calculations on the thermal conditions around a salt diapir temperature modeling around the vejrum salt structure in denmark shows that the heat flow near the top is twice the regional heat flow the temperature in the vicinity of the top of the diapir is thus anomalously high overlying permeable formations could therefore be attractive for geothermal energy exploitation a negative temperature anomaly of 20 c is calculated around the root of the salt body comparisons between calculated and measured temperatures are used to test the model it is shown that measurements of heat flow or temperature gradients in wells penetrating the region of groundwater circulation could be used in identification of salt diapirs

glacier changes in southeast alaska and northwest british columbia and contribution to sea level rise 1 the digital elevation model dem from the 2000 shuttle radar topography mission srtm was differenced from a composite dem based on air photos dating from 1948 to 1987 to determine glacier volume changes in southeast alaska and adjoining canada srtm accuracy was assessed at 5 m through comparison with airborne laser altimetry and control locations measured with gps glacier surface elevations lowered over 95 of the 14 580 km2 glacier covered area analyzed with some glaciers thinning as much as 640 m a combination of factors have contributed to this wastage including calving retreats of tidewater and lacustrine glaciers and climate change many glaciers in this region are particularly sensitive to climate change as they have large areas at low elevations however several tidewater glaciers that had historically undergone calving retreats are now expanding and appear to be in the advancing stage of the tidewater glacier cycle the net average rate of ice loss is estimated at 16 7 4 4 km3 yr equivalent to a global sea level rise contribution of 0 04 0 01 mm yr

messinian evaporites and fluid flow abstract thick evaporite sequences deposited in saline giant basins are traditionally viewed as impermeable barriers to fluid flow this paradigm has recently been challenged by documented evidence of fluid migration pathways through several km thick series of evaporites such as the late miocene messinian sediments in the mediterranean basin deposited during the messinian salinity crisis msc our paper reviews the occurrence of fluid expulsion events in these evaporites in the depocentres of the basin and analyses their potential as seal bypass systems the messinian salt giant was deposited in peculiar conditions where massive sea level changes occurred in a relatively limited time interval and a thick basin centre evaporitic series was deposited between pre msc and post msc deep water sediments consequently rapid water and sediment loading unloading events contributed to the creation of overpressures up to fracture and possibly lithostatic gradient causing the fluids to be released in explosive events examples of fluid expulsion events are here grouped and classified in relation to the long and short term effects of the messinian salinity crisis as well as the local controls and pre conditioning basin factors while peaks of fluid expulsion activity during the short time frame of the msc can be mainly linked to mediterranean wide events local controls appear to play a major role in post msc fluid mobilisation in these cases evaporite breach is largely dependent on the availability of pre msc undersaturated fluid sources and the capability of the pre msc sediments to be overpressured the analysis here presented can be used as a basis to understand the controls on syn and post depositional movement of fluids in sedimentary basins moreover the analysis of temporal and spatial distribution of fluid expulsion events can help define hydrocarbon migration style and pathways in deep seated petroleum plays

potential salinity driven free convection in a shale rich sedimentary basin example from the gulf of mexico basin in south texas we investigate the plausibility of salinity driven free thermohaline convection in sedimentary rocks of the south texas part of the gulf of mexico basin using salinity data rayleigh number calculations and numerical models previous studies speculated that free convection could account for high fluxes evidently required for diagenesis in the basin but low permeability shales are calculated to be a barrier to free convection in the study area salinity inversions occur either above or within the transition zone from hydropressures to overpressures the positioning of brines over less saline fluids provides a significant buoyancy force rayleigh number calculations and numerical simulations suggest that homogeneous shaly systems are unstable near the high end of the expected ranges of shale permeability 10 15 10 16 m2 numerical simulations show that the influx of brine into the permeable layers and permeability heterogeneity in the shales are both conducive to free convection simulations indicate that salinity driven free convection can occur at lower permeabilities 10 16 10 18 m2 that may approximate the permeabilities of shales in the zone of extreme overpressures over geologic time simple rayleigh numbers are inadequate to predict the occurrence of free convection in heterogeneous systems salinity driven free convection at depths in some large sedimentary basins such as the gulf of mexico may be more common than expected

fluid flow in sedimentary basins abstract the pore waters in sedimentary basins are ultimately derived from sea water meteoric water mineral bound water or from the underlying basement geochemically these waters initially have different signatures however the pore water compositions are easily altered by reactions with minerals or by mixing with other fluids meteoric water is driven downwards into sedimentary basins by the gravitational potential which approximately corresponds to the elevation of the ground water table above the sea or lake level it is difficult to model such flow however because the permeability on a large scale is almost impossible to represent realistically the continuity of confined sandstone and limestone aquifers plays an important role in determining the flux of meteoric water received by rocks in different parts of the basin but this is again difficult to predict pore water flow driven by compaction typically has velocities several orders of magnitude lower than what is commonly found in meteoric water flow regimes the average rate of upwards flow is lower than the rate of subsidence and the difference is the rate of incorporation of sea water in the topmost layer at the sea floor the salinity of formation water provides important constraints on fluid flow in sedimentary basins in the north sea basin and the gulf coast basin these types of data indicate that vertical mixing by compaction driven flow and convection is limited compaction driven flow obeys darcy s law but there are complex interdependencies between pressure permeability and compaction given the low compressibility of water the flow which can result from pressure release alone is very limited except on a local scale along permeable faults and fractures the main flow of pore water during burial is driven by compaction which is a slow process even when overpressure is released abruptly with a resulting increase in the net effective stress in the case of high permeability faults the flow into the fault from low permeability sedimentary rocks at depth may be rate limiting the displacement of pore water in adjacent sediments near the top of the faults may also slow down fluid flow on fractures that do not reach the sea floor modelling of fluid flow in sedimentary basins should be based on permeability distributions which are mostly determined by primary facies diagenesis and the tectonic history of the basin extensional tectonics produce a predominantly vertical fracture network which may serve as conduits for pore water flowing deep into the crust upward flow of hot fluids in basement fractures must have a high velocity in order to produce large thermal anomalies concentrations of dissolved components precipitate at the surface and form deposits of quartz and ore minerals if basement fractures are overlain by a thick sequence of soft sediments the rate of flow on the fractures will be reduced because of the low permeability in the sedimentary cover and conductive heat transport will dominate flow of water at high enough velocities to bring hot water to the surface and produce hot springs is most likely to occur in fractured basements rocks or well cemented sedimentary rocks concentrated precipitation of dissolved components will occur near the surface where the rate of cooling is highest also sediment hosted ores precipitated from flow of hot water on fractures are therefore likely to form before accumulation of thick overlying sedimentary sequences

