hydrogeochemical characterization of oilfield waters from southeast maracaibo basin venezuela diagenetic effects on chemical and isotopic composition free water and water in emulsion with oil from hydrocarbon wells onshore offshore lake maracaibo were extracted and analyzed the use of classical and new chemical diagrams evidenced that na hco3 and na cl are the main chemical facies whereas na so4 facies was rare and revealed only in faulted areas in which shallow groundwater was involved in deep circulation cretaceous ca cl waters were not revealed but their imprint on some samples was traced and evidenced by langelier ludwig brine differentiation and caexcess vs nadeficit diagrams these square plots allowing a discrimination between the water contributions from the different source rocks should be more exploited as hydrogeochemical tools in hydrocarbon exploration original data on monocarboxylic anions showed acetate concentration higher than ten times that of formate at sampling conditions but speciation under deep conditions indicated a reversed activity dominance calculation of saturation indexes and kinetic modeling showed an active precipitation of chalcedony kaolinite and clays especially where the temperature was lower t 100 c formation waters and lake water showed quite similar chloride concentration and hydrogen isotope composition however thermodynamic calculations at the oilfield p t conditions revealed chlorite and illite produced during previous diagenetic stages of misoa sandstones recrystallization to smectite and vermiculite in present day stage the diagenetic water produced in these reactions could have enriched the 18o isotopic composition of approximately 2 this isotope diagenetic effect was more evident in na hco3 waters which also showed a decrease in chloride at constant boron concentration as a consequence of clay dewatering in this regard a new boron geothermometer useful for formation waters is also proposed t c 5 1364 ln 1 b mg 1 5 728 0 180 0 164 0 012

campanian bolivinoides and microfacies from the la luna formation western venezuela abstract tres esquinas the upper member of the la luna formation a 1 3 m thick condensed sequence composed of glauconitic phosphorite signals the commencement of the late cretaceous regression in western venezuela this is the last of a series of thin phosphatic beds the others non glauconitic occurring in the upper la luna formation in the state of merida the presence of bolivinoides culverensis restricts these phosphatic beds to the late santonian early campanian with the tres esquinas member assigned to the globotruncanita elevata globotruncana ventricosa zones bolivinoides sp cf b sirticus is also commonly found in these beds although no bolivinoides have been detected in the tres esquinas member in the state of tachira to the west the non glauconitic phosphate bed informally named capa ii as well as the 15 m thick ftanita de tachira member which underlies the tres esquinas member and separates it from capa ii contain bolivinoides culverensis as well as bolivinoides cf b sirticus this occurrence combined with the assignation of the base of the overlying colon formation to the globotrucana aegyptiaca zone suggests a late campanian age for the member in this area and implies that the member is diachronous on the basis of lithology mineralogy foraminiferal content and degree of bioturbation six microfacies and one sub microfacies are identified the microfacies of the phosphatic limestones containing bolivinoides spp are notably different in the two states

geology of a vigorous hydrothermal system on the endeavour segment juan de fuca ridge a high precision high resolution geologic map explicitly documents relationships between tectonic features and large steep sided sulfide sulfate silica deposits in the vigorously venting endeavour hydrothermal field near the northern end of the juan de fuca ridge water depth in the vent field varies from 2220 to 2200 m location of the most massive sulfide structures appears to be controlled by intersections of ridge parallel normal faults and other fracture fissure sets that trend oblique to and perpendicular to the overall structural fabric of the axial valley the fractured basaltic substrate is primarily composed of well weathered pillow and lobate flows as presently mapped the field is about 200 by 400 m on a side and contains at least 15 large 1000 m3 sulfide edifices and many tens of smaller commonly inactive sulfide structures the larger sulfide structures are also the most vigorously venting features in the field they are commonly more than 30 m in diameter and up to 20 m in height actively venting sulfide structures in the northern portion of the field stand higher and are more massive than active structures in the southern portion of the field which tend to be slightly to distinctly smaller maximum venting temperatures of 375 c are associated with the smaller structures in the southeastern portion of the field highest temperature venting fluids from the more massive structures in the northern portion of the field are consistently 20 30 c lower hydrothermal output from individual active sulfide features varies from no flow in the lower third of the edifice to vigorous output from fracture controlled black smoker activity near the top of the structures a different type of high temperature venting takes place from the upper sides of the structures in the form of overflow from fully exposed quiescent pools of buoyant 350 c vent water trapped beneath overhanging sulfide sulfate silica ledges or flanges these flanges are attached to the upper outer walls of the large sulfide edifices two types of diffuse venting in the endeavour field include a lower temperature 8 15 c output through colonies of large tubeworms and 25 50 c vent fluid that seems to percolate through the tops of overhanging flanges the large size and steep walled nature of the these structures evidently results from sustained venting in a mature hydrothermal system coupled with dual mineral depositional mechanisms involving vertical growth by accumulation of chimney sulfide debris and lateral growth by means of flange development

effluent from diffuse hydrothermal venting 2 measurement of plumes from diffuse hydrothermal vents at the southern juan de fuca ridge an array of temperature and velocity sensors was deployed for two weeks in the bottom boundary layer at the southern juan de fuca ridge during the national oceanic and atmospheric administration vents 90 field experiment the instruments were placed close to the seafloor to detect effluent from diffuse hydrothermal sources located 1 2 km distant over the duration of the field deployment we detected effluent from two vent sources the plume from the larger of the two sources was sensed at all of the instrument locations permitting estimates of dilution based on the field measurements our data also permitted estimation of energy flux from diffuse vents approximately 125 75 mw from a source to the north of the instrument array and 12 8 mw from a small source to the east the largest source of error in the data was estimation of the plume width we have described a sensor array that would reduce this error in future work such an array would be suitable for a long term vent activity monitor

estimations of heat transfer from grotto s north tower a neptune observatory case study abstract the overall heat transfer through an active hydrothermal sulfide edifice in particular the north tower of grotto has been estimated at 80 mw or greater based on the following in situ measurements and assumptions 1 the heat transfer by diffuse flow is estimated at 33 380 mw based on extrapolating the acoustically mapped area to all sides of the north tower visible area 30 m 2 extrapolated area 100 m 2 and using the range of available spot measurements of temperature 6 23 c and vertical velocity 0 07 0 28 m s the lower number 33 mw is more likely but there is insufficient knowledge of the temporal and spatial variability of diffuse flow to be certain 2 the heat transfer by focused flow is estimated at 30 70 mw based on summing the estimated individual rates of heat transfer for 4 out of 7 documented black smokers and flanges 3 conductive heat transfer out of the mound is unknown but is likely to be much less than the advective heat transfer additionally the plume transport of heat is estimated at 20 40 mw based on the direct measurement of temperature within the plume at 5 25 m above the top of the edifice despite uncertainties the lower estimate of plume versus smoker heat transfer suggests that heat transfer is dominantly by diffuse flow furthermore not all plumes from individual smokers may merge even for so small an area as the north tower of grotto

recharge of aquifers by flood events in an arid region the process of aquifer recharge by flood events in an arid region was investigated as applied to the hazeva formation the karkom graben the wadi paran watershed israel the hydrological model was established as a complex system with due regard for groundwater and transmission losses of surface runoff it was based on a previously outlined hydrogeological model of the karkom graben and a model of transmission losses in arid watercourses under conditions of data deficiency proceeding from calculation of groundwater balances the contribution of surface runoff as a decisive balance component was confirmed the main characteristics of aquifer regimes such as changes in storage volume and groundwater level as well as lateral flow were all found to be dependent upon the net extraction rate i e pumpage discounting replenishment by flood events analysis and physical interpretation of model parameters enabled assessment of the influence of groundwater extraction on aquifer recharge this became apparent as increasing absorption capacity and recharge availability of the aquifer as a result of the groundwater abstraction copyright 2002 john wiley sons ltd

the first measurements of hydrothermal heat output at 9 50 n east pacific rise abstract despite the importance of the heat output of seafloor hydrothermal systems for the earth s energy budget hydrothermal heat output measurements have been very limited in this paper we report the first measurements of hydrothermal heat output at the ridge 2000 integrated study site on the east pacific rise we focused our work on the bio 9 complex situated at 9 50 n where there has been an extensive measurement and sampling program since 1991 this site is located along the eruptive fissure of the 1991 1992 event and the site of the 1995 earthquake swarm we made direct measurements of advective heat output at several individual vents and at one site of diffuse flow tica although these data do not describe the complete heat flux picture at this vent field the data yield a total hydrothermal heat output of 325 160 mw with 42 21 mw coming from high temperature vents along this 2 km segment of ridge this result assumes a diffuse flux similar to that measured at tica occurs at each high temperature vent site our initial measurements thus suggest that the heat output of the low temperature diffuse venting is approximately 10 times that of the high temperature vents but may also be one or two orders of magnitude greater

