaris re and os contents are 3 78 ppb and 55 1155 ppt respectively the 187re 188os ratios are very high ranging from 300 to 1800 and the os isotopic composition is moderately to highly radiogenic with 187os 188os ratios ranging from 3 3 to 13 7 calculated 187os 188os ratios at 366 ma are variable but an obvious grouping is defined by 11 of 16 analyses on a re os isochron diagram and these data yield a re os date of 374 9 ma mswd 12 model 3 in agreement with rb sr sphalerite and paleomagnetic dates for mineralization at polaris the combined dates suggest that the migration of fluids responsible for both pb zn mineralization and bitumen formation at polaris was broadly contemporaneous and was coeval with the late devonian ellesmerian orogeny though considerable further research is required to understand the re os isotopic systematics of migrated hydrocarbon systems bitumen re os geochronology may provide the possibility of establishing a more comprehensive understanding of mvt deposits sedimentary basin and petroleum systems

the cycle of turbulent dissipation in the presence of tidal straining in regions of large horizontal density gradient tidal straining acts to produce a periodic component of stratification that interacts with turbulent mixing to control water column structure and flow a 25 h series of measurements of the rate of dissipation of turbulent kinetic energy e in the liverpool bay region of freshwater influence rofi have revealed the form of this interaction and indicate substantial differences from regions where horizontal gradients are weak in the rofi system there is a pronounced difference between flood and ebb regimes during the ebb the water column stratifies and strong dissipation is confined to the lower half of the water column by contrast during the flood stratification is eroded with complete vertical mixing occurring at high water and high values of dissipation 3 mw m23 extending throughout the water column the cycle of dissipation is therefore predominantly semidiurnal in the upper layers whereas near the bottom boundary the principal variation is at the m4 frequency as observed in regions of horizontal uniformity toward the end of the flood phase of the cycle tidal straining produces instabilities in the water column that release additional energy for convective mixing confirmation of increased vertical motions throughout the water column during the late flood and at high water is provided by measurements of vertical velocity and the error velocity from a bottom mounted acoustic doppler current profiler

a rare phanerozoic amphibolite hosted gold deposit at danba yangtze craton china significance to fluid and metal sources for orogenic gold systems the danba gold deposit is located in a poorly documented gold province on the north western margin of the yangtze craton it is sited in devonian sequences in a high grade metamorphic terrane that includes an extensional metamorphic core complex around the deposit peak metamorphic conditions of 6 0 5 kbar and 650 50 c at ca 193 ma were followed by retrograde sillimanite grade conditions of 4 5 0 5 kbar and 550 50 c the deposit is hosted in a broadly strata bound ductile brittle shear zone with high t proximal alteration assemblages of biotite amphibole plagioclase and ore assemblages dominated by pyrrhotite but with a strong association between gold and bismuth tellurides alteration mineral thermobarometers together with heating freezing studies of low salinity h2o co2 ch4 fluid inclusions indicate p t conditions of early ore deposition of approximately 4 5 kbar and 500 650 c at around 185 9 ma indicated by re os geochronology on ore related molybdenite in conjunction all data demonstrate that danba represents a lower jurassic hypozonal orogenic gold deposit that formed during post peak metamorphic retrogression the primary high p t nature of the deposit combined with its late metamorphic timing negate that the ore fluid was sourced via devolatilization of the hosting supracrustal sequences a deep externally derived ore fluid source is required the most likely source is the k h2o co2 and ore metal fertilized lithospheric mantle that was metasomatized during neoproterozoic subduction it is proposed that transition from lithospheric transpression to extension in the jurassic triggered the devolatilization of this metasomatized lithosphere to cause the formation of this rare phanerozoic amphibolite hosted gold deposit at danba

late stage evolution of the chemehuevi and sacramento detachment faults from apatite u th he thermochronometry evidence for mid miocene accelerated slip the unique low temperature sensitivity of the apatite u th he ahe technique provides valuable new information relating to the late stage thermal evolution of metamorphic core complexes in the southern basin and range province in all the ranges studied the data show greater complexity than previously seen from other thermochronometers in the chemehuevi and northern sacramento mountains a trend of decreasing ages toward the northeast applies only for the structurally shallowest parts of the footwall this is followed by essentially age invariant segments of 15 1 ma reflecting an increase in the rate of detachment fault movement the timing of the change suggested by the data agrees with recently published ahe results from the nearby harcuvar mountains located 125 km to the southeast suggesting that an underlying regional mechanism triggered this change plate reconstructions indicate that the pioneer mendocino fracture zone migrated northward through the area at this time leaving a slab window in its wake we suggest that the additional heat applied to the base of the lithosphere from the slab window resulted in mechanical weakening of the area and that this combined with the extensional strain regime present resulted in an increased rate of slip within the actively extending metamorphic core complexes this agrees well with timing constraints for extension onset in the central basin and range province of southern nevada and suggests that weakening of the southern basin and range province at 15 1 ma was partially responsible for the onset of extension in the central basin and range these findings demonstrate that improved constraints on changes in extension rate within the basin and range province should be possible through the application of the ahe technique to other metamorphic core complex footwalls