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

penetration depth of interferometric synthetic aperture radar signals in snow and ice digital elevation models of glaciated terrain produced by the nasa jet propulsion laboratory jpl airborne interferometric synthetic aperture radar insar instrument in greenland and alaska at the c 5 6 cm wave length and l band 24 cm frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth or penetration depth p on cold polar firn at greenland summit p 9 2m at c and 14 4m at l band on the exposed ice surface of jakobshavn isbrae west greenland p 1 2 m at c and 3 3 m at l band except on smooth marginal ice where p 15 5 m on colder marginal ice of northeast greenland p reaches 60 to 120 m at l band on the temperate ice of brady glacier alaska p is 4 2 m at c and 12 6 m at l band with little dependence on snow ice conditions the implications of the results on the scientific use of insar data over snow ice terrain is discussed

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

salinity variations in north sea formation waters implications for large scale fluid movements abstract sodium chloride is the major salt dissolved in formation waters even at a considerable distance away from any evaporites chloride anions are not consumed to any significant extent by diagenetic reactions outside the salt deposits chloride ions are therefore preserved in the pore waters and the distribution of pore water salinities in sedimentary basins may help to constrain pore water flow and the transport of dissolved species of silica and carbonate minerals in the north sea basin and haltenbanken mid norway salinity gradients can be inferred from formation water samples measurements of pore water salinity from wireline logs are less accurate than formation water samples but have the advantage that a much larger database can be obtained data from 150 wells in the north sea and haltenbanken show that the salinities measured from well logs range from 20000 to 300000 ppm in the southern part of the norwegian north sea and haltenbanken there is a clear trend towards higher salinities with greater burial depth there is a pronounced salinity increase in the 500 m of section closest to the evaporites in the northern north sea where underlying evaporites are not known there is only a slight increase in the measured salinities with depth there are however no measurements of high salinity pore water 100000 ppm at depths shallower than 2200 m this pattern of salinity distribution in the pore water precludes large scale convection of the pore water during diagenesis it also indicates limited compaction driven flow log derived salinity data from the north sea suggest that the pore waters in upper jurassic and tertiary reservoirs are generally more saline than those of middle and lower jurassic reservoirs at the same depth the constraints on pore water flow that can be deduced from salinity variations puts severe limitations on the mechanisms of transport of dissolved solids in sedimentary basins and thus also on aspects of diagenetic models

thermo erosional notch development at fresh water calving tasman glacier new zealand controls on glacier calving rates are receiving increased scientific interest at fresh water calving glaciers limnological factors might be more important than glaciological ones measurements of thermo erosional notch development at the calving ice cliff of tasman glacier new zealand suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting notch formation rates typically vary between 10 and 30 cm d 1 maximum rate 65 cm d 1 in summer corresponding to an average calving rate of 34 m a 1 notch formation is slower than waterline melt and is controlled by water temperatures and circulation cliff geometry debris supply and water level fluctuations the latter shift the position of undercutting resetting the level of the notch formation process and thereby slowing it the geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation hence water temperatures in the lake are not necessarily indicative of the rate of notch formation the prediction of rate of notch formation from far field variables is hampered by the complex interaction of the influencing factors the significance of thermal undercutting as a calving rate controlling process decreases with increasing ice velocities calving rates and surface gradients

kilometre scale thermohaline overturn of pore waters in the louisiana gulf coast convincing evidence exists for the large scale convection of sea water through the upper oceanic crust even at considerable distances from mid ocean ridges1 2 there has been considerable interest in verifying the existence of convective overturn of pore fluid in large sedimentary basins a mass transport process which could profoundly influence the transport of heat hydrocarbons metals and diagenetically reactive dissolved constituents3 4 the existence of fluid convection in sediments of the united states gulf coast has been inferred on the basis of the large volumes of fluid necessary to account for the observed diagenetic alteration5 and the existence of thermal anomalies that cannot be explained by simple conductive transport of heat3 6 theoretical rayleigh darcy calculations6 7 support the notion that thermally driven convection is possible here i present geochemical and physical evidence for the existence of density inversions in gulf coast pore fluids sufficient to drive large scale convective fluid flow at rates conceivably as high as metres per year the density inversions are caused in part by the dissolution of salt diapirs and the formation of dense saline brines at shallow depths