numerical modeling of phase separation at main endeavour field juan de fuca ridge 1 before being disrupted by a magmatic event in 1999 the vent temperatures and salinities along the axis of the main endeavour field on the juan de fuca ridge exhibited a quasi steady spatial gradient in which the southern vent fluids were hotter and less saline than the northern vent fluids we present 2 d numerical models of two phase flow in a nacl h2o system to understand these gradients we consider homogenous permeability models with a range of bottom boundary temperature distributions and heterogeneous permeability models by imposing layer 2a extrusives with a constant bottom boundary temperature distribution the aim is to understand the impact of both bottom boundary temperature and layer 2a permeability on hydrothermal fluids and to determine what combination of these controlling factors could cause the observed trend we find that variations in bottom boundary temperature alone cannot explain the span of surface temperatures and salinities measured at the main endeavour field heterogeneous permeability within layer 2a that has higher overall permeability in the northern part of the vent field than the southern part can reproduce the observed north to south temperature gradient but such a permeability distribution cannot reproduce the observed salinity gradient we conclude that both deep seated heterogeneous permeability perhaps localized by a fault zone and a heterogeneous layer 2a are required to produce the trend of temperatures and salinities in vent fluids at the main endeavour field prior to the 1999 event

near vent chemical processes in a hydrothermal plume insights from an integrated study of the endeavour segment support from onc for sample collection is gratefully acknowledge as is the analytical expertise of jody spence bruno keiffer and maureen soon who helped generate the data set reported here funding for sample analysis came from an nserc discovery grant to l a c ocean networks canada is supported through the canadian foundation for innovation all data are provided in the supporting information or through onc at http dmas uvic ca datasearch

a boundary layer model for submarine hydrothermal heat flows at on axis and near axis regions hydrothermal discharge from oceanic crust makes up a significant portion of earth s overall heat flux in this paper we investigate two aspects of oceanic hydrothermal heat flux that are not well understood 1 the relative partitioning of heat flux between high temperature and low temperature flows at oceanic spreading ridges and 2 hydrothermal behavior of the near axis region where seismic data suggest that a zone of partial melt extends quasi vertically into the lower crust at the east pacific rise we apply steady state boundary layer theory to each system by assuming circulation occurs near a hot isothermal wall that laterally transfers heat to and induces convection within an adjacent fluid filled medium we vary the permeability of the medium over a range of 10 14 to 10 10 m2 for model 1 we assume a wall temperature of 150 c corresponding to a relatively impermeable anhydrite wall within layer 2a extrusives whereas for model 2 we assume a wall temperature of 800 c that extends to the base of the crust the boundary layer results for model 1 suggest that diffuse flow makes up 50 or less of the heat output at the ridge axis which is at the low end of some observations should more accurate and complete heat flux data be obtained and indicate that a high fraction of ridge axis heat loss results from diffuse flow another mechanism in addition to the boundary layer model proposed here may be required boundary layer results for near axis circulation model 2 indicate that temperature distributions are in reasonable agreement with those inferred from seismic tomographic studies of the oceanic crust and with other numerical models for the near axis model results also show that heat transfer in the hydrothermal boundary layer is greater than the input from steady state generation of the oceanic crust by seafloor spreading this difference in heat input suggests that the width of the partial melt zone may be decreasing with time thus the application of the boundary layer theory to complex hydrothermal processes near oceanic spreading centers provides important insights into key system processes

parameters of subsurface brines and hydrothermal processes 12 15 months after the 1999 magmatic event at the main endeavor field as inferred from in situ time series measurements of chloride and temperature properties of subsurface brines at mef

comments on neogene block tectonics of eastern turkey and northern south america continental applications of the finite difference method by j f dewey and j l pindell

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

a record of long and short term environmental and climatic change during oae3 la luna formation late cretaceous santonian early campanian venezuela abstract the la luna formation was deposited under anoxic dysoxic conditions in a tropical epicontinental sea on the northwest south america margin sedimentological micropaleontological and geochemical evidence provides insights into factors that influenced the sedimentation and controlled the accumulation of organic rich deposits at decimeter and meter scales during the youngest of the cretaceous oceanic anoxic events oae the la luna formation consists of an alternation of black marlstones interbedded with black limestones and black marly limestones the benthic foraminifera assemblages indicate sedimentation in the upper neritic to upper bathyal environment these rocks contain large amounts of organic matter it is interpreted that a combination of warm global and rainy climate and the presence of bathymetric barriers caused poor circulation and low rates of water column ventilation during a high sea level in the early santonian leading to the preservation of carbon rich deposits in this region during the late santonian a cooling trend in global climate increased wind strength and upwelling this change probably reduced runoff causing a weakening of the pycnocline and destabilized the stratification in the water column providing a progressive increase in oxygen in the water column and on the sea floor and a decrease in total organic carbon preservation in a shallower basin these changes and the establishment of full mid and deep water exchange in response to the deepening and widening of the equatorial atlantic gateway could have been important mechanisms for ending the epeiric sea anoxia changes through time in the vanadium nickel fraction planktonic and benthic foraminifera assemblages productivity proxy elements and lithological characteristics support this model superimposed on the general trend variations in calcium carbonate and total organic carbon percentages at the scale of tens of centimeters reveal high frequency cyclic variations which apparently correspond to the main frequencies of orbital forcing this cyclicity is interpreted as a primary depositional signal and is the result of orbital controlled fluctuations in terrigenous dilution and variations in oxygen concentration at the base of the water column variations in the intensity of upwelling can be observed but they did not control the cyclicity

hydrothermal cooling of midocean ridge axes do measured and modeled heat fluxes agree abstract accurate estimates of near axis hydrothermal cooling are keys to understanding many geological chemical and biological processes at midocean ridges at present however field observations h heat flux vent field are few and imprecise and model results h m heat flux km of axis vary widely depending on assumptions about crustal formation crustal composition and the cooling efficiency and spatial and temporal extent of hydrothermal circulation in this paper i compare all published vent field scale measurements of h to a range of published h m for slow 40 mm yr and fast 40 mm yr ridges to assess the present state of knowledge about the magnitude of near axis hydrothermal cooling h has been evaluated 28 times either by point measurements using inventories of individual sources 362 552 mw n 12 measurements or by integrated measurements using water column observations 876 1011 mw n 16 comparable estimates of mean vent field expected h at any spreading rate can be derived by merging h m from various models with the predicted global inventory of active vent sites these estimates range from 1 1 5 gw field and are approximately constant for all spreading rates this range agrees with the best constrained results of h from slow ridge vent fields 1669 1354 mw but is considerably higher than those from fast ridges 245 170 mw inferences about the spatial and temporal variability of h can be gained by defining the parameter l h h m equivalent to the axis length needed to continuously power a hydrothermal field the resultant large l values 13 333 km for slow ridges 1 32 km for fast demand punctuated cooling where for short periods h h m the percentage of time that a given vent field might be active can be speculatively estimated by dividing l by the length of axis the field cools examples of this percentage range from a low of 50 for some fast ridge fields

measuring fluid flow and heat output in seafloor hydrothermal environments we have designed built calibrated and tested new anemometer and turbine flow meter devices to measure fluid velocity at high and low temperature focused and diffuse discharge sites at oceanic spreading centers the devices perform at ocean floor depths and black smoker temperatures and can be used to measure flow rates ranging over two orders of magnitude flow velocity is determined from the rotation rate of the rotor blades or paddle assembly these devices have an open bearing design that eliminates clogging by particles or chemical precipitates as the fluid passes by the rotors the devices are compact and lightweight enough for deployment from either an occupied or remotely operated submersible the measured flow rates can be used in conjunction with vent temperature or geochemical measurements to obtain heat outputs or geochemical fluxes from both vent chimneys and diffuse flow regions the devices have been tested on 30 alvin dives on the juan de fuca ridge and 3 jason dives on the east pacific rise epr we report 102 new measurements over a wide range of discharge temperatures 5 363 c velocities 2 199 cm s and depths 1517 2511 m these include the first advective heat output measurements at the high rise vent field and the first direct fluid flow measurement at middle valley our data suggest that black smoker heat output at the main endeavor vent field may have declined since 1994 and that after the 2005 2006 eruption the high temperature advective flow at the epr 9 50 n field may have become more channelized predominately discharging through the bio 9 structure we also report first direct advective measurements in the lau basin and at the epr 9 39 5 n with flow meters that predated devices described in this work and were used in the process of their development we discuss potential error sources and how they may affect the accuracy of measurements by our and other devices in particular we use the turbulent plume theory to evaluate the effect of entrainment of ambient seawater