further evaluation of the re os geochronometer in organic rich sedimentary rocks a test of hydrocarbon maturation effects in the exshaw formation western canada sedimentary basin abstract re os isotopic analyses of a single organic rich sedimentary rock unit ors of known depositional age and at three levels of regional hydrocarbon maturity show that hydrocarbon maturation does not affect the ability the 187re 187os chronometer to yield a depositional age for such rocks we present re os isotope analyses from the late devonian exshaw formation in the subsurface of the western canada sedimentary basin alberta and obtain a re os isochron age of 358 10 ma 2 model 3 1 666 10 11 a 1 for samples ranging from hydrocarbon immature to overmature this age is within uncertainty of the established absolute age for the exshaw formation hydrocarbon immature and mature plus overmature samples show no significant age differences if regressed individually indicating that hydrocarbon maturation did not greatly disturb the re os isotope system in the exshaw formation as such we propose that the re os geochronometer may be used as a reliable tool for measuring the depositional ages of ors regardless of their level of hydrocarbon maturity we find that minimizing natural variation in the initial 187os 188os ratio is more important than avoiding hydrocarbon maturation in obtaining precise re os ages in particular the exshaw formation appears to contain a nonhydrogenous component of unradiogenic os in addition to the hydrogenous os load a subset of exshaw formation samples with 5 total organic carbon toc which should best reflect the hydrogenous os load alone yields a very well fitted isochron having a depositional age of 358 9 ma 2 1 666 10 11 a 1 with an initial 187os 188os ratio of 0 59 0 05 model 3 mean square of weighted deviates mswd 1 8 the initial 187os 188os ratio of this regression may provide an estimate of the os isotopic composition of local seawater at the time of deposition

residual currents induced by asymmetric tidal mixing in weakly stratified narrow estuaries abstract residual currents induced by asymmetric tidal mixing were examined for weakly stratified narrow estuaries using analytical and numerical models the analytical model is an extension of the work of r k mccarthy with the addition of tidal variations of the vertical eddy viscosity in the longitudinal momentum equation the longitudinal distribution of residual flows driven by asymmetric tidal mixing is determined by the tidal current amplitude and by asymmetries in tidal mixing between flood and ebb in a long channel the magnitude of the residual flow induced by asymmetric tidal mixing is maximum at the estuary mouth and decreases upstream following the longitudinal distribution of tidal current amplitude larger asymmetry in tidal mixing between flood and ebb produces stronger residual currents for typical tidal asymmetry mixing is stronger during flood than during ebb and results in two layer residual currents with seaward flow near the surface and landward flow near the bottom for revers

role of asymmetric tidal mixing in the subtidal dynamics of narrow estuaries 1 the role of asymmetric tidal mixing atm in subtidal estuarine dynamics is investigated using a series of generic numerical experiments that simulate narrow estuaries under different stratification and external forcing conditions the focus is on quantifying the characteristics of atm induced flow and its contributions to stratification and salt transport the flow induced by atm has a two layer vertical structure in periodically stratified estuaries similar to that of the density driven flow it has a three layer vertical structure in the central regime of weakly stratified estuaries and a reverse two layer structure in highly stratified estuaries the changes in vertical distribution of atm induced flows result from the influence of stratification on the covariance of eddy viscosity and vertical shear such covariance represents the driving force of atm induced flow in the tidally averaged momentum equation compared to density driven flow atm induced flow dominates in periodically stratified estuaries with strong tides has the same order of magnitude in weakly stratified estuaries with moderate tides and is less important in highly stratified estuaries with weak tides in contrast to density driven flow that always increases estuarine stratification and transports salt landward the atm induced flow exhibits different behaviors because of its varying vertical structure in estuaries with strong tides atm induced flow tends to enhance stratification and to transport salt landward similar to density driven flow in estuaries with weak tides atm induced flow tends to reduce stratification and to transport salt seaward

tidal asymmetry in an estuarine pycnocline depth and thickness tidal variations in estuarine stratification are revealed by the depth and thickness of the density interface the depth of the interface may be predicted using an inviscid two layer model that combines baroclinic estuarine circulation with barotropic tidal currents helfrich 1995 here we present results from a two layer model modified to include the effects of bottom friction and interfacial mixing modeled layer thickness and speed compare favorably with prior analytic studies farmer and armi 1986 pratt 1986 we use a bulk richardson number criterion to estimate the thickness of the pycnocline from two layer model results the predicted pycnocline depth and thickness compare remarkably well with observations we also investigate the effects of changing bottom friction and barotropic currents on the pycnocline thickness

tidal variations of flow convergence shear and stratification at the rio de la plata estuary turbidity front 1 intratidal variability of density and velocity fields is investigated at the turbidity front of the rio de la plata estuary south america current velocity and temperature salinity profiles collected in august 1999 along a repeated transect crossing the front are analyzed horizontal and vertical gradients stability of the front convergence zones and transverse flow associated to the frontal boundary are described strong horizontal convergence of the across front velocity and build up of along front velocity shear were observed at the front in the proximity of the front enhanced transverse or along front flow created jet like structures at the surface and near the bottom flowing in opposite directions these structures persisted throughout the tidal cycle and were advected upstream downstream by the flood ebb current through a distance of 10 km during peak flood the upper layer flow reversed from its predominant downstream direction and upstreamflow occupied the entire water column outside the peak flood two layer estuarine circulation dominated changes in density field were observed in response to tidal straining tidal advection and wind induced mixing but stratification remained throughout the tidal cycle this work demonstrates the large spatial variability of the velocity field at the turbidity front it provides evidence of enhanced transverse circulation along the frontal boundary and reveals the importance of advective and frictional intratidal processes in the dynamics of the central part of the estuary

