marine ice sheet stability we examine the stability of two dimensional marine ice sheets in steady state the dynamics of marine ice sheets is described by a viscous thin film model with two stefan type boundary conditions at the moving boundary or grounding line that marks the transition from grounded to floating ice one of these boundary conditions constrains ice thickness to be at a local critical value for flotation which depends on depth to bedrock at the grounding line the other condition sets ice flux as a function of ice thickness at the grounding line depending on the shape of the bedrock multiple equilibria may be possible using a linear stability analysis we confirm a long standing heuristic argument that asserts that the stability of these equilibria is determined by a simple mass balance consideration if an advance in the grounding line away from its steady state position leads to a net mass gain the steady state is unstable and stable otherwise this also confirms that grounding lines can only be stable in positions where bedrock slopes downwards sufficiently steeply

assessing the ability of numerical ice sheet models to simulate grounding line migration grounding line migration is a key process affecting the stability of marine ice sheets such as the west antarctic ice sheet wais grounding line motion is often included in numerical models simulating the past and future evolution of the wais however little attention has been paid to the numerical consistency of these models the aim of this paper is to assess the ability of simple versions of existing marine ice sheet models to simulate grounding line migration in particular we investigate the response of the grounding line to external forcing and the sensitivity of the models predictions to their numerics and the mechanical coupling between ice sheet and shelf from the model comparison there is no consensus on how the grounding line should react to changes in boundary conditions a crucial finding is the strong dependency of models using a fixed grid on numerical details such as the horizontal grid size this implies that we should be very wary about grounding line predictions from such models including mechanical coupling at the grounding line does not seem to change the qualitative behavior of the models this suggests that the way the grounding line is treated in marine ice sheet models dominantly determines the grounding line dynamics we find that models that employ a moving grid to explicitly track the grounding line do not share many of the deficiencies of the fixed grid models we conclude that at present no reliable model of the grounding line is available and further model development is urgently needed

planktonic foraminiferal biostratigraphy of the neogene sequence in the adana basin turkey and its correlation with standard biozones the aim of this study is to describe the biostratigraphic chronostratigraphic and ecostratigraphic relationships of the neogene sequence in the adana basin the adana basin is located in southern turkey and bordered by the tauride orogenic belt to the north the amanos mountains to the east the mediterranean coast to the south and the ecemis fault zone to the west from base to top the neogene sequence consists of the gildirli formation continental redbeds the shallow marine kaplankaya formation the reefal limestones of the karaisali formation the shales of the guvenc formation slope to deep marine a thick submarine fan complex cingoz formation the shallow marine and fluvio deltaic kuzgun formation and the shallow marine lagoonal continental handere formation the planktonic foraminiferal biozones identified within the neogene sequence of the adana basin are globigerinoides trilobus and praeorbulina glomerosa curva burdigalian globorotalia fohsi peripheroronda orbulina suturalis langhian and globorotalia mayeri serravallian the late tortonian is characterized by the first occurrence of globorotalia suterae there are no planktonic foraminiferal zones in the messinian but this level may be correlated with a non distinctive zone in the mediterranean region the pliocene is represented by the sphaeroidinellopsis acme zone

late diagenetic redistribution of uranium and disturbance of the u pb whole rock isotope system in a black shale the middle ordovician llandeilo caradoc formation black shales deposited at about 460 ma on the southwest margin of the welsh basin show evidence of a late diagenetic uranium redistribution event evidence for this redistribution event includes a disturbance in the u pb whole rock isotopic system at about 193 ma marked by a large range in the whole rock 238 u 204 pb between 2 and 90 one explanation for this large range is that individual whole rocks have experienced either a gain or a loss of u at the time of the disturbance this hypothesis is supported by the large range in measured u contents from the llandeilo caradoc formation black shales 0 16 to 6 6 ppm upper crust 2 8 ppm post archean average shale paas 3 1 ppm taylor and mclennan 1985 uranium that was likely sequestered during deposition and early diagenesis has been redistributed on a greater than whole rock scale centimeters to meters the u pb isotope systematics identified in this study and other pb isotope data from the welsh basin evans 1996 constrain a reasonable u concentration of 2 91 ppm for an unaltered llandeilo caradoc shale at the time of deposition 460 ma assuming 2 91 ppm to be an average u content at the time of deposition some rocks in the llandeilo caradoc formation have lost as much as 95 of the u likely present at the time of deposition and early diagenesis whereas others exhibit an almost equal enrichment when the u pb isotopic and elemental data from whole rocks and individual u bearing phases i e carbonate apatite monazite organic matter are examined in conjunction with the paragenetic sequence controls on the distribution of u in the llandeilo caradoc whole rocks and a pattern of open system conditions become apparent despite the presence of potential u rich diagenetic phases such as apatite and monazite most of the u in the relatively enriched samples is associated with a non extractable unidentified diagenetic component uranium mass balance considerations and whole rock u pb isotope systematics require that the non extractable component formed at about 193 ma during a late diagenetic uranium redistribution event the redistribution of u within the llandeilo caradoc formation has important implications for the use of u rich sedimentary minerals as geochronometers and for the use of u as a paleo redox indicator specifically a trace element indicator like uranium may in some cases record information about the postdepositional history of a sedimentary rock rather than document the absolute timing and conditions of deposition moreover this unique history can be properly evaluated only through an integrated petrographic geochemical approach that can discern the distribution and source i e depositional versus diagenetic of u in an individual whole rock