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

within plate deformations in the maracaibo and east zulia basins western venezuela abstract subsurface data help in understanding the complex geometry of major structures of the maracaibo basin and surrounding areas during extensional and compressional phases decoupling levels were activated in the upper cretaceous black shales and the paleogene flysch sequences thus inducing frequent disharmony between a rigid basement and thin skinned cover structures two main extensional episodes are widespread across the maracaibo basin the first episode late jurassic in age accounts for the development of north northeast trending basement horsts and asymmetrical grabens the second episode more probably a transtensive one occurred during paleogene times it reactivated older north and northwest trending basement involving faults i e the ceuta and pueblo viejo faults but also generated listric normal faults and negative flower structures in the sedimentary cover by contrast compressional deformations are localized and reactivate older basement faults inducing the frequent inversion of former jurassic or lower to middle eocene grabens shortcuts in the basement and coeval wedging or fishtails in the sedimentary cover thus the major inversion episode in the maracaibo basin is upper eocene in age and probably relates to the emplacement of the caribbean nappes further to the northeast it was followed by an episode of tectonic quiescence and erosion during the oligocene neogene deformations have a limited extent beneath lake maracaibo but become widespread in the west towards the perija foothills or in the southeast near the north andean thrust front where they account for the development of frontal triangle zones east of the lake the east zulia basin is characterized by extremely thick paleogene flysch and a post middle eocene continental molasse superimposed on late jurassic or early paleogene troughs and normal vertical offsets of the basement the upper eocene to oligocene basin fill is largely detached from its substratum along a regional detachment in the eocene mud pile thus these thin skinned extensional structures display a piggyback attitude with progressive migration of depocenters overtime and gentle gliding of the sedimentary cover over underlying basement blocks the faulted borders of these late eocene oligocene basins were subsequently reactivated transpressively during late neogene times accounting for the frequent inversion of former oligocene depocenters

buoyancy driven plumes in rotating stratified cross flows plume dependence on rotation turbulent mixing and cross flow strength a three dimensional time dependent convection model is used to describe circulation and property fields in rotating stratified and moving fluids near a point source of heat the study context and consequently model scales are those of chronically discharging hydrothermal vent fields found at submarine ridge crests hydrothermal plumes having distinctive thermal and chemical anomalies have been observed to rise several hundreds of meters above the deep sea floor before being advected away by background cross flows typically of magnitude 1 4 cm s 1 the model is used to study effects of rotation and indicate differences in plumes with respect to variation of subgrid scale turbulence intensity and cross flow strength counterrotating vorticity couplets in all three coordinate directions develop in the lower plume stem at startup and follow the plume to the level of neutral buoyancy for a nonrotational case 0 patterns resemble those previously found for jets injected into homogenous cross flow ambient fluid entrainment into the convecting column is primarily from the upstream side but deflection of background flow around both sides of the rising column is the root of the relative vorticity z couplet in the lower plume turbulence intensity within the buoyant region of the plume and or globally controls smoothness and temporal variability of distal nonbuoyant plume distributions allowing or preventing oscillations of potential temperature for example at background buoyancy frequency n over the range of turbulent mixing studied rise height of plumes did not change appreciably but breadth of plumes counterintuitively increased for decreasing turbulent mixing strength increasing cross flow strength u0 bends model plumes such that rise height u0 0 4 for the two largest values of cross flow for which r the ratio of maximum vertical velocity to u0 took values of 2 8 and 1 0 plumes showed evidence of bifurcation

the path to covis a review of acoustic imaging of hydrothermal flow regimes abstract acoustic imaging of hydrothermal flow regimes started with the incidental recognition of a plume on a routine sonar scan for obstacles in the path of the human occupied submersible alvin developments in sonar engineering acoustic data processing and scientific visualization have been combined to develop technology which can effectively capture the behavior of focused and diffuse hydrothermal discharge this paper traces the development of these acoustic imaging techniques for hydrothermal flow regimes from their conception through to the development of the cabled observatory vent imaging sonar covis covis has monitored such flow eight times a day for several years successful acoustic techniques for estimating plume entrainment bending vertical rise volume flux and heat flux are presented as is the state of the art in diffuse flow detection

flow and mixing in the rift valley of the mid atlantic ridge high levels of diapycnal mixing and geothermal heating near midocean ridges contribute to the buoyancy fluxes that are required to close the global circulation in topographically confined areas such as the deep median valleys of slow spreading ridges these fluxes strongly influence the local hydrography and dynamics data from a segment scale hydrographic survey of the rift valley of the mid atlantic ridge and from an array of current meters deployed there during an entire year are analyzed in order to characterize the dominant hydrographic patterns and dynamical processes comparison with historic hydrographic data indicates that the temporal variability during the last few decades has been small compared to the observed segment scale gradients the rift valley circulation is characterized by inflow from the eastern ridge flank and persistent unidirectional alongsegment flow into a cul de sac therefore most of the water flowing along the rift valley upwells within the segment with a mean vertical velocity 1025 ms 21 the observed streamwise hydrographic gradients indicate that diapycnal mixing dominates the rift valley buoyancy fluxes by more than an order of magnitude in spite of the presence of a large hydrothermal vent field supplying several gigawatts of heat to the water column hydrographic budgets in the rift valley yield diffusivity values of order 5 3 1023 m2 s 21 consistent with estimates derived from statically unstable overturns the largest of which were observed downstream of topographic obstacles in the path of the along segment flow this suggests vertical shear associated with cross sill flows as the dominant contributor to the mechanical mixing in the rift valley

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

parameters of subsurface brines and hydrothermal processes 12 15 months after the 1999 magmatic event at the main endeavor field as inferred from in situ time series measurements of chloride and temperature 1 phase separation at mid ocean ridge hydrothermal systems is a widely distributed frequently occurring process it is highly sensitive to dynamic subsurface pressure and temperature conditions and has a significant impact on chloride concentrations of hydrothermal fluid although vapor phases produced by phase separation are observed in a variety of hydrothermal settings observation of conjugate brines that must be produced concurrently are more rare and the fate of subsurface brines is still not well understood here we use an array of in situ chloride sensors deployed at the main endeavor field on the juan de fuca ridge in the wake of a magmatic event to monitor the behavior of hydrothermal vent effluent with high temporal resolution our results provide evidence of near critical chloride depleted fluids within the crust up to 486 m beneath the seafloor we estimate that a brine reservoir stored beneath the main endeavor field is constrained to temperatures between 131 c and 326 c for chloride concentrations ranging from 6 to 25 wt nacl respectively our data suggest that subsurface fluids and circulation pathways vary widely over spatial scales on the order of meters under these circumstances simultaneous measurements of multiple fluid parameters at a high temporal resolution are essential to understanding subsurface hydrothermal processes associated with magmatic events

characteristics of magma driven hydrothermal systems at oceanic spreading centers 1 we use one and two limb single pass models to de termine vent field characteristics such as mass flow rate q bulk permeability in the discharge zone kd thickness of the conductive boundary layer at the base of the system magma replenishment rate and residence time in the discharge zone data on vent temperature vent field area heat output and the surface area and depth of the subaxial magma chamber amc constrain the models the results give q 100 kg s kd 10 13 m2 and 10 m essentially independent of spreading rate and detailed characteristics of the amc in addition we find no correlation between heat output at individual vent fields and spreading rate or depth to the amc we conclude that high temperature hydrothermal systems are driven by local magma supply rates in excess of that needed for steady state crustal production and that crustal permeability enables hydrothermal circulation to tap magmatic heat regardless of amc depth using data on partitioning of heat flow between focused and diffuse flow we find that 80 90 of the hydrothermal heat output is derived from high temperature fluid even though much of the heat output discharges as low temperature fluid in some cases diffuse flow fluids may exhibit considerable conductive cooling or heating by assuming conservative mixing of diffuse flow fluids at east pacific rise 9 50 n we find that most transport of metals such as fe and mn occurs in diffuse flow and that co2 h2 and ch4 are taken up by microbial activity

alternative interpretations as to the origin of the hydrocarbons of the guajira basin colombia abstract the origins of the hydrocarbon gases recovered from the chuchupa ballena and riohacha fields located in the guajira basin northeast colombia are examined these gases are composed of methane with trace amounts of wet gas components c2 the gases recovered at three onshore seep localities appear to include a thermogenic component as a result of fractionation it is unclear whether they represent pure thermogenic gases or a mixed thermogenic biogenic origin similar to chuchupa an examination of oil microseepage observed in soil samples recovered from the onshore guajira region point to another hydrocarbon system apparently not related to the three gas fields some of these microseeps include fresh nonbiodegraded oils these microseeps did not correlate with either of the tertiary oil families from the sinu uraba basin located to the southwest of the study area or with cretaceous oils from that basin a better correlation was observed with the la luna formation but significant differences remain implying that the source for the microseeps was less calcareous and deposited in a less restricted environment than associated with classical la luna facies this could indicate either a facies change or that a different source unit is present within the region

