geochemistry origin and accumulation of petroleum in the eocene wenchang formation reservoirs in pearl river mouth basin south china sea a case study of hz25 7 oil field abstract the pearl river mouth basin in the south china sea has accumulated 2 km of eocene sediments in its deep basin and has become the exploration focus due to the recent discoveries of the hz25 7 oil field in the eocene wenchang e 2 w formation in this study the geochemical characteristics of potential source rocks and petroleum in the hz25 7 oil field are investigated and the possible origins and accumulation models developed the analytical results reveal two sets of potential source rocks e 2 w and enping e 2 e formations developed in the study area the semi deep to deep lacustrine e 2 w source rocks are characterized by relatively low c 29 steranes low c 19 c 23 tricyclic terpane 24 tetracyclic terpane c 30 hopane trans trans trans bicadinane t c 30 hopane most 30 4 methyl sterane c 29 sterane 0 2 ratios in contrast the shallow lacustrine and deltaic swamp plain e 2 e source rocks are characterized by relatively high c 29 steranes high c 19 c 23 tricyclic terpane 0 6 high c 24 tetracyclic terpane c 30 hopane 0 1 variable yet overall high t c 30 hopane and low c 30 4 methyl sterane c 29 sterane 19 c 23 tricyclic terpane ratios mean value 0 39 low c 24 tetracyclic terpane c 30 hopane ratios mean value 0 07 high c 30 4 methyl sterane c 29 sterane ratios mean value 1 14 and relatively high c 27 regular sterane content of petroleum in the hz25 7 oil field indicate that the petroleum most likely originated from the e 2 w formation mudstone in the huizhou depression one stage of continuous charging is identified in the hz25 7 oil field oil injection is from 16 ma to present and peak filling occurs after 12 ma thin sandstone beds with relatively good connectivity and physical properties porosity and permeability in the e 2 w formation are favorable conduits for the lateral migration of petroleum this petroleum accumulation pattern implies that the e 2 w formation on the western and southern margins of the huizhou depression are favorable for petroleum accumulation because they are located in a migration pathway thus exploration should focus in these areas in the future

diurnal variations in vertical strain observed in a temperate valley glacier 1 during a period of diurnal fluctuations in glacial flow speed vertical strain was measured with sub daily temporal resolution on unteraargletscher switzerland mean vertical strain in boreholes up to 300 m deep in 400 m thick ice was found to fluctuate diurnally vertical strain rates were tensile in the daytime and compressive at night with a magnitude of up to 10 3 day 1 horizontal surface strain was observed to fluctuate in a manner consistent with the vertical deformation diurnal surface flow speed variations correlated well with basal water pressure suggesting a basal control on temporal flow variations nevertheless the strain rate measurements indicated that changes in surface flow speed are affected by internal ice deformation and not a direct measure of local basal motion basal conditions in the surrounding neighborhood and their temporal variations take an important role in short term glacial flow fluctuations

petroleum systems of oman charge timing and risks after 35 years of exploration creaming of the conventional plays in oman is nearly complete and consequently the search has commenced for new less obvious plays many of the new opportunities occur beyond the known hydrocarbon provinces and are considered to have significant charge risks to define these risks extensive basin modeling studies have been conducted in recent years modeling and empirical data show that mesozoic and cenozoic kitchen areas are restricted to western north oman the only areas currently buried at their maximum temperature large parts of north and central oman depend on lateral migration from these kitchens for their charge progressive uplift of the east flank and basin inversion since the middle paleozoic provides favorable conditions for long distance migration in the post carboniferous interval in central oman geochemical tracer molecules benzocarbazoles suggest that a north south trending reactivated basement grain has funneled charge up to 300 km southeastward charge risks increase in the deeper sequence in which eastward migrating hydrocarbons have to traverse the ghaba salt basin a pronounced syncline at depths greater than 3 km the south oman salt basin is currently cool because of shallow depths and hydrodynamic fluid flow activity the shallow post cambrian reservoirs rely on storage of early cambrian ordovician charge by the ara salt cambrian sequence followed by release of hydrocarbons as the salt edge retreats through time basin modeling has outlined the extent of the different petroleum systems and provided us with risk maps to guide our next exploration phase it has revitalized some of the mature plays for instance the gharif formation where oil exploration is now focused along late cretaceous and tertiary migration paths deeper sections are envisaged to have significant scope for gas

modeling secondary oil migration with core scale data viking formation alberta basin the viking formation in the alberta basin contains approximately 88 7 x 106 m3 5 579 x 108 bbl of recoverable oil which migrated more than 200 km as indicated by oil source rock correlation simulating the mechanisms controlling secondary oil migration hydrodynamics buoyancy and permeability heterogeneity is beneficial for exploration but it remains extremely difficult to predict oil occurrences although core scale petrophysical data for the viking formation are abundant 69 000 core plugs the extent of fracture permeability and permeability alteration due to diagenesis are unknown moreover sampling bias may affect the permeability distribution in unpredictable ways numerical simulations of oil migration were conducted using the highest core plug measurement of permeability from each borehole to obtain an upper bound on oil migration velocities this permeability model is not appropriate for simulating stratigraphic entrapment of oil but it does reveal that core scale data are in the appropriate range of magnitude to have allowed significant oil migration regional groundwater flow was essential for charging several of the largest and most distant oil fields in the viking formation maximum core plug permeability data are useful for modeling the extent of secondary oil migration and may have applications to fluid flow and transport modeling in other foreland settings

impact of an extreme melt event on the runoff and hydrology of a high arctic glacier on 28 30 july 2000 an extreme melt event was observed at john evans glacier jeg ellesmere island 79 40 0 n 74 00 0 w hourly melt rates during this event fell in the upper 4 of the distribution of melt rates observed at the site during the period 1996 2000 synoptic conditions during the event resulted in strong east to west flow over the northern sector of the greenland ice sheet with descending flow on the northwest side reaching ellesmere island on jeg wind speeds during the event averaged 8 1ms 1 at 1183 m a s l with hourly mean wind speeds peaking at 11 6ms 1 air temperatures reached 8 c and rates of surface lowering measured by an ultrasonic depth gauge averaged 56 mm day 1 calculations with an energy balance model suggest that increased turbulent fluxes contributed to melt enhancement at all elevations on the glacier while snow albedo feedback resulted in increased melting due to net radiation at higher elevations the event was responsible for 30 of total summer melt at 1183 m a s l and 15 at 850 m a s l conditions similar to those during the event occurred on only 0 1 of days in the period 1948 2000 but 61 of events occurred in the summer months and there was an apparent clustering of events in the 1950s and 1980s such events have the potential to impact significantly on runoff mass balance and drainage system development at high arctic glaciers and changes in their incidence could play a role in determining how high arctic glaciers respond to climate change and variability copyright 2003 john wiley sons ltd