estimating volume change of mountain glaciers using srtm and map based topographic data this paper describes a method for estimating the volume change of mountain glaciers using the shuttle radar topography mission srtm c band data 2000 and a digital elevation model dem generated from topographic maps this approach was developed with srtm data and topographic maps of 1 25 000 scale 1977 from the akshiirak glaciers tien shan central asia the dem for 1977 was generated using 10 m contour lines from 18 map sheets covering the akshiirak massif and surrounding area the nominal vertical accuracy of the maps is 3 3 m the standard deviation of the differences between the map derived dem and the srtm data on glacier free areas of less than 25deg is 6 3 m a single localized region in the western periphery of the study area with systematic error in the srtm data from 20 to 12 m on a 30 km spatial scale was found and excluded from the error analysis assuming a 10 m map error on the upper snow covered glacier areas the estimated root mean square error of the glacier surface change is 8 2 m from 1977 to 1999 the average glacier surface thinning is 15 1 m and the estimated volume loss is 6 15 km3 the rate of the akshiirak glacier volume loss has increased by 2 7 times compared with historical data from 1943 to 1977 the srtm data show an opportunity for quantifying climatic and dynamic surface elevation changes in mountain glaciers ice cloud and land elevation satellite icesat laser altimetry and srtm data could also be used for the estimation of short term surface changes of mountain glaciers

the effects of salt evolution structural development and fault propagation on late mesozoic cenozoic oil migration a two dimensional fluid flow study along a megaregional profile in the northern gulf of mexico basin sequential two dimensional 2 d forward modeling of fluid flow along a north south 600 km megaregional cross section across the northern gulf of mexico basin illustrates the influence of structural stratigraphic and thermal evolution on oil generation patterns and migration paths twelve megaregional fluid flow models which span from the late cretaceous to the holocene were constructed for this study each model uses a sequential structural restoration and proprietary well data to constrain the structural and stratigraphic development of the study area and to calibrate production depths along the megaregional profile these fluid flow models specifically address the levels of influence that salt evolution sedimentation thermal history and fault development induce on temporal oil migration patterns results from the sequential 2 d fluid flow models across the northern gulf of mexico basin indicate that allochthonous salt evolution and excess pressure development from differential sedimentation strongly influenced late mesozoic cenozoic oil migration patterns along the entire megaregional profile within the lower slope part of the profile early and fairly rapid maturation of source rocks was accompanied by slow elevation of excess pressures as a result oil migration in these regions was minimal and the impact of salt evolution on the fluid flow was restricted to circulatory patterns at the base of salt stocks within the center of the profile begin page 1946 offshore louisiana shelf however the evolution of allochthonous salt and the formation of high excess pressures coeval with the development of listric and normal faults strongly impacted the oil migration patterns penetration of high excess pressure regimes by both listric and normal faults directed fluid flow vertically upward along the fault systems upon encountering salt sheets oil migration in these regions exhibited both divergent and convergent flow patterns flowing laterally along the base of the salt a similar scenario was observed in the northern part of the profile southern onshore louisiana reflected by oil migration beneath the terrebonne salt sheet upon evacuation of allochthonous salt in the central and northern regions of the profile migration patterns were primarily lateral when excess pressures in these regions exceeded 50 mpa however oil flowed vertically through the salt welds and along suprasalt faults a more localized and well constrained study of fault migration in the oligocene miocene detachment province further suggests that faults are important factors as migration pathways with episodic flow directing oil migration into observed shallow reservoirs

geodetic and direct mass balance measurements comparison and joint analysis this paper describes a new compilation of both direct and geodetic mass balance measurements develops a procedure to reduce diverse balance measurements over different time spans to common time spans and presents updated estimates of global average balance of small glaciers based on the enlarged compilation although geodetic measurements are fewer than direct measurements they cover four times as many balance years direct and geodetic measurements are unbiased with respect to one another but differences are often substantial the statistical procedure can be understood by imagining that an n year balance measurement is an average of a series of 1 year measurements the series is hypothetical but we can calculate the uncertainty of each of its elements if in addition to its measured average we can also estimate its standard deviation for this claim to be valid the annual series must be stationary and normally distributed with independent roughly uncorrelated elements for which there is reasonable evidence the need to know the standard deviation means that annual direct measurements from a nearby glacier or equally reliable information about variability are indispensable given this information the new methodology results in moderately more negative balances this is probably because tidewater glaciers are better represented in the geodetic data in any case the most recent published estimate of global average balance 0 8 1 0 mm a 1 of sea level equivalent for 2001 04 is now increased substantially to 1 1 1 4 mm a 1 for 2001 05

simulation of groundwater interception at lake ranfurly victoria incorporating variable density flow and solute transport abstract the movement of salt from lake ranfurly west towards the river murray and the associated groundwater interception scheme has been modelled in cross section using the sutra model recharge from irrigation areas and saline seepage from the lake have been taken into account owing to the salinity contrast between lake ranfurly west and groundwater it was considered appropriate to simulate density dependent flow behaviour concentration profiles in the aquifers and salt loads to the river under various management scenarios were computed under conditions of both density dependent and non density dependent flow the model simulations have shown that the salt load to the river is 1 dependent on the rate of pumping from interception bores 2 dependent on the aquifer s in which groundwater is intercepted and 3 marginally greater 11 15 for density dependent flow behaviour at less than full interception compared with calculations which neglect density dependent flow

perched brine plumes above salt domes and dewatering of geopressured sediments previous studies have shown that there is a brine plume with more than 160 g l 1 total dissolved solids tds in the subsurface perched above welsh salt dome in south louisiana the occurrence of this plume has been postulated to be due to the expulsion of geopressured fluids up a fault on the flank of welsh dome the process that resulted in formation of the anomalous brine plume near welsh dome is of importance because hydrocarbon production is approximately coincident with the brine plume in map plan although in cross sections the brine plume actually occurs a few hundred meters above hydrocarbon production zones using a variable density groundwater flow model sutra we tested the hypothesis that a pulse of fluid flow up the fault could result in brine formation near the top of the dome when the permeability of the geopressured zone was very low in our simulations brine formation in the hydropressured zone occurred entirely by brine density flow and flow was downward along the fault flanking the dome above a certain threshold permeability for the geopressured zone between 10 7 darcy and 10 5 darcy in the vertical direction geopressured fluids were forced up the fault and brine formation occurred above the dome rather than on the flank brines can theoretically form above salt domes in very short geologic times 10 1 ma by expulsion of waters from the geopressured zone below but the fluid effluxes required are gigantic and appear to be unsustainable over large time intervals such as 10 ma