a smoothed particle hydrodynamics model for ice sheet and ice shelf dynamics mathematical modeling of ice sheets is complicated by the non linearity of the governing equations and boundary conditions standard grid based methods require complex front tracking techniques and have limited capability to handle large material deformations and abrupt changes in bottom topography as a consequence numerical methods are usually restricted to shallow ice sheet and ice shelf approximations we propose a new smoothed particle hydrodynamics sph model for coupled ice sheet and ice shelf dynamics sph is a fully lagrangian particle method it is highly scalable and its lagrangian nature and meshless discretization are well suited to the simulation of free surface flows large material deformation and material fragmentation in this paper sph is used to study ice sheet ice shelf behavior and the dynamics of the grounding line the steady state position of the grounding line obtained from the sph simulations is in good agreement with laboratory observations for a wide range of simulated bedrock slopes and density ratios similar to those of ice and sea water the numerical accuracy of the sph algorithm is further verified by simulating the plane shear flow of two immiscible fluids and the propagation of a highly viscous blob of fluid along a horizontal surface inmore the experiment the ice was represented with a viscous newtonian fluid for consistency in the described sph model the ice is also modeled as a viscous newtonian fluid typically ice sheets are modeled as a non newtonian fluid accounting for the changes in the mechanical properties of ice implementation of a non newtonian rheology in the sph model is the subject of our ongoing research less

palaeoenvironmental controls on the uranium distribution in an upper carboniferous black shale gastrioceras listeri marine band and associated strata england the mudrocks associated with the gastrioceras listeri g listeri marine band contain 0 to 200 ppm authigenic uranium several geochemical degree of pyritisation dop c s ratios and framboidal pyrite size distribution and palaeontological indicators oxygen restricted biofacies orb analysis suggest that the highest authigenic uranium concentrations are within marine sediments associated with the most oxygen restricted biofacies orbs 2 and 3 the uranium peaks tend to occur at the transition between biofacies rather than within the middle of more persistently anoxic intervals these horizons may have been deposited when the oxygen minimum zone impinged on the seafloor brief oxygenation of an otherwise anoxic environment was conducive to francolite precipitation which then scavenged dissolved uranium slow sedimentation rates are also important in concentrating uranium and francolite thus enriched u values are only encountered under specific conditions of low but fluctuating oxygen regime and extremely slow sedimentation rates truly euxinic facies lacking any fossils and a uniformly small framboid population do not contain high concentrations of francolite and are not u rich

cosmogenic 36cl accumulation in unstable landforms 1 effects of the thermal neutron distribution cosmogenic nuclides produced in situ within minerals at the surface of the earth are proving to be an effective means of assessing geomorphic histories the use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined however if two nuclides are produced only by spallation reactions the systematic differences in their accumulation rates depend only on the differences in their production rates and half lives the relatively small differences that result require a high degree of analytical precision to yield useful results in contrast to other spallogenic nuclides sup 36 cl is also produced by low energy neutron absorption which creates a different pattern of production as a function of depth we have measured the thermal flux with depth in a concrete block using sup 3 he filled neutron detectors the measured thermal neutron profile agrees well with predictions from a simple diffusion based thermal neutron distribution model calculations of sup 36 cl production using the model suggest that the use of sup 36 cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides 31 refs 7 figs 3 tabs

cosmogenic 3he and 21ne dating of biotite and hornblende stable cosmogenic isotopes such as 3he and 21 ne are useful for dating of diverse lithologies quantifying erosion rates and ages of ancient surfaces and sediments and for assessing complex burial histories although many minerals are potentially suitable targets for 3he and 21 ne dating complex production systematics require calibration of each mineral isotope pair we present new results from a drill core in a high elevation ignimbrite surface which demonstrates that cosmogenic 3he and 21 ne can be readily measured in biotite and hornblende 21 ne production rates in hornblende and biotite are similar and are higher than that in quartz due to production from light elements such as mg and al we measure 21 ne hbl 21 ne qtz 1 35 0 03 and 21 ne bio 21 ne qtz 1 3 0 02 which yield production rates of 25 6 3 0 and 24 7 2 9 at g 1 yr 1 relative to a 21 ne qtz production rate of 19 0 1 8 at g 1 yr 1 we show that nucleogenic 21 ne concentrations produced via the reaction 18 o n 21 ne are manageably small in this setting and we present a new approach to deconvolve nucleogenic 21 ne by comparison to nucleogenic 22 ne produced from the reaction 19 f n 22 ne in f rich phases such as biotite our results show that hornblende is a suitable target phase for cosmogenic 3he dating but that 3he is lost from biotite at earth surface temperatures comparison of 3he concentrations in hornblende with previously measured mineral phases such as apatite and zircon provides unambiguous evidence for 3he production via the reaction 6li n 3h 3he due to the atypically high li content in the hornblende 160 ppm we estimate that li produced 3he represents 40 of total 3he production in our samples and must be considered on a sample specific basis if 3he dating in hornblende is to be widely implemented

easternmost mediterranean evidence of the zanclean flooding event and subsequent surface uplift adana basin southern turkey according to the literature the adana basin at the easternmost part of the mediterranean basin in southern turkey records the pliocene stage with shallow marine to fluvial deposits our micropalaeontological analysis of samples from the adana basin reveal late lago mare biofacies with paratethyan ostracod assemblages pertaining to the loxocorniculina djafarovi zone grey clays rich in planktonic foraminifera lie above the lago mare deposits within the grey clays the continuous occurrence of the calcareous nannofossil reticulofenestra zancleana and the base of the reticulofenestra pseudoumbilicus paracme points to an early zanclean age 5 332 5 199 ma both ostracod and benthic foraminifera indicate epibathyal and bathyal environments 87 sr 86 sr measurements on planktonic and benthic foraminifera fall below the mean global ocean value for the early zanclean indicating potentially insufficient mixing of low 87 sr 86 sr mediterranean brackish lago mare water with the global ocean in the earliest pliocene we utilize the ages and palaeodepths of the marine sediments together with their modern elevations to determine uplift rates of the adana basin of 0 06 to 0 13 mm a 1 since 5 2 5 3 ma total uplift of 350 650 m from surface data and 0 02 0 13 mm a 1 since c 1 8 ma total uplift of 30 230 m from subsurface data