lead isotopes as tracers of crude oil migration within deep crustal fluid systems abstract although pb u and th may be fractionated between crude oil and formation waters pb isotopes are not this unique property makes pb isotopes a particularly useful marker of hydrocarbon generation and migration here we show that pb isotopes offer a new vision of long range secondary oil migration relevant to the formation of oil fields north sea oils are largely generated from jurassic black shales yet their pb isotopes are mixtures of cenozoic to proterozoic end members the same observation is made for crude oils from the paris basin the barents sea libya kuwait kazakhstan and australia bulk pb in crude oil therefore for the most part is foreign to its source rock s our high precision pb isotope data on 195 crude oils worldwide the first such data set in the published literature and 17 northern european black shales indicate that deep seated pb components originating beneath the source rocks are ubiquitous in crude oil this implies that oil fields are embedded in basinal convective systems of hydrous fluids heated from below plumes of hot fluids rise from the lower thermal boundary layer which pb isotopes require douse the basement into the core of the porous flow convective cell where they dissolve the newly formed hydrocarbons sequestered in the source rocks the fluids finally unload unmixed formation waters and crude oil at the base of the upper conductive boundary layer where they can be trapped in favorable sites based on these new insights we argue that pb isotopes in crude oil constitute a good tracer of oil migration

re os dating of maltenes and asphaltenes within single samples of crude oil abstract re os geochronology of oil may constrain the timing of oil formation and improve oil source and oil oil correlations typically asphaltene asph the heaviest and most re os rich oil fraction from multiple oils within an oil field or a larger petroleum system are analyzed to obtain sufficient spread in re os isotopic ratios a mathematical necessity for precise re os isochrons here we offer a new approach for re os geochronology of oil based on isotopic analyses of different fractions within a single sample of crude oil we studied three oils from the gela oil field southern sicily italy recovered from triassic jurassic stratigraphic intervals streppenosa noto and sciacca formations within the gela 1 well asph insoluble in n alkane and maltene malt soluble in n alkane fractions of oil were separated using n pentane n hexane n heptane and n decane solvents the asph contents of the sciacca and noto oils 26 33 wt are notably higher compared to the streppenosa oil 7 12 wt asph we present an optimized re os procedure with sample digestion in a high pressure asher followed by isotopic measurements using negative thermal ionization mass spectrometry very high metal contents of gela oils allowed acquisition of precise re os data systematic variations between the type of solvent used for asph precipitation and the asph content of the oil also known from the literature and the re os contents of the asph and malt fractions first observed in this study provide important practical applications for re os analyses of oil most re and os 96 98 in the noto oil are hosted in the asph fraction in contrast a significant portion of re and os 33 34 is stored in the malt fraction of the lighter but heavily biodegraded streppenosa oil collectively our new data on alkane distribution hopane and sterane biomarkers major and trace element contents and re os concentrations and isotopic ratios of the oils and their fractions support the presence of two oil families streppenosa oil a heavily biodegraded oil generated at an early stage of thermal maturation from a shaly source rock is clearly distinct from the noto and sciacca oils both generated at peak maturation from a carbonate source rock with no subsequent biodegradation two re os ages were obtained crude oil and asph from noto and sciacca oil yield a model 1 isochron age of 27 5 4 6 ma with an initial 187 os 188 os of 3 89 0 43 mswd 1 6 n 19 we interpret this oligocene age as the time of initial oil generation that was probably related to the onset of regional collisional tectonics in southern sicily asph and crude oil from the streppenosa oil yield scattered data perhaps related to effects of biodegradation streppenosa malt yield a model 1 age of 200 0 5 2 ma and initial 187 os 188 os of 1 39 0 11 mswd 0 52 n 4 this age and initial os isotopic composition are consistent with rapid oil generation shortly after late triassic source rock formation perhaps driven by magmatic related heating here we document a potentially powerful geochronological tool that can be applied to single samples of crude oil within each oil the 187 os 188 os and most of the 187 re 188 os ratios in the malt fractions are lower than in the corresponding asph fractions crude oils being physical mixtures of asph and malt have intermediate re os isotopic ratios hence the needed spread in data points for a re os isochron is obtained by analyzing components of a single crude oil this approach eliminates pitfalls in interpretation of re os data from multiple oils with possibly different generation migration or reservoir modification history

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

evaluation of the rhenium osmium geochronometer in the phosphoria petroleum system bighorn basin of wyoming and montana usa rhenium osmium re os geochronometry is applied to crude oils derived from the permian phosphoria formation of the bighorn basin in wyoming and montana to determine whether the radiogenic age reflects the timing of petroleum generation timing of migration age of the source rock or the timing of thermochemical sulfate reduction tsr the oils selected for this study are interpreted to be derived from the meade peak phosphatic shale and retort phosphatic shale members of the phosphoria formation based on oil oil and oil source rock correlations utilizing bulk properties elemental composition 13c and 34s values and biomarker distributions the 34s values of the oils range from 6 2 to 5 7 with oils heavier than 2 interpreted to be indicative of tsr the re and os isotope data of the phosphoria oils plot in two general trends 1 the main trend n 15 oils yielding a triassic age 239 43 ma with an initial 187os 188os value of 0 85 0 42 and a mean square weighted deviation mswd of 1596 and 2 the torchlight trend n 4 oils yielding a miocene age 9 24 0 39 ma with an initial 187os 188os value of 1 88 0 01 and a mswd of 0 05 the scatter high mswd in the main trend regression is due in part to tsr in reservoirs along the eastern margin of the basin excluding oils that have experienced tsr the regression is significantly improved yielding an age of 211 21 ma with a mswd of 148 this revised age is consistent with some studies that have proposed late triassic as the beginning of phosphoria oil generation and migration and does not seem to reflect the source rock age permian or the timing of re migration late cretaceous to eocene associated with the laramide orogeny the low precision of the revised regression 21 ma is not unexpected for this oil family given the long duration of generation from a large geographic area of mature phosphoria source rock and the possible range in the initial 187os 188os values of the meade peak and retort source units effects of re migration may have contributed to the scatter but thermal cracking and biodegradation likely have had minimal or no effect on the main trend regression the four phosphoria sourced oils from torchlight and lamb fields yield a precise miocene age re os isochron that may reflect the end of tsr in the reservoir due to cooling below a threshold temperature in the last 10 m y from uplift and erosion of overlying rocks the mechanism for the formation of a re os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187re 188os values from an oil family