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

an experimental study of secondary oil migration experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions different combinations of bead sizes oil densities oil water interfacial tensions and column orientations have been tested in some experiments the oil was replaced by air the observations included the oil migration pathway the minimum oil column height needed for migration and the rate of advance of the migration front migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone the minimum oil zone height needed for migration can be predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected in most experiments the migration front advanced at a constant rate which depended on the fluid properties bead size initial oil height and pore structure migration rate is dependent on buoyant and capillary forces but the dependence on capillary forces becomes weaker as the oil length increases column orientation also has been found to affect migration efficiency

debris transport in a temperate valley glacier haut glacier d arolla valais switzerland hambrey m j goodsell becky glasser n f 2005 debris transport in a temperate valley glacier haut glacier d arolla valais switzerland journal of glaciology 51 172 pp 139 146

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

modelling of secondary migration and entrapment of a multicomponent hydrocarbon mixture using equation of state and ray tracing modelling techniques modelling of secondary migration and entrapment of a multicomponent hydrocarbon mixture using equation of state and ray tracing modelling techniques

a m gurnell and m j clark eds 1987 glacio fluvial sediment transfer an alpine perspective chichester etc john wiley and sons ltd

analysis of secondary migration of hydrocarbons in the ordovician carbonate reservoirs in the tazhong uplift tarim basin china the process and mechanisms of secondary hydrocarbon migration in the tazhong uplift tarim basin were investigated based on the analysis of the regional structure and by integrating geologic hydrodynamic and geochemical parameters parameters successfully analyzed included the fluid potential fluid properties production outputs and diamantane index the results indicated that hydrocarbons migrated into the tazhong uplift from the northern part of the manjiaer depression through a series of injection points ips during four orogenies that is the early caledonian 510 ma the late caledonian 439 ma the late hercynian indosinian 290 ma and the yanshanian himalayan 208 ma a total of six ips were identified at the intersections of the northeast trending faults and the northwest trending flower strike faults the hydrocarbons migrated from the ips into traps along regional trends from northwest to southeast and from northeast to southwest the hydrocarbon migration process and patterns determined the distribution of hydrocarbon properties and production rates in the tazhong uplift with increasing distance from the ips daily hydrocarbon production decreases and the hydrocarbons become progressively heavier and display lower gas oil ratios

secondary migration of hydrocarbons in the zhujiang formation in the huixi half graben pearl river mouth basin south china sea the process and mechanisms of secondary hydrocarbon migration in the huixi half graben pearl river mouth basin were investigated on the basis of geological analysis of the strata and study of the porosity and permeability of the reservoir rocks fluid potential oil properties and geochemistry of oil source correlation the results suggest that the hydrocarbons of the zhujiang formation in the huixi half graben were derived from source rocks of the eocene wenchang formation and the eocene oligocene enping formation in the huizhou sag the hydrocarbons migrated laterally from northeast to southwest the sandstone in the upper member of the zhujiang formation exhibited superior physical properties porosity and permeability and connectivity than the lower member thin sandstone beds with good physical properties and stable distribution in the upper member of the zhujiang formation were the main carrier beds for lateral hydrocarbon migration

links between acceleration melting and supraglacial lake drainage of the western greenland ice sheet 1 the impact of increasing summer melt on the dynamics and stability of the greenland ice sheet is not fully understood mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding here we compare subdaily ice velocity and uplift derived from nine global positioning system stations in the upper ablation zone in west greenland to surface melt and supraglacial lake drainage during summer 2007 starting around day 173 we observe speedups of 6 41 above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations followed by a late summer slowdown after initial speedup we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting most lake drainages were undetectable in the velocity record and those that were detected only perturbed velocities for 1 day suggesting preexisting drainage systems could efficiently drain large volumes of water the dynamic response to melt forcing appears to 1 be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses and 2 decrease over the course of the summer presumably as the subglacial drainage system evolves to greater efficiency the relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here thus increases in summer melting may not guarantee faster seasonal ice flow

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

a multicomponent coupled model of glacier hydrology 1 theory and synthetic examples 1 basal hydrology is acknowledged as a fundamental control on glacier dynamics especially in cases where surface meltwater reaches the bed for many glaciers at midlatitudes basal drainage is influenced by subaerial englacial and subsurface water flow one of the major shortcomings of existing basal hydrology models is the treatment of the glacier bed as an isolated system we present theoretical and computational models that couple glacier surface runoff englacial water storage and transport subglacial drainage and subsurface groundwater flow each of the four model components is represented as a two dimensional vertically integrated layer that communicates with its neighbors through water exchange governing equations are derived from the law of mass conservation and are expressed as a balance between the internal distribution of water and external sources the numerical exposition of this theory is a time dependent finite difference model that can be used to simulate glacier drainage in this paper we outline the theory and conduct simple tests using an idealized glacier geometry in the companion paper the model is tailored to trapridge glacier yukon territory canada where results are compared with measurements of subglacial water pressure

do debris covered glaciers demonstrate distinctive hydrological behaviour compared to clean glaciers abstract supraglacial debris is known to strongly influence the distribution of glacier surface melt since melt inputs drive the formation and evolution of glacial drainage systems it should follow that the drainage systems of debris covered glaciers will differ from those of debris free glaciers this would have implications for the proglacial runoff regime subglacial erosion and glacier dynamics this paper presents analysis of return curves from 33 successful dye injections into the extensively debris covered miage glacier italian alps it demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system where the debris cover is continuous melt is lower and the surface topography is chaotic with many small supraglacial catchments these factors result in an inefficient englacial subglacial drainage network beneath continuous debris which drains to the conduit system emanating from the upper ablation zone melt rates are high in areas of clean and dirty ice above the continuous debris runoff from these areas is concentrated by inter moraine troughs into large supraglacial streams which encourages the early season development of an efficient englacial subglacial conduit system downstream of this area drainage efficiency from the debris covered area increases over the melt season but dye trace transit velocity remains lower than from moulins on the upper glacier future runoff models should account for the influence of supraglacial debris on the hydrological system

secondary migration of oil experiments supporting efficient movement of separate buoyant oil phase along limited conduits geologic note experimental data suggest that the secondary migration of oil in porous permeable sediments probably occurs in most circumstances along restricted pathways or conduits these conduits are formed after the oil has reached a high enough saturation in the reservoir rock for the buoyancy of the oil to overcome the capillary pressure in the pore throats the oil probably moves vertically until it reaches the top of the reservoir interval the oil then moves updip along the top of the reservoir interval via a narrow restricted pathway until it reaches the trap and begins to accumulate depending on the area of the original oil saturation at the bottom of the reservoir unit and the structural geometry multiple conduits may form along which the oil may flow because these conduits are limited in diameter the amount of oil lost during secondary migration could be limited to the irreducible oil saturation left behind in the conduit provided no small scale traps exist along the path to the main trap rates of oil movement are very rapid in a geologic context suggesting that the timing of primary migration is a good indicator of the timing of secondary migration