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

dynamics of laterally confined marine ice sheets we would like to thank dr m hallworth for valuable help with running the experiments and the technicians of the damtp g k batchelor laboratory for help with the set up of the experimental apparatus k n k is supported by a nerc phd studentship the experimental data are available as supplementary material

anomalous cosmogenic 3he production and elevation scaling in the high himalaya the production rate of cosmogenic 3he in apatite zircon kyanite and garnet was obtained by cross calibration against 10 be in co existing quartz in glacial moraine boulders from the nepalese himalaya the boulders have 10 be ages between 6 and 16 kyr and span elevations from 3200 to 4800 m in all of these minerals 3he correlates with 10 be and is dominantly cosmogenic in origin after modest correction for non cosmogenic components 3he 10 be systematics imply apparent sea level high latitude slhl apparent production rates for 3he of 226 atoms g 1 yr 1 in zircon 254 atoms g 1 yr 1 in apatite 177 atoms g 1 yr 1 in kyanite and 153 atoms g 1 yr 1 in gamet these production rates are unexpectedly high compared with rates measured elsewhere in the world and also compared with proposed element specific production rates for apatite and zircon the data are sufficient to conclude that the 3he 10 be ratio increases with elevation if this reflects different altitudinal scaling between production rates for the two isotopes then the slhl production rates estimated by our approach are overestimates we consider several hypotheses to explain these observations including production of 3he via thermal neutron capture on 6li altitudinal variations in the energy spectrum of cosmic ray neutrons and the effects of snow cover because all of these effects are small we conclude that the altitudinal variations in production rates of cosmogenic 3he and 10 be are distinct from each other at least at this location over the last last 10 kyr kyr this conclusion calls into question commonly adopted geographic scaling laws for at least some cosmogenic nuclides if confirmed this distinction may provide a mechanism by which to obtain paleoelevation estimates

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

micropaleontology and paleoecology of the neogene sediments in the adana basin south of turkey this paper analyses the stratigraphical features and fossil associations ostracod and planktonic foraminifer of the late miocene deposits in the adana basin in this research numerous samples were collected from the sediments both below and above the messinian evaporitic layers which cropped out in the western and middle part of the adana basin due to paleoenvironmental changes during the messinian salinity crisis the fine grained sediments below the gypsum layers surrounding topcu and karayayla villages located in the western part of the basin are sterile nodular anhydrite and enterolithic structures are well developed in these selenitic gypsum layers which are supposed to represent a sabkha environmental condition in the middle part of the adana basin some re sediment detritic gypsum deposits cropped out around semiramis village houses the lithological characteristics and faunal assemblages of the sediments both below and above these evaporites are more or less similar to each other fossil fauna ostracod and planktonic foraminifera demonstrate that these sediments are not older than latest tortonian as suggested by the presence of neogloboquadrina humerosa and not younger than earliest messinian as suggested by the last occurrence of globigerinoides bulloideus similar planktonic assemblages were found in the drill log bored east of the adana basin where there was no evaporitic occurrence both the planktonic species and the presence of globorotalia suterae from 7 81 ma to 7 24 ma point that also these fine granied sediments a late tortonian early messinian in age the quantity of kaolinite recorded is relatively higher in the tortonian early messinian than in the late messinian sediments all data show that during the latest tortonian earliest messinian time interval the area was characterised by shallow marine environments and humid climatic conditions

a petrographic approach for evaluating trace element mobility in a black shale abstract at the time of deposition black shales record geochemical information related to the provenance and conditions of deposition for that rock these initial geochemical conditions are susceptible to alteration and overprinting by the aggressive processes of black shale diagenesis in this study we evaluate a sequence of ordovician black shales from the southern welsh basin for the presence of such a diagenetic overprint through use of cathodoluminescence backscattered electron imaging reflected light microscopy fission tracks and microprobe elemental mapping we can discern textural relationships with in the welsh black shales the relationships observed constrain a paragenetic sequence and overall diagenetic history including the early diagenetic formation of pyrite apatite rare earth element ree rich and carbonate and later formation of diagenetic monazite ree u rich and late stage carbonate the chemical reactions necessary to produce this mineral sequence require postdepositional redistribution of ree including changing cerium anomalies ce ce and uranium as a result ree u and their associated isotopic systems sm nd and u pb can reflect a diagenetic overprint rather than the source area and depositional conditions the paragenetic sequence described in this study records several postdepositional changes in the whole rock mineralogy among these changes are the formation of ree rich apatite and ree and u rich monazite the formation of these phases requires that ree and u are being redistributed on at least a mineral scale and that the initial depositional and provenance information recorded by the whole rock has been disturbed therefore the approach used in this study to carefully characterize the paragenetic sequence from the llandeilo caradoc black shales should be considered necessary in order to fully evaluate the usefulness of trace element proxies susceptible to diagenetic redistribution

an observationally validated theory of viscous flow dynamics at the ice shelf calving front an analytical theory is developed for ice flow velocity in a boundary layer couplet at the calving front the theory has simple quantitative characteristics that relate ice front velocity to thickness strain rate and shelf width matching one set of empirically derived relationships alley and others 2008 and implying that these relationships predict ice velocity rather than calving rate the two boundary layers are where longitudinal and transverse flow fields change from the interior flow to patterns consistent with the calving front stress condition numerical simulations confirm the analytical theory the quantitative predictions of the theory have low sensitivity to unmeasured parameters and to shelf plan aspect ratio while its robustness arises from its dependence on the scale invariance of the governing equations the theory provides insights into calving the stability of ice shelf calving fronts the stability of the grounding line of laterally resisted ice streams and also suggests that the calving front is an instructive dynamical analogue to the grounding line