on the calculation of total heat salt and tracer fluxes from ocean hydrothermal events abstract total heat salt and other tracer masses released during a hydrothermal event are shown to be proportional to but not necessarily equal to volume integrals of resulting water column anomalies proportionality coefficients depend on anomaly definition on background hydrographic and tracer profiles on expansion coefficients of the equation of state at an appropriate pressure and on tracer to heat anomaly ratios at the venting source for gorda ridge event plumes which are described in other papers of this issue volume integrals of conventionally defined heat anomalies underestimate actual released heat by a factor of 2 4 if the discharge is not anomalously saline under certain combinations of hydrographic and source anomaly conditions not unlike those found on the east pacific rise at 10 n the apparent total heat released during an event can be deceivingly zero this analysis also establishes a linear relationship between the ratio of tracer anomaly to heat anomaly at any point in the plume to the same ratio at the source one consequence is that the ratio of anomalous 3 he to heat in gorda ridge event plumes is approximately 2 4 larger in the water column than it is at the source results are independent of the entrainment process involved in event plume formation and they are shown to hold true even for background hydrographic profiles that do not vary linearly with depth

quartz solubility in the two phase region of the nacl h2o system an experimental study with application to the piccard hydrothermal field mid cayman rise

transient infiltration from ephemeral streams a field experiment at the reach scale 1 an infiltration experiment at the stream reach scale was performed to estimate infiltration rates beneath an ephemeral losing stream during streamflow events at a time when the stream was dry a 7 m stream section was dammed upstream and downstream using metal sheets during a 5 day period water was pumped into the isolated section of the stream and the surface water level was maintained at three successive increasing stages the infiltration rate at each water level was thereby equal to the pumping rate required to maintain that water level the advantages of the method are that it samples a much greater area than traditional methods and provides information on infiltration through stream banks as well as through the streambed experimental results provide insight into transient infiltration and recharge processes beneath ephemeral streams although the experiment continued for 5 days infiltration during the first hour accounted for 19 of the total infiltration high transient infiltration rates were also observed following each increase in stream stage experimental infiltration rates were used to calibrate a two dimensional model developed within hydrus which was subsequently used to estimate infiltration associated with a natural flow event in the same stream reach during the natural flow event the total infiltration was 33 greater than would have been estimated assuming steady state infiltration rates dry antecedent moisture content controls the transient infiltration rate and hence increases the total infiltrated volume during flow events but it does not increase the aquifer recharge

constrained circulation at endeavour ridge facilitates colonization by vent larvae understanding how larvae from extant hydrothermal vent fields colonize neighbouring regions of the mid ocean ridge system remains a major challenge in oceanic research1 2 among the factors considered important in the recruitment of deep sea larvae are metabolic lifespan the connectivity of the seafloor topography and the characteristics of the currents3 here we use current velocity measurements from endeavour ridge to examine the role of topographically constrained circulation on larval transport along ridge we show that the dominant tidal and wind generated currents in the region are strongly attenuated within the rift valley that splits the ridge crest and that hydrothermal plumes rising from vent fields in the valley drive a steady near bottom inflow within the valley extrapolation of these findings suggests that the suppression of oscillatory currents within rift valleys of mid ocean ridges shields larvae from cross axis dispersal into the inhospitable deep ocean this effect augmented by plume driven circulation within rift valleys having active hydrothermal venting helps retain larvae near their source larvae are then exported preferentially down ridge during regional flow events that intermittently over ride the currents within the valley

palynology and chronostratigraphy of the upper cretaceous in the subsurface of the barinas area western venezuela palynological and well log analyses of cretaceous strata from southeastern venezuela allow the recognition of third order eustatic cycles and are the basis for a chronostratigraphic framework with a datum approximately every 0 8 m y this definition permits the correlation of events in the local geologic evolution with regionally important sedimentological and tectonic events an early cretaceous marine transgression reached areas north of the andes before 113 ma however according to our framework the transgression extended into the barinas area shortly after 98 ma an interval of relatively low sea level from 95 5 ma to 91 5 ma is represented by oil bearing sandstones and dolomitic limestones a second marine transgression reached the area at approximately 91 5 ma and resulted in the deposition of organic rich clastics that are correlatable with source rocks from areas to the north a major hiatus santonian campanian encompasses approximately 11 m y and probably is related to the emplacement of oceanic rocks in western colombia a younger major hiatus maastrichtian eocene encompasses approximately 26 m y and probably is related to the emplacement of the lara nappes in northern venezuela two other minor intra turonian and intra maastrichtian hiatuses are recognized and encompass approximately 1 5 m y each

bulk properties of hot smoker plumes the hot buoyant fluid from a submarine vent rises as a plume entraining fluid from the stratified ocean until a height is reached where the driving buoyant force vanishes and shortly thereafter the diluted plume fluid intrudes into the ocean interior at its equilibrium depth while a large positive heat flux issues from the vent the potential temperature anomaly of the horizontally spreading fluid at the equilibrium height depends on the oceanic stratification of both salinity and potential temperature and on the salinity of the source fluid at the vent for example in the atlantic ocean the oceanic stratification causes the spreading plume fluid to be cooler and fresher than the surrounding seawater of the same density while in the pacific the spreading fluid is relatively warm here the well known solution for a turbulent plume rising in a linearly stratified environment is used to obtain simple formulae for 1 the potential temperature anomaly of the horizontally spreading fluid 2 the heat flux associated with this injection of diluted vent water at this density level and 3 the nondimensional solution for the evolution of tracer properties e g salinity and potential temperature in the rising plume

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

prediction of petroleum formation the influence of laboratory heating rates on kinetic parameters and geological extrapolations while major variations in predictions of petroleum formation timing are supposed to be related to the burial history of the source rock and the type of organic matter preserved therein it is often ignored that the laboratory techniques used to obtain reliable kinetic parameters for the description of petroleum formation and its extrapolation to natural conditions can be problematic in the present paper bulk petroleum generation by open system programmed temperature pyrolysis of green river shale toarcian shale and westfalian coal samples has been studied comparatively at heating rates of 0 1 0 7 5 0 15 0 and 25 0 k min in order to evaluate the influence of laboratory heating rates on kinetic parameters and geological extrapolations kinetic parameters were calculated from three sets of pyrolytic generation rate versus temperature curves measured at either 0 1 0 7 and 5 0 0 7 5 0 and 15 0 or 5 0 15 0 and 25 0 k min using both the distributed and the tmax shift model frequency factors and dominant activation energies derived from the tmax shift model are found to decrease systematically in going from sets of slow to fast heating rates for type ii and iii kerogens this decrease of kinetic parameters is confirmed by the distributed model for algal kerogens of type i the distributed model cannot be applied the decrease of kinetic parameters results from increasing delay in heat transfer between the inert gas stream and the sample with increasing rate of heating reducing the sample weight can partly but not fully compensate this effect by using the natural maturation series of westphalian coals and toarcian shales it was possible to illustrate that geological extrapolations from slow heating rate experiments fit much better to natural petroleum formation than those from fast heating rates the latter lead to temperature predictions which are too low by 30 40 c which in turn would result in a 1000 m failure when predicting the oil window depth in an average sedimentary basins

anisotropy in seafloor flange slab and crust samples from measurements of permeability and porosity implications for fluid flow and deposit evolution 1 seafloor hydrothermal vents accommodate the convective transfer of fluids from subsurface environments to the oceans in addition to black smoker chimneys a variety of other deposit types form flanges protrude from the sides of edifices as horizontal ledges below which vent fluids pool slabs are hydrothermally silicified layered volcaniclastic deposits crusts are deposits composed of previously deposited material underlain by hot fluids permeability and porosity measurements were conducted on flanges from guaymas basin and the main endeavour vent field slabs from the lucky strike vent field and a crust sample from the trans atlantic geotraverse tag active mound cores taken parallel to textural layers have high permeabilities 10 12 m2 and porosities 30 40 that follow a power law relationship with exponent 1 to 2 cores taken perpendicular to layering have permeabilities from 10 16 to 10 12 m2 and porosities from 20 to 45 with 5 to 8 the two distinct trends result from the heterogeneity of textural layers within these deposits microstructural observations show large variations in grain packing and pore distributions between layers consistent with flow perpendicular to layering being more susceptible to changes in permeability that result from mineral precipitation than flow parallel to layering these results imply that the primary flow direction in these deposits is parallel to layering whereas flow perpendicular to layering is more restricted quantification of anisotropic permeability provides important constraints for determination of fluid flux from these layered deposits and temperatures chemistry and availability of nutrients to organisms living in and at exteriors of deposits

plankton percentage of the foraminiferal fauna in seafloor samples from the australian irian jaya continental margin eastern indonesia abstract plankton percentages of the formainiferal fauna in seafloor samples from the australian irian jaya continental margin show a consistent relationship with waterdepth based on this relationship a regional model has been constructed to estimate paleowaterdepth from the plankton percentage of fossil foraminiferal fauna in addition to paleobathymetric information obtained from the study of benthic foraminifera this model can be applied to reconstruct the paleoenvironment of late cenozoic sections sampled on the eastern indonesian islands