evidence for large scale vertical migration of dissolved fatty acids in louisiana oil field brines iberia field south central louisiana abstract abstract there is considerable interest at the present time in the origin and distribution of dissolved volatile fatty acids vfas in oil field brines this interest has developed as a result of the recognition of the role these compounds may play 1 in subsurface acid attack and porosity enhancement 2 as precursors of natural gas and 3 as possible proximity indicators of hydrocarbon accumulations the detailed study of the distribution of dissolved vfas on a field scale provides much useful information on processes of generation transport and degradation of these compounds at the iberia oil field one of several fields we have studied in the tertiary section of south central louisiana spatial variations in pore water compositions and temperatures indicate the presence of an on going dynamic subsurface circulation system deep brines with vfa levels in excess of 150 mg 1 are migrating up the south flank of the iberia salt dome a vertical distance of at least 2 km 6000 ft the vfas in these waters are dominated by acetate and propionate as these waters ascend they mix with an ambient mass of water having total vfa concentrations of 20 mg 1 or less and dominated by n butyrate preferential decarboxylations of acetate and propionate relative to iso and n butyrate and iso and n valerate are occurring in this system the byproducts of these decarboxylation reactions should be methane ethane and bicarbonate temperatures are cool enough 80 c in the shallower parts of the sequence to permit the existence of bacteria that coud break down acetate through fermentation the spatial distribution of individual dissolved vfa s is complex but systematic and must ultimately be related to the rates of advective transport dispersive mixing and chemical reaction we believe that a potential new application of the study of these dissolved organic compounds lies in helping to unravel the dynamics of some types of subsurface flow systems

salinization problems in the negb results from thermohaline simulations the occurrence of salty waters close to the surface is a well known problem in the north east german basin previous numerical simulations showed that near surface brine occurrences are due to the interaction of hydrostatic and thermally induced forces mixed convection the influence of hydraulic permeabilities and thermal conductivities on the observed patterns remained an open question based on a hydro geochemical dataset thermohaline simulations are carried out in order to quantify the impact of these physical parameters on brine migration the results indicate that the salinity and temperature profiles are strongly controlled by hydraulic permeabilities and can locally be influenced by thermal conductivities

topography and penetration of the greenland ice sheet measured with airborne sar interferometry a digital elevation model dem of the geikie ice cap in east greenland has been generated from interferometric c band synthetic aperture radar sar data acquired with the airborne emisar system gps surveyed radar reflectors and an airborne laser altimeter supplemented the experiment the accuracy of the sar dem is about 1 5m the mean difference between the laser heights and the sar heights changes from 0 m in the soaked zone to a maximum of 13 m in the percolation zone this is explained by the fact that the snow in the soaked zone contains liquid water which attenuates the radar signals while the transparency of the firn in the percolation zone makes volume scattering dominate at the higher elevations for the first time the effective penetration has been measured directly as the difference between the interferometric heights and reference heights obtained with gps and laser altimetry

ephemeral thermal and solute plumes formed by upwelling groundwaters near salt domes geochemical observations made by previous workers indicate that rapid upward advection of hot water has occurred along the flanks of some salt domes in the northern gulf of mexico basin and in the danish central trough the observations are based on pore fluid chemistry and on high temperatures of formation of metal sulfides and other diagenetic minerals near the crests of salt domes some of the diagenetic minerals formed at 40 c to 80 c above the ambient temperature of the host rocks numerical simulations of coupled heat and dissolved salt transport show that thermal perturbations in excess of 60 c can be repeatedly produced near the crest of a salt dome by focused dewatering of a thick strongly overpressured sedimentary interval around the dome in our simulations dewatering was triggered and stopped by cyclically changing the permeability at the salt sediment interface the thermal plumes dissipated within 100 kyr after dewatering ceased stratigraphically shallow brine plumes were also formed by dewatering and these gravitationally unstable plumes dissipated more slowly by sinking within 1 m y simulations showed that free thermohaline convection can also generate thermal perturbations near the crest of a dome in this mode of upwelling thermal perturbations reached 30 c when the vertical permeability of the hydrostatically pressured interval was 10 14 m2 10 mdarcy because such permeabilities seem large for the hydrostatically pressured interval as a whole in the northern gulf of mexico basin the formation of high temperature metal sulfide deposits near the crests of salt domes seems more likely to be due to dewatering of the overpressured interval with very strong focusing of expelled waters along the flanks of salt domes

density driven groundwater flow near salt domes active halite dissolution occurs around numerous salt domes in louisiana forming brines with as much as 300 g l 1 tds tds total dissolved solids most of which is na and cl we numerically modeled the possible dynamics of 1 brine density flow induced by solute concentration gradients and 2 thermal convection induced by temperature gradients around hypothetical salt domes calculated maximum flow velocities due to brine density flow range from 0 01 to 1 m yr 1 even in low permeability sediments much greater than velocities due to thermal convection immense quantities of halite can be dissolved by brine density flow up to 3 km3 myr 1 and formation of brine plumes can occur very rapidly in some cases requiring 1 myr maximum flow velocities increase with bulk permeability and decrease with increasing anisotropy geopressured waters bleeding upward into the hydropressured zone may affect brine formation in the hydropressured zone provided permeability of the geopressured zone is sufficiently high

formation water geochemistry of the sverdrup basin implications for hydrocarbon development in the high arctic abstract the sverdrup basin holds significant reserves of discovered and undiscovered petroleum that have not been produced to date given its remote arctic setting loss of perennial sea ice increases the prospects for producing reserves from this region potential renewed drilling and production requires knowledge of formation water geochemistry to aid both exploration as well as regulatory development historic data shows formation waters typically have a seawater origin although there is high variability in formation water geochemistry salt diapirs lead to localized brine generation with salinities over an order of magnitude higher than average for the basin evidence also shows fresh water influx occurred along the basin margins that initiated biogenic gas generation

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

early evolution of salt structures in the north louisiana salt basin abstract several salt diapirs and pillows in southern and central north louisiana have been studied utilizing approximately 355 miles 570 km of seismic reflection data and information from 57 deep well holes the use of seismic profiles coupled with deep well hole data is the most advantageous method to document regional salt tectonism through time three stages pillow diapir and post diapir stages are required to explain salt stock growth through time in the north louisiana salt basin the pillow stage and its associated primary peripheral sinks exhibit 11 34 thinning over pillow crests and 12 50 overthickening in the primary peripheral sinks in the basin thinning values as great as 87 and overthickening values as high as 400 are inferred for pre diapiric juvenile salt pillows the diapir stage and its associated secondary peripheral sinks exhibit 50 250 overthickening this stage is characterized by piercement diapirisin and the withdrawal of large volumes of salt from the flanks of the pillow the post diapir stage and its associated peripheral sinks exhibit less than 45 overthickening moreover in some instances dome growth is in a steady state with sedimentation growth stages are generally confined to the following stratigraphic units smackover to knowles pillow stage calvin diapir stage and winn and younger sediments post diapir stage the above considerations lead to the following conclusions on diapirism in the north louisiana salt basin 1 onset of the diapiric event was early late jurassic in the southern and central portion of the basin and later early cretaceous in the northern portion 2 the initial diapiric event is much more rapid and intense in the southern and central diapirs when compared with the later diapiric event in the northern diapirs 3 regional depocenter shifting relative sea level local erosion with salt extrusion and rapid depositional loading of sediments are the major controls on diapirism in the basin

fluid circulation and deformational gradient in north pyrenean flyschs example from the saint jean de luz basin france abstract the relationships between fluid circulation and deformation are one of the issues of the sedimentary basin study in the cretaceous flysch of the saint jean de luz basin the evolution of folds geometry and the increasing volume of calcite filled fractures and veins evidence a northward deformational gradient along the french basque coast a combined approach is proposed to assess the corresponding physical and chemical conditions the microthermometric study of fluid inclusions in calcite sampled in different generations of veins and fractures and the x ray diffraction analysis of clay minerals from adjacent marl layers salinity of the trapped h 2 o cacl 2 nacl fluids increases with depth in the series in good agreement with salinity gradients reported in sedimentary basins dispersion of the data also increases with depth from 0 3 to 1 3 wt nacl eq in the shallowest formation haizabia flysch to 9 1 to 23 0 wt nacl eq in the deepest formation guethary flysch minimal trapping temperatures of the fluids in the haizabia and socoa flyschs 79 and 102 c respectively are consistent with the temperatures estimated from the depth of burial which did not exceed 5 km in good agreement with the stability of the smectite illite kaolinite assemblage found in marls in addition the kaolinite proportion significantly decreases with depth in the series as a potential consequence of climate changes and diagenetic transformations whereas the increasing dispersion of illite crystallinity data might indicate fluid mineral interactions we propose a synthetic model of fluid circulation in the folded series that involves the mixing of mainly horizontal fluid circulation potentially meteoric with an upward flow of high salinity fluid throughout the deepest formations potentially related to underlying evaporite rich layers the northward deformational gradient as exposed along the french basque coast is likely to be responsible for such a vertical circulation by increasing the volume of fracture particularly cross cutting fractures in the deeply buried formations

biases of srtm in high mountain areas implications for the monitoring of glacier volume changes because of its nearly global coverage the shuttle radar topographic mission srtm topography is a promising data set for estimating mountain glacier volume changes but first its absolute accuracy must be thoroughly investigated in a glacial environment we use topographic data available in the french alps to assess the usefulness of srtm for the monitoring of glacier volume variations we observe clear biases with altitude both on ice free and glacier covered areas at high altitudes srtm elevations are underestimated by up to 10 m these biases can have a significant impact on any estimate of glacier volume changes if srtm is the most recent of the two compared topographies the volume loss is overestimated and vice versa we cannot conclude definitively on the origin of these biases and whether they affect all high mountain areas but our findings invite reconsideration of previous estimates of glacier wastage based on srtm

basin dewatering near salt domes and formation of brine plumes a previous study noted the occurrence of a subsurface brine plume with more than 160 g l sodium chloride perched above welsh salt dome in southwestern louisiana plumes of saline groundwaters have been reported above other gulf coast salt domes as well the u s geological survey code sutra was used to model the formation of brine plumes around a generic salt dome by basin dewatering along the flanks of the dome and also to study the gravitational instability of a brine plume initially perched above a dome in the absence of an externally impressed driving force for upwelling the simulations take into account the effect of salt concentration gradients on brine density the first set of simulations showed that a brine plume initially perched above a salt dome sank rapidly in the absence of an overpressured section where observed perched brine plumes above salt domes must therefore be either 1 young 2 ma if formed by basin dewatering and vertical fluid expulsion along the flanks of salt domes or 2 formed by a continuous mechanism the second set of simulations modeled the dewatering of a thick initially overpressured sedimentary section extending from a depth of 3 km to a depth of 10 km the deflation rate of the overpressured section profoundly depended on whether or not a permeable conduit along the flank of the dome existed which could collect water expelled radially inward to the flank of the dome from the overpressured sediments and focus it upward along the flank of the dome in most simulations the volume of compaction water was limited to only 10 of the total volume of overpressured sediment around the dome and there was an ample amount of compaction water for a perched brine plume to form in fact when a perched brine plume formed it formed very quickly in 0 01 m y after a negligible degree of deflation of the overpressured section it is conceivable that if cycles of conduit sealing and seal rupturing occurred perched brine plumes could be formed several times during deflation conditions necessary for the formation of a perched brine plume are as follows 1 waters must be focused laterally toward the dome within in the overpressured section 2 there must be a conduit of sediment with relatively high vertical permeability along the flank of the dome and 3 sediments above the dome must be more permeable than sediments along the flank of the dome for some simulations the average linear velocity of upward flow along the flanks of the dome was 3 m yr possibly of large enough magnitude to cause a thermal anomaly if perched brine plumes form by basin dewatering the thermal buoyancy effects associated with such a thermal anomaly may make the plumes rise to depths shallower than indicated in the simulations here the inability of the code sutra to simultaneously model heat and solute transport did not permit an evaluation of this

fluid rock interactions in the salt dome environment an introduction and review abstract the salt dome environment in the gulf of mexico coast u s a provides one of the most diverse and long lived records of fluid rock interactions in an active sedimentary basin dominated by saline formation waters the geochemical record most of which is isotopic appears to span a temperature range between earth surface temperatures and lower greenschist facies most mineral forming processes in the salt dome cap rocks appear to involve mixtures of warm saline formation fluids from deep basin sources and cool dilute meteoric waters papers in this issue of chemical geology document some of the current research on fluid rock interactions in the salt dome environment these papers highlight the diversity of opinion about salt dome processes offering clues for further research the present paper reviews some of the key and more current literature on salt dome geochemistry fluid convection around salt domes and fluid rock interactions within salt and within the salt dome environment

oxygen and hydrogen isotopic composition of clay minerals of the bahloul formation in the region of the bou grine zinc lead ore deposit tunisia evidence for fluid rock interaction in the vicinity of salt dome cap rock abstract the siliciclastic bahloul formation of tunisia is the host for zn pb deposits a detailed study of 18 o 16 o and d h ratios of kaolinite quartz and calcite was done to elucidate the conditions and mechanism of deposition of the diapir related bou grine zn pb ores in the formation d h and 18 o 16 o ratios of the minerals of the host rock have been affected by the mineralizing process the magnitudes of the isotopic shift in 18 o 16 o of kaolinite as well as the intensity of base metal mineralization seem to be governed by the permeability of the bahloul strata due to different water rock ratios in contrast the variability in d h ratios of kaolinite shows no correlation with the estimated permeability of the respective sedimentary section published microthermometric fluid inclusions data and organic geochemical maturation parameters both argue for a maximum temperature between 80 and 120 c during ore formation and host rock alteration the 18 o 16 o ratios of the clay minerals of samples taken over a range of distance from the ore body suggest alteration by hot saline 18 o enriched brines these could have evolved at the flanks of the diapir and would have been capable of remobilizing metals from deeper sedimentary sequences providing the metals now found in the bou grine deposit the 18 o value of the mineralizing fluid is estimated to have been between 8 and 18 the d value was between 30 and 55 the high 18 o values of these basinal brines provide evidence for a control of the isotopic composition of the fluids by 18 o rich carbonate minerals of the post triassic limestones hydrogen isotopic data argue for a meteoric origin of the brines the variability of the d values might be explained by a contribution of evaporated meteoric waters entering the groundwater system and mixing of these waters with the hot saline brines in the contact zone of the diapir

ice wastage on the kerguelen islands 49 s 69 e between 1963 and 2006 1 we observed the wastage of ice masses on the kerguelen islands indian ocean 49 s 69 e using historical information and recent satellite data overall the total ice covered area on the islands declined from 703 to 552 km2 between 1963 and 2001 a reduction of 21 the area of cook ice cap the main ice body decreased asymmetrically from 501 to 403 km2 west flowing glaciers lost 11 of their area while east flowing glaciers lost 28 after 1991 the retreat rate accelerated from 1 9 km2 a 1963 1991 to 3 8 km2 a 1991 2003 between 1963 and 2000 the ice volume loss was 25 30 km3 equivalent to an area average ice thinning rate of 1 4 1 7 m a the glacial retreat took place in the climatic context of a relatively low level of precipitation compared to the 1950s and a 1 c warming that occurred between 1964 and 1982 the acceleration of the ice losses since at least the 1990s indicates that the state of the ice bodies on the kerguelen islands is still far from balanced together with other studies in patagonia south georgia and heard island our analysis is consistent with a pattern of strong and accelerated wastage of ice masses influenced by the southern ocean

the loess palaeosol sequence in the upper palaeolithic site at krakow spadzista a palaeoenvironmental approach abstract the krakow spadzista open air site situated in the loess belt in southern poland belongs to the best known gravettian sites of europe many years of archaeological studies revealed a wealth of faunal remains especially mammoths as well as numerous aurignacian gravettian and epigravettian stone artefacts in several cultural layers field pedogeomorphological investigations 2011 2012 and laboratory analyses geochemical granulometric micromorphological palynological and irsl dating were the basis for palaeogeographical discussion on the conditions of the loess soil sequence development five independent litho and pedological units corresponding to mis 5 to 2 were distinguished primary loess layers are relatively thin and contain many hiatuses diverse structure and development of intra loess palaeosols reflect their origin age and stratigraphic rank the cultural layers were found in weakly developed soils with the traces of subsequent periglacial mainly deluvial solifluction transformations of different intensity the palaeosols represent two periods of interglacial rank eemian forest palaeosol and the overlying postglacial modern soil mis 5 and 1 respectively and two interstadials subarctic soils with the gravettian artefacts mis 3 one weakly developed gleyic horizon with the features of tundra soil occurs within the loess corresponding to climatic pessimum of weichselian glaciation mis 2 in the very local promontory with the site and micro regional sowiniec horst scales the distinguished soils are undoubtedly important palaeogeographical and archaeological key horizons

modelling density dependent flow and solute transport at the lake tutchewop saline disposal complex victoria abstract intercepted saline groundwaters and drainage effluent from irrigation are commonly stored in both natural and artificial saline disposal basins throughout the murray darling basin of australia their continued use as wastewater evaporation sites requires an understanding of existing groundwater dynamics the useful of individual basins their sustainability and possible environmental impacts remain largely unknown in this work the movement of salt to the underlying groundwater system from lake tutchewop a saline disposal complex in north central victoria was modelled in cross section due to the salinity contrast between the hypersaline basin waters and the regional groundwater it was necessary to simulate density dependent flow behaviour under certain conditions these density stratified systems may become unstable leading to the onset of convective behaviour which greatly increases the movement of salt from the basin to the groundwater system modelled concentration profiles in the aquifer system and calculated seepage rates from the basin show that lake tutchewop is stable under its present operating regime the downward movement of salt is mainly controlled by diffusion and dispersion the calibrated model was used to assess the impact of several management scenarios using time dependent boundary conditions for lake salinity and water levels the influence of heterogeneous basin linings on ensuing salt flux rates is examined and results show that increased solute transport will occur under such conditions a sensitivity analysis performed on governing variables showed that salt fluxes were most sensitive to lake salinity levels a solute rayleigh number defined in terms of basin salinity and hydrogeologic parameters is seen to be an effective tool for predicting the long term behaviour of such saline disposal basins the models and concepts developed in this work may find application in the design and management of saline disposal complexes

free thermohaline convection beneath allochthonous salt sheets an agent for salt dissolution and fluid flow in gulf coast sediments basinward migration of jurassic salt in the u s gulf of mexico has resulted in the emplacement of large allochthonous salt sheets into shallow miocene to holocene sediments although comparatively little direct information is available on the environment below these salt bodies it is reasonable to suppose that the formation of dense brines by dissolution of the base of these sheets may induce free thermohaline pore fluid convection within the sediments below we derived equations which make it possible to quantitatively estimate rates of dissolution of these subsurface salt structures from these calculations and by geologically realistic numerical simulations it can be shown that free convection beneath allochthonous salt sheets has the potential for being a significant mechanism for both salt dissolution and mass transport even if the underlying sediments have permeabilities as low as 10 17 m2 0 01 md the calculated maximum darcy fluxes and rates of salt dissolution rapidly increase with sediment permeability when the vertical permeability of the underlying sediment is 10 17 m2 0 01 md salt is dissolved from the base of the sheet at an average rate of 3 5 m m y 1 the corresponding fluid velocities are such that over a 10 m y period the integrated fluid flux in the underlying sediments would be 104 m3 m 2 by comparison integrated fluid flux for compactive expulsion is 103 m3 m 2 thus for the offshore sediments of the gulf of mexico thermohaline convection beneath an allochthonous salt sheet is a significant driving mechanism for fluid flow with potentially important implications for heat and mass transport diagenesis and salt tectonics

fluid dynamics driving saline water in the north east german basin in several areas of the north german basin saline water comes close to or even reaches the surface available data from wells indicate that brine stratification is under unstable conditions in the deeper underground in order to analyse the possible transport mechanisms 3d thermohaline simulations have been carried out for two different scenarios the 3d regional model 230 330 km indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands in addition a smaller scale model 10 10 km has been constructed with a grid resolution accounting for possible convective flow the results indicate that convective flow may play a dominant role in areas with minor topography in summary the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces

diagenesis of eolian and fluvial feldspathic sandstones norphlet formation upper jurassic rankin county mississippi and mobile county alabama norphlet sandstones in seven cores from mississippi and alabama are arkoses and subarkoses deposited in eolian dune interdune and fluvial environments similar to the deeply buried 5 km tertiary feldspathic sandstones of the gulf basin all detrital plagioclase that survived dissolution has been albitized however some k feldspar instead of dissolving was stabilized by k rich brines derived from adjacent evaporites this k feldspar then developed extensive overgrowths fluvial red sandstone lost all initial porosity by the introduction of preburial pedogenic calcite and compaction initial porosity of eolian sands was reduced by compaction to an average of 29 and later by cementation by quartz carbonates anhydrite halite k feldspar and illite quartz and anhydrite cements precipitated between 90 and 100 c approximately 2 3 km deep carbonates and halite cements formed below 120 c 3 km and late stage illite cement formed between 130 and 150 c 4 5 km deep cements are patchy and some especially quartz and anhydrite are texture selective being more abundant in coarser laminae secondary porosity which makes up approximately half the porosity in thin sections formed by dissolution of detrital grains f ldspar rock fragments and cements anhydrite carbonate halite reservoir bitumen records an early phase of oil entrapment reservoir quality is influenced by the abundance of reservoir bitumen and thread like illite both of which bridge pores the radiometric age of illite approximately 55 ma probably reflects its cementation age but may also record a later recrystallization event depleted oxygen and carbon isotopic values for ferroan dolomite reflect the progressive replacement of earlier more enriched carbonate phases by higher temperature phases isotopic data suggest that during the first 30 to 40 m y of burial subsurface diagenesis of the norphlet formation was dominated by deep circulating hot meteoric water this phenomenon may be characteristic of the early diagene ic history of rifted basins