a magnus opus helium neon and argon isotopes in a north sea oilfield this study of the magnus oilfield located in the east shetland basin northern north sea represents the most detailed investigation of noble gas isotope systematics in a liquid hydrocarbon reservoir yet undertaken samples from nine producing wells across this middle jurassic field were taken and the helium neon and argon isotopic ratios and abundances in the oil were determined both the helium and the neon isotope systematics require a contribution from a mantle source if the mantle endmember is modeled using mid ocean ridge mor values 2 3 4 5 of the 4he and 4 3 6 2 of the 21ne is mantle derived the remainder of the 4he and 9 0 12 0 of the 21ne is crustal radiogenic and the remaining 21ne is atmosphere derived the resolved mantle derived he ne ratio is quite distinct from upper mantle values estimated from mor samples but indistinguishable from values resolved in other regions of continental extension this result provides strong evidence that the subcontinental lithospheric mantle not only has a different noble gas inventory to the convecting mantle under mors but also has a near uniform composition the quantity of radiogenic noble gas associated with the magnus oil groundwater system can only be accounted for by production predominantly from outside the volume of the magnus sandstone aquifer reservoir drainage area and the associated kimmeridge clay source rock formation and together with the mantle derived noble gases provides strong evidence for cross formational communication with deeper regions of the crust the 20ne and 36ar must have been input into the oil phase by interaction with an air equilibrated groundwater noble gas partitioning between a seawater derived groundwater and the oil phase at the average magnus sandstone aquifer temperature requires a subsurface seawater oil volume ratio of 110 40 to account for both the 20ne and 36ar concentrations in the central and southern magnus samples the volume of groundwater which has equilibrated with the magnus oil is indistinguishable from the static volume of water estimated to be in the down dip magnus aquifer reservoir drainage volume this suggests that the magnus oil has obtained complete equilibrium with the groundwater in the reservoir drainage volume probably during secondary migration and further suggests that concurrent cementation of the magnus sandstone aquifer has occurred with little or no large scale movement of air equilibrated groundwater through the aquifer system higher concentrations of 20ne and 36ar in the n magnus oil cannot be accounted for by equilibration with a seawater derived groundwater this is qualitatively consistent with the earlier and more mature oil in this section equilibrating with freshwater which is known to have been trapped in the crest of the reservoir structure

application of pyrolysate carbon isotope and biomarker technology to organofacies definition and oil correlation problems in north sea basins abstract detailed sampling of apparently homogeneous potential source rock intervals frequently indicates unsuspected variations in organic facies which may or may not be reflected in the wireline logs carbon isotope analyses of pyrolysates provide a useful technique in these investigations which are essential for valid oil to source correlations in the jurassic of a north sea viking graben well the rich source shales at the top of the draupne formation are significantly depleted in 13 c and correlate with the oils from this area thus suggesting that this interval has acted as the primary source of the viking graben crudes a quite different pattern is evident in a well from the central graben and the data not only explain why the oils of the greater ekofisk area are relatively enriched in 13 c but also demonstrate that the variations within these oils are facies controlled pyrolysate carbon isotopes provide an excellent correlation between the middle devonian upper caithness flagstones of the inner moray firth and the beatrice crude oil this correlation is supported by the biomarker data and there is no need to appeal to a contribution from either an upper or middle jurassic source to achieve a match with the beatrice oil

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

fault charged mantle fluid contamination of united kingdom north sea oils insights from re os isotopes 187 os 188 os as expected from a kimmer idge clay formation source however oils from the viking graben with which the brent fi eld is associated and main east shetland basin display unradiogenic 187 os 188 os in this study we seek to demonstrate that these anomalous results are due to interaction with a mantle like fl uid that propagated through the main fault zone of the viking graben and east shetland basin this study enhances our understanding of the re os oil systematics and supports cur rent ideas regarding fault architecture crustal thinning and associated fl uid fl ow and interac tion in the north sea oil system abstract united kingdom north sea oils sourced from the kimmeridge clay formation contain unradiogenic 0 17 to 0 48 and radiogenic 1 04 to 3 34 187 os 188 os values the unra diogenic 187 os 188 os values are spatially associated with the main basin bounding faults of the viking graben and east shetland basin in contrast the radiogenic 187 os 188 os values are associated with north sea basins located farther away from the basin boundary faults we suggest that crustal thinning and strain localization within the viking graben and east shetland basin are suffi cient to have allowed basin bounding faults to propagate to suffi cient depth to act as conduits for mantle derived fl uids to interact with oil this hypothesis is sup ported by previous geochemical data for north sea oil fi elds furthermore we demonstrate the use of os isotopes as an important tracker of crustal scale fl uid dynamics and petroleum migration pathways in extensional basins