quantitative estimate of heat flow from a mid ocean ridge axial valley raven field juan de fuca ridge observations and inferences a systematic heat flow survey using thermal blankets within the endeavour segment of the juan de fuca ridge axial valley provides quantitative estimates of the magnitude and distribution of conductive heat flow at a mid ocean ridge with the goal of testing current models of hydrothermal circulation present within newly formed oceanic crust thermal blankets were deployed covering an area of 700 by 450 m in the raven hydrothermal vent field area located 400 m north of the main endeavour hydrothermal field a total of 176 successful blanket deployment sites measured heat flow values that ranged from 0 to 31 w m 2 approximately 53 of the sites recorded values lower than 100 mw m 2 suggesting large areas of seawater recharge and advective extraction of lithospheric heat high heat flow values were concentrated around relatively small hot spots integration of heat flow values over the raven survey area gives an estimate of conductive heat output of 0 3 mw an average of 0 95 w m 2 over the survey area fluid circulation cell dimensions and scaling equations allow calculation of a rayleigh number of approximately 700 in layer 2a the close proximity of high and low heat flow areas coupled with previous estimates of surficial seafloor permeability argues for the presence of small scale hydrothermal fluid circulation cells within the high porosity uppermost crustal layer of the axial seafloor

sources and fluxes of hydrothermal heat chemicals and biology within a segment of the mid atlantic ridge we have conducted a segment wide study of the chemical biological and thermal effects of hydrothermal activity in a bathymetrically enclosed 50 km long segment of the mid atlantic ridge at 29 n our study involved long term monitoring of bottom current speeds and temperatures coupled with snap shot surveys of the concentrations of hydrothermal shrimp manganese and particulate plumes occupying the water column enclosed by the axial valley these data are combined with the calculated volume transport rates for the segment and the results compared with the heat and manganese flux from the broken spur vent field located in the center of the segment our current meter data show that the basin like bathymetry acts to restrict and control flow of water warm and shallow water exported from the segment is replaced by colder and deeper water water column profiles showed an increase in temperature of the water within the broken spur segment compared with background stations located outside the ridge axis the average refresh rate for the water column enclosed by the segment was found to be about 262 days from these data we calculate that the segment wide flux of juvenile shrimp is 20 106 individuals per year we show that the flux of manganese exported at a rate of 5 6 mol s is matched by input from high temperature effluent discharge at the broken spur vent field we also calculate that the minimum average heat flux exported from the segment is about 275 mw of this more than 90 is pervasively dissipated throughout the segment floor by conductively heated sea water or simple thermal conduction that carries little or no manganese to the water column the remaining 10 or less of the heat flux results from localized manganese rich high temperature hydrothermal venting

a turbulent convection model with an observational context for a deep sea hydrothermal plume in a time variable cross flow 1 a turbulent convection model for a hydrothermal fluid discharging into a tidally modulated stratified cross flow is used to investigate time variable conditions in plumes such as the one rising from dante a sulfide mound at 2175 m depth on the endeavour segment of the juan de fuca ridge that plume is the consequence of the coalescence of 10 or more small individual plumes from chimneys discharging hot salt diminished fluid into the near bottom ocean at dante the discharge encounters ambient horizontal currents with speeds oscillating from near zero to a maximum of 7 cm s 1 speeds which can bend a plume more than 45 from the vertical model results are compatible with field measurements of the plume footprint size and vertical velocity both 20 m above the source when earlier estimates for dante s heat flux of 50 mw drive the convection the small scale short period variability of velocities and properties distributions observed in the field is mimicked in model results plumes pool above a source during periods of weak cross flows but stream away from the source with more diluted concentrations and lower rise heights at other times plume distributions at identical cross flow speeds differ whether the flow is accelerating or decelerating small changes in background hydrographic profiles create differences in rise heights comparable to those caused by large changes in source buoyancy flux if put into an entrainment context results suggest an entrainment coefficient eff that varies from 0 11 to 0 025 with increasing height 2 76 m above the source

cretaceous black shales of venezuelan andes preliminary results on stratigraphy and paleoenvironmental interpretations abstract this paper deals mainly with the late cretaceous la luna formation on the venezuelan andean platform the studied area the so called transversale de barquisimeto is located at the contact zone between the andes of merida and allochthonous slabs thrusted from the caribbean domain and is crosscut by a major active transform fault the bocono fault which is part of the contact zone between the caribbean and south american plates the la luna formation is made of dark organic rich laminated limestones and shales and though always appearing with black shale facies is different in the areas located in the north or in the south of the bocono fault we provide here some new information about the biostratigraphic frame of the la luna formation and of the overlying colon formation in the studied area the depositional environment of the la luna formation was certainly rather shallow near storm wave base and stratified during deposition of la luna formation dysaerobic to anoxic conditions prevailed which may be linked with a regional anoxic event perhaps related to seasonal upwelling along the northern coast of south america during late cretaceous time

neogene block tectonics of eastern turkey and northern south america continental applications of the finite difference method continental plate boundary zones are generally wide diffuse zones of deformation within which in the upper 5 to 15 km may be recognized blocks which are bounded by fault zones within which strain is highly concentrated and along which slip rates are fairly high 2 30 m ma 1 these blocks may be irregular flakes defined by older crustal inhomogeneities of an upper brittle crust below which strain occurs in a ductile and more homogeneous lower crust with examples from the convergent plate boundary zone of eastern turkey and the southern caribbean plate boundary zone of northern south america we use plate slip rates and trends and slip rates of faults to construct block vector diagrams to deduce the sums of relative motion among block mosaics slip rates and trends of ill defined block boundaries and the extent to which blocks are internally strained

a simulation of mid cretaceous climate a series of general circulation model experiments utilizing genesis have been completed for the mid cretaceous based on geography variable atmospheric carbon dioxide concentrations 2 to 6 times present day concentrations and variable poleward oceanic heat flux 6 to 1 2 1015 w increased from present day by combining all three major variables co2 geography and oceanic heat flux the distribution of mid cretaceous temperatures can be achieved in the simulations increased co2 is required to promote global warmth and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of co2 four times present day co2 with 1 2 1015 w provided the best match to the distribution of mid cretaceous data the best match to the cretaceous observations was achieved with a globally averaged surface temperature increase of 6 2 c at the lower end of past estimates of mid cretaceous warmth this value may be a better estimate of mid cretaceous global warming finally the model experiments can be used to provide a paleocalibration of the global warming expected for a doubling of atmospheric carbon dioxide the best estimates for the mid cretaceous appear to be a 2 5 to 4 0 c sensitivity in the mid to upper range of the sensitivity of current climate models used to assess future global change

magnitude and variance of near bottom horizontal heat flux at the main endeavour hydrothermal vent field 1 we characterize hydrothermal plumes and hydrography within the axial valley of the endeavour segment juan de fuca ridge northeast pacific using data from an autonomous underwater vehicle a lowered ctd and two current meter moorings our survey of the main endeavour hydrothermal vent field mef shows hydrographic variability on scales as short as 20 m and 10 min within the 100 m deep axial valley the mean flow is 1 5 cm s to the north and tidal oscillations have 5 cm s amplitude combining the mean flow with an estimate of the difference in average temperature observed north and south of mef we find that the net along axis horizontal heat flux has a mean magnitude of 8 42 mw an advection diffusion model forced by local current records explains the observed temporal hydrographic variability and shows that mean horizontal flux variance is correspondingly high standard deviation 63 mw a steady state mef heat budget constrained by the observed horizontal flux and measurements of vertical fluxes from other studies has two implications the mef heat flux is partitioned about equally between diffuse and focused vents and about 85 of the flux from diffuse plumes is entrained by focused plumes

lower cretaceous cogollo group maracaibo basin venezuela sedimentology diagenesis and petrophysics the cogollo group consisting mainly of carbonates was deposited over a broad and irregular stable shelf high energy shallow normal marine environments are represented by grainstone packstone bars interbar deposits and pelecypod biostromes low energy restricted shallow marine environments are shown by back bar to tidal flat deposits including lagoonal sediments rich in organic matter shales and glauconitic and quartzitic sandstones on the basis of lithologic markers the cogollo group in central lake maracaibo is subdivided into a series of rock units which indicate two major lithologic environmental subdivisions the lower cogollo is characterized by a combination of carbonates and siliciclastics derived from the guayana shield and associated highs the upper cogollo is represented by cleaner carbonates deposited under higher energy conditions grainstone packstone bars are common together with pelecypod biostromes and muddy lagoonal sediments cogollo carbonate production rates kept pace with subsidence and therefore are mostly a build up type diagenetic models describing the porosity history of the grainstone bars and pelecypod biostromes when superimposed on the depositional model indicate carbonate fabric units processes which destroyed reservoir space mainly cementation were important hence present porosity and permeability values are low thgr 12 k 3 2 md siliciclastic and dolomitic intervals have some reservoir potential detailed correlation between characteristics of the carbonate fabric units and well log expressions is hampered by the complex mineral composition and generally poor texture related porosity and permeability properties of the units core log correlations of the cogollo group show three broad subdivisions 1 shales marls 2 dirty ductile carbonates sandstones and 3 clean brittle carbonates sandstones in order of increasing susceptibility to fracturing this petrophysical subdivision in combination with the environmental model may be of value in future regional studies aimed at tracing rock units with matrix and or fracture related reservoir potential within the cogollo group diagenetic processes were ongoing during hydrocarbon migration thus the modest texture related reservoir space in the carbonates was and still is able to store the oil local fractures and leached intervals in the carbonates allow oil to drain and be produced thus fractures form a significant element in cogollo production capacity