in situ neutron flux 36cl production and groundwater evolution in crystalline rocks at stripa sweden the meteoric input of36cl due to cosmogenic or nuclear weapon produced36cl cannot contribute significantly to the36cl present in the saline groundwaters up to 700 mg l 1 cl from the stripa granite the extent of in situ production of36cl has been estimated on the basis of the neutron fluxes within the granite and its surrounding leptite the36cl present in the groundwaters is attributed to either admixture of labelled cl from the leptite with cl from the granite or to the total derivation of groundwater chlorinity within the leptite followed by radiochemical ingrowth of36cl during subsequent groundwater residence within the granite the chloride derived from the leptite may be either matrix chloride or chloride from an external source which has had a long residence time within the leptite the implications of36cl in situ production for the estimation of groundwater residence times and for the geochemical evolution of groundwater chlorinity are discussed

the formation of grounding zone wedges theory and experiments we present a fluid mechanical explanation of the formation of sedimentary wedges deposited at ice stream grounding zones we model both ice and till as layers of viscous fluid spreading under gravity into an inviscid ocean to test the fundamentals of our theory we perform a series of laboratory experiments in which we find that a similar wedge of underlying less viscous fluid accumulates spontaneously around the grounding line we formulate a simple local condition relating wedge slopes which determines wedge geometry it expresses a balance of fluxes of till either side of the grounding line and involves upstream and downstream gradients of till thicknesses as well as the upper surface gradient of the ice it shows that a wedge will form that is the upstream till thickness gradients are positive when the flux of till driven by the glaciostatic pressure gradient of the overlying ice is greater than the flux of till ahead of the grounding zone this is related to the unloading of the till as the ice sheet crosses the grounding line

cosmogenic chlorine 36 production rates in terrestrial rocks abstract chlorine 36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of 35cl spallation of 39k and 40ca and slow negative moun capture by 40ca we have measured the 36cl content of 14c dated glacial boulders from the white mountains in eastern california and in a 14c dated basalt flow from utah effective time intergrated production parameters were calculated by simultaneous solution of the 36cl production equations the production rates due to spallation are 4160 310 and 3050 210 atoms 36cl yr 1 mol 139k and 40ca respectively the thermal neutron capture rate was calculated to be 3 07 0 24 105 neutrons kg of rock 1 yr 1 the reported values are normalized to sea level and high geomagnetic latitudes production of 36cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates chlorine 36 dating was performed on carbonate ejecta from meteor crater arizona and late pleistocene morainal boulders from the sierra nevada california calculated 36cl ages are in good agreement with previously reported ages obtained using independent methods

a revised stratigraphic framework for later cenozoic sequences in the northeastern mediterranean region this study describes the lithostratigraphic character of mid cenozoic oligocene pliocene sequences in different parts of the northeastern mediterranean area and offers a detailed stratigraphic correlation for this region the sequences concerned are drawn from the camardi area south central anatolia the adana basin the misis mountains and the kyrenia range northern cyprus and the submerged florence rise west of cyprus the stratigraphic relationships identified here indicate the following a following the middle eocene lutetian regression there was uplift throughout the entire region b episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late eocene early miocene interval c following a regionally extensive phase of tectonic compression major marine transgression commenced in the late oligocene in northern cyprus and in the early miocene in adjacent southern turkey with the exception of the ecemi fault zone where continental deposition continued d these oligo miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies including reefal carbonates littoral clastics basinal shales and fan turbidites e deeper marine miocene facies persisted longer in the misis area and in northern cyprus f a regional regression occurred throughout most of the area during the late serravallian to tortonian interval and is marked by the abrupt locally discordant appearance of extensive shallow marine deltaic and fluvial deposits g continued regression in the messinian led to the formation of significant evaporite deposits in the western and southern parts of the region but localized uplift of the misis area is attested by the initial deformation of the neogene rocks there and the absence of messinian sediments from this area h in the pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions the present day drainage pattern was established at this time i marine conditions persisted longer in northern cyprus where emergence occurred only in the latest pliocene

vertical and lateral organization of a carbonate deep water slope marginal to a submarine fan system miocene southern turkey organization is recognized in the forereef deep water slope submarine fan system of the burdigalian langhian kaplankaya formation a basinwards transition from a prograding shelfal reef complex through forereef talus deep water slope and laterally encroaching bypass deep water clastic system is described although the deep water slope makes up the bulk of the succession considerable thickness variations occur between the reef and deep water clastic complexes these are controlled by sea floor topography carbonate foreslope gradient and degree of mass wasting off the platform and foreslope the vertical and lateral heterogeneity of the kaplankaya deep water slope system is described from a number of localities along a 40 km long and up to 3 km wide exposed section of the northern margin of the miocene adana basin a foreland basin setting resulting from thrust sheet loading from the north during the tauride orogeny detailed field mapping is supplemented with vertical sedimentary logs photomosaics palaeontological and petrological data to investigate stratal variation diagnostic architectural elements controls on slope progradation differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep water clastic system onto the slope three dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep water slope system and provide a basis for architectural prediction of geometry and relative position in such environments

evidence for 1 5 km of uplift of the central anatolian plateau s southern margin in the last 450 kyr and implications for its multiphased uplift history

dynamics of viscous grounding lines we have used viscous fluids in simple laboratory experiments to explore the dynamics of grounding lines between marine ice sheets and the freely floating ice shelves into which they develop we model the ice sheets as shear dominated gravity currents and the ice shelves as extensional gravity currents having zero shear to leading order we consider the flow of viscous fluid down an inclined plane into a dense inviscid ocean a fixed flux of fluid is supplied at the top of the plane which is at sea level the fluid forms a gravity current flowing down and attached to the plane for some distance before detaching to form a freely floating extensional current we have derived a mathematical model of the flow that incorporates a new dynamic boundary condition for the position of the grounding line where the gravity current loses contact with the solid base the grounding line initially advances and eventually reaches a steady position good agreement between our theoretical predictions and experimental measurements and observations gives confidence in the fundamental assumptions of our model