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

velocity discharge relationships derived from dye tracer experiments in glacial meltwaters implications for subglacial flow conditions repeated dye tracer tests were undertaken from individual moulins at haut glacier d arolla switzerland over a number of diurnal discharge cycles during the summers of 1989 1991 it was hoped to use the concepts of at a station hydraulic geometry to infer flow conditions in subglacial channels from the form of the velocity discharge relationships derived from these tests the results however displayed both clockwise and anticlockwise velocity discharge hysteresis in addition to the simple power function relationship assumed in the hydraulic geometry approach clockwise hysteresis seems to indicate that a moulin drains into a small tributary channel rather than directly into an arterial channel and that discharges in the two channels vary out of phase with each other anticlockwise hysteresis is accompanied by strong diurnal variations in the value of dispersivity derived from the dye breakthrough curve and is best explained by hydraulic damming of moulins or sub englacial passageways despite the complex velocity discharge relationships observed some indication of subglacial flow conditions may be obtained if tributary channels comprise only a small fraction of the drainage path and power function velocity discharge relationships are derived from dye injections conducted during periods when the supraglacial discharge entering the moulin and the bulk discharge vary in phase analyses based on this premise suggest that both open and closed channel flow occur beneath haut glacier d arolla and that flow conditions are highly variable at and between sites

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

oil composition variation and reservoir continuity unity field sudan abstract a suite of oils from stacked reservoirs in the unity field in sudan has been analyzed by various geochemical techniques for molecular information to elucidate the geological processes which cause variations in oil composition and their resulting oil fingerprints in different reservoir units analyses of these highly paraffinic oils indicate that the chromatographic fingerprint variations are due to differences in the abundances of saturated compounds including branched and cyclic alkanes neither aromatics nor nso compounds have any significant effect on the observed fingerprint variations this association of saturates instead of aromatics and nso compounds with the fingerprint variations precludes rock fluid interactions as a cause of the variations biomarker analyses show that variations in thermal maturity and organic facies of the source rock are responsible for the fingerprint variations thermal maturity increases with the depth of the reservoir suggesting a multiple charge process for the oils to fill these reservoirs over an extended period of time apparently the source rock generated and expelled progressively more mature oils and little mixing occurred during migration thus knowledge of oil compositional variations from one reservoir to another organic facies variation and source rock maturity combined with tectonic history may help explain charging and timing of oil emplacement

incremental subglacial meltwater sediment deposition and deformation associated with repeated ice bed decoupling a case study from the island of funen denmark abstract on the island of funen denmark sediments that are 4 7 m below the land surface consist of a 2 4 m thick sequence of stacked and folded glaciofluvial sediments overlain by a 2 3 m thick basal till the glaciofluvial sediments consist of tabular beds of planar stratified massive and cross stratified sand and gravel with localized channel fills of open framework gravel sand and gravel beds exhibit curvilinear sheath folding often leading to eye folds this folding is attributed to repeated glacier bed decoupling and recoupling with subglacial deposition of sand and gravel by meltwater occurring during the decoupling phase and deformation occurring during recoupling sand and gravel beds are typically separated by silty clay beds and laminations recording slackwater deposition within subglacial cavities folds frequently display attenuated upper limbs reflecting shearing associated with overlying ice movement on lower fold limbs only localized thrusting is observed suggesting water saturation of sands and gravels during deformation and relatively low strain rates folds are frequently truncated by overlying sand and gravel beds no evidence of shearing is found along these contacts which are interpreted as erosional surfaces thus we propose that the glaciofluvial sediment sequence records incremental step wise subglacial deposition and deformation rather than wholesale deformation following emplacement of the entire glaciofluvial sequence specifically we envisage that individual beds were deposited and folded subglacially with ice bed decoupling occurring during sediment deposition followed by recoupling and shearing of the upper bed surface by the ice base to produce folds with attenuated upper limbs incremental deformation and folding were facilitated by elevated porewater pressure within the sediments silty clay beds helped to maintain elevated porewater pressure by acting as local aquitards a general absence of till from the glaciofluvial sequence save for localized cm scale blocks suggests either non deposition or reworking into the glaciofluvial sediments deposition of tabular sand and gravel beds and open framework gravel filling scours within single beds suggest broad sheet like subglacial flows 10 100 m wide that become increasingly channelized we propose that the sedimentary sequence records a highly dynamic glaciohydraulic system characterized by repeated localized subglacial cavity development and storage and release of meltwater leading to glacier decoupling that may have facilitated fast flow of the baltic ice stream

variability in ice motion at a land terminating greenlandic outlet glacier the role of channelized and distributed drainage systems we use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land terminating greenlandic outlet glacier we find a close agreement between horizontal ice velocity vertical ice velocity and modelled subglacial water pressure over the course of a melt season on this basis we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction a process itself driven by fluctuations in basal water pressure originating in subglacial channels this process is not captured by traditional sliding laws linking water pressure and basal velocity which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

molecular characterization of dissolved organic matter associated with the greenland ice sheet abstract subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial interglacial timescales the likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores we examined the composition of carbon pools associated with different regions of the greenland ice sheet subglacial supraglacial proglacial in order to elucidate the type of dissolved organic matter dom present in the subglacial discharge over a melt season electrospray ionization esi fourier transform ion cyclotron resonance ft icr mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes specifically a larger proportion of protein like compounds were observed in the supraglacial samples and in the early melt season spring subglacial discharge in contrast the late melt season summer subglacial discharge contained a greater fraction of lignin like and other material presumably derived from underlying vegetation and soil these results suggest 1 that the majority of supraglacial dom originates from autochthonous microbial processes on the ice sheet surface 2 that the subglacial dom contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism and 3 that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season these conclusions are consistent with the hypothesis that given sufficient time e g overwinter storage resident subglacial microbial communities may oxidize terrestrial material beneath the greenland ice sheet

petroleum generation migration and entrapment in the zhu 1 depression pearl river mouth basin south china sea abstract analysis of crude oils from several fields in and near the huizhou sag zhu 1 depression pearl river mouth basin provides an excellent demonstration of inferring petroleum generation migration and entrapment in areas where drilling encounters hydrocarbons but fails to penetrate the effective generative sequence this paper illustrates the integration of geochemical geophysical and geological interpretations to develop a model of petroleum generation migration and entrapment the zhu 1 depression is one of three subbasins in the pearl river mouth basin sediment fill within the subbasin consists of paleogene synrift units and miocene to recent postrift deposits although drilling in the zhu 1 s huizhou sag and on the adjacent dongsha massif has netted numerous oil discoveries since the early 1980 s it has not encountered any effective or potential source rocks within the penetrated sections however interpretation of the systematic variations in crude oil chemistry within the regional geologic and structural framework has been invaluable in inferring source attributes and delineating location and distribution of the unpenetrated probable source the signatures resulting from genetic and alteration processes suggest that high wax oils were generated in mature lacustrine source facies of the synrift sequence and were expelled into a tightly sealed massive sandstone carrier system they migrated south southeast toward the dongsha massif were entrapped to spill point in traps along the migration route and were altered increasingly within the successively shallower and cooler reservoirs on the massif