quantifying diffuse and discrete venting at the tour eiffel vent site lucky strike hydrothermal field 1 the relative heat carried by diffuse versus discrete venting of hydrothermal fluids at mid ocean ridges is poorly constrained and likely varies among vent sites estimates of the proportion of heat carried by diffuse flow range from 0 to 100 of the total axial heat flux here we present an approach that integrates imagery video and temperature measurements to accurately estimate this partitioning at a single vent site tour eiffel in the lucky strike hydrothermal field along the mid atlantic ridge fluid temperatures photographic mosaics of the vent site and video sequences of fluid flow were acquired during the bathyluck 09 cruise fall 2009 and the momarsat 10 cruise summer 2010 to the lucky strike hydrothermal field by the rov victor6000 aboard the french research vessel the pourquoi pas ifremer france we use two optical methods to calculate the velocities of imaged hydrothermal fluids 1 for diffuse venting diffuse flow velocimetry tracks the displacement of refractive index anomalies through time and 2 for discrete jets particle image velocimetry tracks eddies by cross correlation of pixel intensities between subsequent images to circumvent video blurring associated with rapid velocities at vent orifices exit velocities at discrete vents are calculated from the best fit of the observed velocity field to a model of a steady state turbulent plume where we vary the model vent radius and fluid exit velocity our results yield vertical velocities of diffuse effluent between 0 9 cm s 1 and 11 1 cm s 1 for fluid temperatures between 3 c and 33 5 c above that of ambient seawater and exit velocities of discrete jets between 22 cm s 1 and 119 cm s 1 for fluid temperatures between 200 c and 301 c above ambient seawater using the calculated fluid velocities temperature measurements and photo mosaics of the actively venting areas we calculate a heat flux due to diffuse venting from thin fractures of 3 15 2 22 mw discrete venting of 1 07 0 66 mw and by incorporating previous estimates of diffuse heat flux density from tour eiffel diffuse flux from the main sulfide mound of 15 6 mw we estimate that the total integrated heat flux from the tour eiffel site is 19 82 2 88 mw and that the ratio of diffuse to discrete heat flux is 18 we discuss the implication of these results for the characterization of different vent sites within lucky strike and in the context of a compilation of all available measurements of the ratio of diffuse to discrete heat flux

effects of wadi flood hydrograph characteristics on infiltration abstract the hydrograph characteristics of ephemeral flood flows determine channel bed infiltration losses and subsequent groundwater recharge the present numerical study demonstrates that cumulative channel bed infiltration under time varying surfacewater depth is primarily a function of the infiltration opportunity time and the mean depth of water the temporal distribution of the surfacewater depth is relatively insignificant overall the infiltration process appears to damp heavily the differences in the stage hydrograph

mathematical modeling of diffuse flow in seafloor hydrothermal systems the potential extent of the subsurface biosphere at mid ocean ridges abstract we describe a variety of one and two dimensional mathematical modeling approaches to characterizing diffuse flow circulation at mid ocean ridge hydrothermal systems the goal is to estimate the potential extent of the sub seafloor microbial biosphere based on subsurface contours of the 120 c isotherm as determined from the various models the models suggest that the sub seafloor depth for microbial life may range from less than 1 m in some places to the thickness of crustal layer 2a of 500 m in others this depth depends primarily on how diffuse flow is driven the 120 c isotherm tends to be much deeper if diffuse flow is induced as boundary layer flow near high temperature plumes than if it results from conductive cooling or mixing near the seafloor because the heat flow alone may not allow identification of the flow regime in the subsurface we highlight the use of chemical tracers as an additional constraint that sheds light into the flow and reaction patterns associated with vents we use thermodynamic modeling which connects the temperature of the diffuse fluid to its chemical composition as the temperature composition relationships differ for mixing versus conductive heating and cooling the fluid geochemistry can shed light on subsurface transport using methane as an example the geochemical models indicate subsurface microbial methane production and consumption in different regions of the vent field near epr 9 50 n

palaeoecology palaeogeography and depositional environments of upper cretaceous rocks of western venezuela abstract the end of the early cretaceous in northern south america was marked by regional palaeoceanographic change in western venezuela this change was highlighted near the end of the albian by drowning of the maraca formation shallow water carbonate platform regional marine transgression continued during the cenomanian and turonian in western venezuela with drowning of the more southerly guayacan member capacho and escandalosa formations carbonate platform deposition of organic carbon rich intervals of the la luna and navay formations occurred unconformably on maraca formation and guayacan member shallow water carbonates and continued through the early santonian during this interval the maracaibo and barinas apure basins were characterized by low oxygen or anoxic bottom water conditions away from the basin margins deposition of organic carbon lean upper la luna and navay formation strata show that bottom water oxygen content increased from the late santonian through the end of the cretaceous the siliceous and phosphatic late santonian to early maastrichtian tres esquinas member and the glauconitic late campanian to early maastrichtian socuy member both of the la luna formation represent the final phase of la luna deposition in the maracaibo basin tectonic uplift in eastern colombia during the campanian and maastrichtian caused progradation of the colon mito juan and burguita formation deltas and eventual infilling of the maracaibo and barinas apure basins

complementary acoustic and optical methods for characterization of diffuse venting gas seeps and biota distributions at hydrothermal systems a case study at kick em jenny volcano grenada west indies abstract quantitatively assessing the impact of hydrothermal circulation on geological and biological systems in submarine environments requires accurate characterization of biota fluid flow and in many shallow systems gas discharge in a single vent field surface expressions of hydrothermal venting and vent biology are often widespread presenting a significant technical challenge to such characterizations typically attempts to overcome this challenge involve extrapolation of point measurements to estimate field scale parameters extrapolation introduces large uncertainties however we present a case study at the kick em jenny volcano grenada west indies that jointly applies a set of complementary acoustic and optical measurement methods to significantly reduce uncertainty in field scale flux estimates of diffuse venting bubble streams and distributions of microbial mats two classes of rov based methods are used 1 survey level techniques for accurately locating fluid and gas discharge across entire vent fields and 2 local techniques that accurately measure fluid or gas fluxes just above a vent orifice survey level techniques include a structured light laser system to locate active diffuse venting and biological mats and a high resolution downward facing multibeam system that can resolve individual bubble streams separated by only centimeters local techniques include processing of stereo imagery to determine bubble stream parameters rise rate bubble size and application of the diffuse flow velocimetry technique to determine upwelling rates of diffuse effluent joint application of these methods provides a several times increase in the number of identified bubble streams relative to ship board systems and a difference of up to 40 times in field scale diffuse volume flux estimates relative to currently available techniques

aptian anoxia in the pacific basin marine strata of aptian age in the pacific basin include two distinct levels that represent episodes during which sediments rich in organic carbon were deposited both episodes lasted less than 1 m y as revealed in strata deposited atop submerged topographic highs one unusually widespread episode of early aptian age 117 5 ma correlates with coeval units in europe and thus is analogous to the cenomanian turonian oceanic anoxic event in its short duration and wide geographic extent the second episode of late aptian age 116 5 ma is restricted to allochthonous pelagic deposits in the franciscan complex of california these results support the concept of widespread and narrowly synchronous anoxic events further they show that organic carbon deposition in the pacific basin took place in intermediate water oxygen minimum zones and thus differed in the mode of deposition and hence paleoceanography from that in other middle cretaceous ocean basins

dissolved carbon species in associated diffuse and focused flow hydrothermal vents at the main endeavour field juan de fuca ridge phase equilibria and kinetic constraints 1 despite significant advances in the understanding of hydrothermal processes at mid ocean ridges the linkage between focused flow and diffusively flowing vent fluids has remained elusive here we report the distribution of dissolved carbon species in fluids issuing from associated low moderate and high temperature vent systems collected in 2005 at the main endeavour field mef juan de fuca ridge excess co aq measured in the moderate temperature diffuse flow fluids indicates redox disequilibria between co aq and co2 aq suggesting hydrothermal circulation of short residence time in near seafloor mixing zones according to geochemical modeling the chemical variability of mef fluids is consistent with a combination of conductive cooling reaction transport and subsequent seawater mixing of a single source fluid the similar distribution of c1 c3 alkanes observed in diffuse and focused flow fluids likely indicates a minimal fingerprint of biological and methanogenic metabolism on organic fluxes consistent with a possible short lived hydrothermal near seafloor circulation accordingly dissolved carbon species in low temperature vent fluids can serve as geochemical proxies to distinguish the extent of compositional change in subsurface microbial habitats in the mef hydrothermal fluids and elsewhere part of this reflects conditions unique to the near surface diffuse flow environment but the flux of components from deeper seated hydrothermal processes is important as well in comparison with earlier measurements 1999 and 2000 of high temperature vent fluids at mef the 2005 data set exhibits lower li cl ratios and h2 aq concentrations indicative of higher fluid rock mass ratios and more oxidizing and or lower temperature conditions respectively