regional variations in physical and chemical properties of south louisiana oil field brines abstract knowledge of in situ physical and chemical properties of pore fluids in sedimentary basins is essential in understanding problems of fluid migration and diagenetic reaction we have completed a study of the regional variations in pore fluid temperature pressure and salinity for the entire tertiary section of south louisiana to depths of 4 to 6 km from this information it is possible to calculate values for hydraulic head and in situ pore fluid densities and viscosities parameters necessary in quantifying rates and directions of subsurface fluid migration it is also possible to determine such chemical properties as methane solubility maximum salinities typically in the range of 120 150 g 1 are found in the lower part of the hydropressured zone where salt is introduced by dissolution of salt diapirs hydraulic head increases from essentially zero in the hydropressured zone to values exceeding 3 km above mean sea level deep in the geopressured section fluid densities increase with depth to maximum values approaching 1 07 g cm at depths of approximately 2 km densities decrease with further depth as a result of increasing temperature and decreasing pore water salinity the entire lower portion of the pore fluid column is thus gravitationally unstable a factor favoring fluid overturn fluid viscosities systematically decrease from 1 cp at the surface to less than 0 2 cp at depth as a result of these variations in density and viscosity pore waters will flow five times more efficiently at depth methane solubility decreases upward from over 50 scf bbl in deep overpressured sediments to 10 scf bbl at the base of the hydropressured zone to less than 5 scf bbl at shallow depth significant exsolution of methane should thus occur as a result of upward migration of pore fluid or molecular diffusion of dissolved methane

diagenesis of the carrizo sandstone at butler salt dome east texas basin u s a evidence for fluid sediment interaction near halokinetic structures abstract the eocene carrizo sandstone adjacent to the butler salt dome in the east texas basin was cemented locally as the result of processes similar to those that have created salt dome calcite cap rocks throughout the gulf coast the geometry of this anomalous cemented zone was established using carrizo exposures in a large quarry and cores in the contiguous area the cemented zone is delimited by a steeply dipping normal fault that is radial to the dome the cements extend southeast of the fault for about 750 m the carrizo is a fine to medium grained quartzarenite to sublitharenite with 42 to 50 cement principally poikilotopic calcite with local pyrite pyrite concretions are found on both northwest and southeast sides of the fault as well as along the fault plane whereas the calcite cement is present only to the southeast 13c data for calcite 19 to 37 suggest that bicarbonate was supplied mainly by bacterial oxidation of methane whereas 18o data for calcite 6 to 9 indicate that meteoric water was the principal diagenetic fluid 87sr 86sr values for calcite 0 7073 are within the range for middle jurassic seawater suggesting that dissolution of anhydrite from the louann salt provided the ca pyrite is more 34s rich 34s range of 10 to 16 than typical sulfides in gulf coast salt dome cap rocks and are interpreted to represent h2s supply from deep sour gas reservoirs petrographic and isotope evidence suggests that early h2s supply from deep sour gas reservoirs was channeled upward along the flank of the dome and outward along the radial fault resulting in early pyrite precipitation along the fault zone and in adjacent sediments early pyrite cementation along the fault may have formed a barrier to subsequent fluid circulation blocking the northwestward movement of both ca rich waters from the dome and deep natural gas moving along the fault thus confining calcite precipitation to the southeast bacterial oxidation of this thermogenic gas resulted in calcite precipitation although mixing with shallow ground water bicarbonate may account for the range in 13c values in the calcite cement we propose that this type of cementation occurs in similar settings associated with hydrocarbon leakage to shallow levels including adjacent to many salt domes in the gulf of mexico basin and may represent a previously unrecognized self sealing type of hydrocarbon trap

icesat validation of srtm c band digital elevation models 1 the geoscience laser altimeter system glas on the ice cloud and land elevation satellite icesat provides a globally distributed data set well suited for evaluating the vertical accuracy of shuttle radar topography mission srtm digital elevation models dems the horizontal error 2 4 7 3 m and vertical error 0 04 0 13 m per degree of incidence angle for the icesat data used are small compared to those for srtm using glas echo waveforms we document differences between the srtm c band phase center and the highest centroid and lowest elevations within icesat laser footprints in the western united states in areas of low relief and sparse tree cover the mean and standard deviation of elevation differences between the icesat centroid and srtm are 0 60 3 46 m the differences are 5 61 15 68 m in high relief sparse tree cover areas and 3 53 8 04 m in flat areas with dense tree cover the largest differences occur in rugged densely vegetated regions

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

hydrogeology of sedimentary basins abstract hydrogeologic environments in sedimentary basins are as variable as are the different types of basins important hydrologic characteristics can be used to distinguish the different types of basin 1 the topographic setting as determined by the geologic and structural history of the basin 2 permeability distribution within the basin and 3 potential energy distributions and flow mechanisms these parameters control residence times of waters rates and directions of saline groundwater flow and the origin and chemical composition of the saline waters the gulf coast and palo duro basins texas exemplify two end member types of sedimentary basins the gulf coast basin is a relatively young tertiary age basin which is presently compacting fluid movement is from the overpressured undercompacted sediments up the structural dip or up fault zones into the hydrostatic section natural fluid pressures are either hydrostatic or overpressured the palo duro is an older paleozoic age basin that has been tectonically uplifted fluid flow is gravity driven from topographically high recharge areas to discharge in topographically low areas fluid pressures are subhydrostatic fluids discharge more easily than they are recharged not all flow is derived by a simple recharge discharge model brines may flow from other basins into the palo duro basin and waters may discharge from the palo duro basin into other basins areal differences in the chemical composition of the basin brines may be the result of different origins