3 d palinspastic restoration of normal faults in the inner moray firth implications for extensional basin development abstract balanced cross section techniques and the construction of a restored section permit 2 dimensional palinspastic restorations to be made in both compressional and extensional terraines in 3 dimensions an equivalent restoration can be made by assuming conservation of bedding plane area and considering the volume of a stratigraphic interval rather than its cross sectional area extensional basins displaying upper crustal listric normal faulting are particularly amenable to this approach computerised 3 d restorations have been made of the inner moray firth basin offshore scotland this basin is not isostatically compensated and was produced by 7 8 post triassic extension of which 2 5 3 is post jurassic above a detachment surface at 20 25 km depth close to the base of the crust limited lower crustal thinning and lithospheric stretching has affected the eastern part of the basin but this can account for no more than half of the measured upper crustal extension some of this shallow extension is probably coupled by low angle faults or shear zones into major zones of lithospheric stretching such as the north sea grabens where it may help account for discrepancies between estimates of lithospheric thinning and upper crustal extension

turbulence in an estuarine embayment observations from beatrix bay new zealand 1 this study characterizes turbulence in a stratified estuarine embayment using measurements of temperature gradient microstructure the water column was generally strongly stratified with only moderate tidal forcing dissipation levels and turbulence length scales in the surface mixing layer the pycnocline the fluid interior and the benthic boundary layer were measured and compared with expectations based on previous work in different systems parameters important for modeling including the measured dissipation ratio d and the gradient richardson number rig were calculated the observations highlight a number of points 1 the lack of strong tidal flows means that buoyancy effects in estuarine embayments are more important than in the estuary proper 2 the combination of reduced tidal mixing and interacting thermohaline stratification suggests the importance in certain situations of diffusive convection 3 despite the shallow depths 40 m a number of hydrodynamic regimes vertically adjacent to one another exist resulting in a highly variable distribution of turbulence properties

stratification and turbulence in subtidal channels through intertidal mudflats 1 field observations in san francisco bay of subtidal channels that drain through intertidal mudflats indicate that substantial periodic stratification develops in very shallow flows with distinct asymmetries between flood and ebb conditions the greatest variability in salinity and stratification occurs during the wet winter months very strong longitudinal salinity gradients develop across the intertidal zone between salty subtidal water and fresher water draining into the marsh upstream tidal straining of the longitudinal gradient creates the periodic stratification stratifying through ebbs and destratifying through floods the stratification can be very strong in very shallow flows with n2 0 1 s 2 in about 0 5 m water depth analysis of the data with dimensionless numbers shows that at times the stratification is strong enough to suppress turbulence and mixing the asymmetry in stratification between ebbs and floods results in asymmetries in eddy viscosity and eddy diffusivity with lower values during the stratified ebbs because of the intertidal elevation of the system the strong longitudinal salinity gradient is regenerated each time the mudflats and marsh drain the system approaches a tidally periodic steady state where the flow dynamics are dominated by the sharp front of salty water that advects into the intertidal zone on the rising tide and exits the system by each lower low water the field data are supported by a numerical model with simple mudflat channel bathymetry both the field and numerical work indicate that the shallow low energy flows in mudflat channels transition between strongly stratified suppressed turbulence and relatively unstratified active turbulence each tidal cycle

the role of advection straining and mixing on the tidal variability of estuarine stratification abstractdata from the hudson river estuary demonstrate that the tidal variations in vertical salinity stratification are not consistent with the patterns associated with along channel tidal straining these observations result from three additional processes not accounted for in the traditional tidal straining model 1 along channel and 2 lateral advection of horizontal gradients in the vertical salinity gradient and 3 tidal asymmetries in the strength of vertical mixing as a result cross sectionally averaged values of the vertical salinity gradient are shown to increase during the flood tide and decrease during the ebb only over a limited portion of the cross section does the observed stratification increase during the ebb and decrease during the flood these observations highlight the three dimensional nature of estuarine flows and demonstrate that lateral circulation provides an alternate mechanism that allows for the exchange of materials between surface and bottom waters even when direct turbu

modeling and understanding turbulent mixing in a macrotidal salt wedge estuary 1 a high resolution three dimensional numerical simulation is performed with the parallel unstructured grid suntans model to study the spatiotemporal dynamics of turbulent mixing in a shallow macrotidal salt wedge estuary that experiences periodic mixing and strong stratification unresolved vertical mixing is parameterized with the k kl closure scheme with the canuto a stability functions based on a careful comparison of multiple two equation closure schemes and stability functions via the generic length scale approach the predictions of velocity salinity richardson number and reynolds stress are in good agreement with field observations and the top and bottom salinity predictions achieve skill scores of 0 86 and 0 91 respectively the model shows that the salt wedge starts to strengthen upstream at the beginning of weak ebb and gradually expands downstream during the weak tide mixing is most active along a density interface during the weak ebb while it is most active in a bottom mixed layer during weak flood consistent with the findings inferred from the observations stratification decays during the strong ebb in a mixing event along the horizontal extent of the salt wedge while it is also being advected offshore local mixing is shown to account for roughly half of the decay rate of the stratification in this process numerical experiments are performed to investigate the response of stratification and mixing to changes in the magnitude of the buoyancy high sensitivity is shown under intermediate levels of stratification that occur in the real system which becomes considerably weaker under more extreme conditions