the influence of lateral basinal slopes on turbidite sedimentation in the annot sandstones of se france abstract the deep water deposits of the lower oligocene annot sandstones of se france were deposited in topographically dissected basins axially derived turbidites show marked lateral onlap onto the underlying marls the original lateral slopes were at least 250 m high and up to 12 prior to compaction induced steepening they commonly show a stepped or undulatory profile lateral tracing of individual beds away from their position of onlap termination down the paleoslope reveals a characteristic succession of microfacies thin bedded nongraded fine sandstones with upper flow regime planar lamination pass downslope into medium bedded partially graded medium sandstones with ripple and planar lamination at the base of the depositional slope the turbidites become thick to very thick bed ed fully graded commonly stepwise coarse sandstones to mudstones the most likely interpretation of the lateral transition from lower flow regime to upper flow regime conditions from the axial trough to the lateral margin of the basin involves pulsatory flow conditions episodes of increased flow thickness and velocity deposited upper flow regime bed forms on the higher parts of lateral ramps while periods of waning current deposited lower flow regime bed forms in the axial trough during accumulation of the sands the underlying marls were differentially compacted with maximum compaction under the axis of the basin decreasing to zero compaction at the edges of the basin this resulted in secondary slopes on the upper surface of the sandstones overlying the marl slopes which may have been important in controlling the accumulation of successive sand packages successive onlap and overstep of sand layers onto the marls resulted in a vertical profile that shows the same succession of facies as traced downslope in individual beds the resulting vertical sections coarsen and thicken upwards over 5 10 m the characteristics of the thin bedded fine sandstones at the base of cycles may be used to distinguish between prograding and laterally onlapping turbidite packages sandstone packages in the basin axis are thick 30 60 m sharp based and sandstone rich the laterally equivalent part of a package overlying a confining slope is thinner asymmetric with a coarsening upward signature and more mudstone rich

underground production of radionuclides in the milk river aquifer alberta canada abstract most cosmogenic radionuclides that may be used to estimate groundwater ages in excess of 100 ka are also produced underground by in situ nuclear reactions radioactive equilibrium between in situ production and decay would be approached within such long residence times radionuclide production by in situ nuclear reactions within the groundwater and within its host rock has been calculated theoretically and compared with some measured radionuclide contents of the groundwater the fractional transfer of in situ produced 37 ar 39 ar and 222 rn from rock to groundwater necessary to account for the total measured groundwater contents were found to be similar although site specific the implications for radionuclide release mechanisms and for groundwater dating by the use of cosmogenic radionuclides including those which are applicable for very old groundwaters 36 cl 81 kr 129 i are discussed

mineralogy and trace element geochemistry of gas shales in the united states environmental implications abstract this paper presents a compilation of published mineralogic and trace element data from nine gas shales in the united states formations analyzed include the antrim bakken barnett eagle ford haynesville marcellus new albany utica and woodford these mineralogic and trace element data can be used to assess the potential for environmental impacts during hydraulic fracturing impacts addressed in this study include 1 the potential for acid rock drainage generation during gas shale weathering 2 the distribution of trace elements in gas shales and comparison with regulatory guidelines and 3 the implications for environmental management of well cuttings the use of the mineralogic data to assess the fracability of the gas shales is also considered compilations of the mineralogy and geochemistry of gas shales can be a valuable resource for managing real and perceived environmental problems associated with their exploitation comprehensive environmental assessment to fully address these issues in addition to other potential environmental impacts will require collection and collation of additional data on the mineralogy and trace element geochemistry of gas and other hydrocarbon producing shales

suppression of marine ice sheet instability a long standing open question in glaciology concerns the propensity for ice sheets that lie predominantly submerged in the ocean marine ice sheets to destabilise under buoyancy this paper addresses the processes by which a buoyancy driven mechanism for the retreat and ultimate collapse of such ice sheets the marine ice sheet instability is suppressed by lateral stresses acting on its floating component the ice shelf the key results are to demonstrate the transition between a mode of stable easily reversible retreat along a stable steady state branch created by ice shelf buttressing to tipped almost irreversible retreat across a critical parametric threshold the conditions for triggering tipped retreat can be controlled by the calving position and other properties of the ice shelf profile and can be largely independent of basal stress in contrast to principles established from studies of unbuttressed grounding line dynamics the stability and recovery conditions introduced by lateral stresses are analysed by developing a method of constructing grounding line stability bifurcation diagrams which provide a rapid assessment of the steady state positions their natures and the conditions for secondary grounding giving clear visualisations of global stabilisation conditions a further result is to reveal the possibility of a third structural component of a marine ice sheet that lies intermediate to the fully grounded and floating components the region forms an extended grounding area in which the ice sheet lies very close to flotation and there is no clearly distinguished grounding line the formation of this region generates an upsurge in buttressing that provides the most feasible mechanism for reversal of a tipped grounding line the results of this paper provide conceptual insight into the phenomena controlling the stability of the west antarctic ice sheet the collapse of which has the potential to dominate future contributions to global sea level rise

lateral controls on grounding line dynamics we present a theoretical and experimental study of viscous gravity currents introducedat the surface of a denser inviscid uid layer of nite depth inside a vertical hele shaw cell initially the viscous uid oats on the inviscid uid forming a self similar buoyancy driven current resisted predominantly by the viscous stresses due to shearacross the width of the cell once the viscous current contacts the base of the cell the ow can be considered in two regions a grounded region in which the currentlies in full contact with the base and a oating region the subsequent advance ofthe grounding line separating these regions is shown to be controlled by the thickeningof the current associated with balancing the local shear stresses an understanding ofthe ow transitions is developed using asymptotic and numerical analysis of a modelbased on lubrication theory key words geophysical and geological ows hele shaw ows ice sheets