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

the dhahaban petroleum system of oman the dhahaban petroleum system from a source rock of cambrian age covers some 50 000 km2 and contains 1 6 x 109 m3 of oil and 1000 x 109 m3 of gas in place of which at least respectively 0 35 x 109 m3 and 700 x 109 m3 are recoverable for many years the origin of the so called q oil was enigmatic and defied typing to a source rock integration of recent advances in geochemistry and basin modeling has now permitted us to retrace its source areas model the generation and migration histories and outline the areal and stratigraphic extent of the petroleum system

diurnal fluctuations in borehole water levels configuration of the drainage system beneath bench glacier alaska usa water levels were measured in boreholes spaced along the entire length of bench glacier alaska usa for a period in excess of 2 years instrumented boreholes were arranged as nine pairs along the center line of the glacier and an orthogonal grid of 16 boreholes in a 3600 m 2 region at the center of the ablation area diurnal fluctuations of the water levels were found to be restricted to the late melt season pairs of boreholes spaced along the length of the ablation area often exhibited similar fluctuations and diurnal changes in water levels three distinct and independent types of diurnal fluctuations in water level were observed in clusters of boreholes within the grid of boreholes head gradients suggest water did not flow between clusters and a single tunnel connecting the boreholes could not explain the observed pattern of diurnal water level fluctuations inter borehole and borehole cluster connectivity suggests the cross glacier width of influence of a segment of the drainage system connected to a borehole was limited to tens of meters a drainage configuration whereby boreholes are connected to a somewhat distant tunnel by drainage pipes of differing lengths often hundreds of meters is shown with a numerical test to be a plausible explanation for the observed borehole behavior

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

geostatistical models of secondary oil migration within heterogeneous carrier beds a theoretical example this paper critically evaluates the utility of two different geostatistical methods in tracing long distance oil migration through sedimentary basins geostatistical models of petroleum migration based on kriging and the conditional simulation method are assessed by comparing them to known oil migration rates and directions through a numerical carrier bed in this example the numerical carrier bed which serves as ground truth in the study incorporates a synthetic permeability field generated using the method of turning bands different representations of lateral permeability heterogeneity of the carrier bed are incorporated into a quasi three dimensional model of secondary oil migration the geometric configuration of the carrier bed is intended to represent migrat on conditions within the center of a saucer shaped intracratonic sag basin in all of the numerical experiments oil is sourced in the lowest 10 of a saucer shaped carrier bed and migrates 10 14 km outward in a radial fashion by buoyancy the effects of vertical permeability variations on secondary oil migration were not considered in the study two sets of numerical experiments are presented in this study in the first set computed oil migration patterns and rates through the numerical carrier bed are compared to kriged and optimal estimations based on a suite of 50 conditional simulations to determine the utility of each geostatistical approach the geostatistical models also are compared to a much simpler oil migration simulation using a homogeneous carrier bed an assumption typically made in cross sectional models of oil migration the permeability realizations generated by kriging and the conditional simulation method were constructed using 50 randomly placed sampling points a second set of numerical experiments was made to determine how data sample size 20 35 50 100 and 250 randomly selected points influences p edicted oil migration patterns using kriged permeability fields oil migration patterns through the synthetic carrier bed were quantitatively compared to geostatistical representations of oil transport by computing the degree of correlation r2 of oil lens thickness at 5 10 and 15 m y after the onset of migration quantitative results indicate that both kriging and the conditional simulation method produced realistic representations of spatial oil lens patterns and first arrival times both kriging and the conditional simulation method produced results far more realistic than the simulation with a homogeneous carrier bed after 15 m y the spatial correlations r2 between the known oil lens patterns and that of the kriged and ensemble average of the 50 conditional simulations were 0 67 and 0 74 respectively although the conditional simulation method produced the best results it did so at a significant computational expense computed oil migration patterns based on different kriged permeability maps that incorporated varying amounts of control data points did not improve signif cantly when more than 100 randomly placed wells were used the study provides compelling evidence that secondary oil migration is an inherently three dimensional process for well studied basins geostatistical representations of long range oil migration could be of value in ongoing exploration strategies end page 1679

structure morphology and water flux of a subglacial drainage system midtdalsbreen norway digital elevation models of the surface and bed of midtdalsbreen norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden a distributed degree day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions in addition 78 dye tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady state water pressures beneath the glacier are 70 of ice overburden analysis of the dye return curves together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad low channels average width height ratio 75 the smaller drainage network on the west consists of a hydraulically inefficient distributed system dominated by channels that are exceptionally broad and very low average width height ratio 350 the even smaller central drainage network also consists of a hydraulically inefficient distributed system dominated by channels that are very broad and exceptionally low average width height ratio 450 the channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system

evolution of glacial flow and drainage during the ablation season proglacial discharge is controlled by the geometry of the glacial drainage network and by meltwater processes the glacial drainage systems of some alpine glaciers have been characterised using a model based on a proglacial discharge analysis in this paper we apply high frequency systemic analysis to data collected from the baounet glacier french alps during two successive ablation seasons our approach is based on an analysis of the evolution of daily recession curves during the ablation period the observed data are fitted by a single coefficient dependant recession law changes in are compared to variations in the daily discharge amplitude and the time lag between air temperature and proglacial discharge the changes in the values do not appear to be related to changes in the time lag and the amplitude of the daily discharge there were significant variations in the coefficient during the two ablation periods studied here even if there was no time lag or the daily discharge amplitude change high values of correspond to high drainage velocities therefore increases in values can be used as an indicator of the evolution of the glacier s internal drainage network

subglacial hydrology at rink isbrae west greenland inferred from sediment plume appearance marine terminating outlet glaciers discharge most of the greenland ice sheet s mass through frontal ablation and meltwater runoff while calving can be estimated by in situ and remote sensing observations submarine melting and subglacial meltwater transport are more challenging to quantify here we investigate the subglacial hydrology of rink isbrae a fast flowing west greenland tidewater glacier using time lapse photography modeled runoff estimates and daily satellite imagery from 2007 to 2011 we find that sediment plumes appear episodically at four distinct locations across the terminus and last between 2 h and 17 d this suggests short term variability in discharge and the existence of persistent pathways the seasonal onset of sediment plumes occurs before supraglacial lake drainages shortly after the onset of runoff and only after the wintertime ice melange has begun disintegrating plumes were also visible after the cessation of runoff 23 5 d which is indicative of subglacial storage the lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front

seasonal changes in the morphology of the subglacial drainage system haut glacier d arolla switzerland dye tracing techniques were used to investigate the glacier wide pattern of change in the englacial subglacial drainage system of haut glacier d arolla during the ablation seasons of 1990 and 1991 analysis of breakthrough curve characteristics indicate that over the course of a melt season a system of major channels developed by headward growth at the expense of a hydraulically inefficient distributed system by the end of the melt season this channel system extended at least 3 3 km from the snout of the 4 km long glacier and drained the bulk of supraglacially derived meltwater passing through the glacier the upper limit of the channel system closely followed the retreating snowline up glacier rates of headward channel growth reached c 65 m d 1 although these rates decreased in the upper 1 km of the glacier where snowline retreat exposed a patchy firn aquifer it appears that the removal of snow with its high albedo and significant water storage capacity from the glacier surface resulted in a dramatic increase in the volume of runoff into moulins and in the peakedness of daily runoff cycles this induced transient high water pressures within the distributed drainage system which caused it to evolve rapidly into a channelised system it is therefore likely that at a local scale channel growth occurred down glacier from moulins and that the overall up glacier directed pattern of channel formation was caused by the retreating snowline exposing new moulins and crevasses to inputs of ice derived meltwater damping of diurnal melt inputs by storage in the firm aquifer accounts for the slowing of channel growth in the upper glacier 1998 john wiley sons ltd

