sulfur geochemical constraints on mesoproterozoic restricted marine deposition lower belt supergroup northwestern united states abstract despite nearly a century of study by a diverse group of precambrian workers competing interpretations have persisted that favor both marine and nonmarine depositional settings for the mesoproterozoic belt supergroup of the northwestern united states our data for sedimentary pyrite formation in unmetamorphosed organic rich shales of the newland formation of the lower belt supergroup western montana argue that at least a portion of the belt basin during its early history was characterized by restricted marine conditions with only episodic incursions of seawater this model is supported by ratios of organic carbon corg to pyrite sulfur that once corrected for selective diagenetic and thermal loss of corg and the inferred high reactivity of the corg reservoir in the absence of vascular land plant remains suggest degrees of sulfate limitation consistent with a restricted marine setting the isotopically heavy disseminated pyrite that dominates the black shales shows a broad range of 34s values of bacterial origin 34s ranges from 8 7 to 36 3 mean 7 6 n 41 the pyrite data overlap with the 34s range of coeval barite sulfate within the basin and are similar to independent estimates for the sulfate of mesoproterozoic seawater these relationships have allowed us to delineate a record of bacteriogenic pyrite that formed in a modified marine reservoir where the supply of sulfate was limited a bacterial mechanism is further suggested by the morphological character of this early formed pyrite including the ubiquitous framboids after comparing our results with those from present day localities such as the black sea and sites of lacustrine deposition we conclude that the abundant 34s enriched bacteriogenic disseminated pyrite observed in black shales of the newland formation must record a style of sulfate limitation possible only within an isolated marine basin receiving an intermittent flux of seawater although the entire belt basin likely remained a restricted marine setting throughout deposition of the lower belt supergroup sulfur isotope data from the newland formation at two localities separated by more than 150 km in the eastern belt basin reveal stratigraphic trends in the strength of the marine connection specifically the connection evolved such that inputs of seawater sulfate increased progressively in frequency and possibly strength during deposition of the newland formation overall the hypothesized restricted marine setting when viewed in light of independent tectonic sedimentologic and geochronologic evidence suggests syndepositional and likely episodic continental rifting which helps constrain the proterozoic paleotectonic history of western laurentia

m2 baroclinic tide variability modulated by the ocean circulation south of japan we analyze a concurrent simulation result of the ocean circulation and tidal currents using a data assimilative ocean general circulation model covering the western north pacific with horizontal resolution of 1 36 to investigate possible interactions between them four sites of active m2 internal tide variability in open ocean hot spots such as tokara strait izu ridge luzon strait and ogasawara ridge are detected from both the satellite observation and the simulation energy cycle analysis of the simulated m2 baroclinic tide indicates two types of the hot spots dissipation tokara strait and izu ridge and radiation luzon strait and ogasawara ridge dominant sites energy conversion from barotropic to baroclinic m2 tides at the hot spots is modulated considerably by the lower frequency changes in the density field modulation at the two spots tokara strait and izu ridge is affected by the kuroshio path variation together with the seasonal variation of the shallow thermocline at the other two sites influence from changes in the relatively deep stratification through the kuroshio intrusion into south china sea luzon strat and mesoscale eddy activity ogasawara ridge is dominant in the modulation

dolostones from grand cayman british west indies abstract pervasively dolomitized tertiary strata on grand cayman are dominated by heterogeneous dolostones that are composed of both low ca calcium dolomite lcd 55 mol caco3 homogeneous dolostones formed of either lcd or hcd are rare some dolostones contain dolomite crystals that are characterized by oscillatory zones 1 10 m thick of lcd and hcd whereas others have rims of lcd surrounding cores of hcd in some dolostones bioclasts formed of lcd are embedded in a matrix of hcd an 1 18o difference between the lcd and hcd can be attributed to the natural covariance that exists between the 18o and mol caco3 in dolomite there are no significant differences in the 87sr 86sr ratios of the lcd and hcd there is no consistent vertical or lateral pattern to the distribution of lcd and hcd in the cayman dolostones even in closely spaced sampling sites such variability is more consistent with growth of individual dolomite crystals being controlled by processes that operated around the surfaces of individual crystals rather than by large scale changes in the dolomitizing fluids this interpretation is consistent with the development of oscillatory zoning which is attributed to precipitation of different phases or minerals from the same parent fluid because of competition between interface controlled and diffusion controlled growth kinetics dolomitization of the tertiary strata on grand cayman was probably mediated by seawater or modified seawater nevertheless small scale intrinsic factors controlled the incorporation of ca in the dolomite lattice and accordingly the geochemical parameters that are intimately linked to the mol caco3 these small scale intrinsic controls must be factored into any model to explain the formation of tertiary island dolostones

coastal trapped behavior of the diurnal internal tide at o ahu hawai i the influence of rotation on the structure and propagation of internal tides around o ahu hawai i is investigated using in situ observations and a tidally forced primitive equation model with realistic bathymetry and stratification particular attention is given to the diurnal internal tide which largely has been de emphasized in previous studies of the region because of the dominance of the semidiurnal internal tide but has been determined by recent studies to be a significant contributor to baroclinic variability though both diurnal and semidiurnal internal tides are generated primarily over ka ena ridge to the northwest of the island the diurnal internal tide propagates clockwise around the island as an imperfectly trapped wave while the semidiurnal internal tide propagates away from the ridge unaffected by rotation the diurnal and semidiurnal internal tides fall into the superinertial frequency range however the diurnal frequency apparently is sufficiently close to inertial 1 4f for rotation to affect internal tide propagation the in situ observations support the model finding that diurnal trapping provides the primary source of baroclinic variability along the eastern coast of the island a stretch of coastline otherwise sheltered from the internal tide energy generated over the hawaiian ridge the findings in hawai i suggest that coastal trapping of superinertial internal tides may be a significant source of variability and mixing in other nearshore systems around the world

an indicator of water column anoxia resolution of biofacies variations in the kimmeridge clay upper jurassic u k abstract an indicator of anoxicity ia defined as the ratio pyrite fe oxide fe total fe can be used to recognize sediments deposited under an anoxic water column modern marine sediments deposited under oxygenated bottom waters mainly have ia values 0 5 ia values in the central kimmeridge clay upper jurassic uk for fissile organic rich shales indicate that deposition occurred principally from anoxic bottom waters with infrequent oxygenation events

recognition and delineation of paleokarst zones by the use of wireline logs in the bitumen saturated upper devonian grosmont formation of northeastern alberta canada the upper devonian grosmont formation in northeastern alberta canada is a shallow marine carbonate platform complex that was subaerially exposed for hundreds of millions of years between the mississippian and cretaceous during this lengthy exposure period an extensive karst system developed that is characterized by an irregular erosional surface meter size several feet dissolution cavities collapse breccias sinkholes paleosols and fractures the karsted grosmont formation which contains giant reserves of bitumen subcrops beneath cretaceous clastic sediments of the giant athabasca tar sands deposit the paleokarst in the grosmont formation can be recognized on wireline logs in relatively nonargillaceous carbonate intervals 30 api units on the gamma ray log as excursions of the caliper log off scale neutron density porosity readings and severe cycle skipping of the acoustic log the paleokarst is more prevalent in the upper units of the grosmont formation and the effects of karstification decrease toward stratigraphically older and deeper units the paleokarst usually occurs within 35 m 115 ft of the erosional surface the reservoir properties of the grosmont formation e g thickness porosity permeability and seal effectiveness are significantly influenced by karstification depending upon the location karstification has either benefited or degraded the reservoir characteristics benefits include porosity values greater than 40 up to 100 in caverns and permeability values of 30 000 md in severely fractured intervals detrimental reservoir characteristics include erosion porosity and permeability reduction and seal ineffectiveness

dolomite crystal architecture genetic implications for the origin of the tertiary dolostones of the cayman islands abstract dolostones in the cayman formation on grand cayman and cayman brac which are the product of two and possibly three phases of dolomitization are formed of very small the recognition that individual dolomite crystals irrespective of their size may be architecturally heterogeneous carries important implications for dolomite genesis many interpretations of finely crystalline dolostones for example have tacitly assumed that they formed through one phase of dolomitization in the cayman formation however dolomite crystals as small as 10 m are characterized by internal heterogeneities that record their development through multiple time separated growth phases any model developed to explain dolomitization must take this into account the interpretation of chemical data for example must consider the multiple stage development of the dolostones that is evident from their internal zoning and discontinuities