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

tectonic controls on stratigraphic evolution of the adana basin turkey the neogene adana basin of se turkey was initiated after thrust emplacement of the tauride belt to the north of the basin seismic reflection profiles across the southern part of the adana basin provide information on structural and stratigraphic evolution of the basin based on seismic character and the identification of unconformities three megasequences and two mega sequence boundaries are identified the first megasequence is partly coincident with an early miocene rifting event and it comprises reefs that have grown on fault footwall crests with fore and back reef sediments in intervening lows subsequent rapid flexurally induced subsidence generated an underfilled basin which was then passively filled by turbiditic sediments megasequence 2 showing aggradational character on seismic profiles further extensional faulting and coupled sinistral wrench faulting took place after the deposition of megasequence 2 erosional truncation of its upper part is followed by the deposition of continental and shallow marine sediments of megasequence 3 which shows localized progradational sequences characteristic of shallow water deposition further minor extensional faulting took place after the deposition of megasequence 3

sedimentology of a late cenozoic collisional sequence the misis complex adana southern turkey abstract this study is concerned with miocene sequences formed within part of the cukurova basin of southern turkey a major downwarp created during the early stages of collision between the afro arabian plate and the tauride anatolian microplate assemblage we report here the results of a combined stratigraphical sedimentological structure and geochemical study of the misis complex a structurally elevated segment of cukurova basin fill this analysis has demonstrated the structurally imbricated nature of the misis sequences and the tectonic juxtaposition of originally well separated coeval facies the initial discernible phase of basin filling pre burdigalian was marked by deep marine conditions and marginal tectonic instability probably related to a late phase of tauride nappe advance the subsequent phase of crustal extension burdigalian early tortonian produced expansion of the cukurova basin limits and an upwards shoaling succession in which sediment transport towards the southwest gradually became dominant as a result of earlier suturing and uplift in northeasterly sectors of the collision zone the miocene arenites of the misis complex are petrographically diverse with common siliciclastic and carbonate detrital admixtures and mineralogically immature and their position in petrotectonic fields indicates a compound provenance from both recycled orogen and magmatic arc sources a noteworthy petrographic feature is the compositional similarity of arenites from both shallow and deep marine facies the general succession of neogene facies observed in the cukurova basin and misis complex is consistent with their evolution within a perisutural foreland basin but this interpretation is complicated by petrographic and geochemical features attributed to remnants of an older magmatic arc later stages of basin filling are also marked by the local occurrence of anomalous palaeoenvironmental associations including olistostromic units attributed to contemporaneous intra basinal tectonism

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

experimental evidence of uraninite formation from diagenesis of uranium rich organic matter abstract this study focuses on the experimental diagenetic evolution of an uranium rich lignite from the coutras uranium deposit gironde france located in eocene sediments three samples containing 6 to 15 5 wt uranium were analysed and compared to two barren samples located outside the ore deposit in a stratigraphically equivalent unit uranium in the mineralized samples is present as uranyl carboxylic complexes dry thermal maturation was simulated in a cold seal autoclave at 150 200 250 300 and 350 c at 100 mpa for 24 h with increasing temperature uranyl carboxylic complexes decompose while uraninite forms the chemical composition of the experimentally matured barren samples when plotted in a van krevelen diagram h c vs o c parallels the natural trend of land derived type ill organic matter evolution while mineralized samples are characterized by a higher loss of hydrogen above 250 c reduction to form uraninite is directly related to the dehydrogenation of lignite the resulting uraninite has a similar unit cell edge to that of natural uraninites observed in sedimentary environments uraninite not only forms in the pore space but also replaces the lignite constituents the results demonstrate that uraninite may form during thermal evolution of uranium rich organic matter during diagenesis

dynamics of a viscous layer flowing radially over an inviscid ocean we present a theoretical and experimental study of a viscous fluid layer spreading over a deep layer of denser inviscid fluid specifically we study an axisymmetric flow produced by a vertical line source close to the source the flow is controlled viscously with a balance between radial compressive stresses and hoop stresses further out the flow is driven by gradients in the buoyancy force and is resisted by viscous extensional and hoop stresses an understanding of these different fluid mechanical relationships is developed by asymptotic analyses for early times and for the near and far fields at late times confirmation of the late time far field behaviour is obtained from a series of laboratory experiments in which golden syrup was injected into denser solutions of potassium carbonate we use our mathematical solutions to discuss a physical mechanism by which horizontal viscous stresses in a spreading ice shelf such as those in west antarctica can buttress the grounded ice sheet that supplies it

linking slab break off hellenic trench retreat and uplift of the central and eastern anatolian plateaus abstract the central and eastern anatolian plateaus are integral parts of the world s third largest orogenic plateau in the past decade geophysical surveys have provided insights into the crust lithosphere and mantle beneath eastern anatolia these observations are now accompanied by recent surveys in central anatolia and new data constraining the timing and magnitude of uplift along its northern and southern margins together with predictions from geodynamic models on the effects of various processes on surface deformation and uplift the observations can be integrated to identify probable mechanisms of anatolian plateau growth a changeover from shortening to extension along the southern margin of central anatolia that is coeval with the start of uplift can be most easily associated with oceanic slab break off and tearing this interpretation is supported by tomography deep seismicity or lack thereof and gravity data based on the timing of uplift geophysical and geochemical observations and model predictions slab break off likely occurred first beneath eastern anatolia in middle to late miocene time and propagated westward toward cyprus by the latest miocene alternatively the break off near cyprus could have occurred in late pliocene to early pleistocene time in association with collision of the eratosthenes seamount continental fragment with the subduction zone uplift at the northern margin of central anatolia appears to result from crustal shortening starting in the late miocene or early pliocene which has been linked to the broad restraining bend of the north anatolian fault the uplift history of the interior of central anatolia since the late miocene is unclear although shortening there appears to have ended by the late miocene followed by ne sw extension this change in the deformation style broadly coincides with faster retreat of the hellenic trench as well as uplift of the northern and southern margins of central anatolia these different events throughout the plateau may be linked as faster retreat of the hellenic trench has been predicted to occur after slab break off which could have induced extension of central anatolia and helped to form the north anatolian fault through accelerated westward movement of anatolia relative to eurasia correlative geochronologic evidence that we summarize here supports the hypothesis that the geodynamic activity throughout the aegean anatolian domain starting in latest miocene to early pliocene time defines a series of events that may all be linked to slab break off

marine ice sheet dynamics the impacts of ice shelf buttressing marine ice sheets are continent scale glacial masses that lie partially submerged in the ocean as applies to significant regions of antarctica and greenland such ice sheets have the potential to destabilise under a buoyancy driven instability mechanism with considerable implications for future sea level this paper and its companion present a theoretical analysis of marine ice sheet dynamics under the effect of a potentially dominant control of the buttressing force generated by lateral stresses on the downstream floating component of the ice sheet the ice shelf the analysis reveals critical conditions under which ice shelf buttressing suppresses the buoyancy driven collapse of an ice sheet and elucidates the implications of lateral stresses on grounding line control and overall ice sheet structure integrations of a suitably simplified quasi two dimensional model are conducted yielding analytical results that provide a quick assessment of steady state balances for a given ice sheet configuration an analytical balance equation describing the spectrum of marine ice sheet flow regimes spanning zero to strong ice shelf buttressing is developed it is determined that the dynamics across this spectrum exhibits markedly different flow regimes and structural characteristics for sufficient buttressing the grounding line occurs near to where a lateral drag controlled section of the ice shelf meets the bedrock implying an independent control of the grounding line by the ice shelf the role of basal stresses is relegated to controlling only the thickness of the ice sheet upstream of the grounding line with no significant control of the grounding line itself it is further demonstrated that lateral stresses are responsible for inducing additional secondary contacts between the ice shelf and the bedrock downstream of the grounding line resulting in a rich variety of additional steady states these inducements generate a further stabilising mechanism that can fully suppress grounding line retreat and eliminate otherwise irreparable hysteresis effects the results provide a conceptual framework for numerical and observational interpretation of marine ice sheet dynamics and clarifies the manner in which ice shelves can control grounding line positions independently it is thus indicated that a full resolution of the fine details of the flow of ice shelves and the processes controlling their erosion and disintegration is necessary for the confident forecasting of possible ice sheet collapse over the course of the next few centuries

measurements and interpretations of36cl in groundwater milk river aquifer alberta canada abstract the 36 cl cl ratios of 12 groundwater samples from the milk river aquifer were determined by accelerator mass spectrometry using known cl concentrations 36 cl concentrations were deduced approximately linear relations were observed between the logarithm of the 36 cl concentration the cl concentration and the distance from the recharge area along two flow paths the results are discussed in two approaches 1 in an interpretation of the linear relation between logarithm of the 36 cl concentration and cl concentration excluding and including in situ production of 36 cl 2 in a diffusion model the increase of the cl concentration with the distance from the recharge area is considered to be due to diffusion of cl from the underlying confining colorado shale to the aquifer flow velocities ranging between 0 04 and 0 14 m a and ages of the groundwater between 0 6 and 2 ma are obtained at a distance of 80 km from the recharge area

mineralogic controls on ree mobility during black shale diagenesis abstract the llandeilo caradoc black shales of southwest wales u k record a paragenetic sequence that requires redistribution of rare earth elements ree on a mineralogic scale during diagenesis the main evidence for this redistribution is formation and replacement of ree rich apatite and monazite and variations in whole rock ree patterns the processes that produce these mineralogic changes create a diagenetic overprint on the llandeilo caradoc black shales that obscures geochemical information related to both provenance and paleoenvironmental conditions of deposition periods of open system conditions existed during the diagenetic alteration of the llandeilo caradoc black shales which allow an evaluation of the extent and timing of the ree redistribution inferred from petrography the observed variations in la sm ratios in the whole rock ree patterns are strong evidence that ree were redistributed on a scale greater than an individual hand sample this change in the whole rock ree pattern altered the cerium anomaly by as much as 20 and produced a range in the sm nd ratio from 0 14 to 0 20 this change in the whole rock sm nd ratio indicates a disturbance in the sm nd isotopic system at about 460 ma that can be directly linked to the formation and dissolution of diagenetic apatite and monazite during diagenesis one effect of this disturbance is to alter the range in nd model age for the llandeilo caradoc black shales from 1 6 to 1 8 ga to about 1 4 to 2 25 ga thus complicating any interpretation of provenance the ability to link petrographic observations from a black shale to measurable whole rock geochemical changes provides us with one tool to evaluate the presence of a diagenetic overprint on trace elements commonly used in paleoenvironmental reconstruction

carbonate turbidite sequences deposited in rift basins of the jurassic tethys ocean eastern alps switzerland syn rift sediments in basins formed along the future southern continental margin of the jurassic tethys ocean comprise in the eastern alps of switzerland up to 500 m thick carbonate turbidite sequences interbedded with bioturbated marls and limestones in the fault bounded troughs no submarine fans developed in contrast the fault scarps acted as a line source and the asymmetric geometry as well as the evolution of the basin determined the distribution of redeposited carbonates the most abundant redeposits are bio and lithoclastic grainstones and packstones with sedimentary structures indicating a wide range of transport mechanisms from grain flow to high and low density turbidity currents huge chaotic megabreccias record catastrophic depositional events their main detrital components are upper triassic shallow water carbonates and skeletal debris from nearby submarine highs after an event of extensional tectonism sedimentary prisms accumulated in the basins along the faults each prism is wedge shaped with a horizontal upper boundary and consists of a thinning and fining upward megacycle within each megacycle six facies associations are distinguished at the base of the fault scarp an association of breccias was first deposited by submarine rockfall and rockfall avalanches a narrow approximately 4000 m wide depression along the fault was subsequently filled by the megabreccia association in which huge megabreccias interfinger with thin bedded turbidites and hemipelagic limestones the thick bedded turbidite association covered the megabreccias or formed farther basinward the base of the sedimentary column within the thick bedded turbidites thinning and fining upward cycles are common the overlying thin bedded turbidite association shows nearly no cyclicity and the monotonous sequence of fine grained calciturbidites covers most of the basin area with continuous filling and diminishing sediment supply a basin plain association developed comprising fine grained and thin bedded turbidites intercalated with bioturbated marls and limestones on the gentle slopes opposite the fault escarpment redeposited beds are scarce and marl limestone alternations as well as weakly nodular limestones prevail

control of 36cl production in carbonaceous shales by phosphate minerals abstract when using 36cl to date very old groundwater in regional aquifer systems knowledge of the subsurface 36cl input into the aquifer system is essential although 36cl can be produced through nuclear reactions in the subsurface in many situations the input of 36cl into sedimentary aquifer systems by this avenue of production can be neglected this is a valid assumption when investigating long flowpath groundwater systems composed of sandstones limestones and shales of typical composition these rock types are not sufficiently enriched in radioactive elements to produce significant 36cl in the deep subsurface carbonaceous shales on the other hand can concentrate the radioactive elements necessary to produce significant 36cl in the deep subsurface chlorine 36 ratios 36cl cl for a suite of late devonian and pennsylvanian carbonaceous shales were calculated from bulk rock chemistry as well as measured using accelerator mass spectrometry the poor agreement between calculated and measured ratios is the result of the assumption of chemical homogeneity used by the calculation algorithm an assumption that was not satisfied by the carbonaceous shales in these shales organic matter clay minerals and accessory minerals are heterogeneously distributed and are physically distinct on a micron order scale although organic matter and clay minerals constitute the overwhelming bulk of the shales it is the phosphate minerals that are most important in enhancing and suppressing 36cl production minerals such as apatite and carbonate apatite francolite by including uranium rare earth elements rees and halogens have an important impact on both neutron production and thermal neutron absorption by incorporating both uranium and fluorine phosphate minerals act as neutron production centers in the shale increasing the probability of 36cl production by incorporating rees and chlorine phosphate minerals also act to shield 35cl from the thermal neutron flux effectively suppressing the production of 36cl to reconcile the measured 36cl ratios with the ratios calculated assuming chemical homogeneity the shales were artificially split into three fractions organic clay mineral and phosphate mineral neutron production was calculated separately for each fraction and the calculation results demonstrated that the phosphate fraction exerted much more control on the 36cl ratio than the organic or clay mineral fractions by varying the uranium and chlorine contents in the phosphate fraction a new heterogeneous 36cl ratio was calculated that agreed with the measured ratio for the overwhelming majority of the carbonaceous shales when using rock chemistry to calculate the 36cl ratio rock types that show mineralogical heterogeneity on a micron scale can be divided into bulk fractions and accessory fractions for separate calculations of neutron production and neutron absorption in this manner a more accurate heterogeneous 36cl ratio can be calculated for the rock as a whole

marine ice sheet dynamics part 1 the case of rapid sliding marine ice sheets are continental ice masses resting on bedrock below sea level their dynamics are similar to those of land based ice sheets except that they must couple with the surrounding floating ice shelves at the grounding line where the ice reaches a critical flotation thickness in order to predict the evolution of the grounding line as a free boundary two boundary conditions are required for the diffusion equation describing the evolution of the grounded ice thickness by analogy with stefan problems one of these conditions imposes a prescribed ice thickness at the grounding line and arises from the fact that the ice becomes afloat the other condition must be determined by coupling the ice sheet to the surrounding ice shelves here we employ matched asymptotic expansions to study the transition from ice sheet to ice shelf flow for the case of rapidly sliding ice sheets our principal results are that the ice flux at the grounding line in a two dimensional ice sheet is an increasing function of the depth of the sea floor there and that ice thicknesses at the grounding line must be small compared with ice thicknesses inland these results indicate that marine ice sheets have a discrete set of steady surface profiles if they have any at all and that the stability of these steady profiles depends on the slope of the sea floor at the grounding line

conditions for a steady ice sheet ice shelf junction abstract this paper investigates the conditions under which a marine ice sheet may adopt a steady profile the ice is treated as a linear viscous fluid caused to flow from a rigid base to and over water treated as a denser but inviscid fluid the solutions in the region around the point of flotation or transition zone are calculated numerically in flow and out flow conditions appropriate to ice sheet and ice shelf flow are applied at the ends of the transition zone and the rigid base is specified the flow and steady free surfaces are determined as part of the solutions the basal stress upstream and the basal deflection downstream of the flotation point are examined to determine which of these steady solutions satisfy contact conditions that would prevent i the steady downstream basal deflection contacting the downstream base and ii the upstream ice commencing to float in the event it was melted at the base in the case that the upstream bed is allowed to slide we find only one mass flux that satisfies the contact conditions when no sliding is allowed at the bed however we find a range of mass fluxes satisfy the contact conditions the effect of backpressure on the solutions is investigated and is found to have no affect on the qualitative behaviour of the junctions to the extent that the numerical linearly viscous treatment may be applied to the case of ice flowing out over the ocean we conclude that when sliding is present weertman s instability hypothesis holds