using element geochemistry and detrital zircon geochronology to constrain provenance of the eocene sediments in the deep water area of the pearl river mouth basin south china sea abstract as the largest sag in the zhu ii depression within the pearl river mouth basin the baiyun sag bys lies in an area of interaction among the eurasian plate pacific plate and indian plate the bys mainly experienced the paleogene rift stage and neogene quaternary post rift stage thick syn rift sediments in the bys have recorded the nature of provenance and provide an excellent record of regional tectonic evolution prior to the opening of the south china sea in this study elemental geochemical analysis combined with published zircon detrital u pb dating results are applied to better understand the provenance change and tectonic setting of the bys during the eocene in this respect the chondrite normalized ree patterns of eocene samples from six wells are highly similar to upper continental crust ucc and post archean australian shale paas particularly with respect to lree enrichment significantly negative eu anomalies and slight ce anomalies geochemical results confirm that the bys eocene sediments were derived from a continental island arc to an active continental margin in addition the rock types of sources and the relatively narrow detrital zircon ages show that mesozoic intermediate felsic igneous and metamorphic rocks derived from local topographic highs contributed to infilling most of the bys furthermore the results show that the panyu low uplift began to accept large sediments transported by the paleo pearl river from the south china coast during the active syn rift stage prior to the opening of the south china sea

growth and collapse of the distributed subglacial hydrologic system of kennicott glacier alaska usa and its effects on basal motion nearly 100 days of hourly glacier motion hydrology and hydrochemistry measurements on kennicott glacier alaska usa demonstrate the complicated relationship between water and motion at the glacier bed our observations capture the transient glacier response to seasonal and daily melt cycles and to a jokulhlaup that prompts a sixfold increase in glacier speed sliding is promoted whenever the water inputs to the glacier exceed the capacity of the subglacial hydrologic system to transmit the water sensitivity of sliding to daily meltwater inputs varies strongly through the season implying that the state of the hydrologic system governs the sensitivity of basal sliding a numerical model constructed to explore these relationships reveals the roles of the effective pressure the exponent to which this is taken in the sliding law 0 1 0 6 glacier macroporosity 2 and the cavity generating capacity of the glacier bed which encapsulates the sizes and spacing of bed roughness elements temporal changes in the effective pressure associated with evolution of both water inputs and subglacial water transmission capacity can explain the varying strength of diurnal velocity fluctuations of kennicott glacier spatial patterns of glacier macroporosity and of basal roughness govern variation in sensitivity of sliding to water inputs

secondary migration routes in the brent sandstones of the viking graben and east shetland basin evidence from oil residues and subsurface pressure data the viking graben of the north sea contains a major deltaic reservoir the brent group within the brent group the etive formation a coastal barrier sand is both areally continuous and has excellent porosity and permeability it is sandwiched between the fine grained micaceous sandstones of the rannoch formation below and the impermeable mudstones of the ness formation above consequently the etive formation has acted as the most important regional conduit for secondary migration of upper jurassic sourced oils oil migration through time has left a heavy residue in the uppermost part of the formation these residues are aromatic asphaltic but otherwise resemble locally reservoired oils migration sensitive biological marker ratios obtained from the residues change wi h distance from source secondary migration route mapping based on the movement of oil by buoyancy in well defined isolated pressure compartments integrated with timing of oil generation indicates that the ninian field could be sourced from two areas late cretaceous migration from the southeast in the viking graben and tertiary migration from the west and southwest explaining some of the contrasting reservoir and oil characteristics of the ninian and lyell fields

in situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems continuous subglacial measurements of turbidity and electrical conductivity two indicators of basal water quality can be used to help characterize subglacial drainage systems these indicators of water quality yield information that complements that provided by water pressure measurements quantitative attributes of subglacial drainage systems such as water velocity and subglacial residence time as well as qualitative behaviour for example spatial and temporal variations in system morphology can be deduced using water quality measurements interpretation is complicated by the many potential influences on turbidity and electrical conductivity but when these complications are appreciated a richer interpretation results to demonstrate the utility of basal water quality measurements observations from trapridge glacier yukon territory canada were examined the data reveal complex behaviour of the drainage system but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system the measurement and interpretation methods described and demonstrated are applicable to other glaciers as such they should prove useful for characterizing different subglacial drainage configurations and behaviours thereby improving our general understanding of the hydrology and dynamics of wet based glaciers

supraglacial forcing of subglacial drainage in the ablation zone of the greenland ice sheet 1 we measure hydrological parameters in meltwater draining from an outlet glacier in west greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the greenland ice sheet gris our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system across a catchment 600 km2 to distances 50 km from the ice sheet margin this expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier this system is similar to alpine glaciers these observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the gris

secular and environmental constraints on the occurrence of dinosterane in sediments abstract the distribution patterns of sedimentary a ring methylated steranes have changed markedly over geological time although dinosterane and its isomer 24 ethyl 4 methylcholestane have been tentatively identified in three proterozoic rock units they are either not detectable or occur in low abundance relative to 3 methyl steranes throughout most of the palaeozoic between permian and middle triassic times 260 220 ma ago 4 methyl sterane abundances in marine sediments increased markedly the presence of dinosterane in some middle triassic marine sediments is contemporaneous with the appearance of fossil cysts of uncontested dinoflagellate affinity 4 methyl steranes including dinosterane or their precursor sterenes and sterols then show a continuous presence often in high abundance in marine sediments from the late triassic through to the present day assemblages of 4 methyl steranes and their precursors but with dinosterane absent or in low relative abundance are often the predominant steroids in lacustrine sediments in the cainozoic dinosterane appears to arise predominantly from marine dinoflagellates and as a consequence is a useful biological marker for mesozoic and cainozoic marine organic matter the isomer 24 ethyl 4 methylcholestane is likely to have multiple origins although its very high abundance in tertiary lacustrine sediments and oils compared to older materials suggests that dinoflagellates could also be the source in these cases

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

seasonal variations in greenland ice sheet motion inland extent and behaviour at higher elevations abstract we present global positioning system observations that capture the full inland extent of ice motion variations in 2009 along a transect in the west greenland ice sheet margin in situ measurements of air temperature and surface ablation and satellite monitoring of ice surface albedo and supraglacial lake drainage are used to investigate hydrological controls on ice velocity changes we find a strong positive correlation between rates of annual ablation and changes in annual ice motion along the transect with sites nearest the ice sheet margin experiencing greater annual variations in ice motion 15 18 than those above 1000 m elevation 3 8 patterns in the timing and rate of meltwater delivery to the ice bed interface provide key controls on the magnitude of hydrologically forced velocity variations at each site in the lower ablation zone the overall contribution of variations in ice motion to annual flow rates is limited by evolution in the structure of the subglacial drainage system at sites in the upper ablation zone a shorter period of summer melting and delayed establishment of a hydraulic connection between the ice sheet surface and its bed limit the timeframe for velocity variations to occur our data suggest that land terminating sections of the greenland ice sheet will experience increased dynamic mass loss in a warmer climate as the behaviour that we observe in the lower ablation zone propagates further inland findings from this study provide a conceptual framework to understand the impact of hydrologically forced velocity variations on the future mass balance of land terminating sections of the greenland ice sheet