evaluating re os systematics in organic rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments abstract successful application of the 187re 187os geochronometer has enabled the determination of accurate and precise depositional ages for organic rich sedimentary rocks ors as well as establishing timing constraints of petroleum generation however we do not fully understand the systematics and transfer behaviour of re and os between ors and petroleum products e g bitumen and oil to more fully understand the behaviour of re os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks the permian phosphoria formation toc 17 4 type ii s kerogen and the jurassic staffin formation toc 2 5 type iii kerogen the laboratory based hydrous pyrolysis experiments were carried out for 72 h at 250 300 325 and 350 c these experiments provided us with whole rock extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of re os isotopic and elemental abundance the data from these experiments demonstrate that the majority 95 of re and os are housed within extracted rock and that thermal maturation does not result in significant transfer of re or os from the extracted rock into organic phases based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of re and os than sulphides across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187re 188os ratios show small variations 3 3 and 4 7 for staffin respectively and 6 3 and 4 9 for phosphoria respectively similarly the 187os 188os ratios show only minor variations for the staffin and phosphoria whole rock and extracted rock samples 0 6 and 1 4 and 1 3 and 2 2 these isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the re os systematics in ors as supported by various studies on natural systems the elemental abundance data reveal limited transfer of re and os into the bitumen from a type iii kerogen in comparison to type ii s kerogen 0 02 vs 3 7 suggesting that these metals are very tightly bound in type iii kerogen structure the 187os 188os data from the pyrolysis generated phosphoria bitumens display minor variation 4 across the experimental temperatures with values similar to that of the source rock this indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation these data further support the premise that the os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of re or os 120 and 3 ppt respectively in contrast to natural oils 2 50 ppb and 34 288 ppt for re and os respectively which may suggest that kinetic parameters are fundamental to the transfer of re and os from source rocks to oils from this we hypothesise that at the temperatures employed in hydrous pyrolysis re and os are assimilated into the extracted rock as a result of cross linking reactions

hydraulics and mixing in the hudson river estuary a numerical model study of tidal variations during neap tide conditions three dimensional numerical modeling is performed to study intratidal and along channel variability in stratification and mixing in the hudson river estuary the modeled fields show good agreement

an integrated mineral system model for the gold deposits of the giant jiaodong province eastern china abstract the giant jiaodong gold province with more than 5000 t of proven gold resources is unique in that its mesozoic gold deposits are hosted in a precambrian basement block there has long been debate on the source of gold the mechanism for its extreme enrichment and a holistic genetic model for these spectacular deposits in order to improve understanding of these factors a mineral system model is proposed for the jiaodong gold deposits for the first time it is based on a detailed review of the architecture and composition of the underlying mantle lithosphere the geodynamic setting at the time of gold mineralization the geological and geochemical features of the deposits themselves and mechanisms of their preservation regional geodynamic reconstructions combined with the nature of mesozoic magmatic systems show that late mesozoic breakoff of the subduction slab and rollback of the paleo pacific plate caused asthenosphere upwelling and lithosphere extension and thinning robust geochronological studies demonstrate that the jiaodong gold deposits formed at ca 120 ma during a change of subduction direction of the paleo pacific plate and the synchronous transition of tectonic regime from regional compression to transpression or transtension prior to peak extension caused by thinning of the lithosphere geophysical exploration data and hf nd isotope mapping of the jiaodong peninsula reveal a relatively simple ancient crustal structure cut by near vertical shear or fault zones including the lithosphere scale tan lu and wulian yantai faults that provided the first order architecture for emplacement of mantle magmas and sub crustal fluids in terms of fertility the significant older pre mineralization crustal metamorphism combined with sulfur lead and strontium isotope ratios indicate a dominant sub crustal source for the ore components for the jiaodong gold deposits consistent with evidence for volatile and gold fertilized metasomatized mantle lithosphere beneath the north china block helium ar and c o isotope ratios implicate mantle sources of ore fluids with contamination by crustal components en route to crustal depositional sites in terms of crustal architecture combined geophysical structural mineralogical fluid inclusion and geochemical studies show that the deeply sourced ore fluids and metals advected upwards through lithosphere scale faults to deposit gold via sulfidation and phase separation in crustal scale nne ne trending fault systems at mid to upper crustal levels preservation of disseminated to stockwork style deposits and auriferous quartz pyrite vein deposits was enhanced by deep crustal formation combined with limited uplift and exhumation of the province the jiaodong gold deposits although commonly hosted in granite intrusions clearly post date them on the basis of robust and reliable geochronology the spatial but non temporal relationships of gold deposits with granites their strong structural control and their other characteristics clearly place them in the orogenic gold group it is suggested because of their uniqueness that they be termed jiaodong type orogenic gold deposits

kinematic role of transverse structures in continental extension an example from the las vegas valley shear zone nevada analysis of the slip budget of the las vegas valley shear zone southern nevada leads to a model that explains many of the kinematic complexities that characterize transverse structures in continental extensional settings including 1 abrupt terminations of these structures along strike 2 large lateral translations across relatively short faults 3 apparent lack of strike slip offset or contradictory evidence of shear sense along some transverse structures 4 significant variation in slip magnitude along strike and 5 juxtaposition of differentially extended terranes on opposite sides of faults many major transverse structures may function largely as transfer faults that either link or form passive boundaries between differentially extended terranes

internal hydraulics and mixing in a highly stratified estuary shipboard acoustic doppler current profiler and conductivity temperature depth data obtained during highly stratified conditions in the hudson river estuary along a section of variable width and breadth are presented the observations emphasize tidal period asymmetries in the vertical structure of current and salinity however these asymmetries exhibit significant along channel structure which is determined by channel morphology during the ebb the flow is linearly sheared and steep halocline slopes in the vicinity of channel contractions are maintained by momentum advection a minimum in vertical shear across the pycnocline occurs in channel contractions during food the pycnocline sharpens and flattens with a middepth velocity maximum embedded in the pycnocline which separates a stratified surface layer from a bottom mixed layer the along channel structure in vertical shear is consistent with a lateral vorticity equation estimates of richardson numbers suggest that vertical mixing across the pycnocline is enhanced downstream of channel contractions

thermochronometrically constrained anatomy and evolution of a miocene extensional accommodation zone and tilt domain boundary the southern wassuk range nevada 1 apatite ahe and zircon zhe u th he thermochronometric data from the southern wassuk range wr coupled with 40ar 39ar age data from the overlying tilted tertiary section are used to constrain the thermal evolution of an extensional accommodation zone and tilt domain boundary ahe and zhe data record two episodes of rapid cooling related to the tectonic exhumation of the wr fault block beginning at 15 and 4 ma extension was accommodated through fault block rotation and variably tilted the southern wr to the west from 60 70 in the central wr to 15 35 in the southernmost wr and pine grove hills and minimal tilting in the anchorite hills and along the mina deflection to the south middle miocene geothermal gradient estimates record heating immediately prior to large magnitude extension that was likely coeval with the extrusion of the lincoln flat andesite at 14 8 ma geothermal gradients increase from 19 4 c km to 65 20 c km toward the mina deflection suggesting that it was the focus of middle miocene arc magmatism in the upper crust the decreasing thickness of tilt blocks toward the south resulted from a shallowing brittle ductile transition zone postmagmatic middle miocene extension and fault block advection were focused in the northern and central wr and coincidentally moderated the large lateral thermal gradient within the uppermost crust

rhenium osmium geochronology and oil source correlation of the duvernay petroleum system western canada sedimentary basin implications for the application of the rhenium osmium geochronometer to petroleum systems the re os geochronometer has been applied to many petroleum systems worldwide however it is debated if the re os systematics in petroleum actually record the timing of oil generation here we investigate the re os isotope systematics of the duvernay petroleum system in the western canada sedimentary basin which has been shown to be a relatively simple petroleum system that is associated with oil generated during the late cretaceous early eocene laramide orogeny from a single source the organic geochemistry of the duvernay oils pristane phytane ratios of 1 5 smooth homohopane profile c29 c27 c28 regular sterane distribution and predominance of diasteranes over regular steranes strongly suggests the oil source to be that of type i ii marine organic matter of the upper devonian duvernay formation the asphaltene fraction re os isotope data of the duvernay oil yield an age of 66 31 ma which is in excellent agreement with the timing of the main stage hydrocarbon generation of the duvernay formation based on basin models further the similarity between the 187os 188os compositions of the duvernay formation source rock 0 46 1 48 and the oil 0 55 1 06 at the time of oil generation supports the hypothesis that the 187os 188os composition of an oil is inherited from the source unit at the time of oil generation and therefore shows no or limited influence from interaction with basin fluids this study supports that the re os isotope systematics of an oil can yield the timing of oil generation and be used to trace its source

precise re os ages of organic rich mudrocks and the os isotope composition of jurassic seawater rhenium and osmium isotope and abundance data have been obtained on precisely located samples from three suites of immature organic rich mudrocks from jurassic coastal outcrops in england the data provide accurate whole rock ages of 207 12 ma 181 13 ma and 155 4 3 ma for suites of hettangian toarcian exaratum subzone and kimmeridgian sensu anglico wheatleyensis subzone samples these new re os ages are indistinguishable within the assigned analytical uncertainties from interpolated depositional ages estimated from published geological timescales and establish the importance of the re os dating technique for chronostratigraphic studies early diagenetic pyrite nodules possess levels of re and os which are 1 2 orders of magnitude lower than in the enclosing organic rich mudrocks indicating that these elements had already been removed from sediment pore waters at the time of nodule formation thus the re os isotope system in these organic rich mudrocks has been closed since or from very soon after the time of sediment deposition because most of the re 98 and os 95 99 8 in the mudrocks is shown to be hydrogenous the 187os 188os i of the samples is interpreted to be that of contemporaneous seawater the data thereby provide the first estimates of the os isotope composition of jurassic seawater during the earliest jurassic hettangian the seawater 187os 188os ratio was extremely unradiogenic 0 15 it had increased to 0 8 at the end of the early jurassic toarcian 20 ma later while in the late jurassic kimmeridgian the seawater 187os 188os ratio was 0 59 the most likely explanation for the unradiogenic os isotope composition of hettangian seawater is that the contribution of unradiogenic os to the oceans from the hydrothermal alteration of oceanic crust greatly exceeded the input of radiogenic os from the continents at that time this interpretation is in line with observations suggesting that global weathering rates were low in the hettangian and that increased hydrothermal and volcanic activity preceded the break up of pangea the re os ratios of hettangian mudrocks and by inference of contemporaneous seawater are similar to those of mudrocks deposited at later times during the jurassic and argues against the unradiogenic os in hettangian seawater being derived from extraterrestrial meteoritic sources

tidal asymmetry in an estuarine pycnocline 2 transport flood currents in shallow estuaries are driven by an along channel barotropic and baroclinic pressure gradient that increases monotonically toward the bottom while friction retards near bottom currents therefore in many estuaries there is a middepth maximum in flood currents we explore this phenomenon using a simple three layer model in which each layer has vertically uniform currents and constant density in this model the middle layer is of intermediate density and grows by shear induced entrainment from the other two layers this very simple model produces a middepth maximum in flood currents and simulates observed currents in the columbia river entrance channel within about 10 there is good qualitative agreement between model salinity transport and observed transport the model pycnocline rises and falls tidally in phase with the observed pycnocline although pycnocline depth and thickness are better simulated using results from a two layer model cudaback and jay 2000

modeling the lateral circulation in straight stratified estuaries the dynamics of lateral circulation in an idealized straight estuary under varying stratification conditions is investigated using a three dimensional hydrostatic primitive equation model in order to determine the importance of lateral circulation to the momentum budget within the estuary for all model runs lateral circulation is about 4 times as strong during flood tides as during ebbs this flood ebb asymmetry is due to a feedback between the lateral circulation and the along channel tidal currents as well as to time varying stratification over a tidal cycle as the stratification is increased the lateral circulation is significantly reduced because of the adverse pressure gradient set up by isopycnals being tilted by the lateral flow itself when rotation is included a timedependent cross channel ekman circulation is driven and the tidally averaged bottom lateral circulation is enhanced toward the right bank when looking toward the ocean in the northern hemisphere this asymmetry in the tidally averaged bottom lateral circulation may lead to asymmetric sediment transport leading to asymmetric channel profiles in straight estuaries for the weakly stratified model run advection due to lateral currents is a dominant term in both the along channel and cross channel momentum equations over a tidal cycle and for the tidally averaged momentum equations in the tidally averaged along channel momentum equation lateral advection acts as a driving term for the estuarine exchange flow and can be larger than the along channel pressure gradient therefore it should not be ignored when estimating momentum budgets in estuaries

role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries

graphic derivation of the local sense of shear strain components in stretched walls of lithotectonic boundaries abstract lithotectonic boundaries ltbs are deformed interfaces between rock masses such as sheared strata midcrustal thrust slices or sutured microcontinents structural analysis of strained ltb walls have focussed attention on rock cuts through the foliation normal and mineral lineation direction but this practice is commonly inappropriate for investigating the tangential shear strain a simple graphic technique is introduced whereby one may derive the sense of large shear strain components in two sections across an ltb wall segment one section parallel to the lineation direction the other normal to the foliation the orientation of the strain ellipse is used on each section to deduce the sense of its shear strain component by visual inspection the technique is applicable to metamorphic rocks with l s mineral fabrics but without reliable gauges of large incremental or total longitudinal strain if the factor of prolateness oblateness of the strain ellipsoid is unknown then the direction cannot be fixed within an angle of journal of structural geology 20 969 973 however the direction may be accurately determined if an ltb cross section fortuitously contains the normal to foliation as well as the mineral lineation direction similarly the direction can be determined if the local strain ellipsoid corresponds to an oblate or prolate spheroid where the ellipsoid is nearly spheroidal one can therefore discern which of the two shear strain components under consideration has the larger magnitude this proves advantageous in assessing the sense of alleghanian tangential shear below the brevard fault zone grandfather mountain area southern appalachians here has the sense of a ductile thrust 1 km into the stretched footwall close to the fault zone however has a large sinistral component unless the ltb dip is 40

longitudinal versus lateral estuarine dynamics and their role in tidal stratification patterns in lower south san francisco bay author s hoang olivia abstract the dynamics of shoal channel estuaries require consideration of lateral gradients and transport which can create significant intratidal variability in stratification and circulation when the shoal channel system is strongly coupled by tidal exchange with mudflats marshes or other habitats the gradients driving intratidal stratification variations are expected to intensify to examine this dynamic hydrodynamic data was collected from january 27 2017 february 10 2017 in lower south san francisco bay a small subembayment fringed by extensive shallow vegetated habitats during this deployment salinity variations were captured through instrumentation of 6 stations arrayed longitudinally and laterally allowing for mechanisms of stratification creation and destruction to be calculated directly and compared with observed time variability of stratification at the central station we present observation based calculations of longitudinal straining longitudinal advection lateral straining and lateral advection the time dependence of stratification was observed directly and calculated by summing measured longitudinal and lateral mechanisms we found that the stratification dynamics switch between being longitudinally dominated during the middle of ebb and flood tides to being laterally dominated during the tidal transitions this variability is driven by the interplay between tidally variable lateral density gradients and turbulent mixing relatively constant along estuary density gradients are differentially advected during flood and ebb tides resulting in maximal lateral density gradients around tidal transitions simultaneous decrease in turbulent mixing at slack tides allows lateral density driven exchange to stratify the estuary channel at the slack after flood at the end of ebb barotropic forcing drives negatively buoyant shoal waters towards the channel plain language summary san francisco bay sits within a highly urbanized area the dense population creates large wastewater effluent resulting in high nutrient levels scientists wonder why there have not been annual phytoplankton blooms like observed in other estuaries with lower nutrient levels some have hypothesized it is due to high turbidity levels and tidal breakdown of stratification creating nonideal environments for phytoplankton growth however decadal trends show that the estuary is becoming less turbid and with changes in climate patterns there is potential for persistent stratification we observed development of stratification over the ebb tide and destratification in two distinct events as the tide reverses over the flood tide at the reversal of the tides water in the shoals exchange with the water in the channel creating a pulse of salty water to the channel at the ebb to flood transition and a pulse of fresh water at the flood to the ebb transition destratification occurs in the early flood tide due to a pulse of saline water received from the shoals then due to the advection of less stratified water being pulled to the center channel of the estuary finally stratification is destroyed completely due to longitudinal straining and turbulent mixing