reconciling temperatures of metamorphism fluid fluxes and heat transport in the upper crust at intermediate to fast spreading mid ocean ridges 1 current models of the mineralogical and chemical modification of the crust within mid ocean ridge hydrothermal systems at intermediate to fast spreading ridges are difficult to reconcile with the temperature distribution predicted by the required fluid fluxes in particular the sharp increase in metamorphic grade passing down from the lavas into the sheeted dike complex places important constraints on the flow of fluid through the crust this distribution of metamorphic temperatures has typically been discussed in terms of a step in permeability in the downwelling limb of a single pass convection cell simple modeling of this system shows that downwelling fluid cools the crust too efficiently for high temperature metamorphism of the upper dikes to occur in the downflow zone in fact temperatures throughout most of the sheeted dike complex are too high three alternative models are considered fluid rock reaction during the cooling of each dike from magmatic temperatures is difficult to reconcile with cooling rate estimates for dikes reaction rates required to grow metamorphic minerals and the relatively constant composition of many hydrothermal vents metamorphism during reheating of the crust after fluid flow slows or stops is difficult to reconcile with the required fluid fluxes during metamorphism based on the sr isotopic composition of the sheeted dike complex and cannot produce high enough temperatures in the upper dikes and low temperatures in the lower lavas in contrast fluid rock reaction in the sheeted dike complex as hot fluids migrate upward after being heated by the underlying magma source appears to be consistent with the data in this model downwelling seawater cools the recharge zone and the fluid only becomes hot enough to significantly alter the crust once it approaches the conductive boundary layer overlying the magma chamber metamorphism of the sheeted dike complex then largely occurs in the discharge zone

source rocks and oil families southwest maracaibo basin catatumbo subbasin colombia an extensive evaluation of organic source facies the application of hydrocarbon geochemistry and integrated basin modeling of the southwest portion of the maracaibo basin in colombia referred to as the catatumbo subbasin indicate 1 multiple organic rich horizons occur within the cretaceous and paleocene sections 2 most of the reservoired oil and gas was sourced locally from cretaceous marine carbonate facies by means of lateral and vertical migration 3 two subfamilies of cretaceous oils are recognized that reflect different source facies within the cretaceous section and different maturation and migration histories 4 oil and gas present in the southern catatumbo subbasin indicate a contribution from paleocene terrestrial source facies that required westerly migration from a source area in venezuela possibly within the north andean foredeep and 5 oil generation from cretaceous source rocks began in the oligocene and peak generation occurred in the late miocene these key conclusions are based on source rock analyses of 365 rock samples from eight wells gas chromatography mass spectrometry and isotope and bulk composition analyses from nine rock extracts and seven oil samples

transmission losses infiltration and groundwater recharge through ephemeral and intermittent streambeds a review of applied methods summary aquifer recharge through ephemeral streambeds is believed to be a major source of groundwater recharge in arid areas however comparatively few studies quantify this streamflow recharge this review synthesizes the available field based aquifer recharge literature from arid regions around the world seven methods for quantifying ephemeral and intermittent stream infiltration and aquifer recharge are reviewed controlled infiltration experiments monitoring changes in water content heat as a tracer of infiltration reach length water balances floodwave front tracking groundwater mounding and groundwater dating the pertinent temporal and spatial scales as well as the advantages and limitations of each method are illustrated with examples from the literature comparisons between the methods are used to highlight appropriate uses of each field method with emphasis on the advantages of using multiple methods within a study in order to avoid the potential drawbacks inherent in any single method research needs are identified including quantitative uncertainty analysis long term data collection and analysis understanding of the role of riparian vegetation and reconciliation of transmission losses and infiltration estimates with actual aquifer recharge

effective petroleum source rocks of the world stratigraphic distribution and controlling depositional factors six stratigraphic intervals representing one third of phanerozoic time contain petroleum source rocks that have provided more than 90 of the world s discovered original reserves of oil and gas in barrels of oil equivalent the six intervals are 1 silurian generated 9 of the world s reserves 2 upper devonian tournaisian 8 of reserves 3 pennsylvanian lower permian 8 of reserves 4 upper jurassic 25 of reserves 5 middle cretaceous 29 of reserves and 6 oligocene miocene 12 5 of reserves this uneven distribution of source rocks in time displays no obvious cyclicity and the factors that controlled the formation of source rocks vary from interval to interval maps that show facies structural forms and petroleum source rocks were prepared for this study analysis of the maps indicates that several primary factors controlled the areal distribution of source rocks their geochemical type and their effectiveness i e the amounts of discovered original conventionally recoverable reserves of oil and gas generated by these rocks these factors are geologic age paleolatitude of the depositional areas structural forms in which the deposition of source rocks occurred and the evolution of biota the maturation time of these source rocks demonstrates that the majority of discovered oil and gas is very young almost 70 of the world s original reserves of oil and gas has been generated since the coniacian and nearly 50 of the world s petrole m has been generated and trapped since the oligocene the term petroleum as used in this study includes oil gas condensate and gas but does not include bitumen and other solid and semisolid oil derivatives

modeling the effects of a time dependent wetted perimeter on infiltration from ephemeral channels the effects of a time dependent wetted perimeter on infiltration from ephemeral stream channel cross sections are explored using a conceptually simple mathematical model the model is based on the assumptions of vertical soil moisture flow and the validity of the green ampt model for vertical infiltration by using a simple channel geometry an analytic solution is found for the case in which the gravitational component of soil moisture flow may be neglected an efficient accurate numerical technique provides approximate solutions in the general case application of the model demonstrates that cross sectional infiltration that is infiltration per unit length of channel is a complex function of soil properties channel geometry and hydrograph shape for the channel geometry considered the direct effects of variable water pressure at the ground surface are overshadowed by the effects of variation in the wetted perimeter with the result that the temporal variation in infiltration rate is quite unlike that which would be predicted assuming ponded infiltration alone

influence of subsurface biosphere on geochemical fluxes from diffuse hydrothermal fluids hydrothermal vents along mid ocean systems host unique highly productive biological communities based on microbial chemoautotrophy that thrive on the sulphur metals nitrogen and carbon emitted from the vents into the deep ocean geochemical studies of vents have centred on analyses of high temperature focused hydrothermal vents which exhibit very high flow rates and are generally considered too hot for microbial life geochemical fluxes and metabolic activity associated with habitable lower temperature diffuse fluids remain poorly constrained as a result little is known about the extent to which microbial communities particularly in the subsurface influence geochemical flux from more diffuse flows here we estimate the net flux of methane carbon dioxide and hydrogen from diffuse and focused hydrothermal vents along the juan de fuca ridge using an in situ mass spectrometer and flowmeter we show that geochemical flux from diffuse vents can equal or exceed that emanating from hot focused vents notably hydrogen concentrations in fluids emerging from diffuse vents are 50 to 80 lower than predicted we attribute the loss of hydrogen in diffuse vent fluids to microbial consumption in the subsurface and suggest that subsurface microbial communities can significantly influence hydrothermal geochemical fluxes to the deep ocean

structure temporal evolution and heat flux estimates from the lucky strike deep sea hydrothermal field derived from seafloor image mosaics 1 here we demonstrate with a study of the lucky strike hydrothermal field that image mosaicing over large seafloor areas is feasible with new image processing techniques and that repeated surveys allow temporal studies of active processes lucky strike mosaics generated from 56 000 images acquired in 1996 2006 2008 and 2009 reveal the distribution and types of diffuse outflow throughout the field and their association with high temperature vents in detail the zones of outflow are largely controlled by faults and we suggest that the spatial clustering of active zones likely reflects the geometry of the underlying plumbing system imagery also provides constraints on temporal variability at two time scales first based upon changes in individual outflow features identified in mosaics acquired in different years we document a general decline of diffuse outflow throughout the vent field over time scales up to 13 years second the image mosaics reveal broad patches of seafloor that we interpret as fossil outflow zones owing to their association with extinct chimneys and hydrothermal deposits these areas encompass the entire region of present day hydrothermal activity suggesting that the plumbing system has persisted over long periods of time loosely constrained to hundreds to thousands of years the coupling of mosaic interpretation and available field measurements allow us to independently estimate the heat flux of the lucky strike system at 200 to 1000 mw with 75 to 90 of this flux taken up by diffuse hydrothermal outflow based on these heat flux estimates we propose that the temporal decline of the system at short and long time scales may be explained by the progressive cooling of the amc without replenishment the results at lucky strike demonstrate that repeated image surveys can be routinely performed to characterize and study the temporal variability of a broad range of vent sites hosting active processes e g cold seeps hydrothermal fields gas outflows etc allowing a better understanding of fluid flow dynamics from the sub seafloor and a quantification of fluxes