moulin density controls drainage development beneath the greenland ice sheet this work was funded through a uk natural environment research council doctoral training grant lcag 133 a bowring junior research fellowship st catharine s college cambridge and a leverhulme newton trust early career fellowship all awarded to a f b i j h was supported by a marie curie fp7 career integration grant within the 7th european union framework programme

scaled physical model of secondary oil migration a scaled physical model was constructed to simulate gravity and capillary controlled flow of oil into a water saturated sand during secondary hydrocarbon migration the model provided both visualization of the flow patterns and estimates of hydrocarbon transport rates and efficiencies the dimensions and physical properties of the model were designed so the balance of gravity capillary and viscous forces was the same in the model as in the geologic system the physical model was a sand pack between glass plates the pack was 52 cm high 100 cm long 2 5 cm thick and inclined at a 5 dip its porosity was 42 and its permeability was 7 0 10 10 m2 710 d it modeled a geologic carrier bed 27 m thick with 20 porosity and 9 9 10 14 m2 100 md permeability overlying a source rock a dyed oil was injected into the lowest corner at a rate of 1 cm3 day and it exited the highest corner at atmospheric pressure oil movement was followed both visually and by ultrasonic velocity measurements the behavior of fluids in the model led us to the following conclusions for oil transport through water wet homogeneous carrier beds the rate limiting step in charging a trap is not secondary migration but rather the rate of oil release from the source rock high hydrocarbon loss may occur during vertical migration when the carrier bed lies above the source because of extensive dispersion losses during lateral migration are probably minimal because flow is concentrated below the top seal

sediment export transient landscape response and catchment scale connectivity following rapid climate warming and alpine glacier recession abstract in the face of rapid climate warming rapid glacier recession should lead to a marked increase in the spatial extent of the paraglacial zone in glaciated drainage basins the extent of the paraglacial zone has been well established to be transient but there are very few studies of this transient response and what it means for sediment export there is good reason to expect that glacier recession could increase basin scale sediment connectivity as sediment becomes less dependent on glacier surface transport proglacial streams are more able to migrate laterally than subglacial streams and so access sediment for transport and glacier debuttressing may aid the development of gullies that can dissect moraines and so aid hillslope to proglacial zone connectivity by using records of the flushing of hydroelectric power installations we were able to develop a record of coarse sediment sand and gravel export from a basin with a rapidly retreating valley glacier the haut glacier d arolla from 1977 to 2014 modelling suggested that these data could only be partially controlled by transport capacity implying an important role for sediment supply and potentially for the influence of changing sediment connectivity indeed there was evidence of the effects of glacial debuttressing upon gullying processes and hence a possible increase in the ease of connection of upstream basins to the proglacial area more recently we were able to show possible temperature control on sediment export which may only have become apparent because of the progressive development of better sediment connectivity however whilst rapid glacier recession should result in theory in a progressive increase in connectivity of sediment sources to the basin outlet the supply to capacity ratio does not increase continually with glacier recession until maximum capacity is reached we identified two possible examples of why first gullying was also accompanied by the sediment accumulation at the base of moraines that was too coarse to be transported by the proglacial stream maintaining disconnection of the upper basins second the sediment capacity ratio appeared to be elevated during periods of more rapid retreat and we attribute this to the importance of a continued supply of unworked glacial till before fluvial reworking and sorting of freshly exposed sediment increased the resistance of sediment to entrainment and hence export rates thus the transient geomorphic response of glaciated basins to glacier recession may involve negative feedbacks that can reduce the extent to which increases in connectivity elsewhere in the basin lead to increased sediment export

geoscience the plumbing of greenland s ice observations of the water pressure in drilled boreholes and natural moulins on the greenland ice sheet show how its underlying plumbing system controls ice motion during the course of the summer melt season see letter p 80 increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system

using concurrent dna tracer injections to infer glacial flow pathways author s dahlke he williamson ag georgakakos c leung s sharma an lyon sw walter mt abstract 2015 john wiley a sons ltd catchment hydrology has become replete with flow pathway characterizations obtained via combinations of physical hydrologic measurements e g streamflow hydrographs and natural tracer signals e g stable water isotopes and geochemistry in this study we explored how our understanding of hydrologic flow pathways can be improved and expanded in both space and time by the simultaneous application of engineered synthetic dna tracers in this study we compared the advective dispersive transport properties and mass recovery rates of two types of synthetic dna tracers one consisting of synthetic dna strands encapsulated into biodegradable microspheres and another consisting of free dna i e not encapsulated the dna tracers were also compared with a conservative fluorescent dye all tracers were injected into a small 3 2 km2 valley glacier storglaciaren in northern sweden seven of the nine dna tracers showed clear recovery during the sampling period and similar peak arrival times and dispersion coefficients as the conservative fluorescent dye however recovered dna tracer mass ranged only from 1 to 66 while recovered fluorescent dye mass was 99 resulting from the cold and opaque subglacial environment provided by the glacier mass loss associated with microbial activity and photochemical degradation of the dna is likely negligible leaving sorption of dna tracers onto suspended particles and loss of microtracer particles to sediment storage as probable explanations despite the difference in mass recovery the advection and dispersion information derived from the dna tracer breakthrough curves provided spatially explicit information that allowed inferring a theoretical model of the flow pathways that water takes through the glacier

mechanisms of subglacial cavity filling in glacier de tete rousse french alps the deadliest outburst flood from an englacial cavity occurred on glacier de tete rousse in the mont blanc area french alps in 1892 a subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010 2011 and 2012 to protect the 3000 inhabitants downstream the mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed for this purpose the subglacial water volume changes between 2010 and 2013 were reconstructed the size of the cavity following the pumping was found to have decreased from 53 500 m 3 in 2010 to 12 750 m 3 in 2013 creep and the partial collapse of the cavity roof explain a large part of the volume loss analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate with a time delay of 4 6 hours a permanent input of 15 m 3 d 1 not depending on surface melt was also found the meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed the drainage pathway permeability was estimated at 0 054 m s 1 from water discharge measurements and dye tracing experiments