energetics of m2 barotropic to baroclinic tidal conversion at the hawaiian islands abstract a high resolution primitive equation model simulation is used to form an energy budget for the principal semidiurnal tide m2 over a region of the hawaiian ridge from niihau to maui this region includes the kaena ridge one of the three main internal tide generation sites along the hawaiian ridge and the main study site of the hawaii ocean mixing experiment the 0 01 horizontal resolution simulation has a high level of skill when compared to satellite and in situ sea level observations moored adcp currents and notably reasonable agreement with microstructure data barotropic and baroclinic energy equations are derived from the model s sigma coordinate governing equations and are evaluated from the model simulation to form an energy budget the m2 barotropic tide loses 2 7 gw of energy over the study region of this 163 mw 6 is dissipated by bottom friction and 2 3 gw 85 is converted into internal tides internal tide generation primarily occurs along the flanks of the kaena ridge and

internal tide energy over topography 1 the method used to separate surface and internal tides ultimately defines properties such as internal tide generation and the depth structure of internal tide energy flux here we provide a detailed analysis of several surface internal tide decompositions over arbitrary topography in all decompositions surface tide velocity is expressed as the depth average of total velocity analysis indicates that surface tide pressure is best expressed as the depth average of total pressure plus a new depth dependent profile of pressure which is due to isopycnal heaving by movement of the free surface internal tide velocity and pressure are defined as total variables minus the surface tide components corresponding surface and internal tide energy equations are derived that contain energy conversion solely through topographic internal tide generation the depth structure of internal tide energy flux produced by the new decomposition is unambiguous and differs from that of past decompositions numerical simulations over steep topography reveal that the decomposition is self consistent and physically relevant analysis of observations over kaena ridge hawaii and the oregon continental slope indicate o 50 w m 1 error in depth integrated energy fluxes when internal tide pressure is computed as the residual of pressure from its depth average while these errors are small at major internal tide generation sites they may be significant where surface tides are larger and depth integrated fluxes are weaker e g over continental shelves

reply sulphur isotope composition of the brunswick no 12 massive sulphide deposit bathurst mining camp new brunswick implications for ambient environment sulphur source and ore genesis the brunswick no 12 massive sulphide deposit occurs within a middle ordovician bimodal volcanic and sedimentary sequence that is thought to have formed in a continental back arc rift covered with a thick succession of carbonaceous hemipelagic and turbiditic sedimentary rocks the deposit consists of three en echelon lenses that are zoned from vent complex to bedded ore and bedded pyrite facies the bedded ore facies has the lowest average 34s values 14 2 but are only slightly less positive than laminated pyrite in footwall sedimentary rocks 34smean 15 1 34s values for the bedded sulphides show an upward increase from 14 2 in bedded ore to 16 5 in bedded pyrite average 34s values for vent complex 15 8 and underlying stringer sulphides 16 1 are consistently more positive than those for bedded ore in carbonaceous shales and siltstone of the patrick brook formation that underlie the deposit 34s values that range between 13 8 and 25 6 and the similarity of these values to those of the bru

large sulphur isotopic perturbations and oceanic changes during the frasnian famennian transition of the late devonian the frasnian famennian transition of the late devonian was one of the most critical intervals in the phanerozoic sulphur isotopic pairs of carbonate associated sulphate and pyrite sulphide from coeval sections in south china and poland reveal frequent perturbations of sulphur cycling during this time interval these data suggest a sudden oceanic overturn during a rapid sea level fall probably induced by jerky block tilting in the latest frasnian this event was followed by long lasting photic zone euxinia during a rapid sea level rise in the earliest famennian large increases in continental nutrient fluxes and subsequent primary productivity and organic burial could have greatly enhanced bacterial sulphate reduction producing excessive sulphide through the water columns owing to iron depletion subsequently rapid ventilation of oceanic basins occurred dur ing which direct aerobic oxidation of sulphide into sulphate predominated in bottom waters and even surface sediments with minimal fractionation this oxygenation was probably induced by intensive climatic cooling and or large scale sea level fall the temporal coincidence of two extinction phases with the oceanic overturn and succeeding photic zone euxinia suggests that these extreme oceanic events played an important role in the severe biotic crisis furthermore photic zone euxinia coupled with subsequent climatic cooling may have delayed post extinction recovery of some taxa

pseudospherulitic fibrous calcite in paleo groundwater unconformity related diagenetic carbonates paleocene of the ager basin and miocene of the madrid basin spain abstract massive decimeter thick intervals formed by mosaics of subspherical calcite crystals displaying an intracrystalline fibrous microfabric have been found in paleocene and miocene strata in spain the fibrous microfabric is marked by inclusion defined fibers that radiate from the central parts of the crystals which can be termed pseudospherulites and not spherulites because they are single crystals and not polycrystalline aggregates the horizons of pseudospherulitic calcite appear in meter scale laterally persistent levels of crystalline limestones that exhibit complex pseudospar fabrics they are interbedded with peritidal and or lacustrine deposits they grade downward into bedded dolomicrites and they can be linked to unconformities several meters higher in the section above intervening unaltered limestones the pseudospar zones are interpreted as early diagenetic paleo groundwater alteration products after dolomicrites the pseudospherulites are composed of low mg calcite with low contents of fe and mn and they have a stable isotope composition indicative of precipitation from meteoric water they form xenotopic mosaics in which goethite palygorskite and sepiolite may be present as inclusions and in the intercrystalline matrix cathodoluminescence microscopy reveals peripheral growth of the pseudospherulites which results from several phases of precipitation and even of dissolution the first phase of crystal growth may show rhombic habits and may contain corroded dolomite inclusions interpreted as an indication of growth at the expense of dolomicrite by a dissolution precipitation process the second phase of crystal growth is fibrous sensu stricto exhibits lobate growth laminae and shows indications of displacive growth the pseudospherulitic fabric is not relict and the pseudospherulites do not represent speleothems recrystallized microcodium or neomorphosed spherulitic carbonate instead they are interpreted as split crystals that grew within dolomicritic host sediments in part by dissolution precipitation and in part by displacement the hypothesis of a dolomicritic host is supported by the geological and diagenetic setting by the presence of corroded dolomite inclusions within the pseudospherulites and by the relationship between their growth and the authigenesis of sepiolite palygorskite and goethite the pseudospherulites grew in the shallow subsurface at or near the water table from predominantly oxidizing meteoric water and under periodically fluctuating geochemical conditions saturation redox caused by fluctuations of the water table during periods of subaerial exposure the presence of fossil bacteria within the pseudospherulites the anastomosing pattern of the inclusion defined fibers and the lobate growth forms of the fibrous calcite suggest some bacterial influence in the genesis of the pseudospherulitic fabric

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

coupling global and regional circulation models in the coastal gulf of alaska abstract as part of the us globec ne pacific program we are simulating currents in the coastal gulf of alaska cgoa to explore sources of interannual and interdecadal variability to do so we have developed a coupled modeling system composed of linked regional and global circulation models the regional model configured with 13 22 km resolution in the cgoa is forced at the surface by observed heat fluxes and wind stresses at the continental boundaries by observed runoff and at the open ocean boundaries by a combination of tracer climatologies and sub tidal velocity and tidal elevation provided by a global finite element model in this communication we describe the coupled system including its present method of intermodel coupling describe a series of multi year model hindcasts compare hindcast results with eulerian and lagrangian field data obtained in the cgoa in fall 1996 and assess the impact of global information barotropic sub tidal velocities and tidal elevations on the regional model under the present coupling strategy we find that the regional model produces appropriate current systems alaskan stream alaska coastal current and scalar fields but with mesoscale variability of ssh and velocities at somewhat reduced strength relative to data and with temperature gradients somewhat larger than those observed barotropic sub tidal information from the global model penetrates the regional model interior supplying additional mesoscale variability and modifying regional velocity and scalar fields in both shallow and deep areas tidal information exerts a significant influence on sub tidal scalar and velocity structure only in specific shallow areas where the tides and tidal mixing are strongest pending the exploration of alternate coupling schemes we infer from these results that on a time scale of months purely barotropic information from outside the cgoa will have a modest impact on its mean regional circulation but a potentially stronger impact on the statistics and details of mesoscale eddies