late cretaceous upwelling and anoxic sedimentation in northwestern south america abstract black shales and bituminous limestones were widely deposited in northwestern south america during the maximum transgression of late cretaceous seas these cenomanian to santonian campanian anoxic sediments are distributed in two main subprovinces thick chert and phosphorite accumulated in the trough subprovince landward of a possibly partially emergent cordillera central colombia only minor intercalations of chert were deposited in the platform subprovince lying northward in the maracaibo basin northwestern venezuela faunal evidence depauperate benthic fauna planktic foraminiferal assemblages high dominance clupeoid fish assemblages and sedimentological evidence suggest anoxic condition prevailed throughout the region probably the result of dynamic upwelling in the trough subprovince but the reflection of a global anoxic event within the platform subprovince

establishing a new era of submarine volcanic observatories cabling axial seamount and the endeavour segment of the juan de fuca ridge abstract at least 70 of the volcanism on earth occurs along the 65 000 km network of mid ocean ridge mor spreading centers within these dynamic environments the highest fluxes of heat chemicals and biological material from the lithosphere to the hydrosphere occur during volcanic eruptions however because underwater volcanoes are difficult and expensive to access researchers are rarely if ever in the right place at the right time to characterize these events therefore our knowledge is limited about the linkages among hydrothermal chemical and biological processes during seafloor formation and crustal evolution to make significant advancements in understanding the evolution of mor environments the united states and canada have invested in the first plate scale submarine cabled observatory linked through the global internet spanning the juan de fuca tectonic plate these two networks include 1700 km of cable and 14 subsea terminals that provide 8 10 kw power and 10 gbs communications to hundreds of instruments on the seafloor and throughout the overlying water column resulting in a 24 7 365 presence in the oceans data and imagery are available in real to near real time the initial experimental sites for monitoring volcanic processes include the mor volcanoes called axial seamount and the endeavour segment that are located on the juan de fuca ridge axial a hot spot influenced seamount is the most robust volcano along the ridge rising nearly 1400 m above the surrounding seafloor and it has erupted twice in the last 15 years in contrast the endeavour segment is characterized by more subdued topography with a well defined axial rift and it hosts one of the most intensely venting hydrothermal systems known a non eruptive spreading event lasting 6 years was documented at endeavour between 1999 and 2005 hydrothermal venting intensity chemistry and temperature as well as associated biological communities at both sites were significantly perturbed by the magmatic and intrusive events this paper presents the similarities and differences between the axial and endeavour volcanic systems and identifies reasons why they are ideal candidates for comparative studies the u s has made a 25 year commitment for sustained observations using the cabled infrastructure the highly expandable nature of submarine optical networking will allow for the future addition of novel experiments that utilize ever evolving advancements in computer sciences robotics genomics and sensor miniaturization comprehensive modeling of the myriad processes involved will continue to assimilate and integrate growing databases yielding a new understanding of integrated processes that create the seafloor in the global ocean basins

prospecting for hydrothermal vents using moored current and temperature data axial volcano on the juan de fuca ridge northeast pacific abstract tidal and inertial currents and profuse hydrothermal discharge at recently erupted axial volcano juan de fuca ridge cause relatively large and rapid temperature t changes in the near bottom water column measurements show short term t variations of as much as 0 13 c at 30 m and 0 18 c at 150 m above bottom and currents that have strong tidal components and means of 3 5 cm s 1 locations and magnitudes of the hydrothermal sources leading to the observed t variations have been inferred via an inverse calculation results imply noncongruent source regions around the mooring site for plumes from low and high buoyancy flux sources water column and seafloor observations in the volcano s caldera region generally support the distribution of source types and sites inferred a high buoyancy flux ephemeral venting site unexpected on the eastern shoulder of the volcano is also indicated by the inverse calculation and supported by water column survey data over the o 10 km2 calculation region heat

near field variability of the tag non buoyant plume 26 n mid atlantic ridge we report the initial results of a nine hour monitoring of the non buoyant plume above the tag hydrothermal vent field at 26 n on the mid atlantic ridge a ctd conductivity temperature and pressure and nephelometer particle sensor were continuously raised and lowered through the non buoyant plume for nine hours at a site situated 100 m south of the hydrothermal mound this method permits a detailed record of the variability of the non buoyant plume close to the vent field to be made our results show that the particulate maximum of the non buoyant plume appears 150 m lower in the water column at the start and end of the record compared with profiles recorded towards the middle of the record a corresponding structure also appears in the temperature and salinity records with the result that the plume particle maximum resides on the 27 8035 isopycnal throughout modelling of the rise height of an axisymmetric plume can only account for 95 m of the variability in the final level of neutral buoyancy plume bending due to currents is a likely explanation for the recorded temporal variability

observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar 2 we present a 26 day time series october 2010 of physical properties volume flux flow velocity expansion rate of a vigorous deep sea hydrothermal plume measured using our cabled observatory vent imaging sonar covis which is connected to the northeast pacific time series underwater experiment canada cabled observatory at the main endeavour field on the juan de fuca ridge covis quantitatively monitors the initial buoyant rise of the plume from 5 m to 15 m above the vents the time series exhibits temporal variations of the plume vertical volume flux 1 93 5 09 m3 s centerline vertical velocity component 0 11 0 24 m s and expansion rate 0 082 0 21 m m these variations have major spectral peaks at semidiurnal 2 cycle day and inertial oscillation 1 5 cycle day frequencies the plume expansion rate average 0 14 m m is inversely proportional to the plume centerline vertical velocity component coefficient of determination r2 0 5 this inverse proportionality as well as the semidiurnal frequency indicates interaction between the plume and ambient ocean currents consistent with an entrainment of ambient seawater that increases with the magnitude of ambient currents the inertial oscillations observed in the time series provide evidence for the influence of surface storms on the dynamics of hydrothermal plumes

heat flux from black smokers on the endeavour and cleft segments juan de fuca ridge we have estimated the heat flux from black smoker vents on the juan de fuca ridge to evaluate their importance for heat transfer from young oceanic crust the velocity and temperature of smoker effluent were measured from the manned submersible alvin within a few centimeters of vent orifices using a turbine flowmeter with an attached temperature probe exit velocity was calculated from a simple plume model and vent orifices were measured in photographs and video records the estimated power output from smokers alone is 49 13 mw for the plume site vent 1 and vent 3 on the southern cleft segment near 45 n 364 73 mw for the main vent field on the endeavour segment near 48 n and 122 61 mw for the tubeworm field 2 km north the estimates for the cleft and tubeworm fields could be too low because of undiscovered vents these values constitute only 4 to 14 of the total advective heat flux estimated for these vent fields from measurements in the nonbuoyant plume and of diffuse flow at the seafloor indicating that most of the heat advected at these hydrothermal vent sites is carried by diffuse rather than focused flow values for individual smokers vary from 0 1 to 94 mw with an average of 6 2 mw at the endeavour field and 3 1 mw at the cleft field our estimates agree well at all scales with those of bemis et al 1993 based on measurements made during the same dives in some cases simultaneously up to 50 m high in the buoyant plume the good agreement between the two techniques implies that little diffuse flow at either high or low temperature is incorporated into the buoyant plumes generated by smokers at these sites velocity temperature measurements at vents excavated by alvin could not be modeled successfully suggesting that vent structures may grow in equilibrium with the force of the exiting water such that orifice size is determined by volume flux at the endeavour field the heat flux is focused by faults

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

geothermal heat flux from hydrothermal plumes on the juan de fuca ridge thesis m s massachusetts institute of technology dept of ocean engineering and woods hole oceanographic institution 1991

locating hydrothermal vents by detecting buoyant advected plumes an improved method of detecting buoyant hydrothermal plumes and locating their source vents is introduced plumes are detected by computing fluid stability from conductivity temperature and depth measurements acquired during navigated towed vertically oscillating casts over the endeavour segment of the juan de fuca ridge for each instability detected the maximum range to its hydrothermal source is estimated by multiplying a theoretical plume equilibration time by a measured current velocity using an estimate of current direction the method reliably locates plume sources where they are known to exist in all of the focused vent fields mapped by submersible and in several isolated diffuse flow sites the method generates a distribution of hydrothermal sources that is more consistent with variations in surface permeability than with circulation cells spaced evenly along a uniformly permeable axis axial instabilities are nearly continuous along the heavily fissured and fractured western wall of the axial valley beyond the axial valley instabilities evidence that hydrothermal upflow penetrates the outer slopes of the ridge crest probably along a boundary between sheet and pillow flows