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

transient subglacial hydrology of a thin ice sheet insights from the chasm esker british columbia canada abstract glacier drainage systems are never steady state instead they fluctuate over time and space in response to variation in water input in order to improve numerical models of glacier hydrology it is important to fully understand the processes controlling subglacial drainage system evolution but contemporary ice sheet beds are typically inaccessible thus esker distribution morphology and sedimentology have been used to infer the dynamics and hydrology of former ice sheets however debate remains as to the processes responsible for esker formation and most theoretical investigations have assumed that they formed due to processes that operated beneath thick ice despite many field investigations to the contrary we investigate esker formation during the final stages of the thin inactive and rapidly decaying cordilleran ice sheet cis in interior british columbia canada a combination of geomorphological ground penetrating radar gpr and electrical resistivity tomography ert data suggest esker ridge sedimentary architecture is consistent with synchronous formation during a glacial lake outburst flood glof these data reveal esker ridge deposition most likely took place within an ice tunnel that evacuated late waning stage flow following erosion and partial fill of a broader meltwater corridor esker ridge sedimentary architecture reveals this depositional environment was dynamic reflecting complex interaction between ice thickness ice structure ice tunnel geometry flow conditions and sediment supply under these thin inactive ice conditions ice tunnel location was initially governed by structural weaknesses in the ice and or equipotential gradient because creep closure rates were low the ice tunnel evolved through feedbacks between conduit growth via frictional melting mechanical ice excavation and conduit closure due to sediment infilling rather than ice creep this resulted in a non uniform ice tunnel that enlarged in an upglacier direction and locally unroofed to form open channels during its final stages these data suggest that eskers may record unsteady rather than steady flows in a drainage network and so the assumptions often made when using eskers to inform hydrological components of ice sheet models may not be applicable to all ice sheet settings

seasonal variations in ice deformation and basal motion across the tongue of haut glacier d arolla switzerland records of surface motion englacial tilt and repeat inclinometry are used to determine patterns of surface internal and basal motion across the tongue of haut glacier d arolla switzerland over temporal scales ranging from days to months findings are interpreted with reference to contemporaneous measurements of subglacial water pressures and prior knowledge of the glacier s subglacial drainage system structure long term inclinometry results show pronounced extrusion flow over a subglacial drainage axis with basal velocities up to twice those measured at the glacier surface deformation profiles are more conventional away from the drainage axis with basal velocities 60 70 of surface velocities comparison of long term tilt rates from repeat inclinometry and englacial tilt meters shows close correspondence englacial tiltmeter data are used to reconstruct internal velocity profiles and to split surface velocities into internal deformation and basal motion contributions over spring summer and autumn winter periods although spatial patterns of surface movement are similar between periods patterns of internal and basal motion are not results are interpreted in terms of the location of sticky and slippery spots with temporally changing patterns of basal drag reflecting changing distributions of water pressure

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

geomorphic implications of subglacial drainage configuration rates of basal sediment evacuation controlled by seasonal drainage system evolution abstract although basal sediment evacuation by subglacial meltwater is widely assumed to dominate the sediment budget of most temperate glaciers and ice caps its potential influence for glacial geomorphic processes and landforms has largely been overlooked in the glacial literature data collected at haut glacier d arolla switzerland during the 1998 ablation season are used to test theoretical predictions that subglacial drainage configuration should exert a primary control on rates of basal sediment evacuation by subglacial meltwater seasonal evolution of the subglacial drainage system enables observation of sediment evacuation from both distributed and channelised drainage systems daily suspended sediment load exhibits an extreme nonlinear increase with respect to discharge between winter and summer periods which correspond to periods of predominantly distributed and channelised subglacial drainage respectively these results suggest that subglacial drainage configuration should significantly impact upon a rates of subglacial erosion and debris production b the nature of debris transport and the proportion of sediment in glacial versus fluvioglacial transport pathways and c rates and styles of ice marginal sedimentation in contrast to their distributed counterparts channelised drainage configurations are predicted to encourage subglacial erosion through the removal of basal sediment from the ice bedrock interface and with the exception of supraglacial transport will discourage sediment transport by alternative glacial mechanisms direct sedimentation at the glacier margin may therefore be reduced resulting in smaller moraines despite an overall increase in sediment production an appreciation of the coupling between glacier hydrology and geomorphic processes suggests new frameworks for the understanding of rates and styles of glacial erosion sediment transfer and deposition and the complex geomorphology of ice marginal environments

a hydrological approach to estimating daily glacier ablation reduced meltwater discharge owing to glacier retreat can have severe impacts on downstream water users to assess these impacts it is essential to differentiate between water from glacier melt and other sources we propose a method for doing this on a daily time scale by applying a mixing law to electrical conductivity and proglacial discharge measurements daily ablation is then estimated by applying a recession law to the glacier melt component testing this method on summer hydrology and meteorology measurements from the baounet glacier france taken over six consecutive years 2008 2013 allowed us to reconstruct daily ablation during the ablation period mean ablation rates ranged from 20 to 30 mm day 1 air temperature measurements showed that periods of low ablation during the summer were linked to cooler days and snowfall periods comparisons for three consecutive summers showed that the ablation rates obtained by summing calculated daily ablation were statistically similar to the rates recorded

secondary migration of petroleum along syncline axes a case study of the southern kuqa foreland basin tracing petroleum migration pathways for petroleum exploration in a sedimentary basin is challenging paleo uplifts are generally considered to represent the primary migration directions of petroleum here we propose a model for the kuqa foreland basin in which petroleum migrates along the axes of synclines between paleo uplifts based on an integrated analysis of seismic geochemical and production data interpretation of detailed seismic data indicates that petroleum is unlikely to migrate to the paleo uplifts because of their relatively low positions fault disruptions or a lack of mesozoic reservoirs geochemical parameters including the ratios of alkyl dibenzothiophenes and the gas wetness parameter show that petroleum maturity gradually decreases along the axes of synclines between paleo uplifts from northeast to southwest petroleum production data and gas oil ratios also show decreasing trends from northeast to southwest this evidence suggests that petroleum is likely to migrate along the ax

subglacial drainage system structure and morphology of brewster glacier new zealand a global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of brewster glacier these are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure pw i pw ice overburden ii pw half ice overburden iii pw atmospheric additionally 16 dye tracing experiments at 12 locations were performed through a summer melt season dye return curve shape together with calculations of transit velocity dispersivity and storage are used to infer the likely morphology of the subglacial drainage system taken together the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden by mid summer water pressures are closer to half ice overburden and the channelised drainage system is more hydraulically efficient surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system copyright 2008 john wiley sons ltd

cross coupled flow modeling of coincident streaming and electrochemical potentials and application to subglacial self potential data 1 this study aims to demonstrate that self potential measurements can yield unique information about subglacial drainage conditions which has so far been doubtful at the bed of warm based glaciers arborescent and distributed drainage systems interact and streaming and electrochemical potentials coincide a key secondary aim of this study is therefore the development of a mathematical framework for the analysis of self potentials generated by such interacting flow systems we consider cross coupling between hydraulic electrical and chemical driving forces and apply the resulting model solution to self potential data recorded beneath haut glacier d arolla switzerland we find that 1 the streaming and electrochemical contributions to the total self potential signal can be separated mathematically 2 streaming potentials directly reflect the direction of water flow at the glacier bed 3 combination of streaming potentials with hydraulic conductivity estimates from slug tests allows estimation of in situ subglacial water flow velocities 4 the subglacial zeta potential calculated from estimated values of the streaming coupling coefficient is small 0 022 v due to systematic flushing of clay minerals from the channel area during the melt season and 5 uncertainties in exact electrode location in the borehole are unlikely to produce self potential noise self potential measurements may therefore yield unique information about subglacial drainage conditions and especially the direction and velocity of in situ subglacial water flow are difficult to obtain by other methods we further anticipate that our mathematical framework will be applicable to other areas of subsurface hydrology especially where spatially distributed seepage feeds preferential flow pathways