tidal conversion at a submarine ridge the radiative flux of internal wave energy the tidal conversion powered by the oscillating flow of a uniformly stratified fluid over a two dimensional submarine ridge is computed using an integral equation method the problem is characterized by two nondimensional parameters a and b the first parameter a is the ridge half width scaled by h where h is the uniform depth of the ocean far from the ridge and is the inverse slope of internal tidal rays horizontal run over vertical rise the second parameter b i s the ridge height scaled by h two topographic profiles are considered a triangular or tent shaped ridge and a polynomial ridge with continuous topographic slope for both profiles complete coverage of the a b parameter space is obtained by reducing the problem to an integral equation which is then discretized and solved numerically it is shown that in the supercritical regime ray slopes steeper than topographic slopes the radiated power increases monotonically with b and decreases monotonically with a in the subcritical regime the radiated power has a complicated and nonmonotonic dependence on these parameters as a 0 recent results are recovered for the tidal conversion produced by a knife edge barrier it is shown analytically that the a 0 limit is regular if a 1 the reduction in tidal conversion below that at a 0 is proportional to a 2 further the knife edge model is shown to be indicative of both conversion rates and the structure of the radiated wave field over a broad region of the supercritical parameter space as a increases the topographic slopes become gentler and at a certain value of a the ridge becomes critical that is there is a single point on the flanks at which the topographic slope is equal to the slope of an internal tidal beam the conversion decreases continuously as a increases through this transition visualization of the disturbed buoyancy field shows prominent singular lines tidal beams in the case of a triangular ridge these beams originate at the crest of the triangle in the case of a supercritical polynomial ridge the beams originate at the shallowest point on the flank at which the topographic slope equals the ray slope

numerical modeling of internal tide generation along the hawaiian ridge internal m2 tides near hawaii are investigated with a two dimensional two layer numerical model it is seen that along the hawaiian ridge barotropic tidal energy is transformed into baroclinic internal tides that propagate in both northeast and southwest directions as previously hypothesized the internal tide for a certain beam is seen to propagate well over 1000 km with an approximate decay scale of 1000 km an asymmetric pattern in the baroclinic energy flux is observed to the north and south of the hawaiian ridge due to the spatially inhomogeneous baroclinic energy sources the surface manifestation of the m2 internal tide in the model is compared with analysis results from topex poseidon satellite altimetry the baroclinic short wave variation of a few centimeters amplitude superposed on the barotropic surface amplitude agrees well with the altimeter analyses this together with snapshots of the interfacial disturbance allows the authors to sketch the propagation pattern of internal waves emanating northward and southward from the hawaiian ridge tidal current ellipses in the upper layer are dominated by the baroclinic internal tide with large spatial variability in their magnitude compared to the barotropic tidal ellipses the m2 baroclinic energy flux is over 10 kw m 21 for the strongest energy beam propagating toward the northeast along the western hawaiian ridge about 3 8 gw of tidal power is converted from barotropic to baroclinic motion the average northward or southward flux density for the first baroclinic mode is about 1 35 kw m21 in the western hawaiian ridge also if 2 7 kw m21 1 35 kw m21 to each direction is assumed for the whole 2000 km long hawaiian ridge a total of 5 4 gw is obtained this value indicates that there is still a large uncertainty in the rate of barotropic to radiating baroclinic energy conversion along the hawaiian ridge

saturation of the internal tides and induced mixing in the abyssal ocean as part of an ongoing effort to develop a parameterization of wave induced abyssal mixing the authors derive an heuristic model for nonlinear wave breaking and energy dissipation associated with internal tides then the saturation and dissipation of internal tides for idealized and observed topography samples are investigated one of the main results is that the wave induced mixing could be more intense and more confined to the bottom than previously assumed in numerical models furthermore in this model wave breaking and mixing clearly depend on the small scales of the topography below 10 km or so which is below the current resolution of global bathymetry this motivates the use of a statistical approach to represent the unresolved topography when addressing the role of internal tides in mixing the deep ocean

instability and focusing of internal tides in the deep ocean received 18 december 2006 and in revised form 7 april 2007 the interaction of tidal currents with sea floor topography results in the radiation of internal gravity waves into the ocean interior these waves are called internal tides and their dissipation due to nonlinear wave breaking and concomitant threedimensional turbulence could play an important role in the mixing of the abyssal ocean and hence in controlling the large scale ocean circulation as part of on going work aimed at providing a theory for the vertical distribution of wave breaking over sea floor topography in this paper we investigate the instability of internal tides in a very simple linear model that helps us to relate the formation of unstable regions to simple features in the sea floor topography for two dimensional tides over one dimensional topography we find that the formation of overturning instabilities is closely linked to the singularities in the topography shape and that it is possible to have stable waves at the sea floor and unstable waves in the ocean interior above for three dimensional tides over two dimensional topography there is in addition an effect of geometric focusing of wave energy into localized regions of high wave amplitude and we investigate this focusing effect in simple examples overall we find that the distribution of unstable wave breaking regions can be highly non uniform even for very simple idealized topography shapes

distinguishing cambrian from upper ordovician source rocks evidence from sulfur isotopes and biomarkers in the tarim basin abstract the reported source rocks for the abundant petroleum in the tarim basin china range from cambrian to lower ordovician and or upper ordovician in age however the difference between the two groups of source rocks is not well characterized in this study pyrite was removed from eleven mature to over mature kerogen samples from source rocks using the method of crcl 2 reduction and grinding the kerogen and coexisting pyrite samples were then analyzed for 34 s values results show that the kerogen samples from the cambrian have 34 s values between 10 4 and 19 4 the values are significantly higher than those from the lower ordovician kerogen 34 s of between 6 7 and 8 7 which in turn are generally higher than from the upper ordovician kerogen samples 34 s of between 15 3 and 6 8 the associated pyrite shows a similar trend but with much lower 34 s values this stratigraphically controlled sulfur isotope variation parallels the evolving contemporary marine sulfate and dated oil 34 s values from other basins suggesting that seawater sulfate and source rock age have an important influence on kerogen and pyrite 34 s values the relatively high 34 s values in the cambrian to lower ordovician source rocks are associated with abundant aryl isoprenoids gammacerane and c 35 homohopanes in the extractable organic matter indicating that these source rocks were deposited in a bottom water euxinic environment with water stratification compared with the upper ordovician the cambrian to lower ordovician source rocks show abundance in c 28 20r sterane c 23 tricyclic terpanes 4 23 24 trimethyl triaromatic dinosteroids and depletion in c 24 tetracyclic terpane c 29 hopane thus 34 s values and biomarkers of source rock organic matter can be used for distinguishing the cambrian and upper ordovician source rocks in the tarim basin

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

upper permian carbonates at the northern edge of the zechstein basin utsira high norwegian north sea abstract the first detailed description of zechstein carbonates and their diagenesis along the northern margin of the northern zechstein basin is based on core material from four wells on utsira high in the norwegian sector of the north sea it provides a generic link to the better known southern zechstein basin and northwards to the late permian east greenland basin the zechstein succession consists of shale carbonate cycles and anhydrite only occurs in the uppermost preserved cycle believed to correlate to zechstein 4 the eleven carbonate facies reflect deposition in shallow shelf and arid shoreline environments and resemble zechstein 2 and 3 carbonate facies from the southern zechstein basin the carbonates are pervasively dolomitized by an early texture preserving dolomite characterized by 18o values between 6 and 2 4 similar to dolomites in the southern zechstein basin and 13c values between 0 7 and 5 which is significantly lower than time equivalent dolomites from the southern zechstein basin later subaerial exposure and fresh water infiltration during the late permian or early triassic caused replacement of the upper part of the dolomite by crystalline fabric destructive calcite dedolomite the dedolomitized zone is up to 23 m thick and calcite crystals are characterized by moderately negative 18o values in the range 8 to 5 5 characteristic for meteoric water the utsira high carbonates thus share a depositional history with the classical zechstein carbonates whereas their diagenesis seems to have more in common with the time equivalent succession in east greenland early leaching and dolomitization enhanced porosity whereas subsequent late permian early triassic subaerial exposure and widespread dedolomitization had profound negative impact on reservoir properties of the zechstein carbonates

a simple parameterization of turbulent tidal mixing near supercritical topography abstract a simple parameterization for tidal dissipation near supercritical topography designed to be applied at deep midocean ridges is presented in this parameterization radiation of internal tides is quantified using a linear knife edge model vertical internal wave modes that have nonrotating phase speeds slower than the tidal advection speed are assumed to dissipate locally primarily because of hydraulic effects near the ridge crest evidence for high modes being dissipated is given in idealized numerical models of tidal flow over a gaussian ridge these idealized models also give guidance for where in the water column the predicted dissipation should be placed the dissipation recipe holds if the coriolis frequency f is varied as long as hn w f where n is the stratification h is the topographic height and w is a width scale this parameterization is not applicable to shallower topography which has significantly more dissipation because near critical processes dominate the observed turbul

the role of tidal forcing in the gulf of alaska s circulation 1 high resolution 7 km numerical simulations of the gulf of alaska circulation show an indirect effect induced by tidal forcing tides stir the water column more vigorously in the coastal ocean than in the gulf s interior leading to denser waters there than offshore this horizontal gradient induces a geostrophic current that in general and in most regions flows against the mean general circulation

implications of sulfur isotope fractionation in fracture filling sulfides in crystalline bedrock olkiluoto finland abstract a detailed investigation of 34 s 32 s ratios in fracture bound pyrite and marcasite was conducted at olkiluoto western finland in order to gain information on paleohydrogeochemical conditions in a deep groundwater 0 400 m b s l environment the bedrock at olkiluoto is being considered for a final repository of spent nuclear fuel the 34 s 32 s ratios were measured in situ on individual sulfide grains using secondary ion mass spectrometry sims supplemented by analyses from bulk sulfide material the 34 s values of pyrite and marcasite show considerable variations from 50 to 82 vcdt using published records and new data from fracture filling minerals the pyrite fillings were classified into groups representing distinct episodes of fracture mineral formation the 34 s values of these groups record a transition from hydrothermal activity to a low temperature groundwater environment the 34 s values of hydrothermal pyrite vary between 18 and 34 however hydrothermal pyrite that definitively precipitated at 128 245 c evidenced by fluid inclusion data from co genetic calcite is characterized by a more limited variation in 34 s from 8 6 to 3 9 the high variability of 34 s within the hydrothermal pyrite precipitates indicates that biogenic fractionation effects cannot be completely excluded hydrothermal pyrite precipitation is likely related to hydrothermal systems produced by mesoproterozoic rapakivi granite and diabase intrusions subsequent pyrite generations show a wider spread of 34 s values pyrite types representing formation temperatures from ca 50 to 90 c have 34 s values ranging from 40 to 82 and the latest low temperature 34 s from 50 to 78 the wide range of 34 s values is attributed to bacterial so 4 2 reduction affected by rayleigh fractionation under restricted so 4 2 input it can be calculated that the highest 34 s values in pyrite represent consumption of ca 90 of the original so 4 2 in the deep groundwater in a fracture section furthermore in situ variations of the 34 s values in pyrite grains indicate that pulses of fresh so 4 2 with relatively non modified s isotopic composition have periodically entered the fractures the latest low temperature pyrite formation event most likely occurred during the holocene period when brackish so 4 2 rich waters of the litorina sea infiltrated the fracture network at 8000 4000 bp providing substrate for so 4 2 reducing bacteria due to the complex quaternary history of the site and low temperature conditions existing for millions of years latest fracture filling calcite and pyrite may represent a compilation of several low temperature precipitation events the records of 13 c in calcite and 34 s in coexisting pyrite indicate that paleogroundwaters have been influenced by the migration of a redox front between methanic and sulfidic environments these findings can be used to consider the possible geochemical changes that may affect the materials used to contain spent nuclear fuel

the geometry and petrogenesis of dolomite hydrocarbon reservoirs the wide distribution of dolomite rocks in north american middle and far eastern hydrocarbon reservoirs is reason enough for their intensive study in this volume dolomite enthusiasts review progress and define the current boundaries of dolomite research related particularly to the importance of these rocks as reservoirs as might be expected reviews provide critical analyses of past ideas on origins and why many are no longer tenable discussions range between conceptual models and numerical simulations of the flow paths of dolomitizing fluids geochemical modelling and microbial mediation case studies from areas as diverse as north america the middle east se asia and australia provide a solid background but illustrate important differences in views on the origins of these enigmatic rocks

tidal conversion by supercritical topography calculations are presented of the rate of energy conversion of the barotropic tide into internal gravity waves above topography on the ocean floor the ocean is treated as infinitely deep and the topography consists of periodic obstructions a green function method is used to construct the scattered wavefield the calculations extend the previous results of balmforth et al for subcritical topography wherein waves propagate along rays whose slopes exceed that of the topography everywhere by allowing the obstacles to be arbitrarily steep or supercritical so waves propagate at shallower angles than the topographic slopes and are scattered both up and down a complicated pattern is found for the dependence of energy conversion on e the ratio of maximum topographic slope to wave slope and the ratio of obstacle amplitude and separation this results from a sequence of constructive and destructive interferences between scattered waves that has implications for computing tidal conversion rates for the global ocean

internal tide generation in nonuniformly stratified deep oceans we present numerical and experimental studies of the conversion of tidal motions of an exponentially stratified fluid over two dimensional knife edge gaussian and complex bottom topography to radiated internal waves in a model of the deep ocean we compare the radiated internal wave power for cases of strong stratification where the buoyancy frequency profile n z proportional to the square root of the density gradient is much larger than the tidal frequency to the power radiated for weak stratifications we consider particularly internal wave generation for topography below a turning depth ztd where n ztd for z ztd although the radiated power in these waves is much weaker than in cases without turning depths the radiated power is predicted well by prior analytical theory if the nonuniform stratification is averaged over depths spanning from the bottom boundary up to an effective height zeff in the absence of a turning depth we find zeff is approximately equal to the height of the topography indicating that only the stratification for depths spanned by the topography is relevant however in the presence of a turning depth the vertical scale of the internal tide becomes larger and zeff increases approximately linearly with the turning depth height toward values comparable to the total fluid depth

sulphur isotope geochemistry of pyrite from the upper cretaceous marshybank formation western interior basin abstract variations in the texture and sulphur isotopic composition of pyrite in the upper cretaceous marshybank formation are linked to depositional environment abundant framboidal and lesser euhedral pyrite precipitated in offshore marine rocks moderate quantities of pyrite also crystallized in brackish coastal plain rocks however in contrast to marine pyrite coastal plain pyrite is dominantly euhedral in texture reflecting direct precipitation from a porewater with a relatively low dissolved sulphide concentration in the marine rocks pyrite 34s values range from 35 7 to 27 4 avg 4 8 canyon diablo troilite cdt pyrite within carbonate concretions hosted in these marine rocks has a similar isotopic composition 49 8 to 10 6 cdt however isotopic values are often highly variable within individual concretions as a result of the heterogeneous nature of sulphate reduction and pyrite formation within marine sediments pyrite in coastal plain rocks is characterized by relatively high 34s values 4 2 to 35 5 avg 13 2 cdt while the overlying sideritized conglomerates have the lowest 34s values reported for cretaceous rocks from the western interior basin of north america 49 8 to 41 7 cdt very low 34s values which are only observed in the marine rocks are indicative of microbial sulphate reduction and pyrite formation in a sulphate replete i e open system higher 34s values up to 18 which were obtained for both the marine and coastal plain rocks are indicative of progressive pyrite crystallization in a sulphate limited i e closed system such conditions are expected in marine sediments as burial occurs and in brackish i e low sulphate sediments pyrite with very high 34s values 18 is common in the coastal plain rocks these high values are the result of influx of 34s enriched residual sulphide derived from overlying marine units a minor amount of 34s enriched pyrite is also present within and proximal to marine sedimentary unit h which was deposited at the same time as the coastal plain rocks we hypothesize that porewater containing 34s enriched residual sulphide flowed from the coastal plain and along unit h into the marine sediments thus producing anomalously high 34s pyrite

petrography of finely crystalline cenozoic dolostones as revealed by backscatter electron imaging case study of the cayman formation miocene grand cayman british west indies abstract finely crystalline cenozoic island dolostones like those found in the cayman formation on grand cayman are commonly assumed to be petrographically and compositionally homogeneous backscatter electron images bsei however show that the constituent dolomite crystals 3 content moreover such images allow 1 depiction of growth patterns in the constituent crystals irrespective of their origin 2 recognition of replacive dolomite as opposed to dolomite cement and 3 delineation of stratigraphic packages in the dolomite cements that reflect different episodes of cementation integration of this information forms the basis for paragenetic interpretations of the dolostones on grand cayman the miocene cayman formation can be divided into friable high porosity dolostones and hard low porosity dolostones backscatter electron images show that the hard dolostones are characterized by complex arrays of zoned dolomite cements that have occluded most of the pores caymanite an internal sediment has occluded many of the larger cavities in contrast the high porosity dolostones contain little cement and no internal sediments precipitation of the cements and the deposition of internal sediments were related to the passage of large volumes of water through some of the dolostones thus the hard low porosity dolostones are found in the cap rock of the formation in coastal locations and in areas close to solution widened fractures conversely the friable high porosity dolostones form the lower porous unit of the formation in the interior of the island where the passage of water was more restricted

model estimates of m2 internal tide generation over mid atlantic ridge topography abstract the conversion of barotropic to baroclinic m2 tidal energy is examined for a section of the mid atlantic ridge in the brazil basin using a primitive equation model model runs are made with different horizontal smoothing 1 5 6 and 15 km applied to a 192 km 183 km section of multibeam bathymetry to characterize the influence of topographic resolution on the model conversion rates in all model simulations barotropic to baroclinic conversion is highest over near and supercritical slopes on the flanks of abyssal hills and discordant zones from these generation sites internal tides propagate upward and downward as tidal beams the most energetic internal tide mode generated is mode 2 consistent with the dominant length scales of the topographic slope spectrum 50 km the topographic smoothing significantly affects the model conversion amplitudes with the domain averaged conversion rate from the 1 5 km run 15 1 mw m 2 4 and 19 higher than for the 6 km 14 5 mw m 2 and 15 km runs 12

model estimates of m2 internal tide energetics at the hawaiian ridge 1 a primitive equation model is used to examine the structure and energetics of m 2 internal tides generated at the hawaiian ridge recent estimates based on altimeter data suggest that 20 gw of barotropic tidal dissipation occurs at the ridge with conversion to internal tides believed to be the dominant dissipation mechanism the model simulates an internal tide that accounts for 9 7 gw of radiated energy away from the ridge in the northeast and southwest directions the strongest generation occurs at three sites where enhanced barotropic currents flow across elongated topographic features the depth integrated baroclinic energy flux and energy densities at these sites are on the order of 10 4 w m 1 and 10 4 j m 2 respectively a modal decomposition indicates that 62 of the outgoing energy flux is accounted for by the first internal mode 15 is accounted for by the second mode and less than 5 is accounted for by each subsequent higher mode the tidal dissipation due to bottom friction along the ridge is estimated to be 0 1 gw the level of turbulent dissipation near the ridge owing to tidal energy conversion remains to be determined to assess fully the barotropic baroclinic energy budget

stratification and mixing of a post glacial neoproterozoic ocean evidence from carbon and sulfur isotopes in a cap dolostone from northwest china abstract to improve our knowledge about the geochemical and environmental aftermath of neoproterozoic global glaciations we analyzed stable isotopes 13 c 18 o 34 s and elemental concentrations ca mg s sr fe and mn of the 10 m thick zhamoketi cap dolostone atop the tereeken diamictite in the quruqtagh area eastern chinese tianshan available chemostratigraphic data suggest that the tereeken diamictite is probably equivalent to the marinoan glaciation our new data indicate that organic and carbonate carbon isotopes of the zhamoketi cap dolostone show little stratigraphic variations averaging 28 2 and 4 6 respectively in contrast sulfur isotopes show significant stratigraphic variations carbonate associated sulfate cas abundance decreases rapidly in the basal cap dolostone and 34 s cas composition varies between 9 and 15 in the lower 2 5 m in the overlying interval cas abundance remains low while 34 s cas rises 5 and varies more widely between 10 and 21 the range of 34 s py of the cap dolostone overlaps with that of 34 s cas but direct comparison shows that 34 s py is typically greater than 34 s cas measured from the same samples hypotheses to explain the observations must account for both the remarkable sulfur isotope enrichment of pyrites and the inverse fractionation we propose that cas and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin or a basin with a sulfate minimum zone in this model cas was derived from shallow oxic surface waters with moderate sulfate concentration and depleted in 34 s due to the post glacial influx of sulfur from continental weathering in contrast pyrite was derived from anoxic bottom waters or a sulfate minimum zone with low sulfate concentration and 34 s enrichment due to long term syn glacial sulfate reduction the rapid shift in cas abundance and sulfur isotope composition within the cap dolostone is interpreted to reflect the mixing of the two reservoirs after initial deglaciation comparison with other post marinoan cap carbonates shows significant spatial heterogeneity in 34 s cas which together with strong temporal variation in 34 s cas points to generally low sulfate concentrations in post marinoan oceans

barotropic and baroclinic m2 tides in the monterey bay region abstract a high resolution 250 m primitive equation model is used to simulate the depth averaged and baroclinic m2 tides in the monterey bay region the model shows a high level of skill in comparisons with sea level observations adcp current observations within the submarine canyon are reasonably well reproduced the modeled depth averaged currents have a complex spatial pattern with magnitudes in excess of 0 1 m s 1 near moss landing during the second half of flood ebb tide the flow is into out of the bay through the canyon but out of into the bay over the shelf regions this depth averaged flow pattern is not evident in a diagnostic run implying a feedback between the internal tides and the pressure gradient in the bay the depth integrated baroclinic total minus depth averaged energy fluxes show a complex beamlike pattern due to the interaction of energy from multiple sources the beams have magnitudes up to 1 kw m 1 interspersed with regions of near zero depth integrated flux energy en

pyrite geochemistry in the toarcian posidonia shale of south west germany evidence for contrasting trace element patterns of diagenetic and syngenetic pyrites authigenic pyrite grains from a section of the lower toarcian posidonia shale were analysed for their trace element contents and sulphur isotope compositions the resulting data are used to evaluate the relationship between depositional conditions and pyrite trace element composition by using factor analysis trace elements in pyrite may be assigned to four groups i heavy metals including cu ni co pb bi and tl ii oxyanionic elements as mo and sb iii elements partitioned in sub microscopic sphalerite inclusions zn and cd and iv elements related to organic or silicate impurities ga and v results indicate that trace element contents in pyrite depend on the site and mechanism of pyrite formation with characteristic features being observed for diagenetic and syngenetic pyrites diagenetic pyrite formed within anoxic sediments generally has a high heavy metals content and the degree of pyritization of these elements increases with increasing oxygen deficiency similar to the degree of pyritization of reactive fe the highest gradient in the increase of the degree of trace element pyritization with bottom water oxygenation was found for the elements ni cu mo as tl in contrast syngenetic pyrite formed within a euxinic water column typically is enriched in as mo and sb but is low in heavy metals and the geochemical variation reflects changes in sea water composition

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

marine carbon and sulfur cycling across the ediacaran cambrian boundary in tarim block and its implications for paleoenvironmental changes abstract the ediacaran cambrian transition was a critical period of earth history because of the coincidence among climate change bioevolution and tectonic activity the nature of carbon and sulfur cycling processes spanning the ediacaran cambrian boundary remains debatable this study considers high resolution stable isotope chemostratigraphy of the sugetbrak and yutixi sections of the keping area of the tarim basin northwestern china the sections display a pronounced negative 13ccarb shift the basal cambrian carbon isotope excursion that spans the ediacaran cambrian boundary deposits overlying the negative excursion are characterized by heavier 13ccarb values ranging from 7 8 to 4 1 the biostratigraphically calibrated 13ccarb profiles likely reflect widespread perturbation of the global oceanic carbon cycle and associated mass extinction and subsequent biological evolution the 34spy profiles of the studied sections display a wide distribution of values ranging from 16 4 to 23 8 the variable 34spy signatures of these sections are partially controlled by microbial sulfate reduction rates which are sensitive to local sulfate concentration availability of organic matter and the marine redox state the strong coupling between enhanced organic carbon and pyrite burial the appearance of cambrian type animals and a shift to a more oxidizing marine environment might suggest a temporal causality of higher oxygen levels of the atmosphere ocean realm with bio events during the ediacaran cambrian transition the development of ecosystems across the ediacaran cambrian transition may have significantly impacted the oceanic carbon and sulfur biogeochemical processes in earth s history and in turn affecting themselves

heavy sedimentary sulfur isotopes as indicators of super anoxic bottom water conditions iron monosulfides and pyrite total cr reducible s trs in the bottom sediments of the exceptionally sulfide rich euxinic fjord framvaren south norway are unusually enriched in 34 s most of these trss probably form in bottom waters where reactive detrital iron phases encounter isotopically heavy dissolved sulfide enrichment in 34 s in framvaren is a result of intense bacterial reduction of a sulfate reservoir whose exchange with the open sea is limited by shallow sills and a low salinity surface water layer 34 s enriched trs in the deposits of ancient euxinic environments is commonly interpreted as evidence for early diagenetic sulfide formation where residual less reactive iron phases were in contact with isotopically heavy dissolved sulfide sulfate depleted pore waters for prolonged periods during burial however the framvaren data indicate that isotopically heavy pyrite may form in relatively shallow 80 180 m super anoxic bottom water pools in contrast the presence of isotopically light pyrite does not indicate an absence of restricted conditions but only that most iron sulfide formation was completed before 34 s enriched sulfide could be encountered in the water column

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

hydrocarbon potential of the mississippian carbonate platform bechar basin algerian sahara the western bechar basin contains a 1500 2000 m thick mississippian succession of carbonates consisting of superposed shoaling upward sequences whose porosity or diagenesis have never been investigated to establish the reservoir potential of these carbonates in this paper we present a diagenetic and porosity evolution of the visean part of the mississippian carbonate platform that may lead to the development of new exploration fairways in the region a diagenetic model is proposed in which ooid and crinoid grainstones may have a reservoir potential if hydrocarbon migration occurred before the end of the serpukhovian prior to complete occlusion of porosity

a high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

dedolomitization review and case study of uncommon mesogenetic formation conditions abstract dedolomitization converts a dolomite into a calcite and conventionally is interpreted to form in an eogenetic or telogenetic diagenetic environment where meteoric water dissolves evaporites to supply excess calcium hydrologic connectivity between a dolostone and the surface water may then lead to a dedolomitized interval often times being a diagnostic indicator for an erosional unconformity subaerial exposure and or karst in contrast to the classic models we present a case study for pervasive burial dedolomitization unrelated to meteoric fluids dedolomitization of the zechstein 2 carbonate ca2 gas reservoir in nw germany is strongly altering reservoir quality on a regional scale the ca2 shows a textbook correlation between reservoir quality and mineralogy petrographic analyses show that approximately 80 of all observed calcite reveal a dedolomite microtexture causing a reduction of average matrix porosity by 5 to 10 compared to the dolomite dedolomite follows initial layering and abundantly forms massive concretions which are surrounded by compaction related curvature of the depositional layering in the dolomite host rock such an early burial timing is supported by a slight burial related shift of 3 18o and 1 13c towards lighter values in the dedolomites compared to dolomite an exceptionally large amount of calcium rich fluids must have been mobilized to account for 50 of the ca2 rock volume to be dedolomitized however core fabrics related to meteoric diagenesis such as karst fabrics or typical fresh water stable isotope signatures have been observed neither in the ca2 nor in over and underlying anhydrite beds instead excess calcium likely comes from gypsum to anhydrite conversion and pressure solution within over and underlying anhydrites an influx of strontium rich waters from the anhydrite beds is indicated by up to 5 times higher strontium contents measured in dedolomite fabrics compared to their dolomite host rock homogenization temperatures between 51 and 56 c measured in some early fluid inclusions in dedolomite textures further exclude a pristine meteoric water input and suggest fluid entrapment in a burial depth range of 900 to 1400 m comparing these results with literature data furthermore indicates that mesogenetic dedolomite is either volumetrically underestimated in other carbonate evaporite settings or formed under unique diagenetic conditions across the southern permian basin during zechstein times

dolomitization and calcitization of the devonian grosmont formation northern alberta abstract the grosmont formation upper devonian comprises a platform carbonate sequence which extends over 100 000 sq km in the subsurface of alberta and contains extensive areas of calcitized dedolomitized dolomite reservoir rocks hydrocarbon content of the grosmont formation is estimated to be 50 109 m3 of 7 api gravity oil with bitumen recovery rates as high as 70 percent using thermally enhanced recovery environments of deposition in the grosmont formation range from subtidal and intertidal to supratidal early stratigraphically controlled and later cross cutting dolomites are observed dissolution fabrics are generally related to the uppermost dolomitized units of the grosmont formation below an unconformity which overlies paleozoic rocks calcitization textures are found in limestone and dolomite units and do not bear any relationship to the unconformity petrographic examination shows that calcitization of dolomite occurs in different forms large 0 25 0 5 mm dolomite rhombs observed floating in micrite or at calcitic micrite dolomite contacts have cores replaced by calcite dolomite rhombs that are not calcitized contain cloudy cores with abundant calcite inclusions in some samples fragments of dolomite rhombs are observed with the cores dissolved away indicating that part of the calcitization process involves dissolution a complete range from dolomitic rocks that show no evidence of calcitization to calcitic rocks with the textures of sucrosic dolomites are observed late calcite cements filling the remaining available pore space are also related to the calcitization process there is a strong tendency for dolomites from stratigraphic units to be grouped by their isotopic compositions three phases of dolomitization are interpreted in the grosmont formation an early sabkha dolomite upper grosmont 3 dolomites formed during reflux of hypersaline brines upper grosmont 2 and dolomites related to waters expelled from shales during burial lower grosmont further dolomites in each unit tend to be depleted in the heavy isotopes of both carbon and oxygen with increasing degree of dissolution and or calcitization the geological and geochemical evidence indicates that calcitization was early and related to dolomitization probably with a later stage that took place during uplift and the entry of meteoric water along the unconformity

dedolomitization and calcite cementation in the middle devonian winnipegosis formation in central saskatchewan canada limestone consisting of finely to medium crystalline calcite mosaics is present in the upper part of the winnipegosis formation on the east central margin of the elk point basin where the overlying prairie evaporite deposits have been removed this type of crystalline limestone is interpreted as dedolomite based on petrographic observations the 18o and 13c values of the winnipegosis dedolomite vary from 12 8 to 11 9 vpdb vienna pee dee belemnite and from 0 5 to 1 7 vpdb respectively both values are significantly lower than those for the corresponding dolomite the 87sr 86sr ratios of the dedolomite are significantly higher between 0 7082 and 0 7087 the spatial distribution and geochemical data of the winnipegosis dedolomite suggest that dedolomitization was related to an influx of fresh groundwater and dissolution of the prairie evaporite anhydrite during the latest mississippian to the early cretaceous when the basin was subjected to uplift and erosion the winnipegosis dedolomite displays a series of replacement fabrics showing progressive calcitization of dolomite including the occurrence of dedolomite restricted along fractures and adjacent areas dolomite patches floating in the dedolomite masses and massive dedolomite with sparsely scattered dolomite relicts however the characteristic fabrics resulting from dedolomitization documented in the literature have not been observed in the winnipegosis dedolomite coarsely to very coarsely crystalline subhedral to euhedral calcite cement is restricted in the dedolomite the petrographic features isotopic compositions and homogenization temperatures coupled with the burial history of the winnipegosis formation constrain the precipitation of the calcite cement from a mixing of basinal brines and fresh groundwater during late cretaceous to neogene time the more negative c isotopic signatures of the calcite cement 5 3 to 2 3 vpdb probably reflect a hydrocarbon derived carbon

detailed topography of the devonian grosmont formation surface from legacy high resolution seismic profiles northeast alberta abstractthe devonian grosmont formation in northeastern alberta canada is the world s largest accumulation of heavy oil in carbonate rock with estimated bitumen in place of 64 5 109 m3 much of the reservoir unconformably subcrops beneath cretaceous sediments this is an eroded surface modified by kartstification known as the sub mannville unconformity smu we studied the reanalysis and integration of legacy seismic data sets obtained in the mid 1980s to investigate the structure of this surface standard data processing was carried out supplemented by some more modern approaches to noise reduction the interpretation of these reprocessed data resulted in some key structural maps above and below the smu these seismic maps revealed substantially more detail than those constructed solely on the basis of well log data in fact the use of only well log information would likely result in erroneous interpretations although features smaller than about 40 m in radius cannot be easily discerned at the smu

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

cathodoluminescence in quaternary carbonate deposits abstract the cathodoluminescent oscillatory and sectoral growth zones common in crystals formed in ancient limestone successions in a variety of putative environments appear to be rare or absent from recent and pleistocene marine carbonate sequences the factors controlling cathodoluminescence and reasons for this disparity are examined the cathodoluminescent zones in the cements of ancient rocks have been interpreted as responses to variations in the redox potential of formative pore waters during crystal growth although similar cathodoluminescent behaviour is recorded from some deposits including travertines and quaternary speleothems formed in what are thought to have been strongly oxidizing environments the apparent absence of cathodoluminescence in the most recent and pleistocene marine deposits that presumably reflect deposition and diagenesis in environments that are also characteristically oxidized therefore seems anomalous the controlling influences on cathodoluminescence are reviewed together with evidence relating to observations of pleistocene marine deposits and likely conditions of formation but where it is present the mechanism s for its development remain elusive

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

sulfur isotope fractionation in modern euxinic systems implications for paleoenvironmental reconstructions of paired sulfate sulfide isotope records abstract the sulfur s isotope difference between sulfates and sulfides preserved in sedimentary rocks 34 s has been utilized to reconstruct ancient marine sulfate levels with implications for oxygenation of the earth surface and biogeochemical cycling s isotope data from modern low sulfate euxinic systems illustrate that preserved 34 s values are positively correlated with sulfate concentration however absolute constraints on the range of low sulfate levels over which preserved 34 s values vary with sulfate concentration remain poorly constrained here we present a compilation of s isotope data for modern euxinic systems demonstrating that preserved 34 s values increase with sulfate concentration at low sulfate levels and approach values that are similar to in situ s isotope fractionation values from microbial sulfate reduction at high sulfate levels we compare these results to a closed system model of s isotope cycling in a euxinic ocean in order to evaluate when the size of the sulfate reservoir is sufficiently small that rayleigh fractionation affects the preservation of s isotope signatures we conclude that the reservoir effect places constraints on 34 s values deposited in euxinic settings at sulfate concentrations 34 s values can be used to evaluate ancient sulfate levels at higher sulfate levels 10 mm 34 s values are similar to the kinetic isotope fractionation due to microbial sulfate reduction and therefore provide information about biological and environmental controls on sulfate reduction rates and location of pyrite formation the results of this compilation provide an improved model for the use of 34 s records to evaluate paleoenvironmental conditions in euxinic depositional environments

decline in oceanic sulfate levels during the early mesoproterozoic abstract multiple sulfur isotope compositions 32 s 33 s 34 s and 36 s were analyzed for paired carbonate associated sulfate cas and disseminated pyrite py from the 1 6 ga gaoyuzhuang formation of the north china craton to reconstruct the history of sulfate levels in proterozoic oceans the 200 m thick study interval yielded relatively constant values for 34 s cas 13 0 1 8 34 s py 8 0 2 3 and 34 s cas py 5 as well as relatively constant 33 s 0 0 05 and 36 s 0 35 0 15 for both cas and pyrite limited variation in 34 s py and slightly lower 33 s of pyrite relative to cas suggest water column precipitation of pyrite limited fractionation of sulfur during microbial sulfate reduction as documented by 34 s cas py implies low seawater sulfate concentrations in the early mesoproterozoic ocean we quantitatively constrained paleo seawater so 4 2 using a novel modeling approach based on measured values of 34 s cas py and 34 s cas t max for the study unit 34 s cas py is 5 4 1 4 n 17 and 34 s cas t max is 6 8 34 myr 1 based on sedimentation rates of 30 150 m myr 1 these data indicate early mesoproterozoic seawater so 4 2 of p o 2 after great oxidation event i

pore size and pore throat types in a heterogeneous dolostone reservoir devonian grosmont formation western canada sedimentary basin the devonian grosmont formation in northeastern alberta canada is a giant heavy oil reservoir the main reservoir rocks are dolomitized and karstified platform and ramp carbonates and the best reservoir facies occur in the upper grosmont ugm units 3 and 2 in these units reservoir properties are highly heterogeneous hand specimen thin section uv and sem petrography as well as grading scales mercury capillary pressure curve analysis and statistics have been used to characterize reservoir heterogeneity our investigation led to a new pore size classification for carbonate reservoirs this new classification has four pore sizes microporosity pore diameters 256 mm a combination of microscopic observations and capillary pressure curve characteristics led to the recognition of four pore throat texture types on the microporosity scale and to five types on the mesoporosity scale microporosity pore types include 1 intracrystal dissolution porosity 2 pervasive intercrystal and intracrystal dissolution porosity 3 intergranular and or intercrystal porosity in grainstones and 4 primary or solution microporosity in mud matrix only in limestones mesoporosity pore types include 1 intercrystal porosity 2 solution enhanced intercrystal porosity 3 oversized porosity 4 intragranular solution porosity and 5 intergranular solution porosity some of these types are homogeneous e g non fabric selective dissolution porosity and inte crystal primary porosity whereas others are heterogeneous generally hydrocarbon recovery efficiency is good in the homogeneous pore throat types but poor in the heterogeneous types reservoir heterogeneity has further been characterized by comparison and statistical analysis of plug and full diameter core fdc data that indicate 1 plug porosities on average are higher than fdc porosities 2 plug permeabilities on average are higher than fdc permeabilities 3 plug porosity and permeability show relatively good linear relationships in certain core intervals but fdc data do not and 4 generally the more homogeneous reservoir rocks have relatively high matrix porosity heterogeneity is common in grosmont dolostone reservoir rocks and affects overall reservoir quality at the megascopic scale the reservoir properties can be classified as homogeneous dual porosity and multilayered the dual porosity model has three subcategories fractured channeled and pressure solution derived

long range propagation and associated variability of internal tides in the south china sea the variability of internal tides during their generation and long range propagation in the south china sea scs is investigated by driving a high resolution numerical model the present study clarifies the notably different processes of generation propagation and dissipation between diurnal and semidiurnal internal tides internal tides in the scs originate from multiple source sites among which the luzon strait is dominant and contributes approximately 90 and 74 of the baroclinic energy for m2 and k1 respectively to the west of the luzon strait local generation of k1 internal tides inside the scs is more energetic than the m2 tides diurnal and semidiurnal internal tides from the luzon strait radiate into the scs in a north south asymmetry but with different patterns because of the complex two ridge system the tidal beams can travel across the deep basin and finally arrive at the vietnam coast and nansha island more than 1000 1500 km away during propagation m2 internal tides maintain a southwestward direction whereas k1 exhibit complicated wave fields because of the superposition of waves from local sources and island scattering effects after significant dissipation within the luzon strait the remaining energy travels into the scs and reduces by more than 90 over a distance of 1000 km inside the scs the k1 internal tides with long crests and flat beam angles are more influenced by seafloor topographical features and thus undergo apparent dissipation along the entire path whereas the prominent dissipation of m2 internal tides only occurs after their arrival at zhongsha island this article is protected by copyright all rights reserved

generation and propagation of baroclinic tides modified by the kuroshio in the luzon strait 1 using a three dimensional model with idealized settings this study evaluated the effect of the kuroshio on the generation and propagation of semidiurnal m2 and diurnal k1 baroclinic tides bcts in the luzon strait ls the influences of the varied kuroshio transport the location of the kuroshio and the separation distance of the two meridional ridges were investigated the absence of the kuroshio in the model leads to 30 decreases in the westward baroclinic energy flux fbcx emanating from the west slope of the east ridge compared to the fbcx with the presence of the kuroshio compared to the fbcx without the kuroshio s influence the westward fbcx is increased by 20 40 when the kuroshio is located in either the middle or the west portions of the ls whereas both the westward and eastward fbcx are 25 40 decreased as the kuroshio is moved to the east of the east ridge the wavelength of the mode 1 m2 bct is similar to the separation distance of the two ridges favoring a resonance generation for m2 rather than k1 bcts the increase of the kuroshio transport from 20 to 30 sv 1 sv 106 m3 s 1 enhances the density front but weakens the westward fbcx owing to the effects of energy advection and lateral friction from the kuroshio the influence of the kuroshio on the westward fbcx of k1 is opposite of that on m2 the characteristic slope of k1 is closer to the isopycnal slope across the kuroshio than m2 thereby causing the discrepancy

inside out dolomite abstract inside out dolomite crystals are unusual because their cores are younger than their encasing cortices in the cayman formation middle miocene of grand cayman they developed diagenetically from zoned dolomite crystals that have cores formed of high ca calcian dolomite hcd 55 mol caco3 and outer cortical zones formed of low ca calcian dolomite lcd 3 or oscillatory zoned lcd hcd the cores of these crystals labeled as type i have a euhedral rhombic outline with no embayments or angular reentrants and commonly contain calcite inclusions and or micropores hollow dolomite crystals evolved from these crystals as preferential dissolution removed all or part of the hcd core later calcite or dolomite cement was precipitated inside the hollow crystals the former produced dolomite crystals with a calcitic core i e dedolomite whereas the latter produced inside out dolomite crystals that have a dolomite core lcd or hcd encased by a dolomite cortex the cores of the inside out dolomite crystals labeled as type ii have an irregular outline characterized by angular reentrants and or embayments micropores that are usually larger than those in the type i cores but few calcite inclusions the cortical zones have a euhedral rhombic motif irrespective of the type of core development of insideout dolomite crystals may significantly alter the average ca of the dolostones as hcd is lost to dissolution and lcd or hcd cement is precipitated in its place the 18o may also change inasmuch as it is thought to covary with ca in some tertiary dolostones the genesis of inside out dolomite crystal may offer an alternative explanation for the textures e g clotted cathodoluminescence patterns in some ancient dolomite crystals that have been attributed to replacement and or recrystallization

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada ii ocean anoxia during mineralisation abstract current models of massive sulphide ore genesis in the bathurst mining camp new brunswick involve settling of sulphide particles from a stagnating low salinity hydrothermal plume spreading laterally in an anoxic ocean layer with minimal sulphate content there is fragmentary evidence of ocean anoxia in the form of local fine lamination in the shales that host some of the deposits but the total organic carbon s fe u th ni co v ni and v cr relationships indicate deposition under oxic or dysoxic conditions vanadium and mn values range from oxic to anoxic and sulphate reducing to non sulphate reducing but mn may be anomalously low due to derivation by erosion of acidic volcanic rocks the somewhat equivocal physical and chemical data combined with the likely disturbing effects of penecontemporaneous volcanism considerably weaken the case for an anoxic bottom layer in a static ocean the presence of barite with ambient seawater 34 s values in brunswick no 12 ore and the abundance of sulphate in modern euxinic basin waters make a sulphate free layer unlikely even if anoxic sulphate bearing low salinity fluids mixing with seawater would lead to growth of barite bearing chimneys and baritic rubble mounds which are not observed a model involving brine pool deposition better explains the major features of the bathurst ores

idealized solutions for the energy balance of the finescale internal wave field abstract recent fine and microstructure observations indicate enhanced finescale shear and strain in conjunction with bottom intensified turbulent dissipation above rough bathymetry in the brazil basin such observations implicate the bottom boundary as an energy source for the finescale internal wave field simple analytical and numerical solutions to an equation governing the spatial and temporal evolution of the finescale wave field are described here the governing equation implicitly treats the effects of wave breaking on the vertical propagation of internal waves through a flux representation of nonlinear transports associated with internal wave wave interactions these solutions identify the rate of dissipation of turbulent kinetic energy with downscale energy transports at high vertical wavenumber resulting in an estimate of dissipation versus depth the sensitivity of the turbulent dissipation depth profile to various environmental parameters is examined observed dissipation profiles and shear

tidally driven processes leading to near field turbulence in a channel at the crest of the mendocino escarpment abstractin situ observations of tidally driven turbulence were obtained in a small channel that transects the crest of the mendocino ridge a site of mixed diurnal and semidiurnal tides diurnal tides are subinertial at this latitude and once per day a trapped tide leads to large flows through the channel giving rise to tidal excursion lengths comparable to the width of the ridge crest during these times energetic turbulence is observed in the channel with overturns spanning almost half of the full water depth a high resolution nonhydrostatic 2 5 dimensional simulation is used to interpret the observations in terms of the advection of a breaking tidal lee wave that extends from the ridge crest to the surface and the subsequent development of a hydraulic jump on the flanks of the ridge modeled dissipation rates show that turbulence is strongest on the flanks of the ridge and that local dissipation accounts for 28 of the energy converted from the barotropic tide into baroclinic motion

middle late ordovician darriwilian sandbian decoupling of global sulfur and carbon cycles isotopic evidence from eastern and southern laurentia abstract middle late ordovician sequences from the appalachian basin and arbuckle mountain regions of north america were analyzed for carbonate associated sulfate 34 s cas and pyrite 34 s pyr paired with carbonate 13 c carb and organic matter 13 c org chemostratigraphy two major negative drops in 34 s cas 12 excursions are recognized the older decline in 34 s cas occurs within the histiodella holodentata phragmodus polonicus conodont zones and the younger drop is within the cahabagnathus sweeti amorphognathus tvaerensis baltoniodus gerdae subzone zones these overall these negative shifts in 34 s cas have an antithetical relationship with positive shifts in 34 s pyr 10 and 13 c carb 2 recorded in the same successions the older negative 34 s cas shift is coincident with the widely documented mid darriwilian 13 c excursion mdice and the younger negative 34 s cas shift is coincident with another positive 13 c carb shift in the early sandbian geochemical modeling of these sulfur isotope shifts suggests that a decrease in the global rate of pyrite burial or isotope fractionation between seawater sulfate and sedimentary pyrite could account for these negative 34 s cas trends additionally a substantial increase in the weathering flux of pyrite to the global oceans could also explain these secular sulfur isotope trends while increased crustal weathering is broadly consistent with a sea level lowstand and the seawater 87 sr 86 sr isotope record of change in continental weathering in the late darriwilian stage of the ordovician geologic and geochemical proxy evidence do not support distinct pulses of continental weathering required to generate two separate negative shifts in 34 s cas these antithetical isotope trends may be best explained by changes in the marine redox state that significantly reduced microbially mediated pyrite burial and organic matter remineralization rates pulses of oceanic ventilation would have expanded habitable environments for marine organisms and thus is broadly consistent with major increases in biodiversification during this period of the ordovician

stratigraphy and environmental conditions of the terminal neoproterozoic cambrian period in oman evidence from sulphur isotopes terminal neoproterozoic and cambrian evaporite rocks worldwide record a marked sulphur isotope excursion to very heavy 34 s isotopes that reflect a period of significant burial of reduced sulphur new 34 s data from anhydrite and pyrite of the ara group in oman extend this record to arabia depositional history of the ara group spans c 8 ma across the terminal neoproterozoic cambrian boundary therefore these rocks provide a detailed record of sulphur isotopic evolution in this important time interval ara group sulphur isotope values include a mean 34 s anhydrite of 39 4 2 6 1 range 32 4 46 4 n 61 and a mean 34 s pyrite of 1 4 7 3 1 range 10 8 to 11 4 n 12 the isotope signatures were not altered significantly during diagenesis and are representative of the isotopic composition of parent waters in the basin marine bromine concentrations in halite and marine fossils in associated carbonate rocks indicate that these waters had a marine origin bacterial sulphate reduction was the dominant process leading to the segregation between isotopically heavy sulphur incorporated in evaporite rocks and isotopically light sulphur buried in pyrite and organic matter strong sulphate reduction operated in a hypersaline and partly anoxic basin these environmental conditions were also conducive to the preservation of organic material and make the ara group a prolific hydrocarbon province significant variation of the observed values is attributed to the inherent variability of bacterial sulphate reduction including partially closed system behaviour disproportionation processes limited diagenesis and possibly secular variation of sulphur isotopes within the basin ara group 34 s anhydrite values overlap with data from other terminal neoproterozoic to cambrian basins but the mean 34 s anhydrite is highest in oman this observation cannot be attributed solely to the specific anoxic conditions and strong bacterial sulphate reduction in oman because such conditions were widespread in most evaporite basins of the terminal neoproterozoic cambrian periods instead slight age differences between these basins can introduce a bias in the sulphur isotope curve excellent preservation of ara group deposits and in particular the precise age constraints make the ara group representative for the seawater sulphur isotopic composition at the terminal neoproterozoic cambrian boundary as a result of the inherent variability of bacterial sulphate reduction 34 s values at the lower end of the spectrum should be most representative for the global signal based on results of this study the global signal is estimated to be approximately 35 40

an estimate of tidal energy lost to turbulence at the hawaiian ridge abstract an integrated analysis of turbulence observations from four unique instrument platforms obtained over the hawaiian ridge leads to an assessment of the vertical cross ridge and along ridge structure of turbulence dissipation rate and diffusivity the diffusivity near the seafloor was on average 15 times that in the midwater column at 1000 m depth the diffusivity atop the ridge was 30 times that 10 km off the ridge decreasing to background oceanic values by 60 km a weak factor of 2 spring neap variation in dissipation was observed the observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide e and the depth integrated dissipation d such that d e1 0 5 at sites along the ridge this kinematic relationship is supported by combining a simple knife edge model to estimate internal tide generation with wave wave interaction time scales to estimate dissipation the along ridge kinematic relationship and the observed vertical and cross ridge st

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties

numerical and analytical estimates of m2 tidal conversion at steep oceanic ridges abstract numerical calculations of the rate at which energy is converted from the external to internal tides at steep oceanic ridges are compared with estimates from analytic theories the numerical calculations are performed using a hydrostatic primitive equation ocean model that uses a generalized s coordinate system as the vertical coordinate the model regional ocean modeling system roms estimates of conversion compare well with inviscid and nondiffusive theory in the sub and supercritical regimes and are insensitive to the strength of viscosity and diffusivity in the supercritical regime the nondissipative analytic solution is singular all along the internal tide beams because of dissipation the roms solutions are nonsingular although the density gradients are strongly enhanced along the beams the agreement between model and theory indicates that the prominent singularities in the inviscid solution do not compromise the estimates of tidal conversion and that the linearization used in derivi

internal tide radiation from mendocino escarpment abstract strong semidiurnal internal tides are observed near mendocino escarpment in full depth profile time series of velocity temperature and salinity velocity and density profiles are combined to estimate the internal tide energy flux divergence of this flux demonstrates that its source is the barotropic tide interacting with the escarpment a baroclinic energy flux of 7 kw m 1 radiates from the escarpment corresponding to 3 of the 220 kw m 1 fluxing poleward in the surface tide energy and energy flux are concentrated in packets that emanate from the flanks of the ridge surmounting the escarpment and one site 90 km north of the escarpment coherent beamlike structure along semidiurnal ray paths remains identifiable until the first surface reflection beyond the first surface reflection north of the escarpment the energy flux drops by 2 kw m 1 and beams are no longer discernible turbulence as inferred from finescale parameterizations is elevated by over two orders of magnitude relative to th