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

subglacial modulation of the hydrograph from glacierized basins the extent of basin glacierization has important implications for the hydrograph in part because snow firn and ice impart different delays in water transport through the system here the significance of subglacial drainage morphology in modulating the hydrograph is examined with a one dimensional physically based model the conceptual model of subglacial drainage comprises both fast and slow elements respectively associated with summer and winter drainage regimes the additional possibility of a permeable glacier substrate is taken into account by allowing water transport in a subglacial aquifer forced by prescribed rates of melt water delivery to the glacier bed the model predicts glacier discharge by drainage system provenance the effects of 1 hard versus soft glacier beds 2 subsurface permeability and groundwater flow and 3 glacier geometry are then investigated hydrograph character in the form of peak timing and amplitude symmetry with respect to the forcing and the amplitude of diurnal fluctuations is affected by the partitioning of water through the various flow elements hard beds and impermeable substrates maximize the discharge routed through the fast drainage system in the simulations generally resulting in higher seasonal discharge maxima and stronger diurnal variations in discharge high hydraulic transmissivities either at the glacier bed or in underlying strata hinder the development of the fast drainage system in the simulations producing hydrographs of lower amplitude glacier geometry has a modest effect with adverse bed slopes very thick or very thin ice and short glacier lengths favouring prolonged drainage through the slow system these results suggest that the morphology and evolution of the subglacial drainage system may play a significant role in determining the character of the hydrograph from glacierized basins

evolution of drainage system morphology at a land terminating greenlandic outlet glacier 1 the influence of meltwater on the dynamics and geomorphic impact of the greenland ice sheet is strongly controlled by the morphology of the ice sheet s drainage system however this system and its evolution through the melt season remain poorly understood here we present the results of an intensive programme of dye tracing experiments undertaken along the lower 14 km of a land terminating greenlandic outlet glacier over a period of four months during the 2010 melt season these data are interpreted in conjunction with observations of proglacial discharge englacial water storage surface melt rates and ice velocity to produce a detailed picture of the changing hydrology of the glacier following the onset of melt in the spring inputs to the drainage system regularly exceed outputs causing the englacial water level to rise to the ice sheet surface during this time there is a rapid transition from distributed to channelized drainage in those parts of the drainage system closed by ice deformation over winter as the melt season progresses channel efficiency increases and englacial storage and ice velocity decrease high velocity events continue to be observed following the channelization of the drainage system however indicating that hydrological forcing of ice velocity occurs despite the existence of channels during periods when meltwater inputs exceed the capacity of the subglacial drainage system

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

finite element analysis and ray tracing modeling of petroleum migration separate phase flow is the dominant transport mechanism for secondary migration of petroleum phases commonly two different methods are used for the modeling of separate phase flow full 3d modeling finite element analysis which leads to the physically best description but can only be performed on low resolution grids and flowpath modeling ray tracing which can be performed on high resolution grids but is based on simplified physical assumptions a new approach that integrates both methods allows a physically realistic description without losing any of the original geometric information this new approach cuts processing times considerably

biological marker compounds as indicators of the depositions history of the maoming oil shale abstract the eocene maoming oil shale from guangdong province occurs as a laterally uniform stratigraphic section typically 20 25 m thick from which the aliphatic hydrocarbon constituents of six representative samples were investigated using gc and c gc ms the sediments evaluated included the basal lignite a vitrinite lens from the overlying claystone and four intervals from the massive oil shale bed as expected the lignite and vitrinite differ markedly from the oil shales the lignite is dominated by bacterial hopanoids and components of higher plant origin including c 29 steroids and triterpenoids such as oleanenes visually the oil shale samples show corroded and degraded phytoclasts spores wispy particles of fluorescent organic material attributable to dinoflagellates and especially in the uppermost sample colonial algal bodies the distributions of biological markers in the oil shales show many features in common notably a dominance of dinoflagellate derived 4 methylsteroids and a significant proportion of higher plant derived n alkanes with marked odd over even carbon number predominance overall they exhibit several features that resemble characteristics of the messel shale the hydrocarbons of the lowest shale horizon suggest that there may have been a gradual transition between deposition of the original peat and the subsequent oil shales the aliphatic hydrocarbons of the uppermost shale are dominated by a number of c 31 and c 33 botryococcane homologues and other unusual branched alkanes possibly derived from green algae all of the samples are immature overall molecular and microscopic examination of the stratigraphic succession of the maoming oil shale suggests a shallow lacustrine environment within which peats were deposited this lake subsequently deepened to support abundant algal populations especially dinoflagellates culminating in a dominance of botryococcoid algae

the stability of sapphirine clinopyroxene implications for phase relations in the cao mgo al2o3 sio2 system under deep crustal and upper mantle conditions reaction textures and chemographic relations in sapphirine bearing basic granulites at finero italy suggest that sapphirine and aluminous diopside were formed in mutual equilibrium from an inferred early spinel bearing assemblage finero appears to be the only known locality where this association has been found in situ although it is also known from kimberlite and breccia pipe nodules elsewhere the reactions deduced to have occurred in these rocks suggest the existence of stable invariant points involving the phases sapphirine spinel orthopyroxene clinopyroxene garnet anorthite and sapphirine two pyroxenes garnetanorthite kyanite or sillimanite in the cmas end member system p t estimates for the relevant rocks and the available experimental data suggest that these points lie at around 800 900 c 9 11 kbar a semi quantitative petrogenetic grid incorporating these invariant points with previously determined univariant reactions is proposed it is inferred that sapphirine diopside are stable relative to spinel bearing assemblages below 900 c the relatively low temperature explains why sapphirine has not to date been reported from experimental work on the cmas system it also suggests that sapphirine may be an important aluminous phase in mg rich metagabbros under conditions corresponding to the base of the continental crust despite the observed rarity of such rocks at the surface

nitrate production beneath a high arctic glacier svalbard natural environmental isotopes of nitrate and ammonium are used in conjunction with major ion chemistry and hydrological data to establish controls upon the biogeochemical cycling of nitrogen beneath a high arctic polythermal glacier midtre lovenbreen here high nitrate concentrations in subglacial meltwaters suggest that the subglacial environment may be furnishing nitrate in excess of that released from the snowpack and glacier ice isotopic values of 18ono3 suggest the provenance of such excess nitrate to be microbial in origin and 15nno3 indicates the source nitrogen compounds to have high 15n values relative to supraglacial runoff we address the nitrification of supraglacial ammonium the mineralization of organic nitrogen and the oxidation of geologic ammonium as potential sources of this additional nitrate mass fluxes of n compounds in a subglacial river and their 15n ratios indicate that the nitrification of supraglacial ammonium delivered to the glacier bed can account for much but not all of the excess nitrate the additional source most likely involves the mineralization of organic nitrogen although 15n values in rock samples suggest that the dissolution of rock derived ammonium cannot be discounted if large fractionation effects occur during dissolution our results therefore agree with previous catchment scale mass balance studies at the site which report a major internal loss of nh4 from the snowpack following melt however at the catchment scale the nh4 loss is greater than the excess of no3 observed in runoff indicating that microbial assimilation of ammonia into organic matter in a range of other habitats is also likely the identification of nh4 assimilation and nitrification further highlights the non conservative behaviour of nitrogen in glacial environments and testifies to the importance of microbially mediated reactions in the biogeochemical cycling of nitrogen in an environment that has until recently been regarded as biologically inert

comments on character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies